OPTO "Grinder"

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Gustav

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Joined
Jun 4, 2004
Messages
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DK
OLD, SELF ETCH FRIENDLY REVISION

Ive been working on a PCB for a classic opto compressor with a few minor changes. For my taste,  it sounds excellent after a few revisions.

- So I thought I'd share the files for self etch.

https://pcbgrinder.com/download/OPTO_GRINDER/OPTO_Grinder_docu.pdf


NEW REVISION

New layout available - not self etc friendly (double sided). I call it "Hand of Light" to distinguish.

The projects is being replaced with the MS HOL, so when the current batch of boards is gone, they will be gone.


Gustav

P.S. I have an mental barrier when it comes to entering the intersubjective realm of aesthetic judgments, so I am no good at communicating "how something sounds". If I were pressed, I would say this thing sound "old, like 70s Elton John records" when its pushed into the red and "Very pleasant" when its not.
 
I had a lot of help from Jakob Erland on this - so thank you for that!

And the calibration procedure will be posted when I have an easy step-by-step-guide.

Gustav
 
Hi Gustav!!

Thank you for this!

Do you think if we remove the Output of the Fet and the input of the Opto, we link them and we have a beast a la M@n-Ley SL@m!

Best.
 
Schematic looks mostly straightforward to me. The only part that puzzles me is the 1M resistor from the top of the threshold pot to the 140K resistor feeding the LDR. Can you please explain?

Cheers

Ian
 
ruffrecords said:
Schematic looks mostly straightforward to me. The only part that puzzles me is the 1M resistor from the top of the threshold pot to the 140K resistor feeding the LDR. Can you please explain?

Cheers

Ian

I begged, borrowed and stole my way to this, and although I learned a lot and know exactly how changes in quite a few parts of this circuit will manifest itself in its sound and character, I have to admit, the 1M resistor is something that was "brought over" from a schematic and never brought into question, since I dialed in a sound I loved with focusing on other things.

If you tell me why it puzzles you, I might learn something, though!

Gustav
 
Gustav said:
ruffrecords said:
Schematic looks mostly straightforward to me. The only part that puzzles me is the 1M resistor from the top of the threshold pot to the 140K resistor feeding the LDR. Can you please explain?

Cheers

Ian

I begged, borrowed and stole my way to this, and although I learned a lot and know exactly how changes in quite a few parts of this circuit will manifest itself in its sound and character, I have to admit, the 1M resistor is something that was "brought over" from a schematic and never brought into question, since I dialed in a sound I loved with focusing on other things.

If you tell me why it puzzles you, I might learn something, though!

Gustav

It puzzles me because I cannot see what it does. The output of the op amp after the opto goes via a 2K2 resistor to the threshold pot which is 10K. The 1M goes from the top of the pot to the output of the input buffer amp. As the opto buffer op amp is non-inverting this means the 1M has in phase signals at each end, one from the input and one from the opto buffer.

So the input signal gets fed via the 1M to the threshold pot. The 2K2 resistor in series with the opto buffer op amp is its effective load  so the inout signal reduced by about 53dB is fed direct to the side chain. I cannot see any reason for this.

Also, the opto buffer output appearing at the threshold pot gets fed via the 1M to the input buffer amp output. Since the input buffer amp output impedance is likely to be very low, very little signal gets fed this way.

So as far as I can see all it does is bleed a 53dB attenuated input signal direct to the side chain.

Cheers

Ian
 
Very interesting design (to me) simple in a good way
but is 140k not a little high (noisewise)?

Since vactrols go down to 10M and beyond dark and there´s lots of gain in the
signal path the 1M maybe restricts the voltage divider action?
Not really convincing I know... Does it sound different without ?

Sometimes I suspect designers to put nonsense parts or 137.32k resistors in their designs like watermarks when something is simply copied? ;)

Why did you use the tl072 for output there?

And what is the use of LED driver transistor, when NE5532 puts out 30mA easy (like the Forssell opto way) and with 140k divider even that would be way too much?
Sorry my knowledge is gathered here and there and feels like a swiss cheese...

