Marshall DSL 40C tone stack

[Neal]

Gents, I just picked up a little Marshall DSL 40C amp for the 80s cover band I'm playing with.
I'd like to drop the mid frequency control... in a very unscientific experiment with an old frequency analyzer, it seems the Marshall mid control is centered around 1.6K. My Carlson Turbo-pup, which has the best tone control ranges in any amp I own, has the mids centered around 800 Hz. It's been a long time since I messed with tone stacks... can someone point me to which caps and values I need to swap out to bring the Marshall mid frequency down a little?
Schematic here.... http://www.tangible-technology.com/s...-60-02-v02.pdf

Thanks in advance, guys!

[J M Fahey]

Gents, I just picked up a little Marshall DSL 40C amp for the 80s cover band I'm playing with.
I'd like to drop the mid frequency control... in a very unscientific experiment with an old frequency analyzer, it seems the Marshall mid control is centered around 1.6K. My Carlson Turbo-pup, which has the best tone control ranges in any amp I own, has the mids centered around 800 Hz. It's been a long time since I messed with tone stacks... can someone point me to which caps and values I need to swap out to bring the Marshall mid frequency down a little?
Schematic here.... http://www.tangible-technology.com/s...-60-02-v02.pdf

Thanks in advance, guys!

1)
the BIG question: which channel are we talking about?
Are you interested in clean ch EQ or the dirty one?

2) simulate it in Duncan's TSC and play around with values until happy.

3) that said, and as a starting point, the clean ch does have a tone control, although fixed set.
A`Fendery one with Bass on 10 , Mid on 10 , and Treble around 6 or 7 (or exactly on 6 with a linear pot, which you can simulate)
I wouldn't touch that one.

4) the Main tone stack ... hey !!!! you already have a frequency shifting possibility built in !!!!!!!!!!!!!!!!!!!!!
Simulate both switch positions on TSC .

If you want to go lower anyway, you must double the Bass cap(s) C54/C51/C47 from 22nF to 47nF , or Treble caps, from 470pF to 1000pF or both which will yield a stronger effect ... maybe too much.

To avoid destroying the PCB with repeated desoldering and pulling, I suggest a Plan B, with most of the advantages:
just replace C54 with 47nF , C50 with 10 or 15 nF , C56 with 220/250pF and C53 with 1000pF .
Then you have , switch selectable, the highest of the earlier settings and a new one,lowered one full octave.

In fact you may leave that Mod there forever, since it's switchable.
And it involves replacing 4 caps, just once.

Always pamper the board.

In my book, "the PCB IS the amplifier, parts are parts which can be bought over the counter anywhere for peanuts"
Try that with a PCB

Gosh!!!! , it feels GOOD thinking about a REAL Tech problem

PS: buy regular, fresh caps; avoid Domino caps at all costs, they bring very bad Karma over its user's heads.
you can lower about 1/2 octave by doubling

[Neal]

FANTASTIC response! Thanks, Mr. Fahey!
Yes, I'm talking about the dirty channel. The tone shift button helps a little, but not much. My goal mainly is to make the mid control more usable. I will definitely investigate the changes you've suggested. Thanks for the quick response!

1)
the BIG question: which channel are we talking about?
Are you interested in clean ch EQ or the dirty one?

2) simulate it in Duncan's TSC and play around with values until happy.

3) that said, and as a starting point, the clean ch does have a tone control, although fixed set.
A`Fendery one with Bass on 10 , Mid on 10 , and Treble around 6 or 7 (or exactly on 6 with a linear pot, which you can simulate)
I wouldn't touch that one.

4) the Main tone stack ... hey !!!! you already have a frequency shifting possibility built in !!!!!!!!!!!!!!!!!!!!!
Simulate both switch positions on TSC .

If you want to go lower anyway, you must double the Bass cap(s) C54/C51/C47 from 22nF to 47nF , or Treble caps, from 470pF to 1000pF or both which will yield a stronger effect ... maybe too much.

To avoid destroying the PCB with repeated desoldering and pulling, I suggest a Plan B, with most of the advantages:
just replace C54 with 47nF , C50 with 10 or 15 nF , C56 with 220/250pF and C53 with 1000pF .
Then you have , switch selectable, the highest of the earlier settings and a new one,lowered one full octave.

