Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dscottguitars on August 18, 2013, 05:33:19 pm
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I cannot find much info on installing an LED with a footswitch. I have the Hoffman relay and power supply in my amp. Your diagram shows two lines going from the amp to the footswitch to power the LED. Is that correct? It seems like one should be able to make it work with just the negative connection going through the switch. I have the negative side of three relays going to the jack, and the negative side of the power supply going to the fourth lug on the jack of a four pin jack. I can get the LED to light up, but only when the switch is off.
What am I doing wrong?
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it's going to be a major pain, but the only way I can see it working is if I rewire the relays to be 'closed' for the effect. Is there anything I am not seeing?
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http://www.el34world.com/Forum/index.php?topic=14348.0
If you look closely at Doug's drawing you'll see there are THREE wires going to the footswitch, not two. You can't use that drawing to do what you want to do.
It seems like one should be able to make it work with just the negative connection going through the switch. I have the negative side of three relays going to the jack, and the negative side of the power supply going to the fourth lug on the jack of a four pin jack. I can get the LED to light up, but only when the switch is off.
Yes, you can do that, but as you discovered, the LED will be on only when the switch is off.
Revisit this thread...
http://www.el34world.com/Forum/index.php?topic=14348.0 (http://www.el34world.com/Forum/index.php?topic=14348.0)
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Thanks for that confirmation.... back to the soldering iron. :sad:
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Now I need some help...
I reconfigured all the switches by changing the normally closed lug to the normally open. Everything works except the channel switch. It pops really loud when changing. Here is the original drawing not showing these changes-new preamp1 and another drawing showing the changes (new preamp2) as you can see the only difference is:
On the channel relay- G1 and G2 are switched around and so are C1 and C2. I tried a bleeder resistor 820K on the 0.01 cap coming off of V2-A and that still did not work. :help: :help:
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Since the LED and the relay actuation signal is in effect a digital signal, eg; strictly an on or an off, you could also make a very simple emitter-follower inverter out of a cheap NPN transistor, a 2N2222 or 2N3904, your LED, and 3 resistors, and stick it all inside the pedal housing.
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Everything works except the channel switch. It pops really loud when changing.
OK, it pops. But does it switch channels?
Put a 1M resistor from point "B" to ground. Does that help any with the pop?
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Yes it does change channels. I'll try that after work tomorrow, it's all shut down... Thanks..
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I tried putting an 820K resistor on point B to ground and that still did not eliminate the pop. I am really confused as to why it would pop in the first place when all I did was switch the channels around.
When the master is all the way up is when the pop is loud. If the master is down and the gains are up, its not very loud. But when both are up it is loud.
When adding a bleeder resistor do I put it on the tube pin to ground or after the cap to ground? I placed it after the caps like shown.
I also pops when I turn the power switch off when it did not before.
Do I have to go back to the other way and use a stupid battery for the LED's?? I hope not...
Eleventeen: I don't know anything about that kind of a setup, do you have a drawing?
thank all...
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The "pop" issue, has nothing to do w/lighting up the LED....I will leave that to Sluckey. I am not fully following (with your flip-around) whether, when the effect is activated, you have a positive-going change
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or whether you have a negative going change.
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(http://i172.photobucket.com/albums/w32/ttm4/emitter_4_zpsd32722e3.png)
I suspect you will have to use a PNP transistor because you need an "inverter"....with the switch open and the effect OFF, you have your ground and your +5 vdc. Close the switch....the 5 volt will not pull up ground, ground will pull down the 5 volts. Thus, you have a negative-going signal.
I've included the NPN drawing (even though I suspect you would not need an emitter follower with a positive going signal) because for toobists (myself included) NPNs are much easier to understand. The arrow points INWARD on a PNP.
It's generally the right thing to do to include the 1K or even 5K "isolation" resistors (the ones that run horizontally) just to keep things kosher.
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Thanks Eleventeen, but that's way too much for me to learn at this point with this amp...
I did find the problem though and a very interesting one:
If you'll notice on channel two, I don't have a coupling capacitor because I thought the tone stack would provide that. Normally it did in the past because I used the Fender tone stack, however, I changed to the James tone stack from the Duncan Tone Stack Calculator ( I like it much better.) I decided to add the bleeder resistor at the end of the tone stack going to the Channel switch point C2, but that did not seem to work so I disconnected it with the amp still on-knowing there's no voltage at that point. Well guess what, it made a loud buzz so I checked the voltage and got 10vdc! I thought, why? I looked at the schematic and realized there could be a path through that tone stack that does not go through a cap. I added a cap to V3 that feeds it and voila, no pop! :icon_biggrin: :icon_biggrin: :icon_biggrin:
Thanks for all your guys' help...
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Use 1M resistors on signal points going into and from both signal switching points right at the switch. They're called "pull-down" resistors and eliminate the popping effect.