Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. New: view Recent Searches.
New: visit Schematic Hell!
The sunn still shines online!

Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  

Re: OT impedance

6/30/2004 9:24 PM
SpeedRacer Re: OT impedance
it is what I meant in that not knowing your (or anyone elses) comfort level with the idea I wanted to present an example of IM that anyone with a guitar could test and experience.  
re - phantom fundamentals - the funny thing is that the upper harmonic series describes teh lower tonic (fundamental) and your brain will create it. By an odd coincidence my mother was part of the research into this phenomenon at U. Mich back when. There are old Caruso records where you'd swear you're hearing the bass, but it's not on the recording.. but the overtones which describe it *are*. It's pretty wierd..  
The extra IM tones you get on overdrive in a good amp give it (IMHO) much of the desired character, the 'swirl' or whatever you want to call it when those added tones are musically related (1,3,5, 8av etc)
6/30/2004 8:21 AM
bob p
"In THEORY, evens will cancel in a balanced push-pull output section. There is lots of cool math to prove that out.. in reality no output section is so well balanced - certainly not when being overdriven like crazy.. "
funny you sould mention this. i've just resurrected an old Silvertone from the trash and it has a "standby" circuit that shorts the outputs from the PI. although this does a pretty good job of quieting the amp, you can still hear the unbalanced portion of the signal (imperfect phase inversion) reaching the output section. it would be interesting to do this type of listening test for balance on the other side of the power tubes.
6/30/2004 9:54 PM
Carl Gigun
sound of even and odd harmonics
There are a few java applets on the web that let you play with harmonics to see how they sound and look on a scope. This one is on a guitar specific site:  
There's also a simple experiment you can do right on your guitar. Where you pick along the string determines which harmonics will be excited.  
Pick an open string right over the 12th fret and you will eliminate all even harmonics, leaving only the fundamental and odd harmonics. (I'm not talking about playing "harmonics", just pick normally). This has a unique somewhat hollow sound. Picking just an inch off to either side mostly eliminates this effect.  
Picking at a point 1/3 of the way along the string eliminates all odd harmonics. Picking at other points can set up mixed situations - picking at 1/4 will excite the fundamental and the first even harmonic, but no other evens and lots of odds etc.  
have fun experimenting,  
-Carl Gigun
7/2/2004 3:51 PM
Shea Wow!
That applet is a blast! It really helped me make a mental connection between the stuff I've read about harmonics, the shapes of waveforms on an oscilloscope, and how they actually sound.  
Based on my noodlings with that applet, I think it's a gross oversimplification to say even harmonics sweeten the tone and odd order harmonics make it harsh.  
What I never knew before is that the 2nd through 5th harmonics all together make up a major chord. The 3rd harmonic is the fifth tone in the chord, and the fifth harmonic is the third tone.  
With some amps that I've found particularly sweet, I thought I had heard a harmonic overtone that sounded like a fifth, but I could never correlate that to what I knew about harmonic distortion gets generated in the amp. Now I see it was 3rd-order harmonics.  
6/30/2004 10:26 PM
Re: OT impedance
"If I apply the notion of harmonics based on music theory the "even" ones are all octaves of the fundamental and can add brightness without producing harshness and the "odd" ones can add complexity, but as you increase higher order odd harmonics things can become harsh (approaching square wave clipping). Is this more or less correct?"
All the harmonics that are powers of two (i.e., 2nd, 4th, 8th, etc.) are octaves. The 6th harmonic is actually the octave of the 3rd, and the 10th is the octave of the 5th.  
Judicious addition of low-order even harmonics can make things sound "sweet", but too much can get a bit abrasive....  
Higher order odd harmonics bring "harsh" and "edgy" with them, and are responsible for most of the difference in a trumpet's sound when going from pianissimo to fortissimo--the acoustic power is virtually the same!  
C ya,  
<<First Page<Prev Page 3 of 3