Experimentation only
Im trying to go where no man has gone before - that is mess around with an old Soundstream Reference 200S amp. I've re-wound the transformer for twice the rail voltage. Amp now runs +-44vDC rail whereas before it was only +-22. For regulated voltage, I replaced the 16v zeners with 18v units and now the regulated circuit runs about +-18.5vDC (Which helped boost clipping point on the pre-amp). I know the opamps are going to clip while and always, where +-18vDC did help lift the point of clip, but not enough for the rest of the amp. I cant get the clipping point to come up much further on the output though. The regulated/opamp outputs will clip before the amplifier drive and output circuit.
Been looking at the 300/300S schematic so the following is in reference to that amp.
I tried fiddling with the voltage divider after UC1 (Pin 8) at R42 and R43 which on this amp was a 620/1.2k set, to 47/4.7k and that helped a little - but not by much. Would I need to modify R2 and R3 instead? I believe those are on the driver cards.
Experimentation only
Im trying to go where no man has gone before - that is mess around with an old Soundstream Reference 200S amp. I've re-wound the transformer for twice the rail voltage. Amp now runs +-44vDC rail whereas before it was only +-22. For regulated voltage, I replaced the 16v zeners with 18v units and now the regulated circuit runs about +-18.5vDC (Which helped boost clipping point on the pre-amp). I know the opamps are going to clip while and always, where +-18vDC did help lift the point of clip, but not enough for the rest of the amp. I cant get the clipping point to come up much further on the output though. The regulated/opamp outputs will clip before the amplifier drive and output circuit.
Been looking at the 300/300S schematic so the following is in reference to that amp.
I tried fiddling with the voltage divider after UC1 (Pin 8) at R42 and R43 which on this amp was a 620/1.2k set, to 47/4.7k and that helped a little - but not by much. Would I need to modify R2 and R3 instead? I believe those are on the driver cards.
Experimentation only
Yes actually I found those just after I posted actually. R43 and R44 on the Reference 200s. Thanks for comfirming also.
I was making a monster. Successfully.
Amp made about 125w at 4-ohms per channel. Class A converted now too. Should be a pretty nice amp for tweeters in a bi-amp install.
Amp made about 125w at 4-ohms per channel. Class A converted now too. Should be a pretty nice amp for tweeters in a bi-amp install.
On the 200S, R43 and R44 are 4.7k resistors one for each channel. I noticed the signal on one side was about the same as the output pins from the U1 opamp, but the other side which led to the driver board was a LOT lower by less than about half. I put a potentiometer in place of R43 and adjusted until both the preamp and the amp clips at the same point. Then I measured the pot. About 2k. So I replaced R43 and R44 with 2k resistors. I'm guessing this part is similar for say a Reference 1000 which runs much higher rail voltage. The part that'll possibly bite me is if load crashes the rail voltage as there is no rail headroom now; so it'll clip from rail drop likely first. I may go back in and put drive circuits on replacement IRF3205 fets at a later point. Also the 4-amp breakers are probably not enough as the amp made 5.5A at speaker terminals while drawing 37A from the bench which is probably too much for just the two PS fets.
Run on tweeters above 3kHz and it'll probably work fine. Thats the intention.
Run on tweeters above 3kHz and it'll probably work fine. Thats the intention.
That's 1 of about 3 or 4 ways to do it. In the 1000, the voltage divider resistors are different, only reducing the preamp signal by about 1/2.
I'd go back to 15v on the op-amps if they're running hotter than normal.
I'd go back to 15v on the op-amps if they're running hotter than normal.