Ah, I see now. Dang, timing is a big player as well. I am just wondering how he decided on the gain resistors for Ic1a and Ic2. Maybe Ic2 gave enough of a boost to give a decent current to the LED...

Thanks,
JP

Going from past experience with pedals, I'm gonna have to go with "He tried different colors until it sounded cool", rather than attempt any mathematical explanation.

 

Which op amps were in the original? I have a box of old stuff from a retired family friend who was a TV repairman. He stoped buying discrete parts back in the eighties and most of the junk he left me is from the 60s and 70s. He's 86 now and finally closed his shop 2 years ago. He didn't have the heart to dump them since many were "new" in their boxes so he decided my basement should become a shrine to his old junk. There are even some old GE "top hats" in germanium in that pile. Let me know what you need and we may be able to get your compressor project to sound as bad as the original.

 

Which op amps were in the original? I have a box of old stuff from a retired family friend who was a TV repairman. He stoped buying discrete parts back in the eighties and most of the junk he left me is from the 60s and 70s. He's 86 now and finally closed his shop 2 years ago. He didn't have the heart to dump them since many were "new" in their boxes so he decided my basement should become a shrine to his old junk. There are even some old GE "top hats" in germanium in that pile. Let me know what you need and we may be able to get your compressor project to sound as bad as the original.

You could make a fortune selling "Prime NOS Components" to Audiophools. Make sure to squeeze the capacitors so the distortion just harsh enough (best left for tuning by end user).

 

Going from past experience with pedals, I'm gonna have to go with "He tried different colors until it sounded cool", rather than attempt any mathematical explanation.

lol gotcha. I figured, but you'd think it was less simple than that.

Which op amps were in the original? I have a box of old stuff from a retired family friend who was a TV repairman. He stoped buying discrete parts back in the eighties and most of the junk he left me is from the 60s and 70s. He's 86 now and finally closed his shop 2 years ago. He didn't have the heart to dump them since many were "new" in their boxes so he decided my basement should become a shrine to his old junk. There are even some old GE "top hats" in germanium in that pile. Let me know what you need and we may be able to get your compressor project to sound as bad as the original.

haha nice find. I think the main difference between the sound my compressor will have opposed to his is that I am making my own optocoupler with an LED-photocell shrink-wrapped together. Worse performance than the CLM6000 but I had the parts lying around and it was darn cheap!

IC1 - RC4739 dual low-noise op amp
IC2 - LM201 uncompensated op amp

 

I don't have those, but both are available on eBay for $12 and $5 respectively. The lm201 is even available in the old tin can package to look really vintage.

I have some RC 5532 (also made by Ratheon) but it is the modern 8 pin DIP package dual op amp instead e of the 14 pin version of the 4739 that anderton used.

 

Going from past experience with pedals, I'm gonna have to go with "He tried different colors until it sounded cool", rather than attempt any mathematical explanation.

In those days, the designers for pedals were too stoned to calculate anything. (Been there, done that.)
The circuit was tweaked until it looked good, sounded cool and tasted nice.

Designers and players were all deafened by the very loud acid rock and they could not hear their awful distortion so they added more.
But I toked (oops I mean I took) care of my hearing.

 

In those days, the designers for pedals were too stoned to calculate anything. (Been there, done that.)
The circuit was tweaked until it looked good, sounded cool and tasted nice.

Designers and players were all deafened by the very loud acid rock and they could not hear their awful distortion so they added more.
But I toked (oops I mean I took) care of my hearing.

haha wonderful times I never had the chance to experience.

 

Ah, I see now. Dang, timing is a big player as well. I am just wondering how he decided on the gain resistors for Ic1a and Ic2. Maybe Ic2 gave enough of a boost to give a decent current to the LED...

Thanks,
JP

The input resistor (R9) is decided by the amount of load you want to put on whatever is supplying the signal. The 220 k resistor (R8) is set so that the gain is never more than one. This is necessary because the CdS cell goes to several megohms when fully dark for most of a minute. A gain of 25 to 50 will exceede the voltage rails at the output. Depending on exactly which CdS cell, you might be in the range of 500 ohms when exposed to light. That reduces the gain quite a bit below 1, like .002 V/V

R5 and R10 set the gain for that stage as about 21. That amp is trying to restore enough ampltude to drive the LED. Think of it as a recovery amp because it recovers enough amplitude to drive the LED.

