Fulltone - GT 500

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
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sevinisthenumber
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Post by sevinisthenumber »

madbean wrote:It's disassembled and on my bench. Effects order switching is simply a 4pdt. All the FETs are 2n5457. It seems a bit over-designed at first glance, with approximately 50 odd resistors and I don't remember how many caps. I will have a preliminary schem, but the Blackstone is first in line.

Should be a straight-forward trace, even for me. There are a few tight places around where the switches are wired, but I'm a persistant d00d.

My initial impression from dinking around with it a few weeks ago was "it's pretty good, but I don't know if it's special". I only spent 30 minutes or so with it. Maybe the trace will reveal some magic or originality??? :)

I'm real curious as to how the boost section compares to the Fat Bastard, if at all....
you got a layout to the distortion side?
"The man who says he knows everything will never know the truth"
C.S. Lewis

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view_kevin
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Post by view_kevin »

if you all have ideas for mods fulltone gt-500.you all can comment here ..
I opened this topic because of the lack of forums that discuss about this pedal
Image
nb:if any, can be included more pic for more details

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madbean
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Post by madbean »

Here's a guts shot for you.
gt500)guts.jpg

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devastator
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Post by devastator »

Interesting the inductor ! certainly used for the mid section of tonestack.

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madbean
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Post by madbean »

It's a nice sounding pedal. The basic topology is something similar to Paul Cochrane's Fat Bastard for the boost side, and cascaded mu-amps for the dirt side. I attempted to trace it, but I think it is a 3-layer board. When I had it apart, I could not find some trace connections where they should have been.

I think I have a component list with values somewhere. I can put that up if I find it....things are packed up right now for moving so it will be a while before I can do that. I have more pics, though.

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madbean
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Post by madbean »

IMG_0272.jpg
IMG_0273.jpg
IMG_0274.jpg
IMG_0275.jpg

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view_kevin
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Post by view_kevin »

is there any ideas for mods is the better pedal?

:applause: is a good picture

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jamiefbolton
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Post by jamiefbolton »

madbean...

any luck on this schematic?

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Saruman
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Post by Saruman »

bla bla bla in 4 pages. :shock:
If you have a device and you're on this forum, there is no difficult copy schematic????! :slap:
I wonder...

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madbean
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Post by madbean »

Saruman wrote:bla bla bla in 4 pages. :shock:
If you have a device and you're on this forum, there is no difficult copy schematic????! :slap:
I wonder...
I don't have the pedal anymore. I'm pretty sure the PCB is 3 or 4 layers, too, after looking at the bottom side of the board.

Basically, the boost side is really similar to the Fat Bastard, and the gain side is cascaded mu-amps with and inductor for the mids control.

It would be easy to design something very similar :)

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Post by Dirk_Hendrik »

madbean wrote: I don't have the pedal anymore. I'm pretty sure the PCB is 3 or 4 layers, too, after looking at the bottom side of the board.
I'm fairly sure it's not.
Sorry. Plain out of planes.

http://www.dirk-hendrik.com

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madbean
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Post by madbean »

Dirk_Hendrik wrote:
madbean wrote: I don't have the pedal anymore. I'm pretty sure the PCB is 3 or 4 layers, too, after looking at the bottom side of the board.
I'm fairly sure it's not.

Why's that? I could be wrong, of course, but it did not seem to have enough traces connecting the components together.

However, just by doing a parts list and looking at how they were placed, it was easy enough to deduce the basic design.

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Post by atreidesheir »

Might it not be a good idea to add a good distortion/overdrive to the fat bastard circuit and wire for both with the ability to switch the order. If the distortion is not great in the gt500, why bother really.
Just approach it as an "insert here" type drive.
I was thinking of linking the DOD 250 gray with the fat bastard like this. or maybe the fred briggs overdrive. Something great sounding and not too distinct.
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Post by okgb »

A business has to make money to stay in business and be a business, but
how much is a good question ,
The pots thing looks like he also took a page from the mackie book .
maybe all those years of going to the library has got him in the habit of borrowing ?

I'm in for a PaulC preorder of some sort to help support ,
paul, can you make it cash cheques ?

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sevinisthenumber
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Post by sevinisthenumber »

Is the boost side of this simply a Fat Bastard?!
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C.S. Lewis

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Post by jg »

sevinisthenumber wrote:Is the boost side of this simply a Fat Bastard?!
No, for one, the Fat Bastard is inverting, the boost side of the GT500 is not.

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Post by MullisMan »

I'm a little confused by the wiring diagram provided by dap9. I see only the toggle 3PDT and not the two 3PDT footswitches that would be used for this application. Do you run a wire from the in on the PCB to the In on the toggle 3PDT and then from that lug on the toggle to whatever lug you're using for the in on the 3PDT footswitch?

Or do I simply run two wires for each in/out on the PCBs to the toggle 3PDT?
I want to build it all.

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toneboner
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Post by toneboner »

Something about not having the schem for this is pissing me off. So i'm going to grab one this weekend and give it a go. But if madbean can't do it then I'm definitely gonna come up short!!! Any hints, pointers???

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Post by bajaman »

a good multimeter :wink:
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MKB
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Post by MKB »

FWIW, several things:

1) I have never seen a 3 layer board in 22 years of PCB design. The fab houses I have worked with discourage this, they insist on multiples of 2 layers unless you get a single sided board. This probably has something to do with the available materials to build a board stack with, you want it to be a few mils from 0.062", and it would be hard to do with 3 copper layers.

2) If the board is of a standard multilayer design, look to see which traces disappear in the board. You could start with ground and power traces, these are usually what are run internally. Judging from the pics of the board, there are very short signal trace jumpers present, which most likely would not be on the surface if they run signal traces on an inner layer (at least unless the designer was sloppy or in a big hurry).

3) Also he flooded the visible side of the board with copper pour connected to some net, probably ground, so you won't have any ground traces running around on the board. If you see a via connected directly to the pour area with no wire in it, that means both sides have pour on the same net and they are interconnected (this is normal).

4) Another way to look for a multilayer board is for an isolated via (not attached to a component footprint) that has no wire in it. If a trace goes to the via on one side, and nothing exits or connects on the other side, and the via is not part of an unstuffed component footprint, it probably is a connection to an internal layer. I could not see any such vias in the pics, but there does seem to be a test point on there (which is a via without a connection on one side).

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