My question is about running power to both the Main and Expansion boards.
They both need +15v/-15v so would it be best to run individually to each board from the charge pump, or is it ok to leave a couple of tracks open on the main board, and then run the power through that to the expansion board?
There’s a diagram below that explains it better than I can type it! Just wanted to know which was the best way to go about it, which was a definite no no etc
In theory, they are the same. But in actuality, you might have better results with the 2nd option. Here are some factors:
- Shorter power wiring = lower resistance = lower voltage drop, less chance of picking up interference
- Separate input current path - load fluctuations & interference aren't shared between the two boards
If you do want to share a power rail, keep in mind:
- Keep traces thick - Creates low-impedance path & helps handle increased current draw
- Use separate filter caps for each circuit - Place them after each circuit branches off, and as close to the circuit that will use the power as possible
I built a wallwart AC-DC +-15V PSU, and on the distribution board I included polyfuses (or current-limiting resistors) & filter caps for boards that didn't have sufficient filtering built-in. Do you know the current draw of the circuits you're feeding? Keep in mind the upper limits of the 7660S/1044 are ~30mA, so use an LT1054 if you are worried (it will give you up to 100mA).
Haha yeah, fancy running into you here! What are you making, by the way?
If you're looking to make a PSU to power multiple things, I've also had better luck with dedicated DC-DC converters rather than charge pumps. Traco, Meanwell, and Murata all make good converters that will take +9V (or higher) and generate isolated & regulated +-15V rails. They are more expensive than charge pumps (although not much more than the LT1054), but you can get them in a variety of wattage ratings:
1W = 33mA per +/- rail
2W = 67mA per +/- rail
3W = 100mA per +/- rail
6W = 200mA per +/- rail
8W = 267mA per +/- rail
12W = 400mA per +/- rail
Nice, yeah I'm having a crack at the Diyre colour palette from the schematic you drew up!
I've drawn up a Vero layout for that and the Distortastudio, which as you know run on +/-15v. I found a Bipolar charge pump layout on Tagboard effects, which I will have a go at and see how close it can get to the correct voltage.
But cheers for the DC-DC convertor advice, so I guess something like this or this would work nicely as an all in one power source.
Got this up together and working. I made a adaption to Ivlark's Bipolar powersupply on Tagboard effects, which works fine, but for size reasons I ended up replacing it with a small step up boost convertor I got off of ebay.
I built the colour palette into a 1590bb with 3 modules and a rotary switch to choose between them. I used the 15IPS tape saturator layout from Dirtbox effects and then made layouts for the Colourupter and Distortastudio. They all work and sound very different from one another, although the output level of the Distortastudio is a bit lower than the other two, so I may add a boost circuit on the end of it to bring up the level.
It was so small and fit right at the top of the case above the pots. It helped that I was able to get the jacks and footswitch together at the bottom and the Pots and Rotary in line at the top as this gave the perfect space for all four boards!
I've seen those boost converters for sale, but never thought to use them for audio. How is the noise level?
I want to box my single-module pedal version of the Colour Palette, so I recently made a PCB layout for the LT1054-based bipolar charge pump circuit that Tagboard's layout is based on. It came out much smaller than the vero version I have, and they only end up costing ~$0.25 from JLC PCB:
If you think you're going to make more of these, I'd be glad to send you the .BRD files or Gerber files.
The transformer-based boards are the ones that originally drew me in to the Colour Modules. I think the higher headroom & available gain of the +-15V rails is really needed to drive them properly, which is maybe why I haven't been too blown away by guitar pedals with driven transformers.
The TM79 Multi-Stage Saturation Colour is probably my favorite module, it has this thick, greasy saturation that I haven't been able to get out of anything else. It's a pretty cool circuit, with back-to-back transistors set up as Step Down Xformer -> Heavy 68ohm load w/2N7000 soft clipping -> 2:1 Step Up Xformer. The TY-250P transformers are kinda expensive and have been hard to source as well.
The AWB95 Cassette Tone Colour really caught my interest, but it didn't live up to my expectations. It was hard to get enough gain to drive it in any of my Palette hosts, and was more flabby than pleasant saturation.