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Valve amplifiers

E

esox

Jan 1, 1970
0
Another little question while on the subject.
Long time since I was at college but I remember THD as being third
harmonic distortion. When I looked it up on the net it came back as
total harmonic distortion.
Have I been drinking too much?
 
B

Barry Jones

Jan 1, 1970
0
esox said:
Another little question while on the subject.
Long time since I was at college but I remember THD as being third
harmonic distortion. When I looked it up on the net it came back as
total harmonic distortion.
Have I been drinking too much?
I certainly hope so!

I always took THD as total harmonic distortion. I can't imagine why
anyone would be interested particularly in the distortion caused by the
third harmonic, unless you were creating a Hammond organ or such.
 
A

Andrew Howard

Jan 1, 1970
0
Barry Jones said:
I noticed the same sort of thing in tube vs. solid state stereo amps or
receivers. Since they drove the same speakers, quality of speakers was
not an issue.

I'd be interested to see how the companies defined their maximum output
wattage.

You can drive the amp until there is, say 1% harmonic distortion, and
call that the max wattage. You can drive the amp until there is 5% or
10% distortion, or more, and define that as your max wattage. It may not
be usable wattage, but it sure looks good on the label.

Since tube (valve) amps are mostly older models, they may have been more
inclined to rate their products more conservatively.


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...

Andrew Howard
 
B

Bob Masta

Jan 1, 1970
0
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". 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.
But they got lots-o-watts for the first couple of cycles of output!
I wouldn't be surprised if guitar amp makers got caught up by
this craze as well,

Best regards,


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
 
K

Kevin Aylward

Jan 1, 1970
0
Bob said:
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
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
P

phaeton

Jan 1, 1970
0
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.
 
K

Kevin Aylward

Jan 1, 1970
0
phaeton said:
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
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
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