THAT4301 compressor

[ungifted]

Balanced in and out (likely THAT12XX and 1646) is assumed on a separate board (with XLR sockets and possible relay bypass).
Like lego or JLM projects...

 

[ramshackles]

I've been working on a 1206/1646 I/O pcb with an optional 5532 gain stage

Still a number of adjustments to make

 

[ungifted]

ramshackles
Thank you for your design. Shall you post the schema? Thank you!

 

[Biasrocks]

Look up the Pico compressor project. It's pretty much everything you're doing here and as far as I can see a standard implementation from the data sheet.

Schematics are out there, if you're stuck send me a PM and I'll send them over.

Regards,
Mark

 

[ramshackles]

1206 and 1646 are simply following the datasheets
You can leave out C8 and C9 and use a 1:1 transformer aswell

 

[ungifted]

Biasrocks
Thank you. I have all Pico docs, and I know that the schema is the same (right from the datasheet).

ramshackles
OK. i think i'll post here redrawn in/out and bypass pcb design and schema for discussion soon.

 

[ungifted]

Last schema and PCB version

 

[wolfgang]

Have you already tested the board?

nice work btw!

regards,
Wolfgang

 

[ungifted]

Thank you for support!
The PCB is not tested yet, I'll post report after testings.

 

[ungifted]

In/Out doc based on THAT1626/THAT1200 compiled. Adding bypass...

 

[ramshackles]

1646 gives a gain of 6dB, so wouldnt it be better off with the 1206 on the input (-6 dB) ?

 

[ungifted]

Yes you're right. But is it good idea to decrease input signal at the input?

Can someone explain what is the trick with the +6db?
Datasheet says that "The 1606 and 1646 both provide +6 dB gain (factor of 2) between their inputs and differential outputs. This is appropriate, since with a balanced output, twice the voltage between the power supply rails is available at the output of the stage. ..."

So do we need to use -6db THAT1206 at the input?
Let's imagine we need this project as bal/unbal (12XX stage) only and don't use output stage (1646)?

 

[RuudNL]

Just took a look at the schematic.
I see controls for threshold, ratio and gain.
Shouldn't there also be a control for the release time?
(Or am I overlooking something?)

 

[ungifted]

RuudNL
Release time can be added as a feature. Take a look at THAT doc http://thatcorp.com/datashts/dn115.pdf
This design (and Pico) has no Attack and Release.

ramshackles
Took a look at the similar design from the sevensircle audio. They use THAT1200 and simply added a 6db pad:
"Relay switched 6dB pad and direct bypass"
http://www.seventhcircleaudio.com/B16/b16_about.htm

Anyway we can use 1206 (need just to add 2 zeners in the ESD protection stage) which can be ommited if we use THAT1200.

 

[hazel]

RuudNL
Release time can be added as a feature. Take a look at THAT doc http://thatcorp.com/datashts/dn115.pdf
This design (and Pico) has no Attack and Release.

It's the greatness of this beast, the harder you hit it, the faster attack and release.

I don't want to hijack your thread ungifted, i'm just trying to figure out how to add stereo link feature just by reading Design Notes from THAT:

http://www.thatcorp.com/datashts/dn115.pdf
http://www.thatcorp.com/datashts/dn116.pdf

Would this could be a feasible stereo link?

 

[hazel]

hi again!

I've just drawn a block diagram about stereo link.

I don't know if it's necessary THAT2252 for RMS SUMMING but i added just because i cannot find how to implement summing with just 4301P

 

[ungifted]

In stereo one THAT4301 is master and the second one is slave.
Master RMS (pin 5) (or linked RMS pin 5 of master and slave) goes to EC+ (pin 15) of slave. As I understand no additional ics needed.

Btw do we need this type of stereo THAT4301 compressor (where master RMS controls the slave VCA)? Why not to use two mono for two channels?

 

[hazel]

In stereo one THAT4301 is master and the second one is slave.
Master RMS (pin 5) (or linked RMS pin 5 of master and slave) goes to EC+ (pin 15) of slave. As I understand no additional ics needed.

Btw do we need this type of stereo THAT4301 compressor (where master RMS controls the slave VCA)? Why not to use two mono for two channels?

In stereo compressors the RMS detector must be the sum of both channels or image shifting may occur if one channel contains harder signal to be compressed than the other. This is why i say about summing signals using 2252.

I understand you said one channel is master and other is slave, i don't think this will be good for stereo signals, very few times works.

Reading app note 115 (full adjustable compressor) suggests using 2252 ic for stereo linking

 

[dirtyhanfri]

Maybe the solution is to sum together the two signals before the rms "master" detector, and then apply that to the "slave" EC+??

 

[Script]

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.