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

[modman]

this is schematic for new 10 band EQ m-108 and some gutshots

[IvIark]

Excellent post, thanks for that

[Dirk_Hendrik]

Thanks indeed!

[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!

[night-butterfly]

Do somebody know wich type are these SMD zeners?

[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.

[apollomusicservice]

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

[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?

[Duckman]

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

[night-butterfly]

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

[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.

[Sweetalk]

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...

[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?

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)

[GodSaveMetal]

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.

1) yes, you can
2) yes, you can, but... check this

EQ INFO.pdf

[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.

[SFTFN]

Well, I contacted MXR/Dunlop about the broken slider and they promptly sent me a replacement slider!! My pedal wasn't even under warranty anymore, so they sure seem to care about customer satisfaction.

[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.

[apollomusicservice]

Thanks artaommahe, I checked again and found mistake.

[artaommahe]

Thanks artaommahe, I checked again and found mistake.

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

[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?)