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Old 10th May 2009, 09:29 PM   #41
flysig is offline flysig  United States
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Good question, Gavin. The topic probably deserves its own new thread.

I'm looking at using a LED/Photocell unit for sensing and control. Check out the Aphex Punch Factory optical compressor. There are opto-isolators that combine the LED and the photoresistor in one package. The photoresistor has a memory that depends on the brightness and duration of the light that has struck it. So they make nice natural compressors. The Aphex unit is excellent for acoustic guitar and vocals, and super simple.

There are a number of schematics out there for compressors. Some seem quite complicated without benefit. Most seem to be a preamp with either a variable grid bias or a variable negative feedback.
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Old 1st March 2010, 02:27 PM   #42
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Also interested in building this circuit and including it in a tube bass preamp... wondering if it is possible to eliminate the first Cathode follower stage and replace the diode-connected triode for a silicon diode? Would like to get the design down to one tube. If I cant altogether eliminate the cathode follower stage, I will swap it for a MOSFET source follower, but trying to avoid any solid-state devices because I am building on turret board and it is semi-inconvenient to use OpAmps, optocouplers, etc.

Thanks,

Joe
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Old 1st March 2010, 03:49 PM   #43
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If you mean the circuit in the first post, I would stay away from it, it's an odd duck and I have searched and never found a reference to anyone who ever got it to work.

You can add a compressor to any preamp with just one tube and some diodes. Basically, you need a variable-mu type tube like an ECC189 or a remote-cutoff pentode (it can be strapped as a triode), then either a tube diode such as a 6AL5 or for solid state, small signal such as 1N4148.
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Old 3rd June 2014, 08:13 PM   #44
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Quote:
Originally Posted by Ahmad_tbp View Post
i mean it doesn t work correctly :P ...
it s a very loud sawtooth or square wave around 80/100 hz ( i m not sure bout the wave and freq , i don have a scope ) comin out of it , but when i turn the 2nd pot (25k) all the way down the noise become silence suddenly , i connected my signal generator to it , very very little pulsin sound come out of it !!!
the schematic is wrong..i know why..
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Old 4th June 2014, 10:17 AM   #45
DF96 is offline DF96  England
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How helpful!
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Old 4th June 2014, 11:06 AM   #46
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The grid of the second triode must be conected with the anode to form a diode ,and most importantly the 10uf capacitor in not in series there,it goes like this : The 10uf capacitor is in parallel with the two 10k resistors and all 3 are conected between the cathode and the ground of the first triode (this forms the first time constant).The cathode of the FIRST triode is conected with the anode and the grid of the SECOND triode.The cathode of the SECOND triode is conected in parallel with a 1Mohm RESISTOR,NOT POTENTIOMETER*,and the 0.01 uf capacitor (this forms the second time constant).The first potentiometer in placed instead of one of the two 10k resistors in the first triode and it should be around 47k .In rest the schematic is ok.If you make this changes ,you will have 100% fine working compressor ...salutations from Romania
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Old 5th June 2014, 05:48 PM   #47
Hi_Q is offline Hi_Q  England
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Hopefully I have redrawn the circuit correctly with those changes incorporated.
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Old 5th June 2014, 05:54 PM   #48
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Originally Posted by Hi_Q View Post
Hopefully I have redrawn the circuit correctly with those changes incorporated.
It is corect...you have 100 guarantee of a working compressor ..with the first pot you change the frequency rate,and with the second pot you change the compression level...good luck
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Old 5th June 2014, 06:32 PM   #49
disco is offline disco  Netherlands
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How come the first triode isn't destroyed when the pot grounds its cathode?
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Old 5th June 2014, 06:35 PM   #50
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How come the first triode isn't destroyed when the pot grounds its cathode?
And the third triode as well - nasty!
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