Problem with EHX mini-Q-Tron

[Mialbu]

Evening all,

I've got a problem with my EHX mini Qtron and wondered if anyone had any suggestions.

It was bought new as a present and hasn't worked properly from out of the box.  The music shop said it was from a faulty batch and to return it, but they went out of business before I had a chance to do so.

Problem is, the filter seems to work fine, but only at ridiculously low levels.  For example, if I hit the low open E, the sound cuts out, and you can only hear the effect come back in when the string has almost stopped ringing.   This happens in all modes, but more pronounced with the wound bass strings.

Bypass works fine, LED lights and I've tried it with a new battery.   I was going to try and go through it with a schematic, but cant find one anywhere on the net.

Could it be an incorrect cap/resistor value?

I'll be very gratefull for any thoughts.  If someone needs extra explanation/pictures/audio/video, please tell me what you need.

Many thanks.

M

[Mialbu]

Just as an update....

All soldering looks to be fine, except that the drive pot only sits on solder connections rather than actually being soldered to them.  Is this just an EHX quirk?

Will update again with full list of parts.


http://www.aronnelson.com/gallery/main.php/v/diyuser/Q-tron+001.jpg.html
http://www.aronnelson.com/gallery/main.php/v/diyuser/Q-tron+002.jpg.html
http://www.aronnelson.com/gallery/main.php/v/diyuser/Q-tron+003.jpg.html
http://www.aronnelson.com/gallery/main.php/v/diyuser/Q-tron+004.jpg.html


Cheers,

M

[flo]

the drive pot only sits on solder connections rather than actually being soldered to them

Which of the pictures show this?

Perhaps you can contact EH support. I assume its still under guarantee, right?
http://www.ehx.com/about/contact

[Mialbu]

Hi Flo,

I tried EHX support twice, but never heard back from them.  Plus posting it to the USA is going to cost more than the pedal's worth!

If you look at picture 2, you can see the loose pot in the front left corner.  With it all screwed together, the legs from the pot sit in the holes you can see to the left of capacitor 10 (if you enlarge the picture).  The legs and the solder don't appear broken though.

Cheers,

M

[oskar]

Shame on EHX. They've disappointed me before... Grrr. 
That pot is supposed to be soldered. Properly. Else there would have been something there to hold it analogous to an IC socket, but I see only solder pads ( top right pic. 4 )
Many companies are suffering from problems with soldering lately because of new directives banning the use of led in production. But I don't know if your mysterious pot is one of these children of misfortune.

[Mialbu]

Thanks oskar,

I thought that would be the case.  The holes are there for the legs (which have solder on them) and there are the solder pads on the trace side of the board.  The rotary switch and "Q" pot are soldered properly too.

I'll solder the drive pot in properly and see if that cures the pedal.

Fingers crossed!

M

[Mialbu]

Morning all,

Right, I've soldered the drive pot back in properly, and although we're getting somewhere.....it still ain't right.

As far as I can tell the pedal is now working correctly.......as long as the guitar's volume pot is turned down to 1 or less.  As soon as the pickup is turned up above number 1, the clean signal comes through.  The wah can then only be heard again when the string almost stops ringing.

Is it worth having a twiddle with the trimmer?  Or is it likely to be an incorrect cap/resistor in there somewhere?

Appreciate all your help so far,

Cheers,

M

*Edit*  I've put all component values I could see here
q tron list.doc]http://www.filefactory.com/file/aff6e9c/n/q_tron_list_doc]q tron list.doc
Nothing jumps out as glaringly obvious, well, not to me anyways!

[flo]

The behaviour you described sounds like the drive is turned up high.
What happens if you turn the drive down low and what if you turn it up high?

[oskar]

Flo is right... ( maybe tweek a little? )   plus the gain in a normal qtron is like insane... I don't know if they've changed that for the mini.

As far as I can tell the pedal is now working correctly.......as long as the guitar's volume pot is turned down to 1 or less.  As soon as the pickup is turned up above number 1, the clean signal comes through.  The wah can then only be heard again when the string almost stops ringing.

But isn't that the same problem as from the start?

Problem is, the filter seems to work fine, but only at ridiculously low levels.  For example, if I hit the low open E, the sound cuts out, and you can only hear the effect come back in when the string has almost stopped ringing.   This happens in all modes, but more pronounced with the wound bass strings.

Is it worth having a twiddle with the trimmer?

Yes. I wan't to know what happens when you twiddle it!   

Or is it likely to be an incorrect cap/resistor in there somewhere?

Nah. Not likely... It's a unit that comes from a factory and really it should have been tested somehow. However my EHX Electric Mistress came with the power contact hanging loose... surely they would have noticed it if they would have tested it for functionality.

But seriously.
I wouldn't like to piss this guy off. He fought the russian maffia.

[Mialbu]

But isn't that the same problem as from the start?

Yes, sorry I'm doing a good job of being unclear!  What I should have said was that the pot was soldered in fine, and the pedal was still behaving as before.

The drive pot seemed to be doing almost nothing.  I've hooked my multimeter up to leg 2 and one of the ends, twisted it both ways....and guess what?.....the ohm's reading shows "1" at both ends.  Looks like it might be a faulty pot to blame then?   And after i went to the bother of soldering it in again!

Cheers guys,  I'll see if I've got a suitable replacement and report back.

Thanks again,

M

[oskar]

The drive pot seemed to be doing almost nothing.  I've hooked my multimeter up to leg 2 and one of the ends, twisted it both ways....and guess what?.....the ohm's reading shows "1" at both ends.  Looks like it might be a faulty pot to blame then?   And after i went to the bother of soldering it in again!

- ouch!

[Mialbu]

Ahhhhhhh, it lives!

Turns out drive pot was dead.  Haven't got a 150K, but 100K seems to give a good range.

Thanks so much for your help, I really appreciate it.

Cheers,

M

[oskar]

A happy ending...    - Rock on!

[flo]

That's great! Have fun playing!