Seventh Circle Audio

Howdy,

I'm trying to make some adjustments to raise the voltage on a pair of j99s that keep clipping but can't figure it out. I've built the current version of the card but this design is quite different.

Does anyone have a copy of the original assembly instructions? It would be a great help.


Eric

another to keep ahead of the porn

Each regulator has a pair of resistors that set the output voltage. Check the data sheets at www.national.com for info on how to calculate the resistor values to get the output voltage you want. What voltage are they currently set at?

tpryan \$m[1]:Each regulator has a pair of resistors that set the output voltage. Check the data sheets at www.national.com for info on how to calculate the resistor values to get the output voltage you want. What voltage are they currently set at?

Well, this was enlightening. I hadn't bothered to check the voltages since I had not yet figured out how to adjust them. I was getting 3.5V between pins 4 and 3 and -24.5V between pins 4 and 5. I just finshed one of the current j99s which I set for +/-21V. I assume this earlier model is designed for the same voltage. If that's true then these are more screwy than I thought.

Which resistors set the voltage? is it r23 and 21 for u2 and r9 and 10 for u1?


Thanks,
Eric

One more question...How tricky would it be to use the Jensen transformer with the new PCB? I'm guessing it wouldn't be too bad. I have considered starting fresh with the major components of these pres.

Is there a significant difference in performance between the two designs?


Thanks,
Eric

+/- 24 is a fine voltage for the 990c, but if you want to reset the older boards to +/- 21, for cooler operation and probably longer life, that's a simple switch of two resistors on each regulator.