Many years ago I worked for Cambridge Audio on final test of the P40/50 amplifier. Interesting tests we did on distortion. The basic distortion on that amplifier was really low, less than .01% right up to clipping. If you turned the bias low, THD would not rise but if you looked at the distortion waveform (analogue not digital) you could do this with the HP distortion analyser, you could clearly see a cross over spike. Best viewed at 10khz at 5 watts output. At this point the QI was adjusted to remove the spike completely. Because distortion was so low anyway, buried in the noise, the crossover spike did not increase the overall THD. It's debatable if you could hear it anyway. We did spend many hours listening at different bias levels mostly on the Quad electrostatics. Results were really inconclusive, maybe a little harsh on the HF when under biased?? Regarding the 8000a, customers would add a tuner and stand it on top...now THAT really cooked the amplifier, heated up the tuner which would drift of tune. Problem solved if the tuner was underneath the amplifier. Christmas party's were always good for business, the amplifiers got a high power roasting and came in with the power transistors blown up!! Ahhh the good old days!! A better solution for regulator overheating WOULD have been to use a separate lower voltage winding on the transformer.
Very interesting Michael. The sound is great but the cooling issue and fracturing of phono sockets not so great. All heat related. Re the regulator, yes just a drop in input to them would help a lot.
Hi Michael, pretty sure i've seen your name mentioned in some old Cambridge Audio service manuals ! Cambridge were always funny... some good designs often let down by cheap manufacturing. The stuff they make these days is pretty much garbage
@@jaycee1980 Hi Peter, I could write a book on the early Cambridge days and products, great ideas but MANY production problems. The original P40 was well ahead of it's time in low distortion and a really clean sound.
Hello, i just got to this and thank you on bias pods setting adice ( for amateurs like i am thats full cca 😆, full ca will result in immeduate temp raise). I own a basically the same amp 8000s for the past 25 years. I have recently gone through bunch of capacitor replacement rounds simply because on my DER EE they werent reading in spec or werent reading at all. Interesting how sensitive to sound coloration different capacitor combinatons were. I ended up with upgrading PS caps with 2 x mundorf 15000uf - an immediate change in breadth of sound, went through cheap nichicons in power amp - yes since they were new they brought improvement in high frequency - but overal it was too hot. Afte that i used nichi muse with elna silmic II that balanced things out nicely and brought low frequencies back. I also replaced 6 - 4.7 uf caps in line amplifier with silmic II and 2 - 47 uf with nichi Muse. For the rest of large 470 uf i went with nichi golds. Overall i am very happy. So happy in fact i no longer require a sub and run the amp in integrated mode. Sound is non fatiguing but has plenty of detail at 45-60 db my ideal listening volume. I spent perhaps $100 on capacitors for this amplifier and i am very happy with the result., so much that for now i have abondined idea of going the same route on my 8000p - because S is performing so well solo now.
I’ve just repaired one of my two 8000P’s. I could have done with tracking this video down a year ago. It failed in February 2020 and I knew virtually nothing of component level fault finding. It would work for about 5 minutes then the relays would click and silence from then on until it had cooled down. I spent ages trying to get a schematic, read up on relay speaker protection. I replaced all the electrolytically except for the big smoothing caps(£20 each), the wired ceramic resistors (from China) and some transistors that had obviously got hot as the PCB was brown as per you video. I also add heatsinks to them and had to repair the PCB as the tracks and pads disintegrated when I desoldered. It’s been working great now for the last month. The amount I’ve learnt has been immense, and I’m now working on an Arduino controlled dual fan project with automatic control over three speeds. Anyways, thanks for thee videos.👍🏻
Good work on keeping the old girl going Simon. Some time I wouldn't mind getting a few bits of locally made hi-fi. PS do I spy...no...maybe....a bulg..naahh!
Hmm that pcb looks nicely cooked, i would do much the same as you and leave the leads long so the parts are 10mm above the pcb. Manufacturers always place electrolitics near hot heatsinks, they are taking the micky. A small fan mounted to blow air over the pcb from the outside would be an idea and kind to it. The protection system must be very sensitive to detect a slight static d.c voltage across the speaker terminals. I've never liked boiling silicone transistors or regulators, bigger heatsinks are fitted and if there is enough overhead voltage a big wirewound resistor is placed in the d.c feed to the regulator to lower it's dissipation. Wirewounds are better with heat, well i think so :-D I repaired a mates old beast of a Technics amplifier that had a speaker resistance detector, a dc bias. That caused problems with the circuit jumping in sometimes, i did some relay contact cleaning and it behaved itself for a while. A very dodgy/sensitive circuit. Sorry waffle mode :-(
Your right they do get bloody hot especially when running into a 4 ohm load at moderate listening levels. I owned a late model one (1997) a couple of years ago. They got loads of hype back in the 1980's. I didn't think it was anything special. It certainly didn't stand up to all the hype that it got. They were £500 new expensive for something mediocre. Very poor heat sinking and lack of ventilation.
