Hi folks , I recently built a Guitar amp and it sounds freaking amazeing but yesterday I started getting a Bad intermitant feedback problem .....
What happens is that it sounds Just fine and is dead quiet when not playing any notes but then suddenly i get a loud hum and unyielding feedback and after a few minutes it goes away and sounds awesome again but it comes back eventually....
The amp is a "PAIA Stack In a Box " Tube preamp kit , with a 15 band eq after it going into a TDA7293 Chip ....
here"s the schematic for the preamp ....
http://www.paia.com/prodimages/siabsch.pdf
Does it sound like a Bad Tube or something ?? The tube only has about 25 hours on it .....
any help would be great .....
Thanx
What happens is that it sounds Just fine and is dead quiet when not playing any notes but then suddenly i get a loud hum and unyielding feedback and after a few minutes it goes away and sounds awesome again but it comes back eventually....
The amp is a "PAIA Stack In a Box " Tube preamp kit , with a 15 band eq after it going into a TDA7293 Chip ....
here"s the schematic for the preamp ....
http://www.paia.com/prodimages/siabsch.pdf
Does it sound like a Bad Tube or something ?? The tube only has about 25 hours on it .....
any help would be great .....
Thanx
I don"t think it is 2 hot , the chassis is quite large with lots of ventilation and the Tube only runs off of a 45v Plate voltage and the TDA7293 Chip is on a 8in x 8in x 2in Heatsink and barely even gets above ambient temp ......
There is no feedback with the Volume on the guitar off but there is a lot more hum than usual .....
What I am suspecting is because the Plate voltage is created useing a Cmos hex inverter as a charge pump that maybe the Plate Voltage is suddenly droping which causeing the 12ax7 to overload a lot more than usual which is causeing the feedback .....
Maybe there is a Bad cap in the charge pump which is causeing the Voltage to drop ..... ??
I wonder if I can use the +/-42v DC that goes to the TDA7293 to power the Plate ?? that way I can get 84v for the Plate and get more headroom and gain ....
Thanx
There is no feedback with the Volume on the guitar off but there is a lot more hum than usual .....
What I am suspecting is because the Plate voltage is created useing a Cmos hex inverter as a charge pump that maybe the Plate Voltage is suddenly droping which causeing the 12ax7 to overload a lot more than usual which is causeing the feedback .....
Maybe there is a Bad cap in the charge pump which is causeing the Voltage to drop ..... ??
I wonder if I can use the +/-42v DC that goes to the TDA7293 to power the Plate ?? that way I can get 84v for the Plate and get more headroom and gain ....
Thanx
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