In fact you may leave that Mod there forever, since it's switchable.
And it involves replacing 4 caps, just once.

Always pamper the board.

In my book, "the PCB IS the amplifier, parts are parts which can be bought over the counter anywhere for peanuts"
Try that with a PCB

Gosh!!!! , it feels GOOD thinking about a REAL Tech problem

PS: buy regular, fresh caps; avoid Domino caps at all costs, they bring very bad Karma over its user's heads.
you can lower about 1/2 octave by doubling

[MarkusBass]

1)
the BIG question: which channel are we talking about?
Are you interested in clean ch EQ or the dirty one?

3) that said, and as a starting point, the clean ch does have a tone control, although fixed set.
A`Fendery one with Bass on 10 , Mid on 10 , and Treble around 6 or 7 (or exactly on 6 with a linear pot, which you can simulate)
I wouldn't touch that one.

I wouldn't be so sure about it. What you consider to be a "fixed tone stack" is a fixed tone stack (you may consider it to be a filter before the Gain pot) but later there is a tone stack which is switchable between the Clean and Dirty channel by means of the FRT3 relay. So if you modify the tone stack, the modification will affect both channels.

Mark

[Neal]

I wouldn't be so sure about it. What you consider to be a "fixed tone stack" is a fixed tone stack (you may consider it to be a filter before the Gain pot) but later there is a tone stack which is switchable between the Clean and Dirty channel by means of the FRT3 relay. So if you modify the tone stack, the modification will affect both channels.

Mark

Good point. Yes, the tone controls affect both channels.

But, if I'm reading this correctly, Mr. Fahey's last mod will just affect the 'tone shift' button, and IIRC, that is only the dirty channel. I'll know more after I get home from work and open it up.
Neal

[MarkusBass]

You may be right but your first post wasn't clear for me. So you want to add MID pot to the filter (fixed tone stack) before the GAIN pot in the CLASSIC channel, right? Are you sure it is now 1.6kHz? Let me check it (give me a moment).

EDIT: I asked about the frequency of the filter because mid filters are usually set somwhere between 300 and 600 Hz. The one on the schematic is set to exactly 400 Hz. With 22k linear pot (instead of the R11 resistor) you will get frequency response like below. Are you sure that you measured the first filter and not the PRESENCE, or RESONANCE control? You should measure the frequency resonce on the GAIN pot.



Mark

[J M Fahey]

I was answering as I was reading, so it was a work in progress.
Yes, the visible tone control affects both channels, the fixed one only the clean one.
Usually would have gone to advanced view, click preview post and edit smaller details, but DAB used most of the allowed time slot and then some.
Complain to *him* .

[MarkusBass]

Juan,

I'm reading the discussion about Domino cap with great interest . Hopefully, the problem is solved now.

Mark

[Neal]

You may be right but your first post wasn't clear for me. So you want to add MID pot to the filter (fixed tone stack) before the GAIN pot in the CLASSIC channel, right? Are you sure it is now 1.6kHz? Let me check it (give me a moment).

EDIT: I asked about the frequency of the filter because mid filters are usually set somwhere between 300 and 600 Hz. The one on the schematic is set to exactly 400 Hz. With 22k linear pot (instead of the R11 resistor) you will get frequency response like below. Are you sure that you measured the first filter and not the PRESENCE, or RESONANCE control? You should measure the frequency resonce on the GAIN pot.
[ATTACH=CONFIG]35941[/ATTACH]

Mark

Mark, first, thanks for the responses! Let me recap a little for clarification... when I first played through the little Marshall amp, I noticed the mid control seemed to be voiced for a higher frequency than I was used to (I'm a Fender guy). So, I got out my old frequency analyzer and pumped pink noise through the Marshall. I turned the tone knobs up and down, and noted where the center frequency seemed to be. Naturally, they changed a pretty wide spectrum. On the Marshall, the mid control center frequency seemed to be around 1.6K. Doing the same exact thing with my Turbo-Pup, the mid control seemed to be centered around 800 hz. What I'd LIKE to do, if possible, is to drop the center frequency on the Marshall mid control to 800 hz or so, like it is on the Turbo-Pup.
Does this make sense? The treble, bass and presence controls do exactly what I expect them to do, but the mid control, instead of adding warmth and fatness, just seems to add a harshness that my ears don't like.
Thanks, guys!

