# JMP 2203 build



## no.mop (Dec 21, 2009)

I've been planning this one for a while since I knew I had time off coming up, which really worked out because half of the stuff is out of stock now.  It's the Metro 100W MV kit from ValveStorm and I'm having a headshell built by Sourmash with the extra rounded corners on the front cutout, but that hasn't made it here yet since I left it a bit late. The transformers are Heyboer from AmpPartsDirect. I actually started last week so I'm done a bunch of it, but here are some progress pics anyway. The full album is here if anyone's interested and I'll be adding photos as I go:


http://imgur.com/a/W4GLG8d


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## ezcomes (Jul 28, 2008)

Nice!


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## no.mop (Dec 21, 2009)

The chassis wiring is pretty much done and I've installed the bus wire on the board. The instructions are missing the page with the ~30 board-to-chassis wire lengths so I'm spending some time figuring those all out to post on the Metro forum for anyone who builds this in the future.


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## no.mop (Dec 21, 2009)

I've got the board wired and in the chassis now, with the preamp sockets hooked up. I have to take a break for a few days so I'll be finishing next week. The headshell is scheduled to be delivered next week so it'll be right on time!


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## ezcomes (Jul 28, 2008)

Lookw good so far!


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## no.mop (Dec 21, 2009)

Hopefully done wiring! I had to cut the testing short last night, but so far everything is all good. I'm just scared to screw up drilling the headshell now.


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## Paul Running (Apr 12, 2020)

You're doing a fine job...keep it up.


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## no.mop (Dec 21, 2009)

All the voltages are as expected except for V3, where they're way too high. Pin 1 and 6 seem reasonable based on other voltages that I'm measuring, but 2/3/7/8 seem totally off. I've tried swapping the tube and it made no difference. Not sure what's going on here...

Measured (Expected):
Pin 1 - 276 (218)
Pin 2 - 98 (28)
Pin 3 - 151 (42)
Pin 6 - 270 (214)
Pin 7 - 105 (28)
Pin 8 - 151 (42)


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## Paul Running (Apr 12, 2020)

Here's a hint: pin 1 and 6 are the plates. The voltage is much higher than it should be which means both triodes are not drawing the current that they should...try to figure out what is causing this condition.


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## jb welder (Sep 14, 2010)

I think you got the colour code backwards on the resistor mounted on the presence pot.
So you have 270K instead of 4K7.


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## no.mop (Dec 21, 2009)

jb welder said:


> I think you got the colour code backwards on the resistor mounted on the presence pot.
> So you have 270K instead of 4K7.


That was it, fantastic eye! And now I just have to wait until tomorrow to play...


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## Paul Running (Apr 12, 2020)

Well done lads...very sharp eye jb.
no.mop, I hope that you understand why the voltage measurements were high readings.
A re-cap: below is an excerpt from the schematic, showing the area of concern. Note that the 4700Ω resistor (high-lighted in yellow), is directly in the path to ground from the B+, through both halves of V3, the phase inverter.
Should you decide to experiment a bit, you can open this amp up, by disconnecting the feedback (violet dot) and shunting the 4700Ω resistor...the presence control will not function however those EL34s will run wild.


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## no.mop (Dec 21, 2009)

Paul Running said:


> Well done lads...very sharp eye jb.
> no.mop, I hope that you understand why the voltage measurements were high readings.
> A re-cap: below is an excerpt from the schematic, showing the area of concern. Note that the 4700Ω resistor (high-lighted in yellow), is directly in the path to ground from the B+, through both halves of V3, the phase inverter.
> Should you decide to experiment a bit, you can open this amp up, by disconnecting the feedback (violet dot) and shunting the 4700Ω resistor...the presence control will not function however those EL34s will run wild.
> ...


Totally makes sense! Appreciate the explanation.


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## no.mop (Dec 21, 2009)

I realized that I never posted the final result - here we are:


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## ezcomes (Jul 28, 2008)

Nice!
How does it sound?


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## aC2rs (Jul 9, 2007)

That is a very nice build, it looks great!


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## 2112 (Dec 30, 2020)

Looks fantastic..would love to hear some sound clips


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