Do Vactrols actually work with ac LED drive?

[abbey road d enfer]

i read that ldr gives more distortion with more current through the ldr

Where? LDR are very linear, until they go into thermal problems (takes very large signals).
The LDR is not the main source of distortion, it's the variations of illumination that result from the side-chain timing. If the release time was infinite, distortion would be almost unmeasurable, even with very high level (+20dBu).
In more general terms, in a compressor, the gain cell (FET, vari-mu, optocoupler, VCA) usually generates less distortion than the side-chain, particularly at low fequencies.

So using it for attenuating higher impedance source signal may be cleaner? in place like after stepping up transformer before 1st tube of mic preamp

There is not much flexibility there because the LDR becomes very slow at low illumination.

 

[ruffrecords]

One thing to bear in mind is that the control voltage inevitably has signal content in it which will modulate the gain to some degree at the signal frequency (or twice the signal frequency if fullwave rectification is used) which will then be manifest as distortion. The faster the gain cell the worse this effect will be. The shorter the attack and decay times, the worse this effect will be. And of course the lower the frequency the worse the effect will be.

Cheers

Ian

 

[Egor Reshetnikov]

Where?

found it: VCAs
"Unlike most of the other devices used, an LDR's distortion appears to depend on the current through the device, rather than the voltage across it. To keep distortion low, keep the current to a minimum."

 

[mr coffee]

Has anybody fooled around with using a UV LED and a UV-excited "day-glow" type paint as a light source for the photocell?

Seems you could get the LA-2 type of filtering of the light without any electronic filtering, but with full-wave rectification of the LED drive (the florescent panel runs on AC, the LED doesn't).

Probably would need a small, calibrated amound of the paint and possibly driving a green LED as well to get a fast attack and decay response so the persistence of the florescent paint wouldn't dominate the response, just smooth it.

Different colors of florescent paint have different persistence. UV LEDs are cheap nowdays, especially the ~400nm ones.

Just a thought...

 

[Bo Deadly]

Has anybody fooled around with using a UV LED and a UV-excited "day-glow" type paint as a light source for the photocell?

Just a thought...

I don't think UV would work because you would probably also need the reflective light to get the photocell to reach a really low resistance. I could be wrong but the paint alone probably wouldn't do it.

I suspect another problem would be that the decay of the day-glow paint would be too slow. That stuff can stay illuminated for hours.

But it might be worth fiddling with. If you can get the paint bright enough with an intense source but it's found to have a steep initial decay, it might have the right dynamics / memory effect.

 

[pvision]

I wonder what benefit might be derived from a frequency-sensitive or dual-band sidechain? Faster attack & release for high frequencies and slow for low.

The slower control would swamp the faster control in many instances but, with predominantly low or high-frequency signals, it might measure better - and maybe sound better

 

[abbey road d enfer]

I wonder what benefit might be derived from a frequency-sensitive or dual-band sidechain? Faster attack & release for high frequencies and slow for low.

The slower control would swamp the faster control in many instances but, with predominantly low or high-frequency signals, it might measure better - and maybe sound better

Everything is possible in the side-chain, but you can't make the photoresistor faster than it is natively.

 

[Matt Syson]

Super 'fast' attack and release of an audio signal sounds 'bad' in it's own right even before you consider control voltage breakthrough (depending on technology used). Also RMS or Peak acting sidechain voltage and whatever averaging or other fancy processing you might apply ALL have an effect on what you ultimately hear. Different technologies for compression simply produce a compressor that is 'different' which may or may not be suitable for the signal you are trying to compress, which is of course 'distortion' because the definition of distortion is any effect or artifact that is NOT the original signal (with exception of simple amplificatioon or attenuation).

 

[abbey road d enfer]

I wonder what benefit might be derived from a frequency-sensitive or dual-band sidechain? Faster attack & release for high frequencies and slow for low.

That's what multiband compressors do. You may or may not like it.
I commonly use a 5-band multicomp in Samplitude for mastering.
I tried an analog version but it has many flaws, due to interaction between bands.

 

[Bill Wilson]

On Amason lUNA NSL32. This is specifically designed for audio. $5.36 ea.
was luna electronics; just sold to Advanced Photonics; also sold by digikey u.s.

 

[Bill Wilson]

Further info. on NSL-32SR2; Newark Electronics has 99 in stock; Quarktwin Technology.com has 27,000 in stock u.s. $3.303 ea. or 10 for $2.973 ea.

 

[ruffrecords]

On Amason lUNA NSL32. This is specifically designed for audio. $5.36 ea.
was luna electronics; just sold to Advanced Photonics; also sold by digikey u.s.

I am puzzled by the (sorted) parameter. I can see from the NSL32SR2S datasheet at Digikey that they can be sorted into bands according to the cell resistance 1mA of LED current. However, it is unclear how you might order a batch all in the same band. Also the resistance value at 1mA seem to be very low - much too low to be usable in a compressor. And those values bear absolutely no resemblance the the graph of LED current versus cell resistance later in the datasheet. Am I missing something?

https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/5337/NSL-32SR2S.pdf

Cheers

Ian

 

[abbey road d enfer]

And those values bear absolutely no resemblance the the graph of LED current versus cell resistance later in the datasheet. Am I missing something?

I think the graph matches the "G" code.

 

[MidnightArrakis]

I am puzzled by the (sorted) parameter. I can see from the NSL32SR2S datasheet at Digikey that they can be sorted into bands according to the cell resistance 1mA of LED current. However, it is unclear how you might order a batch all in the same band. Also the resistance value at 1mA seem to be very low - much too low to be usable in a compressor. And those values bear absolutely no resemblance the the graph of LED current versus cell resistance later in the datasheet. Am I missing something?

https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/5337/NSL-32SR2S.pdf

Cheers

Ian

Just in case:


https://www.audioschematics.dk/media/schematics/outboard/la-4a.jpg

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