Pro Audio Design Forum

Cheap micros can have two of more PWM built in but they are often linked to single common counter timebase. Of course you could always always roll any number of oddball outputs depending on timing precision required.

JR

The only changes to consider now is if we were to scale up to say a 250k pan pot, we could lose the 5V rail and derive control voltages from +/-15V rails. My use of 100k for design was because I have a pile of them laying around, and I was originally influenced by THAT's 5V circuitry, but they were ...

I heard back from Gary at THAT. I had sent him a copy of my CV noise canceling scheme. He pointed out that this noise on the CV line is modulated by signal so mainly shows up as N in THD+N measurements. So our improvement will be more for bench test results than audible. I'm OK with that, better is ...

Ironically to save a few pennies, we could do this with only one opamp per VCA, if that non-inverting node is fed to the CV port unbuffered. However, adding a large shunt capacitor at that NI node to get impedance down would actually increase the noise gain of the inverting opamp to 2x, making the n...

No worries about the ball... my (pick-up) team lost the first game, but we won the 2nd (last) game of the night . I'm just happy to not get booed off the court by kids half to 1/3rd my age...

JR

pan.JPG Tough week.. I wasted so much time waffling over this I was an hour late for my basketball game Thurs night, but I did get everything shipped. The order that came in this afternoon doesn't count :D OK.. My subconscious didn't like all those parts either. While it looks at first glance like ...

That sounds to me like two more opamp stages per input. A pair to first generate L and R CV with clamps at something like -100 dB total etc. We can follow that stage with two dedicated pad and buffers, per VCA (one inv, one NI). This does reduce the coherent noise build up from using simple unity in...

My bad I probably found the 179 data sheet... We can live with 4.5nV rt Hz, but I would still use the dual package so boys and girls could sub uber parts if so inclined. I'd be tempted to bench test the big cap, vs, opamp if I had bench gear good enough to measure it, but I don't. It might be visibl...

We can look at this... If I was going to settle on bare opamp I would prefer something lower noise. The perhaps flaky data sheet I looked at was something like 8-10 nV/rt hz for those opamps. In the AES paper Gary sent me there is a comparison of raw TL081 vs AD797 driving one port of CV. Admittedly...

The DC performance is still controlled by opamp so sloppy TL07x offset voltage would still be present 100%. Only the AC loop (noise) is padded down by the the 20 dB, and source impedance is open loop emitter follower, not NF assisted. This is arguably over engineering, since the noise aspect is modu...