What's your favourite voltage regs?
 

On Mon, 21 Jan 2008 12:49:06 +0000, Nick Gorham
wrote:

Don Pearce wrote:
On Mon, 21 Jan 2008 12:14:05 -0000, "David Looser"
wrote:


"Don Pearce" wrote in message
...

I'm aware of what is happening, and how the effect operates. What I
don't have is any kind of feeling for the magnitude of the effect.

A measurement would be simple. A current source feeding the heater,
and an optional capacitor from one end of the heater to the other to
make it a voltage source at audio frequencies.


I no longer have access to the required test kit (my ex-employer wouldn't
let me keep the Audio Precision analyser when I left :-( ) so I couldn't do
that. I'd be interested in the result if anyone else can.

David.



Even the cheapest sound card is more than man enough for this job.
What I lack is a DHT amp.

d


I could set up something simple, want to describe what you need setting
up and I will see what I can do.

OK. For a signal, a 1kHz sine wave will do. There are plenty of
freeware generators around that will produce that from the sound card.

Feed the output of the DHT amp into the sound card, with a couple of
resistors to attenuate the signal if necessary.

Then run a test twice, once with a current source for the DHT heater,
then again with a voltage source. As I said, you can achieve this with
a reasonably fat capacitor across the heater. About ten seconds is
plenty.

Save these as a couple of WAV files (not MP3) and post them somewhere
handy.

d

--
Pearce Consulting
http://www.pearce.uk.com

What's your favourite voltage regs?
 

Don Pearce wrote:


Even the cheapest sound card is more than man enough for this job.
What I lack is a DHT amp.

d


I could set up something simple, want to describe what you need setting
up and I will see what I can do.


OK. For a signal, a 1kHz sine wave will do. There are plenty of
freeware generators around that will produce that from the sound card.

Feed the output of the DHT amp into the sound card, with a couple of
resistors to attenuate the signal if necessary.

Then run a test twice, once with a current source for the DHT heater,
then again with a voltage source. As I said, you can achieve this with
a reasonably fat capacitor across the heater. About ten seconds is
plenty.

Save these as a couple of WAV files (not MP3) and post them somewhere
handy.

d


Ok, I will see what I can arrange.

--
Nick

What's your favourite voltage regs?
 

Don Pearce wrote:
On Mon, 21 Jan 2008 11:20:41 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Don Pearce wrote:
On Mon, 21 Jan 2008 11:07:09 +0000 (GMT), "Dave Plowman (News)"
wrote:
In article ,
David Looser wrote:
As I said in a common-cathode amplifier there is usually little or no
signal at the cathode to shunt.
Be interesting to know just how the heater supply makes any difference
to the sound quality, then?
As interesting would be a couple of sets of measurements to show just
what the difference is that they are hearing.
Don't think you're allowed that sort of question here anymore. People
flounce off in a huff. ;-)

Oops! I'll shut up...

d


No no, you're fine. *As* interesting. Think even I can let that go,
although and as usual with a flounce :-)

Rob

What's your favourite voltage regs?
 

Don Pearce wrote:
On Mon, 21 Jan 2008 12:49:06 +0000, Nick Gorham
wrote:


Don Pearce wrote:

On Mon, 21 Jan 2008 12:14:05 -0000, "David Looser"
wrote:



"Don Pearce" wrote in message
...


I'm aware of what is happening, and how the effect operates. What I
don't have is any kind of feeling for the magnitude of the effect.

A measurement would be simple. A current source feeding the heater,
and an optional capacitor from one end of the heater to the other to
make it a voltage source at audio frequencies.


I no longer have access to the required test kit (my ex-employer wouldn't
let me keep the Audio Precision analyser when I left :-( ) so I couldn't do
that. I'd be interested in the result if anyone else can.

David.



Even the cheapest sound card is more than man enough for this job.
What I lack is a DHT amp.

d


I could set up something simple, want to describe what you need setting
up and I will see what I can do.


OK. For a signal, a 1kHz sine wave will do. There are plenty of
freeware generators around that will produce that from the sound card.

Feed the output of the DHT amp into the sound card, with a couple of
resistors to attenuate the signal if necessary.

Then run a test twice, once with a current source for the DHT heater,
then again with a voltage source. As I said, you can achieve this with
a reasonably fat capacitor across the heater. About ten seconds is
plenty.

Save these as a couple of WAV files (not MP3) and post them somewhere
handy.

d


Ok, this is what I have thrown together. If the level of 50hz is a
problem, it will take me a bit longer, the computer is in a different
room, and the screened cable between the two could have better screening.

Anyway, its a 6sn7 gain stage, then a 2a3, producing 1v RMS into 8R.
First one is a current reg driving the fil, second exactly the same, but
with a 33000uf cap across the fil as well.

