Tannoy Precision 8D active studio speaker dead... - Page 1
Forum section: electronics / repair

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 22, 2014, 06:45:29 pm
content: Tannoy have ceased production of this model and will no longer service them. Neither will they release a service manual for this model. So I'm stuck with a pair of expensive studio monitors that serve little more purpose than a door wedge.So far I have replaced the regulators, the rectifier, the LM3886 power amp chips, but can't seem to bring it alive. The driver is fully working, as I tested it with the other amplifier from the other speaker. I just don't know what to replace next.Any ideas where else I could be looking or where to test next? I'm at a dead end here.

author: wraper
author_rank: Unknown
timestamp: October 22, 2014, 08:03:07 pm
content: Measuring voltages? What is on mute pin?

author: wraper
author_rank: Unknown
timestamp: October 22, 2014, 08:07:13 pm
content: testing != blindly replacing the parts.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: October 22, 2014, 08:09:46 pm
content: First rule of troubleshooting, thou shalt check supply voltages!

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 22, 2014, 09:01:10 pm
content: Quote from: wraper on October 22, 2014, 08:07:13 pmIt's the only option, since there's no schematics or service manuals.Quote from: nitro2k01 on October 22, 2014, 08:09:46 pmI have no idea what the supply voltages should be. The correct voltage is coming from the regulators, but I have no idea how it is distributed after that, as I have no info...So really the only way I can go about this is by blindly changing parts that may be damaged. Just wondered if there was a common problem with active speakers, or if anyone knows about this particular speaker?I have no idea where to go next, which is why I'm asking here...

author: krivx
author_rank: Frequent Contributor
timestamp: October 22, 2014, 09:05:38 pm
content: Quote from: LektroiD on October 22, 2014, 09:01:10 pmYou can figure out likely supply voltages from the IC datasheets and ratings on the filter capacitors. You don't need to know exact values, it's unlikely a voltage rail is a little off. It's fairly likely a supply has been pulled low or disconnected somewhere. What's are the voltages at the power amp IC supply pins?

author: wraper
author_rank: Unknown
timestamp: October 22, 2014, 09:06:50 pm
content: Quote from: LektroiD on October 22, 2014, 09:01:10 pmwtf LM3886 datasheet is for? I have a schematic for less than a 5% of devices I repair, still able to measure somehow.

author: wraper
author_rank: Unknown
timestamp: October 22, 2014, 09:18:03 pm
content: And yeah, replacing diode bridge??? That can be checked for sure. Just by checking AC voltage before and DC after, checking internal diodes with multimeter. Is there some voltage after diode bridge on filter capacitors at all? With such an approach you may end up reworking all pcb with just a blown fuse at fault.

author: Yago
author_rank: Frequent Contributor
timestamp: October 22, 2014, 09:20:17 pm
content: Compare voltages/waveforms etc to the working one?

author: Lightages
author_rank: Unknown
timestamp: October 22, 2014, 11:31:23 pm
content: A friend of mine had a bad set of Tannoys. After looking at his pictures of the circuit board I suggest resoldering every joint. They were very poorly built. This fixed his problem.

author: simingx
author_rank: Contributor
timestamp: October 24, 2014, 12:43:03 am
content: Quote from: wraper on October 22, 2014, 09:18:03 pm... or a faulty power switch, blown line fuse, defective power cord etc...

author: Riotpack
author_rank: Regular Contributor
timestamp: October 24, 2014, 03:04:23 am
content: a chip amp like this should be simple to repair.Start at the power supply, is there both positive and negative voltages on the amp IC?Is there any protection replays after the IC going to the speaker? (download the datasheet and find the pinouts) Can you input a signal straight into the chip amplifier input pin? (lift factory coupling cap and feed signal in to test)Usually after confirming power supply you simply start at one end and work through the amplifier stages until the signal ceases.

author: Riotpack
author_rank: Regular Contributor
timestamp: October 24, 2014, 03:07:36 am
content: Here are the schematics for the 6D which uses the same chip amp - I am unsure of the differences but it may help.

