Tremoverb noise gremlins

[thinskin57]

i have a strange low frequency hum coming from my '99 TOV combo. here's what happens:

first off, it is a low volume hum that stays the same volume whether i crank the volume or turn it off completely. sometimes it is a "constant level" hum, other times it is a "pulsing" type of hum like a tremolo effect. it only happens in the modern high gain channel. if it starts humming, i can switch to the orange channel and it goes away. having said that, if i clone the orange channel into red, then the humming will happen on that channel too. right now this problem is intermittent, but frequent enough. i'll notice it sometimes when i stop playing. i can also make the problem happen by tapping lightly on the chassis, or knocking on the cabinet. sometimes i can even make it stop by taping on it again. kinda like fonzie, but this isn't cool. any ideas, anyone?

 

[Roadifier]

Its probably just hum from the high gain channel, It is normally only when you get into high gain stuff, and remember, don't put the gain on full. I suggest an ISP decimator pedal, It is one of the best noise reduction pedals I have used, and it quiets every thing down, and I like having it in the loop for high gain noise.

 

[thinskin57]

Its probably just hum from the high gain channel, It is normally only when you get into high gain stuff, and remember, don't put the gain on full. I suggest an ISP decimator pedal, It is one of the best noise reduction pedals I have used, and it quiets every thing down, and I like having it in the loop for high gain noise.

no, it is not from too much gain.. i've been using tverbs since 1994 and know the difference between high gain hum and this almost "oscillating" type of hum that i'm getting now. besides, i only keep the gain at 12 o'clock. i DID entertain the idea that it may be the gain but even when i turned the gain down to 9 o'clock, the hum was still present. plus, as i mentioned, it will hum even with the volume completely OFF. i wish it were as simple as "too much gain" but it is not. 94Tremoverb, you out there?

 

[94Tremoverb]

You might not expect this, but it could be a bad power tube. The reason is that the power stage negative feedback is switched off in Modern mode (only) so any problems from the power stage itself will no longer be suppressed as they will in the other modes. Power tubes sometimes do this, and it can be vibration-sensitive, which seems to fit.

If it's not a tube, I would look in the power stage or the NFB loop anyway, for the same reason - possibly for a bad ground contact or something similar.

 

[lambofgod24]

You might not expect this, but it could be a bad power tube. The reason is that the power stage negative feedback is switched off in Modern mode (only) so any problems from the power stage itself will no longer be suppressed as they will in the other modes. Power tubes sometimes do this, and it can be vibration-sensitive, which seems to fit.

If it's not a tube, I would look in the power stage or the NFB loop anyway, for the same reason - possibly for a bad ground contact or something similar.

Ive also noticed after reading this thread that my series 1 rectoverb head is making the same noise in modern mode, i just bought the amp and its my first tube amp how would i go about changing the power tubes and what kind should i use, sorry to post in this thread but my amp has the same symptoms.
Thanks

 

[thinskin57]

You might not expect this, but it could be a bad power tube. The reason is that the power stage negative feedback is switched off in Modern mode (only) so any problems from the power stage itself will no longer be suppressed as they will in the other modes. Power tubes sometimes do this, and it can be vibration-sensitive, which seems to fit.

If it's not a tube, I would look in the power stage or the NFB loop anyway, for the same reason - possibly for a bad ground contact or something similar.

o.k., thanks... but what's a NFB loop?

 

[94Tremoverb]

Negative Feed Back. It's part of the power stage and regulates the circuit to make it more linear and controlled. In most amps the Presence control is part of this circuit, and works by defeating it at high frequencies, so they then sound more cutting and dynamic. Some amps like the Peavey 5150/6505 have a low-frequency version too, usually called Resonance. The Mesa amps with a Modern mode achieve some of the voicing change by turning off the whole NFB loop entirely, which makes the amp a lot more aggressive and looser-sounding (and louder) - the Presence circuit then works slightly differently.

On the Rectoverb (at least the combo, I haven't played the head version), this can make the amp actually get out of control in the Modern mode at higher volumes and you get an after-resonance on some notes which is related to the speaker resonant frequency that's no longer being damped out - especially noticeable on palm muted chords. A friend of mine has one of these and I had to fit a variable control to the NFB-bypass for him to just dial it out, without going fully back to the NFB-on setting which is almost the same as Vintage mode.

To change tubes in a Mesa amp is very simple - get a set of power tubes either from Mesa or rated for Mesa amps by another vendor, remove the old tubes and put in the new ones! Mesa amps don't have adjustable bias so you have to pick the tubes to suit the amp, not adjust the amp for the tubes. Keep the old tubes as spares if they're not actually blown, which you would know if they were since the amp would either sound very bad or blow fuses.

 

[lambofgod24]

A friend of mine has one of these and I had to fit a variable control to the NFB-bypass for him to just dial it out, without going fully back to the NFB-on setting which is almost the same as Vintage mode.
Could you tell me a little more about the variable control you installed?
How would i go about doing this, does it affect the sound at all?
Thank you

 

[94Tremoverb]

There is an LDR (series 1 Rectoverb) or relay (series 2) that turns off the NFB loop in Modern mode. What I did was to find where this is on the circuit board - sorry, I can't remember exactly, but it wasn't too hard if you have the schematic and are familiar with working on modern amps - and connect a pot across it, so that when the switch is on (every mode apart from Modern) the pot does nothing, and in Modern mode the pot allows you to dial back in some feedback. The right pot value was 1M Log.

I used the hole where the FX Mix pot used to be, which I'd already removed to change the loop to series. If you haven't done/don't want to do this, you'd need to find another of the existing holes that you don't need to use (ground switch maybe) or drill one.

Be aware that by its very nature this does change the tone of the Modern mode though, and brings it back closer to Vintage - if you really like the Modern mode you may find that by the time it's got rid of the resonance it's no longer quite sounding how you want it.