Detectors in compressors and Envelop filters.

POTL · Post by **POTL** » 11 Jan 2019, 18:02

Let's discuss them.
I studied the principle of operation of the detectors and began to analyze the circuit, however I asked a number of questions.
1) Why do they use only half-wave rectifier in Envelop filters? Why no one uses a full wave rectifier?
2) Compressors use different types of rectifiers and half-wave and full-wave rectifiers. Why do primitive and classical circuits like Dyna Comp or Diamond use a full-wave rectifier, and modern circuits like THAT use only a half-wave rectifier? Is this somehow related to Peak / RMS compressor types?
3) Classical detector layout in OTA / OPTO compressors, how relevant is it today? Or is it worth looking at a precission full wave rectifier?

bmxguitarsbmx · Post by **bmxguitarsbmx** » 11 Jan 2019, 20:19

Great topic. I did not realize the THAT detector was half wave. Where did you find this info?

I would assume the only reason to use a half wave would be to limit complexity/make it cheaper. In the case of envelope filters, fast attacks are probably not needed, so a half wave could be fine. Ome of these half wave envelope filters do have signal distortion imparted from the control signal however. A good or bad thing depending on what you like.

POTL · Post by **POTL** » 11 Jan 2019, 21:06

bmxguitarsbmx wrote:Great topic. I did not realize the THAT detector was half wave. Where did you find this info?

I would assume the only reason to use a half wave would be to limit complexity/make it cheaper. In the case of envelope filters, fast attacks are probably not needed, so a half wave could be fine. Ome of these half wave envelope filters do have signal distortion imparted from the control signal however. A good or bad thing depending on what you like.

Threshold detector in the circuit for that4301 classic half-wave rectifier.
A few minutes ago I was re-reading the documentation and if I understood correctly, this was done because this is an RMS compressor.
The principle is as follows
1) The signal falls on the RMS, it aligns the voltage relative to the average value of the minimum and maximum (as should the RMS compressor).
2) Our average voltage falls on a threshold detector (half-wave rectifier), which we set to a certain level, as soon as the average voltage exceeds the set threshold, the compressor starts to operate.
3) If the rectifier were full wave, then our compressor would always exceed the specified parameter and the compressor would always be activated

ppluis0 · Post by **ppluis0** » 12 Jan 2019, 02:01

Hi POTL,

Perhaps this link can be useful to you : http://www.geofex.com/Article_Folders/n ... teproc.htm

Cheers,
Jose

bmxguitarsbmx · Post by **bmxguitarsbmx** » 12 Jan 2019, 02:47

POTL, can you link the app note or whtever that you read this? Inquiring minds, would like to know

In this thread PRR declares that it is:

https://groupdiy.com/index.php?topic=54553.0

POTL · Post by **POTL** » 12 Jan 2019, 14:07

bmxguitarsbmx wrote:POTL, can you link the app note or whtever that you read this? Inquiring minds, would like to know

In this thread PRR declares that it is:

https://groupdiy.com/index.php?topic=54553.0

Sorry
I can not find, it was exactly yesterday on the THAT website, perhaps not in the notes, perhaps in datasheets.

bmxguitarsbmx · Post by **bmxguitarsbmx** » 12 Jan 2019, 18:00

Cool. I will look for it.

couple notes about the Ross Dynacomp method of full wave rectification.

Threshold is essentially VBE.

Once threshold is crossed, the transistors turn on with an exponential response. I suppose this would be similar to having the ratio on a knee. The harder you hit it the higher the ratio. Looking at it on a scope these two FWR transistors clip pretty early on. It seems that you could change the response quite a bit by selecting for gain of these two trannies.

POTL · Post by **POTL** » 13 Jan 2019, 18:42

bmxguitarsbmx wrote:Cool. I will look for it.

couple notes about the Ross Dynacomp method of full wave rectification.

Threshold is essentially VBE.

Once threshold is crossed, the transistors turn on with an exponential response. I suppose this would be similar to having the ratio on a knee. The harder you hit it the higher the ratio. Looking at it on a scope these two FWR transistors clip pretty early on. It seems that you could change the response quite a bit by selecting for gain of these two trannies.

The release and attack time can be adjusted by changing the resistance between the emitter and the ground and between the collector and the power supply. Scheme can be found at EQD Warden.
However, the situation is ambiguous, for many manufacturers, the change in resistance between the collector and the power supply is responsible for adjusting the attack, but often on the Internet you can find information that the adjustment actually changes the release time, and manufacturers indicate an attack from marketing campaigns (this is easier for inexperienced users).
In general, I am interested in the option of a good detector with the ability to adjust the attack and release, and working from a unipolar power supply.

bmxguitarsbmx · Post by **bmxguitarsbmx** » 13 Jan 2019, 19:37

I have seen quite a bit of wrong info on the ross detector. Attack would be how fast the transistors can drain the capacitor, so capacitor size would do it. Release is then how fast the collector resistor can charge that cap. But increasing that resistor will also increase gain. It's a neat design, but everything is highly interactive. I spent a lot of time building an envelope filter using the Ross detector and that was a mistake. It is actually quite temperature sensitive. I keep the cover off the bottom so that I can trim it regularly. Total PITA. Somehow we don't notice it with the Ross Compressor. Maybe it is because we are slamming it so hard. it doesn't work reliably in the between saturated and off region.

I am very interested in the THAT compressor and how to build simple attack/release. I suppose I should bust out the breadboard

Best wishes!

POTL · Post by **POTL** » 13 Jan 2019, 20:31

bmxguitarsbmx wrote:I have seen quite a bit of wrong info on the ross detector. Attack would be how fast the transistors can drain the capacitor, so capacitor size would do it. Release is then how fast the collector resistor can charge that cap. But increasing that resistor will also increase gain. It's a neat design, but everything is highly interactive. I spent a lot of time building an envelope filter using the Ross detector and that was a mistake. It is actually quite temperature sensitive. I keep the cover off the bottom so that I can trim it regularly. Total PITA. Somehow we don't notice it with the Ross Compressor. Maybe it is because we are slamming it so hard. it doesn't work reliably in the between saturated and off region.

I am very interested in the THAT compressor and how to build simple attack/release. I suppose I should bust out the breadboard

Best wishes!

I am also interested in the version of THAT compressor with the ability to customize the attack and release time.
However, I am also interested in the project 1176 in the pedal format, but I did not see any circuits without an input transformer and an output transformer, as well as with the replacement of a 5 Mega oM potentiometer.
Unfortunately the schemes Cali76, MXR Studio / Bass compressor, Empress compressor is not on the Internet.

POTL · Post by **POTL** » 15 Jan 2019, 11:56

OK, we discussed the compressors and it gave me a lot of useful information and understanding.
Let's go back to envelop filters.
Why in all popular circuits - Q-Tron / Mu-Tron 3 & 5 / DOD fx25 & 440 / Mad Professor SWAW and many others we see the detector for only one half period, regardless of whether the circuit works from 9V or from bipolar power supply?
Is this somehow related to the mode of operation of the filter up and down? Will the filter capture both half-periods and give strange sounds or is there simply no need for a full-wave detector?

bmxguitarsbmx · Post by **bmxguitarsbmx** » 15 Jan 2019, 19:33

POTL wrote:OK, we discussed the compressors and it gave me a lot of useful information and understanding.
Let's go back to envelop filters.
Why in all popular circuits - Q-Tron / Mu-Tron 3 & 5 / DOD fx25 & 440 / Mad Professor SWAW and many others we see the detector for only one half period, regardless of whether the circuit works from 9V or from bipolar power supply?
Is this somehow related to the mode of operation of the filter up and down? Will the filter capture both half-periods and give strange sounds or is there simply no need for a full-wave detector?

From my experiments, which have been quite extensive, the half wave is only used to be cheap. Superior results are had by full wave rectification. Unless you want that "gargle" distorted VC sound. You cold analyse the "attack times" of envelope filters to see if they tend to use longer times and therefore not needing the better performance that FWR provides.

On the topic of the 1176:
http://www.jhaible.info/compressor/jh_compress.html

You will really appreciate this article POTL

POTL · Post by **POTL** » 16 Jan 2019, 15:03

bmxguitarsbmx wrote:
POTL wrote:OK, we discussed the compressors and it gave me a lot of useful information and understanding.
Let's go back to envelop filters.
Why in all popular circuits - Q-Tron / Mu-Tron 3 & 5 / DOD fx25 & 440 / Mad Professor SWAW and many others we see the detector for only one half period, regardless of whether the circuit works from 9V or from bipolar power supply?
Is this somehow related to the mode of operation of the filter up and down? Will the filter capture both half-periods and give strange sounds or is there simply no need for a full-wave detector?
From my experiments, which have been quite extensive, the half wave is only used to be cheap. Superior results are had by full wave rectification. Unless you want that "gargle" distorted VC sound. You cold analyse the "attack times" of envelope filters to see if they tend to use longer times and therefore not needing the better performance that FWR provides.

On the topic of the 1176:
http://www.jhaible.info/compressor/jh_compress.html

You will really appreciate this article POTL

Yes, it was interesting.

heaterman · Post by **heaterman** » 22 Feb 2019, 17:54

Hey POTL

In general, I am interested in the option of a good detector with the ability to adjust the attack and release, and working from a unipolar power supply

Jea! Me too, im working exactly on that... check out my schematic https://multicornpedals.files.wordpress ... llower.pdf

it is working really nice!
It is working wich unipolar power supply, has attack and decay controls. And reverse sweep.
It needs some gain stage/booster in front of it, since just the direct guitar signal seems to be too weak.

Rectifier: A transistor phase splitter, the negative parts of the signals are cut by the diodes (D1-4)

Attack and Decay Control:
A problem was the attack, because increasing attack really lowered the amplitude of the envelope output. So i tried to compensate that with a dual pot (second pot in the feedback loop of U1B) witch increases gain while increasing attack time.
And i'm not sure in general if this is a healthy way to use an op-amp...
Maybe there are better ways...

it also has reverse sweep, but this is a little bit tricky, one needs to set a starting voltage and one needs to adjust the the envelope voltage going to Q2 so the reverse sweep really goes to zero on the peaks. Maybe there are also better ways to do this...

The envelope output peaks are around 2-3V (also depending on the input), maybe i add a option to scale this voltage.

Not the simplest one i guess, but works well for me so far. I want to use it to control all sorts of things: Filters, VCA's (compressing, sidechain compressing aka Ducking) LFO speeds (for example in a tremolo)... etc

Just wanted to share this, maybe it goes int the direction of what you are looking for, hope you can use it.

All the best!

ranko0537 · Post by **ranko0537** » 31 Dec 2020, 14:46

Is there any chance that someone saved those pages:
http://www.jhaible.info/compressor/jh_compress.html
https://multicornpedals.files.wordpress ... llower.pdf

Both are not available anymore...

CheapPedalCollector · Post by **CheapPedalCollector** » 31 Dec 2020, 23:37

did you check on archive.org ?

cspar · Post by **cspar** » 02 Jan 2021, 04:45

The 1176 link works for me.

I think Heaterman's link might be the schematic which he posted in the link below. Or perhaps with the pots being annotated as being on a dual gang like he mentioned.
viewtopic.php?f=10&t=29851&p=275732#p275732