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 24, 2014, 10:29:02 pm
content: Quote from: Riotpack on October 24, 2014, 03:07:36 amThanks for the file, not sure how you managed to find it, but I wish it was as simple as the 6D, which only seems to have 2 power chips, there's 3 boards which all interconnect on the 8D, one is the power, then what appears to be a filter board, and a digital board. Looks like a pretty complex circuit on the 8D

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 28, 2014, 06:51:15 pm
content: I've done some tests, the 7915 is taking -36.0VDC in and throwing out -26.66VDC. This is a part I have already replaced, so I'm wondering if there's something else in line with it that might be causing the spurious reading?I can't do live tests for long as the 3x LM3886 chips are roasting without heat syncs. The rear panel provides heat syncing, and I can't access anything when it's bolted to it, as you can see in the pic above...

author: wraper
author_rank: Unknown
timestamp: October 28, 2014, 10:11:46 pm
content: Quote from: LektroiD on October 28, 2014, 06:51:15 pmEither it is dead or you measure it wrong. Common (GND) terminal of the 79xx is not the same as on 78xx regulators and is not connected to the heatsink tab.First of all check if LM3886 is using single supply or dual supply, if don't know how, measure if pin 4 is connected to GND. Single supply will have output electrolytic capacitors of 1000s uF too. Then measure (GND referenced) if there is a power on the pins 1,5 V+, and negative supply on pin 4 if it isn't connected to GND (using dual supply) . Also measure voltage on the pin 8 (mute). I'm asking this because if the controller mutes the power amp, you wont get any sound even if amplifier is completely ok.

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 28, 2014, 10:20:58 pm
content: Seems both the 5W resistors are short, and sit before the regulators. Now I need to source a couple of these in the UK... Anyone know where I may buy a couple?Would using a higher wattage mess things up?

author: wraper
author_rank: Unknown
timestamp: October 28, 2014, 10:27:23 pm
content: They do not become short, only open. They might be short only if there is something dead in parallel. unsolder and check if they are 100 and 220 ohm and if there still is a short without them.

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 28, 2014, 10:51:46 pm
content: After a few tests and comparing to the other speaker, there should be 36V/-36 going in and 20V/-20V coming out of the 5W ceramic resistors. On the faulty board, it has the same voltage into the ceramic resistors as what's going out (36VDC) - would this not suggest a short? Whatever it is, something is not right there... I'll desolder them now and see what results I get...

author: wraper
author_rank: Unknown
timestamp: October 28, 2014, 10:56:26 pm
content: Quote from: LektroiD on October 28, 2014, 10:51:46 pmThat suggests there is no substantial load after those resistors, not that they are faulty. You shall check resistors by measuring resistance. This only indicates that something is not ok after those resistors.

author: wraper
author_rank: Unknown
timestamp: October 28, 2014, 10:59:44 pm
content: BTW, the problem might be artificially introduced as well when you blindly changed parts there. Compare with working one if you didn't solder wrong parts or in wrong direction by accident.

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 28, 2014, 11:14:58 pm
content: Aha! Resistor checked out ok, but the 100µF electro behind it had an ESR of 0!!!Unfortunately I only have 100µF in 35V, which wouldn't last long with 36V going through them. I'll grab some on my next shopping spree...

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 28, 2014, 11:36:47 pm
content: *update*I put the 100µF/35V in as a temperary measure just to test, now I have 24V going in, and 9.6V coming out, so looks like I'll have to replace the negative reg again (I have plenty of those in stock).Stay tuned though, chances are, with that reg throwing out more than double the required voltage, I would imagine there may be further damage...I'll order some new 50V or even 63V electro's (just to make sure) and go from there...

author: wraper
author_rank: Unknown
timestamp: October 28, 2014, 11:41:24 pm
content: Quote from: LektroiD on October 28, 2014, 11:14:58 pmWhat, 0? the less the better, don't know how precise your esr meter is thou, usually it should read about 0.1-0.5 OHm. However capacitor shouldn't affect anything at all in this situation unless it is shorted. However it definitely is not.

author: wraper
author_rank: Unknown
timestamp: October 28, 2014, 11:43:57 pm
content: Quote from: LektroiD on October 28, 2014, 11:36:47 pmIt might be overloaded as well. The best would be to desolder it and check using some power supply to power it. Thou voltage before it should drop lower than in working amplifier. So likely it is blown.

