whisper compressor - no go

[kvb]

I have not seen a schematic for the EPFM optical compressor. I read in Mark Hammer's discussion of the SSM2166 that this Whisper compressor is a close relative. Jack Orman's name come's up as the designer, but I haven't seen any info other than what came with the kit.

A kit purchased from SmallBear. I built this quite some time ago, and it did not function properly upon completion.
Recently, I spent some time attempting to figure out why it does not work.

With the tlo61 removed and R10 paralleled with 3k3, signal passes just fine.

I tested the optocoupler (with both chips removed and measured that the resistance does change with voltage applied to the LED - which is in the proper orientation, showing a voltage drop of 1.3V to ground

Both chips have been replaced

The unit oscillates when trying to turn up the volume.
When the compression knob is turned up, the volume drops, there seems to be compression happening, but the volume stays low. There is distortion when playing.

tlo72 IC 1 volts (volts at circuit -8, +8.6)

1. 3mV
2. 3mV
3. 0
4.-8V
5. 0
6. 2 mV
7. 2mV
8. 8.6V

tlo61 IC 2

1. -7.95
2. -0.7mV
3. 0
4. -8V
5. -7.95
6. -0.7mV
7. +8.6V
8. -5,-15mV - jumping around

I was really hoping that replacing the chips would do the trick.

Could it be the octocoupler? I don't want to tear it out if there's nothing wrong with it.  CLM-6000 $6 and only offered as out of spec.
Replacement? I'm not sure of the requirements or what would be better than a CLM-6000.

[Mark Hammer]

Lift one end of R5 so that the sidechain is rendered inoperable.   You should get an audible output that you can vary the tone and level of.  If the problem persists, then clearly it has nothing to do with the optoisolator, and everything to do with some other part of the circuit.

[amz-fx]

Here is the story of the Whisper Compressor...

From 1995 to 1997, I worked on a bunch of projects with Tom Henry, and some of them appeared in Nuts-and-Volts magazine or Electronics Now. The compressor started because Tom had bought a big batch of CLM6000 optocouplers and wanted to use them in a guitar pedal. He had the Craig Anderton comp and wanted me to add some features, which I did. I also designed the pcb artwork and built the first prototype with parts from my stock and a home-etched pcb. Tom built one on a breadboard from his existing parts stock and we both got good results, so with minor tweaking, the project was quickly wrapped up.

However, once the pc boards were produced, Tom built one to check the design and it did not work properly. I checked mine again and it worked correctly. Some troubleshooting revealed that the problem with his circuit was due to the CLM6000. He replaced it with another from the big batch and it worked differently yet. I sent him a CLM6000 from my parts stock and the comp worked correctly once he had put it on his pcb. The problem turned out to be that the CLM6000 optos that he had bought surplus were crap, and only a small percentage of them could be used. They had to be tested one-by-one to find good ones for the project, and the bad optos tossed out.

For a variety of reasons (especially the opto problem), The Whisper Compressor never found a home as a magazine article but subsequently was sold as a kit project on his web site Midwest Analog.

I believe that I still have the original prototype of the Whisper compressor, but I don't have any other files than the one you show in your picture.

The NSL-32 optocoupler sold by Small Bear can be used in the project.

Best regards, Jack

[Mark Hammer]

By "not work properly", did you mean that the LDR value was severely off in some way, or was there some other issue with the CLM6000s?

[jimbeaux]

I have one of the kits that Thomas sold with the instructions - was recently thinking about putting it together (ordering new electrolytics, metal resistors,... first)

Just looked at it & it does have the Clairex CLM6000.

Also I have the 12 page assembly instructions in pdf format - if that would help - let me know & I'll send it to you.

[amz-fx]

By "not work properly", did you mean that the LDR value was severely off in some way, or was there some other issue with the CLM6000s?

The photoresistor would not respond normally. The resistance would be all over the place for different photocells and there was no consistency. Some would be 200 ohms at 5ma while others would be 1k or 3k or even more. Tom sorted them by hand to get enough good ones for his kits.

regards, Jack

[jimbeaux]

The orientation of your CLM-6000 is different than the instructions detail.

(the way you have it connected is probably correct - but I can't tell from the picture where the dot (cathode) is.)




* edited - there is a typo identifying the CLM-6000 as D4 - it is called out as D3 everywhere else (there is no D4)

[rankot]

Datasheets say that CLM6000 fall time is 500ms, while NSL-32 is only 80 (ones produced by Luna Optoelectronics, Silonex are similar to CLM). Also, R_on for CLM is 500 Ohm @ 20mA, vs 40 Ohm @ 16mA on NSL.

I have a dozen of different vactrols, what is the simplest way to test fall times?

Also, does anyone have a photo of original Macron MI1210 vactrol, cause I've bought few on line and I am not so sure they are originals. They should have 500ms fall time and be similar to CLM6000 or Silonex NSL-32 in every aspect.

[kvb]

Well now we're getting somewhere. How nice to see a message from Mr. Orman. Great to hear the story of this circuit.
I have been resisting the urge for years to buy another opto-comp, and I did not want this kit/time to go to waste. I will certainly get the SNL-32 and reply with results.

Jimbeaux - Dot on cathode (not visible in my pic), cathode to ground.
I had tested the LED, in circuit.

