not sure if this is a problem or not

[charvel pointy head]

The negative feedback, presence, does not seem to do much? I've checked at I have it wired to the 8 ohm tap, and I have a 100k resistor there. Thing is I don't hear it doing much, if even anything at all. I thought this on my first 100 watt build as well. On my JTM45, which was wired to the 16ohm tap, it functioned flawlessly. Now the amp sounds good as is, but ought this feature add a bunch of brightness when desired? Did I miss something? Please advise.

[rockstah]

any pictures - u double checked your wiring of the board, presense, feedback?

[charvel pointy head]

ARrrgghhh I changed my email and it took to now to get myaccount reactivated. Ok I rebuilt the entire nfb circuit, grounded to a different location. NO WORKY! That is to say, the knob does not make any perceptible changes. no noise, nothing. it measures 5.1k in the circuit, but the sweep to bright just does not happnen. I changed to the 16 ohm tap, nothing. Could I have a bum pot?

[charvel pointy head]

still a problem. I ordered and installed a new 5k linear, still no change that I can hear whatsoever in the sound whether I dime or turn completely off. Could I have a bad capacitor? I rebuilt the whole circuit, new wires, etc, still not a thing. I rejumpered it over, put a new pot, wired to the 16 ohm tap, nothing. I'm now thinking the cap could be bad or I did something wrong. I know , pics. I'll take some tonight when I get home from work.

This item worked like gangbusters on my jtm45. Maybe I should just leave it alone, as the amp sounds great, but you want it all to work.

[charvel pointy head]

here are 3 links to pics I took of the nfb circuit. Any ideas?

http://i163.photobucket.com/albums/t302 ... uit003.jpg
http://i163.photobucket.com/albums/t302 ... uit002.jpg
http://i163.photobucket.com/albums/t302 ... uit001.jpg

[charvel pointy head]

ok, here is a dumb one. I resoldered everything, NOTHING at all. ok, now I turn the ppimv all teh way up and voila, it seems to sweep again. Hmm. What am I missing here? do these invalidate the nfb circuit? subject to another thread?

[straycat]

The PPIMV does effect the way the NFB operates. Lower settings pretty much makes the presence control useless. This has been talked about before just do a search to find info.

http://forum.metroamp.com/viewtopic.php ... 35fa0c5bfc

Nothin is free
For every action there is a reaction

[bluze81]

ok, here is a dumb one. I resoldered everything, NOTHING at all. ok, now I turn the ppimv all teh way up and voila, it seems to sweep again. Hmm. What am I missing here? do these invalidate the nfb circuit? subject to another thread?

I noticed the same thing on my 1st 100w build, and the 45 presence does have a more efective sweep, I did find that the other tone controls change the sweep of the presence control, so I thought its just the nature of that curcuit?

[rockstah]

yes the presence and feedback are effected by the PPIMV. as u bring up the PPIMV these are less effected.

i have a question about the two wires on each output cap... where do they go? i cant figure out why u have two wires on each side.

should be one wire on each side going to the PPIMV pot and two wires from the pot to the out put tubes...

[charvel pointy head]

they do. They attach to the turrets underneath that strip board. those are soldered to the orange and green goint to the output tubes and the 220 resistors go to ground from there aswel.. yeah, now all is clear to me and the amp sounds great anyway and no noise, no real complaints, just was unaware of my limitations on this one. Now I'm in the middle of building a ross compressor clone and I cannot read the polarity for the life of me on these tantalum capacitors. I think it's time to see the eye doctor.