Let's Get Technical > Troubleshooting Problems

MP-1 A channel much quieter than B

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Mxzx:
I just bought a MP-1, and know very little about it.  I did download the owners manual and have read that.

I don't have a power amp, so just running into front of a Marshall SuperLead.  I do have the switch on top set to the forward position.  When I plug the amp into A output, it is very weak and thin, when swap to B output it is very loud and full?  I have not tried running both outputs together.

i did swap the tubes around, and that didn't make any difference.

Any ideas?

Also noticed this, is this stock or a mod?



Thanks!

hal2000:
I only can say something about that orange capacitor (you mean that?). As far as i know, my mp1 was not modded and this section in your photo looks exactly the same as mine.

MarshallJMP:
yes this cap is standard.

Try to plug in a headphone in the headphone out and listen,are both outs (L and R) the same through the headphone?Let me know.

Mxzx:
Thanks for the info.

When I first fired unit up, I tried the headphone jack with a set of headphones.  They were the same except one side was cutting in and out, like a dirty pot.  I cleaned but haven't retried it, I'll do it tomorrow and report back.

Also, what exactly does the switch on top do?   I just read the warnings about having it forward for guitar amps, but they don't say what i does.

Thanks

rnolan:
The switch changes the MP1 A and B outs to instrument level (millivolts) to plug into your guitar amp (clean) input OR line level (~1 volt(s)) to plug into a power amp (which is designed to be driven by a separate pre-amp/mixer etc at line level).  Your guitar amp has a pre-amp and power amp and it's pre-amp is designed to take guitar (instrument) level signal.  If you send it line level, you'll overload the input (badly and may cause damage).  If you plug the ADA set to instrument level into a power amp, it won't have enough herbs to drive it and it will sound week, thin, yuk, noise etc.
The new(ish) ADA site (http://www.adaamps.com/index.htm) has suggested pre-amp eq settings in the ADA APP-1 user manual for a bunch of guitar amps (Marshall included) to provide the cleanest flatest response (no add colour) for people who want to run their ADA APP-1 into a guitar amp.  These are just as valid for MP-1 into guitar amp.  They are on page 15 of the APP-1 user manual (attached), it also includes some other good advice regarding using a guitar amp with these pre-amps.

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