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| | |-+  Taming bass in my Ceriatone jtm45		 « previous next »
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Author Topic: Taming bass in my Ceriatone jtm45  (Read 10880 times)
strat100
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« on: November 25, 2007, 11:25:42 AM »
I'm noticing that it's pretty tubby/loose in the low end, especially with my humbucker guitars. Even with the bass control down around 0-1 it still breaks up pretty fast on the bottom.

What are the preferred methods for taming the bass?
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Roe
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« Reply #1 on: November 27, 2007, 01:45:51 PM »
reduce the v1 catode cap to 25-3uf
reduce the pi qoupling caps to .047-.o22uf
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Roe
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« Reply #2 on: December 09, 2007, 04:46:53 PM »
also: try reducing the v1 coupling caps slightly (to .018, .015 or even lower on the bass channel)
« Last Edit: December 30, 2007, 07:48:06 PM by Roe » Logged
skydog79
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« Reply #3 on: December 29, 2007, 11:15:30 PM »
hey Roe, could you explain this again?  I'm not quite savy with all these components, wireing and such but I'm have'n the same prob as strat100 Undecided
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Roe
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« Reply #4 on: December 30, 2007, 07:52:29 PM »
the first preamp tube is called v1.  see the cap on pin 3 and 8 (shared cathode) reduce it to 25uf, 16uf, 8uf or even 3.3uf
see the caps after pin 1 and 6 on the same tube - reduce them to .018 mustards (or even .015) - see if you can find originals - .018 aint that expencive.

see the last mullard or mallory tupe caps at the other end of the board (the phase splitter) - remove the 2 .1uf and try a .047uf, .033uf, .027uf or .022uf
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gearheadfred
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« Reply #5 on: March 13, 2008, 11:12:54 PM »
Hi,

New JTM45 user here... Wondering about taming the bass as well..

Just to confirm - the stock V1 cathode cap is 220uf, 25V, correct?  You recommend going to 25uf, or even as low as 3uf in that position?

Also, has anyone else tried these mods and care to comment on the results?

Thanks,
Fred
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stratsrus
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« Reply #6 on: April 06, 2008, 01:33:42 PM »
FWIW - I am a new JTM 45 owner as well. On my amp when jumping the channels going from high treble (1 - lower input) to normal (2 - upper input) gives the most bass response with the guitar plugged into 1 - upper input, I just turn the bass to zero. If I jump high treble (1- upper input) to normal (2 - lower input), guitar plugged into 1-lower input, then I can use the bass control knob. Also, if I do not jump channels at all the bass can be EQ'd easier.  I am playing stratocasters, s-s-s.
« Last Edit: April 07, 2008, 11:27:30 PM by stratsrus » Logged
Roe
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« Reply #7 on: April 06, 2008, 02:38:20 PM »
Quote from: gearheadfred on March 13, 2008, 11:12:54 PM
Hi,

New JTM45 user here... Wondering about taming the bass as well..

Just to confirm - the stock V1 cathode cap is 220uf, 25V, correct?  You recommend going to 25uf, or even as low as 3uf in that position?

...
Thanks,
Fred


correct - that's a standard mod - cf. the metroamp forum, and the yahoo jtm45 group.
In 1968 decreased the v1 cathode cap to .68uf. they went from 330uf to .68uf on the 100watters (sic)
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GTO
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« Reply #8 on: March 20, 2010, 06:58:04 AM »
@ROE

I did some remarks on the JTM45 layout... could you check if its right??

marked with "A"
the first preamp tube is called v1.  see the cap on pin 3 and 8 (shared cathode) reduce it to 25uf, 16uf, 8uf or even 3.3uf

marked with "B"
see the caps after pin 1 and 6 on the same tube - reduce them to .018 mustards (or even .015) - see if you can find originals - .018 aint that expencive.

marked with "C"
see the last mullard or mallory tupe caps at the other end of the board (the phase splitter) - remove the 2 .1uf and try a .047uf, .033uf, .027uf or .022uf

marked with "D"  leave unchanged??
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cmoore
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« Reply #9 on: March 20, 2010, 08:34:55 PM »
Do you realize this thread is Two Years old.?
But yes, you have it right. Follow a path that is close to what "roe" recommended. You should probably go one at a time and see how things progress.
Good Luck
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