Sushi Box FX Space Heater (Got a little TOO hot....)

[MichaelW]

Not sure if this report belongs here or not, @PedalPCB please feel free to move the thread if it shouldn't be here.

So I built the Sushi Box Fx "Space Heater" preamp. It sounded freaking awesome for about 15 minutes.

Exactly what I was expecting, some nice tube warmth at the beginning of my pedal chain with the gain low.

Dial up and the gain and you get some really nice tube pre-amp breakup.

I was under the understanding that this pedal could handle 12volts with no problems. At least from threads I read from @vigilante398.

So I tried it at 12 volts. (150ma) It sounded really good as well, maybe a tad more volume (or maybe I imagined it).

What I DID NOT imagine was the wispy smoke coming from the vents in the box. So I immediately cut the power and let everything cool off.

I plugged it back in at 9v and now I'm getting pretty inconsistent behavior. It seems to work for a while then it gets real noisy, crackly and the gain pot doesn't do much. Then after a while it will start to work normally again.

So I'm not really sure if I fried something or what.....(and I'm too chicken shit to go poking around on the board.....).

I think I want to build another one. Couple of things I want to do differently is that I hacked a couple of A1M pots from 90 degree to straight.
(everything else was built off the BOM list, even sourced it all from Tayda.
I also want to get a dedicated OneSpot with at least 600ma.

I'm not positive if part of the problem I'm hearing is the pots or something else going on. I'm also not positive what the power requirements are for this pedal, I'm pretty sure I read that the Black Eye needs at least 500-600ma and I don't have anything with that kind of supply.

I've tried a number of different tubes and it definitely sounds better with the JJ 12AX7's. I need to go hunt some down for my Black Eye build.

@vigilante398 when do you expect some more Space Heater PCBs?

Totally FUN build and the potential for a fantastic pedal that could see a lot of use for me. I can't wait to start the Black Eye!
THANK YOU @vigilante398 for making these projects available!

 

[vigilante398]

The pedal should absolutely be able to accept 12V as long as you didn't use a 10V cap on the input. I will say however that 150mA is absolutely not enough current. Just the tube heater by itself will pull 150mA at 12V, so for the full pedal you need 300mA bare minimum. Under-currenting the power supply may have caused some issues with the switching bits. Also since the plate voltage for the tube comes from the SMPS, the pedal should sound the same at 9V or at 12V, so if you have a solid 9V supply there really isn't any reason to run it at 12V, it won't sound different.

Have you opened it up to see if anything on the board looks fried? I would particularly be interested to hear if the IRF740 is okay, as I have a repair I just got back with a fried IRF740 and I was wondering how it could have happened, so I'm thinking a switching failure due to not enough current could have done it on this unit.

I actually have 4 more Space Heater boards on hand, I'll get them up on the website. I think I threw some more boards in my last PCB order, I'll have to double check. So there will be 4 more available today, and hopefully a bunch more whenever that order shows up.

 

[MichaelW]

Also, all the caps I used were directly from your BOM with the exception of the 100UF and 47u electro which are both rated 35v. So I should be good on the cap rating.

 

[Bricksnbeatles]

Will it work with a 12AY7 or 12AU7 for a little less gain?

Yes

 

[vigilante398]

Also, all the caps I used were directly from your BOM with the exception of the 100UF and 47u electro which are both rated 35v. So I should be good on the cap rating.

Okay, so the only real explanation was the under-current then. Let me know if you find time to poke around inside the fried one, I'd be interested to see where the smoke came out of.

 

[Feral Feline]

Sorry to hear you released the magic smoke, Michael. Great build-report nonetheless.

 

[MichaelW]

My One Spot with 1700ma is arriving today, I'll try it again with the correct power supply and report back.

 

[steviejr92]

My One Spot with 1700ma is arriving today, I'll try it again with the correct power supply and report back.

Let us know really want to know how this turns out! I’m getting more and more interested in these tube pedals!

 

[Dan0h]

Just ordered the space heater to go with my Black eye. Way to go @MichaelW even your fired build reports are selling boards.

 

[MichaelW]

Well just got a notification from Amazon that my One Spot is gonna be late....sigh.....so maybe tomorrow or the next.

I did do a little poking around (carefully) inside and I can't see anything that looks even remotely fried or damaged.

One thing I'm thinking, it might have been flux that was smoking. This is one board that I did NOT clean with IPA after soldering.
I usually do some pretty thorough scrubbing and dunking in IPA after soldering. But I was not sure about some of the components and how they would handle that, particularly the inductor coil. So I left it with the "no clean" Kester flux on both the main board and the daughterboard.

We'll find out when my power supply shows up.