Thanks for sharing a great video. I had one of these for my 40th ( 25 years ago! ) and it's still going strong. I've replaced some of the input sockets. I'll check my bias now, as it does get warm...

That was very educational, I thank you for such a detailed description of what you did to fix these three. You now answer question I had with my original 8000A as that ran hot. They are very old now guess it's to be expected component failures. Great video

The pre drive transistors in these need additional cooing. I made heat sinks for them from springy screw clips, the type you get with car audio speakers so you can clip the clips to the door panels in order to have a self tapper screw into them. However you can buy small heat sinks for various different package / size transistors.

Nice to see another video and with Audiolabs too 🙂

I learned the hard way not to always touch heatsinks in amplifiers when feeling for warmth. I was working on a cloud cv 1000 where each side of each board has a live heatsink, if you touch both heatsinks at once you will get a huge shock and blow part of the amp. I believe i shorted the small transistor that helps to regulate the bias, it was a ZTX304 which can be used in pairs as a pre drive transistor but, in this case it is bolted to the side of the heatsink and regulates the bias as temperature changes.

thoroughly enjoyed watching the video. ❤👌👍

Fascinating to watch this. I've had one of these since the late eighties and it's still going strong. It could probably do with a service (the volume knob is a bit wobbly since I shipped it to Shanghai 10 years ago and it sends some nasty pops through the speakers when switching off if I forget to turn the volume down ) but I'll probably wait until I move back to the UK next year as long as it lasts until then. 🙂

@GrahamAtDesk

4 ай бұрын

Hi Fras. If it's in use at the moment, it'd be worth just checking how much heat is coming out of the top, and checking whether there are any scorch marks on the circuit board. Once components start to go out of spec on these it's not unheard of for them to get so hot that they burn the board quite badly. I've not seen one myself, but apparently they can go far enough that they can be really hard to fix.

Thank you, this was very helpful as I'm working on an 8000A running too hot. Unfortunately it's a bit of a nightmare since my board doesn't have component marking on the solder side, and on the top side the transistors are marked '1', '5' etc (like the first one in the video) i.e. no relation to the schematic. Resistors may be marked but underneath so you need to remove them to see it!! I guess I have an old board but the s/n is 89... I wonder what I'm missing.

Amazing work on the replacement buttons!

Hi, myalbatech, In the repair you make in "repair of a trio of Audiolabs 8000a" what was the value of the variable multiturn resistor (preset) you used in the adjustment? 4.7kOhm? 10kOhm? 22kOhm? I can't read it on your video. After finding the correct value, the chosen resistor is soldered on the component side or on de copper side of the PCB? Many thanks.

@myalbatech

Ай бұрын

It was probably 10k though the value isn't really important as long as we can add a few k to whats already there. Resistors are then fitted on solder side of the board.

Hi, I suceeded obtaining the 2 pages in fault on the service data manual for the Audiolab 8000a (drawings CST207-036). The famous pages with the pcb drawings as seen from the component side and also for the copper side. Someone interested please send me a private e-mail. Measuring the voltage across each one of the reservoir power supply capacitors (10000uF/40V), with a high impedance digital multimeter as a voltmeter, 45V is a regular value? In each one. The big problem is my 8000A is labeled at rear as 220V but in my country ( Portugal, Europe) I measure normally a mains AC voltage in the range 231V-233V. By the local standard it is nominally 230 V, with extrwme possible limits at -11% and +6%. I'm worried if this may overload the amplifier, stress components by heat...

Beware of charred boards. if there is carbonisation then the board will start to conduct electricity.

Hi, This is still about the bias adjustment procedure on Audiolab 8000 A. One curious question... Did you also see this?. As long as I can see, in page 4 of the Audiolab 8000A service Manual ("Service Manual 207, serial numbers 87... & 89..."), line 10, we can read: " See drawing CST207-036". However, my Service Manual finishes at page 17 with the drawing CST207-028. There is no drawing CST207-036. Is my manual incomplete or Audiolab forgot to include such drawing? Regards. Guilherme

Cheers bud have you a link for the rcas you used for these ?

@myalbatech

2 жыл бұрын

You can find them on Ali express

Is there not a danger of the carbon in the burnt areas conducting?

@myalbatech

6 ай бұрын

There will be some resistance over any carbonised material and we do need to check for leakage. It wasn't an issue for the circuitry concerned here.

I have the 8000A that I bought used plus a 8000p power amp. They both work well but is there anything to look out for?

@myalbatech

2 жыл бұрын

In every one I've seen the Bias has drifted high

@wcg66

2 жыл бұрын

@@myalbatech thanks, I'll have to test it.

I have an early version with 4 to220 outputs per channel (not the darlington sankens)... Does anyone have a schematic for the early mk1's?

@thepuma2012

Жыл бұрын

i have a manual for serial nummers 87.... & 89.... if that helps. it says model 207.

Hi, There is one important question not yet explained. OK, as we can see from the service manual ( bias section) the resistor pairs R809/R811 and R810/R 812 control bias current in the final big output transistors. And thus bias current can be monitored mesuring the tension across the double emitter resistors (0.22 ohm + 0 22 ohm). But in what direction the changes in R809/R811 and R810/R 812 change or affect bias current? Reducing R809 ou R810 will increase or reduce bias current? Many thanks. Guilherme de Almeida

@myalbatech

9 ай бұрын

Its somewhat non intuitive but increasing one or both resistors reduces the bias. You can put a variable resistor in series with the largest resistor of the pair and adjust to find the ideal value. Often simply moving the higher value up one preferred value is a close enough answer.

@guilhermedealmeida2299

9 ай бұрын

Hi, Thank you very very much. It seems a very short space to insert a preset variable resistor jn the component side. I saw in the circuit diagram of the 8000S model (very similar circuit topology) Audiolab used, in paralel with the 1k5 resistor already in circuit (R807 in L channel), a series formed by a 3k9 fixed resistor and 4k7 preset ( in the place of R 809). And R 811 do not exists. These are resistor numbers for L channel (respectively R808, R810, R812 for R channel). Regards. Guilherme de Almeida

@myalbatech

9 ай бұрын

To clarify - when I say put in a variable resistor I mean temporarily. Adjust to perfection then take it out, measure it and then pick the nearest value of fixed resistor to install.

@guilhermedealmeida2299

9 ай бұрын

OK, but the temporary variable resistor, e.g. 4k7 or 10k needs to have space, even temporary.

@guilhermedealmeida2299

9 ай бұрын

Aparently, following the Service Manual, it seems they want the service be done running two long wires from the positions of the terminals of the SOT resistors (resistors already removed) passing below the amplifier cover and testing different resistors at the free ends of these two wires, looking for the correct bias. At same time, two other wires connect the terminals of the double emitter resistors (2×0.22 ohms) to an external multimeter also outside the amplifier box. It also seems the amp designer wants the changes for SOT resistor optimization be done with the amp ON, following at same time the voltage across the emitter resistor in order to obtain 22 mV after waiting for about 5 minutes with box closed... Too much complication...

Witam mam pytanie co trzeba rozpiąć w środku wzmacniacza by rozdzielić przedwzmacniacz z koncowka mocy ?

@myalbatech

10 ай бұрын

The schematics for this are online.

@marek7125

10 ай бұрын

za wiele wlasnie nie ma dobra dzieki

@marek7125

2 ай бұрын

Witam mam jeszcze pytanie które rezystory trzeba wymienić by obniżyć prąd spoczynkowy tak zwany bias?

How can I get in touch for cyrus servicing please?

@myalbatech

2 жыл бұрын

Email me, address at end of video's and under the 'about' tab in KZread

Nice