ANY MARSHALL TRANSISTOR MODS?
Question:
I’ve got a Marshall 2195 JMP Lead + Bass transistor head. It really sounds like crap! I’ve looked for some modification tips to improve this amp but havent found anything on the net. I’ve started replacing transistors with origional models as listed in the schematic: http://www.drtube.com/schematics/marshall/2195.gif It seems that someone has replaced alot of them with more-generic-but-compatible transistors, which i’m hoping is the main cause for it sounding so harsh. I have tube amps that sound great, so making this amp usable is a side project. Does anyone know any tips for improving marshall transistor amps? Are there any decent mods that are worth recomending? Thanks…
Response:
- Hide quoted text — Show quoted text – > I’ve got a Marshall 2195 JMP Lead + Bass transistor head. > It really sounds like crap! > I’ve looked for some modification tips to improve this amp but havent > found anything on the net. I’ve started replacing transistors with > origional models as listed in the schematic: > http://www.drtube.com/schematics/marshall/2195.gif > It seems that someone has replaced alot of them with > more-generic-but-compatible transistors, which i’m hoping is the main > cause for it sounding so harsh. > I have tube amps that sound great, so making this amp usable is a side > project. > Does anyone know any tips for improving marshall transistor amps? > Are there any decent mods that are worth recomending? > Thanks…
There’s not much to the front end of that amp. You could do whatever you wanted. Just for fun on an old Crate G600 head I had laying around waiting to be stripped to build a tube circuit into, I replaced the 1N4148 clipping diodes with germanuim transistors (using one junction). Trimpots went inline with them to gnd to dial in some asymetric clipping. Ended up sounding nicer than before. The guts now reside in the chassis/case from an old style c-band sattelite reciever…..I use it for a test amp.
Response:
>I’ve got a Marshall 2195 JMP Lead + Bass transistor head. >It really sounds like crap! >I’ve looked for some modification tips to improve this amp but havent >found anything on the net. I’ve started replacing transistors with >origional models as listed in the schematic:
Yeah, don’t ya love those ECG/NTE book owners who think all they have to do is throw a 123 or a 159 into it, and BINGO.. hehehehehehe On the other side, I rebuilt a VOX Venue amp with all ECGs, and it sounded better. Sometimes ya have to tweek the bias values. FEW..very FEW SS UK guitar amps sound good from the old days, like the Venue, so it maybe was a plus. Today, the SS UK amp you get most likely was made elsewhere. USA to a $ point too. But..back to your amp… >It seems that someone has replaced alot of them with >more-generic-but-compatible transistors, which i’m hoping is the main >cause for it sounding so harsh.
IF they were replaced with ECG/NTE real replacements, it shouldn’t be that bad, but if by those who think ‘2nxxxx’ is damn flocking close to a ‘BCyyyyAP’ rebuilt it..you’re in for fun. Let’s start with the amp working, but needs a sound tweek. Clean up the V+ in the preamp stage(s), separating between the V+ n R17 & at R11 and TR2/R5, add res/caps there. Reduces hiss. 4700UF of power amp cap is a joke, double it? Add a 1uf cap across it..? Replace every power amp resistor with 1% MF..? This is a BASS amp, you need more cap. R35..R36…R28…R31…R33…R32 ALL as big as 5+ watt, and *1%* Tol. These bias your output Transistors n get hot. R37 MUST be as big a watt as can fit, 1%, WW FP etc. The ‘choke’ might be just a wound wire coil, that can be replaced with a GOOD coil, or ..IF it is just a wound hollow wire, find a piece of (solid dense) wood to fit tight inside WITHOUT moving the coil,then SOAK it in some good lacquer and let it dry..do it again a few times.. ONLY the 1st time, squeeze the coil tight, SOAK the wood too, let it DRY BETWEEN times. When done, scrape the tips and replace it in the amp. Coil will be tighter, and not vibrate. Look at old radio coils. And you can do it at home… Folks here will laugh, as this is stupid overkill, but it WILL improve the sound of any SS amp, spec them there UK/SS things. Sound, you have few options. Caps in the Preamp stage could be made NP (C4 n C5). ALL ‘pf’ caps could be Silver Mica. I wouldn’t mess TOO far from the bias resistor values, the schematic doesn’t show V at certain points, so you can only guess (within range) what they SHOULD be with the transistor you have. BC’s even in production differ big time. >I have tube amps that sound great, so making this amp usable is a side >project.
If ya’ bored, you can bias the preamp transistors to a -V ? Flock around with TR4 n R16, look at better, quieter FETS. Isolate the V+ to the FET. The whole preamp stage can be looked at (so to say) as one big +40volt effect pedal, and tonal changes (within reason) mod’s there could be adapted to your fun. A few Diodes n U got clip, etc. >Does anyone know any tips for improving marshall transistor amps? >Are there any decent mods that are worth recomending?
Hope it helps, this is a nice toy to play with..no ICs.. Then again, I got a H|H Musician, that I replaced the ICs (741s..ugggh) with better ones. Lab5’s too. Tons of fun. Look at schematics for SuperBeatles, Thomas Organ were the ORGAN tone superstars. Get Darr’s Book and look at the HISTORY of USA SS amps. Your amp fits right in. JJT
Response:
– Hide quoted text — Show quoted text -> I’ve got a Marshall 2195 JMP Lead + Bass transistor head. > It really sounds like crap! > I’ve looked for some modification tips to improve this amp but havent > found anything on the net. I’ve started replacing transistors with > origional models as listed in the schematic: > http://www.drtube.com/schematics/marshall/2195.gif > It seems that someone has replaced alot of them with > more-generic-but-compatible transistors, which i’m hoping is the main > cause for it sounding so harsh. > I have tube amps that sound great, so making this amp usable is a side > project. > Does anyone know any tips for improving marshall transistor amps? > Are there any decent mods that are worth recomending? > Thanks…
Did you think of performing the Pete Townshend mod. His was a tube amp but it should be just as effective on a solid state. http://www.youtube.com/watch?v=i0XknwXqLDo&search=the%20who Of course, using a vintage strat with it sounds best. — If it ain’t broken, fix it till it is.
Response:
Thanks for the advice. I’ll be trying some tweaks this week. All the best mate
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