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[ddt]

I'm puzzled. I've come across an ADA MP-1 board revision "E" from year 1989 with the stock looking transformer, which gives over 12V of heater voltage and ~220V of voltage feeding the tube board. It has been modded with 5 Ohm / 5W resistor to step down the voltage for the digital section's voltage regulator input.

The question is, was there anything like that either officially or custom made by A/DA back in time or was this modded by a shop? Does anyone know?

https://drive.google.com/file/d/16vkYGij3qYmDgdfbmqpMB0Efbem4BeGj/view?usp=sharing

[rnolan]

Hey ddt, that looks like a custom transformer.  The stock tranny is one bobbin not 2 like the one in the pic.  Also those specs (12V heater, 220Vdc high voltage) are very similar to the MDRT (12.6V heater, 240Vdc high voltage).  The original trannys are 8-9V heater and 190Vdc high voltage (see MJMPs site https://www.marshalljmpmodshop.net/miscellaneous_parts_and_replacement_tubes.htm).  The MDRT is 2 bobbins but side by side. I'm sure there are other mods and custom transformers around, IIRC Rob Hell was getting some made quite a while ago (I think in China). 

As far as I know, ADA never made anything like it.  My guess is it's been modded with a custom transformer and should sound and perform much like the MDRT.  There should also be a 300k resistor on the tube board to accommodate the increase in high voltage (see attached for location).

[ddt]

Fantastic! Thank you so much for the info.
Looks like the R9 240k resistor remained in place in this MP-1, so basically it's unfinished business. 

[rnolan]

Hey ddt, no worries, others hear may know more  .  So according to the MDRT instructions, not changing the resistor on the tube board (R9) to 300k will mean the high voltage will stay at 190Vdc and not achieve the desired increase, in this case to 220Vdc and for the MDRT 240Vdc.  However, some may prefer it that way?  SC for example likes his MP-1 stock as he prefers the sound.  He even went so far as to source a very early original MP-1 transformer as ADA did change them a bit in later units, probably when they changed the rear jack to inst level and got rid of the inst/line level top switch and went to v2.x firmware.  The increase in high voltage provides for more dynamic range and opens up the sound.  SC preferred the original tone/sound and, in some ways, I agree with him.

[ddt]

Ok, so I've checked some older photos and my other MP-1s and there seem to be two types of transformers. One with black insulation and one bobbin, second type is with 2 bobbins and blue insulation. The blue ones have STEED logo on it. I still have a suspicion that this is a factory made tranny.

[rnolan]

Interesting, MJMP will no doubt know the answer, hope he comes back on board soon.