mods for 70's cry baby?

[JohnForeman]

I have a 70's cry baby and i'm looking for info to add a power plug and true bypass.  And anything else that may be cool mods.  I thought i ran across a site a couple years ago that had all these mods but i cant find it.  any help would be appreciated.
thanks

[jtn191]

This site has some info http://stinkfoot.se/archives/549 RG Keen's article is good too.

[joegagan]

which inductor does it have?

a lot of people have disdain for the TDK brown rectangle, and with good reason. the less common stack of dimes is more in the sweet spot for resistance, which in most cases gives a more lively Q.
so, an inductor swap might be a good first go.

the oil foil caps in those thomas are really nice, as are the transistors.

you can juice up the gain by lowering the Q1 E to Gd resistor, or better yet a 1k trimmer allows you to dial it in. similarly, a 100k trim in place of the input 68k R will let you add more gain, but in a different ( higher ) freq range than the aforementioned 1k  Q1 bias trim.

try lowering the 470k mix R between Q1 collector and the inductor 10 to 30%, and at same time raise the 4.7 u cap to gd off inductor to 10 u or 22 u. this widens the Q, which is helpful as the 70s thomas are known for a fairly narrow sweep.

the widely publicized raising of the 33k paralleling the inductor to 56k or 68k is also a pretty nice mod for these.

if it were mine, i would not drill the case for power supply, instead i suggest swapping the original bottom plate for a later one with a battery hole in and run a power wire up into it from underneath. keep the original bottom for future re-use.

[JohnForeman]

it has the square TDK inductor.  I can find a few sites on the true bypass for the GCB-95 model but not for the 95-910511 model.  I'm still looking though.  i may check my office to see if i printed the ones out i found a while back..

[zombiwoof]

I've been looking at the Thomas Organ wahs from this period, and it seems to me that the ones made in Sepulveda CA usually have the square TDK inductor, and the Chicago-made ones have the Stack of Dimes inductor.  There are sometimes exceptions to this rule, but this is usually the case.  My main bitch with my Sepulveda-made Cry Baby is the quick sweep, so I would try Joe's suggestions to change the sweep, or swap out the pot for one of Joe's heavy-duty sealed pots, which have a more Icar-like sweep (keep the old pot in case you ever sell the wah).  Some people don't mind the TDK inductor, I'd do other non-invasive mods like this before changing it out.  It does have a different type of sound to it, though, than some other inductors, some like it, some don't.  Personally, I wouldn't put in a power jack, but you may have a problem with running a battery-snap adaptor cable, I think the wah may need an isolated power supply for this to work, I believe I tried this in the past and found it resulted in some squealing noise.  If that happens, try an isolated supply.

Al

which inductor does it have?

a lot of people have disdain for the TDK brown rectangle, and with good reason. the less common stack of dimes is more in the sweet spot for resistance, which in most cases gives a more lively Q.
so, an inductor swap might be a good first go.

the oil foil caps in those thomas are really nice, as are the transistors.

you can juice up the gain by lowering the Q1 E to Gd resistor, or better yet a 1k trimmer allows you to dial it in. similarly, a 100k trim in place of the input 68k R will let you add more gain, but in a different ( higher ) freq range than the aforementioned 1k  Q1 bias trim.

try lowering the 470k mix R between Q1 collector and the inductor 10 to 30%, and at same time raise the 4.7 u cap to gd off inductor to 10 u or 22 u. this widens the Q, which is helpful as the 70s thomas are known for a fairly narrow sweep.

the widely publicized raising of the 33k paralleling the inductor to 56k or 68k is also a pretty nice mod for these.

if it were mine, i would not drill the case for power supply, instead i suggest swapping the original bottom plate for a later one with a battery hole in and run a power wire up into it from underneath. keep the original bottom for future re-use.

[joegagan]

true bypass is pretty easy. below is a pic of one i have done, but i don't have an actual tutorial on the subject. basically a new wire from the input jack to the center of a dpdt, relocate the output wire that was the input to the out lug on the dpdt,  the old send from the spdt  to the board is now your 'effect in' and the blue wire is your ' effect out'.

all of the mods i was talking about can be done without drilling any holes in the board if you are crafty. on any older wahs i make my mods reversible in case a thomas is someday worth 1000 dollas

agree with zombi on the difference in the 'quick ramp' taper of the crybaby vs a slower smoother ICAR type or regular log taper. some people like the fast action, some don't. i have an article on the difference:
http://img.photobucket.com/albums/v311/joegagan/wah/wahpothowtopickawahpot_zps64ea1dc9.png

[JohnForeman]

What is that thing next to the inductor?  I think i'll do the by pass this weekend.  As for the other mods, i want to do them one at a time and play with it for a while between each mod.  it sounds like the first tone change mod should be the pot?  As for putting holes in the case, i'm not really to concerned about it.  The case is in pretty bad shape as it is, and I'll prolly be dead and gone before this thing is worth any money just because someone wants a 'classic'.  Mine still has the original jacks in it so i'll order some new ones if/when i add the power jack.  I'm assuming i can just follow a wiring layout for any pedal to get the power working?

[joegagan]

that is a second inductor in series with the TDK for a total of 985mH / 27 ohm. which you can see written in red sharpie to the left, it had a real sweet and deeper tone.

for the power jack, there seem to be 2 different pinouts, verify your jack switching function to make sure your battery is turning off when a power supply is plugged and AND when the pedal inst jack is unplugged. GGG and i think beavis have good diagrams on the power wiring, just be sure your pins are the same as the diagram.