Transformerless Vari Mu Compressor build thread

[Heikki]

Hi Heikki, could the HPF be added to the original board? not the rotary switchversion?

Yes it can. It can be done exactly same like with the rotary version.

Here’s a picture Scott made. 330 ohm resistors are the resistors on the main board and the HPF components are on the switch.

 

[manulaudic]

THanks !!

 

[Heikki]

If somebody want's to save a little money and not use the Hammond 107 transformers here's a circuit that might do the job. I stole the idea from this thread. C3 & C4 can be changed for different values for sidechain HPF.

EDIT:
There might be some problems with this circuit! I'll need to comfirm if that is the case.

 

[Heikki]

The circuit in the previous post wasn't that great. Here is a better one.

 

[Script]

Hammonds scheduled to be taken out again over here for testing

 

[Heikki]

Hammonds scheduled to be taken out again over here for testing

Let us know how it works out. If you need to get the threshold range lower the 100k resistors could be connected to a small positive voltage instead of ground.

Here's one way to make the small voltage. Rs could be 10k and the diode a schottky diode.

 

[Script]

Thanks. Next week the earliest though.

BTW, played with D1 (zener 12V and 8.7V) for THR limit and I see/hear why it didn't make it onto the BOM. It limits the THR, preventing too much compression (potentially 'bad' sound) but I prefer backing off on the THR control.

 

[richiyobs]

hi builders, i m here too
collecting components to start this project..
i d like to know according to the last HPF mod Transformerless Vari Mu Compressor build thread
if U9 and U10 should be ina 2137PA or can leave ina2134 as per the starting schematic?
thanks for your attention
best
richi

 

[manulaudic]

Hi everyone, I am trying to order the components for making another unit and so many parts are backordered on mouser. Anyone got lucky somewhere else?
Manu

 

[MonoCutter]

Hi Manu,

I skipped mouser this time and ordered almost everything from reichelt.de, ICs from TI, Hammond 107V and DC/DC converter from Digikey.

Dennis

 

[richiyobs]

Hi Manu
same problem for ina2137.... tried on TI but can t finalize the order don t know why....
digikey only big stock
i m having the bad idea to replace 2137 with an extra small pcb using ne5532 or tl72 in a proper config, just to start building and turn on... waiting on Mouser for spring time, declared on March

 

[paolomunarini]

Hi Manu
same problem for ina2137.... tried on TI but can t finalize the order don t know why....
digikey only big stock
i m having the bad idea to replace 2137 with an extra small pcb using ne5532 or tl72 in a proper config, just to start building and turn on... waiting on Mouser for spring time, declared on March

Hi richi.
Unfortunately many TI supplies are now backordered... Maybe you could try with two that1240 and a small breakout

Paolo

 

[Heikki]

i d like to know according to the last HPF mod Transformerless Vari Mu Compressor build thread
if U9 and U10 should be ina 2137PA or can leave ina2134 as per the starting schematic?

U9 & U10 are changed to INA2137 to get gain to unity when gain is at middle position with the mastering modifications. If you're just adding the HPF U9 and U10 can stay as INA2134.

 

[richiyobs]

Perfect... Thanks for all infos

 

[Heikki]

The values printed on the board are for 3dB steps. Latest revision of the boards don't have any threshold values printed on the board.

From the latest version of the schematic you can find the values for 1 dB steps on the resistors and on the left side are written values for 3 dB steps.
https://ghr.fi/proaudio/varimut/sidechainrotary.pdf
Edit: I'm not seeing the post this was a response to but anyway there was some confusion about the threshold resistor values on the rotary sidechain board.

 

[manulaudic]

The values printed on the board are for 3dB steps. Latest revision of the boards don't have any threshold values printed on the board.

From the latest version of the schematic you can find the values for 1 dB steps on the resistors and on the left side are written values for 3 dB steps.
https://ghr.fi/proaudio/varimut/sidechainrotary.pdf
Edit: I'm not seeing the post this was a response to but anyway there was some confusion about the threshold resistor values on the rotary sidechain board.

THanks for your answer... i had removed my question cause i realised the values were written on the schematic with the 3db note and i felt stupid i asked.. i was positive i had checked everywhere only to find it checking it all again.

Thanks for the clarity again ! the boards are a pleasure to work with. great quality

 

[manulaudic]

One thing Ive been wanting to ask is a tip on what parts is crucial to match if anyone could share some tips on that

Manu

 

[Script]

Not that many components here after all. Quick build.

I match all resistors and caps in signal path by default (one of the reasons I went into DIY -- and so also never had wrong value anywhere). I also match diodes, but only with DMM. Not power caps and not regulators though.

 

[manulaudic]

Thanks, I've been including this process as well.. obviously with a tube compressor, thinking of the old days, maybe having a little off values is maybe a magic trick? is it?

 

[steves.mastering]

One thing Ive been wanting to ask is a tip on what parts is crucial to match if anyone could share some tips on that

Manu

I’m sure there’s a few caps mentioned in the main board BOM that should be matched. But as people have said, I pretty much match all components the best I can

i think Heikki said he has a few hundred tubes that he may sell as matched pairs one day. The matched tubes will probably make the biggest difference