Testing out my new smpro mpatch2 I got unexpected results with the mpatch2 stereo/mono switch, for rca soundcard inputs and headphone output. Because the results were unexpected I tried these rca soundcard to mpatch combinations:

red to red & white to white
stereo: Right headphone no sound audible, Left headphone normal
mono: same as stereo

red to red only
same as 'red to red & white to white'

white to white only
stereo: Right headphone no sound audible, Left headphone VERY FAINT (had to turn up DAW volume to get this)
mono: Right headphone no sound audible, Left headphone NORMAL

red to white & white to red
same as 'red to red & white to white'

red to white only
stereo: Right headphone no sound audible, Left headphone VERY FAINT (had to turn up DAW volume to get this)
mono: Right headphone no sound audible, Left headphone NORMAL

white to red only
same as 'red to red & white to white'

(DAW always stereo output with master routing simply: 1/2 => 1 Analog Out / 2 Analog Out)

Have I got the routing wrong or misunderstood something or can anyone say how a passive attenuator can give these results?

Another observation: without the mpatch2 power supply nothing is audible in headphones, but soundcard direct to headphones has plenty of volume. I would have thought if the soundcard level is sufficient then the mpatch2 unamplified level would also be ok.

Any advice greatly appreciated

Quote lachha:

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Testing out my new smpro mpatch2 I got unexpected results with the mpatch2 stereo/mono switch, for rca soundcard inputs and headphone output.

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Okay... first thing's first! Does it work correctly when you use the main stereo inputs with TRS or XLR connectors?

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red to red & white to white
stereo: Right headphone no sound audible, Left headphone normal
mono: same as stereo

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Do the main (XLR) outputs work correctly? Is it just the (right) headphone output that appears faulty? The fact that there is no change when you operate the mono switch suggests the problem is with the output of the unit, rahter than the input, and points possibly to a faulty headphone amp or faulty headphones.

It also appears that the left and right channels are swapped over somewhere too!

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Have I got the routing wrong or misunderstood something or can anyone say how a passive attenuator can give these results?

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It would help a lot to know if the main outputs work as intended. That would prove whether the input wiring and volume control are doing what they should.

From your descriptions I suspect a problem with the active headphone circuitry...

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Another observation: without the mpatch2 power supply nothing is audible in headphones

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There won't be. The headphone amp is active circuitry that requires a power supply -- only the signal through the volume control to the main outputs is entirely passive.

hugh

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Technical Editor, Sound On Sound

Hi Hugh, thanks for replying!

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Does it work correctly when you use the main stereo inputs with TRS or XLR connectors?

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Unfortunately I have no XLR gear which would be an input, to test this.

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Do the main (XLR) outputs work correctly?

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XLR outputs work correctly except for these cases:
red to red only, stereo, one speaker normal, other speaker very faint
white to white only, stereo, other speaker very faint, one speaker normal

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points possibly to a faulty headphone amp or faulty headphones

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headphones work correctly when direct from soundcard
the mpatch2 powersupply doesn't fit securely into my mains shaver adapter (this seemed to be the right kind of thing to use because the mpatch2 powersupply plug looks like a shaver plug). The mpatch2 powersupply prongs are too thin, but all the mpatch2 lights come on.

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It also appears that the left and right channels are swapped over somewhere too!

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I think this is from the soundcard. In the DAW, Master 1/2 goes to soundcard 1/2. It's always been bottom of the list to sort out.

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only the signal through the volume control to the main outputs is entirely passive

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That explains that, and more clearly than the manual!

Can anything be safely deduced?

Quote lachha:

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Unfortunately I have no XLR gear which would be an input, to test this.

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Oh dear! That makes it pretty difficult to check the unit and find out what might be wrong. Perhaps you have a friend whith suitable equipment to help out, or you could take it to the shop and try it there...?

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XLR outputs work correctly except for these cases:
red to red only, stereo, one speaker normal, other speaker very faint
white to white only, stereo, other speaker very faint, one speaker normal

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That sounds completely normal to me: One input, one output!

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headphones work correctly when direct from soundcard

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Okay.

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the mpatch2 powersupply doesn't fit securely into my mains shaver adapter (this seemed to be the right kind of thing to use because the mpatch2 powersupply plug looks like a shaver plug). The mpatch2 powersupply prongs are too thin, but all the mpatch2 lights come on.

