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Electro Harmonix - Small Stone - Three decades of phasing
General information:
The origin of the Small Stone dates back to 1974, when Electro Harmonix president Mike Matthews hired former EMS engineer David Cockerell, whos first design for EH was the Small Stone phaser. The design was based on Davids previous work on the EMS Synthi Hi-Fli from 1971 - it is a rather unique design in that it uses Operational Transconductance Amplifiers (OTA) instead of operational amplifiers with variable resistors. It is a 4 stage phase shifter with one additional stage for feedback, which can be activated using the "Color" switch. The strongest rival of the Small Stone, the MXR Phase 90, uses FETs (Field Effect Transistor), which suffer from the fact that the FETs have to be matched in production. This made the Phase 90 more expensive and gave the Small Stone an edge in the market share.Soundwise the OTA based phaser will give it's unique flavour with rather strong third harmonic distortion, whereas the FET based phaser has a pronounced second harmonic distortion - the matter of which one is better is simply a matter of taste.
Throughout its history the Small Stone has had numerous revisions and modifications - all versions are OTA based, but the changes will affect the sound of the unit. Here's a short overview and comparison of the different versions of the EH Small Stone. The controls of the Small Stone have remained unchanged troughout its history - a SPEED-control, a switch labelled COLOR, which adds feedback to the circuit resulting in a deeper and stronger sounding phasing effect with many more notches added to the spectrum, an finally - the footswitch to toggle the effect on and off.
The Electro-Harmonix Bad Stone is not actually part of this family, although it has many similarities, but we'll include it in this review as well.
DIFFERENT VERSIONS OF THE SMALL STONES
 Electro Harmonix - Small Stone USA Version 1 The first version of the Small Stone was made somewhere between 1974-1978 and it used OTAs labelled EH1048. (These were house labeled versions of the CA3094AE OTA). Already from its first appearance the Small Stone nailed that unique swirl and depth. The oldest versions of this unit (pot dates to 1975) have had OTAS in octopod casings. |
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Electro Harmonix - Small Stone USA Version 2The second version of the Small Stone was released shortly after version 1. The circuit underwent some small modifications but still used the same EH1048 OTAs. The graphics were changed to match with many other EH units of that time. |
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 Electro Harmonix - Small Stone USA Version 3 At the beginning of the 80's Electro Harmonix released the third version of the Small Stone. The circuit was again slightly modified to use dual OTAs - two LM13600AN and one LM324N were used. The sound of this unit seems somewhat stronger and more balanced than the previous versions. |
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Electro Harmonix - Small Stone USA Version 4In 1984 Electro Harmonix was pushed into severe financial trouble and was forced out of business. It took several years before the production was started again, first in Russia (see below), later again in the USA. The fourth USA version of the Small Stone was published in the mid 90's (first USA reissue) and was the first USA version to have a status led, a very useful addition to make life easier for the gigging musician. A 3PDT (Tripple Pole Double Throw) footswitch is used to implement true-bypass switching. Again the circuitry and the board layout have been modified heavily from the previous versions, but it is still based on 5 CA3094AE single chip OTAs. |
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 Electro Harmonix - Nano Small Stone (Version 5) The latest version of the Small Stone was released as part of the new Nano-series, which are marketed to offer the same sound as the vintage units in a more pedal-board friendly size. The functionality is unchanged, but the interior of the unit shows a huge difference to the previous versions. The circuit board contains almost only tiny SMD:s (surface mountable devices) instead of the traditional components with pins goings through the circuit board. The circuit topology has been altered and the chips are again changed. Also the Nano Small Stone has true-bypass switching. |
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Electro Harmonix / Sovtek - Small Stone Version 1 (Soviet Union)When Electro Harmonix went bankrupt in the USA in 1984, there was a time of silence in the EH effects pedals production, until in around 1990 Mike Matthews ramped up a new production line, this time in Russia, where the ongoing conversion from military economy to consumer economy well facilitated his business. The units produced in Russia were slightly larger than their USA counterparts and were labelled as EH/Sovtek (Sovtek was a brand name Mike Matthews came up with for the tube production line he started in Russia, which today is one of the largest tube suppliers in the world). The first soviet union version of the Small Stone was an army green unit, and the first Small Stone to utilize a led. The circuit is not exactly identical to the USA version, although very similar, employing 5 CA3094E OTA chips. |
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Electro Harmonix / Sovtek - Small Stone Version 2 (Soviet Union)This soviet union version of the Small Stone is basically very similar to the army green version, although it is not identical. The circuit boards are very similar and also this unit uses 5 CA3094E chips, but many of the components are different and from different manufacturers. It might be that these units were built from surplus parts that were readily available at the time, which results in a variation from sound from unit to unit. Nevertheless they do not fail to deliver the depth and swirl that characterizes the Small Stone. |
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Electro Harmonix / Sovtek - Small Stone Version 3(Soviet Union)The third, newest soviet union version of the Small Stone was again a small modification from the previous one. The circuit board layout has been modified and the components arranged a little bit more neatly, propably to ease the assembly of the units. The design still employs the 5 CA3094E OTA chips, so no big change there. |
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Electro Harmonix - Bad Stone (USA)The Bad Stone was released 1975 and produced until 1981. It was designed by Bob Bednarz and it was the first phase shifter to employ feedback in the circuitry. It compasses 6 stages of phases shifting with variable feedback. One speciality of this phaser is the manual mode, which lets you dial in the phase shift manually instead of using the LFO (low frequency oscillator). This enables a whole new dimension of sounds achievable, although no sweeping will occur in the manual mode. | |
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SOUND SAMPLES
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CONCLUSIONS
The Small Stone has earned its status as one of the most influential phasers in the history of music, and throughout its long existence it certainly has made itself known to most musicians. The unique flavour in the sound of the OTA based phase shifter is distinguishable in all the different versions of the Small Stone, although they all have slight differences.© 2009 Pedalarea. All rights reserved