I've been doing some reading about amplifier design and I'm seeking to understand how this stuff works.
Some things I've read:
Even harmonics are favored and more pleasing to the ear (various websites like mercury magnetics along with hifi amp guru Morgan Jones).
Odd harmonics are more pleasing to the ear (various guitar related websites).
The EF86 pentode creates odd harmonics like power tubes do and this is one reason it sounds good in the front end. However, M. Jones says it sounds bad because it creates odd harmonics.
Jones also asserts that the EF86 suffers from partition noise when compared to a 12ax7. I've never noticed my Route66 to be noisy, quite the opposite, I find it very quiet. Is partition noise something that needs to be heavily attended to in guitar amplifier design?
Anyone know, or maybe nobody knows, if it's even or odd that's more favored in guitar overdrive?
This is my opinion and I'm not an expert so take it for what its worth. My experience with EF86s is they can be noisier than 12AX7 depending on the individual tube brand. New Sovteks I have are quiet, but NOS Daria Miniwatt and Mullard samples I have are much noisier. But the Mullard sounds gorgeous! Lots of mids with a smooth top. Placing EF86s in the first gain postion will have that noise multiplied through the amp as the gain and noise are cascaded in each subsequent stage. Amps that only have the one gain stage (Z28) are less prone to noise issues as it's not being amplified.
As to the even and odd harmonics. I can only relate what my ears tell me. Hypothetically if an amp was producing only even harmonics it should sound smooth and sweet and pleasing to listen too. Odds are sharper, crisper, harder to listen too. I once had an amp that actually made my ears physically hurt after playing it for some time. Both contribute to good sound. I don't care for all even or all odd harmonics. I like a little zip on top of my cream. So the answer is that there is no answer. Both are necessary and how much of each is in an amp is probably is why so many people appreciate different amps.
Post by The Fifth Column on Mar 16, 2007 12:56:47 GMT -7
Ok, I'm not an expert in anyway but I believe I can tell you a little about music theory and even and odd harmonics as I understand it.
Even order harmonics would be harmonics of the 2nd, 4th, 6th and Octave when a note is played. These sound more "Musical" because the ear can tolerate notes being a little off in these so called "perfect" intervals. Odd harmonics are the 3rd, 5th, 7th. These are called imperfect intervals and the ear cannot tolerate any sharpness in these intervals. For guitar amps, from what I understand when an amp clips or overdrives it produces more harmonics as well as making them more prominent in your sound (along with the actually clipping that occurs).
An amp when overdriven produces more harmonics, sounds more full and maybe even distorted because you are adding bits of the 3rd, the 5th and the 7th or the 2nd, 4th and 6th, to the note making something of little mini chords even when playing a single note. This is why 5th chords (power chords) sound great with lots of distortion, because the distortion has a lot of harmonics which add depth to the chord with hints of the notes you're leaving out. The same principle applies to full chords. If you play a full major or minor chord the 3rd is involved and so if you play with a lot of odd order harmonic distortion, the third harmonic that is produced is perfect while the 3rd included in the chord is not because of a guitar's tempered tuning. Because the 3rd is an odd order harmonic this difference between the harmonic third and the tempered third is very very noticeable. I believe this is why you see a lot of guitarists play fragmented chords if they play with some overdrive, to take out the notes that might conflict with the dominant harmonics of the distortion.
Now here is the part I'm not too sure about... Guitarists prefer odd order harmonics because those are the harmonics that produce the more overdriven sound we are familiar with while hifi amp builders prefer even order harmonics because they do not distort and clash as prominently because the ear can tolerate these intervals being off. A hifi amp that produced a lot of odd order harmonics would probably sound distorted to our ear because the ear is far more sensitive to the odd order harmonics being off.
It is a complicated theory and I might be slightly off. I cannot put enough emphasis on the fact that I'm not an expert, but I learned most of this from researching tempered tuning and the Buzz Feiten tuning system as he talks about how it works on pianos and why a piano can sound good all over the keyboard despite having a pretty good range of tuning across its notes.
Hopefully that helps somewhat. I'm sure someone who is more versed in music theory, guitar amps and harmonic theory might be able to elaborate a bit more than I can.
Thank you, gentlemen. This does provide some insight. I think I'm not going to worry about it too much in amp design. I really like the EF86 front end over the traditional 12ax7 so, given the above, I'll stick with it.
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