Odd how that differs from the data sheet I have! This was the cause of much trouble!
Well I put in a pair of SJ56 parts on the other channel. Couldn't get proper bias on that channel. Turned out all of the four NEW zeners were shorted again. Replaced, got both channels working. Now they are doing okay, about 0.3% THD. Clipping is about 83W into 8 ohm load.
Now I just need to wait for Toroidy to make the correct diameter transformer that will fit INSIDE the chassis. Somehow, they'd gotten the diameter spec confused (115 became 150mm).
Well I put in a pair of SJ56 parts on the other channel. Couldn't get proper bias on that channel. Turned out all of the four NEW zeners were shorted again. Replaced, got both channels working. Now they are doing okay, about 0.3% THD. Clipping is about 83W into 8 ohm load.
Now I just need to wait for Toroidy to make the correct diameter transformer that will fit INSIDE the chassis. Somehow, they'd gotten the diameter spec confused (115 became 150mm).
Oh, it's going to get a good workout before I ship it back to the customer, for sure!
It's interesting how the left channel's distortion came down when I installed the parts for the right channel and got it up and running. Must have been reading garbage harmonics polluting the common bus.
Once the correct size transformer arrives, then I can finish the work.
It's interesting how the left channel's distortion came down when I installed the parts for the right channel and got it up and running. Must have been reading garbage harmonics polluting the common bus.
Once the correct size transformer arrives, then I can finish the work.
The thing that bothers me about the schematics vs the transformer winding voltages is that they don't add up. 34-0-34 through a bridge that's got a split via ground only makes about 46 V on each rail, but the schematic shows 70V rails. The amplifier makes about 78W/ch with this rail voltage and the transformer secondary measures right on 68V across the high current winding. The original transformer label says "0-34-68", so that's what I had Toroidy manufacture. But that does not make 70 VDC once it is rectified.
The amp works fine (and I got the right size transformer installed after they sent me a corrected version) and runs cool, draws only 49W idle from the line, but I feel that it should have more "balls" when I crank it up. I don't have another amp to compare it with at the moment though, so my impression is subjective.
The amp works fine (and I got the right size transformer installed after they sent me a corrected version) and runs cool, draws only 49W idle from the line, but I feel that it should have more "balls" when I crank it up. I don't have another amp to compare it with at the moment though, so my impression is subjective.
Dear ampexperts, my sa100 transformer has no 270v output. I likes to rebuilt a new transformer but the shop asking me the current output requirement for each output 1. 0v to 34 to 68v, 2. 0-259v 3. 0-8v. Would you mind to share the information so that I could start the rebuild. Many Thanks
That company is called Toroidy and they are in Poland. Here's a link to their website:
https://sklep.toroidy.pl/en_US/index
https://sklep.toroidy.pl/en_US/index