Deluxe Memory Man distorts on bass notes

[deblacksin]

Hi all!

I've been lurking alot lately regarding how to mod my DAMM to get the best out of it. It is a 5knob model from 2002 with 4 MN3008 chips.

this paragraph is about calibrating, the question is below it.
First I thought it wasnt calibrated properly. So I marked the trimpot's places and started testing them. It wasn't as hard as people usually mention..
There are 4 trim pots which control the bias, and as you rotate them you go from dead silent, to grungy distortion, than the clean zone where it has a sweet spot, and after it goes back to grungy and all the way other side dead silent. You need to find that sweet spot in all of them, and test them all a few times as they are inter-dependent of each other.
Than there's 3 which controls feed back amount, one for gain entering the BBD and one which did nothing..

Question:
My DMM is damn Rusty and beated, awful shape..
It started doing some serious distorted repeats, even on clean settings.
Symptoms are:
1- it is sounds quite like a rattling, blocking distortion in tube amps
2- the weaker the gain entering the circuit, the less distortion there is
3- the more bass there is, i.e lower notes (low b string..) or neck pickup causes more clipping. It barely happens above E3.
4- if a distorted/overdriven sound is entering the DMM, the effect is barely noticeable.

I do get it is an analog delay of old delay, but is there a way of minimizing this effect?
Maybe reducing the bass getting into the DMM?
It's not fun to play chord progressions with thick delay and having that rattling clipping behind of it..

[Plexi]

Sounds like you have a bias problem there.
As you mentioned that and the trimpots, I guess you must to set them by the voltage in some IC's or circuit points.

[StephenGiles]

Definitely a bias problem, had the same on my old unit.

[Govmnt_Lacky]

What you need to understand is that the delay line is in series. This means that when you change the bias on the first BBD, it effects the rest down the line. This is why it is kind of crucial that you use a scope to properly bias this type of setup.

Once you can dial in the bias to the first MN3008 in the series, then you need to progress to the next and onward. If the 1st or second BBD is not properly biased, then the distortion will only be "amplified" down the line.

[deblacksin]

Wow such quick answers. Thank you all!

So it is what I thought in the first place, re-bias.

Before I go any further, can you ensure I assumed right?
4 trimpot's for 4 MN3008 chips, 1 for input gain, 1 for feedback, the other I don't know, and the problem is set within the course of the 4 bias trimpots.

Since it wasn't bias in the first place, I don't mind messing with it.
Is there any ~best~ way to do it rather than using a looper to listen to the repeats as I tweak?
How should I set the potentiometers as I tweak?

Btw- I notice the rattle is abundant even when when blend is all Dry, hence no repeats. The rattle showed up after the time set by the Time knob, means that only the rattle made it through even when blend was dry.

Should I try testing it while blend is dry and by that to hear the rattle more clearly?

[deblacksin]

I made it! Using ears only (:

The difference this time was that I adjusted the trimmers in the correct order, like you suggested, and tried to send into the pedal a very high volume signal so it pushes the pedal to the limits.

Thanks guys!