Re: Understanding Amps

Carl wrote:
Joey Goldstein wrote:
Dave wrote:
rpjazzguitar wrote:
I have a Boogie Mark III. It was the screaming distortion amp of
its era.

And yet, it also produces a gorgeous jazz tone. If it weighed
several hundred pounds less, jazz players would use it.
It's also a 100W amp.


I had one of the early MKIII's that had the Simul-Class power section
with the outer two power tubes wired in "Class A" triode. It had 15
watts for the outer tubes and 60 watts from the inner power tubes
running in Class A/B.
In Simul-Class mode, with all 4 power tubes on, it was rated at 75
watts. The first gig I tried to use it on, the day I bought it, was
an outdoor gig on the street at the Beaches Jazz Festival with a very
loud drummer, and it was breaking up way too early.
The Class A tubes are designed to break up early.

Forgive me for questioning this last statement, and your experience, and for perhaps getting too technical, but I believe that class A amps operate over the most linear part of a signal and that amps operating as class A introduce no clipping of the output signal at all, providing the most exact reproduction of the input signal. If I understand this correctly, then class A amps should provide the least amount of distortion, no matter what volume you play them at. The most fanatical audiophiles desire class A operation for their audio systems for this reason.

That may be true, but they're not driving their audiophile amps into distortion like guitar players do.

I don't know the technical reasons for it, but Class A *tube* amps for guitar players are generally designed for players who like the sound of power amp distortion.

If I'm right, then the OP's 35 watt Class A amp should provide a lot of volume with minimal clipping (ie. distortion) of the signal, certainly a lot less distortion at high volume then the more common class AB design. As someone else pointed out, any distortion would be introduced by the guitar's volume being up too high and/or too high-gain tubes being used in the pre-amp section. Lower the guitar's output in some way (ie. by either lowering the volume control or changing the pre-amp tubes) and, if you turn that class A amp all the way up, you should have a perfectly clean signal. I am aware that many guitarists like to replace their 12AX7 pre-amp tubes with 12AT7s or 12AU7s for this very reason.

That all said, I'll confess that my electronics theory (once strong) is now weak, though I did re-check some information before I posted this. I'm certainly open to correction and re-education, so please don't hesitate to enlighten me! :-)




--
Joey Goldstein
<http://www.joeygoldstein.com>
<http://homepage.mac.com/josephgoldstein/AudioClips/audio.htm>
joegold AT primus DOT ca
.

Relevant Pages

  • Re: Distortion in tube amps, Re: Thanks to Andre Jute
    ... not a description of the sound quality produced. ... > Not many people who dissmiss tubes want to answer this question. ... > made much more volume per watt, and in fact, it was the speaker distortion ... > So if tube amps that are 60 years old and if the ones made now ...
    (rec.audio.tubes)
  • Re: Les Paul and a Marshall? I dont get it.
    ... 900's have the majority of distortion ... as was necessary to get the power tubes to clip. ... JCM800 applies to DIFFERENT models of amps, ... What is closer to insane is spending a mint on a Head, Mods, Pedals, Power Soakers. ...
    (alt.guitar)
  • Re: Sell Your Name
    ... Contrary to what a lot of younger players think, Leo liked Western Swing ... the distortion was basically the side effect of using ... amps and they distorted because of their shortcomings (economy ...
    (alt.guitar)
  • Re: Distortion in tube amps, Re: Thanks to Andre Jute
    ... >Not many people who dissmiss tubes want to answer this question. ... There *are* tube amps which are extremely linear, ... sound just the same as any other highly linear SS amp, ... needs to have that distortion level at 2 watts. ...
    (rec.audio.tubes)
  • Re: Distortion in tube amps, Re: Thanks to Andre Jute
    ... >>Not many people who dissmiss tubes want to answer this question. ... > There *are* tube amps which are extremely linear, ... > sound just the same as any other highly linear SS amp, ... > needs to have that distortion level at 2 watts. ...
    (rec.audio.tubes)