Nice Amp Simon Pity About The Heatsinks Use a Audiolab Q Dac With My A&R A60 Amp And Tannoy Speakers On My Computer For Watching CZcams Thanks For Uploading Just in Case I Get One Down The Road he he Regards mike
Was there enough depth under the PCB to mount the electrolytics on the bottom just out of curiosity? Sounds like a good candidate for a small fan as well. Thanks for sharing Simon!
What i've always found over the years is they overheat & quickly if used as a pre amp & i've noticed you get more issues in summer with them & they start distorting, what i've been doing for years is when it starts happening is blast them with a powerful hairdryer on cold & go & make a brew.
Great article Simon. I have a problem with an 8000A at the moment, I can't get any sound from it and don't know why, it was okay the other day. Horrible hiss coming from it now, no music at all. If you have any suggestions, I would appreciate it, thanks.
What kind of dicklless wonder would give you a thumbs down this was really interesting and didn’t cost me a penny. Thanks for sharing your knowledge and experience everyday is a school day. I would install ceramic spacers under the resistors. I wouldn’t actually I’m too lazy. Did you check the loudness Control ? Regards Chris
It's hard to tell without looking at it but I wonder if the amp might benefit from an external cooling fan possibly mounted on the top vent slots to suck out the hot air while drawing in cooler air from the sides. Don't know if it's worth the trouble to machine it all out though. Stay well. ATB Doug.
A fan would be a good option other than noise. Nothing worse that listening to music at low level with a fan humming in the background. Could put it on a thermostat or make it variable speed with a thermistor?
I was wondering why the schematic I found didn't match up with things I was seeing on the video... particularly the 2SK389's which I imagine are used in the longtail pair instead of BC546's shown in the schematic!
The schematic I found do not match up with my amp. Yours amp looks similar to mine. There are two variable resistors RV701 and RV801. They are not shown on the circuit diagram but shown on the Audiolab 8200A diagram. I guess they are for the Bias setting. Is it correct? I am curios about the Bias setting. The service manual says the current should be 100mA or approximately 50mV across emitter resistor 0.44 ohm. But similar model Audiolab 8200a recommends to adjust 20mV across resistors. So that the current should be 45mA. It is twice less than the current of Audiolab 8000a. Someone reported that he adjusted 20mV for Audiolab 8000A and got good result. The unit was getting much cooler without sound degradation. What is your opinion regarding the current setting? It should be 45 or 100mA?
Yes the manual for our model is not released to the public. These amps run far to hot and dropping back the bias is a great idea. It will make little difference to the distortion.
@@SoddingaboutSi It is a great advice because many people concerned the heat problem. Thanks a lot. So I can safely adapt the Audiolab 8200A the Bias setting procedure for the Audiolab 8000A?
Hi Simon. I am currently taking on a little project of replacing the caps in my Audiolab 8000P (newer model), and was wondering how important the 47pF "caps" (the odd looking one with transparent housing) at the input actually is. You see, I forgot to order enough of these 47pF parts. And frankly, I am in doubt if it's actually ordered the right replacement part to begin with.
@@SoddingaboutSi Thank you for replying. :) I think they are some sort of polystyrene film capacitors? I ordered multilayered ceramics. I guess ceramic isn't as good as polystyrene? The 8000P have two of these at the signal input, and I was just wondering how important they are and if they where prone to fail? I forgot to order replacement parts for them, so I only got 4 instead of 6.
@@SoddingaboutSi I think you are right. However, I am very sure I saw a repair video or a repair blog etc, where they where somehow toast and completely out of spec. Maybe I am wrong? Also, what are their purpose in the audio input? And would I be crazy to replace the ones on the amplifier side with these?: www.mouser.dk/ProductDetail/80-C317C470G2G
It really depends on that the capacitor quality was like originally, what it's has to do in the circuit and if it's in a part of the circuit surrounded by hot components. An amp like this left on for long periods that has poor cooling I would expect a 25% drop in the ESR of the caps within 5 years. Some fail much quicker, some are almost like new.
@@SoddingaboutSi I will open mine tomorrow, haven't done for over twenty years I think. I bought mine in 1991, it has be constantly on, almost since then. The issue with mine has been broken RCA phonos, not all, and sometimes, lately, hum from the toroidal I suppose. I switched it off only this evening after your report, after 30 years... I will make a short video to show the conditions of the board inside.
