(Solved) An audio related question, if I am allowed to ask here - Page 1
Forum section: electronics / beginners

author: JamesHowlett
author_rank: Contributor
timestamp: March 22, 2015, 05:02:50 pm
content: Hello everyone,I am not sure whether here is the right section of the forum or not but the question is following. I have a turntable connected to my amp. The output of the turntable comes directly from the needle of the turntable without amplification. However the signal is still little bit high, thus i cannot turn the volume knob more than 1.5 and if i turn it to 2, there is a huge difference. That's why i want to build a voltage divider box with two potentiometers between the amplifier and turntable, one potentiometer for each left and right channel. So, what should be the value of the potentiometers?Looking forward to hear your answers.RegardsOz

author: Thor-Arne
author_rank: Unknown
timestamp: March 22, 2015, 05:27:31 pm
content: This sounds like a moving-magnet pickup connected as a moving-coil pickup.Is there a MM/MC selector switch?

author: Seekonk
author_rank: Super Contributor
timestamp: March 22, 2015, 05:45:09 pm
content: Inputs used to be about 50K. Anything from 20-50K should work. A two resistor voltage divider should be sufficient with a 33K/10K combo.

author: LA7SJA
author_rank: Regular Contributor
timestamp: March 22, 2015, 09:15:54 pm
content: Two posibilities, moving magnet connected to a moving coil input or a ceramic cartridges connected to a moving magnet input.Moving coil 200 µV to 2000 µV outputMoving magnet 4-10mV outputCeramic .3V to 2V outputSo I have two questions:1) Make and model of cartridge (so we can figur out the type and output)2) Make and model of amplifier and what input you ar using (finding input level an imp.)Then and only then can enyone give you a estimate and not a gestimate. This helps to provide you with the best posble performance from your turntables cartridge.Data for NAD PP375 Phono AmpPP375 Moving Coil Moving MagnetInput Sensitivity 1.6mV 18mVInput Overload >4mV (20Hz – 20kHz) >40mV (20Hz – 20kHz)RIAA Accuracy +/- 0.25dB +/- 0.25dBTHD <0.03% (20Hz – 20kHz) <0.03% (20Hz – 20kHz)IHF A S/N >76dB (100 Ohms load) >77dB (IHF cartridge load)Ch. Sep. 1kHz >80dB >80dB10 kHz >70dB >70dBJohan-Fredrik

author: JamesHowlett
author_rank: Contributor
timestamp: March 23, 2015, 07:04:55 am
content: Wow, lots of responses in a short time. Great! Thanks a lot to each one of you.I do not think that I have a MM/MC switch but i check it when i am back home today.The amp is an old Rotel 340 and the record player is a Dual 1010. Record player still has the original dual cartige on it. But i will confirn it too. I checked the service manual of the amp yesterday and i saw in the part list that the volume potentiometer is 100kOhms. But i do not know why i did not checked the input impedance of the tuner input(aah!). By the way the record player is connected to the tuner instead of phono input because i could not find the proper connector and took the easy solution.So, how do we proceed now?RegardsOz

author: LA7SJA
author_rank: Regular Contributor
timestamp: March 23, 2015, 08:27:45 am
content: Some info about the Dul 1010Specifications: 4 Speed (16.66/33.33/45/78 RPM), Cue Control, Idler Wheel DriveSpec Sheet Data: Motor: 2 Pole, Single Phase Induction TypePlatter: Choice of two: 8-1/2 inch and a 11 inchWow & Flutter: < 0.12%With 8-1/2 inch platter: +/- 0.25% maxWith 11 inch platter: +/- 0.17% maxRumble: (S/N Ratio) Weighted: > 50dBUnweighted: > 42 dBTonearm: No Information AvailableCartridge: Any Ceramic or Crystal cartridge with a 1/2 inch mounting.Standard Stereo Cartidge is the CDS 620/4/45 or the CDS 630/5.Tracking Force: Not AvailableYears Manufactured: 1964-68' Price (New): $70.00 (USD)Whats interesting is that the Ceramic/Crystal cartridge giving you > 1V signal, have you tried the aux input.Johan-Fredrik

