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-   -   Amp repair (rebuild?) question (http://www.diyaudio.com/forums/chip-amps/92931-amp-repair-rebuild-question.html)

hoangduongo 27th December 2006 02:58 PM

Amp repair (rebuild?) question
 
Hi guys,
My friend has recently given me a dead Sansui amp. This amp is in quite bad condition: power supply (include transformer)'s dead, power stage ( using power trans, not chip) is dead too, only preamp stage is still alive.
Since the power stage is in very bad condition, I decided to cut off the pcb of power stage and PSU stage and replace by new ones, still using the preamp.
I like to have some chip amp like Lm3886, 3875 or TDA 7294 for this. But there's a prob: as I've seen on many Japanese amp, this amp use Baxandall tone control, and this section use power stage as feedback (or something like that, I hope you can understand because I'm just a beginer and my English sucks). I don't know how to connect the new power stage( the chip amp) into the preamp, still using the tone control. So I hope you guys here can help me a bit.
The schem of the amp is a bit difficult for me to trace out, but I'll try to post the schem as soon as possible.
Thanks very much.
Regards
Hoàng Dương

Minion 27th December 2006 06:51 PM

2 Attachment(s)
Are you trying to say that the Tone controlls for the amp are in the dead Poweramp stage of the Sansui amp but you would like to use them??

If this is the case you can try building a new Tone controll Circuit and Put it in between the Preamp and Power amp stages and connect it to the Tone controll pots in the amp....

Maybe something like this Circuit:

hoangduongo 30th December 2006 03:03 AM

2 Attachment(s)
Hi Minion,
I'm accidently so busy these days, sorry for not reply earlier
Quote:

Are you trying to say that the Tone controlls for the amp are in the dead Poweramp stage of the Sansui amp but you would like to use them?? If this is the case you can try building a new Tone controll Circuit and Put it in between the Preamp and Power amp stages and connect it to the Tone controll pots in the amp....
You can consider that except the selector and the phono preamp, all the circuit is a tone control circuit, somewhat like your circuit, but the non-inverting type, and the whole poweramp stage act like the opamp. I hope I can do add the new poweramp stage like this, using LM3886 or so without buiding a whole new one tone control.
I had no time to draw the original schematic of the amp, so you may take a look at the schem I add here to get the idea, it doesn't the same though, but I hope you'll understand. I'll draw the schem as soon as I have time.
Thanks very much.
Regards,
Hoàng Dương

danielm 3rd January 2007 05:25 AM

My first chip amp I built was in a Sansui receiver in 1977.
I used a STK chip to replace the receiver's blown descret component power amp that I had no schematic for at the time.
A good friend used it for many yrs afterwards.


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