Mofo

[simon]

The advice at B&Q was not to use a rattle can but furniture paint as they felt I'd get a better finish. 4 coats later, it's okay. From a distance. It doesn't seem to be particularly resilient though.
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With cheapo magnetic computer vents to allow ventilation.
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Finished
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[simon]

One more as it wouldnt go on the last post.
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Under £200 all in. I use it with bass drivers so it was interesting to hear it full range at Dave's. It does lose out to a SET in the mid and treble, but the bass is nice and clean.

The 2A3 amp though... beautiful. All the wonder of valves in the mid and treble but the bass was nicely controlled too.

[steve s]

Loverly simon, not used mine for a year or so.. Will need to give the px4 a rest after my hols

I bought a nice 1930 pye sunburst radio case a couple of weeks ago and can't stop thinking what I could fit in it
... or I could take it down to retrotech and sell it for a £10'r next month? .. That would keep me focused on the crap I already own !

[simon]

Thanks Steve, I've been trying to make more of an effort to box stuff up the last year or so...

If you do want to get rid of that old radio I might be interested, always fancied the retro look but never had one.

[steve s]

Its a big case simon, and needs restoration but it not wormed.. let me know if you want it

[simon]

Thanks Steve, I've sent you a WhatsApp

[MistyBlue]

That’s a great looking case, Simon!

Nice to hear that you are getting good results with a similar setup to the one I’m aiming for.

I absolutely love the upcycling of the CPU coolers, they would make great “features” on top of an amp case, especially with the Noctua fans. A kind of alternative to the glowing valves and transformers! I decided not to do that on the design for mine, however I was sorely tempted, and the Noctua fans are surprisingly quiet (I have one on my guitar rig).

[simon]

Thanks Misty. It's a bit too smart to fit in in my play room, but I aspire to bring the rest of it up to a similar standard!

I got the CPU cooler idea from Steve S. They're 12V powered from a small 12V SMPS with buck converters to wind the voltage down to reduce fan noise. They're running about 6V but could go lower as the heatsinks runs very cool.

The larger SMPS has a fan that kicks in periodically. It's audible if there's no music or very quiet, but I'm very close to the amp, less than 2m. Normally it's unnoticeable.

[MistyBlue]

I used a low cost PWM fan controller on the guitar rig. I think it’s this one, although it was a couple of years ago now:

https://www.ebay.co.uk/itm/194948487077 ... R6am2o_dYw

The original 24V fan was noisy and ran flat out all the time which was a bit annoying as I sometimes play while watching TV on the sofa. I just ran it through a 12V regulator and then into the PWM controller. The NTC probe just went on the heatsink in a tapped hole next to one of the output transistors. The fan was quite expensive as they go (it's a bit cheaper now though), but I went with it because some of the guys on DIY audio spoke highly of it being quiet and I also wanted to test it out for other audio equipment as I was quite sceptical. The amp is an old Hartke HA3500 that has been modified a number of times now. I was very impressed with the fan – it is very quiet and just about silent even when the speed picks up. It was a Noctua NF-A8 PWM 4-Pin (80mm, Brown)

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[simon]

Interesting. Looks a bit more sophisticated than my setup.

[Ray P]

If anyone is interested in a 'Super MoFo'...

https://www.diyaudio.com/community/thre ... st-7655416

[Nick]

Hmm, a lot of that added complexity would make me think that the original point of the MoFo was being lost. Also, the very different rise and fall time in that square wave display would worry me.

[simon]

The MoFo has been in service for a while now and seems to be running fine with the cheap 24V SMPS LED supplying both channels separately through a CMC and CLC filters. I'm thinking about a different supply to do away with the SMPS, say a LT1084 regulator shooting for 19V and 1.7A each channel. Which is a lot of current.

I'm not very clued up on power supplies for solid state stuff, and maybe the chip regulator isn't a good solution. But I've had a play in PSUD and shooting for 21V in to the reg for a couple of volts drop across it, it looks like I need something like a 36V winding with maybe as much as 100VA per channel which has surprised me - it's a long way from the "typical" 1.4x voltage rating for cap input. I've had a guess at winding resistances, but does this look something like right?
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[Nick]

Coupe of thoughts, 2.5R would be more likely for a 300va toroid. Also, 1n4007 would not be the first (or second) choice for a high current low voltage supply. Also, for the sort of cap I would use in this power supply, 30mOhm would be a more likely choice that 2ohm. High current power supplies are not the same as high voltage ones (well they are, but you know what I mean).

Also, I would not bother with a regulator, I would go with the biggest transformer and caps you can get, and reduce all the resistance you have in the circuit. Copper buss bars instead of a 1R resistor in series.

[simon]

Okay, so essentially just a great big multi-cap C filter? Is there a practical limit to the amount of C here?

The benefit of the regulator is it's easy to set Vout, just going passive means I might need to add R to tune anyway? Not that it has to be spot on 19V.

I struggled with rectifiers, I tried a few like the MUR810(IIRC?) but I kept getting floating point errors. So I stuck with 1N4007 just to get it to sim. But something fast, even a UF4007 would be better.

I'll play with PSUD again tomorrow.