An interesting pedal just gifted to me

[pdavis68]

My wife's uncle used to run a Radio Shack in a small town here in Arkansas. He's a ham radio guy and trades in all kinds of stuff, including electronics gear. He's got a handful of amps, boxes and boxes and boxes of tubes and that kind of stuff.

Anyway, we just had a family get together and he brought me this interesting pedal. I'm just assuming it's for guitar, but I'm not sure of that. It's a phaser and compressor in one box. The Phase controls are Blend and Rate. The compressor has a Sustain pot. And then there's a tone control. I'm assuming it goes to the compressor module, but I'm not positive. I haven't traced it out. Everything is tightly bundled and I'll need to cut the cable ties. Anyone recognize these modules? GMS-AH500-900032 and GMS-AH500-900090





I can't find anything on them.

It's a cool little rig. Too bad it sounds like crap. I'll probably end up just finding suitable circuits to build to replace the modules (like a 1 knob compressor) and a phaser with just a rate control (or one with that and a blend, otherwise I'll just wire the blend).

But I'm curious about the modules. Maybe it's not even meant for guitar.

[armdnrdy]

This thing has got to be pretty rare. I wouldn't touch a thing!

This combination of circuits was originally built inside of a guitar for Chet Atkins.

All of the documentation is here:
http://www.tdl-tech.com/chet.htm

More info here:
http://www.misterguitar.us/forum/viewtopic.php?f=6&t=4005

It looks like...after the prototype was developed for Chet Atkins...this circuit was produced and put inside of a Gretsch "Super-Axe" guitar.
Since there is no identification on the newer looking wood enclosure...I would bet that this circuit came out of a Gretsch guitar...and someone built the enclosure...and mounted the effect assembly in it.

[pdavis68]

Wow, that's really interesting! Thanks for digging that up! I live slightly less than 10 miles from Prairie Grove! A guy I know down the road builds pedals and used to work for the old Baldwin plant here. I find that a really odd coincidence! But cool.

Based on the sound of it, I'm guessing some caps have failed.

Well, it looks like there are schematics and they used pin head connectors, so I merely need to rebuild the circuits, use pin head connectors and I might be in business with something sounding better. I'll hang onto the modules and no damage done. It'll retain all its original value and have its function restored.

[Rob Strand]

Very cool.

At first I thought it's the most bizarre construction I've seen, inside and outside.   Then I'm thinking it's out of a guitar!

@armdnrdy.  Thanks a lot of for the links.   It is unbelievable what obscure and cool stuff is on the web.

[thermionix]

As someone who spent years working at a Gretsch specialty shop, I can tell you that there are people out there that would LOVE to buy those guts from you!  If it "sounds like crap" as you say (and I don't doubt it for a second) I would highly recommend selling them as-is on Ebay.  You just can't find that stuff.  I really don't know the value, I would just run a 30-day auction, and I would not be surprised in the least if it ran into the hundreds of dollars.  Seriously.

[Rob Strand]

As someone who spent years working at a Gretsch specialty shop

So you think it would be better to fix it, to leave in the original parts, or to try to fix it with "original" parts (which isn't so great for electrolytics)?

[thermionix]

I guess the "fix it" vs. "leave it as-is" question would come down to how well (or poorly) it is fuctioning, and how original it currently is.  I wouldn't go so far as to try and track down original caps, it's not '59 Les Paul guts.  If it's all dead stock and basically doing what it's supposed to (even though not sounding very good) I would leave it stock, and let the future owner make repair decisions.  If it's essentially dead and can be fixed with a few new components, I would go that route.  The best combination of "original" and "working" you can muster up would surely be the most attractive to a potential buyer.

Edit:  Noticed the master volume has been replaced by a jack (input?) so I guess it's not all 100% original.  I still lean toward selling as-is, most guitar collector types value originality over most everything else.  In this particular case, I would assume that the modules are the real "unobtanium" items and someone looking for this stuff wouldn't mind throwing in a new pot and a couple common caps.

OP if you live near the old Baldwin factory, and the Super Axe was definitely a Baldwin-era Gretsch product, could be that this stuff walked out of the factory in a lunch box and was never actually installed in a guitar.  Very cool either way.

[pdavis68]

Regarding the MV being turned into an input, it makes sense, doesn't it? The input, previously was the volume off the guitar. So that was, really, the input to the effect. So By replacing the wiper with the signal from the input jack, you've got basically the same thing.

As you can see in the photo, both the compressor and the phaser use pin head connectors (see the blue female connectors?). So I can rebuild the circuits using pin edge connectors on my boards and simply replace the existing circuits with the new ones. I'd, of course keep the originals, so all you'd need to do to put it back to normal is to unplug the replacement modules and plug in the originals, and voila, back to stock. No damage done.

I might entertain selling it at some point, but I'm not inclined to at the moment. I think it's really cool looking. I'll definitely take care of it, though.

[GibsonGM]

I wouldn't touch it.  Don't even clean the box with anything.   Sell it on Ebay - seriously.

