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Building A Direct Output Line For An Amp
Building A Direct Output Line For An Amp
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Old 30th October 2004, 07:39 AM   #11
Enzo is offline Enzo  United States
diyAudio Member
Join Date: Sep 2004
Location: Lansing, Michigan
120 watts was not running through the pot. it was just across something capable of putting that power out. Try a plain old 10k resistor across there as an experiment. I bet it won't burn up. The load determines the power, not the amp. You can run a solid state power amp full out, but if there is no load on it, no power is produced. Even if I had 70V rails, a 10k resistor would still only draw about a half watt. Tube amps have their own issues, so we must load them.

ANy chance the pot arced over? Take it apart and see what the failure mode was.

ALso, when it burned up, was there something connected to it? Or was it just across the output with the wiper unloaded? Point being that if something was connected, there could have been some ground currents finding their way home through the pot.

Another clue would be if it worked OK until the pot was turned close to one end or the other. If some current was allowed to find its way across just the end millimeter of resistive element, it might have been stressed. if the ends of the pot were wired across the amp out and the wiper were turned almost all the way up, and whtever the wiper was connected to was grounded, then the last couple ohms of the pot would be trying to conduct the current of the output stage to ground.
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Old 30th October 2004, 07:39 AM   #12
MrGuitardeath is offline MrGuitardeath  United States
Join Date: Nov 2005
Default Musta been the elctrolytic I ran before the pot....

I think I spiked the voltage with an electrolytic cap I was toying with to cut treble just before feeding the hot lead into the pot.

Anyway I designed my own circuit around the 10 k pot and have AMAZING results.

It goes like this:
Speaker hot lead into I believe a 560 pf cap( I'm certain it's somewhere between 470-560pf....hell it might be as high as a 680! this suckers HUGE) --> 100 k resistor --> 10 k pot --> 1/4 output jack.

THEN I added a tone pot to kill off the intense amount of treble. A 50 K pot with two .1 uf caps. One just wasn't cutting enough and all the other values I toyed with weren't working the way I needed.
.....I've always noticed doubling the same value caps in parrallel will give just a touch more treble cut and do so more gracefully.

ANYWAY, my line out sounds damn near EXACTLY like my custom built/loaded 4x12 cabinet and it get's even better.

The 560 pf and 100 k resistor I used as an input buffer did something very important it turned out.
The 10 k pot at about 50-60% stops increasing volume and increases the signal density. It's not like a gain effect but it's like the signal has more mass.
It's like increasng cabinet resonation!

All in all I'm really happy and this sure beats any of the line out circuits I've found online.

......I think I'll work on my own D.I. box now and come up with a fixed EQ circuit to use in conjunction with my line out circuit which with the way the 10 k pot works to simulate cabinet resonation.

Only involved about 10-12 hours of experimenting today but it paid off. Hopefully someone else can benefit........
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