Author Topic: Marshall DSL15H project  (Read 5614 times)

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Offline LPBII

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Re: Marshall DSL15H project
« Reply #15 on: November 13, 2015, 09:09:01 pm »
Well I finally got some mods done.
 
Green Channel:  Changed the slope resistor of the internal tone stack from 100k to 56k.  This is actually a very common mod on black face and silver face Fenders.  It makes the green ch sound more like a tweed and less like a silver face. This alone boosted up the midrange and increased gain. It also reduced bass boom. So it did what I wanted.  I went ahead and lowered the signal padding resistor as well, but I think I'll go back to stock there.  Once that is done, I'm done with the green channel. With the guitar volume all the way up it has some grit, but cleans up when I roll it back a bit. Just the way I like it.

Red Channel: I did most of the established mods for the red ch.  I'm not happy with the results yet. But I don't have the V1b cathode by-pass cap in right now, and the added gain pot load resistor is way off spec, because I read the stripes backwards. :-[ 

Offline LPBII

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Re: Marshall DSL15H project
« Reply #16 on: November 13, 2015, 09:17:38 pm »
BTW, if your a novice don't try this at home.  I have experience playing around with amps and follow the standard safety procedures.

Offline LPBII

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Re: Marshall DSL15H project
« Reply #17 on: November 17, 2015, 09:26:12 am »
Okay, I fitted a more correct value resistor (100K) for the gain pot load resistor, and put the cathode resistor by pass cap back in*, with a 10k resistor between it and ground. Success!  This amp sounds very good now.
 
The fizz and sack full of bumble bees buzz are gone gone gone. The red channel now is actually mostly clean up to 3 on the gain knob. From 3 to 4 its more of a crunch, but by 5 its starting to get some serious gain.  Up to 5 1/2 to 6 you can get a higher gain overdrive with the guitar volume up, but turn the guitar down a bit and/or back off on the pick attack and it cleans up fairly well.  You can just ignore the green channel and play the red channel exclusively if you want. Up to 7 your getting into searing high gain real estate. And its all usable gain, unlike the stock amp.  The tone controls now work quite well if you want more cut or a warmer girth.
 
The amp works this way with my Tone Zone loaded Charvel as well as with vintage output pickups.
 
The main draw back is that it makes the green channel more or less not very useful. The main purpose of the green channel now becomes loud cleans, or a pedal platform, but this only a 15 watt amp. I may revisit the green channel mods, or de-mod, the green channel now.
 
I will have to go through and replace some of the carbon comp resistors I used with metal film, because I had them on hand, to lower the noise floor of the amp.  The noise level is still unacceptable to me.

* The original mod list calls for just clipping this cap out. But I found that it needs to be in there. The tone is fatter and smoother and the amp has less noise.


Offline LPBII

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Re: Marshall DSL15H project
« Reply #18 on: November 27, 2015, 01:38:44 pm »
Well how does the amp do in a gig volume situation with a drummer? I ended up using the Red Channel throughout, because the Green Channel by itself isn't quite loud enough. The Red Channel is loud enough.  Channel switching isn't absolutely needed with the modified Red Channel, because it now cleans up fairly well by turning the guitar down, and you don't disappear in the mix. The down sound is the back ground noise on the Red Channel when a note isn't ringing out.  Is there a small waterfall nearby?

Offline LPBII

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Re: Marshall DSL15H project
« Reply #19 on: January 13, 2016, 12:37:40 am »
I need to post an update, since I solved the noise problem.

I changed the cathode cap on V1 with one of the same value and type.  It is an electrolytic cap.  This got rid of the nasty hiss and back ground noise. It really lowered the noise floor of the red channel. It was a bad cap causing the noise apparently. The green channel is dead quiet now as well.

But this also brought back some fizz on the red channel it seems.  I tried rolling some tubes through V1 to see if that helped.  First, I tried an old Groove Tubes from the 80s. That got rid of the fizz and drastically improved the tone. However, it also brought back a little noise.  I ended up using a Tung Sol re-issue in V1.  No fizz and hardly any noise. That gave it a much fatter and richer tone,  especially on the Green Channel. The Green Channel is no longer sterile.  It's dynamic with the guitar volume and pick attack and has some swirl now.

