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PostPosted: Sat Oct 23, 2021 1:34 am 
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Hello,

I’m hoping someone can help me isolate and solve a mysterious, and likely quite dangerous, shorting (?) issue with my new Trinity 5e3 build, with VRM. Quick background: I don’t have much of one. This is my first amp build (I’ve built some pedals and patch cables, and solder things in and out of my guitars pretty routinely, but that’s about it), so I am very much a novice. But I took my time with the build, have read (and re-read) all of the documentation carefully, and took care with my soldering (I also consulted this board frequently, which was a great help). Initially, I thought this approach panned out—all of my readings looked pretty good, and the amp started up on the first attempt, using a power strip in my studio room. VRM worked like a charm, and the amp sounded great. So far so good—I was very much enjoying the new amp, and plumbing the tonal mysteries of its interactive circuitry. I’d had probably had 10-15 hours of issue-free playing time (the amp started up perfectly every time, etc.). And then things took a turn.

Episode 1: Wanting to show it off to a friend, I hauled it to the back porch and plugged it into a different outlet via an old power strip I had on hand. But the moment I plugged it in to the power strip (power and standby both in OFF position), I heard a pop. Or I thought I did, later... Initially, all I noticed was that the amp didn’t power up—I assumed that I just had an old, dead power strip (dumb maybe, but the amp had been working flawlessly from the get-go; I didn’t suspect anything was wrong with it). So I plugged the amp directly into the wall outlet and…POP. Definitely audible this time, with a spark, and a puff of smoke from inside the amp. Yikes! The fuse in the amp was intact. I opened it up, and found that I had burned through the short ground connection from the mains power input to the nearby star-ground on the chassis. I hadn’t *thought* there was a poor solder joint there, but I did recall from the documentation the advice to be very sure that this was a solid connection. Perhaps I had simply missed it. So I resoldered it with a new cut of wire (using, as I had previously, a segment of the green wire supplied in the kit—though I wondered then, and later, whether I should have gone for a heavier gauge).

Episode 2: After the repair, the amp started right up back in my studio, and I played it there every other day or so, totaling maybe another 5 hours, for another couple of weeks. Always hassle-free, everything again working perfectly. Problem solved, or so I thought. But then a couple of weeks ago, I brought it to a jam at a friend’s house and—same issue. Or a similar one. Threw a breaker in his old house, then tried again (admittedly a bit recklessly, given what happened previously) and blew another power strip. Same popping noise. Like the last time, BOTH the power and the standby were in the OFF position when I attempted to plug in the amp. This time, though, the new solder joint of mains-to-chassis/ground held (and appeared unaffected), but now I had melted part of the tip of the live/hot prong on the actual power plug. Not great! Fuse in the amp was, again, still intact. I also noticed that the cord was unusually warm to the touch—and, later, after a bit of internet sleuthing, wondered if maybe I had a defective power cable that was shorting when I moved it and causing all this trouble. So I tried another power cord back in my studio, in the same power strip I had been using previously, and…everything was fine again. Sounded great! VRM still worked like a charm! I thought I had finally solved the problem, and was congratulating myself for having done so. And then…

Episode 3: Today, after playing for another week or so, I thought…you know I should really test this with a different power source before I take the amp out of the house again. Just to make sure. So I did, in a different outlet in a different part of my house. And guess what—another pop, another spark, and another melted live/hot prong on my (new) power cord. Fuse in the amp still remains intact. Ye gods!

What am I missing here? Given how and when the issue arises (when plugging in, with everything in the off position), coupled with the fact that the fuse never blows, it seems like there are a limited number of scenarios and components that could be involved. But I’m a
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t a bit of a loss. Obviously, the situation is untenable, and likely quite dangerous. But I don’t know what the problem could be. The connections look…pretty good, to my eye. Clean and shiny, and in the right places as far as I can tell. So I hereby refer this frustrating business, with voltage numbers and pictures of the build, to the forum’s collective wisdom. Any help or insight would be greatly appreciated. Many thanks in advance! --Rob

V1 (12AY7): Pin 1 (123); Pin 3 (1.9); Pin 6 (128.6); Pin 8 (1.9)
V2 (12AX7): Pin 1 (169.2); Pin 3 (1.2); Pin 6 (201); Pin 7 (17.9); Pin 8 (43.4)
V3 (6V6): Pin 3 (363); Pin 4 (331); Pin 8 (21.4)
V4 (6V6): Pin 3 (363); Pin 4 (329); Pin 8 (21.4)


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preamp & board view1.jpg
preamp & board view1.jpg [ 246.06 KiB | Viewed 368 times ]
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PostPosted: Sat Oct 23, 2021 9:46 am 
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Is it possible the IEC socket itself is faulty, and there is an internal short, or possibly a stray bit of wire that found its way in between the terminals?


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PostPosted: Sat Oct 23, 2021 11:41 am 
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PharmRock wrote:
Is it possible the IEC socket itself is faulty, and there is an internal short, or possibly a stray bit of wire that found its way in between the terminals?


