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It would make things somewhat easier.
Follow Ups:
This is for example a 6080 OTL and the power supply is a 12V-220W SPS model.
I had a nasty 8/16 KHz spurious coupling only in one case and I had to rearrange the layout.
Omnes feriunt, ultima necat.
Why not use a pre-built linear supply instead? I use one from International Power Supply in a preamp that needed 24v for the filaments (6*4 in series) and also the B+ from 6GM8 tubes.
They come in all voltages and amperage. Physical sizes vary.
I am using a pair per channel of 5v SMPS for lighting the 304TL DHT. They do the trick and are quiet. Way cheaper than trying to build a 25 amp 5 volt linear power supply (and probably much quieter) For the 300b you could get 10v SMPS and run them through the Rod Coleman regulators. The reg will keep the SMPS out of the signal path.
Doesn't a SMPS throw a lot of RF into the surrounding environment?
It's been a while but the ones I have tested with a detuned AM radio sure did.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
.
Have Fun and Enjoy the Music
"Still Working the Problem"
The DC output of these regulated supplies is very dirty. Check with a scope, and you'll see it. There may be exceptions that have more rigorous internal filtering, but they're few and far between.
So it mixes with the desired signals to create random IM distortion all through the audio band. Shielding and filtering are usually both required to resolve this problem.
For a 1.2 amp 5V supply, I agree it is not the absolute best solution to use a SMPS as they are not too difficult to build if you have the right transformers.
But simply using a decent SMPS in a remote box through a 2ohm/10,000uf RC filter into a Rod Coleman V9 regulator, is very functional and dead silent. If builders are struggling with the dreaded 120hz noise and don't have the taps to generate 8 volts of DC for the regulator, it is definitely a workable solution.
Yes, I did this and lived with happily. SMPS into Coleman Regs to GM70s. One thing against, was mine were in close range to other stuff.
I went linear with Rob's suggestion from his website and it was way better for what I was after.
But at a big disadvantage in size, weight and cost.
Technically I was always concerned about the high order products mixing with the audio. Just didn't feel the right thing to do at such a sensitive part of the circuit.
I meant that shielding would work against the airborne RF that these things produce.
I think the rest could be handled with additional filtering but all the filtering in the world won't stop the airborne stuff. Once it's there, it's there.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
nada aqui
"Doesn't a SMPS throw a lot of RF into the surrounding environment?"
A regulated SMPS emits a nasty mix of frequencies that are constantly modulated over a very wide range. They're simply not suitable for this use.
I would only use a switcher for a DHT filament if the supply was A) a single frequency oscillator and B) tuned well above the audio spectrum. I did that in each of my 211 monos by modifying a 12V "60W Electronic Transformer" to operate at roughly 80kHz. It was a long process, but the end result works extremely well and meets the goal of producing no audible hum.
I tried a Mean Well SMPS into Rod Coleman regs and it sounded very much worse than a proper linear supply. Unusable by my standards.
Yes - these little things are tempting, but if you want the best sound steer clear of them.
"I tried a Mean Well SMPS into Rod Coleman regs and it sounded very much worse than a proper linear supply. Unusable by my standards."
That's interesting. I've analyzed the output of several SMPS modules, and the garbage they emit extends throughout the audio spectrum. I would have hoped a regulator could clean this up, but the Coleman design probably isn't intended to do that. It's also possible of course that the level of EMI generated by the SMPS is sufficient to bypass the regulator.
Like I said above, my solution was to use a fixed-frequency switcher. It was a lot of work finalizing and vetting these supplies, but the result has been excellent. My monos sound exactly the same as when I used a standard filament transformer several years back, but with no hum whatsoever. Dead quiet. Not sure if I've posted photos here before, but here they are:
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