Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Effects => Topic started by: Baguette on October 17, 2009, 11:36:27 am

Title: Please help me troubleshoot my Electro Harmonix Small Stone phaser
Post by: Baguette on October 17, 2009, 11:36:27 am
Hello!

I've recently aquired a russian EHX Small Stone. I got it for cheap since it was needing some repairs...
here are the symptoms:

1: the volume is REALLY low, both when engaged AND disengaged
2: there's a motorboating (ticking sound) at every oscillation.

My intuition tells me it could be the filter caps... moreover the power supply required has center positive contrary to the common 9V adapter which is center negative... someone could have screwed up and I'm wondering if plugging the wrong adapter could have damaged the electrolytic caps.

This is my first effect repair... any tip would be much appreciated!!!

Thanks!!!
Title: Re: Please help me troubleshoot my Electro Harmonix Small Stone phaser
Post by: tubesornothing on October 17, 2009, 12:50:47 pm
Is this a 9VDC input or 9VAC input?

If DC, to confirm your suspicions, look at the polarity of the filter caps, and trace it back to the power input - see if it was revered.

Motorboating sure says to me that the filter caps are no good.  Got a scope?
Title: Re: Please help me troubleshoot my Electro Harmonix Small Stone phaser
Post by: Baguette on October 18, 2009, 09:01:15 am
Hey TON,
thanks ftheor the answer!

The AC or DC issue is very confusing on this pedal since both are marked on the pedal!!! ("AC" is marked on the top, and "9VDC" is marked on the side). The 9V adapter sold by Electro Harmonix is a 9VDC unit so I guess the "AC" marking is the wrong one and the pedal requires a 9VDC unit.

Would that confirm the filter caps being faulty?
What would happen if the pedal was run on AC?
Title: Re: Please help me troubleshoot my Electro Harmonix Small Stone phaser
Post by: sluckey on October 18, 2009, 02:24:54 pm
Some pedals have a bridge rectifier connected to the power jack. In such a case, it doesn't matter if it's AC or DC, or even if the DC leads are reversed. It's really idiot proof. Since yours is marked AC and DC, maybe it's such a device. Here's a schematic that uses such a circuit...
Title: Re: Please help me troubleshoot my Electro Harmonix Small Stone phaser
Post by: Baguette on October 18, 2009, 05:21:26 pm
Thx for the hand Sluckey!
I'm pretty sure the russian Small Stone phaser doesn't have such a circuit since there's no bridge recto to be found.

So, what would happen if the power supply had the wrong polarity? was AC instead of DC?
Title: Re: Please help me troubleshoot my Electro Harmonix Small Stone phaser
Post by: sluckey on October 21, 2009, 08:29:27 pm
Quote
So, what would happen if the power supply had the wrong polarity? was AC instead of DC? 
Impossible to say without seeing a schematic. But if there is no reverse polarity protection (could even be a single diode) it's very likely the filter caps and all ICs have been stressed and could all be dead.
Title: Re: Please help me troubleshoot my Electro Harmonix Small Stone phaser
Post by: Baguette on October 23, 2009, 06:58:48 am
Quote from: sluckey on October 21, 2009, 08:29:27 pm
Quote
So, what would happen if the power supply had the wrong polarity? was AC instead of DC? 
Impossible to say without seeing a schematic. But if there is no reverse polarity protection (could even be a single diode) it's very likely the filter caps and all ICs have been stressed and could all be dead.

geez, there's 5 ICs in there, and the replacements are at least 8 bucks each... that would make a 40usd repair, plus a major PITA to replace all of 'em.
However, the phasing sound is there and strong, so I guess the ICs are OK. Hopefully I'll go over the filter caps soon!
Thanks for all the replies!