Coupling Cap Replacement

[KraftyBob]

DSL40C (not CR)

Background: Have had excessive hiss since day 1 with this amp. Tried various tubes, etc and no difference. I dealt with it by putting a noise gate in front (through my Helix). Was playing straight in last week and was reminded of the horrible hiss and decided to try and fix it. Through my troubleshooting I’ve narrowed it down to V1 and V2 and have confirmed it’s not the tubes - it’s either the components feeding those tubes or something is wrong with the PCB. So I’ve decided to shotgun all the components in the preamp signal path. If that doesn’t work I may gut it and build a JCM800 clone. But It’s easy and cheap enough to try this first.

I’m going to replace the plate resistors, grid stoppers and coupling caps and from what little I could find on them, the box metaliized coupling caps that Marshall uses are supposedly garbage. Looking for recommendations on what to put in there instead.

TIA

 

[PelliX]

Background: Have had excessive hiss since day 1 with this amp.

The DSL is not exactly a 'quiet' amp in that regard. When you say 'excessive', is that in comparison to other DSL40's? Don't get me wrong, I'm not saying "shut up and deal with it", just wondering whether the noise level actually more pronounced than in its brethren.

I dealt with it by putting a noise gate in front (through my Helix).

A noise gate in front is sufficient to tackle it? That would imply that the hiss is not actually coming from the amp itself. If you put a noise gate in the loop, of course it would cut any hiss from the preamp...

I’m going to replace the plate resistors, grid stoppers and coupling caps and from what little I could find on them,

Wirewound resistors would aid to tame any noise compared to carbon. Caps don't typically introduce hiss, though ceramic caps can be a little microphonic - unlikely to be a problem here. If you're rattling the amp that bad, you wouldn't notice the hiss, likely. You could of course try playing with the 'bright cap' for a specific channel, but it will affect your overall tone of course.

the box metaliized coupling caps that Marshall uses are supposedly garbage.

I can't recall exactly what they used in the old 40C. While an upgrade/swap won't hurt, I wouldn't expect a world of difference presuming you're substituting them for the same value. Do you have an ESR meter to test said caps?

 

[KraftyBob]

The DSL is not exactly a 'quiet' amp in that regard. When you say 'excessive', is that in comparison to other DSL40's? Don't get me wrong, I'm not saying "shut up and deal with it", just wondering whether the noise level actually more pronounced than in its brethren.



A noise gate in front is sufficient to tackle it? That would imply that the hiss is not actually coming from the amp itself. If you put a noise gate in the loop, of course it would cut any hiss from the preamp...



Wirewound resistors would aid to tame any noise compared to carbon. Caps don't typically introduce hiss, though ceramic caps can be a little microphonic - unlikely to be a problem here. If you're rattling the amp that bad, you wouldn't notice the hiss, likely. You could of course try playing with the 'bright cap' for a specific channel, but it will affect your overall tone of course.



I can't recall exactly what they used in the old 40C. While an upgrade/swap won't hurt, I wouldn't expect a world of difference presuming you're substituting them for the same value. Do you have an ESR meter to test said caps?

Thanks for your reply.

- Lead 2 in the Ultra Gain channel is essentially unusable. Here's a video I took of the hiss:



- You're right, a noise gate in front wouldn't eliminate the hiss from the preamp. I setup this preset a few years ago so the only thing I could think of is I moved it to the loop at some point. I'll have to check the signal path in the Helix.

- I read a couple posts where someone swapped out the plate resistors in a DSL20 and solved a hiss problem. Another tech changed out the coupling caps and it made a big difference in the amp. I'm confident the issue is with the amp and not tubes. In the following video you can hear the noise when I'm prodding the plate resistors/plates. The same plate resistors/plates make noise with two other sets of new preamp tubes. And when I move the tubes around to different sockets the noise stays with the socket. I pulled the board and reflowed all the solder joints for the sockets as well as the components in the area. Nothing looked suspect but I figured it couldn't hurt. Admittedly I'm taking a shot in the dark hear shot-gunning the parts, but something's going on with the amp. I have an Anatek Blue ESR meter but I'm not going to bother checking the caps - just replacing all the components with better quality.

 

[PelliX]

I read a couple posts where someone swapped out the plate resistors in a DSL20 and solved a hiss problem. Another tech changed out the coupling caps and it made a big difference in the amp. I'm confident the issue is with the amp and not tubes.

Fair call, that makes sense and it won't hurt. I'd agree with ruling out the valves for now. As for the coupling caps, it would be interesting to know what they measure like in comparison to the replacements, I'd think.

 

[KraftyBob]

Fair call, that makes sense and it won't hurt. I'd agree with ruling out the valves for now. As for the coupling caps, it would be interesting to know what they measure like in comparison to the replacements, I'd think.

Easy enough to do. I’ll check when I replace them and report back. Going to take a look at Mustard caps and see if I can find something that will physically fit.

 

[Gene Ballzz]

@KraftyBob
FWIW, I've never found the LEAD 2 of the ULTRA channel to be of any use whatsoever on any DSL. Sounds like a cheap foot/stomp/pedal/thingie, to me!
Maybe That's Just Me?
Gene