Smallbear has the  Silonex SNL-32. There are other designations, but I don't know what the differences are.

If a slow responding LDR is meant to help with the inevitable breathing in this non-rectified opto setup, then I hope the silonex does the trick.

At this point I do not care much, just want it to work.

I wonder what a capacitor at the LED/LDR would do. Probably nothing good. It would be pretty easy to test.

I'll need a week to get the part

Thank you all!

The pics have better res in my gallery - "kvb thanks the forum"

Peace

[amz-fx]

Datasheets say that CLM6000 fall time is 500ms, while NSL-32 is only 80 (ones produced by Luna Optoelectronics, Silonex are similar to CLM).

I wasn't aware that Luna made a version of the NSL-32 as I have always used the Silonex. Apparently Luna merged in the last few years with Advanced Photonix who owned Silonex. I hate that they changed the specs on the photocells (thanks for informing us of that!)

80ms is a little fast but might be okay with guitar.

regards, Jack

[rankot]

I have two datasheets for NSL-32, one dated 01-04-16 by Luna, and one for Silonex without the date. I don't know which one's later.

https://docdro.id/D4662Rw

https://docdro.id/AozBBiF

[kvb]

got the snl 32 and had it in the circuit before the mailman was a mile away.

Alas, there is distortion present in the signal

Distortion becomes more noticeable and consistent when the compression knob it turned up.

dig into the strings = distortion that fades as the compression is released. The distortion does not appear to be coming from IC1; it is low and in the background.

I've reduced R10, increased R5, changed the input cap, and have spent way too much time (including years ago) messing with this.

All I can figure is that there is distortion from the octocoupler's LED bleeding into the signal.

[jimbeaux]

Definitely understand your frustration.

Regarding the non-polarized electrolytic caps (C11, C12 & C13)  - the ones in my kit look differently than the ones I see on your board - mine are dark blue & there's no lines on them (since there's no polarity) - just value and rating.

Again - just going by what I can see in the photos.

[Mark Hammer]

got the snl 32 and had it in the circuit before the mailman was a mile away.
Alas, there is distortion present in the signal
Distortion becomes more noticeable and consistent when the compression knob it turned up.
dig into the strings = distortion that fades as the compression is released. The distortion does not appear to be coming from IC1; it is low and in the background.
I've reduced R10, increased R5, changed the input cap, and have spent way too much time (including years ago) messing with this.
All I can figure is that there is distortion from the octocoupler's LED bleeding into the signal.

I'm not saying that this is definitively your issue, but it is a common phenomenon that envelope ripple in a minimal rectifier circuit (and this would certainly qualify as one, is often heard as "distortion".  Really it's simply fast audible fluctuations in whatever is being controlled by the sidechain.  In a filter it would be "micro-sweeps" of the filter.  In a compressor, limiter, or noise gate it will be tiny fluctuations in volume - a sort of "trill" that is certainly audible, but not pronounced enough to be heard as tremolo or ring modulation.

The Whisper is a sort of minimalist compressor, attempting to provide as much flexibility with as few components as possible.  Perhaps a spec-matching CLM6000 would provide enough smoothing of the envelope, via its slow fall-time, to eliminate any residual ripple.  That is, after all, why optoisolators are often chosen for such tasks when the rectification of the signal will be bare bones.  However, if the fall-time is too fast, there may not be sufficient smoothing, in the absence of any averaging cap.

So, consider the following.  The schematic shows a 1k5 current-limiting resistor just ahead of the LED part of the optoisolator.  Split that into a 1k and 470R (the 1k being connected to IC2's output), and run a 10-22uf cap from their junction to ground.  That should provide some extra smoothing and "averaging" of the signal to remove some ripple.  Additionally, consider running a Schottky diode in series from the output of IC2 to the 1k resistor.  That will subtract about a fifth of a volt from the envelope, but will lighten the load on the rest of the rectifier circuit.  IN theory, that should significantly reduce ripple.  And, assuming what you are hearing as `distortion`IS that ripple, the distortion will go away.

[kvb]

I certainly appreciate the suggestions, particularly the way to get a capacitor involved, and I just happen to have some 1n5711 Schottkys to try. Looking at the layout, I also wonder about the octocoupler being right next to the input cap.

The distortion is a crackly fizz not unlike a barely mis-biased transistor clipping in an unpleasant way. One of those mystery sounds I've never seen on a scope.

It might be a while before I can/should get back to this. I was attempting to fix/finish some lingering circuits, in a furious fit of solder smoke, in the race against time (during the holiday break) before my next class started - and it started last week (crazy demanding, subject kind of off limits here).

Minus the problem, this particular compressor, in its simplicity, is acting as I had hoped. It swells, wavers, etc. I was playing through it in spite of the nasty buzz.
For me, this is not meant to be a "don't know it's on" compressor - it's supposed to be an effect. Right? Which is one of the reasons, after all this time, that I haven't just broken down and bought one. I've looked at getting The Warden a hundred times though.

Thanks again, ----[]    <-- that's a hammer

[thermionix]

I have not seen a schematic for the EPFM optical compressor.

This'n?



(Sorry for the blur, book didn't want to lay flat on the scanner)