Valve amp (preferably DIY) to drive apair of Wharfedale Diamond II's
 

In message , Stewart
Pinkerton writes
The series fuse did ring big alarm bells with me also. I have in fact
built several amplifiers which had no internal protection circuitry,
and relied on such a simple, series fuse for survival of the speakers
(or the amp if shorted). However, since you can't buy gold-plated
fuses or fuseholders (now there's another 'audiophool' market niche
for Russ Andrews!), the contacts absolutely *will* tarnish, and I
measured more than 0.5% distortion at low levels after a year or so of
one amp's installation, instantly cured by soldering in the fuse. I
can't say I measured any problems due to dynamic resistance, but it's
a good pint, since a fuse *must* have significant resistance in order
to function, and this is in itself a bad thing. Nowadays, I put fuses
in the power supply, not the signal circuit.

Believe it or not, the big Maplins in Nottingham has gold-plated fuse
holders for the car-audio crowd.
--
Chris Morriss

Valve amp (preferably DIY) to drive apair of Wharfedale Diamond II's
 

"Stewart Pinkerton" wrote in message
...
On Wed, 24 Nov 2004 01:52:31 +1100, Patrick Turner
wrote:

I even know the GSP co-ordinates! :-)

**GSP? A Scottish compass?

:-)


--
Trevor Wilson
www.rageaudio.com.au

Valve amp (preferably DIY) to drive apair of Wharfedale Diamond II's
 

"Kurt Hamster" wrote in message
...
On Sat, 20 Nov 2004 10:26:39 +0000, Chris Morriss used
to say...

ignorance of English grammer

cough




:-)


(Yer hafta fekkin' larf...... :-)

Valve amp (preferably DIY) to drive apair of Wharfedale Diamond II's
 

In message , Keith G
writes

"Kurt Hamster" wrote in message
...
On Sat, 20 Nov 2004 10:26:39 +0000, Chris Morriss used
to say...

ignorance of English grammer

cough




:-)


(Yer hafta fekkin' larf...... :-)




Though I see you went very quiet about your ignorance of the difference
between two little verbs; perhaps one of your cronies let you know you
were making a fool of yourself eh?
--
Chris Morriss

Valve amp (preferably DIY) to drive apair of Wharfedale DiamondII's
 

Patrick Turner wrote:


But still there are sound differences, and tubophiles don't mind that this
difference exists with different tube choices; it makes life more interesting,
and choice can place an amp system amougnst the extraordinary
rather than the mundane.

To paraphrase someone, you have to freaking laugh!


At least mediocity and mundanity is what many tubophiles hear with SS
that uses so much loop NFB that

just admit you tubophiles prefer tube amps. There is no need to air your
prejudices against SS amps.


any character of the transistors is
entirely smothered, but probably just as well,

character? what character?


Many SS amps manage to sound harsh, raw, and just plain wrong.

Fine, thats what *you* think. But you make and sell tube amps, don't you?


The insecure and emotionally wobbly man has to disect and measure everything,
and is dominated by his knowledge "of the facts", and he'd not be able to
make subjective assessments about wine, art, music, tubes, women, in the same
way the more relaxed and together man would make, and be able to share with other
men who know also experience the same colours that are there to be seen.

A bit sexist here, don't you think? non gender specifc terms are the
norm these days like "The insecure and emotionaly wobbly person" ...

Unless, you were specifically refering to men.

Wine, art and music is subjective. Engineering isn't.

Valve amp (preferably DIY) to drive apair of Wharfedale DiamondII's
 

Kurt Hamster wrote:

On Tue, 23 Nov 2004 17:05:33 +0000 (UTC), Stewart Pinkerton used
to say...




You think bull**** technical claims should *not* be corrected?


It all depends one the reasons for the correction doesn't it. The
regulars in here are well aware of your reasons.

Sorry, I am new here. What reasons would those be?

Valve amp (preferably DIY) to drive apair of Wharfedale Diamond II's
 

On Wed, 24 Nov 2004 14:30:04 +1100, Tat Chan
wrote:

Kurt Hamster wrote:

On Tue, 23 Nov 2004 17:05:33 +0000 (UTC), Stewart Pinkerton used
to say...

You think bull**** technical claims should *not* be corrected?

It all depends one the reasons for the correction doesn't it. The
regulars in here are well aware of your reasons.

Sorry, I am new here. What reasons would those be?

This should be interesting! :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Valve amp (preferably DIY) to drive apair of Wharfedale Diamond II's
 

Stewart Pinkerton wrote:

On Mon, 22 Nov 2004 17:26:15 +0000 (GMT), Jim Lesurf
wrote:

In article , Patrick Turner
wrote:

I just built a bjt amp with 10 output devices, each capable of 15 amps,
so that's a peak current ability of 75 amps.

It will never be needed, and never be used. Maybe the amp sounds better.
The owner wanted current ability, so I give it to him.

But I insist he use a 5 amp fuse between the output and speaker
terminals.

Personally I would avoid using a fuse between the amp output and the
speaker. There are two reasons for this.

1) The fuse resistance changes as the fuse warms up. Hence under dynamic
conditions with music it places a time-varying resistance in series with
the amp-speaker. This tend may introduce time-varying modifications of the
frequency response.

2) More contacts in the path to the speaker. Hence more contacts that might
become tarnished.

I'd agree that neither of the above is likely to be serious in many cases.
However my preference is to avoid putting a fuse in such a location.
Indeed, Particularly if the customer asked for large current capability.
They may well want to use nasty loads at some point without having told me
about it.

The series fuse did ring big alarm bells with me also. I have in fact
built several amplifiers which had no internal protection circuitry,
and relied on such a simple, series fuse for survival of the speakers
(or the amp if shorted). However, since you can't buy gold-plated
fuses or fuseholders (now there's another 'audiophool' market niche
for Russ Andrews!), the contacts absolutely *will* tarnish, and I
measured more than 0.5% distortion at low levels after a year or so of
one amp's installation, instantly cured by soldering in the fuse. I
can't say I measured any problems due to dynamic resistance, but it's
a good pint, since a fuse *must* have significant resistance in order
to function, and this is in itself a bad thing. Nowadays, I put fuses
in the power supply, not the signal circuit.

I have soldered in rail fuse links after the 10,000 uF caps, and before the
smaller caps
connected closer to the bjt collectors.

The fuse at the output requires about 4 Kg of pressure to clip it with end on
force..
Unlike many fuse holders, the ones I have in there hold the fuse very tightly.

But you are right about soldering, its good.

I had the fuses in there while I tested and the thd caused by the fuses seemed
to be negligible.

I got active DC detection though.....so no worries.

Gold plated fuses and holders are cheaply available for the auto
audio market.

Patrick Turner.


--

Stewart Pinkerton | Music is Art - Audio is Engineering

Valve amp (preferably DIY) to drive apair of Wharfedale DiamondII's
 

Kurt Hamster wrote:
On Wed, 24 Nov 2004 14:30:04 +1100, Tat Chan used
to say...

Kurt Hamster wrote:

On Tue, 23 Nov 2004 17:05:33 +0000 (UTC), Stewart Pinkerton used
to say...

You think bull**** technical claims should *not* be corrected?


It all depends one the reasons for the correction doesn't it. The
regulars in here are well aware of your reasons.

Sorry, I am new here. What reasons would those be?

Simple really!

His own self-importance and desire to be noticed.

You are kidding, right?

UseNet is hardly the place to be noticed among audiophiles. I don't have the
stats, but I reckons web based forums would be the place to where most
(ignorant?) audiophiles hang out.

Self importance? Well, I have seen much worse behaviour on UseNet where the
knowledgable techies belittle and insult the technical ignorami (is that the
plural?).

Sure, one might get an ego boost by giving out advice or helping others learn,
but if the final result is a gain in knowledge by the people asking questions,
it can't be that bad, can it?

