New JTM45 complete -thanks to the help here

[duriehill]

Hi all

Wanted to make a quick post to lodge the completion of this amp, all made possible really by this forum.

Will post some pics shortly!

I'm really pleased with the result - this is my first amp build. It sounds amazing. There is one thing that I think could be tweaked though. There is a slight buzz on the amp with no input and highlighted when the loudness of the high channel is raised. Any ideas on how to eliminate this? Otherwise the amp is dead quiet! Using Larry grounding.

Thanks

[julkke]

Probably a bad ground connection somewhere. Could also be a noisy tube. Check your solder joints. Gz for your new amp, have fun with it!

[duriehill]

Probably a bad ground connection somewhere. Could also be a noisy tube. Check your solder joints. Gz for your new amp, have fun with it!

Thanks, I'll check the above. I have a strangle feeling it could be something else for some reason.. I've noticed the presence pot is a little scratchy too. It's a PEC pot so good quality. Otherwise the amp is a beauty. I'd post some pictures if I could work out how!

[julkke]

Presence being scratchy is normal. If using 5k pot setup, it will be scratchy no matter what because the pot has DC across it.

[duriehill]

Presence being scratchy is normal. If using 5k pot setup, it will be scratchy no matter what because the pot has DC across it.

Cheers - that makes sense.

I was wondering if the community could check take a look at the insides to check my cable dressing and potentially identify improvements to tame the buzz. This my first amp build, and a steep leaning curve, so your advice is greatly received!

https://picasaweb.google.com/duriehill/ ... 1278870770" onclick="window.open(this.href);return false;

Thanks

[cmb]

I just completed a CT jtm 45 about a month ago . Had a time with it at first, noise and such, but now i love it .As stated above ck grounds and solder joints ect. Just how noisy is it? Mine still has a barly audible hum with vol up, even w larry grounding , its tolerable though actually barly noticable . Congradulations enjoy clint

[julkke]

Every amp hums a bit and the hum can even be dependent on the wall socket you are using. Nothing to worry about.

[VMR]

Very nicely done, especially for a first build! I see a couple of things I would change to attack your hum problem. First thing to try is to reroute the purple presence pot wire so it is away from the other pots. Run it parallel to the board then make a right turn to the pot. I also think the red heater wires on V2 and V3 are too long. Make them go straight back to the edge of the chassis and keep all the wires that cross them away and at right angles as much as possible. See pic of mine below and try to copy the routing (looks like your red and black heater wires are reversed from mine, which is fine).

Lastly, make sure the green signal wires are at right angles to any other wire they cross and make sure they are up in the air and away from the wires they cross as they go from the board to the tube socket. Make them arc down to the socket and don't be afraid to shorten them to do so if necessary. It may be enough, however, to just move them at their current length. The 2 green wires on the first socket are the most sensitive in the amp for picking up hum.

Do those things and I bet the hum is better or gone - unless there is something else I didn't see in the pics. My JTM45 is dead quiet and I didn't even do the Larry grounding stuff.

Otherwise, a very nice build - and a great sounding amp, no?

VMR

[duriehill]

Thanks VMR

Sorry about the delay to my response, I've been a bit pre-occupied by work

I did have a moment to review the comments here last week - thanks all - and as a result I have solved the buzz! Honestly, this is one of the best sounding amps I've heard - I love the JTM45. It's dead quite, no hum or buzz at all, even when on 11. Just hiss. I can't believe I built it actually, a very rewarding process and highly addictive. I think another build is on the cards this year now!

So, while I was reviewing my cable dressing by VMR's post, I found something else that was not quite right. For anyone who want's to take a guess, here's a pic of where the visual fault lies with cable dressing:



The buzz was coming from here:
https://picasaweb.google.com/duriehill/ ... 0792235586
The black heater wire on preamp tube V1 was inducing the buzz on the purple wire of the high channel as it crossed directly underneath it. I re-routed and problem solved. A fault caused by installing the preamp tubes in reverse - doh

[neikeel]

Hard to tell from that pic.

In general you put the plate wires (usually blue in a Marshall) down from the turret to the chassis floor and lift the grid wires (usually green) to minimise crosstalk/hum.