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Bass setting not saving

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revhed666:
gday from Australia guys. i recently scored an MP-1 and all seemed fine but i have noticed the bass setting is not saved correctly when saving patches. i can dial a patch and the bass parameter edits just like it should but with any setting that boosts bass as soon as i change to another patch and back again the bass audibly defaults to zero even though the saved parameter value reads correctly. strangely this only affects boosted bass values (ie +2 +4 + +9 +12 +16) i can save at anywhere from 0 to -16 and it saves and plays back correctly after changing patches but saving a boosted bass setting reverts to around 0db after changing patches even though the value reads correctly. mid/treble/pres all edit and save fine. firmware ver 1.38
any insight is appreciated thanks

MarshallJMP:
So the reading is correctly saved but you hear a difference in sound?

revhed666:
correct. if for instance i save a patch with bass at +16, on reloading the patch the bass level sounds like it is set to zero even though the parameter reads +16. if i then enter edit mode and drop bass from +16 to +12 a huge jump in bass level then occurs and it sounds as it should for +12 setting. it works fine while editing it is only when returning to a saved patch that the bass setting works incorrectly and sounds like it reverts to zero

revhed666:
some more detail to add. when in edit mode if the bass level is at a boosted level, editing chorus or mid, treble or presence value up or down will also cause audible bass level to immediately revert to around 0db even though the bass parameter still reads +2 to +16. still same behaviour when changing patches whether using up/down arrows to change patch or direct selecting the patch

rnolan:
Hey revhead, greetings from Canberra  :thumb-up: Very perplexing, one thing worth doing is the later firmware (v 2.01 EPROM) update (http://www.marshalljmpmodshop.net/miscellaneous_parts_and_replacement_tubes.htm), not that it will/or wont influence this issue.  MJMP will hopefully have some ideas, it seems to me like a problem with the VCA (or whatever bit or circuit controls the bass filter boost/cut).  So the parameter "value" is storing correctly and being recalled correctly just not being applied ( +ve boost only) correctly.  (editing chorus or mid, treble or presence value up or down will also cause audible bass level to immediately revert to around 0db) this is probably because the other parameter settings are being reapplied after each edit so it has the same affect (issue) as changing patch (my guess).

So here's my take on it, the parameter values are just an entry in a file/memory location (kept alive by the battery).  When you initiate/cause (by editing) a patch change various parts of the MP1 circuit are sent updated values to change to.  The MP1 is analogue so the various bits of the circuit are controlled by analogue devices (e.g. Voltage Controlled Amplifiers (VCA)).  These devices accept a signal from the parameter file/memory (or front panel in edit mode) and adjust accordingly.  In this case, the device that controls the bass boost/cut is not reacting to  +ve values properly and is defaulting to 0.  Also it only happens when it's sent a change from memory as you can edit the value directly and it responds appropriately to that (as long as that's the last thing you change).

So I'm thinking there is either an issue in the data/signal path from memory to the bass boost/cut controller (i.e. the  +ve bit/signal is not getting through/being recognised) or the controller device has an issue of some kind (less likely I recon as you can turn it up/down directly in edit mode (the edit signal would be a slightly different (direct) data/signal path than from the memory ??)).  The device that controls bass boost/cut will receive a signal that represents a number (0 to 16) and a +ve/-ve indicator (1 bit in computer stuff, 0 or 1 though not sure how the MP1 circuit does it).  It would seem the +ve value  indicator of the signal is not getting through to the controller device from memory or is being corrupted in some way causing a default to 0 (controller throws the towel in).

Cheers Richard

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