I have not made any effort at geting the best results from this setup,
as I thing its whatever difference there is thats of interest.

http://www.lurcher.org/nick/heater/2a3-I.wav

If there is anything of interest (I haven't look that hard at the
results myself yet), I can throw a three pin reg as a voltage reg tommorow.

http://www.lurcher.org/nick/heater/2a3-I.wav
http://www.lurcher.org/nick/heater/2a3-V.wav

--
Nick

What's your favourite voltage regs?
 

Nick Gorham wrote:

I have not made any effort at geting the best results from this setup,
as I thing its whatever difference there is thats of interest.

http://www.lurcher.org/nick/heater/2a3-I.wav

If there is anything of interest (I haven't look that hard at the
results myself yet), I can throw a three pin reg as a voltage reg tommorow.

http://www.lurcher.org/nick/heater/2a3-I.wav
http://www.lurcher.org/nick/heater/2a3-V.wav


Woops, sorry, same link twice.

--
nick

What's your favourite voltage regs?
 

On Mon, 21 Jan 2008 22:03:05 +0000, Nick Gorham
wrote:

If there is anything of interest (I haven't look that hard at the
results myself yet), I can throw a three pin reg as a voltage reg tommorow.

http://www.lurcher.org/nick/heater/2a3-I.wav
http://www.lurcher.org/nick/heater/2a3-V.wav

--
Nick

Well, there is a difference, but it is very slight. The current source
results in a slight increase in 100Hz hum, but that is down around the
-90dB level so probably inaudible.

For the signal itself the current source has slightly increased second
and third harmonic; the 9th and tenth are a bit lower, then above
that, things are quite different, but at -100dB, probably inaudibly
so. The second and third harmonic change stacks up the wrong way for
the increased linearity with a current source theory, I'm afraid.

Here is a WAV containing both - one second of each. Play it as a
continuous loop and see if you can hear the changes.

http://81.174.169.10/odds/v&i.wav

And the harmonic and hum analyses:

http://81.174.169.10/odds/i_source.gif
http://81.174.169.10/odds/v_source.gif

This all leaves me thinking that any difference is below audibility
and we have a case of minds convincing themselves they have heard
something they haven't. Back to the good old double blind, I'm afraid.

d

--
Pearce Consulting
http://www.pearce.uk.com

What's your favourite voltage regs?
 

Don Pearce wrote:
On Mon, 21 Jan 2008 22:03:05 +0000, Nick Gorham
wrote:


If there is anything of interest (I haven't look that hard at the
results myself yet), I can throw a three pin reg as a voltage reg tommorow.

http://www.lurcher.org/nick/heater/2a3-I.wav
http://www.lurcher.org/nick/heater/2a3-V.wav

--
Nick


Well, there is a difference, but it is very slight. The current source
results in a slight increase in 100Hz hum, but that is down around the
-90dB level so probably inaudible.

For the signal itself the current source has slightly increased second
and third harmonic; the 9th and tenth are a bit lower, then above
that, things are quite different, but at -100dB, probably inaudibly
so. The second and third harmonic change stacks up the wrong way for
the increased linearity with a current source theory, I'm afraid.

Here is a WAV containing both - one second of each. Play it as a
continuous loop and see if you can hear the changes.

http://81.174.169.10/odds/v&i.wav

And the harmonic and hum analyses:

http://81.174.169.10/odds/i_source.gif
http://81.174.169.10/odds/v_source.gif

This all leaves me thinking that any difference is below audibility
and we have a case of minds convincing themselves they have heard
something they haven't. Back to the good old double blind, I'm afraid.

d


Well, just out of interest, I will try and put an actual voltage reg
together tonight, while the rest is on the bread board. Amd maybe check
the freq response using all three methods.

Because with respect, what we seem to have done here, is start with an
assertion that A is better than B, thought of a reason why this could be
so, then created a C that should mimic that process. Compaired A and C,
found no difference, and declared that A is not different to B. It could
just as simply be the case that the reason we have thought of isn't
valid, so C isn't the correct test to do.

--
Nick

What's your favourite voltage regs?
 

On Tue, 22 Jan 2008 08:07:22 +0000, Nick Gorham
wrote:

Don Pearce wrote:
On Mon, 21 Jan 2008 22:03:05 +0000, Nick Gorham
wrote:


If there is anything of interest (I haven't look that hard at the
results myself yet), I can throw a three pin reg as a voltage reg tommorow.

http://www.lurcher.org/nick/heater/2a3-I.wav
http://www.lurcher.org/nick/heater/2a3-V.wav

--
Nick


Well, there is a difference, but it is very slight. The current source
results in a slight increase in 100Hz hum, but that is down around the
-90dB level so probably inaudible.

For the signal itself the current source has slightly increased second
and third harmonic; the 9th and tenth are a bit lower, then above
that, things are quite different, but at -100dB, probably inaudibly
so. The second and third harmonic change stacks up the wrong way for
the increased linearity with a current source theory, I'm afraid.

