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It's my lucky day too. My VTX is fixed and now your also helping me with a must have footswitch. How much better does it get than that. But as a novice I must ask, the heater tap point is pin 2 of either valve (6.3 vac) and a single diode to convert to dc, and a limiting resistor for each led ?
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May I suggest that the amp already has DC supplies in it - the +15 and -15 for the preamp. Clean filtered DC. And if tapping off the preamp supply makes you uncomfortable, they are dervied from +/-27v supplies which you could also use. Only difference would be you wuold have to raise the value of any current limiting resistors for the LEDs. Seems easier than building a new supply to me.Education is what you're left with after you have forgotten what you have learned.Comment
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Enzo, my concern with the +/-15 volt preamp supply was the amount of available current; IIRC, with the Zeners there was only 70 or 80 mA available per rail. Since I had subbed in the NE5532 on a couple of IC's as well as the OPA2134 in the first few IC's, I didn't know how close I was coming to using all of that. I didn't know if the few extra mA from the LED's might've been too much.
So since I had a bridge rectifier handy, and plenty of real estate, I just came off the heater supply since it was nice and close to the FS jack. There was indeed a madness to my method!!
Back to the OP, yes once you have a constant DC, then each LED gets its own dropping resistor. And Pins 2 and 7 on the socket. I kept the DC for the FS totally isolated from chassis ground, IIRC, I did not want to introduce any noise anywhere, so I derived both + and - from the heater supply and did not tie the FS LED ground back to the chassis. Dunno if that was overkill but the FS is quiet.Comment
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Looking at the schematic, the 6.3 vac heater supply offers a robust 6 amp supply vs the pre-amp supply of 15 vdc at 1 amp. I'll assume that the 3 leds needed for the foot switch will consume about 20 ma each. Will that 60 ma led current draw on the heater circuit affect it's operation to any noticable level ?Comment
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Peavey uses the same power transformer on other amps with more tubes on the heater supply, so it's got plenty of heater current capacity. It won't blink at a few extra milliamps.Comment
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Ok sounds good. I will use the Heater Tap point as described. Did you run the ac power to the footswitch enclosure, then rectify or did you send the rectified dc to the footswitch ?Comment
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I rectified it in the amp chassis, then sent DC down the multicondductor cable to the FS. I did not want AC inside the multiconductor cable, might've introduced hum. Don't forget a smoothing filter cap after the bridge rectifier. Any decent value like 1000 mfd or so will do.Comment
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Ok, I'll make sure to get that cap in there. Didn't even think about a cap. Did you use the shielding in the multiconductor cable as a lead or just for shielding the 6 cables ? Sorry for bombarding you with all my questions but you are in fact educating me. Thank you....Comment
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Not as a separate conductor, no.Comment
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I wouldn't be concerned in the slightest over the current capacity of the heater winding.
If you wory over the 15v regulators, then draw off the 27v rails.
Nothing wrong at all with the heater route, I was just looking out for building something more if not necessary.Education is what you're left with after you have forgotten what you have learned.Comment
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Enzo, I saw on the schematic where the 6.3 vac Heater power circuit was fused with a 6 amp fuse and the 15 vdc pre-amp circuit with a 1 amp fuse. Not knowing the current draw of the pre-amp circuit I chose the heater side for powering those leds in the footswitch. Even though we are talking about a small amount of ma's, I didn't want to upset anything in the pre-amp circuit. If Peavey was going to add a footswitch with Leds, how would they have done it ? I'm guessing that they probably would have re-designed the whole circuit to accomodated for the Leds in the footswitch. But thats just a novice guess. I sure would like to have all that proprietary knowledge that the designers have in their head. Wouldn't that be great not to think so much about it. Thank you....Comment
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I would just look at some more recent models that do include LEDs and see what they did. I am not too worried that the preamp supplies are so close that an extra few milliamps would stress the supply. PV has many models that use relays and LEDs in the amps.Education is what you're left with after you have forgotten what you have learned.Comment
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Ok Enzo, maybe I will try that on the pre-amp side. Thank you for your help....Comment
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