Moreplay Complete: No sound on right channel [resolved]

[jminassi]

Hi folks,

I just completed the first of two Moreplay builds....one for a friend and one for me.  I passed the resistance and voltage tests, and then hooked it up to an amplifier and a CD player.  It sounds awesome, but I have no right channel signal.  I flipped the tubes, but it didn't change anything:  no right channel output.  I shut it down and waited for the caps to drain.  I took a look at the wiring of the RCA jacks and the selector switch, but I can't see anything that looks out of place.

I'd appreciate any input that can help me locate the issue.  I have attached photos.

Many thanks,

John

[Doc B.]

Start by checking to see if the bad channel works using a different pair of input jacks. If nothing changes try using a different pair of output jacks. Also swap input cables left and right and then output cables left and right. That will help to determine if the problem possibly lies in the input or output wiring or if it might be external to the preamp.

If none of that shakes out the problem you will probably need to use a test tone to trace the signal. Unfortunately I'm having a little issue with optical migraines tonite and can't scrutinize your photos very thoroughly. Perhaps someone else can look them over for you.

[jminassi]

Thanks Doc.  I'll try your suggestions.  Hope the migraines clear up fast.

Best,

John

[jminassi]

Ok, I'm using two inexpensive cables to connect a CD player to the input of the Moreplay and the output to an amplifier.  I usually use these cables to test new builds.  I ohmed them out and they test good.  I switched outputs and the left channel signal only plays through both outputs.  If I reverse the left and right output, the signal is reproduced in the right hand speaker as expected.  With regard to the inputs:  I only get the left channel signal through the set of inputs closest to the side of the chassis.  Each of the inputs does the same thing when selected: only the left-hand channel signal is produced.  If I reverse the input wires, the signal appears in the right-hand channel as expected.  Somehow I have lost the right channel signal.

Earlier in the year I built an Akitika Oscillator.  It produces a 1 kH sine wave with distortion of 2 ppm.  I could input the signal into the Moreplay, but I have no idea how to trace the signal.  I know my DMM should be set to AC volts, but I need someone to tell me where to place the probes.  Can somebody help me?

Many thanks,

John

[Paul Birkeland]

You can use an old phone or tablet with an 1/8" to RCA cable playing a 60Hz tone to trace signal, but it would be good to check which meter you have since many of them won't resolve low AC voltages.

[jminassi]

Paul,  I have a Brymen BM235, but the AC functionality does not work.  My other meter is an inexpensive Neoteck NT8233D PRO.
I have an iPad and I have the oscillator I mentioned.

But my problem is I can't read the schematic.  What points in the circuit do I attach my test leads to?

Does anything look obviously out of place in my photos?

Thanks,

John

[Paul Birkeland]

The Neoteck is fine for the job.

Start by playing a 60Hz tone into the pre with it turned off and the volume up all the way on your source.  Measure the AC voltage at the center lug on each level of the balance pot with the balance pot centered (with the preamp still off).  I would expect an iPad to put out about 0.3V AC, and there is some loss in the balance circuit, so if you see about 0.2V AC on each center lug, that wouldn't be abnormal.

[jminassi]

Paul,

First I really appreciate your help and patience.  I downloaded a function generator onto my iPad.  I input a 60 Hz tone into the Moreplay.  Moreplay is not powered on.  Volume on iPad is all the way up.  Balance control on Moreplay is centered.

I placed the black lead of the Neoteck on terminal 23 and the red lead on the top middle lug of the balance pot.  I measure approximately 1.3 VAC.  For the bottom middle lug I measure 0.74 VAC.  See pictures.  Does this make sense?

Thanks,

John

[Doc B.]

Just to clarify, you are feeding the signal into both left and right inputs at the same time?

[jminassi]

Yes Doc, I am feeding the signal into both channels simultaneously.  The cable has a stereo mini plug on the end going into the iPad and right and left channel RCA plugs going into the Moreplay on the other end.

John

[Paul Birkeland]

Can you unplug the RCA ends from the Moreplay and use your meter to measure the AC voltage between the center pin and shell at each RCA plug?  That seems like abnormally high signal voltage, so it's good to double check.

[jminassi]

PB,  AC voltage between pin and shell on both left and right channels is approximately 1.3 VAC.  See photos.

Thanks,

John

[Paul Birkeland]

I think what I would do next is to feed your ipad back into the Moreplay with the power off, then set the balance knob so you get approximately equal AC voltage at each center lug. 

I would also check that you have 0V AC on the balance pot where the black wires land.

After you have completed this, now measure the AC voltage at A5 and B5.

[Paul Birkeland]

I'm also not 100% certain that the red wire leaving 9L can do its job.  I would heat up that joint and move the wire so that it touches the terminal strip, then flow some solder between the two.

[jminassi]

PB,  I crimped the connection of the red wire at 9L and re-soldered.  I used the balance control to have balance at .966 VAC and .922 VAC.  Votage at A5 is .97 VAC and at B5 is .92 VAC.......so the signal is tracking the balance pot closely.

I confirm that I have 0 VAC where the black wires attach to the balance pot.

Thanks,

John