Here is a WAV containing both - one second of each. Play it as a
continuous loop and see if you can hear the changes.

http://81.174.169.10/odds/v&i.wav

And the harmonic and hum analyses:

http://81.174.169.10/odds/i_source.gif
http://81.174.169.10/odds/v_source.gif

This all leaves me thinking that any difference is below audibility
and we have a case of minds convincing themselves they have heard
something they haven't. Back to the good old double blind, I'm afraid.

d


Well, just out of interest, I will try and put an actual voltage reg
together tonight, while the rest is on the bread board. Amd maybe check
the freq response using all three methods.

Because with respect, what we seem to have done here, is start with an
assertion that A is better than B, thought of a reason why this could be
so, then created a C that should mimic that process. Compaired A and C,
found no difference, and declared that A is not different to B. It could
just as simply be the case that the reason we have thought of isn't
valid, so C isn't the correct test to do.

Well, not really. Putting the cap across the heater terminals does
indeed force the drive into voltage mode, so test C is fair from that
point of view. If condition B creates a different set of results, then
I think we are entitled to ask if there is a problem in the
implementation of B - has it been done reasonably.

I'm looking forward to the result, though. Adding a frequency response
test is a good idea.

d

--
Pearce Consulting
http://www.pearce.uk.com

What's your favourite voltage regs?
 

"Nick Gorham" wrote in message
...

Because with respect, what we seem to have done here, is start with an
assertion that A is better than B, thought of a reason why this could be
so, then created a C that should mimic that process. Compaired A and C,
found no difference, and declared that A is not different to B. It could
just as simply be the case that the reason we have thought of isn't valid,
so C isn't the correct test to do.


Indeed. The original assertion was that DHT amplifiers with current-sourced
filaments sound better than those with voltage-sourced filaments. I've no
idea how this was first established, how comparable the amplifiers were in
other respects, what the test conditions were, and most importantly *who*
decided that. Only a listening test can really establish whether there is an
audible difference, but such tests are not easy to run.

It is unfortunately the case that human perception is influenced by what
that person believes, I gather that in a recent test wine-tasters rated a
particular wine as tasting better when told it was an expensive vintage than
when told the same wine was cheap plonk. The same principle applies here,
tell people that A sounds better than B and the chances are high that they
will agree, even if A & B are exactly the same. The more "authority" the
person making the claim of difference has the more true this is. Finally if
"everyone" says that A is better than B it takes a really determined
individual to disagree.

This is why only double-blind tests can be relied on to give meaningful
results.

David.

What's your favourite voltage regs?
 

"Jim Lesurf" wrote in message
...
In article , David Looser
wrote:
"Jim Lesurf" wrote in message
...

*Not* the resistance of the valve between its heater
terminals. The point of the resistors being to reduce any effect of
the PSU not being a perfectly floating one.

Why should the PSU *not* be a perfectly floating one?.

Because in reality the PSU will exhibit parasitic capacitance,
inductances,
etc. to its surroundings. For example parasitic capacitance via the
transformer windings (or electrostatic screen if present), and via the
wires. I'm afraid that in the real world you are unlikely to find a
perfectly floating PSU. Just ones which may sufficiently well isolated for
a given use. So the effects may be too small to worry about in some cases.
But that does not mean they don't exist, or can never have a significant
effect.


As I pointed out before we are talking audio here, not HF. The most
significant effect will be capacitance to ground from the PSU and it's
wiring, and since this will be in parallel with a low-value resistor and
probably a high-value capacitor as well the effect will be truly negligible.


I had assumed you would be aware of this, and would have realised that we
were talking about different issues.

We do seem to be. I'm talking about common-cathode audio amplifers, you seem
to be talking about HF amplifiers with signal applied via the cathode.

If you have built and used PSUs you
will, I assume, be aware of possible problems with things like
interference
getting through them, various kinds of parasitic, and how to deal with
this.


I have built many PSUs over the years for all sorts of applications so I am
well aware of those issues, and also when they can safely be ignored.

I suspect you have misunderstood the point that were made,

Whilst it seems to me that your analysis of what is going on is totally
flawed.

Well, IIUR, the 'flaw' seems to be that I analysed what Andy and Nick were
talking about. Indeed I have had emails to that effect. However maybe we
are all out of step except for yourself. :-)


If Andy or Nick want to agree with you that I am "out of step" they are more
than welcome to do so via ukra, I'm afraid that I'm not prepared to accept
hear-say evidence about that.


As I have pointed out repeatedly, though, I have never built or tested one
of the DHT audio amps, so can't comment on how significant these effects
may be in them. Can only point out that they exist. FWIW I have
encountered
them in power tube PSUs of the kind I mentioned where they may affect the
control of the tube when using something like a lock loop.


Which again is a totally different situation

David.
..

David.