THAT4301 compressor

[hazel]

No. On the THAT 4301, pins 5 do not connect to pins 15.
For stereo operation:
(1) Cross-connect RMS pins 5 of left and right channel THAT 4301
(2) Cross-connect EC+ pins 15 of left and right channel THAT 4301
(3) Entire sidechain of "Slave channel" can be skipped/switched out of circuitry.

Summing before the RMS detector works too, but it will cancel out out-of-phase signals (i.e., original Gyraf GSSL approach). And if the VCA In pins are not cross-connected, the VCAs will see any slight difference in Threshold and Ratio settings on left and right channel, resulting in image shifts. This holds true for any (VCA-based) compressor.

Interesting, THAT design note 116 "http://www.thatcorp.com/datashts/dn116.pdf" omits your approach (Script) that seems very easy to implement, just a switch (or relay) that sums both pin 5, both pin 15 and bypass slave sidechain section.

Where would be the best place to add HPF to sidechain?

 

[ungifted]

Example of stereo design is in DN118
http://www.thatcorp.com/datashts/dn118.pdf
Take a look at the schema (EC- is used but it makes no difference, we can use pin 15)
Pico uses the same approach (if I'm not mistaken).

 

[hazel]

Example of stereo design is in DN118
http://www.thatcorp.com/datashts/dn118.pdf
Take a look at the schema (EC- is used but it makes no difference, we can use pin 15)
Pico uses the same approach (if I'm not mistaken).

It's a different approach to stereo linking...i don't know which one would fit better in this compressor...i found easier the solution Script suggested

 

[ungifted]

Yes Script is right about my mistake about pin 5. We get signal from pin 4 of the master.

Script's approach is the same - connect CT pins and let master control left and right channels. No?

Need to draw a full schematics for stereo...

BTW DN115 says: "To make a two-channel stereo compressor, one need only duplicate the circuitry
shown and provide a means to link the two RMS detectors at their CT pins*. Such
coupling results in true power summing and a more euphonic behavior. Note that,
when linking detectors in this manner, means to adjust for the +/-3 dB tolerance on
each detectors' 0 dB reference level must be provided."

 

[Script]

It's a different approach to stereo linking...

No. Look again. It's exactly what I described.

Where would be the best place to add HPF to sidechain?

In the sidechain

Look at where other compressors put the HPF, so look e.g. at all DBX and Behringer compressor schematics in the "Technical Documents" section ("stereo linking" is all hidden in there too, it just looks a bit different).

I'd be interested in one or two of these "newly-developed" THAT4301-based boards, if they stayed really basic (clean main audio signal path, balanced INs and OUTs all on one board) but allowed for a kind of modular "Lego building-blocks" approach for the sidechain. A bit like a stripped down THAT4301 Demo board, but just more useful, cos I don't really see those THAT demo boards inside a rack case.

I'm thinking simple tie points, so people could easily build (e.g., on veroboard) and test any THAT Design Note available (one knob squeezer, ducker, two-slope comp etc.) plus whatever other crazy idea inspired by any other VCA-based compressor's sidechain (I'm thinking parallel paths, downward expander, gate, filters, distortion, you name it). Then people could put together (and maybe even share) whatever they love. Wouldn't that be truly cool and educational?

 

[hazel]

Quote from: hazel on Today at 05:49:47 AM
It's a different approach to stereo linking...

No. Look again. It's exactly what I described.

Oops my fault, sorry Script and Ungifted  :-[

Quote from: hazel on Today at 03:13:02 AM
Where would be the best place to add HPF to sidechain?

In the sidechain

Thanks  i know it seems obvious but i have limited knowledge and i don't know if there'll be impedance issues due to passive HPF

I'd be interested in one or two of these "newly-developed" THAT4301-based boards, if they stayed really basic (clean main audio signal path, balanced INs and OUTs all on one board) but allowed for a kind of modular "Lego building-blocks" approach for the sidechain

this is my main idea, i've just ordered a couple of 4301 demo boards, here you have schemo and data:
http://www.thatcorp.com/datashts/THAT_4301-Demo_Datasheet.pdf

i would like to add:
- hard/soft knee switch
- RMS-Auto/manual mode (manual attack and release control)
- HPF on sidechain (2 or 3 frequencies selectable with rotary switch)