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 29, 2014, 12:10:34 am
content: Strange, I just fired the amp on again, and it is back to -36V going into the reg (and -24V coming out the other end... Hmmmm!

author: wraper
author_rank: Unknown
timestamp: October 29, 2014, 12:27:24 am
content: Does positive regulator output normal voltage? Considering -24V instead of -15V, likely there is some opamp IC already blown too on that power rail. Where did you get that 7915, not ebay by chance? Do you still have original IC?

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 29, 2014, 12:55:13 am
content: The positive reg outputs 15V as expected, although it has 36.0V going in. Unlike the other speaker which at that point has 20V going into each of the regulators. I would assume it is one of the components before the regulators which is not functioning properly. On the working speaker, the voltage going in to the ceramic resistors is 36V but lowers the output to 20V, on the borken one, there is 36V coming out of the resistors...I got the regulators from Farnell in the UK (I have a good stock of components from reputable sources, as I'm building a lot of audio/music projects).

author: wraper
author_rank: Unknown
timestamp: October 29, 2014, 01:11:09 am
content: Quote from: LektroiD on October 29, 2014, 12:55:13 amI'm 99% sure that everything is ok before regulator IC, however it have a very light or no load instead of normal. Maybe opamps already blown because of the increased voltage on negative rail, so no load left.

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 29, 2014, 08:18:14 am
content: Quote from: 3roomlab on October 29, 2014, 01:07:10 amIt is covered in various coloured glue, some soft & gooey, some hard and brittle. I have cleaned most of it off. This is Tannoy's ridiculous idea of PCB design - whatever possessed them? It has made it really hard to identify & solder/desolder components.That said, there are a few traces where the solder mask has worn down to bare copper, but I have probed them and the continuity is ok.Quote from: wraperI'm a little confused: The voltage drop happens at the ceramic resistor on the working unit, this is before the regulator. What components after the regulator could change the input to the regulator on the faulty unit?The thing that concerns me is neither the negative or positive rails are functioning as usual. I would understand if it were just one of the rails.PS. The schematic for the 6D on the previous page has a similar input section to the 8D, but missing a few components. For example, on the 8D there are two 10n ceramic capacitors at the input between ground and each of the rails, this is not shown on the schematic.

author: wraper
author_rank: Unknown
timestamp: October 29, 2014, 08:31:30 am
content: Those resistors are there to reduce power dissipated on the voltage regulators. when there are significant load, voltage will drop on them. As input voltage of the voltage regulator reduces, power dissipated on it reduces too. Blown load will impact both regulators as most of the load likely are powered from both of them. Dual +-15V power usually is used if there are opamp ICs.

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 29, 2014, 09:15:02 am
content: I understand why it uses a bipolar supply, just surprised both rails are having the same issue, I'd understand if it was one or the other, but both regulators are fed over-voltage.Anyway, here are a couple of photos to depict what I'm working with here... As you will see the board is covered in nasty glue/gunk.

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 29, 2014, 09:16:20 am
content: Top view...

author: wraper
author_rank: Unknown
timestamp: October 29, 2014, 09:30:14 am
content: As I see from the pictures there is nothing that regulators could power on this board. Therefore, either another board was disconnected (power goes to it over the cable) while you made measurements or another board is already damaged.

author: wraper
author_rank: Unknown
timestamp: October 29, 2014, 09:34:31 am
content: Likely this particular board have no issues other than blown regulator.

author: wraper
author_rank: Unknown
timestamp: October 29, 2014, 09:39:52 am
content: Quote from: LektroiD on October 29, 2014, 09:15:02 amThey are not fed with overvoltage. There is no voltage dropping on the resistors because of the absence of load after the voltage regulators. 36V is completely ok for 7815/7915. As I said, both rails have the same load which is powered between them.

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 29, 2014, 09:48:40 am
content: Quote from: wraper on October 29, 2014, 09:30:14 amYes, there are two other boards powered by this, a filter board stuffed with LM837's and a digital board for S/PDIF input.The only thing on the power supply board that might draw power is the chip amps LM3886. These all warm up when power is on, in fact they get very hot quickly, but that's probably the blown reg causing that. The fact that they heat would suggest to me that they are working.I'll swap out the reg and see what results I get...

