It had been a while since one of my builds fired up first try without any debugging, so this was refreshing ;D 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:
(https://i.imgur.com/ej7J9hm.jpg)
The board right after milling (the board was a little uneven so one corner of silkscreen is missing):
(https://i.imgur.com/y171ped.jpg?1)
And the populated board. I need to adjust a couple footprints in my library, it was a tighter squeeze than it should have been.
(https://i.imgur.com/4kvA53a.jpg)
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.
Couldn't you find a less bulky L1, Nathan..?? :icon_eek:
(PC switching power supplies is a convenient source for cannibalism..)
I was going to ask, where are you finding the inductor?
Quote from: GibsonGM on March 22, 2018, 06:59:43 AM
I was going to ask, where are you finding the inductor?
It's the big fat round thing in front of the MOSFET. :icon_biggrin:
(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.
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 ;D
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.
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.
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.
Quote from: GibsonGM on March 22, 2018, 09:04:30 AM
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.
Quote from: vigilante397 on March 22, 2018, 07:59:54 AM
the project calls for a 2A
If so, D1 begs for your mercy...!! :icon_rolleyes:
Also, L1 should have a value of, at least, ten times higher.. :icon_wink:
(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".. :icon_redface:) and convinse myself to feel happy for their excellent current regulation.. :icon_biggrin: