ART PRO VLA II vactrol swap?

Hi guys,

I have just done the Kenetek mod to a VLA II. And then I got sidetracked and remembered a little UTC ouncer I had lying around. It's an O-8, basically an output tranny. But it has now found a new home in the second channel input of the VLA in reverse and made it sound like a good 1176 tone. Love it. One side sirupy, round Stancor, the other raw, dry organic and slightly hairy UTC.

But the vactrols in this thingare plenty erratic and I am tempted to give it a go to get something else in there at least in one side. Just I am also not very competent, so rolling my own with LEDs etc isn't going to happen.

So in short, who has done this successfully and what vactrols did you use?

Do you know what vactrols are in there?

Michael

I've read replacing the stock vactrols with VTL5C1 yeilds better results  (I believe stock are VTL5C2). I found them for sale at https://www.amplifiedparts.com/products/optocoupler-vactec-channel-switching

Reference for this info:
http://www.beautyofdecay.net/mod/provla2.html

The VTL5C1 is a faster opto. It may sound better depending on what you use it for. The VTL5C2 is used in the Inward Connections Vac Rac TSL4 opto compressor. It was really popular a while back. So it may not be the actual vactrol but how the sidechain is working it.  I don't see any harm in trying it. just make sure you have the polarity of the LED side of the vactrol correct when installing the new one.

If your brave, you can try  soldering on a regular LED in parallel with the vactrol LED.  This will draw more current from the side chain and effect how the compression sounds. I'm not familiar with the circuit so try that at your own risk

By the way, the ouncer O-8 is a good little transformer. it was also used backwards as a mic input on the ADM console channel strips. I've also used them for tube mic output transformers.

karloff70 said:

But the vactrols in this thingare plenty erratic

Click to expand...

Are you sure? I have never seen an example of a resistive opto failing other than on direct mechanical damage. And being erratic, it can't be the LED blown by experimentations (they fail-full or not)

Jakob E.

I think he means the compression response of the vactrol is erratic. And thats most likely due to the side chain circuit not the vactrol itself.

Hi chaps, sorry to be a spoilsport but not long after modding the VLA I decided that we didn't get on, regardless of vactrol ballistics, so sold it on. Don't let this stop you from putting valuable info on the internet table though I suppose..... ;D

I have a VLA II.  After initially finding it a rather vanilla device, I have realised I quite like it. Very good for bringing mixes forward in a pleasing way, as well as handy for dedicated buss duties.

One very noticeable thing about it is it's subtle brightening effect. I am not aware of any eq design within it's circuitry, so I guess this must be down to 2nd harmonic distortion.  Would this be a known function of the starved plate design, or just a side-effect of less than stellar tube selection, I wonder.

Has anyone else noticed this?

I found the stock VLA to be slower than what I typically use, so I swapped the stock VTL5C2 for a VTL5C1 in one channel. It makes a tremendous difference with the character of the compression. I liked the faster VTL5C1 much better, so I swapped the other channel as well.