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Let's Get Technical => All PREAMP Tech Tips & Support => Topic started by: trader144 on January 26, 2015, 07:30:47 PM

Title: MP-1 problem - lame sound on startup
Post by: trader144 on January 26, 2015, 07:30:47 PM

My MP1 is acting up.

on my normal settings (e.g. 3.8 OD1 and OD2 and 7.5 Master) the distortion has started to act really weak when I turn on the unit, then after about an hour the distortion kicks in to normal...all without changing any settings. Not just the distortion but the overall sound is tinny and lame.

I tried different tubes and it didn't get any better. OD1 and OD2 still adjust the distortion and master still has an effect too, but the distortion is about 25% of what it should be.

Any ideas? I checked the forum and didn't see anything similar.

Using output A. I tried output B and line out. Been doing this for a few weeks..thought it was just a tube but doesn't look like that is the problem.

Should I measure the transformer voltage to the tube board?

Title: Re: MP-1 problem - lame sound on startup
Post by: rnolan on January 27, 2015, 04:56:47 AM

Just to add some ideas', this does sound a little bit like problem MikeB was having (though not exactly and others may have better ideas of whats wrong), but he changed out the tube board (from MJMP) and now all is good, it was burning tubes as well in V1 IIRC but not instantly.
@Mike, does this have parallels to your issues ??

Title: Re: MP-1 problem - lame sound on startup
Post by: trader144 on January 27, 2015, 07:02:26 AM

I hope that is not the fix
I just did the noise mod!!!

I am thinking it is a voltage issue.
Going to read how to measure it

Title: Re: MP-1 problem - lame sound on startup
Post by: MikeB on January 27, 2015, 11:42:36 AM

It does sound like what happened to mine.  However,  mine sounded fine with new tubes for a time. So probably a different issue.  Does seem to be tube related, though.

Title: Re: MP-1 problem - lame sound on startup
Post by: MikeB on January 27, 2015, 11:51:57 AM

You know,  i did always suspect that i could have got away with just changing the tube sockets.  Perhaps they're just dirty.

Title: Re: MP-1 problem - lame sound on startup
Post by: MarshallJMP on January 31, 2015, 11:57:43 AM

Could also be an input jack problem,do you have a V1 or V2 mp-1?Which input do you use,front or back?

Title: Re: MP-1 problem - lame sound on startup
Post by: trader144 on February 01, 2015, 06:52:03 PM

I use the front input.
My unit has (had) the blue caps on the tube board and does not have the knob to adjust the rear input jack.
Attached are some pics. Is that enough or do you need more description?


I really hope that is all it is...that would be a gift.

Title: Re: MP-1 problem - lame sound on startup
Post by: MarshallJMP on February 02, 2015, 03:05:36 PM

Okay i see,it's a V2 unit.V2 can have this kind of problem but only if you use the rear input.What tubes (brand) do you use?

Title: Re: MP-1 problem - lame sound on startup
Post by: trader144 on February 02, 2015, 06:45:05 PM

I am currently using originals.
I have swapped out with a TD and with GV mullard specs in both spots and there was no difference.


Thank you for your help. I have a multimeter.

Title: Re: MP-1 problem - lame sound on startup
Post by: MarshallJMP on February 03, 2015, 03:02:24 AM

Are the replacement tubes new?

Title: Re: MP-1 problem - lame sound on startup
Post by: trader144 on February 03, 2015, 04:53:18 AM

Yes I have one new TD that is original spec and 2 new GT Millard specs all new.
I tried combinations with and without the original tubes in both V1 and V2 swapping around.

Everything reacts to changes in the OD1 OD2 and master settings.
It sounds like it is very underpowered.

I measured the voltage going into the tube board at the small white plug several times and it showed 17 mV with the m.

After about 1/2 hour it would kick in and sound great, but it doesn't kick in anymore.

Title: Re: MP-1 problem - lame sound on startup
Post by: MarshallJMP on February 03, 2015, 09:43:09 AM

Voltage should be 190Vac or 240Vac for the MDRT.