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Marshall DSL15H project
LPBII:
I have always liked the concept of a 6V6 Plexi, so when it became apparent that the DSL15H heads are availabe used for not a lot of money I snagged one with intention of modifying it.
The word on these amps was that the green channel is too clean and the red channel is too much gain. Well the DSL 15 watt only offers those two modes that nobody used on the old JCM2000 amps. What was the thinking here? They probably expected the customer demographic for this amp to complain if the gain was not over the top, and the clean was not clean enough. The amp can be modded, but if your not into modding amps these amps are pretty much useless to players other than modern metal players in its stock form. I will be following the mods pioneered by the guys over at the Marshall Amp forum, and the My Les Paul Forum. I hope nobody minds if I log the journey here.
First impressions:
Not very loud. Even through a 4x12 and cranked up it sounded not very loud. There is no way this amp can be used with a live drummer at this volume level. But then I noticed that the pentode-triode switch on the back was set to 1/2 power, or only 7.5 watts.
In 15 watt mode it was totally different. It can get loud. Exploring both channels through various knob settings and with both humbucker and single coil guitars revealed the following;
Green Channel. Way too clean and rather boring sounding. I had to use the Green channel gain knob on ten at all times for it to have any character at all. Turn it down to 9 and it became very weak and thin. I normally use PAFs and single coils and do not want to back to high output pickups.
There is a tone shift button that should never be used. It makes it sound like one of those 1970s Fender Twinns that we all hated. Even with the gain on ten the Green channel sounded "plinky". It had no sustain. Even more troubling, was that the bass notes were boomy through the Green Back loaded 4x12. It was a like a kick drum when ever a bass string was touched, especially with the Deep Switch engaged. The Deep Switch was not usable with the 4x12 when using the Green Channel.
Both the tone shift and the deep switches affect both the Green and Red channels.
Red Channel- What a fizzy mess! Bright, harsh, and fizzy, and waaaayyy too much gain. It is basically unusable. At least for me. Even with the gain knob at only 9:00 it is too distorted. With very low gain settings the Red is still too distorted although thinner. With low gain settings and the volume whacked up to ten, I think I can hear some mojo from the 6V6s under all that fizz. I think.
With the Green channel on ten/ten it is still too clean. And boomy.
What I disliked most about the amp, though, was how stiff it both sounds and feels. It does not breathe like a traditional tube amp at all. In fact despite the all tube signal path it feels almost solid state. Stiff and tight to the point of brittleness. The Red channel does not sing, and the Green channel is plinky sounding.
Many have modded the Red channel into something usable but left the Green channel alone. I will be modding both.
darkbluemurder:
Cool stuff - and yes, the way you describe it modding both channels seems obvious.
Good luck with the project,
Stephan
LPBII:
Thanks,
I took the chasis out and checked the bias before running it loud at my current loud playing space yesterday. The bias was way out of whack. One tube was dissipating 94% of max dissipation and the other was at 82%. I set them both to 70%. It did improve the basic tone on both channels. The green is much less boomy now, but still needs the gain on max to sound decent. The red is smoother but still fizzy. Gone was an annoying treble spike on the Red Channel.
While I had the amp apart, I noticed that the filter caps are 100uf. This explains the stiffness of the amp. 50uf filter caps are on the list of things to try now.
Previous to the bias check I tried it in some different cabs with Vintage 30 speakers.
V30 1x12 open back- It sounded better than through the 4x12 for the most part. The Red channel was boxy and a bit nasal, but the Green now wasn't boomy at all with the Deep Switch not engaged. This speaker is a 90s Mesa spec that doesn't have the infamous upper mid spike.
V30 large volume 1x12 closed back- Smoother yet and a little less boxy. Solid lows without too much boom.
I also A/Bed the amp against some others of mine for reference tones.
Green CH vs MetroAmp JTM45- Should not have done this. The DSL Green ch sounded like a transistor radio compared to the JTM45 run clean.
Red Ch vs Silver Jubilee 50/25 watt. I expected this. The Jub completely destroyed the DSL's gain channel. The Jubilee gain channel just sings and is so 3d and dynamic. The Jubilee has not near the hiss and buzz when its not playing a note either. The DSL red Ch is real noisy.
Orange Micro Terror 20 watt. Should not have tried this either. The 1/2 solid state Orange sounded way more tubey and organic. And dynamic. Although the Orange only has three knobs you can set the gain knob up to about 3 O'clock and control the tone from your guitar volume. Turn your guitar down and the Orange cleans up (not completely of course) and crank the guitar volume on a humbucker and its a nice driving overdrive with out fizz. It is as loud as the DSL15.
At the rehersal space, which has high ceilings and hard wood floors and plenty of natural hall reverb, the DSL sounded pretty good. The fizz gets lost, for the most part, in the mix and also the woosh of the room. You can still hear it but with the masters cranked up, you can hear the 6V6s starting to take over and overide the fizz and thinness. Below 6 on the masters and it is noticably thinner. The triode mode cranked is good on both channels. I ran it through the V30 closed cab.
darkbluemurder:
--- Quote from: LPBII on October 08, 2015, 10:05:23 AM ---While I had the amp apart, I noticed that the filter caps are 100uf. This explains the stiffness of the amp. 50uf filter caps are on the list of things to try now.
--- End quote ---
Are you saying 100uf also for the preamps? Way too much IMHO. For the preamp 20-22 uf is sufficient. I don't mind 100uf on the power tube plates and screens but 50uf mostly works.
--- Quote from: LPBII on October 08, 2015, 10:05:23 AM ---Green CH vs MetroAmp JTM45- Should not have done this. The DSL Green ch sounded like a transistor radio compared to the JTM45 run clean.
--- End quote ---
The JTM45 is one of my favorite clean tones - hard to beat.
R
--- Quote from: LPBII on October 08, 2015, 10:05:23 AM ---ed Ch vs Silver Jubilee 50/25 watt. I expected this. The Jub completely destroyed the DSL's gain channel. The Jubilee gain channel just sings and is so 3d and dynamic. The Jubilee has not near the hiss and buzz when its not playing a note either. The DSL red Ch is real noisy.
--- End quote ---
It is long ago that I had a Jubilee (the 50W top). I should have kept it. It sounded really nice and was not as loud as the regular 50W Marshalls are.
Cheers Stephan
LPBII:
All the caps are the board. These caps are on the power amp, and the pre-amp derives its power supply from there through a resistor instead of a choke.
50 watt Marshalls have always used 50uf filter caps through out, including 50uf on both sides of the choke. The original JTM45 only used 16uf . Many run a 32uf on the power amp side of JTM45s (including mine) to prevent ghosting.
The 100 watt circuits have general ran 100uf on the power amp side, and 50uf on both sides of the choke like the 50 watt, but there is quite a complicated history of the evolution of the filtering of the 100 watt amps. Early plexi 100s had low filtering (often ghosting) and then by about 69 they had high filtering. Then in about 1986 they reduced the number of the filter caps on the 100s to make them easier to build. A lot of people think that the pre 86 100 watt JCM800s have more punch.
Hiwatt 100s make an interesting comparision. Hiwatts ran 200uf on the power amp, 100uf on the screens, and 50uf on both sides of the choke. (BTW the Jubilee tone stack and taking the signal to the tone stack from the plate instead of the cathode are based on the Hiwatt amps design)
Orange and Matamp ran 100uf and only 16 uf on both sides of the choke.
Fender Tweeds ran about 20uf caps throughout. The Black Face Fender amps started running about 70uf on the power amp side which became more standard after the CBS take over going into the silver face era. By the 70s many Fenders were running 200uf on the power amp side.
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