Valve amp (preferably DIY) to drive apair of Wharfedale Diamond II's
 

Stewart Pinkerton wrote:

On Wed, 24 Nov 2004 01:52:31 +1100, Patrick Turner
wrote:

There simply isn't any reason why an amp must have a flat open loop voltage response.

Bull****, there are very good reasons.

It does mean that if the peak in OLR is at say 300Hz, then at
30 kHz, it might down 40 dB.

Therefore when global NFB is applied so that 60 db is in effect at 300 Hz, only 20 dB
is acting at 30 kHz, and at 300 kHz there is almost none.
This is what one wants.

No it bloody well isn't! You have very little feedback at 30kHz, so
you have a very good chance that there's more than 1 % HF IMD on say
29/30 kHz tones, which you might very well find on SACD, or in
distortion products from stupidly wideband vinyl carts. This may very
well be audible. This is definitely *not* what one wants!

But there are no significant signals from microphones at 29 or 30 kHz.


One does not want much NFB acting at seriously high frequencies, since
maintaining low distoprtion and low Ro
at 300kHz is useless, and very prone to making an amp very unstable.

Agreed, but maintaining good figures out to 30-50kHz *is* important,
not for THD but for anharmonic baseband IMD products, which are much
more audible than low-order THD - and can be very unpleasant.

Can't say I have ever heard of problems with 29 kHz and 30 kHz tones causing
serious 1 kHz tones to appear in the audio...



The first harmonic produced by a 20 kHz signal is at 40 kHz.
So NFB isn't needed at all at 20 kHz, were it not to keep the Ro
nice and low, but nearly all amps do have a varying Ro.
This can't matter much if the Ro is less than 1/10 of the speaker impedance.

See above. HF IMD most certainly *is* a problem, so good linearity to
at least twice the 20kHz audio bandwidth *is* important if the highest
sound quality is your aim.

20 dB of NFB at 30 kHz would be enough to tame most garbage at that F.



Tube amps can't accept so much NFB because of the phase shift caused by leakage inductance,
shunt inductances, and shunt capacitances, and miller C in the tubes ( also in bjt circuits ).

20 dB in a pentode amp is all one should aim for.

Actually, with any tube amp, the garbage can is what one should aim
for........ :-)

Well, I knew you'd say that, hope the can is big enough for a man about your size...



But its far easier to design the OLG that's -3 dB at 10Hz to 80 kHz.
This means the amount of NFB applied can be the same between the poles of the OLG,
and the Ro is more constant, but not as low as most SS amps.

It's easy enough to arrange that with SS amps also.

However, I haven't examined the design of
more than about 0.1% of the world's SS amps, so I bow to your having
carefully examined about ten thousand such circuits..............

Not 10,000, I'd go mad, but enough.

Yeah, riiiiiight................

snip self-advertisement by an amp salesman

So all this BS about mosfet capacitance screwing things up is just BS.

You're an agressive little ****, aren't you? Who said anything about
gate capacitance 'screwing things up'? I simply noted that it's
significant, and must be addressed in any competent design, as should
open-loop linearity in a BJT design.

I am not aggressive, but I would be assertive in the midst of the mosfet doubters,
always chiselling away at the mosfet edifice.

Count me out, my favourite power amps of all time are the Sumo
Andromeda III and the Adcom GFA 5802, while one cannot deny the sheer
technical accomplishment of the Halcro.

Halcro spent a shirt load in R&D, and have something to show for it.



All reactances both L and C have to be addressed in all amps, all the time, lest you
have smoke instead of music.
Capacitance is a problem at mainly the higher F.

No sher, ****lock! Luckily, L is also only a problem at high
frequencies in SS amps.

There is an art to applying gain tailoring in amplifiers, and very few ppl are aware of how
critical it is,
especially in tube amps.

Easier just to avoid tubes, if linearity and the ability to drive
normal high-quality speakers are your goals!

If you are happy in your avoidance, then I am pleased you know where you are.

I even know the GSP co-ordinates! :-)

Each unto their own. I see you wander around feeling lost most days... :-)

Patrick Turner.

--

Stewart Pinkerton | Music is Art - Audio is Engineering