3080-based compressor builders - Do not despair!

[ElectricDruid]

Could someone please educate me as to why this section of the circuit, which I assume to be just gain recovery, is designed the way it is? And why doesn't it work properly, for me at least?

Checking the schematic, the op-amp gain recovery section is a dead-standard non-inverting amp. So yes, it absolutely should work, and if yours isn't working, something is wrong with it - wire in the wrong hole on the breadboard, most likely.

[Greenballs]

Could someone please educate me as to why this section of the circuit, which I assume to be just gain recovery, is designed the way it is? And why doesn't it work properly, for me at least?

Checking the schematic, the op-amp gain recovery section is a dead-standard non-inverting amp. So yes, it absolutely should work, and if yours isn't working, something is wrong with it - wire in the wrong hole on the breadboard, most likely.

Thanks Electric Druid for your reply. I've checked, double checked and checked again. Everything is where it should be. I've even switched out the op amp but with the same result.

What could having to bridge pins 2 and 3 to get the signal to pass through be indicative of, assuming I don't have a bad batch of op amps that all share the same fault?

Also, why doesn't the op amp hook up to the 18v via pin 8 as well as pin 3?

[bluebunny]

For some reason, the schematic seems to omit the power connection to pin 8, as we would expect.  The connection to pin 3 that you're referring will be bias, not power.  Make sure you have power applied to pin 8 via that 220R resistor, and remove your short between 2 and 3 and see what happens.

[ElectricDruid]

Also, why doesn't the op amp hook up to the 18v via pin 8 as well as pin 3?

Ah, that would do it!! +1 what Duck says, make sure that you've got power to the op-amp, otherwise nothing is ever going to work.

[Greenballs]

I thought it was a bit odd that the schematic would omit the power to pin 8 but assumed that the more knowledgeable folks than me who drew it up would know what they were doing! I'll revisit the breadboard and report back. Thanks for the replies.

[duck_arse]

Tom! how do you know what I'm going to say before I say it?

not only take pin 8 to the R124 point, but you need to correctly terminate the unused part of that opamp. wait a minute - there's two R124's on that circuit, a 220R and a 220k. 220R should to pin 8, 220k should probably go to ...... well, V/2, some kind of bias, but there isn't any shown anywhere on that circuit.

[bluebunny]

Duck?  Bunny?  So similar...  An easy mistake to make for a probably-stoned stop-action cartoon dog. 

There seem to be a couple of places where there's a bias being made: R103/R104 on the input transistor; R111/R112 for the OTA; R116/R117 at the start of the peak detector?

Here's a clearer schematic, albeit from the slightly-enhanced UE405 compressor:



The designators are slightly different.  This one has the power arrive via R128.  The bias on the output is supplied by R124 (which is now 100k).  But note also that it's connected to an empty triangle, not a filled triangle indicating power.  Perhaps the confusion arises from a scan of a photocopy of a photocopy of a . . . ?

Anyway, given that this is only part of a larger collection of schematics, then perhaps the bias is made somewhere else entirely?  The chorus part shows a simple 10K/10K/47uF arrangement feeding an empty triangle...

[duck_arse]

+1 what the bunny says.

[Greenballs]

Thanks guys for the responses.

Even though I knew this circuit was from a multi effects unit, it never occured to me that the schematic I was working from is just a smaller piece of a bigger picture, so to speak. What you're saying, duck_arse and bluebunny, totally makes sense now you've caused me to consider it.

I did try the circuit again with the suggested changes but to no avail. In the end, rather than lose my mind trying to figure it out (I only have so many hours in the day to work with!), I replaced the 4558 op amp with an LPB1 style gain recovery circuit and it works just fine.

I'm definitely going to try adding that attack control though. Wild times at chez Greenballs.

[PRR]

Duck?  Bunny? ...

https://www.atlasobscura.com/places/the-bunny-museum-altadena-california
https://www.atlasobscura.com/articles/bunny-museum-expanding

[ElectricDruid]

Duck?  Bunny?  So similar...  An easy mistake to make for a probably-stoned stop-action cartoon dog. 

Lol, *SO* busted...

[bluebunny]

Duck?  Bunny? ...

https://www.atlasobscura.com/places/the-bunny-museum-altadena-california
https://www.atlasobscura.com/articles/bunny-museum-expanding

Ha ha!  Thank you Paul.