AudioControl Richter Scale Series Three (Repairs/Mods) - Page 1
Forum section: electronics / repair

author: Smoky
author_rank: Frequent Contributor
timestamp: September 05, 2020, 02:22:03 am
content: This AudioControl Richter Scale crossover/equalizer came along with a pile of audio gear I bought three years ago.I want to replace the burnt-out lamp and test a few of the electrolytic capacitors since this thing was made in the mid 1980's.Not only that, this thing has a custom resistor bank used to define the crossover frequency. Since I plan on building new subwoofers, the crossover frequency will be adjusted.I also want to test it to see how balaced the channels are by frequency and amplitude and to fix whatever else inside needs fixing

author: Smoky
author_rank: Frequent Contributor
timestamp: September 05, 2020, 02:35:45 am
content: The first thing I checked were the fuses and for anything burnt. Sure enough, a small resistor that is tied to two green wires of the power transformer and two twisted blue wires going directly to the lamp was burnt.Looking closer at the resistor I could only read the first band. It is blue (6). The two holes next to the resistor are where the two green transformer wires are connected to the PC board.The blue pair of twisted wires called out to me being AC voltage going to an incandescent lamp.

author: Smoky
author_rank: Frequent Contributor
timestamp: September 05, 2020, 02:44:03 am
content: Here's a picture where the twisted pair of blue wires attach to the back of the dB meter's PC board. The lamp is the type where it has just wired leads soldered directly to the PC board next to the blue wire's connections. The PC board looks like it has seen some heat and, maybe, this lamp isn't the correct or the original one?As for the transformer's wires, I set up the DMM and measured the voltage of the green wires (~27.5 VAC).

author: Smoky
author_rank: Frequent Contributor
timestamp: September 05, 2020, 03:22:47 am
content: Here's a little info on how the crossover frequency is tailored.Inside of the chassis, there is a 16 pin socketed pad that is fitted with 8 metal film resistors. It easily unplugs from the PC board to be exchanged with a set of resistors of a different value based on the desired crossover frequency.I was able to order extra 16 pin pads from Digi-Key. So when the time comes, I can calculate what is needed for my combination of speakers. Really cool

author: Cybershaman
author_rank: Contributor
timestamp: September 05, 2020, 09:39:05 pm
content: Hello!As luck wood have it, I'm dealing with the same lamp issue on one of two Richter Scale 3s I own! That burnt resistor is blue, grey, black, gold, so 68 ohms.Here's something interesting: my other series 3 is wired differently! A look at the board shows that one was made in the late 80s and the other early 90s. The 90s version has that resistor missing and the lamp wire that goes to the resistor on the 80s board is instead wired between the diodes nearby! The wiring from the transformer on the 90s version is also slightly different.I must apologize because I am doing this all from memory and using a tablet. (Ugh. What a pain.) I am disabled and sitting in bed right now, otherwise I would hop over to the units for more specifics.I am fascinated by the various Richter Scale models. In fact, I also own a Series 1 and 2. I guess you could say I'm a collector.I also recently bought my second Series 3 unit JUST because it still had its microphone with it! (Don't ask me how much I paid for it. I essentially bought it JUST for its microphone!) I noticed that both series 3s had slightly different markings on the front. Both of their bulbs are burned out and when I started poking around inside it was then that I noticed that the black wires for their lamps were wired slightly different. I've seen that there are manuals online for a Richter Scale Series 3 version 2 and it always puzzled me. I guess now we know why!I'm thinking I would like to replace the lamps with LEDs. Again, sorry if I missed specific details in my post. If you would like, I might post some pictures of the differences. I think it would be useful considering these units are getting older and more people might be looking for information. Especially considering how the meters on the series 3 is virtually useless without the lamp working behind the meter. Also, since the ones you see for sale rarely, if ever, have their microphones still with them, it would be great if someone could figure out if one could either make one or build one from scratch to use. I have a Velodyne SMS-1 unit that connects to my TV and shows the frequency response below 200Hz, but I am excited to try out the microphone with my new Richter Scale, just as soon as I fix the darn lamp!Anyway, that's all I can stand to "type" on this stupid tablet (an Amazon Fire 10, no less!), so that's it for now. I would love to banter about these unique pieces of audiophile history. But I'd rather do it when I'm on my PC.Take care and I look forward to hearing more about your work on your unit!Oh! You do know how to build new crossover modules for your unit, right? Short answer is to divide 7200 by the frequency you want to cross over and that is the KILOohms of the resistors you use. You can build your own or try to find the appropriate isolated non-bussed resistor network modules of the appropriate ohm values. They are few dollars these days, I think. I just like making my own, so I didn't look too hard for the right kind. Mouser.com should have them, though. And here's a link to the Audiocontrol manual on making your own:https://www.audiocontrol.com/car-audio/accessories/modules/It looks like Audiocontrol still sells them, but, boy, are they pricey. But, hey, if that's easier than trying to find the right kind elsewhere I totally understand. I guess they still use them in some of their products. They use the same setup in their old Phase Coupled Activities. I actually have two of those, too! A Series 1 and a 3!Fun little things to mess with. Although, not as useful these days. They DO have separate crossover sections, though.ANYWAY, I REALLY have to go now!Take care and hopefully talk to you again soon!(I blame all spelling and grammatical errors on this stupid tablet!)

author: Cybershaman
author_rank: Contributor
timestamp: September 05, 2020, 09:40:15 pm
content: Ha! I see you already know about the resistors! :p

author: Cybershaman
author_rank: Contributor
timestamp: September 05, 2020, 09:47:37 pm
content: I also note that your unit has blue wires to the lamp. Both of my units use black wires!Check your circuit board for a manufacture/revision date. I'm curious if there are even more versions of the Series 3!

author: Smoky
author_rank: Frequent Contributor
timestamp: September 06, 2020, 12:55:35 am
content: Thank you Cybershaman. I was able to get access to the lamp area by taking off the front panel.It doesn't look right. The darkened lamp just flops around on two wires and the solder pads are partially lifted on the backside, plus, there's definitely some heat damage. I can also see a small piece of fine wire laying in the PC board near the resistorsA real bodge-job in my opinionIt surely is 27.5 AC volts going to this incandescent lamp. Wouldn't using an LED would create unwanted noise?Here's what I have in 28v lamps, a 6838 (.024mA) and a CM7009 (~.020mA). I did buy a small box of 7839 (.024mA) lamps but they aren't here yet. The candle-power is ~ .15 MSCP for all three. It doesn't require much light to bring out the meter face.I definitely want it to be cooler-running from here on.