[MarkusBass]

Does this make sense?

The problem is still not clear for me. I understand that you have two amps: Carlson Turbo-Pup and Marshall DSL40. The first one has MID control at 800 Hz and the other at 1.6 kHz - and you want to change it (in Marshall). How about posting a schematic of the first amp - just to be able to compare them? And since you have the first amp, how about opening it and checking what are the differencies in the tone stack?
Someone suggested (I'm not sure if it was you, or not) that you want to modify the MID frequency in the "fixed tone stack" filter in the CLEAN channel. I showed you that the filter is set to 400 Hz. I told you that the "real" tone stack is used in both channels (it seems that you didn't know this previously). And you are saying now that the amp has MID control frequency set to 1.6 kHz. So are we talking about the CLEAN channel, or both? Are we talking about the "common" tone stack - VR5, VR6 and VR7 pots?
How do you measure the frequency response of the amp? On the speaker output, or on the GAIN pot in the CLEAN channel (VR1)? I would measure it on the GAIN pot, just to check at what frequency is the fixed tone stack set.
The amp has several other controls and switches. There is SW4 switch directly in the tone stack. It switches the frequencies of the tone stack. Is the 1.6 kHz frequency measured in both positions of the switch? Then you have PRESENCE and RESONANCE controls. During your measurements is the RESONANCE switch on, or off?
I'm affraid that some other part of the amp influences the frequency response of the amp and in order to learn more about it, you should measure the frequency response stage by stage. And of course inform us about switches and other tone controls (how they are set) during the measurements.

Mark

[Neal]

The problem is still not clear for me. I understand that you have two amps: Carlson Turbo-Pup and Marshall DSL40. The first one has MID control at 800 Hz and the other at 1.6 kHz - and you want to change it (in Marshall). How about posting a schematic of the first amp - just to be able to compare them? And since you have the first amp, how about opening it and checking what are the differencies in the tone stack?
Someone suggested (I'm not sure if it was you, or not) that you want to modify the MID frequency in the "fixed tone stack" filter in the CLEAN channel. I showed you that the filter is set to 400 Hz. I told you that the "real" tone stack is used in both channels (it seems that you didn't know this previously). And you are saying now that the amp has MID control frequency set to 1.6 kHz. So are we talking about the CLEAN channel, or both? Are we talking about the "common" tone stack - VR5, VR6 and VR7 pots?
How do you measure the frequency response of the amp? On the speaker output, or on the GAIN pot in the CLEAN channel (VR1)? I would measure it on the GAIN pot, just to check at what frequency is the fixed tone stack set.
The amp has several other controls and switches. There is SW4 switch directly in the tone stack. It switches the frequencies of the tone stack. Is the 1.6 kHz frequency measured in both positions of the switch? Then you have PRESENCE and RESONANCE controls. During your measurements is the RESONANCE switch on, or off?
I'm affraid that some other part of the amp influences the frequency response of the amp and in order to learn more about it, you should measure the frequency response stage by stage. And of course inform us about switches and other tone controls (how they are set) during the measurements.

Mark

Hey guys! Just dropping in to let you know I'm still pursuing this issue. Thanks for all the responses!
Mark, the Turbo-Pup was built by Mark Norwine, and the schematic is not available. I've thought about drawing one up for my own reference, but it's Mark's own design and I wouldn't post it without his permission.
My schedule has been pretty crazy lately, but yesterday I found time to tinker on the Marshall a little. I disconnected the bright cap, put 12AT7s in the second and fourth position, and put in an EV speaker in place of the stock Celestion. The tone is MUCH better, although now the amp is a lot heavier. Between working, gigging and trying to winterize the house before the Ohio weather changes, I haven't had time to dig any deeper. When I do, I'll post back. Thanks again, everybody!