Multi-Volty: All-in-one breadboard power solution :)

[vigilante397]

It had been a while since one of my builds fired up first try without any debugging, so this was refreshing Lately I've been breadboarding some pretty weird junk. I'm basically taking all the circuits I usually build (boost, overdrive, reverb, distortion, tremolo) and re-designing them to utilize Russian sub-mini tubes. That's right, not just the gain pedals, modulation junk too. I just finished my 6N16B + BTDR-2 reverb prototype and I really dig the sound, maybe I'll start a thread for that later.

But anyway, as I've been doing this, I've needed a lot of power rails. For the reverb I needed 200V for the tube plates, 6.3V for the heaters, and 5V for the reverb brick. For my RAT distortion I'm keeping the LM308 and replacing the output buffer so I need 200V for tube plates, 6.3V for heaters, 9V for the IC and 4.5V for reference voltage. This created huge messes on the breadboard and I would often bump things and ruin one or two power rails, then have to troubleshoot or re-build my power supply, or I would forget which rail is which and fry something, and frankly it was a big mess.

Then I had the thought, I have a well-calibrated CNC machine and some killer software, I should be able to throw together a board with all of my power supplies on it and make it small enough that I can fit it in a stompbox enclosure with a terminal strip on top so I have easy access to the rails, I can label them, and there are no exposed components for me to bump. Behold, THE MULTI-VOLTY (it's more fun if you say it out loud, try it!). It has a nixie-style SMPS for tube plates, adjustable from about 50V-400V, 7806 with a diode between middle pin and ground to bump the voltage to 6.3V, a 7805 for 5V, and a simple voltage divider for Vref (4.5V). And to top it off every single component on the board is available from Tayda

As you can see the schematic is nothing remarkable, just a bunch of separate power supplies with a single input:


The board right after milling (the board was a little uneven so one corner of silkscreen is missing):


And the populated board. I need to adjust a couple footprints in my library, it was a tighter squeeze than it should have been.


It would easily fit in a 1590B with plenty of room for wiring (the board is 1.9" x 1.3"), but I have a 125B that I had gutted a while back that's been sitting around, I'll probably fill in the holes and paint it then throw this inside with a terminal block on top so I can attach wires conveniently to run to the breadboard.

[antonis]

Couldn't you find a less bulky L1, Nathan..?? 
(PC switching power supplies is a convenient source for cannibalism..)

[GibsonGM]

I was going to ask, where are you finding the inductor?

[bluebunny]

I was going to ask, where are you finding the inductor?

It's the big fat round thing in front of the MOSFET.   

(Sorry, Mike - couldn't resist!)

On a more serious note: were you going to fit a heatsink to the MOSFET, Nathan?  I seem to recall from way back that Rick advised this when he used the same PSU for his Superfly amp.

[vigilante397]

I found much smaller inductors at Mouser and Digikey, as this one is rated for 2.9A and the project calls for a 2A, but I don't like what I have to pay in shipping from them, and as I mentioned this is an inductor Tayda stocks.

When I finalize designs and it's time to lay out boards I may reconsider (Mouser has a 2A inductor about 1/4 that size), but for a one-off just used on the breadboard this does the job

As for MOSFET heatsink, I had planned on it originally as I remembered that as well, but when I had it on the breadboard it ran cool as a cucumber with a load on it. Oddly enough when I ran it without a load was the only time it got noticeably hot. But if it becomes a problem, since this is just for benchtop use, I could throw a small fan on the enclosure.

My 6V regulator runs pretty hot when I run more than one tube (300mA load per tube) but I don't plan to do much of that. This was thrown together to handle the dozen or so prototypes I have on the drawing board now and should do the trick just fine

[GibsonGM]

Thanks.     And thanks marc, for letting me know where it is   (ha ha ha!).    I found a junk box old PSU inductor, like Antonis was talking about...but it's hard to know what value they are.     It worked, anyway! 

I didn't need a heat sink for my mosfet, but YMMV.  I run 2 12AX7s, and I bet I draw no more than 30ma, and that's probably a VERY high estimate (more like 10mA tops, probably).   I'm running heaters on 12V, and the regulator isn't getting more than warm.

[vigilante397]

12V on heaters seems to be a more common way to do it, but I like being able to throw it into a daisy chain with a OneSpot and not have to worry about having a dedicated power supply just for that.

[GibsonGM]

Yeah, it's not a bad idea at all.   I built a stand-alone preamp, uses an 18V wall wart to power everything.  SMPS to get 240 for the tubes, and of course the regulator for 12V.   

I didn't dare try to build a tube preamp as a pedal, LOL.  Some do, with good results, but I was afraid someone would step on it.

[vigilante397]

I didn't dare try to build a tube preamp as a pedal, LOL.  Some do, with good results, but I was afraid someone would step on it.

That's part of why I really like the sub-miniature tubes. I have built loads of 12AU7 and 12AX7 pedals but there was always the trade off of size vs robustness. I can squeeze a single 12A*7 tube preamp into a 1590B with the tube sticking out the top or I can put it in a 1590BB and mount the tube inside. With the sub-minis I can mount a pair of them with a reasonable circuit inside a 1590B without a problem. My tube reverb fits the SMPS, a single 6N16B-V, the belton brick, and a 16MM pot all inside a 1590B, so I get the form factor I love and I don't have to worry about stepping on a tube.

[antonis]

the project calls for a 2A

If so, D1 begs for your mercy...!! 
Also, L1 should have a value of, at least, ten times higher..
(its current value of 100μH doesn't harm but doesn't also provide any significant benefit..)

@Mike: I often use to throw such inductors into my benchtop PSs after a rough estimation of their current rating (only by visual wire gauge "calculation".. ) and convinse myself to feel happy for their excellent current regulation..