Electro Voice ELX-1A?

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Bo Deadly

Well-known member
Joined
Dec 22, 2015
Messages
3,266
Location
New Jersey, USA
I can't find a schem for the ELX-1A but here are the critical bits for the ELX-1R:

ELX1R.png


IMO this circuit is not horrible. The mic circuit is nothing spectacular but perfectly ok. The TL072 mix amp could probably be replaced easily. It's got an oscillator, a decent headphone amp, an LDR limiter (which is really more like a compressor) and transformer out (but with weird wiring that could also be fixed pretty easily).

There are piles of these things on Ebay for nothing. Why?

Does anyone know what the difference is between the 1A and 1R?

UPDATE: Just noticed it uses a virtual ground so that +30V phantom can be made with only single supply transformer.
 
rackmonkey said:
Link to ELX-1A owner’s manual. Schematic is included:

https://www.electrovoice.com/binary/ELX-1A%20Owners%20Manual.pdf
Ah, of course. The Electro Voice website. Why didn't I ... ehnm.

I can't see any significant differences in the circuit. So it looks like an A is as good as an R even though it looks like the R was a later model. I suppose it does have a bit of commercial-installation-anti-mojo. Could be good for the budget home studio for a personal monitor mix.
 
I've found that good little commercial/broadcast mixers like this - which can often be had for a song - are often worth dropping some change on. Whether you modify the circuit or use as is, they can be useful for a number of things, including a personal monitor mix as you suggest. I converted a similar Rane unit to 4 independent channels using THAT 1646s on a strip of protoboard and it made a nice little clean preamp. It had SSM2015 ICs on the input, and I had originally thought I'd swap those out, but they sounded good and I kept them.

I've also found that at minimum, they make great DIY chassis/cases. For less than a Mid-Atlantic or Bud box, you get pre-installed input jacks and can sometimes even re-use the power supply. Rivet a new faceplate on front or design a whole new front panel and swap it out with the original and you're off and running.
 
> The TL072 mix amp could probably be replaced easily. It's got an oscillator, a decent headphone amp, an LDR limiter (which is really more like a compressor) and transformer out (but with weird wiring that could also be fixed pretty easily).

The mix amp works easy, just 4 inputs, not usual virtual earth, hi-Z loading. The mike amp has BJTs to mask the TLO hiss. None of the signal TLOs works at less than 10k load. Switching to a bipolar input chip would raise scratch-noise in pots and switches.

The limiter circuit is remarkably complex considering it drives an LDR in a high-level position. I'd expect mild but un-musical distortion if it is ever made to work. (That may be better than splatting-out.)

The mike input will not take a high-level mike on a Marshall or heavy percussion.

The Phantom is sub-standard. 90% of mikes will work, a few won't.

I think it is too boring to be excited about. But if you need a lot of unobjectionable inputs at low cost, this may be your kitty.
 
PRR said:
The limiter circuit is remarkably complex considering it drives an LDR in a high-level position. I'd expect mild but un-musical distortion if it is ever made to work. (That may be better than splatting-out.)
Wouldn't it have to be better than "splatting-out" since even a fast LDR is going to be at least a 20ms recovery time. And there is a little bit of an RC there on the CV. With that timing is it even really a "limiter"?
 
I simulated the limiter circuit in LTSpice.

EvExl1Limiter.png


The first stage is just a full-wave rectifier. The second stage amounts to gain (diode does nothing since already rectified). The PNP level shifts to the negative rail. So that poor op amp spends it's live hard neg.

Unfortunately it seems there is a mistake here IMO. Because of the PNP inversion, the spikey part of the waveform is positive. So the LED is on more with signals that are just above the threshold. But as the signal gets hotter, it actually starts to turn the LED on LESS. I can't imagine that was there intention. I guess they didn't have LTSpice back then!

But of course my circuit and / or the sim could be a little off.
 
Here's an alternative "fix" to make the limiter work in a sane way:

EvExl1LimiterFix1.png


Notice that this doesn't source or since current from ground (which again is virtual in the ELX-1).

The first stage is the same. Just a full-wave rectifier. D1 sets the threashold. NPN provides decent gain so it's got a nice snappy on at ~+4dBu and it's completely off at 0dBu.

There should be a little bit of an RC there though.
 
> it seems there is a mistake here IMO.

I'd tend to believe that E-V did it OK and your spiky sim is mis-copied. (Or possibly E-V drew it wrong and built it right.)

As the limit level is far above nominal line level and really just-shy of clipping level, I would not worry about its "sound". It prevents splatt. If you have a "nice" limiter, don't splatt the E-V, let your magic box caress the signal.
 
PRR said:
> it seems there is a mistake here IMO.

I'd tend to believe that E-V did it OK and your spiky sim is mis-copied. (Or possibly E-V drew it wrong and built it right.)
That's possible. Simulations do not predict the dynamics of something with delicate timing like this. There is no LDR in the loop in the sim. So attenuation could kick in enough to limit the input to the sidechain, the PNP would not clip and there would be no "mistake".

I'm just trying to think of a way to take a cheap item that is "blah" and make something different that does something unique. There's a really nice one on Ebay right now that's been re-re-relisted for $40 + shipping. I'm definitely not buying it though! I just sold ~10 things.
 

Latest posts

Back
Top