JTM45 Clone little problem!

voodoo.chile · Post by **voodoo.chile** » Wed Aug 31, 2005 2:46 am

Ho Flames Yes!
The ground buss on pots is well made and securely soldered.
The wiring of the board is OK.
My last chance is the PT Wiring. I want made it accordly with the JTM45 Manual posted by George.

voodoo.chile · Post by **voodoo.chile** » Wed Aug 31, 2005 5:21 pm

PT Wiring re-made but........... nothing!
The disturb remaing.
It seems a series of scratches, not properly a hum/hiss.

I try touching the Treble pots, and "seems" to vary a little.

Can be the treble pot broken?

I am desperate!!!

Help!

(I don't have idea what other test I can try!)

voodoo.chile · Post by **voodoo.chile** » Wed Aug 31, 2005 5:24 pm

PT Wiring re-made but........... nothing!
The disturb remaing.
It seems a series of scratches, not properly a hum/hiss.

I try touching the Treble pots, and "seems" to vary a little.

Can be the treble pot broken?

I am desperate!!!

Help!

(I don't have idea what other test I can try!)

voodoo.chile · Post by **voodoo.chile** » Thu Sep 01, 2005 7:49 am

I have tried without result to change the TREBLE pot......

According to you

my fund noise problem (I remind you it is affected by the TREBLE control, is incostant it and looks like some discharges) it can depend on the fact that I have mounted both the FILTER CAPS under the board?

Or from the fact to have PT and OT position neighbours very much? (almost touch themselves).

I thank you in advance for your help.

Flames1950 · Post by **Flames1950** » Thu Sep 01, 2005 5:36 pm

I don't think the positioning of the PT and OT is the problem, they're very close on original JTM45's too. And lots of guys have used that Weber chassis with good luck.
As for my comment on the filters, I don't really like having all the filters right above the board if I've got other options. But that's not to say it can't work with proper wire routing.
I also don't believe the treble control or cap itself is the problem -- I think it just brings the problem to the forefront very quickly when you turn up the treble, since that is the frequency range that much of the hissing resides in.
But if you can't find the hissing/crackling in the grounding, a bad tube or a bad connection, you may have to start swapping components on the board out until you track it down.

voodoo.chile · Post by **voodoo.chile** » Fri Sep 02, 2005 3:00 am

OK, I try this.

I have measured the two 68K resistor on channel 2 inputs, and hes measured circa 35K!?!?

I start from this!

Thanks Flame

PS: I have the wall current (europe) on 215-225 V AC range: what the best connection on my PT input: 220V or 240V?

Flames1950 · Post by **Flames1950** » Fri Sep 02, 2005 7:02 am

I think I'd stick with 220V for that range of wall voltages.

Because of the way the jacks are wired and switched, you're reading the two 68K's in parallel, coming up with the 35K figure. That's OK. You can use more or less resistance there anyway, depending on your playing style and how hot your pickups are. Less resistance on the inputs means slightly better high end and overall signal fidelity.

voodoo.chile · Post by **voodoo.chile** » Fri Sep 02, 2005 9:30 am

OK Flames!
And for the 27K resistor linked to presence pot and to 16ohm OT tap, why I read only 4K?

With the 220V input I read the right values on all pin tubes, but the problem remains.

I try to record a sample of disturb to make You hear!

Flames1950 · Post by **Flames1950** » Fri Sep 02, 2005 4:31 pm

And for the 27K resistor linked to presence pot and to 16ohm OT tap, why I read only 4K?

Many spots cannot be read without removing the part from the circuit....the meter's curretn can find alternate paths around the component you want to measure.
Sound clips could be helpful although I still have a hunch it will come down to one component and connection at a time to find this, if it's not tube related.....get out the recording gear!!

voodoo.chile · Post by **voodoo.chile** » Fri Sep 02, 2005 5:34 pm

I think I can record the soundclip monday, during the jam with my band.
Meanwhile, how I can try the board components?
I must desolder and substitute all?
I think the resistors is all OK (all have the correct value).
For the caps? If I have the correct reading the cap is OK?
And the silver mica in pf range (I cannot measure it)

During the firsts tests I have try to swap all the tubes (with old 6L6 and 12ax7) but no result.

PS: This morning, during the last test, the disturb is vanished for a little time, but I don't known why!

voodoo.chile · Post by **voodoo.chile** » Fri Sep 02, 2005 5:35 pm

I think I can record the soundclip monday, during the jam with my band.
Meanwhile, how I can try the board components?
I must desolder and substitute all?
I think the resistors is all OK (all have the correct value).
For the caps? If I have the correct reading the cap is OK?
And the silver mica in pf range (I cannot measure it)

During the firsts tests I have try to swap all the tubes (with old 6L6 and 12ax7) but no result.

PS: This morning, during the last test, the disturb is vanished for a little time, but I don't known why!

Flames1950 · Post by **Flames1950** » Fri Sep 02, 2005 10:26 pm

PS: This morning, during the last test, the disturb is vanished for a little time, but I don't known why!

What was the "last test"? What were you substituting, or trying differently? Focusing on some little thing that may not seem important could lead you to the answer!!

voodoo.chile · Post by **voodoo.chile** » Sat Sep 03, 2005 3:07 am

Hi have swap to 220 V tap and check the pins voltages (All OK).
Then I try to move around the wires from pots, rotate the control pots and playing the guitar a lot.
At "normal" crackle hiss I haved for a seconds a high frequency squeal.

After playing guitar, the disturb vanish for a little time.

Can is a grounding problem, but I think have all the ground OK.

voodoo.chile · Post by **voodoo.chile** » Wed Sep 07, 2005 8:31 am

This is the clip of disturb / crackle.
I hope you can hear it!

I remember you that this disturb is presnet with or without the guitar cable in.

Flames1950 · Post by **Flames1950** » Wed Sep 07, 2005 3:51 pm

That clip almost sounds like the gain is WAY too high. I'll have to scout back through your pics and see if anything looks out of place to cause a big jump in gain. Does it sound too high-gain when you play or is the noise too obnoxious to play over?