Pro Audio Design Forum

I think for now I'll align them using equal C values. That's how I usually see them. The Ec will be bused and they ought to track well. I may experiment with having an inverted CV to four of the (eight) poles so that as one goes up the other sweeps down. I also need to revisit Thomas Henry's Barber ...

Should I continue with this?

Ever since I built an 8 pole "DynaPhaser" prototype back in the early 80's using a pair of SSM2040s I've wanted to rebuild that prototype using modern VCAs. I recalled that listening to it was such a mindf**k (pardon my English) it was worth revisiting. One of the things the SSM2040 had go...

I decided to make a THAT2180 VCA (actually three) into an all-pass filter. This is a three pole demo. I'm not going to stop building until I get to eight. A stereo output is derived from polarity inversion and a sum/difference network. Here's a quick and dirty demo. https://www.proaudiodesignforum.c...

There should be a trim for the crowbar threshold. If it's an older power supply the carbon comp resistors that may have been used could have drifted significantly. The crowbar might also have an electrolytic for noise filtering that's failed.

I'll have to check but I think many of the used Leaders can be made to run on 220V. SInce they're Japanese they run fine on 50Hz. I have a collection of Tek, Leader and Philps analog Scopes as well as a Velleman USB scope. Though I like the Velleman - and used it for a lot of the Phantom Menace II w...

Do you suppose that on start-up, even without tubes installed, that the B+ supply is making it to the filament output? Put a scope on the output of the filament supply and see if you see some transient when the B+ is turned on. Maybe there's some leakage current from B+ to filament which causes it t...

Could the MPSA92 be selected for low noise? They're common and in production.

Those look to be discontinued Sanyo. I keep seeing more openings for Central Semi and Linear Systems. These HV/LN parts - and discretes in general - are going EOL fast.

My original thought that led to this was that high voltage capability and low noise in the input transistors were almost mutually exclusive. Flying the rails around allowed less critical HV parts to be used. Hopefully someone will pickup production of the 2SA1084 and 2SA1085 like Central, Linear Sys...