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 30, 2014, 02:50:16 pm
content: Regulator swapped, same results! This time I made sure all the boards were interconnected to ensure there is a load, but still I have ±36V coming into both regulators instead of ±20V

author: wraper
author_rank: Unknown
timestamp: October 30, 2014, 04:15:18 pm
content: Quote from: LektroiD on October 30, 2014, 02:50:16 pmSo did the output become -15V as it should be? As I said, another board(s) which is powered from this regulator is dead or some wire is broken. It was obvious from the beginning that replacing regulator IC wouldn't change this in any way. Check if there is +-15V on power pins of the opamps located on two another boards..

author: LektroiD
author_rank: Frequent Contributor
timestamp: October 30, 2014, 04:59:55 pm
content: Still the same output from the -reg as before (these are rated for a max 35V, so maybe it's unhappy about receiving 36V).I tested the pins 2, 6, 9 & 13 on a few of the LM837's, no negative voltage going in at all. I also checked the interconnect header, there is no negative voltage there either. Looks like something is open somewhere...

author: wraper
author_rank: Unknown
timestamp: October 31, 2014, 01:08:29 am
content: Quote from: 3roomlab on October 31, 2014, 12:56:28 amObviously on top layer. My guess if voltage regulator is ok, there might be something in parallel to it what is leaking a small current. As load is absent, voltage goes up.

author: wraper
author_rank: Unknown
timestamp: October 31, 2014, 02:21:52 am
content: Capacitor won't cause this. It could leak only to GND, therefore no voltage increase possible. IMO that is likely not fault, the fault is absence of load and voltage will return back to normal when load appears again.

author: Refrigerator
author_rank: Super Contributor
timestamp: October 31, 2014, 08:23:50 am
content: You should take both of those big caps and clean all the snot around them because that glue is known to absorb moisture and become conductive/corrosive ( i see there is some of that on component leads and it seems pretty bad ).

author: LektroiD
author_rank: Frequent Contributor
timestamp: November 01, 2014, 01:18:38 pm
content: took C22 out to check, ESR was 0.5r, I swapped it with a newer cap anyway. Going to clean off the remainder of the snot around the components to see if that reveals anything, although the rubbery stuff in places is near impossible to remove...

author: wraper
author_rank: Unknown
timestamp: November 01, 2014, 02:35:11 pm
content: Are you guys crazy or what? Leave that gunk alone. It is used for holding parts, if you remove it with brutal methods, PCB won't look any better and it is not a cause of increased voltage. Even if it is low quality and became slightly conductive, it's resistance would not be nowhere close to be able increase output voltage by a tiny bit. IMO it's pretty useless to do anything on power amp board at all for now. To check if voltage is regulated correctly, solder something like 0.5-1W 1k resistor between regulator output and GND. If it returns back to -15 volts, just leave this board alone and search why there is no power on another board.

author: Refrigerator
author_rank: Super Contributor
timestamp: November 01, 2014, 04:52:17 pm
content: Here.https://www.youtube.com/channel/UCc--CFzOjEViwUwrMCOGVhgGo to this channel and watch all the audio amplifier repairs, this should help.

author: LektroiD
author_rank: Frequent Contributor
timestamp: November 03, 2014, 10:47:18 pm
content: OK! I'm back after the weekend, I wasn't AWOL just a busy weekend, and with nothing to report, I didn't see the need to post... I have every bit of enthusiasm to get this speaker working once again, and appreciate everyone's keenness to help out too, very much appreciated. I hope all you guys had a good weekend too...The latest:As suggested, I put a load resistor between the ground and output of the regulator... 10K was the nearest 500mW resistor I have in stock, if 1K is preferable, you'll have to wait until I can source one, as I'd imagine a 250mW would smoke, although I can try if you think it would make a difference. Anyway, now I'm down to -20V out of the regulator, but the input side remains at -36V (not -20V I'm getting on the other unit).Here's a few pics of the filter & digital board. - Ignore the trimmer in one of the pics, it hasn't fallen out of anywhere, I just used it to prop the board level so I don't get any weird depth of field issues...

author: wraper
author_rank: Unknown
timestamp: November 03, 2014, 11:07:39 pm
content: Quote from: LektroiD on November 03, 2014, 10:47:18 pmForget about input side voltage, It will drop with proper load. 2k 0.25W would do as required power decreases with resistance increase. First of all you should check is there is -15V (-20 or whatever) on the connector of the other board which is connected to the power amp board. Or just check continuity. It might be just broken wire or trace, This 47R resistor looks suspicious too. It has either broken terminal or there is solder blob on it, check it.

