Marshall head playing tricks

[karambos]

Hi,

hope I've posted to the correct part of the forum. Apologies if not.

I've got a Marshall head called "100 watt lead and bass" with a gold coloured front. Model number: 2195; voltage: 120/240; frequency 40/60~; watts: 190. I don't know if it's a valve amp or not but when I opened it up there were these two blue cylinder things about two inches tall and about an inch wide. I don't know if they are valves or not but it takes about 10 seconds to warm up before you can play through it. I acquired the amp in England and it had an english plug on it but I live in Germany where my studio is and I've changed the plug. The amp works if you plug a guitar direct into it (i.e. without going through any pedals and effects).

Nonetheless, I've got a problem with it. I've recently been and bought a DOD power supply to power my foot pedals. When I power the foot pedals with batteries, plug my guitar into the pedals and output to the amp, everything's fine. I get a sound and I get the effect. If I use my J-Station (guitar effects prcessor) I also get sound and the required effects. However, if I use the DOD power supply to power the pedals, I get no sound and of course, no effect although the LED's light up on the pedals.

So I took the power supply back to the shop together with my pedals and asked them to check it out. So he plugged everything in - the power supply, my leads, my pedals, a different amp and a different guitar and they all worked fine. I got sound and I got effect.

Just guitar and amp - fine
Guitar, battery-powered pedals, amp - fine
Guitar, effects processor, amp - fine

BUT

Guitar, pedals powered with new supply box, amp - not fine

although the power supply works, the pedals work, the amp works and the guitar works.

Can anyone give me any hints as to what the F is going on? I'm tearing my hair out.

Many thanks

Karambos

 

[karambos]

it's a transistor amp

Hi,

I looked around all day today on the net and found this information:

"2195 JMP Lead & Bass, 100W head 100W cabinet
This amp (and cabinet) was in production from 1976 up to 1980. It was an all transistor Master Volume amp."

I found this info, together with a schematics diagram there. However, I still don't know what could possibly be wrong with it.

I'm grateful for further help

Karambos

 

[tschrama]

Hi,

could you post the link?

Maybe it got something to do with your 'neutral' and 'live' wire connections, since you changed the power cord .. or the earth connection? Can you try another adaptor for a supply of your pedals? Or leave some pedals out of the signal-chain.. etc..

I'm afraid it will take some experimenting to find out what is wrong?

Goodluck,
Thijs

 

[karambos]

the link

Hi tschrama,

the link is: http://www.drtube.com/marshall.htm
then CTRL+F for 2195. It's about halfway down.

I tried it with each individual pedal on it's own and the shop don't have any more of this power supply.

Thanks

 

[ir]

do you have the pedals inline with the guitar or in the effects loop?

try it in both and that might narrow the probelm down

 

[Centauri]

Your statement that the amp takes 10 seconds to warm up may give a clue, as according to the circuit, this should not happen.

If you have a multimeter, plug up your pedals and power supply box and see if there is any DC voltage at the jack which normally plugs into the amp. the problem could be voltage cutoff of the input transistor due to a faulty coupling capacitor C2 on the schematic.

Cheers

 

[karambos]

@iR - I don't know what you mean by "inline or in the effects loop" but what I can tell you is that there's an instrument cable going from guitar to pedal 1 and then a patch lead from pedal1 to pedal 2 etc until last pedal where an instrument cable goes to amp.

@centauri - I'll get me one of those meters and check it.

thanks all for the helpful hints

 

[ir]

yeah so inline then

does it have an effects loop ie a socket labelled send and one labelled recieve (or labelled effects loop even) at the front or back

also the 10second warmup could be due to a tube preamp? does the amp have standby and power switches or just power? - i don't know of any guitar amp manufacturer who bother with standby switches on amps without pre or power tubes (it'd be pointless for a start!)

 

[TaylorG]

I don't blame you for pulling your hair out... this just sounds strange! My advice is 1) don't worry about the startup delay in the amp, I doubt if that is contributing to your problem, and the previous post about a tube preamp sounds reasonable to me. I've never seen a marshall head that powers up immediately, although I don't know why(Im a drummer, not a guitarist). 2) the blue cylinders that you mentioned sound like filter caps to me.

I would focus on the footpedal/power supply combination. have you tried different electrical outlets in your home? You said that it powers up, but maybe the outlet is wired incorrectly, or maybe there is a loose contact with the p.s. to footpedal plug? I'm just guessing here, but I really think the amp is fine.