Pro Audio Design Forum

Looking at Wayne's gain trim circuit above the only downside I see is that the mono sum will be between 3dB and 6dB up already. Having 3dB of gain at the input might have headroom issues. It seems that to "fix" this you would give up the precise level matching by having makeup gain set by...

Thanks Paul and Roger. Here's the variation of the circuit using a pot: https://www.ka-electronics.com/Images/jpg/M-S_Variable_Gain_Trim_Pot.jpg https://www.ka-electronics.com/Images/jpg/M-S_Variable_Gain_Trim_Pot.jpg Not shown of course are the detailed 1243 or follower connections... The layout lo...

OK, so it's not as tall. Cool.

RF; I think a 797 would be fine but we ought to try one for follower unity gain stability issues. I think it will need a 100R Rfb and an optional 100R series resistor with the In+ input pin 3. See http://www.analog.com/static/imported-files/data_sheets/AD797.pdf#page=13 Figures 36 and 37. I used the...

Does it fit the same layout? Is it bigger or smaller than the original one? I'm confused.

Here's a gain trim idea I'm kicking around which only requires a single-pole rotary switch. Something Paul said earlier made me think of this. https://www.ka-electronics.com/Images/jpg/M-S_Variable_Gain_Trim.jpg https://www.ka-electronics.com/Images/jpg/M-S_Variable_Gain_Trim.jpg There may be a more...

OK, back to plan A. I love it. From just quickly looking at it you can see the symmetry. And it's simple with everything clearly labeled. Looking at the layout you have a good low inductance path from the 1646 pin 3 to ground. That whole plane, to the left of the 1646 gets shunted back into Vcc by t...

Roger - Having the relay bypass become pads for optional switches works for me. I don't have a problem using a good switch and since it's only DPDT at that location it's do-able. My thinking was that for a field-recording battery-powered rig, the relays would be off for normal operation using the NC...

Roger - I'm happy with the board pic you posted yesterday which has the one DPDT. You may want to change the labeling and pad orientation but I'd keep that one soft-bypass relay. No one has to stuff it and I think we're going to find a lot of people will use it . The size was OK too. With that board...

Paul - Having a 2 pos switch in (addition to the pot) which has "fixed" (calibrated) and variable positions wouldn't require a center tap on the pot. (There would be one switch each for M and S.) The center position on the pot wouldn't have the 0.05 dB/0.005% accuracy. But that accuracy wo...