MXR - M-108 Ten Band EQ new version  [schematic]

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Re: MXR Ten Band EQ M-108 new version schematic

Postby apollomusicservice » 09 Feb 2013, 11:56

All of them 1n is correct.
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Re: MXR Ten Band EQ M-108 new version

Postby gtr2 » 18 Feb 2013, 16:41

I understand how to change the freq of the gyrators but how do you calculate the last 16kHz band? This is common among many of the EQ's out there but I can't wrap my head around how to calculate a different freq here.
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Re: MXR Ten Band EQ M-108 new version

Postby artaommahe » 18 Feb 2013, 19:37

gtr2, it's simple RC-filter )
f = 1/(2*pi*R*C)
f - cutoff frequency

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Re: MXR Ten Band EQ M-108 new version

Postby agung » 19 Feb 2013, 10:57

IVIark, please do a vero layout for this EQ! :hug: :lol:
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Re: MXR Ten Band EQ M-108 new version

Postby gtr2 » 19 Feb 2013, 16:30

artaommahe wrote:gtr2, it's simple RC-filter )
f = 1/(2*pi*R*C)
f - cutoff frequency


Thanks, I just used an RC calc. I guess I didn't visualize it as such.
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Re: MXR Ten Band EQ M-108 new version schematic

Postby drewl » 04 Mar 2013, 19:54

SFTFN wrote:I just troubleshot one m-108 eq that had a problem with half of the EQ LEDS being off and rest of the LEDs on. It turned out that an LED socket had gone bad on one of the sliders.

Fortunately only one socket was bad so I rearranged the sliders so that all EQ frequencies have their LEDs lighted up, but the gain and volume slider LEDs are off... At least it looks symmetrical now.

Anyway, does anyone know are these sliders possible to get anywhere? They're 20k miniature type with center detent.


I found the sliders at Mouser.
They've been stocking alot of oddball pots used in newer amps and FX.
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Re: MXR Ten Band EQ M-108 new version schematic

Postby SFTFN » 12 Mar 2013, 19:11

drewl wrote:I found the sliders at Mouser.
They've been stocking alot of oddball pots used in newer amps and FX.


Good to know. Thanks for mentioning that. :)
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Re: MXR Ten Band EQ M-108 new version

Postby JimmyDS » 02 Jan 2014, 22:54

hey guys...sorry to dig this up -new guy here. Does anyone have a schematic layout for this, by any chance? I tried it a billion times but I'm getting REALLY confused with grounding and voltage connections on IC's, so...any help would be extremely welcome!
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Re: MXR Ten Band EQ M-108 new version

Postby SFTFN » 02 Jan 2014, 23:53

JimmyDS wrote:grounding and voltage connections on IC's

Check the datasheets for the ic's mentioned on the schematic. Should help. :)
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Re: MXR Ten Band EQ M-108 new version

Postby JimmyDS » 07 Jan 2014, 02:01

thanks for that! so, if I got this right...

1.every pin 4 from those ICs must be connected to the VCC arrow from IC4A
2.every arrow facing downwards must be connected to the bias (through a common plane or something like that)

more questions...:
Does every pin 11 need to be connected to the ground plane?
Do the Bias connections also need vias to the ground?
What is the arrow coming from R43..? Another connection to Bias?

I'm really sorry guys, this is all new to me..! Thanks in advance.
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Re: MXR Ten Band EQ M-108 new version

Postby apollomusicservice » 07 Jan 2014, 09:06

Yes JimmyDS you right, all pins "4" are connected together with arrow "up" on R43 and point R1- R4 to VCC.
Point from pin 1 of IC4A ,named BIAS, connect with all the same arrow symbols (it does not matter whether
they are/not oriented in the same direction) and do not connect this point to ground . All pins "11" are connected
to ground. Also if you use base for IC's you can use TL074 which can be easier to find but with reduced performance
even after replaced with original. Good luck in building this unit. 8)
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Re: MXR Ten Band EQ M-108 new version

Postby JimmyDS » 07 Jan 2014, 13:35

Thanks a billion! That covers pretty much everything!
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Re: MXR Ten Band EQ M-108 new version schematic

Postby DuctTapeRiot » 23 Jan 2014, 23:32

SFTFN wrote:I just troubleshot one m-108 eq that had a problem with half of the EQ LEDS being off and rest of the LEDs on. It turned out that an LED socket had gone bad on one of the sliders.

