#1
First of all here is the schematic:
http://music-electronics-forum.com/attachments/33886d1431127848-dsl40-60-02-v02.pdf

I only use the lead 1 setting, with gain just a bit less than 6, but it`s not enough gain for me so I am forced to use a booster pedal because if I set the gain to 7 it gets too muddy, with a very dirty, loose bass.

There is a resistor R32 (near GAIN pot VR3). If I removed it, would I get the gain of Lead 2 with a frequency response of Lead 1 ?
Maybe you suggest just replacing it with a larger value resistor, like a 300K ?
Has anyone done a mod like this?
Last edited by ArturPr at Aug 26, 2016,
#2
The switch SW3b takes the signal thru the R32 to ground, so shorting it would just mute it, and removing it would make the b-half of the switch do nothing. SW3A shorts the R22 and puts more gain thru the cathode of V1B. What I would to to tighten thing up:
C12 -> 1uf, boosts less low frequencies, also affects other channels
C13 -> 0.47uF, same as above, only lead channel

I can make up other mods if I can be arsed and you want more
#3
If I did the mods you suggested AND the "c19 mod", would it make the bass response even across the whole gain range?
#4
a lot of people use boosts. if you like how it sounds with the boosts, who cares?

also have you changed the speaker?
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#5
Quote by ArturPr
If I did the mods you suggested AND the "c19 mod", would it make the bass response even across the whole gain range?


I'm pretty sure that the answer is yes. The C19 is the bright cap, and it passes too much treble for many ears.
The DSL40 circuit is very similar to the JCM2000 DSL circuit, and I have that amp, very modified. And I really recommend to remove the C19, or at least replace it with 100pF cap. I removed it straight.
#7
Quote by ArturPr
Can you tell me what more mods did you do to your jcm2000?


Oh boy, so many of those... I did around 25-30 component swaps or removals. I'd suggest you to check out this thread at Marshall Forums. There I gathered most of the information and mods. I believe there is also other threads in the forum specially about your amp.

I can throw some ideas now by looking at your schematic.
  • Remove R117 and C90
  • Jumper R118 and C91

These make the amp more touch sensitive, and classic Marshalls have only 68k and 1M resistors at the input, which are R13 and R9
  • Remove C20

I believe this is mudding up the Lead 2, I removed this in my JCM2000

Is this enough? I can go all the way to the gain structure and such, but not at the moment, because of my personal obligations . Goes for the next week

P.S be safe with the voltages
#8
Thanks for so much info. I guess we could spend years talking about modding amps :P.
I think I will do the following:
-Remove C19 and C20. C20 is simply a low-pass filter just killing all the highs on the LEAD 2 mode.
-Remove R117 and C90 and jumper R118 and C91.
-Replace C12 with a 1u cap

I am not sure about theese few things:
-Is installing a choke a good idea?
-Can I solder the components without removing the whole board? If it`s plated through-hole design then it may be possible... but I want to be sure.
-I may change R32 to 220K

Is shorting the power supply capacitors a safe way to discharge it, or can it damage those caps?
#9
A choke is a taste preference-kind-of thing. I myself liked the sound very much. It basically makes the low end tighter and warmer. The negative traits would be the price of the choke, installing it (more soldering and drilling) and the combo is so small that I'm not sure can you hear the difference so dramatically.
I recommend to remove the boards for less hassle with the iron, and the tight spaces.
I don't believe the capacitors would suffer, I believe they also have a small drain that minimizes the maximum peaks that would damage it.

Have fun with the modding!
#10
Actually... putting it back together would be a bigger problem than removing the board haha. I can imagine myself connecting wrong cables to wrong places... and there is quite a bit of them. I will wait with modding, I need to get the parts, which may be hard, especially with the choke. Anyways - I will open the amp up today to see exactly what I am dealing with. And I hope I survive it
#11
Ok I ended up modifying the input board by removing all the elements and adding a jumer. It changed something.... I can`t describe it, but it feels better and reacts to pedals better
#12
Ok I seriously consider installing a choke. Any recomendations for inductance, resistance and such? Theese are the chokes I can easily get:
(10H, 125mA, 115Ohm) and (4H, 90mA, 105Ohm. They claim it`s a Fender Twin choke)
I can try getting a 20H choke, but I would have to wait a longer time for shipping.

BTW: If posting a few replies one under another is illegal, please tell me. I didn`t find anything about it in the rules section, sooooo......

Edit: what do you think about puttin KT66 valves in?
Last edited by ArturPr at Jul 22, 2016,
#13
Ok I know why I hated the amp so much.... I am almost sure the tubes were dead. They were running at 48mA at 490V. And it played a few gigs, so I guess they were red-plating. What power tubes do you recommend? Again, can KT-66 be good?
#14
Sorry for the inactivity, I can't reply threads on my mobile and I just got on my computer.
I have a 3H 250mA choke on my DSL (Hammond 194G), I think the same value works on your amp too. Too much henries and the sound may sag too much.
I think you mean KT-77, 66 is a tetrode, which is like a 6L6. And for both, they draw more heater current, so your power transformer may not withstand it. I have no experience. But if you just need new tubes, JJ EL34 is my suggestion. I have only little experience on changing power tubes on my amp, I still run the original tubes (2010-) on my DSL and I like the sound.
#15
The datasheet says el34 draw 1,6A and kt77 draw 1,4A at 6,3v. I bought the last choke they had in store but it was broken when I got it so I had to return it :/
#16
i run mine with a jhs(I know, everyone thinks the co. is suspect) prestige, sounds rad, I keep it on all the time and use a ts808 as od. To my ears, it sounds really tasty!
#17
Oh, I would definitely change the speaker. I know this isn't the most obvious choice, but I put an Eminance swamp thang in, it sounds huge!!
#18
SacredJones, I don`t want to mess with removing the board again, and I need the bass even tighter, do you think removing C22 is a good idea? I can`t change it`s value without removing the board so it`s either stock, or removal. What do you think?

EDIT: new schematic ( also changed in OP ) http://music-electronics-forum.com/attachments/33886d1431127848-dsl40-60-02-v02.pdf
Last edited by ArturPr at Aug 26, 2016,
#19
Quote by ArturPr
SacredJones, I don`t want to mess with removing the board again, and I need the bass even tighter, do you think removing C22 is a good idea?


C22 only takes out some of the shrill high end, it's not gonna make a difference in the low register. I suggest you keep it, it's a basic component in the Marshalls. The only real way to tighten the tone is to alter the cathode bypass capacitor values. Or to lower the coupling cap values, but altering them affects more on the EQ-basis on the tone, not really on the tightness, expect if it is before the major distortion stage. But yes, you really have to remove the main boards, even if it's a hassle