It's possible the board discolouration is from excessive current flow through the tracks rather than the resistors themselves... but i guess you have given it a finger test!
Is it basically impossible to buy one of these 2nd hand and it work as normal??? I really fancy one, but can't be arsed with buying a headache and needing an electronics background to fix the fcuker.
Yeah, don't bother with them. They're all heat damaged and the mechanical switches go bad. These blue Elna caps are garbage, I've seen them in younger amps already dead. The Chinese 8000S from 2004-8 era should be the most reliable being the youngest. Mind you these don't have a phono preamp.
It's a piece of crap. All of the inputs on mine are busted. I'm using it on the PC while another amp is being serviced, but once it's back, this piece of crap Audiolab is back to being a standby.
Well that's a bit harsh Stikibits! It's a good amp that is under cooled and as a result the phono sockets become brittle. It's a shame they couldn't rectify this issue over the production run.
Many years ago I worked for Cambridge Audio on final test of the P40/50 amplifier. Interesting tests we did on distortion. The basic distortion on that amplifier was really low, less than .01% right up to clipping. If you turned the bias low, THD would not rise but if you looked at the distortion waveform (analogue not digital) you could do this with the HP distortion analyser, you could clearly see a cross over spike. Best viewed at 10khz at 5 watts output. At this point the QI was adjusted to remove the spike completely.
Because distortion was so low anyway, buried in the noise, the crossover spike did not increase the overall THD. It's debatable if you could hear it anyway. We did spend many hours listening at different bias levels mostly on the Quad electrostatics. Results were really inconclusive, maybe a little harsh on the HF when under biased??
Regarding the 8000a, customers would add a tuner and stand it on top...now THAT really cooked the amplifier, heated up the tuner which would drift of tune. Problem solved if the tuner was underneath the amplifier.
Christmas party's were always good for business, the amplifiers got a high power roasting and came in with the power transistors blown up!!
Ahhh the good old days!!
A better solution for regulator overheating WOULD have been to use a separate lower voltage winding on the transformer.
Good stuff Michael, that was an interesting read.
Very interesting Michael. The sound is great but the cooling issue and fracturing of phono sockets not so great. All heat related. Re the regulator, yes just a drop in input to them would help a lot.
Hi Michael, pretty sure i've seen your name mentioned in some old Cambridge Audio service manuals ! Cambridge were always funny... some good designs often let down by cheap manufacturing. The stuff they make these days is pretty much garbage
Michael Beeny Thanks for sharing the information fascinating. Regards Chris
@@jaycee1980 Hi Peter, I could write a book on the early Cambridge days and products, great ideas but MANY production problems. The original P40 was well ahead of it's time in low distortion and a really clean sound.
Hello, i just got to this and thank you on bias pods setting adice ( for amateurs like i am thats full cca 😆, full ca will result in immeduate temp raise). I own a basically the same amp 8000s for the past 25 years. I have recently gone through bunch of capacitor replacement rounds simply because on my DER EE they werent reading in spec or werent reading at all. Interesting how sensitive to sound coloration different capacitor combinatons were. I ended up with upgrading PS caps with 2 x mundorf 15000uf - an immediate change in breadth of sound, went through cheap nichicons in power amp - yes since they were new they brought improvement in high frequency - but overal it was too hot. Afte that i used nichi muse with elna silmic II that balanced things out nicely and brought low frequencies back. I also replaced 6 - 4.7 uf caps in line amplifier with silmic II and 2 - 47 uf with nichi Muse. For the rest of large 470 uf i went with nichi golds. Overall i am very happy. So happy in fact i no longer require a sub and run the amp in integrated mode. Sound is non fatiguing but has plenty of detail at 45-60 db my ideal listening volume. I spent perhaps $100 on capacitors for this amplifier and i am very happy with the result., so much that for now i have abondined idea of going the same route on my 8000p - because S is performing so well solo now.
Good to see you back and thanks for the electronic-therapy ASMR session. Going to go out to howl at the moon tonight & listen to theremin. Cheers.
I’ve just repaired one of my two 8000P’s. I could have done with tracking this video down a year ago. It failed in February 2020 and I knew virtually nothing of component level fault finding. It would work for about 5 minutes then the relays would click and silence from then on until it had cooled down. I spent ages trying to get a schematic, read up on relay speaker protection. I replaced all the electrolytically except for the big smoothing caps(£20 each), the wired ceramic resistors (from China) and some transistors that had obviously got hot as the PCB was brown as per you video. I also add heatsinks to them and had to repair the PCB as the tracks and pads disintegrated when I desoldered. It’s been working great now for the last month. The amount I’ve learnt has been immense, and I’m now working on an Arduino controlled dual fan project with automatic control over three speeds. Anyways, thanks for thee videos.👍🏻
#well all I can say is well done you. Its great to repair broken gear and these Audiolab amplifiers deserve it.
