Crawls Backward (When Alarmed)

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Version 1, V1 Small Stone Mods and Restoration, Pt. 1

In this episode of our blog, we (that means me, Yr Fthfl Blggr) take on the legendary Electro-Harmonix Small Stone Phase Shifter!

For those of you who know what a phase shifter (aka phaser, phasor) is, well, you know what it is.  For those of you who don't, a brief description.  It's an electronic effects device, mostly used with electric geetars, that produces a swooshy, whirling sound by combining out-of-phase signal with the straight signal.  Some famous examples in rock music:  the beginning of "The Cradle Will Rock" and "Unchained" by Van Halen, or the whole-band effect on "Listen to the Music" by the Doobie Brothers.


There are a number of 'classic' phasers, the Small Stone, along with the MXR Phase 90 probably being most well-known.  Electro-Harmonix (EH, or E-H) has made 4 variants of the Small Stone since the mid 70s.  Here's a great page with info on all of them and their differences

I'm fortunate to have one of the first models, now known as a "Version 1" or "V1."  I've had it for a while - I'm at least the second owner.  I've been accumulating pedals lately, and I pulled my Small Stone out of storage and played with it some.  One of the issues it has - common to all Small Stones - is there is a volume drop when it's engaged.  So I set about trying to mod it.

There is plenty of info on the web about modding the later versions, but virtually nothing on the first version.  I suspect that's because it's less common today, and because nobody who has figured out how to mod it has documented it.  The common mods for the later versions (the Model J variant) were documented by RG Keen and here's one place you can find them, along with the later schematic.

Problem for me (and others...) was that the first version uses 6 ICs instead of 5, and the circuit has quite a few other differences.  But armed with the schematic and a basic understanding of what I needed to do, I plunged in.  Since the idea was to increase the value of the resistor between the emitters of the two input transistors, I suspected I could suss it out.  While I'm at it, I'm going to put in a 3DPT switch so I can have true bypass and an LED. 

Here's the back side of the board.

I've highlighted a couple of things with arrows (you can click on most of these pictures to see larger versions - not something that's true on most of my blog photos but for these I made larger versions).

The green arrow shows the DC adapter input.  It was disconnected at some point and a switch stuck on the front to turn the battery on and off.  I'm going to change out the switch and wire it through the input jack the way it was originally.  I don't think I'm going to rewire the adapter, though - I'll just run it on a battery.

The yellow arrow points to the input from the input jack to the color switch.  This is different than the later versions; we'll need to run this input through the footswitch.

And finally, the red arrow shows the output from the board - we'll need to run this to the switch also.

Now I'm disassembling the Small Stone.  The switch just has 2 screws that hold it on. 

I took off the nuts holding the input and output jacks on, then popped off the rate knob.  A 1/2 inch wrench fits the nut for the potentiometer. The pot is what holds the whole board to the cabinet.

There's a knurled nut holding the footswitch on - if you carefully use needlenose pliers you can get if off without hacking it up.  In my case, I'm not going to reuse it, but I will save it for some future project that I've yet to dream up!

Here's the top of the board after it's been removed.

I'm going to change (recap) the big electrolytic and the smaller cap (yellow arrow).  The big one is 1000 uF- the ones I've seen on the interweb all have 500 uF caps.  I'm going to keep this same value.

The small cap is 10 uF.  I don't keep any low-voltage caps like these around, since I don't do a lot of transistor stuff.  So I go off to my local Rip Shack and pay exorbitant prices (try $2.49 for the big cap) cause I need them NOW!

The date code on the big cap is 1974.  So we get an idea of when this thing was made...

...and that's confirmed by the date code on the pot.

The code is 1377547.  So we know it's a CTS pot, made the 47th week of 1975.  Here's how I know this stuff.  Isn't the interweb great?

So my guess is this Small Stone was built in late 1975 or early 1976.

I'll be back with more, stay tuned.


Post a Comment 1 comments:

  • Didier Pelligra said...
    April 27, 2015 at 5:16 PM

    The schematics you refer to for the 3pdt wiring doesnt exist anymore. Any way you could explain to me how you wire the jack input and the effect input with the color switch in the middle?

    Thanks a lot!

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