MXR - M-108 Ten Band EQ new version

Henz · Post by **Henz** » 05 Apr 2022, 16:41

Man, I want to post the links from mouser but it doesn't paste the entire link to show you the exact parts. But I think I found the .68 there as well. When i paste, it just pastes mouser.com.

Henz · Post by **Henz** » 05 Apr 2022, 17:15

In the descriptions they say: 3,300pf 0805 2012 mm cog dielectric . The .68uf says 1206 3216mm. Should I be concerned about the 2012mm on the 3.3 ? Thanks, James

floris · Post by **floris** » 05 Apr 2022, 17:29

The 0805 series = 2012 in metric, so that is correct.

Henz · Post by **Henz** » 09 Apr 2022, 19:06

Hey brother, I really, really hate to keep bothering you but I tend to over think. Should I be concerned of the material? .68uf . Can I just get a multi layer ceramic instead of the poly film? Mouser has many hits with the ceramic. None with the poly film. Thanks brother! Thank you for your time!!

Henz · Post by **Henz** » 20 May 2022, 04:41

Greetings. This thread may be worn out but I really need some answers before I trash my mxr. When activated, mine is very microphonic. Its in front of my amp. And mine makes a very loud pop when turning off and on. Mine hisses but that has always seemed to have been an issue with these. Hope to hear from someone. Btw, this is prior to the work being done to it as mentioned above. Thanks for your time. Blessings! Jim

rmroza · Post by **rmroza** » 18 Nov 2022, 02:10

I have an old (1978-1980) MXR M-108 without the overall and gain sliders. It is powered by 120VAC with a 15-0-15 stepdown transformer and I'm reading like 36V!
It is regulated by full bridge. I'm looking to pull out the AC power cord and power it by a MXR brick or ISO brock with 18VDC and want to confirm how to install.
Am I correct in the negative would go to the negative side of C27 and positive to positive side of C26??
PLEASE CONFIRM. Thanks in advance. The vintage pedal sound killer!

FuzzMonkey · Post by **FuzzMonkey** » 18 Nov 2022, 04:28

I believe 'Ground' is the line between what you have ID'd as +18VDC and GND as it is a dual power supply.

Jarno · Post by **Jarno** » 18 Nov 2022, 11:09

Unless you rip out the power supply and replace it with a DC/DC converter which has two sets of outputs, powering it from a single DC voltage will mean significant changes to the circuit.
But, if there is room inside enclosure, you could fit a 9-36V input dual output DC/DC converter, like one from Traco Power or Meanwell (or CUI, or a number of others). Possible option would be Traco Power TDR 2-2422WI or TDR 2-2423WI

rmroza · Post by **rmroza** » 19 Nov 2022, 01:12

FuzzMonkey wrote: ↑18 Nov 2022, 04:28 I believe 'Ground' is the line between what you have ID'd as +18VDC and GND as it is a dual power supply.

Yeah, that's the way I'm taking it also. The other old MXR pedals just need positive B+, so still use a transformer, but just rectify it with 2 diodes and center tap to ground, then regulator to whatever voltage....15V or 12V.

In regard at the EQ, they use a positive and negative voltage! I'm assuming to allow for more headroom is the overall difference of +18V and -18V = 36V!

Now, what happens if you hook up 18VDC like the way I did?? Someone communicated it will effect the circuit overall. I actually did it and it is working and the sliders are doing something....but does that mean the frequencies changed or since you only have the positive, your headroom has decreased as only 18VDC in total available??!?

Can anyone supply a circuit to supply the +18 and -18V to ground off of an already regulated +18VDC input, like from an ISO brick??
Also, if you just apply voltage like I outlined to one of these old pedals, do you need to remove the transformer or lift the legs, or ok to still be in there?!??

Jarno · Post by **Jarno** » 19 Nov 2022, 14:00

I did, please read

rmroza · Post by **rmroza** » 19 Nov 2022, 16:37

You did generally, but I meant a schematic and/PCB layout!

The vintage MXR pedals all have different voltages also. The Chorus is 12V, The Flange is 15V, and as above, the EQ seems to be +18V and -18VDC!!

Attached are the marked up schematics and where using an already isolated and regulated +18VDC feed from the ISO Brick to the Chorus and Flange to the input and capacitor of the regulator to regulate it further to the voltage it needs.

Have to work out the EQ...wish it was just the same as the other pedals and be easy. Now, need a work around.

rmroza · Post by **rmroza** » 19 Nov 2022, 17:03

I did some searching around, but not seeing any off-the-shelf dual output +18/-18VDC converters, only up to 15VDC, which should work, but since lower B+, compromise headroom, so not getting the full effect if the pedal

For the EQ, I actually pulled out the 120VAC cord and put in this normally DC jack. It's only rated at 50VDC @ .5A, so why I'm weary of continuing to use them in this manner, but do have an inline fuse, so if any problems SHOULD pop first.

Another jack thru Tayda only shows Max. voltage rating of 12V at .5A and a third, that doesn't even show these spec, fyi.

I did find an isolated unit with +/-18VDC outputs! However, looking at the spec sheet, it looks like it only handles 6VDC input!! Soo, even using the 9V tap instead of 18V tap of the ISO Brock....could have a problem!! Output current may be a problem also. :O

https://www.taydaelectronics.com/datash ... 2237-1.pdf
https://www.taydaelectronics.com/nebj21 ... ocket.html
https://www.taydaelectronics.com/dc-pow ... unt-1.html
https://www.electronics-lab.com/project ... wer-input/

FuzzMonkey · Post by **FuzzMonkey** » 20 Nov 2022, 07:39

You're probably looking at something like the circuit shown in Figure 22 in the LT1054 datasheet:

https://www.ti.com/lit/ds/symlink/lt1054.pdf

Jarno · Post by **Jarno** » 20 Nov 2022, 09:46

The difference between 15 en 18v will not be audible for guitar/bass signals, and the datasheet for the converter will have the mandatory components to make sure it is stable (but in practice, you do not need any components on there for it to work fine). Simply splice the rails onto the mxr unit. Given that they are two independent outputs in a lot of the cases, you will need to tie the "-" of output1 to the "+" of output2 to make a 0v, and tie that to ground.

rmroza · Post by **rmroza** » 23 Nov 2022, 04:12

Jarno wrote: ↑20 Nov 2022, 09:46 The difference between 15 en 18v will not be audible for guitar/bass signals, and the datasheet for the converter will have the mandatory components to make sure it is stable (but in practice, you do not need any components on there for it to work fine). Simply splice the rails onto the mxr unit. Given that they are two independent outputs in a lot of the cases, you will need to tie the "-" of output1 to the "+" of output2 to make a 0v, and tie that to ground.

Can you draw a mock up in MS Paint or something??

Jarno · Post by **Jarno** » 23 Nov 2022, 15:03

Why? Everything is here, and if you are not able to deduce the rest from what is on this very page, I think this is not the project for you. It might be better to try out different projects first to learn.
In my view, but that might just be me, starting from scratch (with circuits or kits which are not too difficult, and work your way up), is a lot easier than hacking/repairing an existing project. I myself am a lot better skilled at designing and building, than I am at troubleshooting.

It might be that this is a bit too difficult for you at this moment, better to realise this and build something else, than getting frustrated. Frustration is not a good motivator.

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