TwinLineAmp Opto Compressor TLA2A

[All Ears]

I think there is still fair bit of work to do in selecting the right Vactrol device. I have been corresponding for quite a while with on DIYer who has now pretty much built the compressor described in the document - with one exception - he made his own Vactrols. He used an NSL 19M51 light dependent resistor which has a peak spectral response at 550nm which is somewhere between green and yellow. This is close to the spectral response of Perkin Elmer type 3 material which is used in the VTL5C3. He placed the NSL along with a green LED in some heat shrink tubing and cooked it. He was much happier with the sound, especially at high signal levels.

Cheers

Ian

Hi Ian,

Thanks for your work on this topology. I'm thinking I might build myself a mono tube opto compressor for tracking vocals. Your design looks like a candidate. Any updates or new ideas on your design in this last year ?

I've found i can get a local version/clone of the Silonex NSL 32SR2s, NSL 32SR3, and NSL 32R3S opto resistance couplers. Would those be able to be put to work in your design ?

Cheers

Peter

 

[ruffrecords]

HI Peter,

Yes, any of those can probably be made to work. I bought some myself not long ago with the idea of trying them out but I may be some time before I get round to it.

Cheers

Ian

 

[All Ears]

Cheers. I also have got a few of the VTL5C3's to compare or switch between.

Turning to the metering side of things. I'm only planning on building a mono version of this just as a proof of concept of this cheap optocoupler with tubes idea. Would you suggest simply strapping a meter across the 200 ohm load from the LED's ? Or would you send the signal though further circuitry to drive the meter?
How would you calibrate the meter ? In the circuit in the implementation section there seems to be no meter calibration components (though there is in your first rough sketch)

Peter

 

[ruffrecords]

Metering depends on the current required for maximum attenuation and this depends on the opto used. The resistor in series with the opto LED is a crude voltage to current converter. The side chain will drive 20V rms into a 2K load in which case the maximum current would be 10mA. In the initial sketch the meter is shown connected in parallel with this resistor along with a series resistor to set the maximum. The current is an ac current so the meter will need some kind of rectifier and I think I assumed a VU meter would be used.

The latest info is in the document I posted in post #111

Cheers

Ian

 

[All Ears]

Hi Ian, Just thought I'd finally give feedback on my TLA2A. (pics below)

I've been using it for over a year, and I can honestly say this is the best, nicest sounding compressor I have ever owned. I was quite stunned at its performance actually and it has become my main compressor of choice for basically everything. I'm still enthralled with it a year later.
I leave it on the "2:1" ratio for everything and as you know, with opto, that is actually a variable ratio that is way more useful than it sounds on paper.
I added relay switching to switch between two opto devices for a really nice and equally useful change in character. Added in solid-state meter drive/buffer circuit because of my desire to switch between metering compression and output. Tricked it out with 1960's oil in paper caps. All in all this compressor sounds like the warm soft, voice of yesterday. World class compression.
Anyway, I have to declare Ian Bell, that you sir, are a genius of the tube world.

Cheers, Peter

 

[ruffrecords]

Excellent build. Point to point too. Very well done and of course I am delighted that after a year of use you still like the sound.

Which optos did you end up using?

P.S. Can I nick those pics to send to my friend Pierre who hosts an independent gallery of people's projects based on my designs?

EzGallery

Cheers

Ian

 

[All Ears]

Excellent build. Point to point too. Very well done and of course I am delighted that after a year of use you still like the sound.

Which optos did you end up using?

P.S. Can I nick those pics to send to my friend Pierre who hosts an independent gallery of people's projects based on my designs?

EzGallery

Cheers

Ian

Yes, of course, feel free to use the pics. The thing would not have existed without your well written "research report".

The optos I went with were the VTL5C3's (since you had data) for the A switch position and for the B position I went with the Silonex NSL32SR3 type I think (perhaps the NSL32SR3's i used were made by Luna Optoelectronics not Silonex). I did not really expect the NSL32SR3 to work out, but to my surprise, it worked equally as well as the 5C3's with literally no circuit changes when switching. Puzzling, but I'll take a win when I get one. The NSL optos have a possible slightly harder knee ?? (it's hard to tell just by ear) but both sound excellent and have been using the NSL's more recently. What amazed me was how the compression seems to start off gentle and rolls over into a limit as input increases, making it the most perfect tracking compressor of all time. Who needs an LA2A when you can have a switchable TLA2A ?

Cheers,
Peter