DHT Heater using VCCS - PCB or Kit (Possible Group buy)

[Andrew]

OK, cool.

It does seem to fill out the upper bass tone , so far.

That is what I would have hoped for.

Not sure if I've lost something, but I'll update you in the next day or two how it goes as I do more running/listening .

And that's unexpected........but useful info, nonetheless.

Looking forward to hearing if it runs in, it hasn't been used much yet, but at those currents I would realy expect much in he way of change, but you never know.

Keep the comments coming, great stuff, least its not let its magic smoke out.

Andrew

[Andrew]

Hmmm, I wonder if the DC heater supply isn't quite quiet enough for a gain stage, I have only tried it on an output stage.

If that's the case, assuming you have a suitabe toroid, we could trying powering the current reg from one of the voltage reg boards so that the DC heater isn't trying to to do the line regulation itself, sort of like a pre-reg, if you get my drift. Basically making sure the current source gets a clean supply to work with.

Andrew

[IslandPink]

No - it's very quiet, more than the V-reg one, apparently .... and the 2kHz ringing has gone ! excellent
Definitely sounding fuller and very natural through the mids and bass .
Oh, however .... as far as I can tell, there is a slight loss of the fine upper treble detail and air that I had
It sounds very similar to the trouble I had with by-passing the Cerafine cap of the KT88 shunt in the power supply , but not as much .

Is there anything that might cause a subtle phase change in the 5-20kHz area... or a shift of AC current modulation from one component to another in that region ?

I was trying to look at the unit to see if there was or wasn't a cap across the output , but it's too far under the shelf now to see ! - just wondering if I could experiment by adding a small high-quality cap across the output - for no particular reason, just an experiment .

[Andrew]

Adding a cap woud turn it back into voltage supply, let me have a think and a play on Spice, perhaps we need to tweak things a tad. Although I do recall Nick's theory on a slightly broken reg sounds better at higher freq. All good stuff!

Good news its quiet enough

[Nick]

Although I do recall Nick's theory on a slightly broken reg sounds better at higher freq

What are we? Lawyers? hypothesis at best.

[Andrew]

Although I do recall Nick's theory on a slightly broken reg sounds better at higher freq

What are we? Lawyers? hypothesis at best.

Very true, it was just a random thought! A possible explanation, Spice will tell us all! Least I hope so.

[IslandPink]

Yes, I think my feelings about the pros/cons were about right , after another 3 hours running approx this evening .
The DHT heater seems to have traded extra fullness and bass tone for a loss of low-level detail and presence and some treble finesse .
Very interesting listening though : there's a track called 'Dreamland' on Joni Mitchell's 'Don Juan's Reckless Daughter' which has a big bass drum in the mix, and the tone and dynamics on that nearly blew my mind earlier this evening .

However there's a feeling there is no air on one side of the soundstage , compared to the V-reg supply on the other side . It sounds less lively and I found myself turning up the volume on that side to get the 'balance' back .

[Andrew]

OK, so good news (mostly) but a bit more work to do. I will try and build up that other PSU PCB I have and see where that takes me, least see if I can replicate what you get.

Andrew

[Dave the bass]

The DHT heater seems to have traded extra fullness and bass tone for a loss of low-level detail and presence and some treble finesse .

Sorry to butt in but... that description ^^^ is exactly what happened when I voltage reg'd the 2A3 filament supply on one channel on that 76/2A3/811a breadboard amp I took to Owston. I went back to AC heating on 2A3 which is what we all heard at the weekend but its still not mega fabbo IMO, I don't think its the whole reason, just part of the reason on my amp.

Just sayin' like!

DTB

[Paul Barker]

mine was ac heated.

[IslandPink]

We've been exchanging some e-mail today, and Andrew has produced a few Spice plots that show some interesting behaviour , where the current modulation on the supply increases abruptly above 10kHz ( from the audio signal ) - this is probably enough to explain the problem, from my recent experiences with the T-Rex main supply ; Andrew is going to look into what can be done design-wise to alter/improve this.

[Andrew]

Yes, hopefully we're making progress, I think the topology is sound and the idea too, but we just need to tweak a bit. Many thanks to Mark for his efforts so far.

Andrew

[Andrew]

OK I have built a copy of reg Mark has so I'll try this out and see if I can replicate his findings.

[Andrew]

Mark, for a real life test, have you got a particular track, or tracks, in mind?

Andrew

[IslandPink]

Mmm..Tough question.
Depends how much overlap there is between our record collections !
The one that was crucial for me in telling there was something not right was '(Walk me out) In the Mornin Dew' from side 6 of The Grateful dead triple album 'Europe '72 ' which I would hazard a guess isn't in your stack ?

Any good live record would be good - maybe Genesis Live ( 1972 again ) , or more recently how about 'Mainstream' from Lloyd Cole which has some 'space' to it . You're looking for air and space and a sort of 'ease' in the treble where the music is spreading into the room, rather than being closed-in .