author: Cybershaman
author_rank: Contributor
timestamp: September 07, 2020, 12:27:41 am
content: Where do you get your lamps from? I would like to get both of my RSs' lamps fixed and then possibly sell my extra one.I'll be honest, my electrical knowledge/experience is VERY limited. Between difficult times in relation to my disability/medical issues, I dabble with little "mad scientist" projects/ideas I have and learn as I go. The thought that LEDs gave off significant RF interference never occurred to me! A while ago, I swapped out some incandescents on the meters of two Carver TFM-15cb amps I have and have seen others do the same and I haven't had any problems I know of. Well, that's not entirely true.After a while, I noticed that my meters seem to be reading a littlesomethingwhen there is nothing playing through them. I don't hear anything other than your usual tiny bit of hiss coming out of my speakers. I assumed I was just picking something up from a cable that was too close to a power cord or some other source. Maybe it's the LEDs interfering? Can they do that? I've never heard complaints/warnings from others who did that mod. Anyway, I don't want to get TOO off topic.I took some pictures of my RS series 3 units and thought you (and anyone else who stumbles on this thread in the future) might find them interesting. I was very mistaken about the years! Both boards were from 1989! Oops!They are actually just two revisions; B and C. Anyway, I just thought I would just throw them up for future reference.I will have to post them later. Having a rough day today physically.Take care and talk to you soon! Oh, and I would love to hear more about your setup and how you are planning on integrating your Richter into your system! BTW, do you have an original microphone? Or are you using another method or just going by ear?Later!

author: Smoky
author_rank: Frequent Contributor
timestamp: September 07, 2020, 02:27:55 am
content: The first lamp I'm going to try is the 6838. It's rated at .024mA. I installed a 270 Ohm resistor instead of the original 68 Ohm which, I believe, will limit the current of the circuit to ~100mA. You can see the lamp is about 1/3 the physical size of the old one too. I haven't wired it in yet.I went ahead and replaced the original Paccom capacitors in the rectifier circuit with new matched 105c Nichicons. I also replaced the original 1N4003 diodes with new UF4004 types.I found two other 220uf capacitors out of tolerance but I don't have any on hand. Looking around the board I can see that the IC's are dated around 1986.I have the original microphone and User's Manual too.I plan to go through the unit with a fine-tooth comb!

author: Cybershaman
author_rank: Contributor
timestamp: September 08, 2020, 06:18:06 pm
content: Ho HO! You have definitely piqued my interest, sir! I will be following this project with rapt attention! In fact, I will be following your lead, especially since, like I mentioned, I am pretty inexperienced as far as electronics are concerned. And, hey, if I mess something up, I have a backup unit!A couple of questions/comments...- Can you enlighten me on your decisions concerning the rectifier circuit? Were the components just old? And in what way do the higher quality components help with the function of the unit itself? Just more stable power? (Always a good thing!)- Where were the other two caps that were out of tolerance? Did you go around the board with your meter testing every cap?- Were you just noting the date of the ICs to reflect the manufacture date? Or is there something significant about that?- Amazing that you got the mic AND the original manual!OK. I'm having a particularly bad day pain-wise, but I managed to get some pics of my two units and am throwing them up simply for reference.Looking forward to hearing your results with the lamps and with any other mods/improvements/repairs you do!Oh! By the way, I was looking over my units again and I noticed where I got that 1993 date for the Rev. C unit! I'll include it in the pics below. Note: The text underneath "Revision D" just says "CIRCUIT SIDE". I couldn't get it to show up when I took the pic from a higher angle. I'm assuming that just means "Put this side facing all the circuit thingies, dumby.Maybe you could help me decipher what is going on there and what information it is conveying. I sometimes have a hard time mentally when my pain gets bad.One other little note: you'll notice that one unit came with a self contained resistor network DIP for the crossover and the other has a handmade one (80.6 ohm which I believe comes out to almost 90Hz). I wonder if they made some by hand at the factory? I just can't see someone (well, at least after the year 2000, maybe?) wanting to use a 90Hz crossover. But, hey, who knows?EDIT: The last picture showing the front panel of the two units, the unit with the Rev. B board is on the bottom and the Rev. C is on top. Personally, I like the Rev. B version!

author: Cybershaman
author_rank: Contributor
timestamp: September 08, 2020, 07:04:50 pm
content: PS: I am curious what you think of the different wiring configuration for the lamp in the Rev. C board. Looks like they just did away with that resistor altogether! Maybe they were having repairs coming in with them blowing out?I would love to hear what you think!Well, I have to take it easy. Having a rough time. Ordered some components so that I can start soldering when I get better. Am I a nerd if I really enjoy purchasing semiconductors? heh, heh.

author: Smoky
author_rank: Frequent Contributor
timestamp: September 08, 2020, 08:50:38 pm
content: I found out that the Richter Scale III that I own is the first version.Here's one comparison between your boards and mine. Notice how AudioControl added a trim-pot in the microphone circuit. I was told it was added to allow adjustment to the microphone's sensitivity.If possible, let me know if you can read the value on that trim pot and of the resistor that is swung over to it. Plus, let me know what part number is stamped on the four diodes to its immediate left.

author: Smoky
author_rank: Frequent Contributor
timestamp: September 08, 2020, 09:23:01 pm
content: The following issue most probably pertains to your unit. I won't know for sure if it is also an issue in mine until it's back together and tested.The first picture is of the area of the board relating to the infrasonic filter.When the equalizer is enabled, an anomaly appears on the waveform. It is supposedly caused by the incorrect selection of the stock capacitor and resistor values. The issue shows itself on a graph in picture two.In picture three, and with the modified capacitor and resistor values installed, the graph shows that the issue is almost completely resolved.Let me make it clear too, I'm being helped by a very generous individual on AudioKarma.org

author: james_s
author_rank: Super Contributor
timestamp: September 08, 2020, 09:24:48 pm
content: I've always thought lighted analog meters look really classy.Wow the back of that one is cooked! I'd be tempted to replace the lamp with an LED, feeding it with DC so it doesn't flicker, that will prevent further deterioration of the plastic meter scale.

