Horrible Noise from Hybrid Amp

[Stub Mandrel]

In the last half hour my Joyo Bantamp (50W hybrid) has started making farty/crackly noises if I dig in on the E string. I have volume low and gain modest. It seems to be very biased towards low frequencies. It doesn't sound like distortion as much as a really noisy volume control and appears to be independent of gain and master volume settings. I can turn up loud and play gently without the nasty noise. Turn it really quiet and dig in, and it crackles and snaps.
 

It's a hybrid amp, and my worry is that something 'mechanical' has gone awry in the 12ax7preamp stage. Is this possible?

[Bunion]

Could be the tube on its way out, do you have a spare? 

[Stub Mandrel]

32 minutes ago, Bunion said:

Could be the tube on its way out, do you have a spare? 

 

I have 12ax7 tubes in two other amps, so I OUGHT to have a spare. Don't want to cannibalise, so I've just ordered one. See if it sorts it in a few days.

[Dan Dare]

12 hours ago, Stub Mandrel said:

I can turn up loud and play gently without the nasty noise. Turn it really quiet and dig in, and it crackles and snaps.

 

If this is the case, might you be overdriving the tube preamp stage, causing it to behave like an overdriven guitar amp? The difference between playing gently and digging in, in terms of the signal you are sending to the amp, is pretty large. There isn't a lot of headroom to play with with 50w, either.

 

12AX7s are not all the same. If you have a higher gain version, it will increase the likelihood of overdriving. I swapped the 12AX7 in one of my heads for a lower gain version because it got dirty too quickly, with only a small increase in gain. A lower gain version gave a more gradual transition into overdrive.

 

Watford Valves were helpful in helping me choose a suitable tube.

Edited April 17, 2023 by Dan Dare

[Paul S]

I've always had a similar horrible noise.  Class D, hybrid, tube amp - always the same horrible noise.  Swapped to FRFR and a pedal, yup, same horrible noise.  It's just my playing  

[Waddo Soqable]

35 minutes ago, Paul S said:

I've always had a similar horrible noise.  Class D, hybrid, tube amp - always the same horrible noise.  Swapped to FRFR and a pedal, yup, same horrible noise.  It's just my playing  

Nah, It's them 'orrible lil' basses with mudbucker PUs you like so much.... 😁

[Bunion]

7 hours ago, Dan Dare said:

12AX7s are not all the same. If you have a higher gain version, it will increase the likelihood of overdriving. I swapped the 12AX7 in one of my heads for a lower gain version because it got dirty too quickly, with only a small increase in gain. A lower gain version gave a more gradual transition into overdrive.

Try changing the 12AX7 for a 12AT7 they put out less gain so give you more clean headroom I have one in slot 1 of my Handbox WB 100 

[Stub Mandrel]

It seems better today... might be an intermittent issue, see what happens after the valve has run hot for a few hours, like yesterday.

[Bunion]

Have you tried just reseating the valve? 
Sometimes just a bit of a wiggle or pull the plug and push back in can clear corrosion 

[Stub Mandrel]

Good point, if it starts again I'll try that.

 

My brother's new valve  amp had a rectifier tube that was 'buzzing' mechanically but it turned out to be an internal fault.

[Lozz196]

55 minutes ago, Bunion said:

Have you tried just reseating the valve? 
Sometimes just a bit of a wiggle or pull the plug and push back in can clear corrosion 

Good call, I had a similar issue in a hybrid amp a few years back and reseating the valve sorted it.

[Stub Mandrel]

Seems OK this evening... hmm.