4301 Demo Board is plenty of space for prototyping, according to my maths i should be able to fit a couple Demo Boards in 1u rack

I'm thinking parallel paths

That would be awesome, a dry/wet knob for parallel compression

I'm thinking simple tie points, so people could easily build (e.g., on veroboard) and test any THAT Design Note available (one knob squeezer, ducker, two-slope comp etc.) plus whatever other crazy idea inspired by any other VCA-based compressor's sidechain (I'm thinking parallel paths, downward expander, gate, filters, distortion, you name it). Then people could put together (and maybe even share) whatever they love. Wouldn't that be truly cool and educational?

Hey man! we should talk seriously, i had the same idea months ago and i'm just trying to finish my preamp project to start with little modules

 

[dogma]

The PICO as mentioned is based off of those datasheets, as is the B16. The pICO is unavailable to the DIY community as its now a commercial product but is cheap as chips, as is the B16. I have the last stereo PICO 38 board that Roger sold - still waiting for time to stuff it. I'm going to buy Tims B16 as its just so cheap for the quality of sound. I'm repeating the obvious because unless you dont want to make music or produce and your only interest is re-inventing electronic wheels for the want of a better analogy, buy the B16 and add a simple PSU. You should be able to source a PSU for well under $50 - you dont have to buy the rest - chasis, wiring harness, ect. Ive built a couple of N72s and bought the chassis and sold it because I just didnt need that many pres and at that point thats all he sold (this was years ago). Please dont take my reply as belittling or anything - just its been done and done by some crazy smart designers.

 

[ungifted]

The PICO as mentioned is based off of those datasheets, as is the B16.

Do we want to "re-invent" THAT4301 compressor again based on the THAT datasheets? Is it diy forum? Or forum where everyone is selling copyrighted kits?

 

[plimousse]

Concerning HPF on SC, please read attachement about GSSL SC Filter

 

[hazel]

Concerning HPF on SC, please read attachement about GSSL SC Filter

Thanks for this!!!

 

[ungifted]

Previous design is etched and roughly tested. It passes audio.
Some bugs are fixed. New version is attached.

Added two pinheads for stereo (pin 5, pin 15). Stereo scheme will be a bit later.

One question is about Threshold: fully CCW we get maximum compression. What is the morden tradition for threshold pot? Max compressionm at CW or CCW?

 

[JohnRoberts]

One question is about Threshold: fully CCW we get maximum compression. What is the morden tradition for threshold pot? Max compressionm at CW or CCW?

That appears correct. Threshold corresponds to the signal level where gain reduction begins, so higher threshold when turned CW results in less compression. CCW or lower threshold results in more compression.

JR

 

[gemini86]

I've seen it done both ways. Threshold pot can be labeled in dB, ccw being - (below 0dB) cw being +  (above 0dB) and middle being 0.

 

[ungifted]

gemini86
JohnRoberts
Thank you for your replies! Sure, DN115 shows it as - -30db, +10db. But we added 2M to skew the adjustment range of threshold pot... Need see THAT docs...
I've drawn stereo. Attached.

 

[Script]

Only a very brief glance. C3 is the wrong way round.

 

[ungifted]

Script
Yes, my mistake. I'll fix it. Thank you!

 

[plimousse]

Hi,
I would like to share with you my build ...
Based on THAT DN115, DN132, and DN114 for adaptive attack and release.

 

[ungifted]

Nice build!
Have you redrawn the schema? What GR meter is used?
Thank you!

I've got a bunch of PCBs (v1.5), need some time to solder and to be tested. More info to come.

 

[plimousse]

The GR Meter is based on LM3914 (1,25 V full scale, 3 dB step ~125 mv for 3 dB)
I have a little redraw the schema to include auto attack and release.
I must build a printed borad for GR Meter.

 

[ungifted]

I've finished soldering and testing. Everything works as it should.
The latest version - 1.5.
What we got.
1. Single side PCB - ready for home etching
2. Has connection points for the stereo
3. Has connection points for attack / release (I'm going to make addon PCB)
4. Has connection points for GR meter
5. Fits in 2u vertically if someone decides to build a multi-channel version (and I think 5XX too).

More info to come...