author: JamesHowlett
author_rank: Contributor
timestamp: March 23, 2015, 09:13:51 am
content: No, i did not try the aux becaus there i connected a Bluetooth audio receiver. Is there a different input impedance for the different inputs? I also added your suggestion to my list for the things which i have to check/try. Thanks

author: LA7SJA
author_rank: Regular Contributor
timestamp: March 23, 2015, 11:11:00 am
content: No so much different input impedance as Input Sensitivity and Input Overload!Why not "borrow" the AUX input for a quick test? A picture/scan of the input selector and preamp schematic would be helpful to.If you have the specs for the input channels on the amplifier would also help a lot.Johan-Fredrik

author: KJDS
author_rank: Super Contributor
timestamp: March 23, 2015, 11:15:50 am
content: Both MM and MC cartridges have outputs that are not flat with frequency, which is why amplifiers have specific phono inputs. If your amp doesn't have a phono input then it's worth the effort of building a phono equalizer.

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 23, 2015, 11:51:59 am
content: The RIAA standard for the common MM (moving-magnet) phono pickup cartridges is a 47K ohm terminating impedance. Also, as KJDS mentioned, the phono input is RADICALLY frequency shaped to the "RIAA curve" It is NOT "flat" like the line-level inputs. See:http://www.graniteaudio.com/phono/page5.htmlThe turntable plays no part in any of this as it simply passes the audio signal directly through from the cartridge out to the cables and into the phono preamp. There are some (rare) turntables that include the RIAA phone preamp inside, and offer line-level outputs for better integration with modern hi-fi gear in this post-vinyl era.Traditionally, moving-coil ("MC") phono pickup cartridges had a lower output than the more common moving-magnet ("MM") cartridges. So a gain (and often impedance) switch was provided to accommodate both kinds of cartridges. It is VERY unusual for a phono pickup to have TOO MUCH gain. Most of the important details (the identity of the phono pickup cartridge, and the phono input details of the amplifier) are not in evidence here, so we can only speculate.

author: LA7SJA
author_rank: Regular Contributor
timestamp: March 23, 2015, 12:17:49 pm
content: Most common cartridge of the 50's and 60's was the ceramic phono cartridge. Typically, these were supplied as turnover cartridges in early (non Hi-Fi) tube and solid state stereo systems, record changers and children's players. Some were higher quality versions such as the Decca Deram. Ceramic cartridges are high impedance and high output voltage (200-1200mV) devices. Another feature of this type of cartridge is that its response is amplitude based pick-up instead of velocity based like magnetic cartridges. This means that phono equalization is not required. A record player with this type of cartridge may be plugged directly into an high impedance (tube) input. So no RIAA, MM or MC just a linear high impedance input that can handle 1V rms.Johan-Fredrik

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: March 23, 2015, 03:19:42 pm
content: Quote from: LA7SJA on March 23, 2015, 12:17:49 pmYeah, but those require about 10 tons of tracking force IME. Goodbye records!

author: Thor-Arne
author_rank: Unknown
timestamp: March 23, 2015, 03:29:23 pm
content: "RIAA equalization is a specification for the recording and playback"All newer (after '54) records should have been recorded with the inverse RIAA curve, so you really need to have it connected to the phono input for these records.

