[Aman]

Hi hi hi, Head-Fi!

I'm taking an electric engineering course and have decided to take on the task of analyzing the schematic of a DBX 160x compression unit. I have a few questions about how this circuit works...

The circuit can be found here: ftp://ftp.dbxpro.com/pub/PDFs/discon...0Schematic.pdf

The electrolytic capacitor called C154 is really bothering me. I am thinking it may have something to do with setting the timing constant, which later becomes important when dealing with the release controls of the circuit... but I'm pretty much at a loss here.

Also, what exactly is JP108 doing??

Any help would be greatly appreciated! I know there's a lot of knowledgeable people in this forum, so I would be enthusiastic to any ideas/suggestions.

Thanks!

 

[Pars]

Quote:

Originally Posted by Aman /img/forum/go_quote.gif Hi hi hi, Head-Fi! I'm taking an electric engineering course and have decided to take on the task of analyzing the schematic of a DBX 160x compression unit. I have a few questions about how this circuit works... The circuit can be found here: ftp://ftp.dbxpro.com/pub/PDFs/discon...0Schematic.pdf The electrolytic capacitor called C154 is really bothering me. I am thinking it may have something to do with setting the timing constant, which later becomes important when dealing with the release controls of the circuit... but I'm pretty much at a loss here. Also, what exactly is JP108 doing?? Any help would be greatly appreciated! I know there's a lot of knowledgeable people in this forum, so I would be enthusiastic to any ideas/suggestions. Thanks!

C154 is a bypass cap on V- of the LF353 (pin 4), much as C122 is performing the same function on V+. LF353 is run as a single-supply opamp, so V- is actually ground.

JP108 is probably just a jumper across some trace or traces. This is quite common, particularly in '70s-'80s electronics where the board was done single sided. There will be alot of jumpers because the routing cannot be done on a single side.

 

[Aman]

Thanks for the response, Pars!

Those answers open up a couple of other difficulties for my group. Do you (or anyone else) have any idea exactly what the diodes (D101-D102) are doing in relation to the push-pull transistor circuit?

We're seeing only the negative (half) of the audio wave form is being amplified, since we understand what D103 and D104 do, but are just stuck on D101 and D102. Any insight on this would be highly appreciated!

More generally, could anybody provide insight as to how the threshold and ratio are set? Specifically, which OP-AMPS are dealing with these functions?

Thanks again!

 

[Pars]

Well, I'm not an EE, so this is likely wrong or incomplete, but my guess would be they limit the amount of the output of U103 that is allowed to drive the bases of the two unmarked transistors to +/- 0.7V approximately. As to your other question, I have no idea. How is it controlled? Rotary control (like a pot) or by switches? I see lots of switches (S103B, etc.).