Damn sub-harmonics....

trazan

Member
Messages
821
I've done some changes to my rig, didn't really notice exactly when or if it happened gradually or not...but now it's become extremely annoying :messedup Those deeper extra notes produced when playing two or more strings simultaneously. I can hear them clearly even on completely clean sounds, and it really muddies up chords.

What's the reason for these sub-harmonic nasties? Any way to diminish or remove them? Electronics, speakers, tubes, pickups....?
 

riffmeister

Silver Supporting Member
Messages
16,775
They're called "ghost notes" and result from underfiltering of the power supply, I think.
 

Silverboy

Member
Messages
135
They're called "ghost notes" and result from underfiltering of the power supply, I think.

That's my understanding too, and when I've encountered it, my amp tech and I have played around to get to an acceptable point. The catch is that, if you OVERfilter, you lose some of the beauty of the amp's sound. I've noticed many great sounding Voxes have low ghost notes, and my Super Reverb did. And there comes a trade-off point where you may have to accept a little of it, or else lose some of the rawness and beauty of your amp's tone. For me, when I first became aware of ghost notes, they stood out more because I paid so much attention to them that I started to exaggerate them in my mind. But now, if they're only minor, I live with them. I can play a certain two-note combination and hold it in such a way that I go, "wow, that ghost note is horrible." But then, in my actual playing, I never actually hold those two notes that long in that way. Now if they're really prominent and bumming you out, you need to have a tech look at it.

One thing I've noticed is that ghost notes happen more often on great amps. Class A Matchless-type amps. old Voxes or old black-face amps. Because those amps are a little more direct and less filtered, less stuff in the tone path to gunk up your tone.

More savvy technical folks will have more to say, but that's my novice-tech take on it.
 

Hacksaw

Time Warped
Messages
10,208
I've done some changes to my rig, didn't really notice exactly when or if it happened gradually or not...but now it's become extremely annoying :messedup Those deeper extra notes produced when playing two or more strings simultaneously. I can hear them clearly even on completely clean sounds, and it really muddies up chords.

What's the reason for these sub-harmonic nasties? Any way to diminish or remove them? Electronics, speakers, tubes, pickups....?

could you provide us with what you changed? it seems you didnt have this before you started the changes, correct? ( that is the impression I got from reading it) did you change a speaker?
 

trazan

Member
Messages
821
Okay, I can still hear those ghost notes just recording the output of the preamp. The room and cabinet exaggerates them a bit, but I'm guessing it's mostly that they feel really loud when you focus on them :)

I have no other preamps here at the moment, but I'm definitely going to compare when I get some in here.
 

Unburst

Member
Messages
4,215
There is a difference between "ghost notes" which are common in older, badly maintained Voxes, which occur on single notes and the phenomenon that's being described here.

The "sub harmonic" that you can hear when two or more notes are the result of inter-modulation distortion, you can hear it a lot when doing oblique bends.
 

trazan

Member
Messages
821
There is a difference between "ghost notes" which are common in older, badly maintained Voxes, which occur on single notes and the phenomenon that's being described here.

The "sub harmonic" that you can hear when two or more notes are the result of inter-modulation distortion, you can hear it a lot when doing oblique bends.

Ah, I defined them correctly in my first post then! :cool:

Yes, you can hear these sub-harmonics especially well when using an octavia or similar. Then sound kinda funny then, but when they're prominent on just slightly gritty sounds..it's not that funny.

Guitar, power amp and speakers doesn't matter (other than maybe boosting "offending" freqencies...bassy cabinet, neck pickup etc). They come from the preamp.

As I said, it may be that they were always there, and that I just started focusing on them now. But I'm still wondering...what in the design of a preamp could be causing more or less of these?

Update: Switching a couple of 12AX7's in the preamp with 5751 tubes made it much less pronounced. Even when raising the gain on the preamp to make up for the lesser gain in the 5751's. Hm...is it the tubes themselves, or is it the higher gain from the AX7's that causes more intermodulation distortion elsewhere in the design?
 

Bob Arbogast

Gold Supporting Member
Messages
1,202
I recently read a book titled How Equal Temperament Ruined Harmony. To make a long story short, certain intervals (thirds and fourths especially) are inherently out of tune using the equal temperament tuning that is ubiquitous in Western music. Not that there aren't issues with amp circuitry, speakers, cabinets, etc. But if you listen closely, you may be able to hear this intermodulation of poorly tuned intervals coming from your unplugged guitar. An amp with good bottom end response will reproduce this noticeably; an amp with exaggerated bottom end response may reproduce it annoyingly. Just another angle to think about.

Bob Arbogast
 

loopjunkie

Member
Messages
132
you know whats funny is I think that those sound cool..........I actually try to bring out that slightly dis-harmonic content out in my music. I think that sounds way more pleasing then when someone bends and doesn't quite hit the note (intentinally; i hear this in Zep, Allman bros; Warren Haynes..)
Its just weird that people would try to get ride of it; unless it caused to much boominess?
 

candid_x

Member
Messages
9,667
Another possibility is that, certain preamp tubes could be microphonic, especially some NOS or newer long plate versions, such as the JJ ECC803S, and especially if your amp is a combo. This is most noticeable in the V1 tube position, usually.
 

electroid

Member
Messages
200
This is probably more related to preamp design than anything else. One version of the Fender Blond Bassman is really bad about it and I've traced it to the preamp design. Unfortunately, fixing it greatly alters the vibe of the amp.
 

trazan

Member
Messages
821
This is probably more related to preamp design than anything else.

Yes, seems to me that it indeed is.

One version of the Fender Blond Bassman is really bad about it and I've traced it to the preamp design. Unfortunately, fixing it greatly alters the vibe of the amp.
Funny thing is that it was a "Bassman" module in an Egnater M4 that had these strong subharmonics...Lower gain tubes really helped though.
 




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