troubleshooting RH speaker wiring

[Bill S]

I just finished assembling my S.E.X kit yesterday. It went pretty well considering it's my first kit and I hadn't done any soldering to speak of in many years. All resistance values checked out reasonably close (except potentiometer, but I then found forum posts stating the values in the manual are incorrect), all voltages checked out reasonably close.
I hooked up speakers but have no output on RH speaker binding posts. I then plugged in a old set of Realistic headphones (I wasn't yet confident enough to plug in the Grado's) and both channels sound fine. I used my DMM to check the wiring to both channel speaker binding posts. The resistance values on the RH aren't quite what I expected to see.

LH channel red to black-  1.3 ohm
RH channel red to black-  0.3 ohm

LH channel black binding post to lowest headphone jack connection (closest to chassis plate)- .9 ohm
LH channel red binding post to upper headphone jack connection- 1.3 ohm
RH channel black binding post to to lowest headphone jack connection- .3 ohm
RH channel red binding post to middle headphone jack connection-  .9 ohm

I assumed I have a bad solder joint at the headphone jack connection but I thought I'd be getting a higher resistance reading, not lower. Did I make a wiring mistake? Any ideas of what to do next?

Thanks, Bill

 

[JC]

Well, readings below 1 Ohm are always dicey, but perhaps it would be good to know the reading you get by simply touching the two probes together.  I am more inclined to think that you have a short circuit between + and - on the right side, and that the short is after the headphone jack.

 

[Bill S]

  You are correct about these low readings being dicey.  When I touch my probes together my DMM reads "OL"    The resistance values I gave are "approximate"  as they jump around a bit when touching the connections with the probes.

Bill

 

[Grainger49]

Bill,

You deserve a better meter.  My opinion is well documented here.  I have two old Flukes and somewhere there is a picture of Doc's test bench with an even older Fluke on it.  If you want to stay with this long enough you can invest under $100 and buy a meter you will never replace.

 

[JC]

Well, Bill, I think if it were me, since your phones seem to work on both sides, I would assume that you are good up to the jack.  Make sure, though, that you are convinced that you are really getting left AND right on the phones, and not just one channel coming out of both phones.

If you convince yourself of that, then it it seems to me the next logical step would be to disconnect the wiring from the jack to the output in question, and see if somehow the wiring to that output got shorted somewhere along the way.

Just my .02, but I think that's how I might proceed.

 

[Bill S]

First I should apologize for mistakenly saying my DMM read OL when touching leads. That is when NOT touching. It has .2 ohm when touching.

I am getting stereo from the headphones so up to that point seems OK. I can't see anything visibly shorted.
I was able to borrow a Fluke DMM and got more accurate readings.    ...and yes, it is much, much better and I'll need to purchase one if I do anything more!

LH (working speaker channel)
black to red binding posts- 1.0 ohm
black to bottom of headphone jack (closest to chassis plate)- .7 ohm
black to middle of headphone jack- 1.0 ohm
black to top of headphone jack- .1 ohm
red to bottom of headphone jack- .6 ohm
red to middle of headphone jack- .1 ohm
red to top of headphone jack-- 1.0 ohm

RH (non working speaker channel)
black to red binding posts- .1 ohm
black to bottom of headphone jack- 0 ohm
black to middle of headphone jack- .6 ohm
black to top of headphone jack- .6 ohm
red to bottom of headphone jack- 0 ohm
red to middle of headphone jack- .6 ohm
red to top of headphone jack- .6 ohm

Any ideas where I've gone wrong? 

Thanks,  Bill

 

[Doc B]

One difficulty lies in the fact that the output transformer secondary has a very low resistance so these reading look very close but may indicate a short. From what you measure it looks like maybe the red binding post is somehow shorted to ground. Are the red and black posts on the right channel maybe connected backwards to the headphone jack? (by the way, the revamped SEX will include black and red wires rather than just black, to make this kind of thing easier)

 

[Bill S]

I'm up and running and it's sounding great through a pair of Fostex full range drivers.
The problem was just a really stupid wiring mistake. I should have noticed this but sometimes when you look at the same thing too long you don't notice an obvious mistake.  Chalk it up to working too late one night .......and having all black wires running from the headphone jack to speaker binding posts.  I had the connections for RH black and LH red speaker posts reversed. I'm not sure why the LH speaker channel worked when hooked that way.
The multi colored wiring in the revamped kit will be a big improvement.

Thanks for help.

Bill 

 

[JC]

Nothing succeeds like success!  You found it!

You are entirely correct, IMO: It's easy to stare at the same error over and over again once you have convinced yourself that it is correct, and never see it.  It is why I have often recruited a fresh pair of eyes when I'm stumped.  Even a non-technical pair will often see what I've overlooked dozens of times.

Good for you!