Bob-I wrote:Damn, it's still bright. Gotta mean something
Bob
If you take the Jazz/Rock switch and position it in the middle so the contacts release you should get a kind of simulated PAB..If it works like a PAB then this might give us a clue as to if the switch has gone bad..
Tony
" The psychics on my bench is the same as Dumble'"
The mid control isn't doing anything to the tone at all. I replaced the cap, replaced the pot, it sweeps from 1.2 ohms to 246K. Why would this have no effect at all
The mid control isn't doing anything to the tone at all. I replaced the cap, replaced the pot, it sweeps from 1.2 ohms to 246K. Why would this have no effect at all
The only things left are it's lost its groiund, or its connection to the mid cap, or the mid cap has lost its connection to the slope resistor.
Bob-I wrote:The bass control works, I measured from the mid cap to ground, it goes from 1.2 to 248k. The connection to the slope resistor is sound, measures 0.
This is like the twilight zone
Here is what I would try.. In rock mode take your clips and short the .002 cap to ground, this way you can isolate just the bass and mid controls...With the .002 grounded you should get plenty of bass and mid sweep (with the bass turned up)..This is a weird one!!
Tony
" The psychics on my bench is the same as Dumble'"
Bob-I wrote:The bass control works, I measured from the mid cap to ground, it goes from 1.2 to 248k. The connection to the slope resistor is sound, measures 0.
This is like the twilight zone
Here is what I would try.. In rock mode take your clips and short the .002 cap to ground, this way you can isolate just the bass and mid controls...With the .002 grounded you should get plenty of bass and mid sweep (with the bass turned up)..This is a weird one!!
Tony
Sounds like a good idea. Somehow the signal isn't getting to the mid control so I'll have to isolate and troubleshoot that.
This will have to wait, sandy came through last night and left us powerless. Everyones fine and no real damage other than a few branches down.
Bob
Glad you made it through Sandy and no real damage..It was pretty much a non event here in Richmond although my summer home in Rehoboth will need some cleaning up..
Let us know what you find on the amp!!
Good Luck
T
" The psychics on my bench is the same as Dumble'"
We made it through the storm ok, power returned Sunday at 2:00PM so 7 days without power.
Back to my amp now.
I listened using a probe at all the tone caps, everything is putting out what it should but still the mid control does next to nothing, barely audible change. The treble mixer seems to be working as expected.
I had a mid pot go bad once - intermitant on top of that so was a real pain to track down - worked fine whenever it was on the bench. sounds real similar.
it really is a journey, and you just cant farm out the battle wounds
briane wrote:I had a mid pot go bad once - intermitant on top of that so was a real pain to track down - worked fine whenever it was on the bench. sounds real similar.
I thought of that, and even though the pot checked good I swapped it.
OK, this is a stab in the dark but do you have a little mirror (dental) that you can look underneath the board and elsewhere that is normally hidden from view?
I had a piece of scrap wire one time that shorted out part of the preamp circuit.
Another thing that can happen on eyelet boards, where you have changed a lot of components, is a solder blob can hang down from the eyelet.
Then another time I had a piece of a broken screw that I tapped out that that went behind my pedal supply board and shorted it out.
That one was pretty easy since it fried the small transformer.
Structo wrote:OK, this is a stab in the dark but do you have a little mirror (dental) that you can look underneath the board and elsewhere that is normally hidden from view?
I had a piece of scrap wire one time that shorted out part of the preamp circuit.
Another thing that can happen on eyelet boards, where you have changed a lot of components, is a solder blob can hang down from the eyelet.
Then another time I had a piece of a broken screw that I tapped out that that went behind my pedal supply board and shorted it out.
That one was pretty easy since it fried the small transformer.
Another stab in the dark. But I would consider completely taking the tone stack out of the circuit, removing the connections to both v1a and the volume before v1b. Then run a new coupling cap from v1a to the volume control before v1b. Then I would listen with an audio probe at each stage, after the stages coupling cap.
This way you'll know if it is the tone stack, or something else weird going on downstream.
Last think you want to do is rebuild a tone stack only to discover it was something else, like a bad coupling cap somewhere else.
So the mid control is now working. I was chopsticking around and it started working. I ripped and replaced all the wires, cleaned up everything and it's working consistently.
But still it's like tin. If I dime the bass it's not terrible, but anything less and it's like a transistor amp.
Once again I connected another amp's pre to the power amp in, rich and full, then this amp's pre to the other amp's power amp, tin.
It's something in the pre and I'm at a loss. I even pulled the filter caps and checked them.
