I'm experimenting with a Yamaha CR-440 receiver that had both output modules bad as received. While waiting for real IG02990 modules to turn up, I thought I'd swap in a pair of TDA7293 amps. The mount right up and the wiring allows me to quickly remove and restore to stock if the right replacement amps come along.

Using these:
https://www.parts-express.com/yuan-jing-tda7293-dual-mono-amplifier-board-set-2-x-85w--320-6532
(if you take the trouble to look at the supplied spec document, the modules as delivered are improved - C1 is 2.2uf and other tweaks recommended by others.)

I have everything working well except what seems to be inadequate gain from the pre-amp stage. I pulled the driver transistors and they all test good, and also swapped in new KSC1845's to try. Rail voltages are good at +/- 32vdc. Disconnecting the TDA7293 module input and connecting an external pre-amp works well.

Thoughts on better matching the input circuit? Reduce R317, increase R325?

Maybe change TR303 to a Darlington transistor.

Cool idea. Thoughts on a part num? I have some TIP120's laying around but look too slow, and Ce, Cb are lower. Originals are 2SC2240's and have an fT of 100mhz.

It is not gain of the preamp stage that you want to increase but the gain of the audio PA!

From that grainy schematics it looks as the gain of the original amp is about 66, what is quite big, relatively speaking.
The gain is the ratio of R342 over R336. Those are 22kOhm and 330 Ohm.
Usual gains for audio power amp stages are between 10 and 30, so it is possible that those TDA modules are also configured as such.
In the info page of that module they do not give the schematics or the specs.
If you go to the TDA datasheet, Fig. 8, the application info, from there the gain is R16 over R3, 13 kOhm and 680 Ohm. That gives a gain of 19.
You would want to increase the gain in your TDA module to match what was used in the original Yamaha module.
You should increase R16, and the matching resistor in the other channel, to 44.88 kOhm, or to 47 kOhm, or 43 kOhm (assuming R3 is 680 Ohm).
As with this you decrease the loop-gain you should not have any trouble with stability.

Regards, Peter

Excellent info - thanks Peter.

As delivered, the modules (boards) are quite a bit different than the TDA spec sheet examples. I will draw out how these module are currently and use your info.

Thanks

Yamaha IG 02990 is an STK080 IC, from Sanyo.



I'd continue with whatever you are replacing it with - the STK080 has long been obsolete, and any out there for sale are likely pulls or counterfeits.
EDIT: One exception: The SK7660 on eBay is genuine - RCA exited the replacement semi business BEFORE the counterfeits became commonplace. The SK7660 is a remarked STK080. And, no , I'm not the seller nor do I have any relationship with the seller.

NTE should [hopefully] be authentic/good, especially if sourced from them directly.

For STK080/SK7660: http://dilp.netcomponents.com/cgi-bin/n ... r1=NTE1327

Direct from NTE means ntepartsdirect.com, but the NTE1327's are almost always cheaper elsewhere.

https://www.ntepartsdirect.com/ENG/PRODUCT/NTE1327

I did find a pair of NOS NTE1327 I might grab. Not from overseas and in original bags.

Description: MOD-AF PO, 35 W

"Yamaha IG 02990 is an STK080 IC, from Sanyo." Looks like a match from the original schematic. Is the STK080/NTE1327 cross-referenced to the IG02990 somewhere. I trust you folks, but wanted to triple check before I pull the trigger.

Still fiddling with the TDA7293 - mostly for fun, but would like to send this back to my buddy as original if I can.

Thanks

If equivalents worry you and you want the original part: https://www.utsource.net/pro/IG02990.html

Hurry, they only have 86,934 left!



Disclaimer: I have nothing to do with that vendor, and thus make no guarantees what they are selling are OEM and not counterfeit. Buy at your own risk.