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THAT 4301 VCA, Better Sounding Replacement ?
Old 27th November 2019
  #1
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stevep's Avatar
Question THAT 4301 VCA, Better Sounding Replacement ?

My D&R Octagon has dynamics for the channels. The circuit uses a THAT 4301 VCA.

The compressors work fine, very clean... to clean. What i would like to do is dirty them up a bit Maybe close to the DB160XT or like a DBX 202 VCA.

Maybe i will have to start diging through data sheets but i wanted to ask first to see if anyone has experience with a pin for pin swap for a THAT 4301 ?

Here is a screenshot of the schematic. I can post the full schematic if needed.
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Attached Thumbnails
THAT 4301 VCA, Better Sounding Replacement ?-d-r-compressor.jpg  

Last edited by stevep; 27th November 2019 at 06:00 PM..
Old 27th November 2019
  #2
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emrr's Avatar
change the distortion trim shown on the schematic
Old 27th November 2019
  #3
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stevep's Avatar
Quote:
Originally Posted by emrr View Post
change the distortion trim shown on the schematic
Ok,. thanks,. i will give it a try.
Old 27th November 2019
  #4
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Brian M. Boykin's Avatar
If you just want to dirty it up do it by ear. Biasing tricks on 2” decks were used to distort the kick and bass tracks to make them sound fat. Run an isolated kick through it and turn. Index the trim pot so you can put it back when you realize that’s not what you want.
Old 27th November 2019
  #5
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Quote:
Originally Posted by Brian M. Boykin View Post
If you just want to dirty it up do it by ear. Biasing tricks on 2” decks were used to distort the kick and bass tracks to make them sound fat. Run an isolated kick through it and turn. Index the trim pot so you can put it back when you realize that’s not what you want.
Yea, i will check the value of the pot first with a MM so i can go back if needed. also there should be a recommended setting, i will have to look at the data sheet.
Old 27th November 2019
  #6
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Brian M. Boykin's Avatar
I’ve only used the 2180a when upgrading and the trim circuit is removed. Either direction should cause distortion though. Whether a higher or lower value is preferred idk. Maybe someone smarter than me will chime in.

What are your actual goals? There are other ways to add distortion without making the entire compressor only a distortion box. If you add the distortion prior to the compression a clean compressor will not remove the distortion, however, if you have a clean signal and want to keep it clean, the compressor will add distortion you do not want.
Old 27th November 2019
  #7
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What i want to do is have more character, these compressors are very clean sounding and dont add any sound of their own.

Maybe more like a DBX 202 ? or even the 2180, i like the sound of both of those VCAs
Old 27th November 2019
  #8
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Brian M. Boykin's Avatar
Typically people want to add character via harmonic distortion which is much easier to achieve using tubes and transformers and driving them to saturation. That’s much more musical than solid state distortion from VCA’s and op amps. I routinely replace DBX 2150’s with THAT 2180a’s and always feel the improvement is more musical. I have 3 Symetrix 501 compressors here and two were upgraded to 2180a VCA’s and the 3rd has the Valley People VCA in it (which is coveted) and I prefer the THAT 2180a models.

Give the trimmer a twist and see what happens. I’m all about experimentation, but I think putting a color piece with tubes and transformers in front of it will help you achieve your goals better. My 2¢.

I’ve built a pretty decent studio doing the opposite of this. I buy older used equipment for pennies on the dollar and then upgrade them either myself or send them out to be professionally done.
Old 27th November 2019
  #9
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There are three types of THAT 2180 - A, B and C. A is the cleanest (and most expensive) and C has the most THD. Recently I updated my Alesis 3630 with version B and it is quite alright.
Old 27th November 2019
  #10
The 4301 is what it is, a self contained VCA plus opamp. I have used the similar 4305 VCA in designs. That one lets you use a external opamp of your choice. It's pretty darn good with a top notch opamp. The 4301 isn't laid out to use one so as Frank Zappa said;

"You are what you is".
Old 28th November 2019
  #11
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Quote:
Originally Posted by Jim Williams View Post
The 4301 is what it is, a self contained VCA plus opamp. I have used the similar 4305 VCA in designs. That one lets you use a external opamp of your choice. It's pretty darn good with a top notch opamp. The 4301 isn't laid out to use one so as Frank Zappa said;

"You are what you is".
Thanks Jim.

Are you saying it is too much work to mod this circuit ? Its not as simple as just swapping the VCA ?
Old 28th November 2019
  #12
No pin compatible replacements are available. It's more than a VCA, it also has the I/V stage opamp built in.
Old 28th November 2019
  #13
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Quote:
Originally Posted by Jim Williams View Post
No pin compatible replacements are available. It's more than a VCA, it also has the I/V stage opamp built in.
Thank you Jim

I will continue to use them as they are, They dont sound bad,.. just not great
Old 29th November 2019
  #14
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JohnRoberts's Avatar
 

All distortion is not the same so be careful about wishing for even more distortion.

In dynamics processing (compressors etc) the majority of audible differences between units comes from side chain variation, like time constants and smoothing approaches.

JR
Old 30th November 2019
  #15
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Quote:
Originally Posted by Jim Williams View Post
No pin compatible replacements are available. It's more than a VCA, it also has the I/V stage opamp built in.
But in theory, one could cobble pin compatible replacement on a pcb out of separate THAT VCA, op amp etc. and plug the appropriate wires into a socket.
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