Finally a True Steggo BMP

Fingolfen

Well-known member
Build Rating
4.00 star(s)
Unless you've been under a rock, you know I really like the BMP circuit. That being said, I'd never come up with a truly "Steggo" enclosure / pedal name for it, so I decided it was high time to rectify that.

LC BMP - Big Mutt Phi - 73 Gil - SN01 - 01.jpg

For my first build with the new name / enclosure style I'm using a board I got through Ukraine support laid out by LoudCancer - a Polish builder. This particular build is very similar to some of my early builds in that it is a '73 Gilmour (using the AionFX Halo excel sheet as a guide). This particular one uses vintage Allen Bradley carbon resistors. The capacitors are a mix of panasonic film and some ceramics. The transistors are vintage 2N5133. The diodes are also vintage 1N914s. Once getting the board together, I attached the pots and ran a quick test - which is where I found one problem with the board - the potentiometers are set up backwards.

LC BMP - Big Mutt Phi - 73 Gil - SN01 - 02.jpg

I double checked to make sure I hadn't soldered them to the board incorrectly, but no, they were right. I then checked the circuit diagram, and all three potentiometers are reversed on the diagram. So while the board is a correct translation of the diagram, the problem was at the circuit diagram. I simply reversed all three and now the pedal works perfectly.

The wiring follows my normal process using a daughter board for the 3PDT footswitch. I'm also running a star ground to the input. I did have to flip the Switchcraft jacks to ensure they fit above the board (as the board is a little higher than I'd like because of the reversed pots). I also decided to go ahead and add the battery snap since all of my BMP enclosures are set up to accept one, and this is an old school pedal.

LC BMP - Big Mutt Phi - 73 Gil - SN01 - 03.jpg

So I promised a dinosaur, and here he is! The Muttaburrasaurus - that's right, it's the Big Mutt Phi pedal!

Given the Greek letter reference, I went hunting for a suitable background for Mutt to inhabit. I found an old painting in the public domain - Religious Ceremony in Ancient Greece by Francis Oliver Finch from 1835. At this point I'm using actual EHX knobs, but I may change them out at some point.

As to the sound - it is a little bit of a mixed bag. Because of the Allen Bradley carbon resistors, the noise floor is fairly high, but the sound is unmistakably BMP. On its own with a noise gate, the noise floor is easily dealt with, but if you add boost pedals or other effects, the noise is a bit higher than I'd like. I'm planning on making up a 100% modern pedal with the same values (though I may still use vintage transistors - or at least modern transistors with similar gain as the vintage ones) to see if I can bring the noise floor down.

Tiny bit more at the blog: https://steggostudios.blogspot.com/2022/11/finally-true-steggo-bmp-clone.html
 
That looks awesome, Steggo! I'm just a sucker because I love the look of the carbon comp resistors even though I know they're noisier and worse tolerances than modern ones. I need to order some and build a vintage component muff, probably triangle style one. It's been a while since I built one.
 
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That looks awesome, Steggo! I'm just a sucker because I love the look of the carbon comp resistors even though I know they're noisier and worse tolerances than modern transistors. I need to order some and build a vintage component muff, probably triangle style one. It's been a while since I built one.
Honestly the Triangle is one of my favorites. I've only built one with mostly modern components on a Tayda board, but it sounds amazingly good.
 
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