author: JamesHowlett
author_rank: Contributor
timestamp: March 23, 2015, 06:19:34 pm
content: Some quick feedbacksSchematics are here:http://imgur.com/1LvIyAI,EqiQkqy,FYz1QCC,4usVicj#0I tried the aux input but made not much of a difference than the tuner input.The cartridge is a Dual DN5.There is a phono jack but i did have the male phono connector, that's why I choose the easiest way to connect. I may go to a shop and buy a connector tomorrow to try it with the phono input.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 23, 2015, 07:27:02 pm
content: Seems like the Aux and Tuner inputs on your Rotel should have (mechanically) worked with male RCA plugs (one for the right channel and one for the left channel if you have stereo) and so should the Rotel Phono input - so not sure why you need another cable/plug. In any event, it is possible you will get better sound when using the Phono input (with the proper cable/plug). On the other hand, the stylus and cartridge you are using might be a flip over ceramic type - it's been a while since those were in vogue - I'm not sure how it's output will work with the phono input - let us know what you hear. (I think it is possible that you have a ceramic cartridge which has a higher output than a moving magnet and therefore it might not be ideally suited to the phono input.)Once you get the cabling/plug and input squared away you might experiment with a moving magnet cartridge for better sound (and probably less record wear). Modern phono inputs (like what you probably have on your Rotel) generally look for outputs from a moving magnet cartridge (some higher end systems will use a moving coil but it's doubtful your turntable and amp were designed with a moving coil cartridge in mind). However, before investing in a moving magnet cartridge you should check first to see if your 1010 has anti-skate on the tone arm. If not, you might just enjoy the current cartridge/stylus.If it sounds good and gives you the gain control you are looking for when you plug in to the phono input(s) enjoy the music. If it doesn't work properly, post a photo of the cartridge in the headshell mounting and the back of the Rotel.- -Any chance the inputs on the Rotel look something like this? (The top is a Rotel RA-310 that had phono inputs for both magnetic and "X.TAL" (ceramic?) cartridges; the bottom is a Rotel RA-312 that had phono inputs marked more clearly for both magnetic and ceramic cartridges.)Having said all that.... if you are happy with the sound quality and just want to change the gain your original question/suggestion about a voltage divider might not be a bad way to go

author: katzohki
author_rank: Frequent Contributor
timestamp: March 23, 2015, 10:32:05 pm
content: Btw, if you're using pots as a volume control for L and R channel, you should get "ganged" pots. Unless youWANTto vary the L and R volume independently.

author: LA7SJA
author_rank: Regular Contributor
timestamp: March 24, 2015, 06:28:35 am
content: Quote from: JamesHowlett on March 23, 2015, 06:19:34 pmAccording to circuit diagram you provided you have an input for ceramic pickup that should do the trick. It is marked PHONO CER, try this and report back with the results.Johan-Fredrik

author: Electro Fan
author_rank: Super Contributor
timestamp: March 24, 2015, 04:25:22 pm
content: JamesHowlett, That's cool - maybe the turntable and the Rotel were purchased together? Otherwise kind of a lucky break - not a lot of integrated amps around these days with a ceramic phono input. Should be optimum for this setup.Definitely let us know what happens when it gets all plugged-in correctly.---Johan-Frederik, you have been on top of this since the get-go of this thread; impressive! I'm guessing you might be somewhere near the intersection of electronics and hifi?Quote from: LA7SJA on March 24, 2015, 06:28:35 am

author: LA7SJA
author_rank: Regular Contributor
timestamp: March 24, 2015, 06:31:55 pm
content: Quote from: Electro Fan on March 24, 2015, 04:25:22 pmMy first formal education was a 3 year study in radio and television techniques with additional specialization in video and digital control. So these "old" things are not entirely new to me.Johan-Fredrik

