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Temp "Time Format" issue Fix in Discussions

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 on: Time Format 
Started by red2203stack - Last post by bunkyloo
Looks like these guys may have it if its not a mistake.   

 on: Time Format 
Started by red2203stack - Last post by red2203stack
Yep, I emailed MJMP. No luck. He did give the part number. MJ-188LP-8 made by Pro Signal. Cany find one anywhere.

 on: Time Format 
Started by red2203stack - Last post by red2203stack
Slow is smooth, smooth is fast. Waiting on parts. The parts were reasonable so I decided to tighten up the power supply a little better before moving on..

New transistors (VR1, VR2, VR3, VR4) same values

New .047uf ceramic disc capacitors at (C119, C120, C122, C123, C125, C127, C129, C136). Replaced with .047uf 1kv 105° 10% ceramic

New 33uf/25v electrolytic caps rated at 105° at C121, C124, C126, C128

New 2200uf/40v 125° electrolytic at C129 & C130

New 3300/16v 105° electrolytic at C131

That should restore the power supply to its glory days. The original electrolytics were getting bad quick.

 on: Time Format 
Started by red2203stack - Last post by bunkyloo
Was just going to suggest MJMP website but it appears to be an obsolete part from what I can see. This may be a problem :facepalm:

 on: Time Format 
Started by red2203stack - Last post by red2203stack
Looking for a replacement effects return jack for an MP1 in new or very good used condition. Anyone have one to spare?


 on: Time Format 
Started by AndiK - Last post by AndiK
Just measured R151 - reading 176k, so this should not be the reason for the issues. Has to be in the signal path of the clean tube mode....


 on: Time Format 
Started by astrobushido - Last post by astrobushido
Great info, MarshallJMP, that's exactly what I need to know!

A few final questions:
- do you (or anyone else) know what is the crossover frequency of the high-pass filter on the MB-1 and what's its slope?
- does the high-pass chorused signal gets combined with the bass full range dry signal or a low-passed dry signal?

Thanks a lot once more!

 on: Time Format 
Started by red2203stack - Last post by red2203stack
I cut it out to make for a clean removal with the 3300uf cap. Replacing that with a Sprague 105°. The old resistor still measures 4ohm on the meter without juice. I"ll order the correct replacement from mouser. Thought I had one. With this order might include replacement transistors, just to have. Are there any benefits in noise reduction by replacing those?

 on: Time Format 
Started by astrobushido - Last post by MarshallJMP
How does the MB-1 only chorus the mid and high frequencies of the full signal spectrum?
Is it by way of splitting the signal with a high-pass filter before the chorus section input, feeding the chorus processor with only the high-pass filtered signal and then combining the processed signal with the dry full range (or bass-frequency content only) signal near or at the preamp's outputs?

==>That's the way it works in the MB-1

And by the way, all ADA's guitar preamps' (not the MB-1) claim that the chorus is stereo.
What sort of stereo are they referring to? From what I recall, it doesn't seem to divide the Left/Right signal into chorused vs dry only signals - L/Wet | R/Dry (as the Roland Jazz Chorus amps' seems to do).

==>the signal in the MP-x is divided in L/wet R/wet signal (wet is180° phase shifted on one side), all of the stereo chorus effects I know off work this way

The MP2 manual also states that the stereo chorus is the point where the signal splits and becomes stereo.

At the same time, the MP1 manual says that if you sum its two outputs on a mixing board (i.e. without fully panning those outputs), it will result in phase cancellation of the chorus.
This seems to support the L / 50% Dry + 50 % normal phase wet | R / 50% Dry + 50% inverted phase wet theory.

But how do they achieve a mono chorused signal without any phase cancellation if one only uses the mono output A of the preamp?
Instead of simply being a mix/sum of both outputs, does it only output the original Left signal, i.e., discarding the inverted phase chorus signal altogether and only outputting a mix of the dry and normal phase chorused signal?

==> for the mp-1 the A out is the original signal with the chorus signal mixed in, the B out is also the original signal but with the chorus signal phase shifted 180° mixed in , so if you plug in in either side you will get one of these signals, but if you hear it in mono it doesn't matter, now if you mix both signals together you will only get  the original signal due to the fact that the 2 chorus signal are 180° out of phase ,when you mix them together they cancel each other out

 on: Time Format 
Started by red2203stack - Last post by MarshallJMP
Oh ok, that explains it. Thanks for the reply MJMP. I Replaced the 6 diodes with new 1n4007's and changed the 2200uf & 3300uf caps. Now i'm gonna have to wait on a new 4ohm resistor, closest i have is 5.6ohm. The original was 5w ceramic wirewound. Is that the best option for that?

Why would you replace it? Never seen these fail. You can also remove it but then you need put a wire bridge over those traces that are cut. Also be carefull with a bigger resistor, make sure the voltage drop isn't too big. The 7805 need a voltage difference of 3V between in and out.

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