The original module is described by Barton as follows:
This is an all analog synthesizer module used to create new timbres and waveforms with your existing VCOs. It uses a CD4046 phase locked loop chip in combination with a binary counter to multiply the frequency of the input signal. It then has 7 outputs divided down from that multiplied frequency which are mixed together. It’s simple to use and has a distinct sound.
In Barton’s design the seven signals (which are 0, 1, 2, and 3 octaves above and below the input signal) go into a simple mixer with a potentiometer attenuator on each channel to produce the module output. This modification replaces that simple mixer with a voltage controlled mixer, allowing use of control voltages to modulate the mix. If any of the seven control voltage jacks does not have anything plugged in, the CV is normalled to +10 V allowing the pot to behave like a signal attenuator.
An additional modification to Barton’s design is that the gain on the output stage can be varied using a pot on the panel. This allows reducing the gain to avoid clipping when mixing multiple large signals, avoiding the need to turn down all the channel pots and allowing use of their full range.
The module consists of a front panel and three PCBs. One of these is the PCB for the original 4046 Wave Shaper, available from Barton, assembled mostly as designed but with a few things changed. The second is a PCB holding the board mounted pots and switch as well as the parts associated with the voltage controlled mixer and the power input section. The third just holds the board mounted input and output jacks.
A lot of clipping is going on at ±10 V. With the original Barton module if you wanted to avoid that clipping, you’d have to back all seven attenuators off. With this version you can just turn down the Level pot which reduces the final stage gain.
The signal looks like it is being chopped. Is this because of how you implemented the VCA (using a 4066 as an attenuator by pwm of the switching frequency) ?
The switching frequency should be high enough not to be audible (and visible given the time scale of the plot I expect, but I’m not sure), or else you get an effect similar to a ring modulator.
Do you filter out the VCA chopping frequency from the output signal or don’t you have any dogs in your neighbourhood ?
It’s not chopped, and there’s no PWM. It’s just what you get by adding square waves in octaves. For perfect square waves the result of adding octaves -3 to +3 would look like this:
but in the module it gets distorted by the decoupling capacitors.
It’s the same output you get from the original Barton design if you back off the attenuators to avoid clipping. The only difference here is you can use the single gain control to prevent clipping instead.
In this instance the frequencies being added are 55, 110, 220, 440, 880, 1760, and 3520 Hz, so no dogs were harmed in the making of this post.
Added: If you add ideal square waves in ratios of 1 : 1/2 : 1/4 : 1/8… (instead of 1 : 1 : 1 : 1 as above)… you get a sawtooth!:
Its been a fun exercise and I am getting ready to do a smoke test. There are some decoupling capacitor shenanigans going on but I think its ready to go.
Does the +10v power run anywhere other than the CV sockets? It appears that the Barton board just piggy backs off of the eurorack power lines if I am understanding correctly.
It’s not power but a voltage reference, and it’s only used to provide the normal for the CV jacks, i.e., with no CV plugged in the pot varies 0 to 10 V.
One iteration of mine would’ve failed a smoke test if I hadn’t checked continuity with a meter first!
I have the two boards and the face plate all built and assembled. @analogoutput I thought if I stared hard enough at the schematic that I would be able to figure this out - but I am just going to break down and ask you about how to marry everything together if you dont mind!
J1 on the schematic is pretty much the stand in for the ribbon cable - going from the capacitor pads on the barton board to the cd4066’s and the opamps.
The CV in jack sockets connect to pin 3 on the potentiometers.
The connections between the 1k and the diode to ground are the other cd4066 inputs (pins 4, 1, 8, 11).
J1 in my build is an IDC header mounted on the auxiliary board. A ribbon cable plugs in there and the other ends are soldered to the Barton board. The 4066 connect to what was supposed to be the capacitor pads connecting to the 4046 and the op amp outputs to the other supposed-to-be capacitor pads.
Jack tips connect to potentiometers’ pin 3 (clockwise from front). Jack tip switches connect to the 10 V reference.
Yes on the 1k/diode.
Also in my build the power header and power reversal diodes and 10 µF caps are on the auxiliary board, not the Barton board, and ±12 V and ground connect to the Barton board. RV7 pins 1 and 2 connect to the Barton board instead of the 100k resistor at the end of the TL072.
I was thinking I might try to do the last of the assembly in stages so I could locate problems a bit easier.
I hooked up the 0 volt section and it as well as the associated CV jack were working perfectly on their own. I hooked up the +1 and -1 sections then spun up the module for another test but things seem all out of wack. The 0 oct slider seems as if it is fully on no matter where I put it, the -1 oct does nothing and the +1 sounds like I would expect a -1 to sound.
Do all of the sections need to be hooked up for everything to function properly? Or should I try to do more troubleshooting?