author: JamesHowlett
author_rank: Contributor
timestamp: March 24, 2015, 09:41:28 pm
content: Hello again,First I want to say thank you all. I have not had so much feedback in a forum for a question before. There are too many information that i cannot digest in a short time but i will try my best.I could not buy the 5pin+gnd cable today for connecting the record player to the phono input of the amp because the shop is closed when i have been there after work. I will try again on Thursday. Or I will try to connect it to the ceramic and magnet inputs of the Rotel amp.I have been asked whether i am happy with the sound of the record player. Not really. That's why i can think about buying a new cartridge/needle after we improved the current situation. And I bought the amp and record player separate from ebay as an answer toThere is another point which I should explain. When I bought the record player, it had a mono speaker built into the cover and a single valve mono amp for the speaker. I cut the cable which came from the tone arm and was connected to the input of the internal speaker amp and soldered the cable to a phono connector which I use to connect to Rotel amp, there is no electronics in between the tone arm and the Rotel right now . You can see related info and at the link below.http://www.radiomuseum.org/r/dual_p1010vp_1010.htmlI have been also asked about the inputs of the Rotel RA-314. I attach a picture. It did not work from my smartphone browser. But i will try to modify the post from the laptop. hopefully you will see the picture too.I am trying to follow your answers and educate myself. And I will keep you posted answer your questions more specifically soon.One addition: I tried the ceramic and magnetic inputs (but only with headphones, because it is 11pm here right now and i do not want to disturb the neighbours:)). I can first report that the sound from aux or tuner input were more crisp and more on the treble side with lots of noise, whereas the sound from the ceramic or magnetic inputs were more clear and bass, so that I had to turn the bass knob to min and the treble knob to max, even though it was not enough to balance the tone. I will try tomorrow with speakers again and report back.

author: JamesHowlett
author_rank: Contributor
timestamp: March 25, 2015, 06:14:12 pm
content: Hello again,the results of the trials today.I connected the record player to the amp via ceramic input of the amplifier. Sound quality has been improved drastically! However the volume control started to work as an on/off switch. Volume knob below 1: silent, 1.5: loud but tolarable, volume knob 2: leave the room and go on listening from the kitchen( approx. 7m away). That's why I should first try it with the 5pin+gnd socket and in case it does not reduce the volume, I should build the potentiometer in between, or follow any other solution you had already or may suggest.I also attached some pictures of the needle and cartridge. The needle has 2 sides one is 78 and the other side is LP/S. At LP/S side the needle sits further back of the cantilever of the needle. However, at the 78 side the needle is almost at the tip of the cantilever.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 25, 2015, 09:52:07 pm
content: Good news about the sound quality improving drastically.As you can hear there is a lot of good audio information stored in the groove of the record. If you happen to have 78 RPM records the 78 side is useful but most records that are still lying around are more likely to be LPs ("Long Playing" 33 1/3 RPMs). As you noticed the tip of the cantilever (the stylus) and the cantilever itself change position relative to the record when you switch from one side of the needle to the other. Records were (are) made with the anticipation of a particular stylus and cantilever geometry. In addition to getting the right cartridge loading on the input, getting the geometry right is a key step in accurately retrieving the information in the grooves. The geometry generally includes getting the tonearm parallel (or nearly parallel) to the record and at the right height above the record so that the cartridge when mounted in the headshell puts the cantilever and stylus at the proper angles relative to the record. Additionally more "modern"/advanced tonearms will include a setting for the tracking force (in grams high enough to keep the stylus properly engaged in the record groove so as to properly retrieve the information in the grooves but not so high as to wear out the record, the cantilever, or the stylus). Further, tonearms often have an anti-skating mechanism that counter-acts the tendency of the record groove (one long spiral) from pulling the record too much to the inside of the groove; the proper anti-skate setting will keep the stylus evenly balanced between the inside and outside of the groove. These are not 100% precise settings but they can have an audible impact on the sound (as well as the long term wear). The reason it's important to get this geometry set correctly is that in stereo records each side of the groove represents one channel (left or right) of the original recording - which probably had two microphones placed to the right and left of the center of the stage and musicians being recorded.The reason for noting this is that you can continue to make some improvements with your cabling and input and also the gain you get (perhaps by changing the potentiometer) but if you want to continue further down the path of "drastically improving the sound quality" a next step might include getting two speakers. With just the one speaker built into the record player a listener hears mono rather than stereo. With a stereo system (including two speakers on a plane apart from one another) you can better recreate the sense of left to right sound imaging that was captured when a stereo recording was made. Whether this is important to a listener is a personal decision but in general the purpose of "hifi" was to reproduce sound in a manner that had "high fidelity" to the original sound being recorded. With two speakers you will hear more of what the audience would have heard had they been present for a symphony or orchestra, or rock and roll band, or jazz club performance, etc.The sound reproduction process can go further as once you get the mechanical energy accurately captured in the record groove and convert it to a magnetic and then electrical signal and then amplify it enough to drive the speakers, the speakers then convert the electrical energy back to mechanical energy as the speakers generate sound waves. What you will find next is that the system extends beyond the speakers to the enclosure (ie, the room) in which the speakers reside. As the sound waves travel out from the speakers they will begin to bounce off the floor, the ceiling, the sidewalls, the wall behind the listener, the wall behind the speakers, and anything else in the room. Depending on the room and it's furnishings some of the frequencies will be overly emphasized (reflected) and some will be deemphasized (absorbed). Altogether his will effectively act as a physical tone control that impacts the sound you hear well beyond the electronic tone control(s) of the system. By moving the speakers relative to the walls you can change the sound to some extent. Not only will moving the speakers relative to the room impact the frequencies emphasized or de-emphasized but you will find that in some rooms if you place the speakers at a distance apart from one another that is comparable to distance from the speaker plane to where you sit facing the speakers the sound will begin to "image" with more focus, and not only left to right but also front to back. In this manner you can begin to recreate not only left to right spatial imaging but also front to back depth imaging of the audio signal. With some recordings you will be able to hear the relative placement of the instruments and/or vocalists on the stage both side to side and front to back. This doesn't necessarily require expensive stereo equipment but it would ideally include a tonearm and cartridge setup with good geometry and two speakers for stereo. (You will find some recordings were much better made than others.)Net, net: you might try a new potentiometer to smooth out the gain control but after that the next step might be to consider two speakers for stereo. Enjoy the journey!PS, somebody here will say skip the records and go for CDs but my recommendation would be to stick with the turntable and records until you get the stereo speakers and the room placement dialed-in and then simply add a CD player which can be connected to an aux input. Then you can find a copy of the same music recorded in a record format and a CD format and determine if you hear any differences and if you have any preferences for one or the other.PSS, somebody else will say skip the entire system including the CD and just listen to MP3's or AAC's with earbuds on an i-something. YMMVEF

