Valve amplifiers

[Kevin Aylward]

Bob Masta wrote:

On Mon, 04 Apr 2005 06:06:22 GMT, "Andrew Howard"
ask.me@somewhere.net> wrote:


Don't forget the old display-the-peak-to-peak-instead-of-RMS trick.
That usually multiplies the actual figure by 140% or so (I think).

But the thing about the distortion is a good point. I once saw an
amp that was rated at "100W RMS", yet it started to distort at about
65-70W...


The other feature of some of those power amps of the ratings
wars of the '70s was "instantaneous power".

Did you not read my posts on this

The power supply
was underrated for the peak load, so as soon as the (smallish)
supply caps sagged after a few msec, the output would clip.

This isnt really "instantaneous power", its "average transient power"
during those ms.

RMS power really means "average power over a cycle". "Instantaneous
power", is the single instant VI product, that dont really mean much.
"Instantaneous power", would be the power at *max VI*, not average of
the cycle, and would normally be specified under *steady state*
conditions *after* the supply had sagged!!!

I doubt that many manufactures specified max power by a burst sine test.

Yeah, this is all a bit confusing aint it. "Instantaneous power" isn't,
and "average power" isn't necessarily long term average power, it might
be only the average power during the first few ms.

But they got lots-o-watts for the first couple of cycles of output!

Which is all that is required for clean guitar picks.

I wouldn't be surprised if guitar amp makers got caught up by
this craze as well,

As I explained in another post, capacitor size/cost can make this effect
automatic.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[Kevin Aylward]

phaeton wrote:

Oh dear....now don't get offended, but this is completely incorrect.
... I don't know of any other way of putting this to soften the
blow to your ego

No offense taken, ego is fully intact... In fact, I feel the need to
thank you for setting me straight.

Say Kevin, it sounds as if you play guitar or some musical
instrument(s) yourself, yes?

Yes. Some info on that is here http://www.anasoft.co.uk/band/index.htm

Music and electronics for music went hand in hand.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

esox wrote:

Hi
Guitar question.
It is said that a 30w valve amplifier is very loud compared to a
transistor amp. I've heard that 30w valve puts out more than 100w
tranny.
Why do they sound so loud?
I had thought it might be that they are often class A.
Any ideas?
Cheers

Is it that the distortion is more 'graceful' so you just push it
harder?
GG

 

[phaeton]

esox wrote:

Hi
Guitar question.
It is said that a 30w valve amplifier is very loud compared to a
transistor amp. I've heard that 30w valve puts out more than 100w
tranny.
Why do they sound so loud?
I had thought it might be that they are often class A.
Any ideas?
Cheers

First off, careful with this question. I've asked it several times
(not in this ng, but other places where electron-heads hang out) and
i've gotten a lot of response to the effect of "tube amps louder?
that's b.s.- watts are watts".

While "watts are watts" is definately true, my best scientific guess is
that tube amps have a much broader and more powerful frequency response
in the midrange, which means they put out more of the waveforms that
the human ear can pick up best. SS amps can put out the same power
(watts) but the frequencies will always be different, some of which are
in the frequencies that the human ear can't hear so well, some more of
which might be "wasted" in freqs that we can't hear at all (above 20khz
or below 20hz).

There is also something like an empathetic vibration amongst harmonics
that tube amps are better at creating- i.e. the whole even-order /
odd-order harmonics difference. SS amps tend to create more odd-order
harmonics that clash and fight with each other, so some of the power is
affected that way before it even gets to the speaker.

(I don't have any references to data or any better explanation to hand
out, so it is very possible that someone may come along and correct
me.)

I don't know about the 30w Tube == 100w Transistor comparison (this is
like saying 1 Mhz on a Mac == 4 Mhz on a PC... too much other things to
consider)...

But i will say that my 5W Reverend Goblin (All-tube) will completely
blow away my 45W Peavey Pacer (All Solid-State). Yeah we're talking
different qualities of amplifier and different price points, but the
proof is still in the puddin' :-D

If there are any non-believers, i usually suggest them to go into a
music store, and ask one of the sales d00ds to plug into a 30W or 60W
Peavey Classic or Fender Blues Deville with the eq set flat. Let the
non-believer twist the gain and volume knobs around. Then have them go
to a Solid State amp of the same wattage and repeat. Another good
comparison is a 10W Champ vs. just about any SS amplifier on the floor
under $300.

Nobody's ever done it tho... or at least has told me afterwards..

 

[phaeton]

Well yeah, then there's compression- natural (tube) or otherwise
(compressor/limiter), and that plays a big part too... gently clipping
the peaks off the louder stuff so you can bring the softer stuff up...

Sometimes i find modern music mixes, where everything is squashed to be
somewhat fatiguing to the ear... but that's another subject for another
rainy day

 

Suggested reading:

http://milbert.com/tstxt.htm

 

[phaeton]

Oh dear....now don't get offended, but this is completely incorrect.
....
I don't know of any other way of putting this to soften the blow to
your ego

No offense taken, ego is fully intact... In fact, I feel the need to
thank you for setting me straight.

Say Kevin, it sounds as if you play guitar or some musical
instrument(s) yourself, yes?

P.S. I wouldn't be any better at giving play tactics for American
Football.