Steve L.|| October 22, 2014 - 08:09 am|
I really appreciate you sharing your story here. The M-140 will be an excellent way to transcribe your LP collection, I'm sure. The MXR preamps did indeed use epoxy-glass PC boards, which is unusual in consumer products. I also noticed that caps used in critical places (e.g. RIAA compensation) looked like high-class parts.
I would love to add scans of the schematic and layout with the article. If you are able to share those, you can email me at: [see homepage ABOUT].
Any other information about the M-140 and 150 would be most appreciated. I heartily agree that they are very special and unique.
Best Regards, Steve
Nate Mudge|| July 12, 2011 - 05:26 pm|
I just ran across this site, and would like to add my 2 cents worth. From 1975 to 1980, I was the MXR manufactures rep for the state of Florida. At the end of my days as a rep, I had a rep sample of the M-140 System Preamp, which made its way into my home stereo system. It has been with me to this day. I am using it in my audio duplicating setup, where I am digitizing my entire LP collection. The only problem I have had with it was dirty contacts on the switches, which I cleaned with Caig Labs contact cleaner. It still performs perfectly. As I recall, when this unit was first introduced, the factory bragged about using military grade PC boards and components. I also have a poorly xeroxed copy of the original schematic and pc board layout. This is a very special unit, unlike anything else.
Steve L.|| May 17, 2011 - 11:08 am|
It's so nice to hear from another MXR Preamp owner! Sounds like you have found a great application for its unique features. I take it that the M-140 was titled as "System Preamp" instead of "System Preamp II" ?
The mods I made weren't much. The basic performance of the preamp is excellent as-is. I removed one of the two phono preamps, making that input line-level for a CD player. I also made the power outlet switched, so that I can control the whole stereo system with it.
Very glad that the schematic and manual are helpful. Thank you for the kind message.
Matt|| May 17, 2011 - 10:26 am|
|Just wanted to say thanks for the schematic and manual! now I understand what the low pass filter button does...|
I must have one of the rare M-140s, but more or less looks exactly the same (minus the stereo reverse function I think). I bought it on HarmonyCentral 5+ years ago and have been using it as my guitar rig preamp since. I used to run the loops into my eq and fx, which let me balance wet/dry easily... Works great, sounds great, looks vintage cool of course too!
What mods did you do to yours? anything easy you would recommend?
Steve L.|| March 25, 2011 - 08:32 pm|
|Fascinating, Mark. Thanks for checking-in. I will contact you by email. |
Mark C|| March 25, 2011 - 08:11 pm|
|They where from MXR...never completed. I was trying to find out what they where and came across your site|
Cameron_amps "at" yahoo com