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 25, 2015, 10:34:35 pm
content: The reason for the "flip-over" stylus is because 33-1/3 LP discs use MICROGROOVE which are substantially narrower than the old 78 RPM records. Using the wrong tip will ruin the disc. In either direction.As for the excess gain, that remains a mystery. Perhaps something is wrong with the circuit. For example, if a feedback resistor has failed open, it will cause a large increase in gain. We are sure there isn't any active circuit inside the turntable?

author: JamesHowlett
author_rank: Contributor
timestamp: March 25, 2015, 10:44:02 pm
content: Great! thanks for your effort that you summarized all the valuable info for a beginners in the records world!There are some responses below.Quote from: Electro Fan on March 25, 2015, 09:52:07 pmUnfortunately the Dual 1010 only have a spring balanced tone arm and no anti-skate function. It is quite hard to adjust the force precisely I believe.Quote from: Electro Fan on March 25, 2015, 09:52:07 pmThe whole system is following: Dual 1010 (without cover speaker and internal speaker amp is not connected)> Rotel RA-314 amp> Hitachi HS-540 speakers. I realized that I have not mentioned about the all setup, my mistake, Sorrybut i am already in the stereo world.Quote from: Electro Fan on March 25, 2015, 09:52:07 pmI am ok with the practicality of the mp3 and CDs on the go, but if I lsiten music at home, I rather listen the 70's(Pink Floyd, Hendrix, King Crimson...) and earlier times with its own technology. warmth of the sound even noise from the record are the parts of the music.So, since here is an electronics forum lets talk about my plan for tomorrow; hopefully going to the electronic supplier, buying 5pin+ gnd cable (it is called as DIN connector i think), 4 RCA connectors, 1 metal project box and stereo potentiometers (i want to try 50k and 100k first).I will report back soon...RegardsOz

