Monday, 31 August 2009

Doepfer A-134-2 VC Crossfader



Here's a quick look at - and a rather longer listen to - Doepfer's voltage controlled crossfader. This is my favorite sort of module: small, versatile and inspiring. The two VCAs accept either audio or CVs and can be configured via jumper to cross-fade either asymmetrically or symmetrically. A simple modification turns the A-134-2 into a 4-in 1-out two-dimensional x-fader.

Before I bought the A-134-2, I tried to patch my own crossfader using a Cwejman VCA-2P. While this worked to an extent, purpose-built modules tend to cut down the time spent cabling and yield quicker results. Within a couple of minutes with the Doepfer, I was up and running.

AUDIO EXAMPLES

Doepfer A-134-2 VC Crossfader Demo by navs

1) Audio fade/ symmetrical. Two VCO sequences. LFO as modulator.
2) Audio fade/ asymmetrical. Ducking effect with envelope follower.
3) FM modulator fade/ asymmetrical.
4) FM modulator fade/ asymmetrical.
5) FM modulator fade/ asymmetrical.
6) CV fade/ symmetrical.

IN USE

Provided you don't overload the VCA by applying too high a CF CV, the audio quality is good. I did notice a slight imbalance in one VCA when used asymmetrically (input one was not at unity at 0V, but rather needed about -0.5V), but I'm sure this can be calibrated. When used symmetrically and with 0V applied, inputs 1 & 2 are balanced at 50/50 rather than at full level. This might bother some users. I personally would prefer the option. Due to the nature of fading, I found the A-134-2 more useful for audio rather than CV sources, where I felt a sequential switch might be more appropriate.

Fading between audio sequences or FM sources are two obvious uses of the A-134-2. In conjunction with an envelope follower, it's also capable of sidechain/ ducking duties (the A-119's sluggish response adding to the severity of the effect!). I don't have a Wiard Boogie, but I could also imagine that, paired with a joystick, a modified A-134-2 would be great for dynamic vector-filtering.

7 comments:

Pete Shambler said...

Yes! I've been waiting for someone to demo this module. It's tied with the A-156 in the "next purchase" race.

Question: which op amps does it have installed? I've read about swapping the TL064s in the A-119 for TL074s (they're socketed, so it's a pretty straight forward operation) to improve headroom, bandwidth, etc., and was curious if the same mod could be done for the A-134-2.

Tom said...

great review, sounds like a module i need too!

Navs said...

Cheers!

The A-134-2 has two LM324N Op Amps (& two LM13700N OTAs). Don't know if you would need to/ could swap these out. As I said, they sound pretty clean to me and only distort if fed more than the +/- 5V needed for the crossfade.

Anonymous said...

Neat. What effects are you using?

Navs said...

Electro-Harmonix Stereo Memory Man with Hazarai.
Great fun, funky box of tricks :)

Navs said...

BTW Check the archive for a review and more sounds!

waveplant said...

Are there jumpers for both crossfaders - meaning, is there the option to put one in symmetrical mode and the other in asymmetrical?