CBS Model 450 Dynamic Presence Equaliser

[PRR]

Need to get into Depression-era thinking and improvisation with parts and practices..... We've gotten lazy and spoiled.

https://youtu.be/jm5Z7yLUlcU?t=131

 

[NOON]

I've managed to restore the power supply to working and much safer order. Fired it up briefly this morning to run some audio through and it's working! Boosting high frequencies as expected. Adds a nice twang to a DI'd bass.

However, after about 10 mins of being on it started developing some crackling noises. Will try and narrow it down to which stage when I get a chance. Could be zener regulator/s in PSU going noisy, could be a noisy transistor somewhere.. Won't have time to investigate for a few days.

 

[NOON]

Still makes noise with the output volume control down, so either noisy transistor in the output stage or the 20V rail.

 

[NOON]

It was a transistor in the output stage, solved and working well now.

Does interesting things on vocals, but really need to bring all the controls out to the front panel to be able to tune it in. Also interested in making the attack and release times variable. With the dual CV sidechains for 'normal' and 'presence', I'm guessing I'll have to use dual gang pots and tune them together. Anyone got other interesting ideas on adding more control?

 

[abbey road d enfer]

Does interesting things on vocals, but really need to bring all the controls out to the front panel to be able to tune it in. Also interested in making the attack and release times variable. With the dual CV sidechains for 'normal' and 'presence', I'm guessing I'll have to use dual gang pots and tune them together. Anyone got other interesting ideas on adding more control?

There's a total of 5 Attack/Release cells in this piece.
I would suggest you tweak each one individually in order to evaluate their effect on performance.

 

[NOON]

What I would normally consider the release resistor in most cases seems to be involved in the biasing of the next transistor. I'll have to do some careful investigations into the impacts of making these variable.

 

[abbey road d enfer]

What I would normally consider the release resistor in most cases seems to be involved in the biasing of the next transistor.

That's not the case for R58, R67, R75 & R87, but changing R64 probably implies also changing R63.

 

[NOON]

Experiments going well. The release timing in the main audio sidechain didn't seem to make a significant difference.  (R58) The main lamp driver timing section makes the most difference, as expected (C27 R67).  I've set up a switch to swap C21, C23 and C27 for caps of half the value to reduce the attack time. Replaced R67 with a 33k resistor and 500K pot at the moment. All the action seems to be in the first few degrees, so I think I'll replace it with a log 250K tomorrow.

It's a much more usable and interesting device with the option of a faster attack and the ability to tune the release time.