author: JamesHowlett
author_rank: Contributor
timestamp: March 25, 2015, 10:49:25 pm
content: Quote from: Richard Crowley on March 25, 2015, 10:34:35 pmI am sure, I cut the cable which comes from the tone arm and soldered it to a female DIN connector. from there it goes to the Rotel RA-314 amp. I want to check the schematics of the amp and try to find some clues on the circuit board of the Rotel. but if it's a resistor, it will not be easy to measure it on the circuit, i believe...would it be helpful if I measured the voltage of the signal with a multimeter?

author: Electro Fan
author_rank: Super Contributor
timestamp: March 25, 2015, 10:56:02 pm
content: Very cool; glad to hear you are already in the 2 speaker stereo world! And not only that but you are listening to Pink Floyd and Jimi Hendrix - you are well on the path to music nirvana!Yes, it is "DIN".While your tonearm doesn't offer anti-skate or height control at the pivot point you might be able to make some further adjustments at the headshell - possibly by adding spacers for up and down adjustments (if needed) and depending on how the slots were made in the headshell maybe back and forth for the cartridge mounting and stylus location.Here is a link to a site where you can print out alignment templates; it's a free way to possibly further tune your setup.http://www.vinylengine.com/cartridge-alignment-protractors.shtmlIf you really get into it here is a tool that helps:http://www.ebay.com/itm/Shure-SFG-2-Precision-Stylus-Force-Tracking-Gauge-for-Turntables-Vintage-75-/271768718595?pt=LH_DefaultDomain_0&hash=item3f46ad8d03&nma=true&si=lnZcAxuqrHrSW1C%252F5viCKobYT84%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 25, 2015, 11:09:51 pm
content: The DIN phono input is wired to the magnetic input circuit. So we are assuming you abandoned the DIN cable and substituted a pair of RCA/Cinch cables.With the RCA/Cinch cables you can try either the MAG or the CER phono inputs.It still seems very strange that a magnetic cartridge should have such extraordinarily high output.

author: Electro Fan
author_rank: Super Contributor
timestamp: March 25, 2015, 11:25:30 pm
content: maybe something in here that might shed some light on something with respect to cartridge output, input values, etc:http://www.avforums.co.za/index.php?topic=32113.0

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 25, 2015, 11:42:55 pm
content: Quote from: Electro Fan on March 25, 2015, 11:25:30 pmQuoteSo what information was there that we haven't been through already?

author: JamesHowlett
author_rank: Contributor
timestamp: March 26, 2015, 12:03:27 am
content: Quote from: Richard Crowley on March 25, 2015, 11:09:51 pmwhat could be a good method to measure the output cartridge output? would it be helpful, if i play some different records and measure the voltage over the RCA terminals per channel. would it give us an approximate clue?

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 26, 2015, 12:14:42 am
content: The audio signal from a magnetic cartridge is on the order of a few millivolts. Nothing you could measure with a typical test meter.

author: JamesHowlett
author_rank: Contributor
timestamp: March 26, 2015, 08:20:11 am
content: Ok, I want to go further with the build of the potentiometer box between the output of the turntable and the Rotel amp. As I mentioned before, I will buy a metal project box, 4 RCA/Cinch connectors and a double terminal potentiometer to turn the volume down. I sketched something. Please see the attachment.I have related questions please correct me, if I am wrong. If I connect one of the terminals of each channel to the ground and if I turn the potentiometer in the sketch to zero, the signal(current) will flow to ground from the input and will not transmitted to the output terminals (to the Rotel amp), unless I start turning the potentiometer. First question is: Should I place resistors between the ground and the pins of the potentiometer to avoid shorting the signal to the ground? Question two: Since the output of the cartridge is not dc, will the right component between the ground and the potentiometer be a resistor or a capacitor? And what will be the recommended values of the resistor (1k, 10k ?) and the capacitor (10nf ceramic?) ?

