My Son of Ampzilla

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Dappel

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Joined 2008
#1
Yes, I am a newbie here. I am looking for help and I hope I might be able to help others here someday as well.

I bought this amp in 1982, I guess that dates myself doesn't it. Well it has a few minor issues. Where I'd like to begin is to find a decent description of the bias setting procedure. I've read in another post about a 8 pages description that may be out there, but it wasn't posted the best I can tell.

I do have the schematic already, that was pretty easy to find.

Thank you in advance-
 
#2
Dappel said:
Yes, I am a newbie here. I am looking for help and I hope I might be able to help others here someday as well.

I bought this amp in 1982, I guess that dates myself doesn't it. Well it has a few minor issues. Where I'd like to begin is to find a decent description of the bias setting procedure. I've read in another post about a 8 pages description that may be out there, but it wasn't posted the best I can tell.

I do have the schematic already, that was pretty easy to find.

Thank you in advance-
Click to expand...


In fact while I'm at it, there are actually 4 pots per board. One is for the bias, one is for DC offset, but the other 2, I'd certainly like to know where they should be set.
 
#3
Have a look at member ACD from Denmark website.

http://www.audio-circuit.dk/
-> Schematics -> D-G ->
Gas Ampzilla Power Amp (Schematic)
GAS Ampzilla III Power Amp (Schematic)
GAS Ampzilla 2 Power Amp (Schematic)
GAS Ampzilla 2 II Power Amp (Schematic)
GAS Ampzilla 2 III Power Amp (Schematic)
GAS Grandson of Ampzilla Power Amp (Schematic)
GAS Son of Ampzilla Power Amp (Schematic)
GAS Thoebe RIAA (Schematic)

Now, the Son if Ampzilla schematic is not very high quality.
But maybe useful, anyway.

Regards 😉 Lineup
 
#8
djk said:
The last two pots are for the current limiting.

Set them to fold back above 250W into 2R.
Click to expand...


DJK- I know which two you are referring to, but unfortunately I'm not sure how to go about what you suggested. If you would be willing to shed a bit more light on the how to: it would be great.
 
#10
A friend has given me his old Son of Ampzilla, which does appear to have some problems. I've got a decent stable of test equipment, so I'll be taking a crack at the thing in the near future.

Sounded good at first but after a few hours there was audible distortion at very low power, some hum (ground loop?) and the amp simply never warmed up in the slightest. I'm guessing bias problems.

Anyone done any modifications to them? Looks like the famous IC in the bias circuit is really a transistor array--this unit actually has four discrete transistors inserted in the IC socket! I'm guessing they're a matched set.
 
#11
Er, the socketed transistors are the input different pairs. which are MPS8599 and MPS8099. The bias IC seems to be located against the heatsink, as should have been obvious were I thinking at all about it...

Any ideas for the driver and VAS transistors are?
 
#13
QSerraTico_Tico said:



Look here:
http://www.diyhifi.org/forums/viewtopic.php?f=5&t=1065&hilit=ampzilla
Click to expand...


Thanks for the pointer; that thread contained a lot of useful information.

I've got the amplifier apart and changing some parts; the schematic shows a lot of parts changes but some of them are very difficult to read. At least one channel has a significant bias problem that appears to go away when warmed up; it goes from sounding distinctly distorted to perfectly clean and residual distortion shows very sharp crossover notch peaks that also disappear.

Hope it's not the bias IC...
 
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