Audiolab 8000 amp - Webby is this like yours?

[UV101]

Lee (webby) asked me about mods for his audiolab 8000 amp.

I've obtained a schematic from one of the other forums.

Assuming it is the same as yours Lee, I'd start with PSU smoothing caps (dependant on age (Black Elna in pic but not on diagram)). There is a cap on the input (c101 1uF) that would be worth changing to something decent (I like Mundorf Supreme). Amps aren't really my thing but I'd start changing the components in the signal path for 'better' parts. Resistors to something like RC55Y welwyns maybe.

Any other suggestions welcome!

[leo]

If the op-amp used for the servo is still a TL071 change it to one with better PSSR, (make sure its FET input) you will hear a difference after changing this if the stock one is a TLO71.

Use the raw PSU to supply the output stage and try cleaning up the supply to the LTP, something like a cap multiplier (make sure the voltage drop isn't too low) or even use a separate traffo and regulation to the input stage

Just a note regarding RC55Y, although precision resistors they are also magnetic with steel end caps, I wouldn't go over board with them as they can tip the balance of the sound to over bright and spitty (just my opinion)

If you want to give it a kick up the arse use an external psu converting it to dual mono supplies

[UV101]

Interesting point on the servo Leo.

I changed my servo opamp on the output my Meridian 207 to a LME49720. I'm not sure if it really made much of a difference and I removed the final buffer stage from the o/p at the same time.

Does it make much difference using a decent opamp for the dc servo? I'm interested in your opinion.

[webby]

Thanks Ian, I'll take a look sometime. Bit snowed under at the moment. Is this an 8000a or S?

[UV101]

Hi Lee,

the .pdf is marked as 8000p???

Not sure what the differences might me.

Ian

[leo]

Interesting point on the servo Leo.

I changed my servo opamp on the output my Meridian 207 to a LME49720. I'm not sure if it really made much of a difference and I removed the final buffer stage from the o/p at the same time.

Does it make much difference using a decent opamp for the dc servo? I'm interested in your opinion.

Hi Ian,

The effects of the servo depends how its been implemented , with the amp I would want the least amount of crap injected into the amps input section as possible, the supplies and regulation supplying the op-amp are not the best either so i'd go for the chip with best PSRR, TL071 is an old work horse but not the best in this application imo.
Its easy to fit a DIL socket to allow for easy comparing, the differences may not be huge but its a fairly cheap thing to try

BTW I would not recommend using a bipolar input op-amp in this circuit , FET input types tend to be better suited

Cheers,
Leo

[DSJR]

The 8000PX, MX and S have a different output configuration which isn't cap decoupled.. Don't know about the rest of it....

[UV101]

BTW I would not recommend using a bipolar input op-amp in this circuit , FET input types tend to be better suited

Cheers,
Leo

So something like a BB2604 could be better here than an LME49720?

The 8000PX, MX and S have a different output configuration which isn't cap decoupled.. Don't know about the rest of it....

Ah! they are different then! what model is it you ave Lee?

[DSJR]

S'cuse me for interrupting, but the pic is of an 8000P i think. I'm sure there are four caps in the middle, two for supply and two for output coupling? The speaker connections seem to go to the board in the middle rather than the power boards.

The PX had a leaner-meaner sound to it, with a tight bass yet more clarity which suited cheap ported boxes better..

[StanleyB]

S'cuse me for interrupting, but the pic is of an 8000P i think. I'm sure there are four caps in the middle, two for supply and two for output coupling? The speaker connections seem to go to the board in the middle rather than the power boards.

I am afraid to say that you must be mistaken. Looking at the picture, I can deduct that:
1. The power supply is split independently to the Left and Right Channel. Each channel has a + and - power cap, which makes it four pieces all together.
2. The speaker output connections from the power output transistor boards go to a PCB on the rear, which appears to be a relay driver, DC detector, and Zobel network. There is one circuit for for each channel on the same PCB. There appears to also be a regulated DC supply coming from this PCB and going to the L and R channel PCB. That means that each channel is supplied with two DC power rails. One for the output stage and one for the input stage.
3. The green wires appear to be the GROUND wires, with all ground wires soldered onto a single fixed point on a PCB that is standing upright. The power caps are also soldered onto this PCB.
4. The thin yellow wires are for the Left speaker + output, and the thin orange ones for the Right speaker + output.