author: LektroiD
author_rank: Frequent Contributor
timestamp: November 03, 2014, 11:22:20 pm
content: 1.5K load resistor in, and we're down to the required -15V on the output.there's no -V going out of the header from the power board, only +V.There were a few broken wires which is why you'll notice 3 wires soldered onto the back of the header, but these are all fine now.The 47r was just covered in Tannoy snot, tested in circuit: 46.7r

author: wraper
author_rank: Unknown
timestamp: November 03, 2014, 11:28:54 pm
content: Then there is broken trace on the top side of the power amp pcb. I see some suspicious things between tho voltage regulator heatsinks (might be broken trace).

author: wraper
author_rank: Unknown
timestamp: November 03, 2014, 11:32:45 pm
content: Check marked places.

author: LektroiD
author_rank: Frequent Contributor
timestamp: November 04, 2014, 12:22:59 am
content: Well spotted!I have rerouted the trace and we now have power, proper input and output voltages at the regulator, expected voltages at the header, and the power LED on the front of the speaker is now operational once again.However, no sound... I'm going to check out all of those opamps on the filter board next (unless there are other suggestions)...

author: wraper
author_rank: Unknown
timestamp: November 04, 2014, 12:36:42 am
content: Well, one of my first suggestions about LM3886:Quote from: wraper on October 28, 2014, 10:11:46 pm

author: LektroiD
author_rank: Frequent Contributor
timestamp: November 04, 2014, 01:17:59 am
content: Mute pin (is just bouncing around a few .mV. Same response on all of themPin 4 and 7 both go to ground.

author: wraper
author_rank: Unknown
timestamp: November 04, 2014, 01:57:14 am
content: Are you sure that pin 4 goes to GND? It is negative supply and should not be connected to GND. Even in single supply connection it cannot be connected to pin 7 in principle. Also I see thick negative supply trace on the top side of the PCB going behind LM3886's along the edge of the PCB.As of considering normal dual supply connection (but check first pin 4, there must be -35V, must measure continuity to ceramic resistor on 7915 input):Voltage on mute pin must go below zero to approximately -2.6V according to how I understand datasheet (it is current, not voltage driven). If current is not sinked, voltage will stay at zero and mute is on. I suppose all those pins are connected to one point, likely through resistors and further go to connector. Check where traces go and parts connected there.

author: LektroiD
author_rank: Frequent Contributor
timestamp: November 04, 2014, 02:10:42 am
content: Just tested with the front soft power switch connected and activated, there is -1V going into mute, and pin 4 was only earthed while there was no power, it is in fact, -36.6VDC

author: wraper
author_rank: Unknown
timestamp: November 04, 2014, 11:06:07 am
content: Quote from: LektroiD on November 04, 2014, 02:10:42 amThat means it was not earthed, you just made wrong measurements somehow. I guess LM3886s should be working then. I would try to put some audio signal directly to power amp pcb. Maybe just touch audio input with tweezers or small screwdriver while touching metal part of it and listen if the hum appears in the speakers. Just be very careful to not short something, or some part may explode. I'm going to business trip today, so my further help might be delayed if any.

author: LektroiD
author_rank: Frequent Contributor
timestamp: November 04, 2014, 04:20:10 pm
content: It's not easy to do any tests while the speakers are connected, the extra short cables are fixed into the cabinet (I don't want to tug at them too much as I know how flimsy these things are). The back needs to be virtually closed before I can attach the cables. This is one of the worst designs I've seen when it comes to maintenance, not to mention all the snot the boards are covered in. Considering these were £1000 each when new, I certainly won't be considering Tannoy when I next upgrade the studio.Hopefully this pic will give an indication of the constraints I'm working within...

author: wraper
author_rank: Unknown
timestamp: November 04, 2014, 05:01:43 pm
content: I see you have oscilloscope. Connect it instead of speakers.

author: wraper
author_rank: Unknown
timestamp: November 04, 2014, 05:15:45 pm
content: Or you can check with oscilloscope if signal is present on power amp input instead. If not, check preamp.

author: LektroiD
author_rank: Frequent Contributor
timestamp: November 04, 2014, 06:00:02 pm
content: Good call... I'll feed in a 1Khz square from my FG, see how far into the circuit it goes.

