Yet another DSL20CR hiss thread

[calzone]

Guys, check this:

I bought it yesterday. The amp is from December 2019. After reading this forum I thought all the early problems were finally fixed by Marshall. To my surprise, the floor noise (hiss, wind) is still there with no gain, no volume, no nothing...

One interesting thing is that the tone of the hiss can be changed by presence and resonance knobs. Other eq (low, mid, treble) do not change anything. It means that the noise is generated by amp power section, not preamp, right? If this is so the all known supposed fixes (resistors, C14 cap) cannot do anything about it as these are all located in preamp?

I notified the shop and wait for their response.

 

[ampmadscientist]

Guys, check this:

I bought it yesterday. The amp is from December 2019. After reading this forum I thought all the early problems were finally fixed by Marshall. To my surprise, the floor noise (hiss, wind) is still there with no gain, no volume, no nothing...

One interesting thing is that the tone of the hiss can be changed by presence and resonance knobs. Other eq (low, mid, treble) do not change anything. It means that the noise is generated by amp power section, not preamp, right? If this is so the all known supposed fixes (resistors, C14 cap) cannot do anything about it as these are all located in preamp?

I notified the shop and wait for their response.

The DSL20 CR is a known defect.
Return it to the vendor or service center.
Some people exchanged it 3 times before they got a good one.

 

[calzone]

@ampmadscientist, I found your posts about repairing DSLs. Here are my R70/R56/C39 guts. It looks like an "old" version before the fix. I'm not sure if the resistors need to be replaced with another set of 1MOhm, but different material? And what about the value of capacitor instead of 47nF? Can you help me with this?

 

[ampmadscientist]

@ampmadscientist, I found your posts about repairing DSLs. Here are my R70/R56/C39 guts. It looks like an "old" version before the fix. I'm not sure if the resistors need to be replaced with another set of 1MOhm, but different material? And what about the value of capacitor instead of 47nF? Can you help me with this?
View attachment 73070

If this is a new amp, return it.
If this is an old amp, take it to Marshall service center.
Contact K Dog and find out what the best solution for updates may be.
(the updates might be free if you are the original purchaser)
Kevin (Kdog) Drury
Marshall USA Service
1000 Corporate Grove Dr.
Buffalo Grove, IL 60089
800-877-6863
kevin.drury@USMusicCorp.com

Please do not try to work on the amp.
The PC board can be very easily damaged by soldering.

 

[calzone]

I have pretty solid skills in electronics and can deal with smd with my soldering station The shop/service in my country already told me that the noise is "normal" and I don't want to play russian rulette game with them finding the good piece now and again. Replacing a few components is not a big deal for me.
I'll try to contact Kevin anyway, thanks.

 

[em07189]

It can be the phase inverter preamp tube problem, try replace this tube with a good one, and see if it solves the problem.

 

[scozz]

Wow,...another Dsl20 hissing,...and one from just a few months ago! December 2019 build date and still the problem exists?

Unacceptable,..


Man I came soooo close to buying a new Dsl20hr in December of 2018.

I decided to wait for NAMM in January 2019 to see what, if anything, Marshall was offering.

I’m so glad I waited, I bought a 2020 SC20 head!

 

[calzone]

It can be the phase inverter preamp tube problem, try replace this tube with a good one, and see if it solves the problem.

I tried switching V2 and V3 as well as replacing V3 with a spare 12AX7. Didn't help.

There is one thing that bothers me. It's the "AUDIO IN" input. I tried to connect my guitar there and noticed that it can be quite loud(!) This additional input is meant for external audio sources like mp3 players, smartphones etc. These devices operate on line signal levels or higher (headphone level) which is much higher than instrument level. My guitar has passive pickups yet it sounded very loud. It means that there is a kind of preamp connected to AUDIO IN and it has some significant gain typical for instrument level. Also, as we all know, this gain cannot be controlled as the level of audio should be set by external source (as Marshall claims).

So even with guitar preamp muted to zero (both channels, gain and volume) there is still another source of signal driving amp power section, set to its full gain, uncontrollable. Maybe the noise (uniform windy sound) coming from the speaker at idle is causing by noisy, gainy preamp in AUDIO IN circuit? For me it looks very so. The noise is typical "white noise" type, uniform, no popping, no crackling, just steady level of static. It's typical for early stage preamps, generated by active components (transistors, lapms), not passive ones.

