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#1
Building your own stompbox / Re: SMPS for tube pedals
Last post by printer2 - Today at 11:04:20 PM
Quote from: PRR on Today at 10:51:54 PM
Quote from: printer2 on Today at 10:05:12 PM6V6 in SE (359V 55 mA)

That's a lot of heat for a 6V6. 19.7W, maybe 17.7W if you allow for bias and screen. Rated 12-14W. Also 315V. Yes, there is a report of Fender pushing modern Champs to that power zone.

Your Russian 6L6-alikes may be fine.

Yeah I know, but I did not have a better way of dissipating the power. Nothing glowed red so I was not too worried. I have more tubes than I will ever need so not a big concern. About 25 NOS 12V6's in the upper left, a hand full of used also beside them.



#2
Building your own stompbox / Re: SMPS for tube pedals
Last post by PRR - Today at 10:51:54 PM
Quote from: printer2 on Today at 10:05:12 PM6V6 in SE (359V 55 mA)

That's a lot of heat for a 6V6. 19.7W, maybe 17.7W if you allow for bias and screen. Rated 12-14W. Also 315V. Yes, there is a report of Fender pushing modern Champs to that power zone.

Your Russian 6L6-alikes may be fine.
#3
Building your own stompbox / Re: SMPS for tube pedals
Last post by printer2 - Today at 10:05:12 PM
Swapped the 6V6 for a 6N3C Russian tube, on 310V I had 80 mA, 25W out of the module and the original heatsink heated up to 55 C. I did not get to measure the foil as the diode popped. By the time I got the thermistor on the foil it was also measuring 55 C so I am sure it got hotter.

The module with a 6V6 in SE (359V 55 mA) seems like it would be fine with my little makeshift heatsink. I need to look at replacement parts for the diode with sucking the heat away in mind.
#4
Building your own stompbox / Re: SMPS for tube pedals
Last post by printer2 - Today at 06:43:32 PM
"Oh, you were looking for Elegance? Keep walking and it will be three doors to the left. This is Just Get The Damn Thing Done"

Only got it up to 19W with the power supply I have at the moment and the 350V caps I got in the circuit. The brick does not like when the module is set for 350V on startup and shuts down and restarts. Turning down the set voltage and then turning it up it does not get upset. Set it to 350V and 50mA through a 6V6 in SE.

The heatsinks are pretty cool. With ambient being 24 C I have 37 C on the foil (0.2 mm, 0.1 mm that I folded on itself and run some solder between them) and 33 C on the big old heatsink after an hour and a half. OK that was fun, how about if I put the original heatsink back? This time 19.7W out I got 35.2 C on the foil, 38 C on the heatsink. Seems the foil really does help. I will have to run more power through it, maybe even with a higher supply voltage.

 

#5
Quote from: Matthew Sanford on Today at 03:58:06 PMMind posting the schematic you're working from for lazy people like me that don't want to search?
Good call, my apologies! Here are a couple - one is Aion's schematic which is only slightly tweaked, and the other is the basis of a pcb someone gave me which has further mods.





Quote from: Mark Hammer on Today at 04:14:17 PMThe FY-2 and FY-6 are different beasts.  Going from one to the other is no simple matter.  Actually simpler to build both and use a switch to go from one circuit to the other.

As for cancelling the octave (not that it's as strong an octave as the Foxx Tone Machine in the first place) the mod involves cancelling one of the two phase reversed copies of the signal from the phase splitter.  The transistor after the "Expander" control, with a 10K resistor on both the emitter and collector is the phase-splitter.  Breaking the connection between the emitter and the cap immediately after it will remove the octave.
Gotcha - thanks so much, Mark. I had the feeling going from FY-6 to FY-2 was not as easy as going from Tonebender MKII to MKI.V. I'll shelve that idea for now! Fredric Effects must have both circuits in one box in order to do that: https://fredric.co.uk/nouveau-super-unpleasant-companion

Great, great input on removing the upper octave! Sounds like I would simply put a SPST on/off switch between Q3's emitter and C8 on Aion's schematic. Now that I think about it, SPST on/off may not be the correct switch... hmm. I've never dealt with a polarized component on a switch, so I have to figure out how best to set this up...

If I'm successful with that, there is another problem that pops up - noise. I've found that things get much noisier when I remove the upper octave from a Foxx Tone Machine or Superfuzz (based on John Lyons' incredible version). I've found that playing with the FTM's Q2 collector resistor helps a bit, as does adding a pot right after the power supply to starve the whole circuit - plus, it creates some very interesting sounds!

