Equalizer with 10 channel style MXR M108s

[Ashura]

Hello all.
I want to design (or better, redesign ...) a guitar equalizer, and, watching this video ( https://www.youtube.com/watch?v=adTRin6cu6U ), I really liked this MXR M108S pedal.
The Dunlop website says that the MXR Ten Band EQ has been upgraded with noise reduction circuitry, true bypass switching, brighter LEDs (that seem to obscure the user's vision ... https://www.youtube.com/watch?v=XgzIpydmC9E ) and a second output (which for me, I do not know if it has any usefulness ... ??). I imagine that when they talk about updating, they should be relating this pedal with the MXR TEN BAND EQ
M108 ( https://www.jimdunlop.com/product/m108-7-10137-01224-0.do ).

As for the latter, I can see that there are already schematic of it online.


But this pedal seems to be a bit noisy, and, to stay quiet seems to need modification ( https://www.youtube.com/watch?v=OIi-R7VjKAw ).

Here in my country this MXR M108S is not for sale, and considering that its predecessor is very expensive, I can imagine how much this M108S would cost ... So I think of putting together a clone myself; and learn something in the process.

I wonder if anyone would have any schematic of this MXR M108S or some PCB photos of pedal. In the absence of a schematic, if someone has access to a model and can take some photos of the PCB so we could compare with that of his predecessor model, it would be very good.

Thank you to anyone who can attend.

[mth5044]

I know this isn't what you asked for, but I don't think I can help providing info on the specific pedal BUT I did build a functionally similar pedal using the Simple, Easy Graphic EQ schematic at GEOFEX:

http://www.geofex.com/article_folders/eqs/paramet.htm

With a bit of calculation and copy/pasting the gyrator section, you can replicate EQ bands of the MXR pedals. I did put a simple buffer infront of the schematic as with dual opamp chip you have an extra opamp doing nothing. Was quite quiet and worked as an EQ should. Besides that, what else were you looking for in a pedal?

[Mark Hammer]

I have held for many years that the "ideal" guitar equalizer has 6 knobs:
- a "shelving" bass boost-cut control as found on many stereos
- two bands of semi-parametric equalization (boost/cut and sweepable frequency)
- an adjustable 2-pole lowpass filter

That lets the user identify two resonant frequencies they would either like to emphasize or tame, compensate to bass-heavy pickups, or bass-light speakers cabs, and adjust how much "bite" you want the guitar to have, as well as precondition the signal for less harsher overdrive.

Multi-band equalizers like 10, 12, 15, 17, or 31 band, are based on the idea that the manufacturer doesn't know which frequencies matter to you, or will matter to you, so they give you lots of them to choose from.  But that increases cost, build complexity, and size.  The 6-knob pedal I describe will let you easily dial in many different sounds, and lets YOU pick where you want the boost or cut to be situated, rather than offering a "knob cafeteria" and asking "which ones of these do you need to use?".

True parametric equalizers also have a Q or selectivity control, such that boost/cut can be broad or very narrow in nature.  But since your goal is not to diminish standing waves or compensate for dips in crossover networks to "equalize" a listening space, the 3rd control is not really required.  Set the Q for something not too wide, not too narrow, and you're good.

Build the two middle bands from this one, and you'll be in good shape:  https://i.pinimg.com/originals/4b/fa/44/4bfa44e01c8dacf39febd569ec1b4bc6.jpg

[Ashura]

BUT I did build a functionally similar pedal using the Simple, Easy Graphic EQ schematic at GEOFEX: http://www.geofex.com/article_folders/eqs/paramet.htm

Hello mth5044.
Thank you for responding to my post. Very interesting this article that you indicated me. It was of great help to understand a bit more about the functioning of an equalizer.
I do not speak English natively, so I can not always understand everything I read. Especially when there are specific phrases or words with technical terms or specific expressions of a specific group of people or subject. When I try to translate them I often see words that do not seem to be related to the context, leaving the text very confusing... but I think I understood the article well. And he also helped to understand Mark Hammer's response.
Have you built a pedal equalizer based on this article? Could you tell me more about this construction?

Besides that, what else were you looking for in a pedal?

In the case of the equalization pedal, I'm not sure what I'm looking for. In principle I look for one that is able to change the timbre of the guitar when necessary; and soften the sound of certain notes when they seem too strident. It would be nice if he could do the opposite as well: leave notes that appear too soft with a more audible sound. But hearing this MXR M108S in the video I mentioned above, I can say that it would be, at the moment, what I'm looking for; because it seems to do everything I expect for a pedal equalizer.

I have held for many years that the "ideal" guitar equalizer has 6 knobs:
- a "shelving" bass boost-cut control as found on many stereos
- two bands of semi-parametric equalization (boost/cut and sweepable frequency)
- an adjustable 2-pole lowpass filter

Thanks for replying Mark Hammer. I also think any less bands can be enough for an equalizer. I also do not like the idea of ​​having a big pedal.
I've been researching the Boss GE-7, precisely for believing that it might be enough for me, in terms of quantity of bands. But listening to him I could not tell if he really could satisfy my imagination when I think about what I intend to do with the notes on the songs I want to play.
On the other hand, as I said above, this MXR M108S seems to suit my musical desires, and, being possibly more than I need! This is not bad... in any way, the way I think the songs I'm going to play is just like you said ("so they give you lots of them to choose from"), having many possibilities to make the sound. I play in church and the way we do, we can and we want to do, it's very eclectic. I believe, then, that an equalizer like this MXR M108S, after all, would be ideal.

[Max999]

Ashura I actually have two modded MXR108's done by the exact person in your youtube link.

I opened up the pedal to find out what he did: he swapped all the opamps with low noise Burr Browns ( opa2134 I think I remember).
He also added a resistor in the powersupply in an attempt to reduce the extra strain on a resistor because of the added current draw, but I found out the pedal is actually fine without it.

My guess is that MXR did the same thing to create the mxr108s. If you can (de) solder smt it is an easy upgrade.

I always liked graphic eq's and if you want to buy one my advice would be to take a higher voltage one if you want it to boost. When combining sliders you boost more then what the sliders say because adjacent bands combine in proportional-Q equalizers and you can quickly run out of headroom.

[Ashura]

Ashura I actually have two modded MXR108's done by the exact person in your youtube link.

Do you refer to this link?

I opened up the pedal to find out what he did: he swapped all the opamps with low noise Burr Browns ( opa2134 I think I remember).
He also added a resistor in the powersupply in an attempt to reduce the extra strain on a resistor because of the added current draw, but I found out the pedal is actually fine without it.

My guess is that MXR did the same thing to create the mxr108s. If you can (de) solder smt it is an easy upgrade.

This is really very interesting! Could you take some photos of the PCB of this modified version and post here so we can see? That would be of great help.

[Max999]

Yes that is the Youtube link I was talking about.

I made a few pics for you:








The changes in the moddel pedal are:
U1, U2, U3 and U4 are changed to Opa4134
R1 is in parallel with a 42 Ohm resistor