Unfortunately there is no schematic to check my theory. If I knew where the AUDIO IN preamp is located I'd disable it or attenuate it to lower the noise. What do you guys think? Does it make sense?

 

[Deerhunter1972]

If this is a new amp, return it.
If this is an old amp, take it to Marshall service center.
Contact K Dog and find out what the best solution for updates may be.
(the updates might be free if you are the original purchaser)
Kevin (Kdog) Drury
Marshall USA Service
1000 Corporate Grove Dr.
Buffalo Grove, IL 60089
800-877-6863
kevin.drury@USMusicCorp.com

Please do not try to work on the amp.
The PC board can be very easily damaged by soldering.

Do exactly this ^^^^ I've had 4 DSL20's....3 Heads and 1 combo. Heads took 2 trips back to Sweetwater to get one that was perfect.. My DSL20CR I bought used with exactly your problem. It cost me $20 to ship to Marshall and they fixed it for free and had it back to me in under 2 weeks. Don't waste your time trying to figure out what Marshall will do for free. These are awesome amps once you get one that actually works. I've had my DSL20HR for almost a year and a half now and it has been flawless.

 

[Musicmaniac]

I agree. Had mine serviced and all is well.

 

[em07189]

The PI tube is the closest to the powertubes, it shoud be v4.

I tried switching V2 and V3 as well as replacing V3 with a spare 12AX7. Didn't help.

There is one thing that bothers me. It's the "AUDIO IN" input. I tried to connect my guitar there and noticed that it can be quite loud(!) This additional input is meant for external audio sources like mp3 players, smartphones etc. These devices operate on line signal levels or higher (headphone level) which is much higher than instrument level. My guitar has passive pickups yet it sounded very loud. It means that there is a kind of preamp connected to AUDIO IN and it has some significant gain typical for instrument level. Also, as we all know, this gain cannot be controlled as the level of audio should be set by external source (as Marshall claims).

So even with guitar preamp muted to zero (both channels, gain and volume) there is still another source of signal driving amp power section, set to its full gain, uncontrollable. Maybe the noise (uniform windy sound) coming from the speaker at idle is causing by noisy, gainy preamp in AUDIO IN circuit? For me it looks very so. The noise is typical "white noise" type, uniform, no popping, no crackling, just steady level of static. It's typical for early stage preamps, generated by active components (transistors, lapms), not passive ones.

Unfortunately there is no schematic to check my theory. If I knew where the AUDIO IN preamp is located I'd disable it or attenuate it to lower the noise. What do you guys think? Does it make sense?

 

[JBA]

Guys, check this:

I bought it yesterday. The amp is from December 2019. After reading this forum I thought all the early problems were finally fixed by Marshall. To my surprise, the floor noise (hiss, wind) is still there with no gain, no volume, no nothing...

One interesting thing is that the tone of the hiss can be changed by presence and resonance knobs. Other eq (low, mid, treble) do not change anything. It means that the noise is generated by amp power section, not preamp, right? If this is so the all known supposed fixes (resistors, C14 cap) cannot do anything about it as these are all located in preamp?

I notified the shop and wait for their response.

Did you not try it before buying? These are great amps but there are definitely some duds out there. Folks sell because they want something new, need money, don’t gel with there amp, or because something is wrong with it. Ya gotta try before you buy! Even with CoVid, have the guy do the run through of all the pots n buttons etc.. while you stand at his door. I really am sorry you got stuck with a dud (fingers crossed it’s only a tube) but your situation is a good reminder for others. Your issue (board or tube) is after the tone stack. Good luck with the fault finding and repair.

 

[calzone]

The PI tube is the closest to the powertubes, it shoud be v4.

There are only 3 ECC83s in DSL20CR.

Did you not try it before buying? (...)

The amp is brand new, production date Dec'19. It came all factory sealed, I'm sure never been used before. But I bought it from an internet shop, so you're right - I didn't try it before.

BTW, Kevin from Marshall USA wrote to me that he's from USA service team. And I should seek help in UK (even that I'm from EU). He did not answer my questions about the real source of the problem, faulty resistors etc. I was naive expecting this...

