Apogee mini dac or Benchmark DAC1
 

Andy Evans wrote:

you still have a DAC feeding the tube stage (if I have interpreted you
correctly) which can then (as you say) feed the grid of the tube
amplifier with DC as well
as the analogue signal.

I think you've misunderstood this. The DAC - or my DAC to be precise -
outputs an analogue signal of about 1.3v AC with about 2v DC
superimposed on it. To eliminate the DC one could put a capacitor at
this point (i.e. "something" on the end of it) But what I'm saying -
and what my setup does - is to put the analogue signal (both AC signal
and DC) directly into the grid of the triode of what we should call the
"line stage". At the output of this line stage, which has some gain, we
have the usual coupling cap

So, you're saying it's OK to have a cap here but not *there* ?


and volume control. You can't put the
volume control in front of the grid because of the DC on the signal,
but the tube stage rather neatly incorporates the 2v DC into the bias
requirements of the stage. To be precise, my DAC has a balanced output
into the grids of a diff pair with a CCS under it, so the CCS
determines the current through the stage.

Meaningless waffle, selective ignorance and obfuscation.

Graham

Apogee mini dac or Benchmark DAC1
 

Andy Evans wrote:

The advantage of a tube stage is that the output with DC on it can be fed
directly into the grid of the tube, and the DC included in the biasing.

Are you claiming this is impossible for non-tube stages? JLS

Bad choice of words - I can see what you mean. Let me rephrase "it's
convenient to go directly into the grid because you don't need a
coupling cap at this point". You're the expert at ss, and I'd be
delighted to see a schematic for a ss solution with no coupling cap.

It's trivially simple.

Graham

Apogee mini dac or Benchmark DAC1
 

On Sat, 09 Sep 2006 16:42:49 +0100, Eeyore
wrote:

There is precious litle 'modern' about any valve circuit. I learnt on
them btw.

I've no doubt you know valves from ( ?50s, 60s?, 70s?), but you'd be
very surprised at how much things have changed.

There has been no change whatever. Tube technology peaked in the early 50s.

Not the function of the
triode itself, which is well known, but the support circuitry is now
quite complex - cascode active loads, constant current sinks etc. - a
whole cuisine of modern ss devices and traditional stuff like glow
tubes. It really is "nouvelle cuisine" if you pardon the expression.
We're not talking Mullard circuits with EF86s and ECC83s any more.

Indeed, toobists now use semiconductors to help cure the inherent flaws of
thermionic devices.


Well, make your mind up! Either valve circuits have changed or they
haven't.

Apogee mini dac or Benchmark DAC1
 

Andy Evans wrote:

But of course, some DACs may be made so as to alter the results in
specific ways. Hence someone might then prefer this to a result
indistinguishable from the original prior to ADC conversion. :-)

I see all the signs of you being rather sly here, and if I can rephrase
this it looks like "some people prefer colourations to accurate sound",

That would seem to be an accurate statement.


which we know from a litany of posts about valve equipment. No, I'm
speaking about instrumental timbre which appears to be more faithful
rather than less. I can only ask people posting on this subject to hear
this for themselves, since neither scientific method nor adjectives
will substitute for the actual sound itself.

Since musical timbre entirely *depends* on rich harmonics to sound good, it's
hardly surpising then that a toob will 'flatter' them is it ?

Graham

Apogee mini dac or Benchmark DAC1
 

Andy Evans wrote:

Eeyore wrote:
Jim Lesurf wrote:

In article .com,
Andy Evans wrote:
Precisision and linearity can be measured scientifically and
objectively. The remainder are in the ear and brain of the listener.

So? The purpose of the DAC is to listen to it.

The purpose of the DAC is to reconstruct an analogue waveform as defined by
the series of sample values.

Unforunately due to Mr Evans half-assed method of quoting you mixed his comments
with mine.

I did indeed say " Precisision and linearity can be measured scientifically and

objectively. The remainder are in the ear and brain of the listener ".