Thank you for your reply. I've wondered about that IEC socket without knowing how likely a defect like that might be; subbing in a new socket may be one of the steps I take here shortly. As for the stray wire hypothesis--that was the first thing I thought of, and looked for. I don't see anything--but who knows, I guess it's possible a stray wire clipping got wedged under the IEC socket, or elsewhere, during the build, and is somehow causing it to short intermittently. Or maybe it's something in the VRM?

In a way, that's what I'm trying to get a handle on--what's possible here as a cause, and what isn't. I saw a thread on a different forum in which folks were speculating about a similar issue on an old Marshall (it was throwing breakers upon plugging in, with everything in the off position), and the list of possible culprits people suggested ranged from a bad solder joint (easy fix) to a bad power transformer (catastrophic). Unfortunately, I don't know how reliable any of those particular conjectures were, or how applicable they might be to the present case... So I'm hoping to get a more complete sense of what *must* be a finite (and fairly small) number of possible causes, in order to devise a sequential process of elimination, from most to least likely. Many thanks again.


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PostPosted: Sun Oct 24, 2021 10:51 am 
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Since this is occurring when the amp is off and in standby, and also when you move the amp and plug it in, it seems the issue is the IEC socket....you ruled out a short within the cord so unless you had another bad cord, then that's not it. Maybe when you move the amp, or wiggle the socket when connecting a power cord, the contacts get shorted.

The burned up ground wire means you passed a lot of current from the IEC to ground likely via a short. This is also why the breaker is tripping and your amp fuse is fine...there is no current passing through the fuse since the power switch is open.

Those IEC sockets are only about $2, and is the simplest place to start with only 3 connections which are easy to get to. I'd definitely replace that, and for the mains ground wire from the socket, use 18g stranded. I would use a "crimpable" ring terminal for this. Crimp the wire lead then solder the connection. Bolt the terminal to your chassis using a nyloc nut or a regular nut (or two) with a star washer. The mains ground wire is the most important connection in the entire amp.


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PostPosted: Sun Oct 24, 2021 10:15 pm 
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PharmRock wrote:
Since this is occurring when the amp is off and in standby, and also when you move the amp and plug it in, it seems the issue is the IEC socket....you ruled out a short within the cord so unless you had another bad cord, then that's not it. Maybe when you move the amp, or wiggle the socket when connecting a power cord, the contacts get shorted.

The burned up ground wire means you passed a lot of current from the IEC to ground likely via a short. This is also why the breaker is tripping and your amp fuse is fine...there is no current passing through the fuse since the power switch is open.

Those IEC sockets are only about $2, and is the simplest place to start with only 3 connections which are easy to get to. I'd definitely replace that, and for the mains ground wire from the socket, use 18g stranded. I would use a "crimpable" ring terminal for this. Crimp the wire lead then solder the connection. Bolt the terminal to your chassis using a nyloc nut or a regular nut (or two) with a star washer. The mains ground wire is the most important connection in the entire amp.


I like it! Thank you for this follow-up response, and for spelling out your reasoning so clearly. Makes good sense to me. I'll order the part and do the repair this week; will report results back here. Many thanks again, and fingers crossed.


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PostPosted: Sat Nov 06, 2021 6:48 pm 
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Problem solved! And it turned out to be something I hadn't anticipated. I discovered that, without realizing it, I had damaged the live wire running from the IEC socket to the fuse when I installed the amp chassis into the cabinet--the teeth on the keps nut had bitten into the wire and exposed the braid while I was tightening it in place, and that was what was shorting intermittently (the intermittency due to small movements of the chassis or wire during transport). But I never noticed the damage because: a) the damage happened to be located exactly on the dark side of the nut, and wasn't visible from front inspection (plus the wire still moved freely when I was prodding around with a chopstick; it wasn't pinned down, just fatally exposed in immediate proximity to the ground/nut; and, b) I never bothered to remove the chassis when I resoldered the ground previously (it was such an easy repair, and so easy to reach that it didn't seem necessary). But I removed it this time to install the crimpable ring terminal, as per PharmRock's excellent suggestion--and then the damage was obvious. Duh. This possibility never crossed my mind. I did, though, go ahead and follow through with the replacement of the IEC socket ground connection with a larger braided wire, with the ring terminal bolted to the chassis. Seems bulletproof now. Lesson learned, &c., &c.

Many thanks PharmRock, for your prompt consideration and advice. I really appreciate it.

p.s. I kept the original IEC Socket from Trinity, which was perfectly fine--and is also built far more robustly than the replacements I bought off amazon (which had very cheap/thin terminal ends). Not sure where one sources proper amp-grade IEC sockets and cable, but if you're ever looking for some trust me when I say amazon ain't the place.


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PostPosted: Mon Nov 08, 2021 10:10 am 
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Glad you got it figured out! "Dark Side of the Nut"...sounds like a Pink Floyd parody album!

I'm still learning all this stuff, but I've found that most of the problems I encounter end up being something really simple (and oftentimes unexpected). I built a Tramp a while back that blew fuses every time I turned it on. Turns out an under-board power rail resistor was shorting against a transformer bolt when the board was bolted down. Took me forever to figure that out.

Anyways, nice job on the troubleshooting!


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