Building a "headless" LA2A without meters (on purpose!?)... circuit advice

[groovypower]

Hi GroupDIY!

As crazy as this may sound, I would like to build my DIY LA2A without any VU/GR meters whatsoever! I have my reasons for this, the main one being to FORCE myself (literally) to use my ears and not my eyes. It will also serve as a training tool for my friends and I, to strengthen our ears and steer us away from "visual" mixing habits, not to mention endless possibilities in sighted listening fun, ala "the meterless one sounds wwaaaaaay cleaner", or maybe it really does ... 

I plan to setup the unit (calibrate etc) using external equipment, and once the setup is complete, leave it completely "headless".

Now, if we can ignore for a second that my idea is completely nutty (and a tough sell - hence DIY), I would love to ask the technical experts how much of the LA2A schematic I could safely skip? I’m not very familiar with the GR (gain reduction) metering circuit. Obviously, I wouldn’t want the lack of a meter to negatively affect the actual operation of the compressor - I just don't want to include any extra stuff.

I have attached an LA-2A schematic to this post and highlighted in yellow the portions of the circuit I believe could be safely skipped. I was hoping some of the veterans could maybe chime in and let me know if there's anything I've missed, or if I'm skipping-out on something critical.

I know it's tempting to make fun of this idea (or say "just put tape over the meter"), but please hear me out, and I promise to show you guys photos of the minimalist LA2A when it's complete

PS This is my first post ever (long time "lurker") so please be gentle! I love this place and all its loveliness.
PPS I wasn't sure if this belonged more in the Drawing Board, but figured since it's specific to LA2A, The Lab was a good start

 

[gemini86]

Hi!

Everything you highlighted.. EXCEPT....you can't take out half of the t4... I mean you could technically open it up and remove one of the photocells but...really...don't.

 

[groovypower]

EXCEPT....you can't take out half of the t4...

Oops, Nice catch! You're right, obviously I'm not going to cut up a T4b to remove half of it  :-[

 

[MagnetoSound]

I actually think this is a really brave, and cool, idea.


(Although, having a VU hardwired just to show output level might be practical, you know, just to assist with gain staging. Or not.)

 

[baadc0de]

Well, but it could be made like the LAZ LA3A where there is no T4B inside, rather a photocell. No need to implement the yellow area then?

 

[Kingston]

It sounds like a good idea the way you explain it, and really, unbuffered VU meters do distort audio signals at around -70dBu. Gain reduction part of LA2A is practically buffered though.

Just that of all the dozens of units with VU meters I've used and owned in my life, LA2A single handedly has the most natural VU meter response with gain reduction. It perfectly reflects what the audio is doing. No other unit quite does this and I hate to admit it but it's a compressor that you could set up even if completely deaf!

And T4B's are a bit on the expensive side and I would hate to lose any functionality of it.

I think there are better candidates for building a VU-less unit.

 

[groovypower]

Good ideas guys... I agree that the unused half of the T4b feels like a waste... but I just had a crazy idea for the unused half of the T4B:

What if I had an optional switch (let's call it turbo-mode) that flips in the unused half of the T4b alongside the existing one in parallel, thereby dividing the resistance roughly by two for the same amount of source signal (provided they decently match), and THEN we would have two very different behaviors in one compressor! (like having a fast and slow in the same unit?). What about going even further, and adding a trimpot setup as a variable resistor in series with the 2nd-half of the T4B, to allow a full range of tweaking? This might allow us to do unusual compression behavior? This could sortof "extend" the behavior of the limit/comp switch into unknown territory...

But before I get ahead of myself here, I'm so new at this I'm not so sure what would be affected... recovery time? Ratio? Something else? Just thinking out loud here... waiting for somebody correct me here, but excited at the thought of trying this