trinityamps.com

Greetings folks

First off, what an incredible sounding amp! Just amazing harmonic grind and note definition. I now completely understand what all the fuss is about with regards to the 18Watt circuit. Thanks Steven for putting together such a fantastic kit. When I first plugged in it made me instantly realize that my previous single ended build was a muddy piece of .... you know.

Anyway, when I first sparked up the plexi some time ago I had no problems with channel 1. However, the signal wasn't getting through channel 2 (TMB). I was able to trace it to the input with the "pop" test, and subsequently removed the dual cliff jacks and replaced it with a single jack I had laying around and paralleled the 68K resistors to reflect 34K at the input to simulate the high input (I assume I have this correct?). After making this change it worked straight away. A bit more gain than I expected .. not complaining at all .. but I guess this may have something to do with active pickups in my SG.

When I looked at the dual jack set-up I couldn't see anything obvious that I had done wrong. It looked the same and appeared to behave the same as channel 1 with regards to continuity with and without jacks plugged in. When installed it produced a lot of hum from the hi input with no signal getting through but had a very quiet response in the low input with just a whisper of signal getting through. So I have been using it with a single input for some time but would like to put it back to the dual inputs so that it’s set-up as intended. The question I have is this. Is there any type of testing that can be done to the assembled jacks on the bench to confirm it is operating properly before I install it? I find it hard to work on it once it’s in-place in the chassis. Also, I get a bit confused by the operation of the dual jack concept.

If you pre-wire the two jacks outside the chassis there is testing for continuity you can do with an ohm meter.

With nothing plugged into the jacks, you should see 0 ohms from the tip terminal of each jack to the ground terminals on both jacks.
The tip terminals are the ones where the inner leads of the shielded cables connect.

With a patch cord plugged into the LO jack you should see pretty much 0 ohms from the tip terminal on the LO jack to the tip of the plug at the other end of the cable. Measuring from the tip to ground should read as an open circuit. The tip terminal of the HI jack should still be grounded.

With a patch cord plugged into the HI jack you should see pretty much 0 ohms from the tip the plug at the other end of the cable to the tip terminals on both jacks. Measuring from the tip to ground should read 1 meg ohm.

If you wired the TMB jacks as shown on the layout drawing and the same way as the other two input jacks, your problem was most likely bad connections to the shielded cables that run to the 68K resistors. Once you get the jacks wired up back in the chassis, repeat these tests except now measure to each 68K resistor instead of the tip terminals on the jacks.

Make sure the shields on the two cables that run to the 68K resistors are connected to ground at the jack end only and the inner conductors aren't accidentally shorted to the shields.

One trick that makes pre-wiring a couple of input jacks easier is to mount them in their holes but on the outside of the chassis instead of the inside. This keeps them in the proper position but gives you a lot more space to work.

Mitch, thanks for the input. I suspected a grounding issue with the shield but everything appeared to pan out properly when I checked it with the multimeter. Anyway, I am going to re-assemble it from scratch and follow your suggestions. Assembling it attached to the outside of the chassis first... duuhh ..can't believe that never crossed my mind ..what a great idea!

Is this the same Mitch as Mitch Markin over at AX84.com?

Yes, that's me at AX84. It's a great site but I hear its days are numbered as we know it. Chris Hurley has other priorities these days and wants to stop hosting it. Hopefully somebody can take it over and keep it going in one form or another once Chris moves on.

Good luck with your jack wiring.