Page 1 of 3

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

PostPosted: 13 Jul 2012, 18:29
by apollomusicservice
this is schematic for new 10 band EQ m-108 and some gutshots

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

PostPosted: 13 Jul 2012, 18:32
by IvIark
Excellent post, thanks for that :thumbsup

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

PostPosted: 14 Jul 2012, 09:13
by Dirk_Hendrik
Thanks indeed!

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

PostPosted: 06 Aug 2012, 16:48
by drewl
Any idea where to get those lighted sliders?

Got one here with a couple broken, and none of the frequency sliders light up, only the gain and volume.

Thanks for the schem, it will be a big help!

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

PostPosted: 25 Sep 2012, 17:08
by night-butterfly
Do somebody know wich type are these SMD zeners?

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

PostPosted: 27 Sep 2012, 13:15
by xeroxdc12
Thanks to the shematic.
One question.
Which diode is D1, D2, D3, on shematic is not presented notation.
Symbol is Zenner diode, but which voltage end etc.
:?:

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

PostPosted: 27 Sep 2012, 17:50
by apollomusicservice
D1=D2=D3=BAS40
General-purpose Schottky diodes in small Surface-Mounted Device (SMD) plastic packages. BAS40

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

PostPosted: 27 Sep 2012, 21:39
by Duckman
The dumb question of the day: There is a technical basis to use all these fixed 470 resistors and vary only the remaining components in each gyrator or just a designer choice? I mean, you could also set one value for all the bias resistors and so the other being those to be adjusted to the needs of each gyrator, so... is there any difference?

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

PostPosted: 27 Sep 2012, 23:13
by Duckman
The dumb question of the day II: That´s not exactly True Bypass, right?... or yes it is?

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

PostPosted: 01 Oct 2012, 07:49
by night-butterfly
Yes that's not a true bypass but it can be modified to be that way easily

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

PostPosted: 01 Oct 2012, 11:34
by dorothegreat
noob question:

1) can I eliminate certain frequencies (e.g. 4kHz to 16kHz); and

2) can I eliminate certain frequencies in between two frequencies? (e.g. 8kHz only)

thanks in advance. :hug:

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

PostPosted: 01 Oct 2012, 12:46
by Sweetalk
Duckman wrote:The dumb question of the day: There is a technical basis to use all these fixed 470 resistors and vary only the remaining components in each gyrator or just a designer choice? I mean, you could also set one value for all the bias resistors and so the other being those to be adjusted to the needs of each gyrator, so... is there any difference?


The 470 resistor sets the Q and gain of the gyrator, so, in order to have a similar Q on each band uses the same resistor. The GGG eq uses the same negative loop resistor and the same pull up to bias resistor and only changes the caps...

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

PostPosted: 01 Oct 2012, 18:50
by Duckman
Sweetalk wrote:
Duckman wrote:The dumb question of the day: There is a technical basis to use all these fixed 470 resistors and vary only the remaining components in each gyrator or just a designer choice? I mean, you could also set one value for all the bias resistors and so the other being those to be adjusted to the needs of each gyrator, so... is there any difference?


The 470 resistor sets the Q and gain of the gyrator, so, in order to have a similar Q on each band uses the same resistor. The GGG eq uses the same negative loop resistor and the same pull up to bias resistor and only changes the caps...


Yeah, I was checking that in every gyrator based EQ that I found in the net and seems like none of them are very picky about Q, so values can be very approximate, but nothing perfect. In fact, most of them uses a 1M pot in series with the bias resistor to vary the frequency, but that means a change in Q from 1 or 2 (up freq) to 4 or 7 (low freq) :!: in some cases (depends on the arrangement of the gyrator)

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

PostPosted: 01 Oct 2012, 18:53
by Duckman
dorothegreat wrote:noob question:

1) can I eliminate certain frequencies (e.g. 4kHz to 16kHz); and

2) can I eliminate certain frequencies in between two frequencies? (e.g. 8kHz only)

thanks in advance. :hug:


1) yes, you can
2) yes, you can, but... check this
EQ INFO.pdf

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

PostPosted: 22 Jan 2013, 23:37
by SFTFN
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.

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

PostPosted: 07 Feb 2013, 13:45
by SFTFN
Well, I contacted MXR/Dunlop about the broken slider and they promptly sent me a replacement slider!! :horsey: My pedal wasn't even under warranty anymore, so they sure seem to care about customer satisfaction.

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

PostPosted: 08 Feb 2013, 16:01
by artaommahe
Is R48 place correct? I have a simulation at LTSpice and when connect gyrators in/out there is -10db pit. If R48 removed and gyrator's out conected to ICD4 13th leg - all is fine.

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

PostPosted: 08 Feb 2013, 20:09
by apollomusicservice
Thanks artaommahe, I checked again and found mistake.

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

PostPosted: 08 Feb 2013, 23:41
by artaommahe
apollomusicservice wrote:Thanks artaommahe, I checked again and found mistake.

thx ) just now did so in the simulator and came to write =)

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

PostPosted: 08 Feb 2013, 23:48
by artaommahe
apollomusicservice, at first schematic we have 12n at IC4C, 15n at IC4D and 2.2n at IC2C. At last - all of them 1n. Last one is correct?)