Good work on keeping the old girl going Simon. Some time I wouldn't mind getting a few bits of locally made hi-fi. PS do I spy...no...maybe....a bulg..naahh!
Hmm that pcb looks nicely cooked, i would do much the same as you and leave the leads long so the parts are 10mm above the pcb.
Manufacturers always place electrolitics near hot heatsinks, they are taking the micky.
A small fan mounted to blow air over the pcb from the outside would be an idea and kind to it.
The protection system must be very sensitive to detect a slight static d.c voltage across the speaker terminals.
I've never liked boiling silicone transistors or regulators, bigger heatsinks are fitted and if there is enough overhead voltage a big wirewound resistor is placed in the d.c feed to the regulator to lower it's dissipation.
Wirewounds are better with heat, well i think so :-D
I repaired a mates old beast of a Technics amplifier that had a speaker resistance detector, a dc bias.
That caused problems with the circuit jumping in sometimes, i did some relay contact cleaning and it behaved itself for a while.
A very dodgy/sensitive circuit.
Sorry waffle mode :-(
Your right they do get bloody hot especially when running into a 4 ohm load at moderate listening levels. I owned a late model one (1997) a couple of years ago. They got loads of hype back in the 1980's. I didn't think it was anything special. It certainly didn't stand up to all the hype that it got. They were £500 new expensive for something mediocre. Very poor heat sinking and lack of ventilation.
Nice Amp Simon Pity About The Heatsinks Use a Audiolab Q Dac With My A&R A60 Amp And Tannoy Speakers On My Computer For Watching CZcams Thanks For Uploading Just in Case I Get One Down The Road he he Regards mike
Was there enough depth under the PCB to mount the electrolytics on the bottom just out of curiosity? Sounds like a good candidate for a small fan as well. Thanks for sharing Simon!
That is a great idea. I wish I had thought of that earlier. Did that on my Sondek to move the caps away from some hot resistors.
What i've always found over the years is they overheat & quickly if used as a pre amp & i've noticed you get more issues in summer with them & they start distorting, what i've been doing for years is when it starts happening is blast them with a powerful hairdryer on cold & go & make a brew.
Great article Simon. I have a problem with an 8000A at the moment, I can't get any sound from it and don't know why, it was okay the other day. Horrible hiss coming from it now, no music at all. If you have any suggestions, I would appreciate it, thanks.
What kind of dicklless wonder would give you a thumbs down this was really interesting and didn’t cost me a penny. Thanks for sharing your knowledge and experience everyday is a school day. I would install ceramic spacers under the resistors. I wouldn’t actually I’m too lazy. Did you check the loudness Control ? Regards Chris
Cheers Chris!
A larger grille on top (and bottom) could make a difference heat wise. Also, a small, silent fan in the back panel might surprise you.
I would prefer that than adding a fan.
Witam mam pytanie co trzeba rozlaczyc zeby rozdzielic pream z końcówka mocy jakieś rezystory?
It's hard to tell without looking at it but I wonder if the amp might benefit from an external cooling fan possibly mounted on the top vent slots to suck out the hot air while drawing in cooler air from the sides. Don't know if it's worth the trouble to machine it all out though. Stay well. ATB Doug.
A fan would be a good option other than noise. Nothing worse that listening to music at low level with a fan humming in the background. Could put it on a thermostat or make it variable speed with a thermistor?
I've had mine since the 90s. Never turned it off. When it's cold it doesn't play as good but it's never overheated as far as I'm aware
I bought mine but it go mute after a while until I plug in a trs pin then it gets back again, what could be the problem?
Hi Simon. My audiolab 8000a is still going strong but the rca pcb board has deteriorated. Any advice on how to change it please
Thanks
The Audiolab 8000a was one of the last of the British built audiolab products before being outsourced to China
My Amp dead!
How does one replace the internal fuse please?
Pete
I was wondering why the schematic I found didn't match up with things I was seeing on the video... particularly the 2SK389's which I imagine are used in the longtail pair instead of BC546's shown in the schematic!
Yes. Never found a schematic.
The schematic I found do not match up with my amp. Yours amp looks similar to mine. There are two variable resistors RV701 and RV801. They are not shown on the circuit diagram but shown on the Audiolab 8200A diagram. I guess they are for the Bias setting. Is it correct?
