Modifications for Marshall MS2

[Big Monk]

Here is the schematic:

https://4.bp.blogspot.com/_VuFNYQK52XE/TAi_l6o-J7I/AAAAAAAAARk/3KRThCRfahA/s1600/MS_2+schematic.png

Anybody have any insights on some tonal improvements for these? These are the little amps my 6 year old and I jam together with. Looking at ways to alter gain (up/down) and alter frequency response.

[mth5044]

Wow, that's quite a little guy!

You could try removing everything pre-volume control and copy/paste in a decent small part count circuit that emulates a preamp to give you gain/tone/volume controls. May need to relocate the powder/channel switch. Maybe something like the son of scream/tube screamer without the buffers.

[Big Monk]

Wow, that's quite a little guy!

You could try removing everything pre-volume control and copy/paste in a decent small part count circuit that emulates a preamp to give you gain/tone/volume controls. May need to relocate the powder/channel switch. Maybe something like the son of scream/tube screamer without the buffers.

Yeah! We are a musical household!

I'm going to dig into the circuit to see if some tweaking can be had. I'm thinking more tweaks to just the stock circuit rather than rebuilding or adding anything.

[Eb7+9]

You could try removing everything pre-volume control and ...

just wire the master volume pot straight to the input jack, bypassing the single gain stage and tone controls ... almost any dirt box can play the role of preamp and this way you're not stuck with one sound // look up Doug Hammond's Meteor while you're at it

[Big Monk]

You could try removing everything pre-volume control and ...

just wire the master volume pot straight to the input jack, bypassing the single gain stage and tone controls ... almost any dirt box can play the role of preamp and this way you're not stuck with one sound // look up Doug Hammond's Meteor while you're at it

I'll look into it. I'm also going to look into the devices currently in it and play with the circuit as well.

[DIY Bass]

My son has a Marshall MG-15 practise amp and I thing the dirt channel is not too different from a Guvnor from memory.  Tone controls are shared between the 2 channels. A lot of what you can do will depend on how much space you have to play with.

[ElectricDruid]

How about adding a couple of diodes to the transistor stage with a little SPST toggle so that you can switchably turn it into a big muff fuzz stage instead?

I mean, it might sound like a wasp trapped in a tin can, but we'll never know until you try it!

[Big Monk]

All great suggestions!

I think I may start by doing some cap swaps to tame some high end harshness, then adjust the overall gain structure of the drive channel by adding a gain control and modifying the booster stage.

The tone control may be a good candidate for modification as well. Thanks everyone!

[bluebunny]

I have this modded version amongst my stash:



BTW, the original schematic needs correcting so that the 510R resistor is only engaged for the phones output.

[Big Monk]

I have this modded version amongst my stash:



BTW, the original schematic needs correcting so that the 510R resistor is only engaged for the phones output.

Nice!

I was also thinking about tinkering with the 470pf across pins 1 and 4.

[j_flanders]

Are you actually using that built in one inch speaker?
If so, I'd make a speaker out and run it through a 12" guitar speaker.
You might not need to change anything else.

So many of these cheap, small SS guitar amps sound a LOT better through a real guitar speaker.

Often times on these small ss amps I also prefer the tone of the headphones out. You can use it as a speaker out. For low volume bedroom playing it's just loud enough through a Celestion Vintage 30 for example. You may need to lower the 220uF cap if it sounds too dull.

[Big Monk]

Are you actually using that built in one inch speaker?
If so, I'd make a speaker out and run it through a 12" guitar speaker.
You might not need to change anything else.

So many of these cheap, small SS guitar amps sound a LOT better through a real guitar speaker.

Often times on these small ss amps I also prefer the tone of the headphones out. You can use it as a speaker out. For low volume bedroom playing it's just loud enough through a Celestion Vintage 30 for example. You may need to lower the 220uF cap if it sounds too dull.

Well the internal speaker is 3.5" I believe and yes, when my son and I are playing we use the internal speakers. I have a few tube amps and smaller cabs to use but in general these are practice and family jam amps for my 6 year old and me so I'm just looking to improve the base tone of the amp and the internal speaker.

[Steben]

Are you actually using that built in one inch speaker?
If so, I'd make a speaker out and run it through a 12" guitar speaker.
You might not need to change anything else.

So many of these cheap, small SS guitar amps sound a LOT better through a real guitar speaker.

Often times on these small ss amps I also prefer the tone of the headphones out. You can use it as a speaker out. For low volume bedroom playing it's just loud enough through a Celestion Vintage 30 for example. You may need to lower the 220uF cap if it sounds too dull.