The Red Channel seemed brighter than the Green Channel now as well. I lowered the red channel bright cap to 150pf. This seemed to do the trick and its not a really problem sharing the Eq controls.

Overall, the amp sounds really good now. It sounds like a much more expensive amp. Not quite the overdrive higher gain tone of a Silver Jubilee, but quite acceptable, and this amp is no longer headed for ebay.

The Green Channel gets huge clean tones going now. It presents a big sound stage at playing with a drummer volume levels. I'll have to see how well it takes an overdrive pedal next.

To recap the mods:
)Adjusted the bias from 93% to 70%
) Changed the slope resistor in the internal Green channel fixed tone stack.
) Changed the Red Channel from the Lead 2 to Lead 1 specs of that of the big DSLs.
)Rolled some tubes with a Tung Sol RI in V1 when done.
)Lowered the Red Channel bright cap from 470pf to 180pf and then to 150pf.

Replaced a bad electrolytic cap.

The Red channel sounds best through Vintage 30s or Green Backs. The Green Channel sounds really good through G12T75s for cleans, especially in a big room with some natural reverb, but the 75s don't sound good with the Red channel for my style of playing, in my opinion. They just don't sing.

The deep switch is not needed unless your at absolute bedroom volume levels. At gig or rehearsal volumes the bottom end is plenty strong.

Offline darkbluemurder

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Re: Marshall DSL15H project
« Reply #20 on: February 05, 2016, 07:43:37 am »
Congratulations to the successful tuning project!

Cheers Stephan
Own: Area 67, Area 61, Area 58, VV Pro 54, Injector n, HB2, Cruisers, VSolo, SDS-1, Area T set, Virtual Hot T, Chopper, Chopper T, Bluesbucker, Breed set, Air Norton, Super D, DLX+, DLX-90, DP240, DP198, VHPAF, AT-1, Morse set
Owned: PAF Pro, Fred, Mega Drive, HS-1, HS-3T, Shock Wave set, Tone Zone

Offline cboysen

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Re: Marshall DSL15H project
« Reply #21 on: July 24, 2016, 06:09:20 pm »
Sorry for reviving a good old thread, but hopefully LPBII will read this


To recap the mods:
)Adjusted the bias from 93% to 70%
) Changed the slope resistor in the internal Green channel fixed tone stack.
) Changed the Red Channel from the Lead 2 to Lead 1 specs of that of the big DSLs.
)Rolled some tubes with a Tung Sol RI in V1 when done.
)Lowered the Red Channel bright cap from 470pf to 180pf and then to 150pf.


I have already modded the red channel to taste as per instructions from other fora.
I do however agree that the clean channel is a little 'dull' sounding, and I want to know what number on the schematic is the slope resistor (R??).

Also, did you adjust the R75 value with good results?
lastly; have you revisited any of the modifications and/or made new ones since this topic closed?

Kind regards, Christian.

EDIT: After studying the schematics again, I'm assuming R97 is the slope resistor?

« Last Edit: July 25, 2016, 05:54:43 am by cboysen »

Offline darkbluemurder

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Re: Marshall DSL15H project
« Reply #22 on: September 02, 2016, 04:37:03 am »
EDIT: After studying the schematics again, I'm assuming R97 is the slope resistor?

You are correct, R97 is the slope resistor of the non-adjustable tone stack, which is the equivalent of a Fender style tone stack with bass (R72) and mid (R73) controls turned up full, and the treble turned up partially. Adjust R74, R75 and R76 to get a different treble control setting.

Cheers Stephan
Own: Area 67, Area 61, Area 58, VV Pro 54, Injector n, HB2, Cruisers, VSolo, SDS-1, Area T set, Virtual Hot T, Chopper, Chopper T, Bluesbucker, Breed set, Air Norton, Super D, DLX+, DLX-90, DP240, DP198, VHPAF, AT-1, Morse set
Owned: PAF Pro, Fred, Mega Drive, HS-1, HS-3T, Shock Wave set, Tone Zone

Offline LPBII

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Re: Marshall DSL15H project
« Reply #23 on: November 01, 2016, 09:58:41 pm »

lastly; have you revisited any of the modifications and/or made new ones since this topic closed?

