Welcome to Solid State Guitar Amp Forum | DIY Guitar Amplifiers. Please login or sign up.

February 23, 2024, 07:58:08 AM

Login with username, password and session length

Recent Posts

 

Marshall 2199 Master Lead Combo 30 Capacitor Replacement

Started by luke gibson, August 26, 2023, 05:30:26 PM

Previous topic - Next topic

luke gibson

#15
Quote from: Tassieviking on September 12, 2023, 02:15:33 PMI would guess its in the first couple of transistors in the preamp, TR1 TR2 TR4 TR5 is the most likely in my opinion.

It would be easy to see if it is in the power amp or the preamp, if you turn the gain up all the way and leave the volume pot really low do you have distortion ?

I like how you laid out the schematic, very easy to follow!
If the amp distorts at low volumes  then it is being generated in the preamp, if you get a clean signal with full gain and low volume then its most likely distorting in the power amp section.

The preamp section goes up to the volume pot, and the power amp starts on the output of the volume pot, C18 is the first component in the power amp.

Cheers
Mick

Mick, it does distort at low volume (sorta fizzy distortion) so it is generated in the preamp. Which makes total sense, similar to a tube amp which Marshall was trying to replicate with Solid State devices.   

I like how you laid out the schematic, you made it very easy to follow.

luke gibson

#16
Opened her up today to replace the power supply filter caps and found that my amp was a little different from the schematic. On my amp C18 is a .047uf yellow square capacitor from the factory. Not sure how different it sounds from the 25uf cap shown in the schematics.

I appreciate the help you have  given me, thank you!

Tassieviking

It might be you have a different style of PCB, possibly an earlier or later version of the same amplifier.
Marshall would release the same model but with several different layouts but basically the same circuit, they did however completely renumber all the components with several new revisions.

If you have the same circuit you should have 2 47nF capacitors in there, C14 and C15.
Can you find 2 47nF capacitors in there ?
Can you find a 25uF capacitor on the PCB ?, there should only be one.

If you can take some pictures of the top and bottom of the PCB I will see if I can trace your version out for you properly, the more pictures the better.
If I can see the top and the bottom and then compare where the traces go to what component it's fairly easy to do.

Cheers
Mick
There are no stupid questions.
There are only stupid mistakes.

luke gibson

Quote from: Tassieviking on September 17, 2023, 01:29:02 PMIt might be you have a different style of PCB, possibly an earlier or later version of the same amplifier.
Marshall would release the same model but with several different layouts but basically the same circuit, they did however completely renumber all the components with several new revisions.

If you have the same circuit you should have 2 47nF capacitors in there, C14 and C15.
Can you find 2 47nF capacitors in there ?
Can you find a 25uF capacitor on the PCB ?, there should only be one.

If you can take some pictures of the top and bottom of the PCB I will see if I can trace your version out for you properly, the more pictures the better.
If I can see the top and the bottom and then compare where the traces go to what component it's fairly easy to do.

Cheers
Mick

There are 2 47nf caps remaining. I traced it using the schematics and when I removed the cap it had C18 screen printed under it.  I have it buttoned up, next time I remove the chassis I will take a picture. Also noticed someone had replaced Q6 (2N3819) at some point with a different transistor.