Crawls Backward (When Alarmed)

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Small Stone version 1, v1 Volume Drop Mod


Argh.  In doing a quick web search to find other cited examples of phasing on famous records, I found (and remembered) Billy Joel - "Don't Go Changing."  Yes, kids, that is a phase shifter on the electric piano.  (Sometimes cool effects wind up on lame songs by bad artists.  No offense to Mr. Joel or his fans...I just don't dig it).

So, back to our regular show.  In Part One, we opened up the Small Stone.  Now we're getting down to work.

I'm replacing the two electrolytic capacitors on the board - they're over 35 years old and due to be replaced.  I'm used to recapping old radios and amps but this is a first.  In this picture, the smaller, 10uF cap is done, and I'm taking the big 1000uF cap off the board.  With the electrolytics replaced, the volume mod is the next step.

I used RG Keen's mod instructions as a general guide to eliminate the Small Stone volume drop problem.  Again, since the version 1 schematic is nowhere to be found, I just followed the circuit from the input to suss out the resistor that is between the emitters of the two preamp transistors.  And here it is - it's a 1k ohm resistor.  The later models use a 4.7k, but again, this one is a different animal.

I experimented with different values all the way up to 6.8k.  At 4.7k or above, the volume drop began to get worse - I would guess since the bias is affected.   Also, as I went up in value, I experienced the squealing feedback from the phase return that goes along with the preamp gain increase.  More on this later.

What I wound up with is a 2.2k in this position, as seen on the left.

If you consider the RG mod involves doubling the value of the resistor (4.7k to 10k), this is about right to go from 1K to 2.2K. There may be a tiny bit of volume drop in mine now, but it's a tremendous improvement. Success!

If you have a version 1 Small Stone, you should be able to easily find this resistor.  Note that the printing on the board only shows values - the components are not assigned numbers, so the image is the only reference.

I mentioned the squeal/feedback earlier.  I had this in the 'dark' position of the color switch when I had 4.7k, 6.8k, and 10k resistors in for testing.   Once I heard the feedback, I went after the phase line resistor to increase in order to reduce it.  I found that increasing the one pictured with the green arrow on the lower left corner of the board, stopped the feedback.

However, I ultimately found that with a 2.2k resistor in the 'volume' position, I didn't have the squeal and my volume drop is gone.  Your mileage may vary, which is why I wanted to note which resistor may need to be changed if you have squeal.

At this point, the main objective has been achieved...but I'm going to add a 3DPT for true bypass and an LED.

 
 
 
 

Post a Comment 5 comments:

  • Ivory said...
    November 1, 2011 at 12:00 AM
    Hi Yr Fthfl Blggr (what a crazy name :-))

    thanks a lot for this improvement report about the EH Small Stone Phase Shifter! Generally I'm not a guitar player of western and electric guitars but of acoustic (classical) ones. Nevertheless I've got an old Epiphone western guitar from the 70th (FT-135) that I bought a pickup for several years ago. A few month from now I grabbed this Beauty out of its dirty corner to play it again.
    I connected it to my Ibanez Troubadour amp and loved its forgotten sound.

    When I was young I used to experiment a lot with electric-acoustic effects (let this be 35 years ago…). Two or three I soldered myself according to schematic print-board layouts I found in several articles.

    I remembered that I somewhere had two EH-Effect-Boards lying around. I searched and found them. One was a Small Stone Phase Shifter from 1975/76 (according to the code on the pot [1377559]). I connected it between guitar and amp, switched from dry to wet and instantly recognized the drop in volume when switched to wet.

    Helpfully YOU came in! I changed the 1k ohm resistor to 2.2k as you suggested and it works!

    The other EH effect is an Electric Mistress (same age, I guess). This one suffers of "swirling" LFO-sounds that disturb when playing soft or medium. I think the previous owner made some changes because of resistors and capacitors wired loosely on the back of the board )-:
    Perhaps I can fix it finding an original circuit layout…

    Again, thanks for this help!

    Regards
    Ralf

    (Send from Germany. Please ignore spelling and/or grammatical mistakes. My school-english is old and very rarely used…).
  • João said...
    February 1, 2012 at 2:10 PM
    This is great. Thank you so very much!
    From Portugal
  • Unknown said...
    February 15, 2012 at 10:14 PM
    You are my freakin' hero for posting this! Thanks sooo much!!!
  • Anonymous said...
    April 24, 2013 at 8:28 PM
    version 1 schematic in this site:
    http://geograffff.chat.ru/schemes/modu/
  • Anonymous said...
    February 19, 2014 at 9:41 AM
    ahoy there, thanks for your explanations,
    unfortunately this mod does not work work on my v1,( the older version with the octopods), i will give a try with a trimpot in instead of the 1K resistor.
    cheers david from amsterdam, the netherlands

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