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

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apollomusicservice
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Post by apollomusicservice »

this is schematic for new 10 band EQ m-108 and some gutshots
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MXR Ten Band Graphic EQ M-108.png
photo 3.jpg
photo 2.jpg
photo 1.jpg

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IvIark
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Post by IvIark »

Excellent post, thanks for that :thumbsup
"If anyone is a 'genius' for putting jacks in such a pedal in the only spot where they could physically fit, then I assume I too am a genius for correctly inserting my legs into my pants this morning." - candletears7 - TGP

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Dirk_Hendrik
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Post by Dirk_Hendrik »

Thanks indeed!
Sorry. Plain out of planes.

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drewl
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Post 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!

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night-butterfly
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Post by night-butterfly »

Do somebody know wich type are these SMD zeners?

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xeroxdc12
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Post 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.
:?:

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apollomusicservice
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Post by apollomusicservice »

D1=D2=D3=BAS40
General-purpose Schottky diodes in small Surface-Mounted Device (SMD) plastic packages. BAS40

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Duckman
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Post 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?

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Post by Duckman »

The dumb question of the day II: That´s not exactly True Bypass, right?... or yes it is?

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Post by night-butterfly »

Yes that's not a true bypass but it can be modified to be that way easily

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dorothegreat
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Post 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:

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Sweetalk
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Post 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...

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Duckman
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Post 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)

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Duckman
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Post 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
(247.18 KiB) Downloaded 767 times

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SFTFN
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Post 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.

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SFTFN
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Post 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.
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Post 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.

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apollomusicservice
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Post by apollomusicservice »

Thanks artaommahe, I checked again and found mistake.
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MXR Ten Band Graphic EQ M-108 ver1.1.png

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Post by artaommahe »

apollomusicservice wrote:Thanks artaommahe, I checked again and found mistake.
thx ) just now did so in the simulator and came to write =)

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Post 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?)

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