goye2cz
Rookie Solder Flinger
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Post by goye2cz on Apr 26, 2006 5:55:03 GMT -5
I bought this Crate GX-15R in about 1996 I believe. It's been a faithful little guy though it lacks the obvious nice things, footswitch, effects loop. I got to thinking I may be able to handle the modifications myself if there was an instruction. Of course the warranty is out and I'm not afraid to poke around, cautious of potential.
I just think it would be convenient to have the effects loop and footswitch like my gigging amp does.
Any help?
Waylan
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Post by sumgai on Apr 27, 2006 5:33:13 GMT -5
Waylan,
I've fixed about a Sagan of these things, and I can tell you right off, there isn't much under the hood beyond a handful of IC's on a printed circuit board, and that's it. The upshot of this is, do you feel comfortable breaking printed circuit board traces? And then soldering wires to them to run out the the newly installed jack(s) on the back panel? If not, then you need to reconsider your priorities right now, before you make plans you can't keep.
If you want to forge ahead, then you'll need to trace out the circuitry, because Crate has never released the schematics for those little guys. Whenever I have to dig in, I just trot out my trusty o-scope and signal generator, and have at it. Of course, it also helps to know what kind of IC's I'm looking at, but even then, it's usually easy to figure out where the signal goes in, and where it comes out (albeit, louder).
Take the Line In/Line Out points just before the volume control. Be sure to use a shorting jack on the Line Out, and a interrupt jack on the Line In.
Assuming that you want to use the footswitch to change channels, then you should be able to simply bridge the switch found on the circuit board with your own wires. Essentially, that puts the external and internal switches in parallel, which is fairly common practice. Unless your solder job is sloppy, this shouldn't cause any problems.
If you're intending to modify the behavior of the reverb circuit (on/off), the simplest way would be to just short the output of the reverb tank. Again, solder your wires right on top of those that come back from the tank, and if your solder job is good, then all should be well, and closing the switch should kill the reverb.
HTH
sumgai
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goye2cz
Rookie Solder Flinger
Posts: 14
Likes: 0
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Post by goye2cz on Apr 30, 2006 9:15:44 GMT -5
Thanks for the reply and the suggestions.
Take the Line In/Line Out points just before the volume control. Be sure to use a shorting jack on the Line Out, and a interrupt jack on the Line In.
I thought about that for a while, I don't have so much a main volume though. There's a volume for the clean and another for overdrive. So that blows that plan I guess. Well, tell me if I'm wrong about that please. The amp has a heaphone jack that cuts off the external speaker when a jack is inserted in it. I'm wondering if that comes straight off the preamp or if it's a separate circuit? I guess if it were coming off the preamp it's a possible point to do the effects loop.
Assuming that you want to use the footswitch to change channels, then you should be able to simply bridge the switch found on the circuit board with your own wires. Essentially, that puts the external and internal switches in parallel, which is fairly common practice. Unless your solder job is sloppy, this shouldn't cause any problems.
Yeah, that's what I want to do. The only problem I see, maybe not a problem, is the channel switch has 6 contacts. I don't know if it's possible to hook that to a jack. Guess I could do some exploring here...
Wish I had an O-scope. I could improvise on the signal generator. I'm not afraid to solder in there. Let's put it this way: I've fixed a broken power contact on the motherboard of my Toshiba laptop. I doubt I'll get heartburn oer the Crate. ;D
I don't know if it would be more help if I posted pics on here of what I'm dealing with? If I'm succesful in this, I'll certainly post a documentary of what I did.
Thanks again.
Waylan
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Post by sumgai on Apr 30, 2006 22:23:56 GMT -5
Waylan, Well, only partially wrong, that's all.  You can insert the pair of Line jacks after the point where the two volume controls meet, to go to the Power Amp stage. However, this is not the normal place for Line connections. Usually, they come before the volume control, but we do have to make allowances for special cases.  Nope, sorry. That Headphone jack is fed by the output stage, it has a current limiting resistor to save the 'phones, but otherwise, it should be a direct replica of the final output signal. It doesn't usually make a good line out, but it is worth a try. However, be aware that nearly all of those things are stereo jacks, meant for stereo 'phones (of course). That means, if you plug in a regular two-conductor plug, you'll be shorting the output signal directly to ground. Don't do that! Make sure that you plug in a stereo plug only, or the Lords of Dogtown will be skating through your wallet, taking a fat repair fee to fix the smoking hulk left on your bedroom floor! I don't have one of these in front of me at the moment (and there's never been a schematic published, to my knowledge) so I'd say, find the two connections that force the channel change, and deal with them. The caveat here is, if one is not ground, then you'll need to use an insulated jack on the back panel. That adds expense, but not horribly so. The alternative is to simply use an "odd" multiple pin (or multi-conductor) jack, plug and cable to your switch, instead of the simple two-wire kind. More expensive, but you could then make it do the job correctly, and you could also put both the channel change and the reverb on one jack/switch assembly. I use an o'scope because I have one. While I consider it more important than having a second guitar, I don't think it's absolutely necessary for everyone to have one of these. They are the cat's meow when it comes to troubleshooting, but they aren't the only way to skin a cat. (Did I just say that?  ) You can trace a signal almost as well with an old, old device called, what else, a signal tracer. It is really nothing more than a small amp with a large-value input control potentiometer, and a speaker. As you inject signal at one point, you inspect for the resultant signal at another point further along the chain. The o'scope tells you if it's distorted in any way, what the phase is, and the amount of gain, if any, but you just want to know if there is a signal present at all - the o'scope is a bit of overkill for that.  Still and all, a reasonbly usable instrument can be found on craigslist most every day, and eBay is full of them. It's always nice, though, if you can check it out before you plunk down your hard-earned cash. ;D Pix - your call, I don't need 'em, but others might like to see what we're talking about. Documentary - yowsa, that's right friendly of you to make that offer! Bring it on, if and when. sumgai |
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You can insert the pair of Line jacks after the point where the two volume controls meet, to go to the Power Amp stage. However, this is not the normal place for Line connections. Usually, they come before the volume control, but we do have to make allowances for special cases. 
) You can trace a signal almost as well with an old, old device called, what else, a signal tracer. It is really nothing more than a small amp with a large-value input control potentiometer, and a speaker. As you inject signal at one point, you inspect for the resultant signal at another point further along the chain. The o'scope tells you if it's distorted in any way, what the phase is, and the amount of gain, if any, but you just want to know if there is a signal present at all - the o'scope is a bit of overkill for that. 
Still and all, a reasonbly usable instrument can be found on craigslist most every day, and eBay is full of them. It's always nice, though, if you can check it out before you plunk down your hard-earned cash. ;D