MP-1 bass is weak (centered on low mid freq). Install MOD 3?

[dracoaran]

So I play hard rock through a Marshall TSL-100.  For a light-weight backup my ADA MP-1 has plenty of gain, cut, and great cleans, but I am always wishing it had the bass frequency centered a little lower.  The bass control seems to target a mid frequency instead.

The easiest fix would be a rack EQ to boost around 80hz and shelf frequencies below that, but then I came across this sample of a MOD 3 on youtube:

https://www.youtube.com/watch?v=Rd_Mmf3SxSI

The guy who performed the mod told me that it is MOD 3.1.  Looking at the instructions it seems really easy and it sets the bass control at a lower frequency.

Questions:

1.  Is the MOD 3 schematic on this forum the same as 3.1?  Or does someone have the instructions for 3.1 elsewhere?

2.  What were your findings after installing MOD 3?  Did you lose a lot of dynamics?  Is the bass muddy?  How were the other frequencies affected in your opinion?

[rnolan]

Hey dracoaran.
This is more MJMP territory as he IIRC designed the MP1 mods.  The other upgrade worth doing is the MDRT transformer replacement (http://www.marshalljmpmodshop.net/miscellaneous_parts_and_replacement_tubes.htm).
If you dig around here you'll find various post about the different MP1 mods and quite a few 3TM users (and even a couple of Randall users, go Steve  ;) although I think he's now a 3TM convert  :thumb-up: )

Cheers Richard

[MarshallJMP]

Well you could try to replace R168 (5k1) with a 10k trimpot.This way you can alter the center frequency of the bass tone section.It's all explained in the mod 3.666 instructions.If that doesn't help you can always do the mod 3.There's not much difference between the 3 and 3.1.The 3.1 has a tad more gain and the od2 control is shifted to the last triode.IMHO the 3 sounds better then the 3.1.

[dracoaran]

That would be great, a stock MP-1 with a real bass control.

I am having trouble finding the 10K trimpot mentioned in the MOD 3.666 pdf.  Everywhere it says it is discontinued.

Would something like this work?:
http://www.mouser.com/ProductDetail/BI-Technologies-TT-electronics/25SR10KLF/?qs=sGAEpiMZZMvygUB3GLcD7lv7xXtevcsqMhxW%2fbUPV7k%3d

Or maybe this?:
http://www.mouser.com/ProductDetail/BI-Technologies-TT-electronics/82MR10KLF/?qs=sGAEpiMZZMvygUB3GLcD7lv7xXtevcsqoykIDxyA5yU%3d

[MarshallJMP]

The first one isn't good,according to the datasheet it's a side adjusment and you need a top adjustment.This is a major problem with mouser,the pics are in alot of the cases wrong.They show a pic of a top adjust and they sell you a side adjust.ALWAYS check the datasheet with mouser.!!!!!!

Second one,according to the datasheet should work.

[realdealblues]

Thanks for the tip.  I'm going to try adding that trim pot myself. 

The lack of low end push is the only thing missing from the ADA in my opinion.  The tonal characteristics and gain levels of the stock unit are perfect for me.  I can get any tone I want out of it and make it sound like any of my other amplifiers, but it just doesn't have that low end push that every single one of my other amplifiers have.  No matter what power amp I pair the ADA with or which tubes I try, it is always lacking with the low end push compared to everything else. 

The BBE has been the only way I can get that low end push.  Seems like I remember Vito Bratta from White Lion saying that's why he used the BBE.  If I could get that low end push without the unit getting muddy or having to use the BBE, the ADA would be absolutely perfect.

[El Chiguete]

So you would only do the part of the mod that targets the change in the bass freq??? This sounds interesing!

Are you wanting to have a deep low end or just a little more for to have a better low end push and still play hard rock/classic rock/metal? This is what I play too.

[dracoaran]

Thank you, Marshall.

And yes, I am just trying to shift the bass frequency a little lower.  I don't need the bass to be huge, just fatter.

[RobbHell]

The weakest link of the ADA is the Bass and Mid Eq points. 180hz is not a a bass frequency 50-80hz was a punchier and tighter sound. The BBE gives the signal a bump at 50hz thats why your hearing more bass. Ibe gotten rid of all of my BBBE's and just have modded my Mp1's to.sound the way I want. The Mids are also very Narrow and been muddy and nasally at times.

[Micky]

Well you could try to replace R168 (5k1) with a 10k trimpot.This way you can alter the center frequency of the bass tone section.It's all explained in the mod 3.666 instructions.If that doesn't help you can always do the mod 3.There's not much difference between the 3 and 3.1.The 3.1 has a tad more gain and the od2 control is shifted to the last triode.IMHO the 3 sounds better then the 3.1.

Hi MJMP, to "solve" this question about bass frequencies was looking at 3.666 pdf: R168 or R165?

Anyone tried this trimpot installation in a stock MP-1?

Thanx and Happy New Year

[MarshallJMP]

R165,it's a 5k1 resistor.

[RobbHell]

The 10k trimpot helps but doesn't cure it. If you want serious bottom end add a Parametric eq. Ive made semi parametric bass and mid mods for my mp1 similar to Lee Jacksons work with Ampeg amps ..but still use outboard eq for that chunk. MP1's by themselves are very thin,don't have much body but have everything else to be wanted.... Get an EQ and start Djent away.