Dan Armstrong Blue Clipper

Very Odd V_Ref...

Schematics show the non-inverting input biased by a voltage divider of a 20k and 240k set of resistors.

20k/240k = 1/12, and swapping around for the voltage division, that means the divider output will be 12/13ths of the input voltage, as opposed to the general (near universal) approach of having the output be 1/2 of the input voltage.

This means for a 9V battery, the non-inverting input sits at about 8V, the output sits at about 8V, and the signal will have very little to no room to swing upwards before grossly clipping.

A Dan Armstrong interview in Art Thomson's "Stompbox" seems to confirm that this is no error, as he mentions something about an "offset resistor" that gives the Blue Ringer "more presence in the mix." At the same time, most ads regarding the Blue Ringer note that it is smoother than others, which isn't what I'd expect from a grossly clipped op amp.

The Tech 21 XXL distortion pedal also makes use of this sort of "intentional mis-biasing" in the form of the "Warp" control. The Vref is made variable, with stop resistors to confine the controls range.

Early (Non-Mutron) UK Made, Pre 1975

Early UK made Blue Clippers seem to be extremely rare. It wouldn't surprise me if schematics traced from those units haven't appeared yet. I am curious if there are any differences between the UK and USA versions.

Dan's interview in Art Thompson's "Stompbox" (1997) contains some years by Dan's recollection. He says he began making the effects in London in 1973 with George Merriman as the electronics designer. He recalls that the Green Ringer was first, inspired by the Scrambler, which had been given to him circa 1971 as a parting gift when he left Ampeg. Dan says the Blue Clipper was next, and alleges a MXR employee ripped off the idea after seeing one in London. He lists the next effects as the Red Ranger, Purple Peaker, and Yellow Humper. Next date given is 1974 and that marks the Orange Squeezer. He says they were working on the Squeezer for a "couple of years" which is curious considering his story started in '73, just a single year (possibly less than a year) earlier. Dan says he met with Mutron in Frankfurt (Musikmesse?) in 1974 and Merriman worked on the Mutron Octave Divider.

Mike Beigel's personal collection shows an original UK made Blue Clipper. http://www.mu-tron.org/list.html

Note the black nut, likely Cliff brand jack. Mutron branded units began in 1976. UK made ones are said to be made "before 1975" on Beigel's website.

Grafton Electronics began releasing reissues of the early boxes in December 2006. The website says they are built to "authentic 1975 specs." I am curious what op amp they use, and whether or not they adhere to the odd reference voltage seen on unofficial schematics.

Mutron Blue Clipper 1976-78

http://c-nelson.com/1970s-dan-armstrong-blue-clipper/

Great photographs of a vintage Mutron Blue Clipper. The op amp is a TI RC4558, date code is either the "M727" (27th week of '77) or "0821" (I don't think this is the date). All the schematics I see for Blue Clipper online are 4558 based. The RC4558, according to the scant op amp histories out there, was released in 1974, which makes me think the UK version may use an older number, like a 741.

Was it a first?

This is a contender for "first op amp drive + passive shunt diode clipping" alongside the MXR Distortion + and the Gretsch Controfuzz/Expandafuzz. All three have good claims for 1973.

Allegations that MXR copied the Dan Armstrong Blue Clipper

Dan Armstrong makes the strong allegation that MXR copied a Blue Clipper in Art Thompson's "Stompbox." I am curious how that allegation stacks up against the release dates of these devices. In the Thompson interview, Dan says an MXR rep came to London to sell Phase 90s (most likely MXR employee Ron Wilkerson) and asked Dan about the Blue Clipper. Dan then goes on to say that MXR copied their design, expect for:

"The only change they made was adding a tone control, but they left out one offset resistor that gave the Blue Clipper more presence in the mix."

The added tone control might be a reference to the "distortion" control on the MXR pedal, or Dan could be thinking of another pedal. The "offset resistor" comment is interesting as the Blue Clipper indeed seems to have a very odd reference voltage for the non-inverting input according to unofficial schematics. This intentional mis-biasing is also seen in the "WARP" control of the Tech 21 XXL distortion pedal.

The allegation is repeated again on this website: http://www.danarmstrong.org/effects.html

However, here the story changed to the MXR rep trying the Blue Clipper at a NAMM show, which would have taken place in the USA. The inconsistency of the story isn't helping me believe it.

Richard Neatrour (First employee of Barr and Sherwood) recalls in AMGTVE, "The first two things we started working on were the Phase 90 and the D+." This is a very vague comment, but it could be interpreted as the Phase 90 and the Distortion + being developed simultaneously, which would undermine Armstrong's allegations if true.