Mod suggestions

chopperferrari · Post by **chopperferrari** » Mon Sep 01, 2014 5:13 pm

Hi guys,

i built my JTM45 about a year ago, and over that time i have done some modding. I'm looking for some other mods to try, any suggestions of stuff that you find is sounding really good?

I have changed
V1a cathode capacitor to 250uf
Put in 470k mix resistors
swapped the tone section to 33k & 500pf
phase inverter caps
solid state rectifier

All of them have made the amp way more usable tonally. I'm looking for more in this direction.

I have read about 0.68uf on the input, what does this do?

Thanks
Ben

stef · Post by **stef** » Mon Sep 01, 2014 10:39 pm

split cathodes V1

(1987spec)

chopperferrari · Post by **chopperferrari** » Wed Sep 03, 2014 4:11 am

Thanks, how does the spit cathode on V1 effect the sound. More gain? less bass?

stef · Post by **stef** » Wed Sep 03, 2014 10:39 am

Yes, less bass on channel 1 and moderate increase in gain-overdrive

chopperferrari · Post by **chopperferrari** » Wed Sep 03, 2014 3:06 pm

Thanks! very cool. i've been searching the forum for a guide as to how to implement this spit cathode on V1. Any tips?

neikeel · Post by **neikeel** » Wed Sep 03, 2014 3:20 pm

Look at a shared board with a split board and compare to spot the difference:
Split:
http://forum.metroamp.com/download/file.php?id=3877
Shared:
http://forum.metroamp.com/viewtopic.php?f=26&t=11946

Sorry can't post just jpeg as the forum board has this irritating 722 pixel wide limit!

You will see that the bridge wire on V1 socket has been removed, that there is an extra turret between the existing cathode turret and the V1a plate turret (usually set a little lower in space). You can glue a new turret in with epoxy if you do not fancy lifting the board.

Take a new piece of yellow wire and solder between new turret and the pin where the removed link was (pin

Then solder your components in place, the resistor is either 820R (early plexi) or 2k7 (later plexi and more recent) and goes first, then the 0.68uF capacitor over that (in parallel).

That is it!

stef · Post by **stef** » Wed Sep 03, 2014 7:42 pm

I like SDM's layouts
http://home.comcast.net/~jbjdav26/1987r17.jpg

chopperferrari · Post by **chopperferrari** » Mon Sep 15, 2014 4:07 pm

Thank you chaps!

chopperferrari · Post by **chopperferrari** » Mon Sep 15, 2014 4:25 pm

One question, what type of capacitor should i be using?

stef · Post by **stef** » Mon Sep 15, 2014 7:11 pm

Mallory 150 white, NOS Mustard phillips, phillips yellow chicklet etc.. .68uf

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