100uF is a nice statement. ;D
And thanks!
 
First of all, dont mistake me for someone who knows a lot about this stuff. I am learning as I go along, and the two projects (this and the FET Grinder) has taught me a lot of things that would probably cause me to implement some things differently from the start - but as long as I ended up on a sound I liked, I did not change things from my first starting points, if that makes sense.

L´Andratté said:
Very interesting design (to me) simple in a good way
but is 140k not a little high (noisewise)?

The unit is not noisy at all, so that has not been an issue.

I tweaked this resistor by putting in a 200K pot, tweak it, take it out and measure it. I did it on various days to "start blank", and I always ended up around 130-150K, so I settled on 140K as a golden "middle of the road" value. The Opto I used started misbehaving badly at settings under 110K

L´Andratté said:
Since vactrols go down to 10M and beyond dark and there´s lots of gain in the
signal path the 1M maybe restricts the voltage divider action?
Not really convincing I know... Does it sound different without ?

Sometimes I suspect designers to put nonsense parts or 137.32k resistors in their designs like watermarks when something is simply copied? ;)

Going by sound alone, I can say that the odd resistor values can be changed in most cases, but I have found cases where it depends on another resistor value to be changed into something regular to make it sound good.

L´Andratté said:
Why did you use the tl072 for output there?

Honestely, if I did it now, I would start with TL071 for the meter driver and a single 5534 opamp for the output side. I found that it sounded excellent with this configuration, so I decided to not mess with the good result, even after I found the answers!

My first reason for doing it was simply because I was a little unsure of how to configure the unused pins when using  single opamps instead of the dual (quad actually) from the schematic I borrowed from. Since this was a learning project, I do know now, but again - left a good sounding result alone rather than change it.

Two singles would also have made it easier to make the routing a little more elegant, to be honest.

L´Andratté said:
And what is the use of LED driver transistor, when NE5532 puts out 30mA easy (like the Forssell opto way) and with 140k divider even that would be way too much?
Sorry my knowledge is gathered here and there and feels like a swiss cheese...

100uF is a nice statement. ;D
And thanks!

As long as the cheese to holes ratio keeps increasing, we should all be happy! I still have too many holes to answer everything. I just know it works now and sounds good, and learned a little something about optos and opamps along the way :)

Gustav
 
LA4, anyone?

Anyway, it's reported to be a nice comp. I've made some attempts to clone it also, but for some reason can't get it to behave properly. Otherwise ok, but it's stubbornly wayyy too slow.

J.
 
Unfortunatly parts designators are missing (please turn on the eagle 'names' layer 95).
For pro-level audio either the 3K3* input resistor after the debalancing stage looks on the low side or the 33K feedback resistor looks on the high side, setting a voltage gain of 10 that would clip this stage in the audio path with inputlevel above 3.3dBu before the vactrol can decrease it. This probably as well explains your vactrol misbehaviour with decreased 140K following this clipped stage.
In the rectifier stage (your 3x 5K1 and 10K resistor values) maybe use two 5K1 resistors in series instead of the 10K for the wanted 10K2 value or decrease the 5K1 values to 4K99 resistors. The shown 10V diodes (zener value with diode symbol) are simple maybe 1N4148 diodes.
Better use a NE5532 instead of the TL072 or decrease your supply voltages. A +/-18V supply (that will have +/- tolerances) would be the abs.max. rating of the TL072 that you don't want to exceed and the TL072s high input impedance isn't needed here.
As always YMMV.
 
Script said:
LA4, anyone?

Yes, Luny Tune:

http://groupdiy.com/index.php?topic=32615.0
::)

Its pretty different from what Luny did, even though we both refer to the same fundamental, and the inspiration to do it was to get a much easier-to-build opto comp running.


Its no secret what primary circuit this is based on, but I did change some central things, and like I wrote in a different thread.