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 26, 2015, 10:32:01 am
content: Quote from: JamesHowlett on March 26, 2015, 08:20:11 amNo, not necessary.QuoteNothing more is required. Your circuit is fine as you show it. Recommend using a 50K ohm potentiometer. Something like:http://www.taydaelectronics.com/potentiometer-variable-resistors/rotary-potentiometer/logarithmic/50k-ohm-logarithmic-dual-taper-potentiometer.html

author: JamesHowlett
author_rank: Contributor
timestamp: March 26, 2015, 11:08:31 am
content: Quote from: Richard Crowley on March 26, 2015, 10:32:01 amAha! you suggest a logarithmic pot instead of linear!Thanks, I will do the shopping today and build the box on Friday evening. I will report back as soon as possible.

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 26, 2015, 11:11:02 am
content: For a fixed "trimmer" application like yours, you could use a linear pot, but it is slightly more "fiddly" to set.The logarithmic pot makes the adjustment easier for audio signals.

author: JamesHowlett
author_rank: Contributor
timestamp: March 28, 2015, 10:20:00 am
content: Hello,Just as a feedback. This will be put together today. I will report the results back after I solder everything later today.RegardsOz

author: JamesHowlett
author_rank: Contributor
timestamp: March 29, 2015, 10:20:06 am
content: Hello again,I finally finished building the box. I attached an image of it and the sketch per channel. It works a treat! I can turn the volume down from the box so that I can use a wider range of the volume knob of the Rotel amp. Logarithmic potentiometer was a good choice as well.The black wire which goes out from the right back side of the box goes to the chassis ground of the amp and directly connected to the box. Without this wire, I hear a big hum like the terminals are shorted.I thank everybody for sharing their experiences. Along the way, I not only find the solution to the problem, but also learnt lots of stuff about record players/cartridges etc...You are great EEVblog forum people!Regards,Oz

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 29, 2015, 10:29:17 am
content: Congratulations on your success.Note that the diagram you show "as built" is actually backwards from what your originally showed in #31.By wiring the INput to the pot "wiper", you are changing the load resistance on the phone cartridge pickup.That may change the frequency response of the cartridge, but if you are happy with the performance, then that is only of academic interest.The normal convention is to use the "top" of the pot as the input, and the "wiper" as the output.But, as I read in an antique IBM computer service manual:"Never attempt to repair or replace equipment which is operating to the customer's satisfaction."Of in more colloquial terms: If it ain't "broke", don't attempt to "fix" it.

author: JamesHowlett
author_rank: Contributor
timestamp: March 29, 2015, 10:53:06 am
content: I actually bread-boarded the initial sketch I posted before but for some strange reason it did not work. After trying the other variations, I finally found that this is the only combination which actually works. What you saw about in the IBM manual is actually a ground engineering principle, never try to fix a working systemSince the problem is solved, I think I can try to overhaul my Dual record player a little bit (even though it does not sound right after talking about the engineering principle above:))Thanks for your support again!RegardsOz

author: tooki
author_rank: Super Contributor
timestamp: March 30, 2015, 12:30:41 pm
content: Glad to see it worked for you!What you built is basically identical to what I built 20 years ago, when I was but a 15 year old grasshopper, for a MiniDisc deck I had. For some reason, Sony MD decks I've ever used have line outs that are substantially hotter than the inputs on their own receivers, so I had to bring the level down to be of similar level to the other components in the system.