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Re: What's the single ended deal, anyway?

2/12/2000 2:50 AM
Re: What's the single ended deal, anyway?
What is the reason for not wanting parallel tubes?  
2/13/2000 4:17 AM
Jimmy Page
There are very small phase differences between parallel tubes. When the output from each tube is combined to form a single signal, there is an slight increase in inter-mod distortion compared to using a single tube. It's hardly noticable but it does exist. Personally, I wouldn't worry about it.  
Some tubes, like the venerable 2A3, for example, are available in single plate and bi-plate versions. The bi-plate is really a parallel tube built into a single envelope and hence is inferior to the single plate version. This is well known stuff for afficianados of tubes like the 2a3 and is accordingly reflected in price differences between the two versions. Personally I don't care but some people take this kind of stuff seriously.  
Your pal,  
2/14/2000 8:25 AM

"When the output from each tube is combined to form a single signal, there is an slight increase in inter-mod distortion compared to using a single tube."
I wouldn't worry about it either.  
But, I'd really like to hear your definition of intermodultation distortion products and how it applies to push pull audio circuits using an iron core center tapped transfomer to mix a single signal in comparsion to a SE output and an iron core non-center tapped output transformer used to mix a single signal.  
Phase differences, single signal, intermodulation distortion....  
Anybody can throw this terminology crap around with inpunity, I guess.  
2/12/2000 9:31 PM
Ken Gilbert

"Loss of dynamic range is not necessarily bad. Some people call it compression. Single ended amps just don't respond with instantaneous bursts of power the way PP does. In other words, they tend to carry less transient information. Again not necessarily bad, depending on what your looking for. Great for blues amps."
Whoah, hold on a minute here...  
By what mechanism do you suggest this "compression" takes place? I've never heard this opinion espoused by anyone else before. Perhaps you are basing this on the fact that SE amps are historically much lower-powered than their PP bretheren.  
As far as conveying less transient information, I'll simply heartily disagree with you. In fact, in terms of detail, I've heard many learned people tell me something about PARALLEL tubes messing with the resolution. In short, the differing dynamic characteristics of the tubes tend to cloud the truely low-level information.  
A PP amp, although it doesn't look like it, is actually two tubes in parallel, and would thus obscure the detail that could be resolved if there were only a single active element. The only topology that can work with a single active element is our old friend, single ended.  
2/13/2000 3:46 AM
Jimmy Page
SE requires your amp to be biased in class A. Most PP amps are biased slightly before cutoff and operate near class B. Since a class A amp operates in a higher portion of the linear curve, it's got less headroom than a PP amp using the same pair of tubes. Because of lower headroom, high level transients tend to flat top more under SE than under PP. This gives rise to a perceived compression effect.  
Secondly, SE amps tend to have an abundance of even harmonics as compared to PP. Even harmonics are mushier sounding than odd harmonics. Mushy harmonics obscure detail more than dissonant harmonics. In a strange way, the effect of harmonic mushiness reinforces the low headroom compression effect perceived by the listener.  
Psychoacoustically, even harmonics sound warm. Warmth in sound is associated with slurring of detail rather with the the enhancement of detail. Contrary to popular belief, even harmonics are not always better than odd harmonics. It depends on what sound you're looking for. I personally like SE amps and their mushiness but they are not for everyone.  
Your pal,  
2/13/2000 4:07 PM
Gee, you know what? Throwing in discussions of operating points and bias has nothing to do with toplogy.  
What you're insinuating is that a 30W PP amp will be louder and punchier than a 30W SE amp. That's simply not true.  
How about discussing how the transconductance increases with increasing plate current? That's the opposite of compression... ask any player around here if the amp sounds more touch sensitive when you crank up the Ip. I'll bet the answer is a resounding "yes."  
Your pal,  
John Bonham
2/13/2000 8:43 PM
Jim Wheeler

If ya wann find out for yourself - plug into an old Champ Amp.  
you can buy SE kits from Nothin' Shockin' for a nominal fee. Nice sound, low power, excellent education. Lemme know and I'll dig up the URL, or gor to ebay and search for "Class A", Andy sells a lot that way.
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