author: Smoky
author_rank: Frequent Contributor
timestamp: September 08, 2020, 10:01:58 pm
content: These little 16 pin plug-ins came in today too and gold plated on top of that. I even bought a cover so to hide my special resistor "recipe"As for the lamps, I'll stick with the incandescents. The smallest one of them all arrived today. It's the CM7009 and runs at .020mA. The largest one is a 2185 that looks really similar to the original. The one with a base is a CM7839. All of the lamps are 28 volt types.

author: Smoky
author_rank: Frequent Contributor
timestamp: September 08, 2020, 10:28:26 pm
content: This area of the board is of the equalizer/frequency filter circuit. Unfortunately, AudioControl will not release any of their schematics. I back-lit the board to be able to see the traces better.Looking close at it, I realized that these are all coupling capacitors, both film and electrolytics. Starting from the left and going right, it is easy to see where the channels separate and then repeat themselves even though the capacitors appear random.I did some research on these Paccom capacitors and found that several of the black "EV" types have failed. But the capacitors in blue stamped "EVL" are low-leakage types that still measure good, and not only good, they measure better than brand new Nichicon UKL's!The only capacitors that beat the "EVL" caps were PP film caps that I have in one equivalent value and voltage.The green capacitors are also Paccom brand but they are the Polyester type of film capacitors. Not the greatest for audio in today's World.I'm debating on replacing them with PP and PPS caps, and that goes for the low value electrolytics too.

author: Smoky
author_rank: Frequent Contributor
timestamp: September 09, 2020, 12:22:57 am
content: To me, this is goodThe guy on AudioKarma.org just described as to how he figured out the "infrasonic" filter issue inside of the Richter Scale Series Three.After studying the Eq, infrasonic, and rumble filters for a while he discovered that AudioControl had placed two hi-pass filters in the signal processing circuitry. If the EQ section was switched in, it would put two hi-pass filters back to back prior to the infrasonic filter. When the infrasonic filter was switched out, it was still being powered and its input was still connected to a common capacitor that caused feedback/interaction. And he went on...He discovered that the infrasonic filter topology in the Richter Scale was exactly the same as the infrasonic filter found inside of an APT preamplifier!As he explains it, AudioControl used large value caps with small value resistors, while APT used small value caps with large value resistors in its similar circuit. He, literally, plugged in APT's values and the issue disappeared!Would this be described as intellectual property infringementSo with the modified components installed and both the Eq and infrasonic filter in/on, the roll off is at 0.4dB down at 20Hz, as seen in the graph below. Btw, the graph shows both of the filters on and also off.The second picture is of the capacitors and resistors that need to be changed-out.Here are the new values:Replace 1uF with 0.1uF (100nF) 5% film capsReplace 4k7 with 75k 1% MFReplace 1k2 with 27k 1% MFReplace 68K with 640k 1% MF**The last picture was drawn by HalfApt describing the circuit with the Equalizer switched in.Many thanks to HalfApt of AudioKarma.org

author: Cybershaman
author_rank: Contributor
timestamp: September 09, 2020, 05:33:06 am
content: In bed and on phone. About to hit the lights. Will dig in to what you wrote tomorrow, Smokey.I just wanted to thank you for sharing SO MUCH information. I feel like I've hit pay dirt, here. I've had a nearly lifelong love of the Richter (as well as another AudioControl toy, the Pase Coupled Activator, of which I have a Series 1 and 3) and am looking forward to giving attention to my units. As I mentioned, I have a lot of physical/medical challenges and things have been rough these last few years. I haven't felt this good in a long long time.Thanks, again. I'll check that pot value/number tomorrow.

author: Cybershaman
author_rank: Contributor
timestamp: September 09, 2020, 09:36:44 pm
content: (Post 1 of 3)OK! I have some interesting things to report!I'll try to be brief and to the point.First up, the trim pot you are interested in is marked as a 1K 524M on the Rev. B board unit and a 1K 104M on the Rev. C board unit.The Resistor attached to the pot in both revisions is 270 Ohms 5% (Red - Violet - Brown - Gold). (I'm including the colors with resistors so you can verify in case I make a mistake.)The black diodes on the Rev C board are marked 818. I tried measuring them, but I'm not sure if I'm getting the right results. My multimeter might be dying and I've ordered new batteries.Did some searching and I came up with a 1N5818. Does that sound right?I'm including pictures of both boards.I also noted that it looks like something funny is going on with the the Rev. C board. Looks like they took out a nearby resistor.(EDIT: Nope. A resistor was hiding under the pot on the Rev. B board!) I tried to illuminate the board traces on the Rev. B board for comparison.Hope this helps! Let me know if there's anything else that I can do. As always, I would love to hear your thoughts/plans!EDIT: I find it interesting that they used clear diodes on the Rev. B board. Are those "signal diodes"?

author: Cybershaman
author_rank: Contributor
timestamp: September 09, 2020, 09:47:14 pm
content: (Post 2 of 3)Each board has some different jumper wires in the rear. Each unit uses a different style of RCA connectors, so this might not be anything special. I'm just posting it for posterity.

author: Cybershaman
author_rank: Contributor
timestamp: September 09, 2020, 09:51:33 pm
content: (Post 3 of 3)Posting this last because I didn't want to end on something mundane.On the Rev. C board, they put a 26 kOhms 5% (Red - Blue - Orange - Gold) resistor on the pot that changes the frequency of the warble tone!Take care!

author: Smoky
author_rank: Frequent Contributor
timestamp: September 10, 2020, 12:16:52 am
content: Thank you for the pictures Cybershaman!I asked about the diodes because mine are clear glass and I thought that they were Zeners having one green band. When you mentioned 1N5158, I turned to the internet for an answer. The diodes turn out to be a PNPN 4-layer Shockley diodes. This is all a guessing game for me when schematics aren't available. Anywho, I found a picture of an early Motorola 1N5158 part in a glass version, so they appear to be the same part.About that added resistor on the Warble-tone pot. I would guess that the resistor was a patch needed to refine the range of the potentiometer so that when the knob was turned its pointer would align correctly to the printing on the faceplate. I'm not sure. Everything will be tested on my end since no resistor is present. As you can see, the pot used in this first version Richter Scale is different than the ones used in later models.Now back to the stock capacitors used in the equalizer/frequency filter circuit. Mine are a mix of brands while your units have the same uniform types. I pulled four of mine just to test because "low-leakage" is a requirement in this area. Surprisingly, the bright blue Paccom 1uf 50v caps performed better than two brand new Nichicon UKL capaictors. But for those two small green Capar 1.5uf 50v caps, the leakage on my Sencore Z Meter would not drop to zero while the blue caps dropped to zero in under 5 seconds. This is the area I'm going to try PP and PPS film capacitors.

