Hello

[3LD_guitar]

Just wanted to drop a line and say hello to everyone in this forum. I just finished a Mojo JTM45 and it sounds awesome. The only thing I can't figure out is that I'm getting a hum / hiss on the treble channel, but the normal channel is dead quiet up to 10. I also get a crackling that seems to be vibration induced - I may have a loose ground wire somewhere. Developing... If anyone has had the same problem with the treble channel hum/hiss, I would like to hear how you cured it

More than anything, just wanted to say Hi to the group and hope I can help out folks that have build questions on a JTM45

Regards,
Mike

[cmb]

Welcome form another new member . I have been a member for only a short time. You will find alot of good information and helpful experience here. Regarding the hum/hiss you described ,I think you may be on the right track . Check all your grounds and solder connections first. I do not have as much experience as some here , but thats where I would start. Also depending on how your amp is grounded , a low level hum may be normal. I will look your pics over again and ponder this more welcome again Clint

[Reeltarded]

Reterminate your bright channel input pair ground connections..

Move your normal channel grid wire to the bright channel grid. Is it quiet now? Aha. It's the bright jack wiring...

Then, if no change:

Start at the input jack and go all the way to v2a just touching up the solder points and checking for a cold one. I can't see the area around V1 so much. Make sure the plate wires and grid wires are well separated. I use extra short plate wires and dive them straight to the deck then straight to the tube. The grids I pick up off the deck and pull them up into a similar half-loop as you usually see them laying flat.. in.. prepositional ending to a.. never mind...

Then it is just as likely to be the lead dress at the input jack. You can move your input resistors (better!) to the tube inputs and terminate from the inputs to them right there. Great RF supression.

I am rolling dice on the jack wiring.

Welcome, Merry Christmas.

[3LD_guitar]

Well, I traced the source of the crackling to 3 ground wires coming from the terminal board that I didn't solder to the bus behind the pots. I had them hooked on the bus, but not soldered SHEESH! - crackling solved! But now that those grounds are connected, I'm getting quite a bit of hum as I increase the volume.

Has anyone built a Mojo JTM45 that could recommend an alternative grounding scheme?

Thanks again, happy new Year!!
Mike

[cmb]

Good to hear you solved it. I am taking the hum is not very loud w/ vol at 0. If it is loud and constant at any vol it may be an OT polarity issue . Sounds more like grounding ,but as i said before im no expert . check out the thread on larry grounding in the jtm 45 section . I think this will help point you in the right direction . Clint

[julkke]

Try a different wall socket just for the hell of it.

Have you got any pedals in front of the amp? If so try straight in.

[3LD_guitar]

Hi again, thanks for your ideas! And no, this is with no pedals plugged into it - Good idea about simply trying a different outlet.

There's no hum when the volume is at zero. The hum is very low when the volume knobs are in the 1-3 range. It gets noticeable when I get up into the 4-6 range. Would this be considered "normal" level hum for this design?

Thanks,
Mike

[julkke]

Hi again, thanks for your ideas! And no, this is with no pedals plugged into it - Good idea about simply trying a different outlet.

There's no hum when the volume is at zero. The hum is very low when the volume knobs are in the 1-3 range. It gets noticeable when I get up into the 4-6 range. Would this be considered "normal" level hum for this design?

Thanks,
Mike

No, some hum is normal but it is usually constant low level and doesnt get louder when turning up volume.

Try different preamp tubes if you haven't already.