But after ordering all the parts, I’ve discovered that the large stripboard from Tayda isn’t quite long enough. Tracking down a correct-sized one and paying postage on a single item is just annoying after having sourced everything else.
I was thinking that maybe I could squeeze this layout down and rearrange it a bit. It looks like there is room, though a more cramped layout will be more annoying to solder.
I also figured it’s worth asking if there aren’t any alternative layouts that already fit the Tayda board. I’ve tried googling it but no luck. Sam’s performance VCO wth the arduino tuner looks like it’s overkill while the other 3340 VCO with only ramp and triangle is a bit basic.
Alternatively, are there any tools or techniques or words of advice to make sure a revised layout is still electronically the same circuit, before i start soldering?
Modifying stripboard layouts on the fly is usually a source of error for me, I think it’s better just to go back to the circuit and lay it out youself if necessary. Or you could get some pin headers or little jumpers (like cut-off legs) and just connect two boards together to make a double wide.
To save a little space I often also connect components directly to potentiometers or jacks
Here on the right of the stripboard it is possible,
1K resistor on triangle out jack
100nf on FM pot
100k on extra cv in
100k cv 2 in
…
same thing on the left with all the 1nf cap on the jacks
which would make it possible to gain more than ten columns
I am working with eurorack format and because my case isn’t too deep, I try to fit all my modules on roughly 10x10 cm. This means a lot of work since I would need to make existing stripboard layouts a bit more compact. Here is the layout for the VCO I built:
I’m 90% sure it is correct, but please compare it to sam’s layout. You shouldn’t trust the pot values since I might have copy-pasted them without thought. I added FM and I’m doing my own PWM with an opamp because the PWM delivered by the 3340 has some issues.
One useful feature that is not in here is a fine-tune pot which I highly recommend and doesn’t take space on the stripboard.
In my experience a regulated -5 V supply (one each L79L05, capacitor, and diode) and a 1M resistor between pins 4 and 5 handles those issues. Admittedly if you have an op amp to spare then the external pulse wave approach might arguably be easier. But Alfa recommends the -5 V supply anyway for other reasons.
The Arduino tuner is essentially separate from the rest of the VCO and can be omitted from the design. Aside from that I’d assert there’s no overkill, in fact I wanted features Sam’s design didn’t have like a sin wave and standardized ±5 V outputs. Certainly there’s nothing besides the tuner I’d be willing to give up. Is there a stripboard version of the Performance VCO, though?
Further down is a stripboard layout that adds the pulse wave.
Eddy Bergman’s website seems to say that the Digisound 80 VCO has better tuning over a wide range than when he attempted Sam’s circuit. Also, I’ve already got all the parts for it, minus the correct sized board.
I think I will just try to do my own layout from the schematic, as per BD’s advice.
If I understand what i’m looking at, it seems like the negative supply voltage is being limited with a series resistor. That seems a bit unusual but then so is the supply requirement.
I have a 7905 already though, am I better off using that? they’re not super pricey, it’s more a question of space.
Something I tried to do with stripboard is the make PCB sandwich type layouts, with the jacks, pots, LEDs and switches on the front board to make a ‘control board’, and the components on the ‘main board’. This isn’t too difficult when working from Eddys layouts as he plots them out for pots etc to be panel mounted with wires running from the stripboard anyway. From there, you can look at which components you can move from the main component board to the control board, there’s usually at least 1 resistor going to each pot/jack/led that you can relocate on the control board. I had success with his MS20 filter this way and I planned to do the same with the VCO, but got into kicad and making PCBs professionally before I started that.
The 3340 can have -12 V (or -15 V in the datasheet) connected via a resistor to pin 3. There’s an internal Zener that drops that down to -7.4 V and that becomes the negative supply for the chip. They designed it that way for convenience so you’d only need the usual ±15 V supply.
But you also can just connect a regulated lower voltage directly (without the resistor).
Alfa says
An on-chip 7.4 volt Zener diode allows the device to operate off ±15 volt supplies, as well as +12, -5 volt supplies. For voltages greater than -7.5 volts, a series current limiting resistor REE must be added between pin 3 and the negative supply. Its value is calculated as follows:
REE = (VEE - 7.4) / .008
To minimize self-heating and improve thermo-stability it is recommended to keep VEE = -5V (external power supply).
and my experience is that using regulated -5 V fixes the pulse width frequency shift problem.
