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Just planning my Christmas project. Have all the parts to build a JTM45 with added master volume. Already have a small head and chassis from a different project, so to save me making another I wondered if I could make an ultra compact JTM45 ...
So here are all the parts laid out - what do you think - too close together? Any issues you can forsee noise wise. I know it will be a tight build, I'll be paying extra attention to lead dress inside, but would this work as a chassis layout?
I'm thinking I'll get away with it, but I don't want to spend hours building to find that everything hums from proximity to the transformers!
@ICBM @MJW maybe one for you guys if you have the time to have a little look.
Thanks!
Comments
here is one post:
http://www.tdpri.com/forum/shock-brothers-diy-amps/493592-dragon-slayer-custom-jcm800-build-3.html#post5889776
you are missing the rectifier valve
You can buy a JTM45 size blank chassis in the UK for not too much money.
if you want to check for hum use the headphone trick:
From the AX84.com FAQ: THE HEADPHONE TRICK
"First set up the power transformer. If it's not installed yet, all the better, but if it is, this will still help. If the PT is not installed, wire up the primaries to a power cord, but do not wire up any secondaries-- tape the ends of the secondaries. If the PT is installed, fine, just make sure there is no circuit on any of the secondary leads (pull all tubes, and disconnect leads and tape them as necessary).
Now set up the signal transformer (output, reverb, whatever). Hook one set of OT secondaries (your choice, but I usually go from ground to the highest impedance tap, don't worry about impedance matching here!) to a set of headphones. Tape the primary leads.
Put the headphones on, plug in the power cord, and start moving the signal transformer around. Try it all over the chassis, and also rotate it. While you might expect the least hum with the transformers as far from each other as possible and at right angles (and that may be the case for you), it might come at an odd angle and/or position. Sometimes the least hum occurs when the transformers are side by side. When you find the quietest spot, use a permanent marker to mark where the mounting holes should be."
Unfortunately, no-one can tell you if that layout will work unless they've already tried it with those exact components. There are so many variables, that's it's (in practical terms) impossible to predict what will interact with what. Consequently, we could only offer gut feelings - mine is that it's too cramped and I wouldn't do it. Heat dissipation would be one of my prime concerns, even if noise isn't.
In your favour, the JTM45 is a low-gain amp, and is quite tolerant of less-than-ideal layouts. A lot of Hifi amps and other non-audio vintage equipments use what we would think of as very cramped layouts without problems, so maybe it would be fine.
I would definitely recommend a headphone test, as you might find simply turning the OT on it's end (for instance) makes a huge difference to background noise.
BTW I put JTM45 style amps on 17" chassis in 53cm cabs that rarely overhang a 1x12.
Good luck and stay safe.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
I've never been too bothered about valve rectifiers, apart from if it's a 5Y3 in a 5E3 circuit where I have been able to hear a small difference at higher volumes. There's so little sag with a GZ34 that it just seems like a waste of a socket.
I'll probably mount the can capacitor internally too, or just use two decent 32uf axial caps instead. Having the cap above the chassis seems like another waste of space!
Hell, I might just try it like this. The worst that will happen is I'll have to take it apart an install in a bigger cab if it doesn't work out.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
So with that in mind, I should be good to go? The only question I have is whether transformer hum can be picked up via close proximity to the preamp/output valves?
Not from the OT - although it can from the PT - but it could potentially cause instability.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein