Help with prescence control 5f6a
Moderators: pompeiisneaks, Colossal
Help with prescence control 5f6a
Hi
Trying to install a presence control in a 5f6a circuit. Not 100 procent sure about the circuit no my original build. Tried to mod from rob robinett with a 25k lin pot, 0.1 uf cap and 4.7k resistor. When I insert it in the circuit the amp goes dead quite. Can anyone give me some pointers, and yes Im a newbie so my soldering needs improvement but im getting better even if it still looks like a year old.
Trying to install a presence control in a 5f6a circuit. Not 100 procent sure about the circuit no my original build. Tried to mod from rob robinett with a 25k lin pot, 0.1 uf cap and 4.7k resistor. When I insert it in the circuit the amp goes dead quite. Can anyone give me some pointers, and yes Im a newbie so my soldering needs improvement but im getting better even if it still looks like a year old.
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- martin manning
- Posts: 13355
- Joined: Sun Jul 06, 2008 12:43 am
- Location: 39°06' N 84°30' W
Re: Help with prescence control 5f6a
Did you have a feedback loop connected before you tried this? Dead quiet might mean it's oscillating at some ultrasonic frequency, and I'm wondering if you need to reverse the primary leads on your OT.
Re: Help with prescence control 5f6a
Hi
There is a negative feedbackloop its the resistor and the white cable thats connected to the 8ohm tap. Dead quiet is an exaggeration, theres some noise from the amp almost sounds like the the loop is canceling out all the sound. But theres no difference if you turn the pot.
There is a negative feedbackloop its the resistor and the white cable thats connected to the 8ohm tap. Dead quiet is an exaggeration, theres some noise from the amp almost sounds like the the loop is canceling out all the sound. But theres no difference if you turn the pot.
- martin manning
- Posts: 13355
- Joined: Sun Jul 06, 2008 12:43 am
- Location: 39°06' N 84°30' W
Re: Help with prescence control 5f6a
Maybe the lead routing of the added circuit is causing the problem?
Re: Help with prescence control 5f6a
Its strange the 27K NFB is connected to the tailresistor from the PI so the insertpoint should be correct. But when the prescensce control is inserted the amp has no sound? This over my understanding.
Re: Help with prescence control 5f6a
My multimeter says it 2.6k when i measure across it?
Re: Help with prescence control 5f6a
You were right 68k and this i what i found under the board.
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Re: Help with prescence control 5f6a
Did this amp have a functional standard Fender presence pot before you started modding it? That last pic you posted is not a typical 5F6A circuit. How do you know this is even a 5F6A amp?
I'd like to see a hi-rez gutshot of the amp that clearly shows the entire board, tube sockets, and control panel.
I'd like to see a hi-rez gutshot of the amp that clearly shows the entire board, tube sockets, and control panel.
Re: Help with prescence control 5f6a
You`re right I dont no if thats the case Its probaly some modded version of an 5F6A and I dont have a schematic for it. I unsolderd the board today and measured every component on it. Going to change it all out with a better board and new components. Here are some pics. The master volym is disconnected it whas there the prescence control was meant to be.
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