 

[JBA]

There are only 3 ECC83s in DSL20CR.

The amp is brand new, production date Dec'19. It came all factory sealed, I'm sure never been used before. But I bought it from an internet shop, so you're right - I didn't try it before.

BTW, Kevin from Marshall USA wrote to me that he's from USA service team. And I should seek help in UK (even that I'm from EU). He did not answer my questions about the real source of the problem, faulty resistors etc. I was naive expecting this...

Wow, ya then I demand an exchange.

 

[calzone]

I returned it. They checked the noise and said it's "normal". Whatever, I grabbed DSL40CR and... it's simply quiet. Maybe because it has master volumes

 

[JBA]

I returned it. They checked the noise and said it's "normal". Whatever, I grabbed DSL40CR and... it's simply quiet. Maybe because it has master volumes

Normal lol, those fools. The 40 is better anyway.. you win!

 

[muskogeee]

Sorry for digging up an old thread but I just received my DSL20CR today from Sweetwater today with this exact same problem:



This one was manufactured in September 2020. Pretty unacceptable if you ask me.

Guess I'll roll the dice and see if the replacement they send is good.

 

[JBA]

Sorry for digging up an old thread but I just received my DSL20CR today from Sweetwater today with this exact same problem:



This one was manufactured in September 2020. Pretty unacceptable if you ask me.

Guess I'll roll the dice and see if the replacement they send is good.

Ya what a pain in the ass. Marshall needs to get their shit together. Hopefully you get a good replacement because they do sound great! Just sucks to have to deal with this BS to get an awesome amp.

 

[muskogeee]

OK Now I'm officially confused. I sent an email to Marshall support with a link to the video I posted here and the response I received was from Kevin Drury, and I remembered his name mentioned here. The problem is... He said it sounded normal....... Now I don't know if I should return it.

Do exactly this ^^^^ I've had 4 DSL20's....3 Heads and 1 combo. Heads took 2 trips back to Sweetwater to get one that was perfect.. My DSL20CR I bought used with exactly your problem. It cost me $20 to ship to Marshall and they fixed it for free and had it back to me in under 2 weeks. Don't waste your time trying to figure out what Marshall will do for free. These are awesome amps once you get one that actually works. I've had my DSL20HR for almost a year and a half now and it has been flawless.

I agree. Had mine serviced and all is well.

Not to be redundant, but Deerhuter1972 and Musicmaniac, if you happen to read this can you please confirm that you had DSL20s with the same issue and either got a replacement without the issue, or had the issue repaired?

 

[Max Gahne]

First off I agree with the folks here who've advised that if you aren't happy with it send it back. I actually have a 20 on order so I'm interested in the issues that might come with it. Looking around this forum - and you can find 20 schematics here, I can't remember where but they're on here - and looking at threads that posted gut shots of before/after fixes I think this: From the pics of the fixes it appears the problem might be in the long cable connecting CN23 with CN21. Hopefully I don't get my numbers wrong. That cable connects the volume control outputs to the phase inverter. There's also a long cable connecting the the volume inputs but if the volume controls don't affect the noise then it would be the output cable of the 2. The cable isn't shielded, it's long, and is possibly, probably, one big antenna. It looks like the fix has been to move that cable to connecting CN20 to CN21 directly which actually takes the volume controls out of circuit. So I figure, assuming people's volume controls do work after the fix, that they jumper under the board to connect the volume controls at R43 which in effect moves them to the same place as they are on a DSL40/100. A DSL20's volume controls are actually where the DSL40/100s master volumes are. If I'm right about their fix then the volume controls would work on the emulated out after the fix. Where they are stock they aren't supposed to work on the emulated out so that's a design flaw, not a manufacturing defect. Actually you could move the volume controls as a mod. So my thought is this if mine comes in noisy. First to simply try to shield that cable. Wrap it in shielding material, ground one end - not both ends - of the shielding material, wrap that in insulating material and see how it sounds. I may be able to test this theory on a noisy 20 by simply lifting up the cable with a chopstick and listen to whether it changes the noise. Anyways those are my thoughts from the pics and schematics that have been posted. To repeat what I first said, if you aren't happy send it back. I enjoy tinkering with amps but while mine is under warranty and unmodded I'll probably send mine back too.