Author Topic: Compressor Mods  (Read 12289 times)


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Re: Compressor Mods
« Reply #30 on: October 17, 2017, 01:44:49 AM »
Yes standard 5mm Green LED's (wired back to back) hard up against the LDR inserted into a short length of black shrink tube.
[/qu ote]

Hi Phil,

I breadboarded up the oscillator Rod Elliot's IC based tremolo circuit ( which works really well. So as an adjunct to making these LDR/LED units, which LDR did you use? Both Altronics and Jaycar carry the same 2 versions of these CdS cells

One is a ORP-12 equivalent: Dark 10m   to   Light 48k - 140k,

while the other one is: Dark 500k   to   Light 2k8 - 8k4,

I think the ORP-12 was what was used in the old Goldentones and the EA Playmasters 116/117 tremolo circuits



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Re: Compressor Mods
« Reply #31 on: October 17, 2017, 11:56:32 PM »

This is the LDR I have used in 2 builds
As you noted,, Jaycar sells 2 types,, while testing I found the larger unit seemed to work better.
Both types will work and they are not expensive,, I can't recall why I went with the RD3485 but it felt better to my ears.

I tested the circuit with TL072, LM883, LF353 and some 4558 chips that I had in the bitz box. They all seem to work the same with no notable difference.
Green leds have a special quality which is beyond my ability to explain,,, some time back there was a whole posting on the subject of LED colour differences and why some are better than others. Something to do with doping If I recall?


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Re: Compressor Mods
« Reply #32 on: October 18, 2017, 01:36:27 AM »
The super bright leds will drop the resistance to virtually zero from my tests so far with an old LDR from that original Playmaster 116/7 parts list, but that is probably not really what is required I suspect.

Varying between a few K up to 1/2 meg seems to make more sense too especially with that tremolo circuit where you want to vary the volume level up and down but not turn it completely off. I guess the same goes for that compressor circuit of mictesters that you utilize.

Standard green, yellow, orange and red leds gave varying degrees of resistance with that LDR with red & yellow dropping lower than orange and green. That LDR varies from 10m+ (Dark) down to virtually zero (Light) using a white led.


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