Kind regards, Christian.

EDIT: After studying the schematics again, I'm assuming R97 is the slope resistor?
Sorry I missed this.  I have a love hate relationship with the amp.  A few weeks ago I played it for a few minutes and turned it off as I thought about selling it.  Then a few days ago I grabbed it because it was handy and light weight for a jam. It sounded great! Just killer! Then at the same place yesterday, but through a small 1x12 cab, it was kind of disappointing again. Before, when it sounded so killer, it was through a THD design 2x12 with Vintage 30s.

What I think is very important with this amp is the speaker cab.  It loves Vintage 30s and needs at least a 2x12 cabinet.

Offline darkbluemurder

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Re: Marshall DSL15H project
« Reply #24 on: November 02, 2016, 05:02:17 am »
The speaker cab is an often underestimated piece of the sound chain.
Seems like this amp needs low end support from the two V30s.

Cheers Stephan
Own: Area 67, Area 61, Area 58, VV Pro 54, Injector n, HB2, Cruisers, VSolo, SDS-1, Area T set, Virtual Hot T, Chopper, Chopper T, Bluesbucker, Breed set, Air Norton, Super D, DLX+, DLX-90, DP240, DP198, VHPAF, AT-1, Morse set
Owned: PAF Pro, Fred, Mega Drive, HS-1, HS-3T, Shock Wave set, Tone Zone

Offline LPBII

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Re: Marshall DSL15H project
« Reply #25 on: November 09, 2016, 09:54:51 am »
Well I forgot to engage the deep switch with the smaller cabinet.  It doesn't need the deep switch with the larger cabinets, but its a good thing its there if you need to play through a smaller cab. I played it last night through the same 1x12 cab, and with the deep switch engaged. It sounded great!

The red channel modded is great to play through.  It really responds to volume knob riding well. Even with the gain cranked up to 7.5 you can clean up fairly well just turning down the guitars volume knob. But with the volume knob,  turned up, it can still do heavy. Just a great range in the sweep of the gain knob compared to stock. And that is even with a PAF clone. Even with the gain at 7.5 it doesn't get farty or mushy.  Most EL84 powered amps in this class can't say that. At lesser gain settings below 5 you can go from semi-clean to heavy blues with the sweep of the guitar's volume knob.

Here's a youtube of some of the Johnny Eggz mods that I used:

 https://www.youtube.com/watch?v=ewx4U5Hiv5I

Offline LPBII

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Re: Marshall DSL15H project
« Reply #26 on: November 09, 2016, 10:18:35 am »
I have already modded the red channel to taste as per instructions from other fora.
I do however agree that the clean channel is a little 'dull' sounding, and I want to know what number on the schematic is the slope resistor (R??).
Kind regards, Christian.

Stock, the green channel can be a good pedal platform -for front of the amp pedals.  The green channel gives a better range of tones with the 56k slope resistor in my opinion.  At least you don't need to run the green channel gain on 10 all the time. Stock, the green ch seems very scooped to my ears.

This amp is best used as a single channel amp. Pick the red channel and dial it in, or pick the green channel and dial it in, but it's not a great channel switcher mid song or mid set. The big DSLs are that way too in my experience.






Offline Gbob61

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Re: Marshall DSL15H project
« Reply #27 on: February 14, 2017, 11:11:24 am »
Greetings, my first post to this forum. I like this head a lot. I had the first 3 steps of the johnnyeggz mod done but the C34 was just snipped. I'm going to do the rest and was wondering if I should replace C34 and add the 10k resistor?  Also, is the green channel mod worth doing at the same time? Does it add gain or change the tone?
  On the subject of speakers, I've played mine through a few cabs. At a pickup jam one night I ran through the speakers of a Peavey Duel and it was amazing, I don't know if it was the Black Widows or 16 ohms or even the weight of the amp (80 pounds) but it rocked!
   I know this is an old thread but any advice would be appreciated. Thanks, Bob

Offline LPBII

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Re: Marshall DSL15H project
« Reply #28 on: March 20, 2017, 10:05:20 am »
Yes, you should replace C34 not just snip it. C34 just snipped can be a source if back ground hum and noise as well as hiss.