Multi-pedal power supply questions

[pdavis68]

I primarily do tube amp electronics, but GuitarPCB.com had a sale going on pedals and I couldn't help myself, so I bought like 6 or 7 of their PCBs. I've got 2 started (short on components, so I'm going to do what I can on each pedal and then order the components I need to finish them all).

What I want to do is house all the pedals in a single chassis. I'm probably going to use a small rectangular cake pan mounted to a piece of plywood with foil shielding, or something like that and just have all the switches and knobs in one place...

My question is regarding the power supply. Should I do separate, isolated supplies for each pedal, with each pedal being fed by its own voltage regulator? Or would it be okay to have several share the same regulator? Does it matter what kinds of pedals they are?

The pedals I'm doing are:

Angry Red Camel (with Emerald Ring octave mod)
DSOTM Fuzz
SWAH autowah
Big Muff Pi
Zenith Pro Overdrive
D'Lay w/daughterboard

Not from GuitarPCB, I have a few others, like a clean boost and a fairly simple overdrive.

I don't know if certain pedals are more amenable to power sharing than others.

I can do whatever will work best.

[blackieNYC]

I've done two 7-in-1 pedals. Its a great time and resource and SPACE saver. I have had no need to use separate supplies. I do have the usual filter caps located at each circuit (individual perf boards), but since you are using pcbs, just put the caps in. If there is a series resistor in each circuit keep them there for better supply filtering.  depending on their application, you could put one polarity protection diode/circuit in there and bypass/skip the individual circuits.  I distribute the LED voltage separately thought I don't know if that is needed. I guess that won't apply for pcbs.  Use the unused ground to ground the input of the circuit.  Or, if there is an LFO involved, use this ground to disable the LFO in a way that doesn't draw current or melt things.
I did a 3P2T stomp for each. (with the LED).  I've had no need for pedal-order switching capability.  On one, I do have in/out 1/4 switching jacks for each circuit, which is useful but I skipped all that for the 2nd multi.
Instead of the cake pan, consider a used/dead piece of 19" rack mount gear.  Studios, repair shops, radio stations all have some broken crap laying around, which you can use for a box. The height of a 1u piece is perfect - 1 3/4 inches I think. Saw the ears off.  You might even find one that has holes on the back for jacks. If there are way to many holes, or big ones I can't use, I cover them with a 1u blank panel.  This has been helpful to me in that the box I use is thinner aluminum than most - the 1u blank panel allows me to jump up and down on the stompswitches without denting the box.

[pdavis68]

Thanks for the info.

This guy does amp chassis pretty inexpensively (http://www.juicyamps.com/17x7_5x2_5.html). I might break down and go with one of those. I have a few weeks before I'm going to start installing stuff in a chassis (going to be at least 3 weeks before I order the parts I need, then 1-2 weeks for delivery from Thailand). I'll think it over.

The only rackmount chassis I have is 3U or 4U. Too big for this application.

Yes, I'm going to do the 1/4" jacks for input and output on each board. I want to be able to re-order the effects. Which reminds me, I'm short on 1/4" jacks, so need to add those to my shopping cart.

[GibsonGM]

What Blackie said.  If it makes you feel better, you can add up the currents drawn by all your pedals, see if you are within what your PSU can deliver.  The LEDs are the hungriest parts, usually!!

Provided your PSU is already regulated and filtered, a nice fat cap at each board's input should be all you need, with perhaps a 100R resistor before it.

[blackieNYC]

I try to put my pickup-responsive fuzzes first. But order only matters if you use more than one at a time, so - delay last, unless you use the overdrive (or another) to hit the amp hard (well above unity gain). You don't want to clip the delay. Then a boosty thing.
http://www.diystompboxes.com/smfforum/index.php?topic=115903.msg1071529#msg1071529

[pdavis68]

Over Thanksgiving I spent a lot of time reading and I came up with the following idea for my pedalboard power supply and just wanted to get some opinions.

I've been building pedals like crazy (for me). I'm averaging about 3-4 a week. So one cake pan of pedals isn't going to be sufficient. So what I was thinking was maybe building the power supply separately. When I started thinking about that, I thouhgt, well why just do 9V or even +/- 9V. So instead, I think I'm going to do a power supply with +/-9V, +/-12V, and +/-15V, with some pedals (that can take it and would benefit from it) having a switch to choose a voltage. Some of the pedals I've built I know will work fine at 12V and 15V and it will change their headroom and/or dynamics to change the voltage. So I think that's kind of a cool feature. As I build them in the future, I'll keep alternate voltages in mind for possible circuit mods.

The idea was the power supply might have a couple of 8-pin DIN connectors and I'll put 8-pin DIN jacks in the cake pans. That way I can build as many pedals as I want, put them in cake pans with the DIN and I've got a power supply ready to go.

I actually have a transformer that's about perfect for this. It has a 9V@1A tap, a 15V@500mA tapand a 15V@1A tap.

I was thinking of setting up the supplies with:

+9VDC from the 9V@1A
+12VDC and +15VDC from the 15V@500mA
-9VDC, -12VDC and -15VDC frrom the 15V@1A

Anyone see any problems with this idea?

[pdavis68]

This is what I've got in mind. The schematic is just for the negative supply. They're pretty standard supplies, I think, but I've never done a negative supply so I'd appreciate it if someone could just check it real quick to see if they see any issues, particularly with the negative supply. If you notice any issues with the positive supply layout, that'd be good to know as well.

So the positive side will get its supply from one pair of transformer taps and the negative side will get its supply from a separate pair of taps.

So, for my needs (+/-9V, +/-12V and +/-15V), I'd need 3 of these boards.

For 9V, R1 = 470R & R2 = 3K  (should give +/- 9.23VDC)
For 12V, R1 = 300R & R2 = 2.6K (should give +/- 12.08VDC)
For 15V, R1 = 270R & R2  3K (should give +/- 15.14VDC)

These are resistor values I know I have. I believe new batteries are a bit over 9V exactly, so I went up a little bit to account for that.

Negative supply schematic:


Bipolar supply vero layout:



Thanks.

[blackieNYC]

If I were to do a power or control cable, I keep thinking a 9 or 15 pin dsub would be best. The thumbscrews, pre made cables and extenders available in many lengths, solderable chassis mount connectors.  Dins are a little messy. With a vga cable you could swing a pc monitor around over your head. 

[pdavis68]

That makes a great deal of sense, thanks. I'll go with a 9-pin dsub. I'm sure I've got some 9-pin dsub cables around here in boxes.

[PRR]

> I've never done a negative supply

Pin-out for LM337 is *different* from LM317!!

I think. I have not squinted your layout, because even if you knew that someone else will have missed this annoying detail.

(There's a good reason for the different pin-outs, but I wish they hadn't done that.)

[pdavis68]

Wow, thank you so much for that. I googled "LM337 pinout" and of course the first image that comes up is an LM317 and that's what I looked at. Well, that's really annoying because I've done everything but put in the LM337, at this point (I've only done the negative supply. I was doing it for a test). I've got room on the board, though. I can move the LM337 and use jumpers to correct the pinout issue for this particular board. It's just swapping two pins.