author: Cybershaman
author_rank: Contributor
timestamp: September 10, 2020, 02:03:44 am
content: Hi, Smoky!Headed for bed right now, but I just read your post. Very interesting! One quick note before I dash, though. Just wanted to make sure you understood that I was only able to read the numbers "818" (and I can tell they are the last 3 digits) on the diodes and that I was coming up with "1N5818" not "1N5158" in my searches. NOT implying you're wrong in ANY way! I just wanted to make sure that you read what I wrote correctly. Truth be told we are treading into areas where I am struggling to catch up in my understanding of electronics. I THINK I'm understanding everything OK, but bear with me if I ask many questions/clarifications!Anyway, goodnight and I'll be letting what you said sink in. Might be back later with some questions.Peace!PS: At some point, I might try and put things into a list to help me keep track of where you're at as far as repairs/replacements/mods go. I am definitely going to be following your lead on, likely, both of my series 3 units, so I want to be triple sure that I'm doing things correctly and understand the reasons. Also, I'm sure that there will likely be some other Richter fans that will come along and just devour this post in the future. There's just so very little information on these things that's easy to get to, as I'm sure you are more than aware. OK. Gotta run!PPS: I have OmniMic (the PC program with microphone) and was thinking that I could maybe test the output of the warble tone generator on each of the units I have to see if there is any difference in the frequency compared to what's indicated on the front panel dial. It could be that the change the resistor makes is very subtle and I might be unable to tell the difference, but do you think it's worth a shot? OK. I REALLY have to go now! Nite!

author: Smoky
author_rank: Frequent Contributor
timestamp: September 10, 2020, 03:15:32 am
content: Thank you Cybershaman,I'm guessing that your units are probably working just fine besides the lamps needing to be replaced. I wouldn't get too carried away.I think the one I own has seen many miles and I'm just looking to take a few of those years off of itI have the film caps on order, and when it's all wrapped up, I'm going to clean the sliders and pots with DeoxIT and put it through some bench testing. I'll take some voltage measurements around the board too.My problem is that I have no way of doing a frequency response test.I want to see what the "baseline" looks like first before any filter modifications are done.Plus, some really nice stereo equipment will be connected to this thing and I don't want it adding extra noise or distortion.The specification in the manual states its Total Harmonic Distortion is 0.005%.*I also have a thread regarding the Richter Scale Series Three on AudioKarma.orghttps://audiokarma.org/forums/index.php?threads/audiocontrol-equalizer-and-paccom-capacitors.928669/The replacement of the electrolytic capacitors are done. The UKL opposing pairs of caps are matched well under 1% in tolerance. The green Polyester capacitors are next. HalfAlt on AudioKarma says it's critical that the L&R channel capacitors match. He said even a 5% difference between the left and right channel capacitors will cause a noticeable deviation.Since the this original version of this Richter Scale did not include a potentiometer in the microphone circuit, I added one.I had three used 500mW Bourns 1K Ohm pots that have legs that point downward. The original 200 Ohm resistor measured 197.3 Ohms. Next I took a 100 Ohm resistor and soldered it to one leg of the pot. I then measured the minimum and maximum of the resistor/pot combination. It's range is from 100 Ohms to 1.1K Ohms. I set the pot to 200 Ohms and installed it. What's nice is that it reads correctly in circuit and easily fine-tuned in the futureAs for the lamp, it's installed. I applied small pieces of Thermo-Tec heat barrier tape to the PC board which allowed me to place the lamp further away from the back of the meter. I works great!And in the last picture, here's the Richter Scale with the new lamp installed and the front panel back in place. I also plugged-in the microphone and, while humming a low note, notice how the meter reflects it. This is going to be interesting to see how well this thing works

author: Cybershaman
author_rank: Contributor
timestamp: September 19, 2020, 08:21:05 pm
content: Wow! Great job! I'm very envious of both your knowledge and the test equipment you have. I wish I could drop one of my RS units off for you to massage. They obviously deserve better than I could ever do for them. :/Which lamp did you end up using again? I want to make sure so I can get a couple on order to install in my units. I would like to get one of my RSs into my audio system and don't want to do that until I can actually read the meter.BTW, I've been messing around with a pair of Polk Monitor 70 Series II speakers with their passive crossovers removed for a while now. Truth be told, it's been more of a crossover learning project and the unusual "2 1/2-way" design Polk used with these speakers has fascinated me for some reason. It's actually only been fairly recently that I really got them dialed in (using a MiniDSP 4x10 HD digital crossover). They sound pretty nice for a pair of fairly inexpensive speakers. I'm driving them with two vintage Carver TFM-15cb amps (the lower two and upper two woofers) and a two baby kit built S-5 Electronics monoblock tube amps (for the tweeters) that sit on top of each speaker. I use the MiniDSP to crossover to my subwoofer, too. I think I've got it dialed in pretty much where I want it right now, so I'm going to start soldering up a few resistor arrays around the value I'm using to plug into the RS. I plan on using the RS crossover because...,,,I just bought a pair of DCM TFE200s that I just couldn't pass up. I used to have a pair of Timeframe 700s a long time ago (I lived in Ann Arbor, MI where they were made) and was always sad I sold them when I went on "walkabout" as a young lad. I know for a fact that the TFE200s "have complicated crossover problems" and I am planning on eventually doing to them what I've been doing with the Polks for the last (checks calendar), oh, jeeze, almost eight years now.I seem to have an addiction to forming obsessive relationships with complicated gear.Anyway, if you could tell me what lamps you got, I'd really appreciate it. I'll keep following your progress and can't wait to hear how things go when you finally get them into your system. As always, the more details the better! If I can't work on my RS units like you can, I can at least live vicariously through you!(Seriously though, I wonder if there are any people out there who would work on my units? I wouldn't shy away from paying some good money to have them inspected/tweaked properly by someone who knows what they're doing and has the equipment. Know of anyone?)

