How?can be used for variable gain controls.
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How?can be used for variable gain controls.
Why not use the simple IC in post #82?Here I attached a LTSpice simulation drawing for expert to test the circuit in precise way.
Hi Ron,Why not use the simple IC in post #82?
I spiced around with the circuit in spice. The MOSFET I used year ago, made a good voltage to resistance converter. The 2n7002 has a sharp knee. It goes form little attenuation to great attenuation in a small number of mV. I did not get it to work well.
Hi Ron, I have few THAT2252 (RMS Detector) and THAT2155 (VCA) chips, though working principle of simpler circuit is visiable and interesting. Also chips are limited with me but have many mosfets.Why not use the simple IC in post #82?
The original one has 2N7000 mosfet. Will you try using this one?I spiced around with the circuit in spice. The MOSFET I used year ago, made a good voltage to resistance converter. The 2n7002 has a sharp knee. It goes form little attenuation to great attenuation in a small number of mV. I did not get it to work well.
Too many years ago. I do remember getting a MOSFET with out a internal diode. I don't remember if it was better.Which mosfet had you used in your limiter in past days?
A photo-resistor is too slow to control the gain of a high quality audio circuit such as a compressor. But it is OK for a telephone.
Hello,
Well the devices i was referring to were made specifically for audio applications such as compressors.
There have been lot's of them used, perfectly fine for audio as that was their intended purpose.
Hi there Nigel,
That's what i thought too, but we can check the spec's if anyone has any doubts i guess. I've have to find a data sheet, but not sure if i have the part number anymore.
I guess i could test one also, just to get some real life data in.
I used an opto-Jfet as a good compressor. I think the attack time should be fast like Rod Elliot says at Elliot Sound Products. He also agrees that an LDR is too slow.
Rod Elliot says most LDR compressor circuits have an attack time too slow at 15ms. Most Jfet circuits use a simple distortion cancelling capacitor that increases the attack time to 100ms and attempting to reduce it to 20ms results in clicks and overshoots.
He shows a Jfet circuit with low distortion and a 5ms attack time.
When I used LDRs, I went to the store and got one of every kind they had. Then I mail ordered more kinds and they all were slow. I used an op-amp to speed up the response. I frequency sweep the LED-LDR circuit and added high frequency gain to make it faster.The word "most" can be translated into "many, but not all"
When I used LDRs, I went to the store and got one of every kind they had. Then I mail ordered more kinds and they all were slow. I used an op-amp to speed up the response. I frequency sweep the LED-LDR circuit and added high frequency gain to make it faster.
If you can find LDRs with 3mS response I would use these. They have very good distortion.
Using the 2N7000 MOSFET in spice I have distortion. I used a linearizing circuit and it gets better but I just can't make it good. It could just be SPICE. When I built these things in real life I used MOSFETs with very high gate turn on voltages.
View attachment 95206
I tried using an LDR as a compressor but it was obviously too slow, "HELLo". The hell part of hello was finished before the LDR reduced the level. It was a no-name-brand Chinese one. I used a little light bulb then a fairly bright LED but I did not try an Xenon flash tube to make the LDR conduct. I do not see how positive feedback can speed up the physical part.
Claims for The Batterizer voltage booster product also use the words many, most then all then says disposable AA cells are thrown away when their voltage drops a little. They make The Batterizer and sometimes it drains a battery cell instead of making it last longer.
A photo-resistor is too slow to control the gain of a high quality audio circuit such as a compressor. But it is OK for a telephone.
Here is the MOSFET-drain and Vin, with 1.605 volts on the gate. (compressor shut down and a "battery" on the gate) Vin is 20mV pk. It only takes mVs to make huge changes in gain. I think this is the wrong FET! I know how to remove much of the distortion but.....Hi there Ron,
I guess you would have to check into what exactly causes that distortion. It looks like the response of the compression is too fast for the frequency in question, unless that is across the board distortion that happens even when the compression is not changing. Do you know which it is?