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Oh dear again! The mains plug is a European style plug. It is not compatible with a shaver socket, although it might look superficially similiar, which is why it doesn't fit securely! Assuming you are in the UK the best solution would be to get a 13A to Euro plug adapter, like this one:

http://www.amazon.co.uk/Euro-Pin-Converter-Plug-Adapter/dp/B000NJ30QO< br />

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Can anything be safely deduced?

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Not from what you've said so far. As I said earlier, I'd hazard a guess that there's something amiss with the headphone amp, but without proving that the RCA inputs arrive at the main outputs intact, and tha the mono switching works properly for the main outputs, it's hard to know for sure.

hugh

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Technical Editor, Sound On Sound

Many thanks for your guidance Hugh. I have been able to send a much more together sounding fault report -

fault description
no sound in left headphone, for both rca inputs and xlr inputs, when mono and when stereo
(sounds like a CV)

test
stereo test signal having a low pitch on the left channel and a high pitch on the right channel.

headphones direct from soundcard,
daw stereo on: gives low pitch in left can, high pitch in right can
daw mono on: gives both tones in both cans
shows headphones work correctly

connect soundcard to mpatch2 (via a cleanbox to convert soundcard rca to xlr)
xlr inputs, mpatch2 stereo on:
xlr outputs1, low pitch in left speaker & high pitch in right speaker
xlr outputs2, low in left speaker & high in right speaker
headphones from mpatch2, high pitch in right can only, nothing audible in left can at same volume and daw centre panning.

xlr inputs, mpatch2 mono on:
xlr outputs1, both tones in both speakers
xlr outputs2, both tones in both speakers
headphones from mpatch2, both tones in right can only, nothing audible in left can at same volume

rca inputs, mpatch2 stereo on:
xlr outputs1, low in left speaker & high in right speaker
xlr outputs2, low in left speaker & high in right speaker
headphones from mpatch2, high pitch in right can only, nothing audible in left can at same volume and daw centre panning.

rca inputs, mpatch2 mono on:
xlr outputs1, both tones in both speakers
xlr outputs2, both tones in both speakers
headphones from mpatch2, both tones in right can only, nothing audible in left can at same volume.

Hopefully this impressive report will get a replacement. Definitely worth the subscription!

Seems pretty clear cut that the left headphone amplifier or its associated wiring is defective then.

Hugh

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Technical Editor, Sound On Sound

Quote Hugh Robjohns:

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Quote:

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the mpatch2 powersupply doesn't fit securely into my mains shaver adapter (this seemed to be the right kind of thing to use because the mpatch2 powersupply plug looks like a shaver plug). The mpatch2 powersupply prongs are too thin, but all the mpatch2 lights come on.

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Oh dear again! The mains plug is a European style plug. It is not compatible with a shaver socket, although it might look superficially similiar, which is why it doesn't fit securely! Assuming you are in the UK the best solution would be to get a 13A to Euro plug adapter, like this one:

http://www.amazon.co.uk/Euro-Pin-Converter-Plug-Adapter/dp/B000NJ30QO< br />

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Hi both,

That's identical to the PSU I received with my M-Patch2 direct from the German distributor when I reviewed it for SOS:

www.soundonsound.com/sos/dec06/articles/smprompatch.htm

However, I'm surprised that a UK PSU didn't arrive with an official purchase by a UK customer


Martin

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YewTreeMagic

Mine came from DV and had a Euro plug, so seems pretty standard for UK punters.

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ScanProAudio & 3XS Audio Systems
ScanProAudio Blog

That's a shame, particularly when the Euro plug is of the captive wall wart variety, so you can't snip it off and replace with a 3-pin UK mains plug

I've actually replaced by M-Patch2 PSU with another +12-volt DC/500mA one with UK mains plug that I had spare.


Martin

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YewTreeMagic

I use the headphone amp section about once a month on mine so hadn't considered it, but handy to know you had no issues in doing so Martin.

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ScanProAudio & 3XS Audio Systems
ScanProAudio Blog

There's a 7812 regulator inside the M-Patch2 that converts incoming DC to a nicely stabilised supply, so an incoming DC voltage of anything between around 15 to 24 volts ought to be OK.


Martin

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YewTreeMagic

happy ending: the shop sent a replacement which works perfectly. I want to thank you guys for your support.

Now the difficult bit...

Yay - a happy ending!!!


Martin

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YewTreeMagic