Audio circuit needs a second look.

[solo2racr]

I noticed only the one pair of decoupling caps also. I just copied what was on the ESP page. I looked and still don't see the second pair of parallel resistors. But here are the schematics from ESP that I went from after the Rane design signal combiner circuit.....

Pre-amp first gain stage

I modded this some for just the volume and no balance

Pre-amp second gain stage

And then the phase control section

I didn't really put any thought behind this and just copied what was there, adding the circuits inline with each other. The one other thing I did that wasn't just like the above drawings is since I am only using one channel and not stereo, I used only one 2 channel opamp for each of the gain stages. The drawings are meant for a stereo signal in which they use a single 2 channel opamp for the first gain stage (1 channel right and the other left) and the second 2 channel opamp for the second gain stage. I didn't see a point in using 2 single channel opamps if both are in a DIP8 package.

One way to eliminate the parallel resistors that I know of would be to swap the configuration to have the phase section first and then the pre-amp.

As you can probably tell, I know just enough about this stuff to be dangerous.

 

[(*steve*)]

From your schematic in post #6, R21 and (edit) R9 are effectively in parallel for the audio signal. VR2 and R14 are also in parallel which might yield an unusual pattern of control. And you're already aware of R18 and R1 which will change the characteristics of this filter.

I would consider removing R1, R14, and R21.

I would possibly also consider R19 and R20 each in series with their own capacitor (C4 and C4a), but that's less important.

 

[solo2racr]

That whole first section (R19, 20,21) is straight from Rane. I don't understand what you are saying about R21 & R19 "effectively in parallel for the audio signal". Both R19 & R20 are in series with the signal. R21 ties to GND after they (R19 & R20) are merged. Below is the diagram from Rane.

I am aware of VR & R14. Rod Elliot's reasoning can be found here toward the bottom of the page...http://sound.westhost.com/pots.htm
Below is a diagram of the pot's law (approx). Yes, R14 could be dropped very easily and use the pot's own law.

The only real difference (that I know of) is to put all three (stereo to mono, pre-amp, phase control circuits) on one board. From what I have read from the sources I have gotten these circuits from, each are really a stand alone circuit and I could construct all three in their own enclosure and tie them together with a patch cable.

BTW.....Just so Rod Elliot of ESP is happy, with the exception of the Rane stereo to mono circuit and the ones I drew based on his circuit, all credit for these circuits are his.

 

[(*steve*)]

Sorry, that should be R21 and R9,

Edit: Add if that resistor R14 is there to give the pot a funky law, then it's certainly going to do that

 

[solo2racr]

OK...I managed to get the problems that this thing would take care of sorted without having to build this. Instead of just using the MAIN out from the Soundcraft mixer I use, I ran the MONITOR out to the sub. That took care of the all but the phase part. What I did there is a compromise. I overlapped the frequencies between the main speakers and the sub so that they blended better. Not a perfect solution but, workable.


As some of you may remember, I got a lot of help with a +/-15vdc and +48vdc PSU I was needing on here (THANKS AGAIN btw). In the end, we got the original SMPS that was originally in the Soundcraft mixer working. So now I have the PSU I built just sitting here.....but, not for long.

I think it's time to put it to use and build a couple microphone preamps. Opamp based and not tube based. I have two designs I'm looking at that will use THAT or Ti Burr Brown opamps. I'll post when I get something worked out.