Pro Audio Design Forum

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...

Thanks for the input everyone. Another option is, of course, a knob with a pushbutton to switch between "fixed" and variable. With only +/- 3dB range the knob would have fair repeatability (and less chunkiness compared to a switch) based on pointer position. The switch or relay would only ...

Let me expand on Roger's question: What gain trim amounts and number of steps would be required?

+/- 3 dB 6 dB?

6 steps, 12?

Roger - Nice tight simple layout. I like it! FWIW: The type of resistors that would be needed for external gain trimming that equal the matching accuracy of the balanced line receiver's internal ones would be something like these Vishays: http://www.vishay.com/docs/63001/s.pdf The 1240 line receiver...