Hi fellow TweRPs, I thought it was time to do a brief update regarding my original post, having rebuilt my outboard filament power supply with some convenience mods.
Original Post
For fun, I'm calling the project box the Voltinator™. The ™ is just a joke; I invented nothing and have no interest in selling anything here.
I decided there was no value in having both barrel and aviation connectors on the front and also decided a single switch on the rear of the chassis for switching the output voltages was preferable over the two switches on the front (one for each channel). The aviation connectors I had used were kind of a pain in the neck from a mounting perspective in the 1/4" acrylic. So I swapped them out for ones with a mounting flange.
The back now has a single SPDT switch determines which of the two pairs of buck converters gets power - one pair is set for 2.5v and the other pair set to 6.3v.
I swapped out the power switch for a DPDT and integrated a simple 12v optocoupler to provide an additional power-up choice: input trigger. Pity the Lampizator doesn't have an output trigger option, but my preamp does.
Now, you might well wonder why I would choose to have 6.3v as an output option when the DAC itself sends 6.3v to the tube socket - so why use the Voltinator™ at all for 6.3v tubes... True, and originally I had 2.5v and 3.0v as my output options. I really like the sound of the 2.5v type 27 tubes, they are some of the best sounding options I tried in the TRP. I have a small number of 3.0v tubes I have yet to try and I'll get there eventually, but one of the things that really stood out by not standing out was the pitch black background. Wow, were the 27s ever quiet! Now noise has never even been on my radar with the TRP and I've always marvelled at how clean sounding and pure it is. But there was something almost eerily silent about the 27s and how that increased their apparent dynamics.
@Designsfx , who is similarly experimenting with outboard filament power, and I compared notes and postulate that this "extra" silence may be a function of the outboard filament power. Whether due to removal of that load from the Lampi or isolating that power circuit outside of the TRP chassis, we didn't know, but it was worth a try. And, as it turns out, I do have several type 37 tubes and these are very nearly the same as the 27 except they are 6.3v and consume demand less current...
So I put the old Philco type 37 tubes directly in my TRP, using a passive tube adaptor (no Voltinator™) and listened to them for a week. I had previously used them and really liked their performance and, in fact, had likened the type 27 to them after first heard the 27s.
After a week my ears were re-acquainted with them and I then switched them over to Voltinator™ power. It's only been a couple days but there is something a little more compelling about them. I have to say it's been worthwhile, if only subtle. Indeed the sound does seem like it's coming from a pitch black eternal background. As I say, subtle, but readily apparent. Bass impact did not seem to be affected and is to the same high standard as I've come to expect from these tubes when powered conventionally. But I was surprised that midrange dynamics seem better and seemed to be a little more saturated in detail. Reverb trails in empty recording spaces seem to go on beautifully. I didn't note any surreal "microphonic euphonics" that I occasionally experienced with the type 27 tubes, but the music definitely has a very lively presence.
This was an easy experiment because the type 37 has the same pin out as the 27. But now I wonder about all the other 6.3v tubes I've already listened to and how they would fare with external filament power.... groan....
Cheers,
Robert
