Tube Amps / Music Electronics
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|4/24/1999 8:29 AM|
||Re: Crate Stealth 50 watt|
This amp was also designed by Lee Jackson and it's one of his best sounding
I think in making this amp for Crate he lost his Ampeg deal
That Ampeg I.M.O. is one of his worst sounding amps.
Since the Ampeg and Crate brandnames were owned by the same company, I doubt there was any conflict of interest.
I agree with you about that Ampeg. It's terrible, and a bitch to work on.
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|4/26/1999 12:35 AM|
I think S.L.M is a distribtor of those amps not owned?
Let me know if you see his name on it.
|4/26/1999 5:07 AM|
Crate, Ampeg, and Audio Centron (now discontinued) are all SLM products and, as best I can tell, all come off the same production lion - there ain't a lot of difference between Crate and Ampeg "guts."
|4/26/1999 8:54 AM|
Well, We replaced the power tubes with a matched quartet of Sovtek 6V6 GT and it sounds real good. (Before I read this) I have a meter and some electronics skills , soldering etc. But, I would prefer not to mess with it if I didn't have to. Mainly because it's not mine. So, if it sounds good should I mess with it? Also, why in the world do you have to use the footswitch to access the gain2 didstortion? There isn't any way from the front panel. He lost his footswitch for it when his band broke up. Will a regular footswitch change thru all the channels? Also, you say -37v, is that negative 37 volts?
Pardon my ignorance. All I know about these amps is what I read here!
|4/26/1999 12:57 PM|
re: missing footswitch
Maybe Doc can look at the schematic for a more specific answer to your questions, but here's a generic answer:
With the volume controls set to 0, plug a bare stereo plug into the footswitch jack and measure for dc and ac voltages between all 3 of the terminals. If you get a fairly accurate 5 or 12 vdc, they may be using electronic and/or logic switching. If you get a dc voltage reading between maybe 5vdc and 30vdc (not close to 5vdc or 12vdc) my guess is that there is a mechanical relay involved. If you get no voltages at all from one of the terminals (the "R"ing in T-R-S) and the footswitch is toggling more than a single function, there is probably some sort of logic circuitry involved (which would require an OEM footswitch from Crate).
After making those tests, try turning the volume and reverb up a bit. If you can hear a click when touching the tip or ring terminal, that terminal might be what switches off the reverb (like on a BF/SF Fender amp in which the footswitch grounds out the reverb signal to turn it off).
I'd suggest temporarily adding a jumper between T & S and then R & S to see what effect it has, but if there is a fancy electronic switching circuit involved that could possibly damage something. (It'd be best if they designed the switching circuit with the assumption that someone somewhere would plug in a regular footswitch at some timeó and either bulletproof the circuit against that happening or use a non-standard plug and jack).
P.S. As for not being able to access one of the channels without the footswitch, have you checked to see if any of the controls use a push-pull pot? If it was added on as an afterthought, they might not have changed the label accordingly. You might want to check the other switches to see if they may have a second function when the footswitch is not plugged in.
|4/26/1999 2:57 PM|
The amp has 2 channels. It has one switch to change from clean to distortion. The distortion channel has 2 gain controls. The second gain control doesn't do anything. I thought it might be a cicuit problem until Jason told me it had a footswitch with 3 or 4 buttons including one for gain 1 and one for gain 2 corresponding to the gain1 pot and the gain2 pot on the front panel. But, apparently no way to access that mode without the footswitch. I'll look for a push pull pot. Then, I'll try the test.
|4/27/1999 8:23 AM|
The switching circuitry in this amp does not use any mechanical contact relays. All switching is handled by FETs and bipolar junction transistors. There are also a pair of LDRs associated with channel switching, toggling the signal path.
There is a panel mounted channel switch button, which is wired in parallel with the external footswitch, but there is no panel mounted feature for gain switching modes. Gain switching can only be done by external footswitch.
The schematic does not show the footswitch unit wiring, but it does show the connecting jack and circuitry. The jack is standard stereo TRS. The tip is for channel selection, the ring is for gain switching. There is a panel mounted red LED to indicate gain boost mode. The panel mounted switch gets disconnected when plug is inserted. The ring terminal is floating open (no switch contacts attached) until plug is inserted. The footswitch works on the base terminal of a 2N5210 transistor switch in each case. From the base terminal, there is a 100k series resistor. At the junction of the outboard end is the footswitch connection and a 2.2k resistor up to the +16v supply. On the ch. switching side (tip), there is a red LED to ground. On the gain switching side (ring), there is a 3.3v zener (1N746) shunt regulator.
It seems that a footswitch unit with a pair of mechanical pushbuttons is all that is needed. I'm not sure if an LED can be added in series with the switch to show status at the footswitch box, that will light when the switch is closed. It's certainly not necessary. You can buy a 2-button Peavey footswitch, which has red & green LEDs, in a music store for about $20. It's terminated in a stereo plug. Just rewire the inside the way you want it for the Crate.
If you would like to test the footswitch jack, a simple test plug/harness could be made up with 3 wires and a stereo plug. Touch the tip wire and/or the ring wire to the shield (ground) wire to act as a switch. You can twist the ends together, or use alligator clips.
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