author: LektroiD
author_rank: Frequent Contributor
timestamp: November 04, 2014, 06:23:51 pm
content: Fed a 1KHz square in at +/-1V, I got a sine out of one of the chip amps (pin 3 - output), the others displayed nothing. Then, due to the tight space I'm working in, I managed to short out two of the pins on one of the other chip amps, nearly welding the probe to it.Now the sine I'm getting is modulated with another lower frequency sine, this added carrier sine is present on nearly all the connections of the chip amps.

author: Yago
author_rank: Frequent Contributor
timestamp: November 04, 2014, 06:26:54 pm
content: Is the lower freq 50Hz?Could have knackered a diode or cap in the PSU section and AC is getting through.

author: LektroiD
author_rank: Frequent Contributor
timestamp: November 13, 2014, 04:44:11 pm
content: Back after waiting for some new test probes to be delivered. I seem to have misplaced my Tektronix probe adaptors which are safer for probing chip pins - those standard hook things are too clumsy for chip pins. Anyway...I seem to be getting a waveform back into the power board, but I'm getting strange results from the chip amps...There is a waveform going into two of the chip amps, but the output is flatline (zero/zilch/nada).Mute pin has -1.06VDC going to itI hope the sketchy illustration clarifies what's going on.

author: Yago
author_rank: Frequent Contributor
timestamp: November 13, 2014, 05:18:48 pm
content: Saw this and thought of you Lektoid! :http://www.ebay.co.uk/itm/Tannoy-Precision-8D-Amplifiying-Unit-tested-and-working-/191411958647?pt=DE_MusikInstr_Lautsprecher_Monitore&hash=item2c910ab377Might be handy for the future to have a spare!

author: LektroiD
author_rank: Frequent Contributor
timestamp: November 13, 2014, 05:41:53 pm
content: Quote from: Yago on November 13, 2014, 05:18:48 pmIt would be perfect, except shipping only in Germany.

author: krivx
author_rank: Frequent Contributor
timestamp: November 13, 2014, 06:36:50 pm
content: I would contact and ask about shipping. Most sellers will, especially if you have good feedback already.

author: LektroiD
author_rank: Frequent Contributor
timestamp: November 13, 2014, 09:00:41 pm
content: I asked about shipping, and he got back to me saying it would be somewhere around €20 depending which courrier, I asked if he could give me the exact shipping cost so I could buy it and not had a reply.I would rather get the unit I have up and running to be honest, this evilBay thing is like chasing my own tail.Anyone got any suggestions regarding the tests I did today?

author: LektroiD
author_rank: Frequent Contributor
timestamp: November 13, 2014, 10:54:07 pm
content: Quote from: 3roomlab on November 13, 2014, 10:34:29 pmLooks like I ripped the trace up when I swapped out the regulators. That's fixed now and I haven't noticed any other problems on the PCB

author: LektroiD
author_rank: Frequent Contributor
timestamp: November 14, 2014, 01:04:12 am
content: R23? I just checked for continuity, and yes it's tied to ground

author: LektroiD
author_rank: Frequent Contributor
timestamp: December 03, 2014, 04:07:46 pm
content: Quote from: 3roomlab on December 03, 2014, 12:59:37 pmI battled long and hard, but eventually caved in and went for the evilBay option. Now the other speaker seems to have a slight issue making intermittent noises (without audio input), probably one of the crap caps drying out. I'll have a look when I can next muster the strength to get it off the stand (they seem to weigh about 15 tonnes, and I can't lift too much after a car accident last year).Anyway, here they are in all their glory...

author: pinyoro
author_rank: Contributor
timestamp: December 03, 2014, 10:14:09 pm
content: Beautiful studio!!

author: LektroiD
author_rank: Frequent Contributor
timestamp: December 04, 2014, 12:36:34 am
content: Quote from: 3roomlab on December 04, 2014, 12:09:12 amI use the analogue inputs on the speakers, not the digital.After nearly 25 years working as a studio engineer, I found the dual concentric design much easier to find the sweet spot than separate tweeter/driver combination, which is why I have favoured Tannoy for many years. Up until the 8D's were working I was using my System 800 passives (which are now on back on my hifi separates next door). Once you have tuned your ears to a particular brand, it's absurd to move to another; just to spend the next 6 months tuning your ears to them. In many cases, speaker placement and room mode tuning is much more important than the speaker itself. Therefore, money is much better spent treating the room acoustics once you have found your weapon of choice. If the Meyers work for your ears then that's great, but I have no plans to jump ship any time soon.Yes the sampler is fully working, also has USB card, which apparently is quite rare... However, I was thinking of selling the sampler as I don't use it much.

