Pro Audio Design Forum

Thought this was very interesting. Reminds me a little bit of the Soundcraft pan pot using NICs. https://proaudiodesignforum.com/images/pdf/Synthesize_Variable_Resistors_With_Hyperbolic_Taper_TL_Flaig_EDN_January_8_2009.pdf https://proaudiodesignforum.com/images/jpg/Synthesize_Variable_Resistors_Wit...

Thanks guys. I need to run a few more tests and then I'll order us some boards with silkscreen and solder mask.

Chris - thanks for posting. Good question. That 200 pF between the inputs reduces the differential input impedance at RF at the device pins. The differential capacitance at the XLR is 470 pF/2. The added 200 pF directly at the input appears in parallel with that but is after the ESL of the coupling ...

Thanks Randy! I appreciate the drawing and your data. If you look at the Vishay datasheet for the GP there's conflicting info. They're good diodes though. http://www.vishay.com/docs/88504/1n4001gp.pdf They show 100 nA max in the bullets then 5 uA at 25 degC. The ones I tested were excellent at aroun...

+15-20V to the cathode and a series resistor of 100K on the anode to ground. 1 nA would be equal to 100 uV. Randy - to test those you could just reverse bias them. Use a series R to ground and a DC voltmeter to read the leakage current indirectly as a voltage across the sense resistor. +20V (or mor...

Randy - Your switch wiring looks exactly like mine. I opted for a "one of twelve" approach (as opposed to series-connected) since it makes the switch wiring easier and the resistor errors non-accumulative. The gain switch does open during transitions but the 1510/1512 does not go open loop...

I had a chance to build the latest version with the added 1240 in the decoder. It works great. https://www.ka-electronics.com/Images/jpg/M-S_Matrix_V127_Proto.JPG This particular board is wired for single ended L&R inputs and outputs. The jumpers can be seen on the left-hand and right-hand side ...

Randy; The T-Bias scheme does allow the use of smaller values because of the higher CM impedance on the right-hand side of the caps. I wouldn't go much lower than 22 uF though which eliminates the use of film caps due to size. On the single-supply preamp non-polarized capacitors are required because...

The drawing looks good Randy. Can the "pin2 to 3"..200pf cap be either a 220 or 180 ?? Yeah either one. I'm reminded of the movie "Mr. Mom" where Mr. Mom is asked "Are you rewiring for 220?" Mr. Mom answers "Yeah 220, 221." As you point out those 1R5 stop resi...

The OP07 (or OP77) trimmed would be inexpensive. That's the option I've considered for the DC preamp. Either that or an LT1012.