Faulty Sansui BA-F1 could use some help

[Netlist]

Would anyone happen to have this diagram?

Much obliged.

/Hugo

[janneman]

Hugo, you can order the service manual from Lange for 12 euro's or so.

http://www.schaltungsdienst.de/index.php?id=22

Jan

[Netlist]

Jan,

I know and thanks but the amp 'was' supposed to play tonight so I tried here first.

/Hugo

[Netlist]

I changed the thread title a bit to give this post more sense.

Left top TR01 most likely a current source for the dual Jfet (FET01) diff pair below it.
Middle, eight transistors (TR02-09), not sure what they are doing.
Next TR10, TR11, D03, D04 which would be the bias circuit.
TR12, TR14 pre drivers and TR13, TR15, drivers.
When the amp came in, two of the four NMA1012 were broken as well as a 2SC2238 driver (TR13). I replaced the outputs with MJ21193 and the driver with MJE15032.
A bad soldered cap is most likely the culprit. (Base to collector cap of TR12)
Now, without outputs connected, the emitter R of TR11 went up in smoke.
TR11 is still fine.
I replace the R and can’t measure any ohmic difference between both channels.
All transistors, diodes and resistors seem fine, still TR11 is heating up quickly when I power up with the variac. Vbe, however, is higher (0.7V and up) compared with the other channel, a steady +/-0.6V.

/Hugo

[Netlist]

Top

[Zen Mod]

did you checked diodes?

[Netlist]

Yes.
Next I'll do some voltage and current measuring on both channels.

/Hugo

[anatech]

Hi Hugo,
I didn't have exact diagrams, but something that may help.

YGM!

-Chris

[Netlist]

That's extremely close except for the output (complementary instead of quasi), which is not important.

Thanks, thanks, thanks...and thanks

/Hugo

[ilimzn]

Originally posted by Netlist

Middle, eight transistors (TR02-09), not sure what they are doing.

Heh, which probably means you should find out before continuing to poke around the amp!

The BA-F1 uses Sansui's DD-DC setup, basics go like this:

1st stage is a FET follower (IIRC... it might be a differential).
2nd stage is a commplementary LTP with tails tied one into the other. The collectors are cascoded (hence 8 transistors total). Because you need a voltage difference between the emitters of the LTPs to get tail current, the bases of the PNP and NPN LTP are separated by a tripple or quadrupple diode (I think tripple in the BA-F1), that is fed by stage 1.
3rd stage is a complementary VAS, with Vbe multiplir for output stage bias.
4th, 5th, 6th stage are a tripple darlington arrangement.

This is from memory so don't take it literally, but you should be able to follow the circuit using this basic template. IIRC the BA-F1 is, circuit-evolution-wise, between the AU919 which quietly introduced a version of the DD-DC circuit, and the AU-X1, and then the latter AU-D9/11 which introduced feedforward.