Spectro Acoustics SR200 amp

[ekaerin]

Hi everybody,

I have an old Spectro Acoustics SR 200 Poweramp. When I bought it
it was pretty trashed with some bad repairwork done to it.
I fixed it up, changed all outputs, drivers, "emitter" resistors, supply caps
and bridge.
It works nice but have some audible distortion at low levels.
I have tried the trimpot but it didn't help.

Does anyone have the schematics for this amp ?

Even if I don't use it to often it would be nice to know more about it
and see if I can get rid of the dist.

/ Regards / Mattias

[djk]

Gave my schematics away about ten years ago on that one.

The basic topology is the same as the HK Citation 12

http://www.passdiy.com/pdf/citation.pdf

The Spectro runs on a higher voltage, about ±67V, and has four outputs per channel, RCA 1B05 (obsolete, use MJ15022/24), use MJE15030/31 for the drivers.

The VAS was a house number TO5 from RCA, the industry standard numbers are 2N3440/2N5415, and the diff pair MPSA06/A56 (I can't remember if the diff pair was NPN or PNP, I've listed both. The VAS would be the opposite polarity).

The bias circuit is a little different, you will have to draw it out.

Change the cap in the feedback loop, change the bootstrap cap.

If the bias doesn't work right, the bootstrap will not work right.

The reverse is also true.

There was a factory mod involving the inputs and grounding for same, that was for hum.

[ekaerin]

.... Yes the outputs were marked SPECTRO and some MJxxxx No.
I do not have it here but I know I put in the same types except for the
drivers which are japs now.
Intresting points about the bootstrap and bias. I wiil go back and try to
draw a schematic as you suggested and do some measurements.
(Just called my friend who keeps it in his studio to bring it home today)

Thanks again for your input / Mattias

[Ekus]

Hello, My name is Henrik and i'm also live in sweden .. So i will write swedish now because my english isn't very good.

Det är så att jag tycker väldigt mycket om ljud och spelar som dj ibland som ett Fritids intresse För några år sedan köpte jag på mig en rack med Spectro Acoustics Radio, förförstärkare, slutsteg och equlaizer .. en dag när jag spelade lite musik på "normal" volym , inget överdrivet med andra ord. Så gick ena kanalen helt plötsligt :S har haft in den hos en bekant som lagar elprylar, han konstaterade vad det var för fel men hittade inga reservdelar. Så nu är min fråga om du vet vart man kan hitta reservdelar passande till detta slutsteg ? Väldigt tacksam för svar Mvh Henke