And he said " So? The purpose of the DAC is to listen to it. "

Graham

I really have to stand up for my quoting here. The above looks like the
Battle of Agincourt on my AOL system

AOL ? Good God !


- enough arrows to bring down the
cream of the French aristocracy. Hopeless for a quick comment. In
addition although the first comment is attributed the rest are not. And
even worse, AOL hides the whole previous text so you have to click on
it to see it al all - one more click stroke. In ordinary conversation
(you can imagine the oak dinner table and the bottle of Chablis) one
would say something like "to pick up your point about "skin deep" I
believe it was S J Perelman who said that after the USA, even though
politeness in Britain was only skin deep, that was deep enough for
him". One would not repeat the whole previous conversation word for
word. You may see newsgroups as a literary experience, but I consider
them as essentially conversation, and I believe that picking up on a
point somebody makes is quite enough in the omnipresent information
overload of the Net.

I suggest you use a decent 'newsreader'. Your problems are entirely of your / AOL's
own making.

Graham

Apogee mini dac or Benchmark DAC1
 

Laurence Payne wrote:

On Sat, 09 Sep 2006 16:42:49 +0100, Eeyore
wrote:

There is precious litle 'modern' about any valve circuit. I learnt on
them btw.

I've no doubt you know valves from ( ?50s, 60s?, 70s?), but you'd be
very surprised at how much things have changed.

There has been no change whatever. Tube technology peaked in the early 50s.

Not the function of the
triode itself, which is well known, but the support circuitry is now
quite complex - cascode active loads, constant current sinks etc. - a
whole cuisine of modern ss devices and traditional stuff like glow
tubes. It really is "nouvelle cuisine" if you pardon the expression.
We're not talking Mullard circuits with EF86s and ECC83s any more.

Indeed, toobists now use semiconductors to help cure the inherent flaws of
thermionic devices.

Well, make your mind up! Either valve circuits have changed or they
haven't.

That's a hybrid circuit not a tube one.

Such improvements as exist are due to semiconductor use. Tubes themselves
haven't changed in any significant way since the advent of new types with radar
for the most part ( and also UHF TV ).


Graham

Apogee mini dac or Benchmark DAC1
 

On Sat, 09 Sep 2006 18:09:31 +0100, Eeyore
wrote:

That's a hybrid circuit not a tube one.

So what? What DO you allow? Resistors, caps....?

Apogee mini dac or Benchmark DAC1
 

Well, make your mind up! Either valve circuits have changed or they haven't.

That's a hybrid circuit not a tube one.

It's my experience that "hybrid" amplifiers have both tube and ss
amplification stages, not ss current sinks, active loads etc. It would
be deviating from common practice to call a circuit where the
amplification stages were all tube a "hybrid" circuit, although clearly
as you say the technology is hybrid.

Apogee mini dac or Benchmark DAC1
 

So, you're saying it's OK to have a cap here but not *there* ? EY..

What I'm saying is you eliminate one cap by DC coupling to the grids of
the amplification stage (I believe Jim says you can do this with ss
devices, which is absolutely fine). The conventional way would be
capamplification stagecap.


To be precise, my DAC has a balanced output into the grids of a diff
pair with a CCS under it, so the CCS determines the current through the
stage. AE


Meaningless waffle, selective ignorance and obfuscation. EY...

Well it may be meaningless to you, but I've built four of these so far
and done a range of comparative listening tests over the last 6 months
with a number of colleagues (engineers, if that makes a difference). If
I built them in ignorance and hid them under a tarpaulin I must have
been bloody lucky they all worked.

Apogee mini dac or Benchmark DAC1
 

Laurence Payne wrote:

On Sat, 09 Sep 2006 18:09:31 +0100, Eeyore
wrote:

That's a hybrid circuit not a tube one.

So what? What DO you allow? Resistors, caps....?

Are you being simply obtuse or actually monumentally obtuse ?

Graham