Well the internal speaker is 3.5" I believe and yes, when my son and I are playing we use the internal speakers. I have a few tube amps and smaller cabs to use but in general these are practice and family jam amps for my 6 year old and me so I'm just looking to improve the base tone of the amp and the internal speaker.

well uhm.... thats hard. A 12" speaker is 1000% better tone.
You could add 12db/octave low pass filters at somewhere between 3 to 5 kHz but you will loose some volume.

[Big Monk]

Are you actually using that built in one inch speaker?
If so, I'd make a speaker out and run it through a 12" guitar speaker.
You might not need to change anything else.

So many of these cheap, small SS guitar amps sound a LOT better through a real guitar speaker.

Often times on these small ss amps I also prefer the tone of the headphones out. You can use it as a speaker out. For low volume bedroom playing it's just loud enough through a Celestion Vintage 30 for example. You may need to lower the 220uF cap if it sounds too dull.

Well the internal speaker is 3.5" I believe and yes, when my son and I are playing we use the internal speakers. I have a few tube amps and smaller cabs to use but in general these are practice and family jam amps for my 6 year old and me so I'm just looking to improve the base tone of the amp and the internal speaker.

well uhm.... thats hard. A 12" speaker is 1000% better tone.

I agree 100%. But i'm not planning to play it through a bigger cab. My son and I play through them together at low volumes, which is what they are best for.

Hence the challenge!

[Big Monk]

I've had a few of these little guys since my son and I got them a few years ago. I had come off a long hiatus from playing (having kids, going back to college, etc.) and they seemed like a good option for a 4 year old and his crusty old Dad for low volume practicing.

My son's became a sort of labor of love after his input jack failed. I replaced is but also his speaker made the amp sound pretty ratty. We ended up practicing more unplugged and when he got drums, we typically trade off in jams on guitar and drums.

Fast forward to a few weeks ago. I'm putting together a little single-ended tube amp from a donor PCB from a Version 3 Epiphone Valve Junior. I built a head and speaker cab and found a good deal on a Celestion G10N-40. I started the cabs around 2 weeks ago and put the finishing touches on the speaker cab a few days ago. Installed the Celestion and remembered that the MS-2 stereo headphone jack can function as an Ext. Cab out with a jumper across the limiting resistor and only inserting the plug half way in.

Yowza! This thing is certainly not a toy after running through the 10" Celestion. I was impressed by the output but it is WAY too loud for practice, so i plugged the speaker into my un-modified MS-2. Since the limiting resistor was still there, plugging the cab in gave a perfect practice volume but with fully cranked tones. So, I removed the jumper on my other MS-2 and wired in a 1kB pot as a variable resistor. Goes a little lower in volume than the stock 510 ohm limiting resistor but also all the way up to full volume with the pot wide open.

So now to the real question: Anyone ever taken a look at the schematic for this? I'll post it here and if anyone has any suggestions for tone related mods, i.e. capacitor swaps, resistor changes, control mods, etc., i'd like to learn more about this little guy.

Here is the schematic:



Here is the datasheet for the KIA6213:

https://pdf1.alldatasheet.com/datasheet-pdf/view/69377/KEC/KIA6213S.html

Here is the datasheet for the C3198:

https://datasheetspdf.com/pdf-file/1056951/Elite/C3198/1

[vigilante397]

Looks like your power chip is rated for 1/2W, which anyone that has built a Ruby or similar knows that's nothing to scoff at through a decent sized speaker.

Looking at the preamp it's hard to know what mods to recommend. The "clean" setting sends the input straight through the tone section into the power amp, whereas the "OD" gives you a vaguely LPB-1ish boost in front. It would be interesting to see what would happen with a different preamp section, obviously I would encourage you to try a tube preamp, but frankly replacing the whole input section with a low-mid gain overdrive could be interesting.

[tonyharker]

There is already a thread about modding the MS-2 here https://www.diystompboxes.com/smfforum/index.php?topic=123618.0

[Big Monk]

There is already a thread about modding the MS-2 here https://www.diystompboxes.com/smfforum/index.php?topic=123618.0

My thread! 

Sorry about that guys. I vaguely remember either starting or chiming in on a thread about this. My bad.

[PRR]

>> There is already a thread about modding the MS-2 here
> My thread!    Sorry about that guys. I vaguely remember either starting...

Threads merged.

[Big Monk]

>> There is already a thread about modding the MS-2 here
> My thread!    Sorry about that guys. I vaguely remember either starting...

Threads merged.

Thank you for that!