 

The input resistor (R9) is decided by the amount of load you want to put on whatever is supplying the signal. The 220 k resistor (R8) is set so that the gain is never more than one. This is necessary because the CdS cell goes to several megohms when fully dark for most of a minute. A gain of 25 to 50 will exceede the voltage rails at the output. Depending on exactly which CdS cell, you might be in the range of 500 ohms when exposed to light. That reduces the gain quite a bit below 1, like .002 V/V

R5 and R10 set the gain for that stage as about 21. That amp is trying to restore enough ampltude to drive the LED. Think of it as a recovery amp because it recovers enough amplitude to drive the LED.

Thanks! Yes, this all makes sense. I'm just wondering if the CdS for this circuit was designed to be used strictly as a high gain or low gain (off/on) resistance or if more of its mid-range characteristics were to be used.

I am just wondering how Anderton deduced the Vout vs. Vin plot based on his design.

 

The CdS will be in midrange most of the time. The first amp is always at a gain of less than one. These cells are notoriously slow and there is not much difference between them as far as this circuit is concerned. Any CdS cell you can find will probably work because of the way the circuit is built.

You can do a Vin/Vout by usng a fixed amplitude, 1 Khz input signal, of about 1 volt p-p. However, the slow response of the CdS cell is responsible for the attack and decay results, and the Vin/Vout will not show these movements.

What I'm really thinking is, "Are you tying to math this to death or play a guitar?"
Knowing Anderton's designs, and especially this one, he built it by ear, not with so much math. This circuit will compensate for any CdS cell I've ever seen, and that's the beauty of it. It's almost impossible to screw up. You're trying to arrive at a sound, not an answer. All the necessary adjustments are provided...no skimping here. Plug it in, adjust the knobs, and enjoy.

Regardless of which CdS cell you use, you can adjust this to the sound you want. That's the point of this circuit.

 

haha wonderful times I never had the chance to experience.

I was raised in Vancouver before it became Hongcouver.
Then I went to university in Toronto when the hippies here (and their Marywanna) went to Vancouver. But I met a few hippies who stayed in Toronto. I did not become a hippie.
When my parents visited me in Toronto they didn't know what I was growing.
But that was a long time ago and I have not met with Marywanna since.

 

The CdS will be in midrange most of the time. The first amp is always at a gain of less than one. These cells are notoriously slow and there is not much difference between them as far as this circuit is concerned. Any CdS cell you can find will probably work because of the way the circuit is built.

You can do a Vin/Vout by usng a fixed amplitude, 1 Khz input signal, of about 1 volt p-p. However, the slow response of the CdS cell is responsible for the attack and decay results, and the Vin/Vout will not show these movements.

What I'm really thinking is, "Are you tying to math this to death or play a guitar?"
Knowing Anderton's designs, and especially this one, he built it by ear, not with so much math. This circuit will compensate for any CdS cell I've ever seen, and that's the beauty of it. It's almost impossible to screw up. You're trying to arrive at a sound, not an answer. All the necessary adjustments are provided...no skimping here. Plug it in, adjust the knobs, and enjoy.

Regardless of which CdS cell you use, you can adjust this to the sound you want. That's the point of this circuit.

Awesome post. You hit the nail on the head with this one and made me realize that I probably am pushing the math too hard on this one.

Thanks a lot!
JP

 

I was raised in Vancouver before it became Hongcouver.
Then I went to university in Toronto when the hippies here (and their Marywanna) went to Vancouver. But I met a few hippies who stayed in Toronto. I did not become a hippie.
When my parents visited me in Toronto they didn't know what I was growing.
But that was a long time ago and I have not met with Marywanna since.

haha did work take you to the Loo?

 

haha did work take you to the Loo?

A loo is a toilet in England. I visited England but work never took me there.
I worked all over Canada and all over the USA (without a green card).

One time I was sent to Colorado when it was hot there so I dressed for the heat. Then I was sent from there directly to Winnipeg when the temperature was so cold it was not even listed. Instead they say the few amount of seconds before your exposed skin freezes. The number was 10.
I had no winter coat, no hat, no gloves, no boots and I was jumping from store to store along the street to prevent freezing. On the way back to the hotel some of the stores were closed so I had to run fast.

My part of Canada has a moderate climate. Not too hot in summer and not much snow and not too cold in winter.

 

haha did work take you to the Loo?

Audioguru, I think he meant "Waterloo".

 

I never worked in Waterloo but I visited my daughter many times when she was in university there.