Fortunately only one socket was bad so I rearranged the sliders so that all EQ frequencies have their LEDs lighted up, but the gain and volume slider LEDs are off... At least it looks symmetrical now.

Anyway, does anyone know are these sliders possible to get anywhere? They're 20k miniature type with center detent.


I am having a very similar problem to this. Can I ask how you tested to know which slider's socket was bad??
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Re: MXR Ten Band EQ M-108 new version

Postby JimmyDS » 07 Feb 2014, 21:56

ok guys...this is not fun anymore! reacreating the schematic and finding the parts was super, even testing PCB making techniques and services but this one is way over my head..! if anyone could help with the PCB layout I would owe him my life!! pls help :?
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Re: MXR Ten Band EQ M-108 new version

Postby matt239 » 01 Mar 2014, 18:45

apollomusicservice wrote: .... Also if you use base for IC's you can use TL074 which can be easier to find but with reduced performance
even after replaced with original...


What does this mean?
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Re: MXR Ten Band EQ M-108 new version schematic

Postby joeyshakespeare » 08 Mar 2014, 02:19

drewl wrote:
I found the sliders at Mouser.
They've been stocking alot of oddball pots used in newer amps and FX.


Do you know which slider you bought on Mouser?
My 62.5 Hz is broken.
There are a bunch of sliders made by Bourns that seem to look the same.
http://www.mouser.com/Passive-Component ... ?P=1yzekj2

Thanks!
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Re: MXR - M-109 6 Band EQ new version problem

Postby alexradium » 23 Jul 2017, 17:14

hello everybody,
i have an MXR 6 band,the interesting problem is i have 8V on the last output opamp,and after some measurements i came to the conclusion that its not faulty,but that voltage comes from the 9V rail that powers the leds and goes to those pins and in consequence to all the slider pots by means of an 8,5kohms resistance,which obviously is not there, i could imagine that some conductivity is in play somewhere between the 9V rail and the Vbias rails.
I tried to clean the surface with isoprop alcohol and all the pots with proper cleaner,but nothing new happened.
Has anyone experienced anything similar with smd boards?
i'd like to know before i start removing all the sliders and jacks.
thanks in advance.
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M108S new new version

Postby x-tn » 02 Dec 2017, 16:17

There is a 'newer' version called M108S.
It says "...it's been upgraded with noise-reduction circuitry, true bypass switching, a lightweight aluminum housing, brighter LEDs, and a second output."
https://www.jimdunlop.com/product/m108s ... 09564-9.do
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Re: MXR - M-108 Ten Band EQ new version

Postby floris » 06 Dec 2017, 22:07

I think the sliders in the black M108 Ten Band EQ are:
RA2545F-20 RED LED
See:
http://www.taiwanalpha.com.tw/english2014/p_e_086.htm

Looking at Mouser the Manufacturer Part Nr should be:
RA2545F-20R-15LC-B20k-C
Slide Potentiometers 25mm Travel LINEAR 20K RED LED PC MOUNT
(although Mouser only has RA2045F, RA3045F and RA4545F)

Series: RA2545F
Termination Style: Through Hole
Travel: 25 mm
Resistance: 20 kOhms
Power Rating: 100 mW
Voltage Rating: 200 V
Tolerance: 20 %
Taper: Linear
Length: 40 mm
Width: 9 mm
Height: 7 mm

Anyone knows a place where one can buy the Alpha RA2545F RED LED 20k?
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Re: MXR - M-108 Ten Band EQ new version

Postby floris » 08 Dec 2017, 11:31

Reply from Dunlop regarding, replacing a slider pot in in the black M108:

The part number for the replacement slider pot is #ECB046.
For pricing and ordering you can contact (for the Netherlands):
AB Music
Stephane Verbeurgt
stef@algambenelux.be
+32 (0) 15 33 80 00
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