Need a second opinion and suggestions please.

[Sprocketdrox]

Hi guys,
I have a marshall dsl 100h, and here is my problem
https://youtu.be/6Q7f-ywfVSs
The amp was bought brand new and originally I didnt find this problem since I didnt have it cranked when testing and reviews said it was a pretty good amp for the price.
Anyway, my guess is the preamp tubes are shot or just cheap. Was planning on replacing them. Thoughts and suggestions?

Other things to note about the problem:
-Please dont get snarky and say things like "buy a better amp." It isnt helpful. This is the amp i have and I need some solutions.
-i always let the amp warm up for 15 minutes and know the basics of tube amp care.
-running into a 1960a on 16ohms
-the amp starts making this noise after the 4 on the volume with or without the power attenuator i use.
-adjusting the gain and tone controls DOES NOT get rid of the noise.
-changing to fresh cables did not fix it.
-changing guitars does not fix it.
-I DO NOT hear it on the clean channel, only gain.

Thanks in advance!

 

[Empty Pockets]

Re: Need a second opinion and suggestions please.

Sounds like a bad preamp tube. You might be able to find the culprit by tapping your tubes with a chopstick and listening for the noise but if it were my amp I'd take it to my tech for a whole new set of tubes and a proper biasing. Good luck.

 

[Myaccount876]

Re: Need a second opinion and suggestions please.

The quickest and easiest thing to check would be switching all of the preamp tubes with preamp tubes you know to be good. A tube can be microphonic, or have a tiny shard of glass broken off on the inside and rattling all over the place. If that's not it, then considering that the noise happens when the volume (which is a voltage divider) passes 4, I'd say something, whether it be a resistor or capacitor etc, in the preamp section (if it only happens on the gain channel and the attenuation changes nothing, the power amp section should be fine) is out of spec/failing and cannot handle the voltages it is supposed to. All it takes is for a crack in one of those components, and things start acting up. I'd visually inspect the board and every single part within the preamp section. Check for anything that appears to have experienced physical trauma or overheating. It may be multiple parts; for example, a carbon comp resistor may have overheated (which changes its resistance) and now has a lower resistance, allowing either too much current or voltage to pass on to the next part in the circuit, causing that to malfunction etc.

But this should be fixable. Try swapping the tubes first. Preamp tubes don't fail as often as power tubes, but it still happens - or they could be dead on arrival.

Sounds like a bad preamp tube. You might be able to find the culprit by tapping your tubes with a chopstick and listening for the noise but if it were my amp I'd take it to my tech for a whole new set of tubes and a proper biasing. Good luck.

It most likely wouldn't be the power tubes, so those don't need to be changed - therefore nothing requires re-biasing. If there was a problem with the power tubes/power amp section, then both the clean and gain channels would be affected.

 

[Sprocketdrox]

Re: Need a second opinion and suggestions please.

Thanks. Really hoping its the tubes since Im trying to avoid expensive repair work. Its a practically brand new amp out of the box, so hopefully it just shipped with bad tubes. I mean, not exactly great considering it should ship no problems, but a minor fix is a minor fix hopefully. Any suggestions on some good quality preamp tubes? I like a lot of crunch and for the amp to be very bright.

 

[VinceT]

Re: Need a second opinion and suggestions please.

Yup, check the tubes first, it sounds like electromagnetic interference getting amplified - the high-pitched reaction sounds very much like a microphonic preamp tube.

I agree with others that if the clean channel is not doing it, then the power tubes aren't likely culprits - two diagnostics there: 1) hit the front end of the (maxed out) clean channel with a high-volume boost (not distortion, you want to hear the amp's reaction). If you still get nothing, then it really does suggest pre-amp tubes as they're involved in the hi-gain stage; 2) if the DSL has an effects loop, plug your guitar direct into the loop return and play - doing that you eliminate the pre-amp completely - and it'll confirm whether you can ignore the power tubes (I agree with others that this is likely the case).

If it is a pre-amp tube, then likely the chopstick-tap will show it up.

Best of luck.


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[Myaccount876]

Re: Need a second opinion and suggestions please.

Thanks. Really hoping its the tubes since Im trying to avoid expensive repair work. Its a practically brand new amp out of the box, so hopefully it just shipped with bad tubes. I mean, not exactly great considering it should ship no problems, but a minor fix is a minor fix hopefully. Any suggestions on some good quality preamp tubes? I like a lot of crunch and for the amp to be very bright.

Probably Tung-Sol and Mullard. The Sovtek 12AX7LPS (NOT the 12AX7WA - those are garbage) is also a good low-noise tube that is bright, but doesn't have as much gain, so I think it is best for the phase inverter. I've seen people call JJ's dark, but I don't really hear it. They have a strong midrange and overdrive nicely with relatively low noise, and are usually the cheapest consistently made tube. You can also mix and match. You could get a Tung-Sol, a Mullard, a JJ, rearrange those in any position (V1 usually has the most effect - see what positions you like best), and a Sovtek 12AX7LPS in V4 for the phase inverter.

 

[Darg1911]

Re: Need a second opinion and suggestions please.

http://i1091.photobucket.com/albums/i384/LS74/DSL100FlowChart5911.jpg

 

[VinceT]

Re: Need a second opinion and suggestions please.

I would use and then bookmark this page:

https://tubedepot.com/tube-comparison-tool

I've used it many times to help mix-and-match tubes (e.g. a lower output Tung-Sol for V1 in my Budda Verbmaster 18W removed a shed-load of noise)


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