MXR M222 talkbox

[12afael]

Happy new year to all on this forum! I haven`t been here in a looong looong time.

I have something interesting here. a friend of mine brings me his MXR M222 talkbox, it have a 10 class D power amp so you don`t need an external amp. This is a recent model and the PCB say revision A, I think it have some design problems but I can`t be sure without the schematic. first of all when you activate the talkbox part of the signal bleed to the "normal" amp. I have seen an extreme case in youtube, in the unit at my hands I have to put the amp loud the hear it but it is there. strange because it have a relay for the bypass. provably they didn't ground the output to the amp correctly. again, not sure without a schematic.

my friend bring me this unit because it just change the "channel" one time.

1 sounding through the guitar amp ok (talkbox by pass)
2 changing sound to talkbox amp ok (talkbox on)
3 fail to return to the guitar amp, not sound at all.
4 it return to the talkbox normaly.

the problem is a design problem. it is not so easy to solve completly.
the strong magnet of the speaker is atracting the relay switch and it is not able to turn back again.

I would like to hear ideas to solve this problem, as far as I remember the magnetic field is not posible to be isolated right?


best regards!
Rafael

[armdnrdy]

There is no schematic (that I could find) available for this unit.

Also, an internet search failed to find any problems with the switching.

I highly doubt that a company like MXR would release a product with an issue such as you described.

Without seeing the schematics, I would look to the bypass switch being defective.

You mentioned "relay switch". Is there an actual relay incorporated in the switching design?

[12afael]

Without seeing the schematics, I would look to the bypass switch being defective.

You mentioned "relay switch". Is there an actual relay incorporated in the switching design?

that was my first thought, but the dpdt is working good and it just complete the relay circuit.  yes it have a small DPDT relay.

any company can have a bad design, they make revisions that solve some problems.

here is a video of other problem of this pedal.

http://www.youtube.com/watch?v=rI-55DvgHr0

[armdnrdy]

Interesting video.

I wonder if it has something to do with a shared power supply. One of the pedals is not playing nice with the other pedal!

Are you using a separate power supply or shared. The M222 comes with an 18VDC transformer which would isolate the power.

In the video, It looks like his talk box might be plugged into the pedal board power.

[12afael]

the pedal use it's own power supply, 18V 1A switching mode. if it is well designed and just share the ground it should not be a problem.
I`m using it just with my Engl Savage.

I belive that his problem is that the bypass system is not well designed,  if he use a distortion pedal after the talkbox it is amplifing the signal that bleed from the pedal. provably they didn't read the switching article of R.G.

[armdnrdy]

Contact MXR.

See what they have to say, and if there have been other reports of issues with the switching circuit.

It's kind of tough to figure out what the problem is without a schematic.....we can just guess. 

[12afael]

I already sent an email to tech support. with some luck I will have a reply today.

I will try to "move" the magnetic field adding some metal to the magnet of the driver.

best regards

[12afael]

today I received an email from the tech support, they cannot provide an schematic but the have a new board, they can send me a new PCB if I send the old PCB. I`m a bit far but if it solve the issues worth it.