author: Smoky
author_rank: Frequent Contributor
timestamp: September 20, 2020, 12:19:25 am
content: Hi Cybershaman,I come on EEVblog asking for help 99% of the timeNow about the lamp. My Richter Scale is setup for the lamp to run on 28VAC. Later versions of the RS use one half of the transformer winding and use a 14v lamp.The transformer winding measured 27.5v actual so the #6838 wired lamp that I used does run a little dimmer than it should, and since the original lamp discolored the back of the meter from heat, I'm fine with it not being so bright.I thought about adding a little rectifier board to power an LED but I'll wait and see how well the 6838 lamp holds up.As for your 14v circuit, you may need to experiment. The only 14v lamp I see with a low candle-power and current requirement is a #9388. Again, you may want to measure the actual voltage because I see a couple 13.5v lamps listed too.I think that AudioControl realized that the 28v lamps were running a little hot so they switched to a 14v circuit in later modelsSpeaker crossovers are a different animal. I have a friend willing to sell me his ADS L1530's but they are long over-due for the capacitors in the crossovers to be replaced. Plus the drivers are most-likely needing of a re-cone job too so the deal may not happen (too risky).I'd be happy to go through your units but I want to wait to see if my HP 35660A is able to run a frequency response test on them. That way, I can see how well all of the adjustments work.I did check the ripple current on the 14.70v rail in the rectifier circuit. It measured ~28mV, sort of high IMO. I ordered some 560uf /35v caps (in place of the 470uf) to experiment with to see if it'll bring the ripple down a tad and not effect the voltage all that much.Again, I'm just practicing/playing with this thing. Btw, here's a copy of the schematics uploaded by HalfApt on AudioKarma too.

author: Cybershaman
author_rank: Contributor
timestamp: September 22, 2020, 05:05:22 pm
content: I'll try to measure the voltage for the lamp leads on my RSs soon. I just got new batteries for my multimeter, so I'm good to go now, measurement-wise. I just have to wait for a a good day when my pain issue isn't being that much of a bother. :/ I think I'll go ahead and order up some lamps, though.Yeah, AC really messed up on those lamps. On the series 1 and 2 units, they only turn on when you engage the Analyze button. I guess throughout the three series they kept trying to up the cosmetic appeal of the units and figured that having the lamp for the meter on full time would make it look nicer, even though you hardly ever really use it. I guess they just used the same ol' bright/hot lamps they'd been using and, man, I haven't seen a single listing for a used Series 3 RS come up where the lamp wasn't burned out.I'm fascinated by speaker crossovers. Now that am getting the DCM TFE200s to play with, I'm thinking of making some nice external passive crossovers for my Polks that will look nice enough to display. I am inspired by a guy who for a while was making these insanely expensive crossovers for nicer Polk speakers (and a very few other makes/models) for people. He went by VR3 Mods and, OMG, his crossovers were works of art. Worthy to be displayed. Unfortunately, he (and I guess he had a few others helping him) stopped doing that sort of thing. He's still active on the Polk forums. I dug up one of his posts that have pics so you can see the sort of thing/level of quality he was shooting for here:https://forum.polkaudio.com/discussion/174528/polk-audio-sda-srs-2-3-crossover-modification-threadHe helped me out a few times. In fact, he modified some of his binding post plates to make it so that I could have three pairs of them on each plate so I could tri-amp my Monitor 70s, along with another plate for my Polk CS2 center channel speaker that I redid the crossover for as a fun little side project. So, I want to do something like that for my Model 70s. Just so they are "plug and play" instead of having to re-setup the digital active crossover. Plus I could maybe sell them. They sound pretty nice now, IMHO. I just can't decide if I want to replicate the stock Polk crossover (easy) or try to replicate my tri-amp setup.I'd be honored to have you look at my RS units. Let me know when you get some free time and I'll send them to you. I will make it worth your while. We can talk via PM when we get to the point where you're done with yours.I went to your other thread on Audio Karma. I've just been having a hard time lately physically, so it's been a bit of a challenge to do anything fun with my electronics/sound system. :/ I have to spend a LOT of time just sitting in bed and the pain makes it hard to concentrate. Hopefully things will improve. We'll see. I take life as it comes and try to live each moment to the fullest. Carpe diem is my motto!Take care and talk to you later! (I'll try to chime in at Audio Karma. I don't think I misread that resistor on the trim pot, did I.Check the pic for the Rev C board I posted. I'll double check the one on the Rev. B board. That one was shoddily soldered and kind of mushed down on the board. I must defend my honor! heheheh)

author: Smoky
author_rank: Frequent Contributor
timestamp: September 22, 2020, 08:13:35 pm
content: As for that resistor/potentiometer combo, I don't believe that the resistor value is too critical as long as it is below 300 Ohms or so. HalfApt on AudioKarma measured his combination in circuit and he read ~450 Ohms. I think each unit had its pot adjusted on the bench to best match its microphone. The 1KOhm pot adds quite a bit of adjustability. I installed a 100 Ohm resistor in mine.When you find some time, locate the two solder pads on the back of your boards that correspond to the resistor/pot combo and publish what you measure on your DMM for resistance. It'll be interesting to see where your units are set at.Anywho, I'm making some test leads for my signal analyzer. I own some Harbour Ind. RG-316 coax but I'm also going to try some RG-400 (double-shielded) to make the BNC cables. I ordered some Amphenol ends and the proper crimping tool too

author: Cybershaman
author_rank: Contributor
timestamp: September 25, 2020, 06:46:33 pm
content: Sorry I haven't got back with you. Been having a rough go of it physically/medically these last couple of weeks.I'll try to get that measurement for you soon.

author: Cybershaman
author_rank: Contributor
timestamp: September 25, 2020, 07:05:18 pm
content: Rev. B unit: 672 ohmsRev. C unit: 648 ohmsDoes that sound like I measured it right?

author: Cybershaman
author_rank: Contributor
timestamp: September 25, 2020, 07:09:47 pm
content: PS: I ordered some lamps...Eiko 6838 T-1 Wire Terminal Halogen Bulb, 28V/0.024 AmpEiko 2182 14V .08A T1-3/4 Wire Terminal Halogen BulbI'm not sure about the 14V bulb. Like I said, I've been having a rough time lately and I ordered them with my phone after I went to bed. I was, like, "I'm ordering some lamps!"