I am curios about the Bias setting. The service manual says the current should be 100mA or approximately 50mV across emitter resistor 0.44 ohm. But similar model Audiolab 8200a recommends to adjust 20mV across resistors. So that the current should be 45mA. It is twice less than the current of Audiolab 8000a. Someone reported that he adjusted 20mV for Audiolab 8000A and got good result. The unit was getting much cooler without sound degradation. What is your opinion regarding the current setting? It should be 45 or 100mA?
Yes the manual for our model is not released to the public. These amps run far to hot and dropping back the bias is a great idea. It will make little difference to the distortion.
@@SoddingaboutSi It is a great advice because many people concerned the heat problem. Thanks a lot. So I can safely adapt the Audiolab 8200A the Bias setting procedure for the Audiolab 8000A?
@@olegau12 I would set the bias as you mentioned and leave it on for an hour checking regularly for heat buildup. Output should just be slightly warm.
hate these amps to fix i think it use a large feedback network put your volt meter on the emitter resistors inside to test for DC
Hi Simon. I am currently taking on a little project of replacing the caps in my Audiolab 8000P (newer model), and was wondering how important the 47pF "caps" (the odd looking one with transparent housing) at the input actually is.
You see, I forgot to order enough of these 47pF parts. And frankly, I am in doubt if it's actually ordered the right replacement part to begin with.
The 47Uf do you mean?
@@SoddingaboutSi No, it really says 47 pF I think. You can see them in your video at 7:20. It's those glass looking things.
@@SoddingaboutSi Thank you for replying. :)
I think they are some sort of polystyrene film capacitors? I ordered multilayered ceramics. I guess ceramic isn't as good as polystyrene?
The 8000P have two of these at the signal input, and I was just wondering how important they are and if they where prone to fail?
I forgot to order replacement parts for them, so I only got 4 instead of 6.
@@Mr_Wh1 leave them. Only the electronics will deteriorate with age. All other caps will be like new.
@@SoddingaboutSi I think you are right. However, I am very sure I saw a repair video or a repair blog etc, where they where somehow toast and completely out of spec.
Maybe I am wrong?
Also, what are their purpose in the audio input?
And would I be crazy to replace the ones on the amplifier side with these?:
www.mouser.dk/ProductDetail/80-C317C470G2G
Is there a point of diminishing returns for audio capacitors? Does the quality of the circuit they are in stark to let them down?
It really depends on that the capacitor quality was like originally, what it's has to do in the circuit and if it's in a part of the circuit surrounded by hot components. An amp like this left on for long periods that has poor cooling I would expect a 25% drop in the ESR of the caps within 5 years. Some fail much quicker, some are almost like new.
@@SoddingaboutSi I will open mine tomorrow, haven't done for over twenty years I think. I bought mine in 1991, it has be constantly on, almost since then. The issue with mine has been broken RCA phonos, not all, and sometimes, lately, hum from the toroidal I suppose. I switched it off only this evening after your report, after 30 years... I will make a short video to show the conditions of the board inside.
It's possible the board discolouration is from excessive current flow through the tracks rather than the resistors themselves... but i guess you have given it a finger test!
No Peter the resistors are dropping the secondary voltage via a zener regulator. The resistors are hot to the touch.
Is it basically impossible to buy one of these 2nd hand and it work as normal??? I really fancy one, but can't be arsed with buying a headache and needing an electronics background to fix the fcuker.
Yeah, don't bother with them. They're all heat damaged and the mechanical switches go bad.
These blue Elna caps are garbage, I've seen them in younger amps already dead.
The Chinese 8000S from 2004-8 era should be the most reliable being the youngest. Mind you these don't have a phono preamp.
My audiolab 8000A , when I pressed the tone default , there was a zhi Zhi sound came form both speakers ,any helps? Thanks
I cleaned mine with electrical contact cleaner and doesn't make a distortion click now
@@whatyeonaboot thanks,bro
Should be no issue with heat you want to sell it? I'll give you 250£ with a service if you pick one up let me know I don't do eBay
John, why do you say no issue with heat? Can't you see the burnt board?
It's a piece of crap.
All of the inputs on mine are busted.
I'm using it on the PC while another amp is being serviced, but once it's back, this piece of crap Audiolab is back to being a standby.
Well that's a bit harsh Stikibits! It's a good amp that is under cooled and as a result the phono sockets become brittle. It's a shame they couldn't rectify this issue over the production run.
@@SoddingaboutSi I agree and that's why it's a piece of shit.