THAT4301 compressor

[Nescafe]

Hi ungifted,
I'll try to find in that dn, and why, I found that for acoustic music with percussive sound (mixbuss) FB mode is really helpful :-D maybe it just me......

 

[Nescafe]

Hi,
just got info from THAT apps support about feed backward, it can be done just switch the input of rms detector between input and output, but in feedback mode the ratio number is not the same.

anybody know how to calculate the value for resistor and pot to change the ratio to max 1:2 or 1:4?

Thank You.

 

[Nescafe]

Hi,
Could somebody explain to me what for and what is the goal when adjusting the trimmer in THAT 4301 symetry PIN 14 and also is that need implement the trimmer in detector input PIN 1 when using in stereo link mode?

Thank You.

 

[Nescafe]

Hi,
still lookin for the way to adjust the symetry, what software to use and what is the ideal goal?

Thank You.

 

[JohnRoberts]

Hi,
still lookin for the way to adjust the symetry, what software to use and what is the ideal goal?

Thank You.

It could help if you told us which THAT design not you were referring to.

The symmetry trim in VCAs are generally to reduce distortion so you would play a clean sine wave through the VCA and adjust the trim for lowest distortion.  THAT should provide some advice in one of their documents for how to trim.

JR

 

[JohnRoberts]

Hi,
just got info from THAT apps support about feed backward, it can be done just switch the input of rms detector between input and output, but in feedback mode the ratio number is not the same.

anybody know how to calculate the value for resistor and pot to change the ratio to max 1:2 or 1:4?

Thank You.

Which design note are you talking about? The compression relationship is quite different in feedforward vs feedback.

JR

 

[Nescafe]

Hi John,
it's DN115 that I try to implement FB and FF. And the symetry question is in THAT Demo Schematic like in the attachment file. Could You please give me the direction to adjust it?

edit: someone give me short explanation:
set gain to min then masure DC voltage at pin 12 (will be about -1mV) then set gain to max, adjust 50K pot to the same value (about -1mV).

so I don't need any distortion analyzer / software?

Thank You

 

[L´Andratté]

I would put a 1k sine wave into the vca at 0db and check the output with an oscilloscope
(possibly software), if it is clean sine on + and - swings or distortion (deformed sine on one polarity) and adjust the trimmer accordingly. Some 4301 that I tried had no (to me) audible distortion even untrimmed.

 

[Nescafe]

Hi L´Andratté,
Thank You for the direction, and which one do You reccomend: trim from the output pin 12 or pin 13?

Thank You.

 

[L´Andratté]

If you have the same value resistor in front of the vca as in the feedback loop of the output buffer and no cv to the inputs the signal is unity gain, so the buffer will add no distortion of it´s own and you can measure pin 12

or you get really freaky ;D
http://www.thatcorp.com/datashts/dn121.pdf

 

[Nescafe]

Hi L´Andratté,
Thank You for appointing to the DN121 and now I more understand about symetry and the THD relation, I wil try to implement that someday in 4301 and see what is the result 

 

[ungifted]

I'm thinking on addon PCB design for THAT4301 compressor.
Attack Release and rms options (peak, rms, auto).
Found two versions for attack release.
One is simple (just one TL072):
http://burnit.co.uk/sdiy/images/boxotrix/schematic_compressor.gif

Second is more complex version of attack release feature from THAT DN115 doc.
http://www.thatcorp.com/datashts/dn115.pdf

Wich one is more "correct"?

 

[druu]

Bump! I'd like to add attack/release to the pico i'm currently building so keen on any development on this.

 

[ungifted]

Well, I think both work.
Need some time to update schematic build prototype and make some tests.

 

[ungifted]

Made rough tests. TL072 based schema is working (attached). Here is a pic:



So I see no problems with adding this feature to Pico boards if you have one.
BTW can anybody comment on the 500ms for release? Is it usable?

Next is DN115 schema...

 

[druu]

Ideally I'd be keen on 20-30ms range for both attack and release. Would this just be a matter of pot value to determine the range? Really interested to see how the DN115 schem turns out..

 

[druu]

Bump!

 

[dirtyhanfri]

I'm looking closely at this thread, looks like a promising project.

Keep on pushing...

 

[Nescafe]

Hi ungifted,

is the timing circuit also works for the rms mode or just the peak mode?

Thank You.

 

[ungifted]

When attack/release is on it must affect control (sidechain) signal in any position of RMS detector action...