Dual compressor in 1RU (other than SSL)?

[Whoops]

Some people praised and praise a lot the Pico Compressor based on the THAT 4301 IC datasheet,
the Pico project doesn't exist for some time but there was a project developed here based on the same IC datasheet and very similar, I think it's this project:

https://groupdiy.com/threads/that4301-compressor.52021/
From what people say it should be a quite good stereo compressor

 

[scott2000]

the Pico project doesn't exist for some time but there was a project developed here based on the same IC datasheet and very similar, I think it's this project:

yes...THATs the one I was trying to think of...

The couple of compressors I've tried, Pico and another nice one, that have the THAT4301 are stunning...

The design is everything I'd imagine. Or everyone would be all over those Presonus multi channel deals...

 

[Script]

The 'THAT Comp' by member diy-tubes(??) is a THAT design notes / dbx at heart.

 

[abbey road d enfer]

Note that the 4301 is not made anymore.
It's been replaced with the 4305, SMD only.
There are 4301 replacements made, using a 4305 and two dual opamps, and pin compatible, though.

 

[PermO]

I have a couple of the original pico boards.... I think they're unbalanced...

If you ever run into these, and they are indeed unbalanced, I'm very much interested in a DIY stereo compressor that would integrate well with an unbalanced insert point.

 

[scott2000]

Note that the 4301 is not made anymore.

Not sure if Wayne has any left . There's a USA seller on Ebay that has a bunch. Seems like a legit thing with 100% seller feedback but idk.. maybe they bought all of Wayne's lol...

If you ever run into these, and they are indeed unbalanced, I'm very much interested in a DIY stereo compressor that would integrate well with an unbalanced insert point.

I remember emrr saying it was

First version unbalanced Pico, add THAT I/O daughter boards to finish it off if needed. There's a couple of cheap prebuilt modules for that too.

 

[tonedude]

I used to have a stereo pico but of course I sold it...

I then stumbled upon the LA Audio TCX 20 or TCX 2 which is a THAT 4301 design, with the addition of tubes in the in/out circuit. To my ears they sound great as is, and they are useful as a starting point for modifying and rebuilding. For example implement a switch to move the rms detector to feedback position, the pico had that feature, or filtering the sidechain, etc etc...Google and GroupDIY is your friend when modifying...

https://www.audiotechnology.com/PDF/6/AT6_LA_Audio_TCX2_Compressor.pdf
Here in Sweden nobody seems to care for the LA Audio stuff, and luckily so even the TCX 20 / TCX 2, so i got two of them for cheap, paid less than €120 for each...

Schematic:
https://gearspace.com/board/showpost.php?p=4038646&postcount=16

 

[MidnightArrakis]

Or everyone would be all over those Presonus multi channel deals...

[Or everyone would be all over those Presonus multi channel deals] -- You mean.....like these???



/

 

[MidnightArrakis]

I wish there was a dual JFET or Diode Bridge project in 1RU.

[I wish there was a dual JFET or Diode Bridge project in 1RU] -- I have been working with another forum member who lives in Italy and he has been busy designing and prototyping a "Diode-Bridge Compressor". The last I had heard from him, he had handbuilt a prototype and had taken it to some Italian recording studios for "real-life" testing and he had written back to me saying that the engineers who have used his design all had exuberant reviews!!!

This Italian member had contacted me for assistance with the design of his PCB's using KiCAD and help with the mechanical design of his 500-Series module. Somewhere along the line, I believe he had also mentioned possibly also designing a 1U rack-chassis for his circuit for those who don't have or use 500-Series modules. I will send him a message to let him know that at least -- someone -- has an interest in a "1U Diode-Bridge Compressor" and see what his response is, OK??? I can also remember my making a comment to him once or twice about putting a "kit" together for his projects that DIY'ers could build themselves.

Here's an old photo of an audio-limiter that I had handbuilt down in my basement back in 1978:


While you can barely discern what this audio-limiter chassis is sitting on, I had it placed on top of my handbuilt "light table" that I used to manually "hand-tape" my PCB's. You can just barely see some of the PCB "artwork" underneath the rack-handle over in the lower-left corner. Yeah.....that was "life" before computers and CAD-software!!!

/

 

[audiohead7]

True! Joe Malone’s “MAC” compressor is a great LA-3a(ish) compressor in 1RU. I already have a pair of his LA500a’s though (same circuit in 500 series).

I wish there was a dual JFET or Diode Bridge project in 1RU.

The dual monolithic VCR11 JFET VCR is a good choice for the gain control element in a compressor.

Cheers,
Bob

 

[altfidelity]

I used to have a stereo pico but of course I sold it...

I then stumbled upon the LA Audio TCX 20 or TCX 2 which is a THAT 4301 design, with the addition of tubes in the in/out circuit. To my ears they sound great as is, and they are useful as a starting point for modifying and rebuilding. For example implement a switch to move the rms detector to feedback position, the pico had that feature, or filtering the sidechain, etc etc...Google and GroupDIY is your friend when modifying...

https://www.audiotechnology.com/PDF/6/AT6_LA_Audio_TCX2_Compressor.pdf
Here in Sweden nobody seems to care for the LA Audio stuff, and luckily so even the TCX 20 / TCX 2, so i got two of them for cheap, paid less than €120 for each...

Schematic:
https://gearspace.com/board/showpost.php?p=4038646&postcount=16

@tonedude how does it TCX 20 sound like, is it any good?
Is it usable across mix buss?

 

[Whoops]

I used to have a stereo pico but of course I sold it...

Why did you sell it?

 

[13engrsapper]

Two Studer 189 type would fit in a 1U.

Most any diode bridge compressor would fit.

 

[tonedude]

@tonedude how does it TCX 20 sound like, is it any good?
Is it usable across mix buss?

I think its very good, I mostly use it for drumbus but its absolutly usable on the mixbus to. A nice feature is the tubestages, adjust how much you drive them and you have a lots of usable colours from the comp. I tried different tubes and have a pair of NOS Sylvania 12AU7 in there now, made it superclean sounding when hitting it gently. Or you could modify it to something supersupersuperclean like the pico....

 

[tonedude]

Why did you sell it?

I have no use for that type of compression outside the box. I thought it was better to use the money on something else...

 

[altfidelity]

I think its very good, I mostly use it for drumbus but its absolutly usable on the mixbus to. A nice feature is the tubestages, adjust how much you drive them and you have a lots of usable colours from the comp. I tried different tubes and have a pair of NOS Sylvania 12AU7 in there now, made it superclean sounding when hitting it gently. Or you could modify it to something supersupersuperclean like the pico....

Thanks for the answer, would you be so kind ( I mean next time, when you'll be rendering smth) to post some examples? There is virtually no talk on them in the forums, and absolutely no demos whatsover. LA audio seems to be completely under radar...

I am thinking on picking TCX 20 or a pair of aphex 661, right now.... I do like a bit of character, but I still want something that would be overall versatile...

 

[My3gger]

What projects are out there that can fit two channels of compression into one rack unit? I already have a GSSL, so I was hoping for a diode bridge, PWM, FET, or something else. It seems like larger meters are typically the reason for larger enclosure, but controls and transformers can make 1ru for a pair of channels tricky as well.

Ian posted very interesting mono/stereo opto, it can have solid state or tube gain stages and sidechain. Getting tube version into 1U rack would be possible by mounting tubes on an L profile and some wiring to the board.
I'm sure he got stereo matching right, most other simple stereo optos like his don't match between channels and lack documentation about this part.