I want to fix the Attack Time to a slower value, Release Time as an automatic Release, how should I do it, or please tell me how to calculate them. Because there is no place on the front panel of my case to install them. As far as I know LA2A photoelectric compression, can I do this without these two functions?thank you very much
Questions about Forssell Opto Compressor attack, release time
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The LA2A's compressor action only relies on the timing of the LDRs used. There are fast ones and slow ones and the LA2A's are on the slow-ish side. The 'automatic' part comes from the fact that most light dependent resistors get slower the longer and/or stronger light has been applied.
The design shown is supposed to use pretty fast LDRs where the release/attack timing is set by caps C1 and C2 and pots VR2 and VR3 respectively. Replace the latter with fixed resistors. Use your ears to find the best values. Auto release as mentioned above can be simulated by a stacked resistor/capacitor combination like in the SSL bus compressor - see attached image. Again, experiment with different values and choose what sounds best to you.
The design shown is supposed to use pretty fast LDRs where the release/attack timing is set by caps C1 and C2 and pots VR2 and VR3 respectively. Replace the latter with fixed resistors. Use your ears to find the best values. Auto release as mentioned above can be simulated by a stacked resistor/capacitor combination like in the SSL bus compressor - see attached image. Again, experiment with different values and choose what sounds best to you.
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fripholm said:
Thank you very much for your patience for your answers. After gaining your experience, I have successfully built it.
I read the information（They are in the attachment）, but because I am a novice and the picture is too blurry to understand some of its marks；I do n’t understand the way he labeled the electrolytic capacitor polarity. As far as I know, the in-phase amplifier circuit is here The capacitor (C3) should be grounded negatively, but its shaded part is on the other side. Including its capacity, I remain skeptical of the 4700UF. I don't think it should be used so much, but I can't see clearly. In addition, the value of R3 is only 100 ohms, but the feedback resistor RV1 has 10K. Does it really need so much gain?
I look forward to hearing from you, because no one around me can tell me, thank you!
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With these values, the circuit will have a gain of about +40dB which is a lot. I think 20dB is good enough for a compressor makeup gain stage. Just replace the 100R resistor with a 1k and the 4700u cap with 470u. Low frequency roll off will still be at about 0.3 Hz but you can get away with an even smaller cap (roll off for a 100u is at ~1.5Hz).
If the DC offset is small (up to +/-100 millivolts) you can get away with either orientation of C1, C3 and C5 - it won't do any harm to most caps. But to be on the safe side, you could also use bipolar caps. Also, when using a +/- power supply, the offset voltage at C3 can be either positive or negative respective to ground.
If the DC offset is small (up to +/-100 millivolts) you can get away with either orientation of C1, C3 and C5 - it won't do any harm to most caps. But to be on the safe side, you could also use bipolar caps. Also, when using a +/- power supply, the offset voltage at C3 can be either positive or negative respective to ground.