I'm not sure I've seen a Super Fuzz with either a transistor bias knob or global starve. The starve seems pretty straightforward (add a pot to the +9v signal coming into the pedal - right?), but I have no idea where a transistor bias would go... I'm VERY curious about this, as I think it might help reduce noise and create some strange textures...
#6
The FY-2 and FY-6 are different beasts.  Going from one to the other is no simple matter.  Actually simpler to build both and use a switch to go from one circuit to the other.

As for cancelling the octave (not that it's as strong an octave as the Foxx Tone Machine in the first place) the mod involves cancelling one of the two phase reversed copies of the signal from the phase splitter.  The transistor after the "Expander" control, with a 10K resistor on both the emitter and collector is the phase-splitter.  Breaking the connection between the emitter and the cap immediately after it will remove the octave.
#7
Mind posting the schematic you're working from for lazy people like me that don't want to search?
#8
Building your own stompbox / Re: Boss ge 7 won't turn on
Last post by Jun1001 - Today at 03:49:16 PM
Thank you all again for your help. I'll use it well. :icon_mrgreen:
#9
If anyone could help me navigate adding a switch to go from FY-6 (6 transistors) to FY-2 (2 transistors) and a switch to simply cut the octave from the FY-6 I'd be thrilled.

I'd also love to add a transistor bias knob, but I'm not sure which resistor on which transistor I'd need to replace with a pot...

I haven't been building long, so this kind of guidance helps me in future builds too. I really appreciate it!
#10
Building your own stompbox / Re: SMPS for tube pedals
Last post by printer2 - Today at 02:37:32 PM
Quote from: R.G. on Today at 11:23:23 AMI did some quick (and very dirty) estimation on the switching diode losses for the circuit in question. The US3M looks like it ought to work, mostly, which might account for the stories of it working until the voltage gets high. The UF4007 surprised me in that it has a shorter trr than the US3M, 75nS vs 85nS; I had expected the purpose-packaged US3M to be better, but both are pretty good.
Both have similar thermal characteristics. The US3M has a thermal resistance of 26C/W to its terminal when mounted on 0.53" X 0.73" pads of 2-ounce copper. This reflects the fact that most of the heat is conducted out the terminals into the PCB copper, not through the body. The UF4007 has a similar situation, in that it specifies thermal resistance of 30C/W to its leads. It too relies on the PCB copper for heat sinking. The UF4007 doesn't specify a PCB pad or area size, only a max power dissipation of 2W.
Some of the very dirty stuff is in estimating (not calculating or simulating) the reverse recovery losses. If the diode is conducting current into a cap full of 300Vdc, then tries to stop conducting, it takes trr seconds to stop conducting. During that time, it has to conduct the reverse current and (to a first approximation) the DC voltage from the output capacitor. This is a big assumption based on thinking that the transformer capacitances and reflected voltage conditions can pull the cathode nearly to ground(ish) to get the capacitor voltage across the diode.
Another dirty assumption was that the reverse recovery current was a square pulse of 1A. The datasheets show a curve for reverse recovery current peaking at 1A, and trr being at recovery to 1/4 of that. Rather than do the integration graphically or with math in my head, I reasoned that it has to be better than 1A for trr. So each turn off event could be about 300V * 1A = 300W. This power only lasts for trr, so the energy is 300W*85nS, or 25.5uJ. Doing that at a switching frequency of 100kHz gives 2.55W. This goes down with switching frequency, of course. If it's 50kHz, the dissipation is only 1.28W, etc.
Two-ish watts in a diode with 30C/W thermal resistance would make the junction about 60C over ambient, and so yes, it gets hot. The same reasoning applies to both diodes. That makes me feel better about my intuition that there wasn't enough power being converted to heat the diodes. There is, it's just that there's quite a bit going into the diodes.
I then wondered - why does the UF4007 survive? Probably because there are two of them and they are close-enough matched to share dissipation. Or that the UF4007 semiconductor process and packaging is somehow better inside. The PCB area isn't particularly great compared to the datasheet notes on the US3M, so maybe that's an issue.
The high voltage output is an issue if my thinking isn't way off. The diode reverse losses would go up with output voltage. They would also go up linearly with switching frequency.  Yeah - if my thumbnailing isn't too far off, the diode could get into heat stress and not live long because of thermal effects as the output voltage goes up. Turning the output voltage down lets it cool off. There might be an option to lower the switching frequency if the inductor can take the longer on-time, or if the inductor can be subbed for one with enough energy storage at the lower frequency.


So you are saying, "It depends?"

Just kidding. Your back of a napkin analysis is at the level I can absorb easily. Now I have a a few more data-points to use with Digikey's selection.

Thank you.