author: Cybershaman
author_rank: Contributor
timestamp: September 25, 2020, 07:45:12 pm
content: BTW, I took a look at the diodes in the rectifier circuit of my Rev. B unit and they're 1n4002 diodes. Thinking of doing what you did and swapping in some UF4004s and the caps while I'm at it. (I have some nice 470uF Nichicons looking for a home.) While it might not make a HUGE difference, it would be something to do just for fun. I need to stay busy and distracted from the other stuff I have going on. I can't just sit around my house/in bed all of the time. It's really not healthy.At any rate, can you think of any reason NOT to? Oh, yeah, I'll swap in a 100 ohm resistor like you did for the lamp, too. I definitely don't want to replicate what AC did when they first produced these units.After your done with yours, I still wouldn't mind you taking a look at one or both of my units. Again, I'd make it worth your while and we could work something out via PM. Maybe do one at a time since I need to get one into my system mostly for subwoofer crossover duty. Anyway, hope all is going well with your RS. Can't wait to hear how it works in your system! Take care!

author: Smoky
author_rank: Frequent Contributor
timestamp: September 26, 2020, 12:59:23 am
content: Hi Cybershaman,My policy has always been, if I pull a 30 year old electrolytic capacitor out to test it, it doesn't go back in, even if it's good. The reason I tested the four 470uf caps in my Richter Scale is because one was bulged on the top. Before you decide to replace any of the capacitors in the rectifier circuit, you need to measure the level of ripple. I'd like to see what your waveform looks like too.I did not use a 100 Ohm resistor in the lamp circuit, I used a 270 Ohm. I used the 100 Ohm resistor in tandem with the 1K Ohm pot in the microphone circuit which gave me some adjustability (100 Ohm to 1.1K Ohm). I'm going to make a small rectifier board and use an LED if the lamp doesn't last. Btw, the amperage draw on the Halogen lamp you bought for your 14v circuit may burn hot. Did you check its candle power?Your resistance measurements prove that each unit was aligned individually. HalfApt isn't sure what the bench reference is though or how to perform it.I wish I could spend more time on electronics but my day job is kitchen and bath remodeling and it's been long hours lately!

author: Cybershaman
author_rank: Contributor
timestamp: September 26, 2020, 11:27:30 pm
content: Hey! It's a good thing you have steady work!But, yeah, that does cut into fun time, though. :/- That 14V lamp is 1 watt. Yeah, I had a feeling it might be too bright when I bought it. I don't really know where to get tiny lamp bulbs, so I got those from Amazon. Where do you recommend to get them from?- So, you think they dialed in each mic for each RS it was packaged with, eh? Well, I better remember that when I finally get one of mine set up. I just have the one mic between them.That does seem pretty labor intensive when your shipping, what, thousands of units to customers. Wouldn't they have had to use some sort of (tiny) anachoic chamber or something? Maybe they just had a reference resistor circuit or something and just plugged that in to dial them in on the assembly line?- I'll have to get back to you with the rectifier circuit ripple when I next have a relatively pain free day. I don't have a scope for the waveform, though. Just my DMM. I've actually been thinking of getting one. Suggestions?- I was going to replace those caps and diodes just for something to do. I have the opposite situation from you; I have too MUCH time on my hands! (Pain/medical issues willing, of course.) I do have to be careful to not get too carried away sometimes. Especially when working on old equipment.Anyhoo, let me know a good place to get lamp bulbs and I'll see about ripple soon.

author: Cybershaman
author_rank: Contributor
timestamp: September 26, 2020, 11:50:01 pm
content: PS: I just remembered that AC's Phase Coupled Activator Series 3 had a programmable 18db infrasonic filter. I THINK it was built into the crossover circuit, which also used a 16 pin resistor array to set the frequency just like the RS series 3. It was 14 pin with 6 resistors (there's no resistor in the middle slot). You calculated the frequency just like the crossover module. I could be wrong about where the filter resides, though. It might actually be in the bass restoration circuit. It's not shown on the simple signal flow diagrams in the manual. :/ Anyway, I just thought that was interesting. Peace!

author: Smoky
author_rank: Frequent Contributor
timestamp: September 27, 2020, 02:16:30 am
content: Here's a quote from HalfApt on AudioKarma:"I've had a thought to adjusting the mic sensitivity without a calibrated signal:AC instructions say to turn the volume control up until the meter reads 0dB.instead, pre-set the volume control to your normal listening level, then adjust the trimmer to get 0dB. Best for your system."Since I know that a fixed 200 Ohm resistor was installed in my unit, that's where I'll set the resistor/potentiometer combo for starters.What I'm looking forward to is the comparing of the Hi and Lo output crossover points on the DSA.About speakers, I've been following Troels Gravesen of Denmark. He builds custom speakers and sells the crossovers and drivers for each of his designs. The drivers he uses are state of the art, amazing stuff. I plan to build a pair:http://www.troelsgravesen.dk/Diy_Loudspeaker_Projects.htmHe also created a subwoofer enclosure using ScanSpeak 30W/4558T00 subwoofers as one of the options. I have four new in the box from a trade-deal two years ago to put to good use! Woodworking tools, I have plenty of

author: Cybershaman
author_rank: Contributor
timestamp: September 29, 2020, 05:24:53 pm
content: That's an interesting idea for adjusting the sensitivity.I'll peruse Troels Gravesen's website. Looks pretty interesting. Thanks for sharing!I would like to try and build a set of these someday:https://www.linkwitzlab.com/LXmini/LXmini+2.htmPartially because it looks like something that would be a little easier to build from a wheelchair standpoint.We'll see. That's a ways off in the future, though. I really do need a new subwoofer. I'm currently using a BIC Acoustech PL-200. They have a PL-200-II version now which moved the port from the rear to two in the front. Anyway, it's alright. But being in my small apartment it's standing wave central. I really need to find a new house soon so I can let my system breath a bit. Especially since I just got a pair of mint condition DCM Time Windows (build date: about 1983 or 84). I got them mostly for sentimental reasons. They really need space around them to sound properly. Anyway, I'm getting a bit off topic!Should I just move over to the Audio Karma site for further RS discussion? Or is this your main thread? I'm not sure when I'll feel well enough to dig back into my RS project. :/ Hopefully it will be soon.Talk to you later!

author: Smoky
author_rank: Frequent Contributor
timestamp: September 29, 2020, 09:51:36 pm
content: Things are going well Cybershaman!I mostly post here on EEVBlog. I'm geared more towards improving my audio equipment that I have while I'm in the process of remodeling my houseI'm planning to have it all come to completion around the same timeAnyway, I spent over six hours ordering parts for the two electronics projects I'm working on! This vintage gear takes some time to find the best fitting parts. My goal was to replace all of the Polyester caps with Polypropylene. I had to go through Digi-Key, Mouser, Arrow, and Newark to find them. Pin spacing had to be measured and crossed-over to make sure lead-length was sufficient on each part but they also needed to fit the space. I also wanted the Brand to be uniform and no distributor carried all of one series. Lots of fun though.I ordered RG-400 cable, Amphenol BNC's ,and an Amp Pro Crimper, to make test cables for the analyzer too. I'm in no hurry.Troels knows his stuff too. Click on one of those speakers and check out the drivers and tweeters he uses in his builds. Incredible.

author: Cybershaman
author_rank: Contributor
timestamp: September 30, 2020, 01:01:03 am
content: I can feel your good vibes, buddy! I'm happy your projects are coming along. Yes, I can relate to trying to find That One Kind of component. I am always amazed how places can stock all of these tiny things of such a wide variety of such and such a specific specification. And it seems like half the fun is hunting for the ones you need.I might hop in the other thread once I feel better. Hopefully soon. I'm sorry I keep bringing up my physical condition. It's just that it's such a big obstacle for me. Playing with my hifi, both working on it and listening to it, is one of the few things that makes me happy. I just have to keep going, one foot in front of the other. The alternative just isn't an option for me.Anyway, I will get those measurements soon.OH! Speaking of measurements! I am getting a pair of mid-80s DCM Time Windows speakers (they are in near perfect condition, in original boxes, from a collector, and the price was just too good to pass up AND he's going to deliver them to me himself because he comes to my area regularly! ) and the seller also just happened to have a Speco Model SA-1000 analog multimeter. He's going to have his tech check it out and make some leads for me, too. He wants just 18 bucks for it. I have NO idea what to look for in an old multimeter. Does that sound reasonable or is it a waste of 18 bucks? Any advice would be greatly appreciated!Anyway, that's it for now. Oh! I'm going to go ahead and put that 14v lamp in my Rev. C RS. I tried it out by just touching the leads to the solder pads behind the existing lamp, and while it hot warm, I was still able to hold it in my fingers for a while without it hurting.Ok. That's REALLY it for now! Take care and keep the reports on you progress coming! Peace!

author: Smoky
author_rank: Frequent Contributor
timestamp: October 03, 2020, 01:35:51 am
content: Here's another update since tons of parts came in. I revisited the new Nichicon UHE 470uf 35v capacitors I installed in the rectifier circuit to replace the original Paccom caps. The measured ripple current seemed high with the new caps since the rails are only 14VDC. The first two pictures show the DC voltage and the AC ripple of the new 470uf caps.I went ahead and ordered a bunch of Nichicon UHD 560uf 50v caps to experiment with. I matched four of the new 560uf caps right at 520uf actual. That's about 10% higher in value from the original 470uf's. In they went.The last picture is of the new 560uf UHD caps installed with one of the 470uf UHE caps sitting loose for comparison.

author: Smoky
author_rank: Frequent Contributor
timestamp: October 03, 2020, 01:40:32 am
content: And here are the results from the new 560uf UHD caps.The voltage of the 14v rail increased from 14.61 to 14.80 VDC.The ripple dropped from 27.8mV to 19.4mVSo increasing the value of the capacitor 10% caused the voltage to rise 1.5% yet dropped the ripple 30%!I also noticed that the voltage readings with the 560uf caps remains very stable compared to the 470uf capacitors, where the 14v rail jumped around 2-3 hundredths of a volt DC.I think when choosing a capacitor in a rectifier circuit, shy away from using a miniaturized cap if possible. Ripple current capacity rules and size mattersI also read the data sheet of the LM4136CN IC's scattered all over the PC board. The minimum supply voltage for them is 12v, typical is 14v, and their maximum is 18v.The crimpers, BNC's, and crimp-on RCA jacks came in so I made new RG-400 cables for the HP 35660A to compare the frequency response curves of both channels. I measured the custom resistor module and found that a few of the eight resistors didn't match very well so the analyzer should be able to show the irregularities. I have also been told that there are eight 22nf capacitors around the LM4136CN IC's that can cause the response curve to vary too if they are out of tolerance amongst each other.

author: Smoky
author_rank: Frequent Contributor
timestamp: October 15, 2020, 03:50:48 am
content: The AudioControl Richter Scale has one input and two outputs for each channel. One of the outputs is the "Low" signal and the other is the "Hi" signal based on the crossover frequency.I connected the HP 35660A to the Richter Scale one output at a time. At this point, I didn't know how to set the marker's position but it didn't really matter because the graphs looked obviously different. Here are the results for each output. The factory crossover resistor module is installed and makes the signal split at ~80Hz. Here is the order of the pictures:Left channel Hi-out.Right channel Hi-out.Left channel Low-out.Right channel Low-out.Notice how the roll-offs don't quite match when compared to the opposite channel.The Left channel Hi-out even appears to climb higher in dB than the other three.So, definitely, something is wrong

author: Smoky
author_rank: Frequent Contributor
timestamp: October 15, 2020, 03:55:34 am
content: There are eight 22nF "feedback" capacitors in the crossover network. I removed and measured them. Opposing pairs varied ~7% in value so I replaced them. I installed eight PP caps that all measured .0215uf.I also made a new resistor module using eight 100K Ohm resistors. All eight measured 99.12K Ohms. This will also shift the crossover point to 73Hz. I used a new Aries 16 pin header and cover.While I was installing the new 22nF caps, I noticed that pin 14 of an LM4136CN in the crossover circuit appeared to be open. Just a little bit of solder was on the pad.I wonder if this is why the Left channel Hi-out had a higher dB level?Wait until you see the new results from the HP 35660A

author: Smoky
author_rank: Frequent Contributor
timestamp: October 15, 2020, 04:11:11 am
content: Here are the Left and Right channel Hi-output graphs.I learned how to set the marker to a fixed 100Hz. Take a look at these beauties nowThe difference in the channels is reflected by the marker's "Y" dB-down reading.The Left channel now fades off at the same level as the Right!

