Vari-Mu Sidechain/Hi-Pass compression filter

[Rompstomp89]

Hey guys,
Im trying to add a side chain filter to my Am864 Federal Limiter build and can't seem to figure out how to make that happen correctly.  All the ideas I had have ended up getting me a low pass filter..... DOH! Anybody have done this or attempted this? any schematics you can lead me to? Any help would be great!

Link to Schematic:
http://www.preservationsound.com/wp-content/uploads/2014/02/AM-864_Schem.jpg

 

[DerEber]

Try answering this questions and you are very close to a solution:

What role does V4 play in this circuit? Where does it get signal from?

 

[Rompstomp89]

Try answering this questions and you are very close to a solution:

What role does V4 play in this circuit? Where does it get signal from?

V4 is in charge of the compression.  It gets the AC signal from the center tap of the input transformer and goes through the 47K resistor (which sets the attack timing) to pins 4 and 5 on the SQ7. Am i correct?  If so I don't understand how to implement the high pass filter.  I have inserted caps ranging from .022 to .1 bleeding to ground from that 47k. I have also tried jumping over that 47k resistor and I end up getting a Low pass filter instead with both tries.  I feel like I'm on the right page but am falling short in the implementation of it. 
Rob

 

[DerEber]

V4 is in charge of the compression.  It gets the AC signal from the center tap of the input transformer and goes through the 47K resistor (which sets the attack timing) to pins 4 and 5 on the SQ7. Am i correct?  If so I don't understand how to implement the high pass filter.  I have inserted caps ranging from .022 to .1 bleeding to ground from that 47k. I have also tried jumping over that 47k resistor and I end up getting a Low pass filter instead with both tries.  I feel like I'm on the right page but am falling short in the implementation of it. 
Rob

Nop 

V4 creates the DC to bias V1/V2 so they work on different operating points, leading to less gain in case of compression.
On C1 there is no  AC in reference to Ground, beside what V4 puts out to change Bias.
It is in the middle of the transformer.  You´d have AC-Voltage in reference to "A" and "B" of the attenuator. But not on the Centertap itself.
V4 doesn´t get its input signal (for creating the Bias of V1/V2) from there
Neither it gets the AC-signal from the CT of the output transformer. Same as before.
V4 gets his sniff of Musik delivered to its Grind (Pin2) via......
C5!

Hope my explaination is technicaly correct, but somehow it works like I said.

 

[Rompstomp89]

V4 is in charge of the compression.  It gets the AC signal from the center tap of the input transformer and goes through the 47K resistor (which sets the attack timing) to pins 4 and 5 on the SQ7. Am i correct?  If so I don't understand how to implement the high pass filter.  I have inserted caps ranging from .022 to .1 bleeding to ground from that 47k. I have also tried jumping over that 47k resistor and I end up getting a Low pass filter instead with both tries.  I feel like I'm on the right page but am falling short in the implementation of it. 
Rob

Nop 

V4 creates the DC to bias V1/V2 so they work on different operating points, leading to less gain in case of compression.
On C1 there is no  AC in reference to Ground, beside what V4 puts out to change Bias.
It is in the middle of the transformer.  You´d have AC-Voltage in reference to "A" and "B" of the attenuator. But not on the Centertap itself.
V4 doesn´t get its input signal (for creating the Bias of V1/V2) from there
Neither it gets the AC-signal from the CT of the output transformer. Same as before.
V4 gets his sniff of Musik delivered to its Grind (Pin2) via......
C5!

Hope my explaination is technicaly correct, but somehow it works like I said.

Wow, well that would be why I wasn't figuring it out. Thanks for the explanation. So to implement a high pass switch I would change the value of c5? Or would I add a bleed cap at that junction. Sorry for all these noob questions!

 

[DerEber]

Yes, if you lower C5 less Bass will come to the detector.
If you want a lowpass in the sidechain it will need to be solved differently.
You'r welcome.