Don't change caps, don't solder or remove anything...put it back the way it was when you got it, throw up an add/do an auction.  It's possible that one part removal could make this go from $300 to worthless.   Don't be afraid to explain AS-IS, and WHY you are leaving it as is - buyers of old things like this do not care, they care that it is original.

Just my 2 cents.   

[pdavis68]

You understand the modules are pluggable? I unplug the old, plug in the new. It's simply a matter of unplugging the new ones and plugging the old ones back in, to put it back to absolutely 100% original condition. Nothing that's currently inside the box would be soldered, cut, or otherwise modified in any way. I would simply unplug the current modules. I'd even leave them inside the box. There's plenty of room for both the old and new.

[pdavis68]

Incidentally, I've sent photos to Ron Tipton, the inventor, and told him my plans, so I'll be curious to see what he has to say.

[pdavis68]

Came across this article: http://gretschpages.com/guitars/axes-chets/

"Unfortunately, the electronics have failed with age on many of the Supers Axes, and schematics are extremely difficult to find."

So apparently not an uncommon problem with these.

Also, regarding the post before my last post, I'm not trying to be argumentative, I'm merely having trouble understanding how I can possibly hurt the value of this with my plan, as nothing is really being altered.

[armdnrdy]

My thoughts after looking at the drawings of the phaser, and reading through the notes from the "designer"

He (Chet Atkins) told me (Ron Tipton) I could buy whatever commercial units I wanted, tear them apart and then design something smaller and (hopefully) better.


It looks like Ron did just that. This circuit is an Electro Harmonix Small Stone without the color switch.

By the end of August I had an assembled guitar ready for trial. Chet came to Prairie Grove about mid September to give it a try. He was generally pleased with the performance of the modules but he wanted to make some changes in the arrangement on the control panel and he thought the phaser volume was too low at the "full on" (CW) end of the blend control.

The only difference in this circuit and the Small Stone is...a transistor is added at the output. This is probably the fix to the lower output problem that Chet noted.

If you want to build this circuit...CA3094s are hard to find...pricy when you do find them....and there are fake 3094s running around.
There is a different version of the Small Clone that uses LM13600/LM13700. Look around for the schematic of that version.

[pdavis68]

Nice! Thanks for the info. Found a vero layout: https://4.bp.blogspot.com/-7K6qKBaaL0c/WCwqrDkY5CI/AAAAAAAABF0/Mur0Moetpk8F2BViQlXhy1IFkqMFZsVgACLcB/s1600/EH%2BSmallStone.png


I was wondering about the CA3094. I looked on e-bay and the only reasonably priced ones were out of China, which made me suspicious. And needing 6 of them would definitely cost a pretty penny.

And honestly, I don't even care if it's the same circuit, just as long as the existing pots will work with whatever I build. The compressor looks pretty straight-forward, component-wise.  All stuff I have in my drawers.

Thanks again.

[Kipper4]

I just found this

http://www.diystompboxes.com/smfforum/index.php?topic=75124.0

[GibsonGM]

Also, regarding the post before my last post, I'm not trying to be argumentative, I'm merely having trouble understanding how I can possibly hurt the value of this with my plan, as nothing is really being altered.

The only way you could possibly hurt the value is if you start using it, break a pin of a module, damage something so that now nothing works at all...dried up, leaky caps and so on....that's all I was getting at.   It's your pedal - by all means, use it if you like! 

If it was an original Small Stone, you'd probably keep it and use it.
I was working on the premise that it stunk for guitar but might be collectable, and therefore have real value to someone else...

[pdavis68]

I understand. The pins are on the modules I'm replacing. So if one broke, it would break on my copies, not the originals. If I were to use it, I'd only use it at home. I wouldn't gig with it or anything. I definitely plan on taking care of it. But I'd also like to have it be functional as well.

[GibsonGM]

Oh, I understand...the instinct with us it to improve, repair, clean up, etc.  It's hard to just leave something alone 

[EBK]

If you decide to repair/replace stuff, I'd recommend that you take careful pictures first and keep all parts you remove in a labeled container.
Could help preserve some resale value down the road.

[amptramp]

There is a comprehensive article on restoration here:

http://antiqueradio.org/FirstStepsInRestoration.htm

It is written by Phil Nelson, someone who restores radios and televisions to a meticulous finish, worthy of a concours if such a thing existed in radio.  His other article on replacing capacitors includes one technique you may not have seen elsewhere - restuffing old capacitor bodies with new capacitors and capping them so they look original but have new guts:

http://antiqueradio.org/recap.htm

I have done some electrolytics this way in radios where there was no room for an additional capacitor under the chassis or the capacitor terminals were an essential part of the layout.  Since modern electrolytics are smaller than the old ones, I usually end up with plenty of space.  He also tends to use film capacitors to stuff old paper capacitors.

In the era when your unit was made, capacitors had not specialized to the point where low voltage ratings and capacitors specifically made for solid-state circuitry may not have existed.  If that is the case, you are in luck - a 200 volt capacitor can be stuffed with a 63 volt cap of the same value and the combination of modern dielectrics and lower voltages allows the modern capacitor to be hidden entirely in the old cap body.