I do not usually post about individual Eurorack factory assembled modules. But the ADDAC805 warrants it. Look! I have serial #22, so that must make me an early adopter. It’s been out less than a year.
Currently the only ADDAC module I have, the 805 Signal Router fit what I was looking for in the VCA category. It comes with an excellent block diagram.
The module has so much flexibility that I drew six simpler block diagrams, illustrating different uses.
Clockwise from top left:
- Dual VCA or dual VC cross-fader
- VC panner
- Stereo VCA
- VC Cross-panner with master VC level
- VC Stereo Dry/Wet mixer
- 4-Quadrant Fader/Mixer (fade between 4 sources)
- 2-Input VC stereo mixer
And this isn’t the end of possibilities. For instance the Stereo Wet/Dry Mixer can be followed by the Stereo VCA for master level control. It is also possible to cascade another stereo mixer output into the ADDAC805.
Checking out the response curves
The user manual omits a specification of the response curves of the VCAs. So I did the following experiment to discover the curves and CV sensitivities. Since the module is DC-coupled, I patched a +5.0 volt constant voltage (conveniently provided by Mordax Data) into the signal inputs. Then I tried various linear control inputs and discovered the following.
The top (green) trace displays a 0 to about 3 volt triangle wave sent to the inputs of both left and right cross faders. The middle trace (blue) is the left output and the bottom trace (red) is the right output. Normalizing on the ADDAC805 signal and control inputs simplified sending the identical input and control signals to both channels.
Discoveries
1) The response is exponential.
2) The responses on the left and right are (unfortunately) different. Clearly the right cross fader has more gain, leading to a steeper slope.
3) The channels do not overdrive or distort: upon reaching unity gain, increasing the control voltage has no more effect.
4) The CV inputs are quite sensitive. All have reversible attenuators and these are needed to reduce stronger CVs. In one case I could get unity gain with about 1.5 volts of CV.
I also checked the response of the master cross fader/VCA and found that, gladly, both channels exhibited the same response.
Conclusions
The ADDAC805.VS2 seems to be a well-designed and engineered module. The build quality is excellent. It is the first time I have seen nutless jacks used on a panel. The signal flow block diagram included is a practical necessity and lays it out very nicely.
Drawbacks
I’m unhappy about the different responses on the left and right cross faders. I could find no trimpots on the boards, so this error must be due to a difference in parts that should have been matched. I’m contacting ADDAC about it.
UPDATE: ADDAC sent me a fix. Apparently this only affects a few units.
The only other downside for me is that the panel labeling is in very small type and it’s hard for me to read without reading glasses. But this is a negligible complaint, because once I get familiar with the module, I’ll know what everything does.