author: Smoky
author_rank: Frequent Contributor
timestamp: October 15, 2020, 04:19:32 am
content: And here are the Left and Right channel Low-out graphs.I adjusted the span of the DSA to move it more towards the low frequencies and set the marker to a fixed 50Hz setting.Are we Rock'n or notThe last picture is the schematic to the Linkwitz-Riley crossover circuit. I put red dots next to the eight new 22nF "feedback" capacitors and the green dots are next to the eight new 100K Ohm matching resistors that were installed.Let me tell you, that HP 35660A is bad-to-the-bone

author: Smoky
author_rank: Frequent Contributor
timestamp: October 15, 2020, 06:01:22 am
content: But then, there's the $1,000,000 questionHow accurate is the resistor module in relation to the actual crossover frequency being set in the Richter Scale?In the manual, there is a formula. Divide 7234315.59 by the wanted frequency to get the required resistance of the needed 1% resistors.So, since I used 99.12K Ohm resistors (actual), I plugged in 7234315.59 and divided it by 99,120. The result is 72.985Hz.Now how can I confirm this?I set up the Siglent waveform generator to a sine wave at 100mVrms. I sent that to the Left channel input of the Richter Scale. I then attached two BNC to RCA cables from the Left channel's Hi and Low outputs of the Richter Scale into channel 1 and 2 of my TDS420 oscilloscope.I turned the frequency dial of the Siglent until the amplitude of both channels of the oscilloscope were equal.Guess what? The frequency on the oscilloscope reads 74.424Hz.So, 74.424Hz minus 72.985Hz by AudioControl's calculation means something is off a whopping 1.439Hz

author: Cybershaman
author_rank: Contributor
timestamp: October 16, 2020, 07:46:52 pm
content: Hey, Smokey.Been having a rough time of late, but I've been trying to follow your progress.Yes, something is off on AC's formula. It's interesting that they later just said to use 7200 instead of 7234315.59. If you use 7200 with your 99.12K resistors it comes out to 72.64 (rounded) which is 1.784Hz off.Clearly something in the equation needs work.Is this after you swapped out the resistors and caps?I had another question for you concerning how you are hooking your RS into your system. I ran into trouble when I realized that with the series 3 they did away with the dedicated warble tone frequency output and lumped it into the main output. That kind of sucks with newer systems these days that don't have tape loops. So, if you want to use the warble tone generator you have to manually swap the main output on the RS to another input on a modern preamp in order to adjust the volume until you get a reading of 0db on the meter @ 250Hz. That's pretty inconvenient for someone like me who is regularly swapping in different speakers. :/ It's really hard for me to swap cables when I'm sitting in a wheelchair. Anyway, I'm curious how you are integrating your RS into your system. Do you have your RS installed in a tape/processor loop or are you going straight pre-out to the RS and then to your main left/right inputs on your amplifier?Anyway, that's it for now. I've been having a very rough go of it lately, so I haven't been able to do much work on my system. I actually just got a Emotiva MC-700 which does all of the bass management very nicely. HOWEVER, I am also expecting a pair of DCM Time Bass subwoofer modules soon and I think I will have a job for the RS when those arrive. Stay tuned.

author: Smoky
author_rank: Frequent Contributor
timestamp: October 16, 2020, 09:43:58 pm
content: Hang in there Cybershaman!I think AudioControl realized that the value of the resistor module wasn't going to move the crossover point in every RS the same. It probably varied between units so the formula is just a general one. As you can see, you need to test your unit to verify the crossover point.I plan to make several more resistor modules for my unit but that won't be until I build my speakers and measure their responses.My stereo system consists of a Cary Audio SLP-98P preamplifier which, Btw, has a monitor switch. The amplifiers I have are two Cary Audio CAD-211FE mono tube amps for the Hi-outs going to the main speakers and a Nakamichi PA-7 for the Low-outs going to the two sub-woofers.I'm about to move the cables of the DSA to the Richter Scale's Main Rcvr/Pre-amp connections. There is a known issue that HalApt identified regarding a dip in the 20Hz area and who has found a fix for it

author: Smoky
author_rank: Frequent Contributor
timestamp: October 16, 2020, 11:17:40 pm
content: The cables from the HP DSA are now plugged into the input and output of the Left channel Main Rcvr/Pre-amp connections. I did measure both channels and they are the same so here is the Left channel graphs to show the issue.The first picture is with the signal passing through the Richter scale without the Equalizer Program or the Subsonic Filter activated.The second picture is with the Equalizer Program activated.The third picture is with the Equalizer programandthe Subsonic Filter activated.And the fourth picture is just the Subsonic Filter activated.Notice the dip around 20Hz without anything activated and then it gets even worse when the EQ Program is turned on. A member of AudioKarma, HalfApt, believes it's caused by incorrect values of several capacitors and three pairs of resistors in the infrasonic circuit when none, one, or all of the filters are energized.

author: Smoky
author_rank: Frequent Contributor
timestamp: October 17, 2020, 06:05:07 am
content: Check this out Cybershaman!Here is the before and after of the required component change-out in the infrasonic filter circuit. 1uf electrolytics are replaced with 0.1uf PP film caps. Three factory matched pairs of resistors were changed out with the required modified values.

author: Smoky
author_rank: Frequent Contributor
timestamp: October 17, 2020, 06:22:06 am
content: And here are the graphs to show the change.The first graph is the Richter Scale with no programs switched in or activated.Followed by the second graph with just the Equalizer Program activated.The third graph reflects the Equalizer Program and the Subsonic filter activated.And the final graph is with just the Subsonic filter activated.Absolutely amazing!Next was checking the equalizer's sliders for proper operation. I set the waveform generator to a 30mV sine wave corresponding to each of the slider's frequency. At first, many of the sliders made no difference when moved up or down??? So out came the DeoxIT D5 and F5, and wow!, the sliders went from a heavy feeling to a smoooooth glideEvery incremental movement of the slider raised or lowered the amplitude of the waveformAll of the sliders at center (0) measured 29.1 to 29.4mV. All of the sliders would max-out at ~115mV and bottom-out at ~7mV.Next is the removal of the 22uf Capacitors in the infrasonic filter.