TDA7052A for compressors etc

[merlinb]

(rightly or wrongly) I'm only seeing it as ....when the trannies are off the resistance to ground will be very high & when the trannies are fully on the pin 4 resistance to ground will be between 3k & 50k (depending on where p2 is set) - where does your 100k come into it?

What matters is the impedance at AC, since we are interested in AC/transient conditions. The cap gets periodically drained by the transistors, so the TDA has to supply current to try and fill it up again, which is what causes its gain to fall.

[Lurco]

Doesn`t R9, P2 and R10 supply that current from the battery? The voltage that Perfboard Patcher measured reminds me of the controlpin voltage to be overcome  in CA3080 or LM13700. Maybe the TDA is made up very similar, but has an additional internal high-ohmic pre-bias resistor from the Vp to exactly that internal controlpoint, while a currentlimiting internal resistor connects from that internal controlpoint to pin 4?

[merlinb]

Doesn`t R9, P2 and R10 supply that current from the battery?

The current comes simultaneously from the battery and the TDA. As I said earlier, the pull up resistor appears to have been added to alter the release time.

[Perfboard Patcher]

My gut feeling tells me this design needs to be modified.

To me there seems to be one phase splitter too many, remove R6, T3, R7.

Add a resistor to connect pin 8 to C10, 100 ohms (or more)
Add a resistor to connect pin 5 to C8, 100 ohms
Add a resistor to connect pin 2 to earth, 5k in data sheet.
Adjust the bass cut by experimenting with C4.

[pedalgrinder]

the biggest thing you are missing with this chip is that the variation is between 0.3v and 1.4v so as long as the superimposed signal on the dc voltage rides either above 1.4 and dips down further in order to compress which leaving the attack and release points to one side while i explain the variation of the gain control. once either transistor has been triggered essentially as a form of a drain to ground the voltage will drop enough to keep it within this range. if you go below 0.3 v this is a mute option on this chip. so the idea is to keep it definately above 0.3v but trigger it by the superimposed signal voltage so the transistors act as variable resisors and act as voltage dividers controlled by superimposed dc voltage controlled by the signal. Hope that all makes sense. The graphs in the data sheets explain more than the writing.

[pedalgrinder]

Another thing i wanted to add with a bit of thought this chip has huge potential. It also is a great candidate to be adapted to all those ca3080 compressor out there that hiss like snakes half the time. to make them quieter and more transparent. I know everyone calls it that vintage sound i call it that dead and no top end sound but anyway thats another debate in it self. But yeah so so much potential for the price of it. Iam playing around with a prototype now i will post how i go.