Bass overdrive "crack" rumble on Clean. Feature or Faulty?

[Rob Snelders]

Hi.

Im the proud owner of an Express 5:25 Plus 12". I have a question on a bass nasty crack distorted sound on the Clean channel when driven hard(er). Sometimes.

I use my amp on gigs and on jamsessions. Think of a band practice session with 5 to 9 musicians.

So I play my amp louder than at home of course. Most sessions the amp sounds and shines amazing. More than loud enough and ample gain and volume left: Im not driving the amp on or over the edge.

But when digging in deeper and hitting and spanking the strings in the bass range sturdy hard there is a nasty distorted bass "crack" on the clean channel. Also when guitar straight into the amp. Lowering volume, gain and bass level helps. More profound with humbuckers than with lower output P90s.
It s at a level I suspected the tubes were burned out but back at home the issue is mainly gone.

What could be the source of this?

Faulty tubes? Loose tubes in their sockets? IC, board, component, electrical issue? Comes with the amp? Tubes at lifespan end? (the set is in there more than 5 years, played daily muktiple hours).

The first valve is not an AX7 but an AY7. Could that be a reason?

I have a set of old (used) tubes but not at all experienced or at ease changing them eadily myself.

Could someone shead some light?
Would be massive !!!! Tx in advance.
Regards, Rob.

 

[DrKev]

My first guess would be a loose component somewhere that rapidly connects and disconnects when you hit the big low note. If that's due to a cracked solder joint it could be impossible to find but there's more obvious things to go after first.

First do a tap test tap on each tube. If you get your noise, or a glassy ringing noise, get rid of it.




Then swap each tube, one at a time, with a spare known-working tube. If you swap out a tube and you still get the noise, you know it's not caused by the tube you took out, so it can go back in. For the EL84s, try them in 5 watt mode and swap the tubes around.

Also gentle wiggle each tube in their socket. Any pops or noise or crackles suggest the sockets need clean and retensioning.

I would also check inside the amp to make sure that the control pots are not loose and that no terminal or older joint on the pots could touch the lip of the of the chassis. They should just gently bend down away from the chassis lip if necessary.

At tis point if you still have the problem, I'd take it to a good amp tech.

There is no reason why a 12AY7 would cause that noise. But note that in the Express series amps the tubes are in a non-standard order. (V1 closest to the input jack, V5 closest to speaker). V2 is the first gain stage, and V4 is the phase inverter and power amp driver. So if you want to reduce overall volume put it in V4. If you want to reduce gain/distortion for the channels, put it in V2, or V1, but test the differences in volume between the channels to see what result you prefer. Half of V3 drives the effects loop and V5 is for reverb so don't put it those positions.

 

[Rob Snelders]

My first guess would be a loose component somewhere that rapidly connects and disconnects when you hit the big low note. If that's due to a cracked solder joint it could be impossible to find but there's more obvious things to go after first.

First do a tap test tap on each tube. If you get your noise, or a glassy ringing noise, get rid of it.




Then swap each tube, one at a time, with a spare known-working tube. If you swap out a tube and you still get the noise, you know it's not caused by the tube you took out, so it can go back in. For the EL84s, try them in 5 watt mode and swap the tubes around.

Also gentle wiggle each tube in their socket. Any pops or noise or crackles suggest the sockets need clean and retensioning.

I would also check inside the amp to make sure that the control pots are not loose and that no terminal or older joint on the pots could touch the lip of the of the chassis. They should just gently bend down away from the chassis lip if necessary.

At tis point if you still have the problem, I'd take it to a good amp tech.

There is no reason why a 12AY7 would cause that noise. But note that in the Express series amps the tubes are in a non-standard order. (V1 closest to the input jack, V5 closest to speaker). V2 is the first gain stage, and V4 is the phase inverter and power amp driver. So if you want to reduce overall volume put it in V4. If you want to reduce gain/distortion for the channels, put it in V2, or V1, but test the differences in volume between the channels to see what result you prefer. Half of V3 drives the effects loop and V5 is for reverb so don't put it those positions.

Tx Mr DrKev.
This weekend I will have and take the time to have a good peek.
Will get backbto you for sure.
Else I will take it to a tech. I will surely let you know.
Tx again!! Rob.