author: LektroiD
author_rank: Frequent Contributor
timestamp: December 09, 2014, 05:17:34 pm
content: I have a problem with the replacement unit. This is an intermittent fault so may be why it wasn't picked up when it was sold.Occasionally (usually after it has had No audio fed into it for a while), it drops by a few decibels, the only way to kickstart it is to send a few short bursts of high volume audio to it. Then it works normally, but this is not ideal as I have neighbours who I'm sure don't appreciate bursts of high volume audio emanating from my property.I have tried the amp in both units to ensure it is not a faulty driver or cable.I'm suspecting a dead opamp, but I don't want to look into repairing just yet as I'm in discussion with the seller to try to resolve this, and the unit may need to be returned in the same condition as it arrived. I just want some ideas as to whether this may easily be repaired, and whether to ask for a part refund on that basis. Provided it can be repaired.

author: KhronX
author_rank: Frequent Contributor
timestamp: December 13, 2016, 08:04:02 am
content: On these models (actually, both Reveal and Precision 6D/8D's), the most common issue is one or both of the 5W ceramic dropper resistors ahead of the voltage regulators failing open-circuit.The brown glue drying out and turning corrosive and conductive is a ticking time-bomb, and the switches can go wonky too.Most recently, the 80Hz high-pass switch on one of my Precision 6D's had kicked the bucket, after i took the back off to take care of an intermittent contact on the tweeter output connector.Nothing a squirt of contact-cleaner and 20-30 operations couldn't fixYou can find the schematics here:http://91.121.194.115/tannoyschematics.zipThe filter board is almost definitely the same. The only (electronic) difference between the 6D and the 8D is that the 8D has two bridged LM3886's driving the woofer, where the 6D only has a single one.I hope this doesn't violate any forum rules, but there's a considerable-ish thread on this subject over on the badcaps.net forums:http://www.badcaps.net/forum/showthread.php?t=16644

author: Messtechniker
author_rank: Frequent Contributor
timestamp: December 13, 2016, 11:20:02 am
content: After reading all this, I am glad I decided at the time (mid 2010)to go with the passive Precision 8s (without the very expensive "D")for my voice recording studio and instead completely refurbish an old Quad 303I happened to have. I fully agree - once you are used to concentricsas I have been all my life starting with Tannoy HPDs, you would notwant to change.Seeing such bad manufacturing, I would be inclined to completely throw outthis Chinese crap and roll my own electronics for these speakers.Time permitting of course.Anyway, I hope you get this sorted out.Yours Messtechniker.

author: KhronX
author_rank: Frequent Contributor
timestamp: December 13, 2016, 01:42:10 pm
content: In case you've read through the thread about this over on badcaps.net, rolling my own electronics is exactly what i plan to do in the very near futureOn the bright side, i caught my Precision 6D's for a steal (a bit under 200eu shipped), with one of them dead - i most definitely could never have afforded them (or been willing to pay that much, ie. retail or close) otherwise.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: December 13, 2016, 05:48:39 pm
content: Quote from page 2 of this thread:Quote from: LektroiD on October 29, 2014, 12:55:13 amIf this should be normal for this piece of electronics then beware!The 78xx data sheet specifies 30 V max. for the 7815 as recommended,and 35 V as absolute maximum rating. These figure could evenbe much lower for LM78xx regulators of unknown origin.Pretty bad by design....

author: KhronX
author_rank: Frequent Contributor
timestamp: December 13, 2016, 06:59:51 pm
content: If memory serves, that reading was taken with no load (ie. neither the filter board nor the S/PDIF i/o board connected).The analog filter board draws around 60mA from the +/-15v rails, and the digital board draws another 100mA or so - those white ceramic resistors will drop the voltage the regulators see at their inputs (even further).Quote from: Messtechniker on December 13, 2016, 05:48:39 pm