"The FET Grinder is based on a very popular circuit. If you look at the schematic for 5 seconds, you might be able to see which. I am just reluctant to  use those types of names on the projects I conjure up myself, since I have no illusions of grandure or even hope to live up to the genius of the people who designed them or make carbon copies of them."

The same goes for this one, so no points for guessing, and no sense in clawing on to this as being a clone.

Different opamps throughout, changes in the  compression behavior and a few other "small" improvements. You will not get an La4A clone out of it, but to me, it does really sound really good.

You might hate it, but only one way to find out!


Gustav
 
Harpo said:
Unfortunatly parts designators are missing (please turn on the eagle 'names' layer 95).
For pro-level audio either the 3K3* input resistor after the debalancing stage looks on the low side or the 33K feedback resistor looks on the high side, setting a voltage gain of 10 that would clip this stage in the audio path with inputlevel above 3.3dBu before the vactrol can decrease it. This probably as well explains your vactrol misbehaviour with decreased 140K following this clipped stage.
In the rectifier stage (your 3x 5K1 and 10K resistor values) maybe use two 5K1 resistors in series instead of the 10K for the wanted 10K2 value or decrease the 5K1 values to 4K99 resistors. The shown 10V diodes (zener value with diode symbol) are simple maybe 1N4148 diodes.
Better use a NE5532 instead of the TL072 or decrease your supply voltages. A +/-18V supply (that will have +/- tolerances) would be the abs.max. rating of the TL072 that you don't want to exceed and the TL072s high input impedance isn't needed here.
As always YMMV.

I tried a much lower feedback resistor (3,3K), and in practice, it did not change the opto clipping at set levels under the mentioned range - on the contrary, I like the sound much better (Range also makes much more sense to me).

The choice of Opamps,  I already mentioned as something "learned for the next time, before I start", and I love the current sound of the unit.

Ill see what changing the resistor in the rectifier stage does for the sound, if anything.

Thanks!

Gustav
 
Hi,

I had absolutely no intention to blame about the circuit being based on an already familiar circuit. I just was rather exited that was able to name it. Sorry.

As I wrote I have also tried to copy it, but the results haven't been what expected so far. Hope others have better luck. Meanwhile, I keep on debugging:)

Jyrki

 
Stonetaper said:
Hi,

I had absolutely no intention to blame about the circuit being based on an already familiar circuit. I just was rather exited that was able to name it. Sorry.

As I wrote I have also tried to copy it, but the results haven't been what expected so far. Hope others have better luck. Meanwhile, I keep on debugging:)

Jyrki

Hey Jyrki.

And sorry to you, if my response came across that way - I diidn't see it as blame, I just think I do'nt want the "praise" of being able to clone anything. :)

When I dial in and adapt, I do it by taste - not with a real one by my side, so I don't want builders to be disappointed, and I don't want to use the name of people who do the "real thing" and know what they are doing, thats all :)

Gustav
 
@Jyrki. Sorry, seems I got your excitement wrong. Luny Tune (and other people in the "LA-4 Help" thread) tested and reported on the use of the NSL32 opto cell. There, faster response was more like a byproduct, which might be good or bad (likes/dislikes) for a clone, and it requires some resistor value change. Maybe worth a try while you are debugging :)


So as far as I can see all it [the 1M resistor] does is bleed a 53dB attenuated input signal direct to the side chain.

Hypothesis 1:
It's got to do with sound.
1) forward-feeding the sidechain mildly (sidechain acts a tad more on the signal)
2) parallel compression by bypassing the gain stage (feeds back in a tad of the uncompressed signal)
--> Being 1M, the overall effect is next to none. Yet, I assume it might sound either a tiny bit clearer (less dark), or a tiny bit thicker (bass / below THR level?), or a tiny bit more distorted (signature sound ;D). We should kindly ask Gustav to test this: no resistor vs 1M, 2M vs 500K.

Hypothesis 2:
It tunes the LDR.
The 1M also goes via the 10K THR pot to ground.


Either way, love the double meaning of "Grinder" ;) Nice work here, Gustav.
 

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