4 4 0 loud hum

[mehfuzhoss]

Hello,

i built an ax84 4 4 0 according to the layout. it is quiet at volume 0. at volume 2 it starts loud hum. as i increase the volume slowly to full, the hum gets worse. i have tried different ac sockets. the hum is not coming from the guitar. the audio was recorded with no guitar plugged in. all preamp and power tubes are secured in place. any suggestions!

[pompeiisneaks]

This looks to me to be a lead dress issue. The wires in the amp are all over the place and extra long. You should run wires directly from where they need to go, to the exact length, and avoid signal wires getting near high voltage and mains. Heaters also need to be kept away from the signal wires. The wiring in the amp seems pretty busy. You can try to isolate the specific wire(s) that are most impactful by getting a wooden chopstick and gently moving wires around to see if the noise worsens or diminishes. Look at some example builds, and see how heater wires are usually run, and how the signal wires are kept very short and the like.

I think if you clean up the lead dress it will go a long ways towards helping with the hum.

~Phil

[pompeiisneaks]

Additionally looking at the amp/board you have the board installed backwards. You ahve the power section of the board on the preamp side and the preamp side on the power end. This is a recipe for disaster. You need to keep all the preamp components on the board near the preamp tubes, and the power amp side near the input etc.

You're going to do better if you basically take that out and flip it end to end even if the components are on the bottom (if that's possible?) Because right now, you're running high power, high current cables past the preamp tubes, and all premap wires from the preamp side to the side with the most noise.

~Phil

[MakerDP]

Yes, as I stated in another thread and as it is clearly stated in the documentation of this amp, proper lead-dress and layout is absolutely critical to the success of this amp. In some lower-gain designs you might be able to get away with that but in this one, no way. The routing of the wires in the build documents at AX84 were done through iterations of trial-and-error to get it just right. They really really need to be followed exactly.

[mehfuzhoss]

now its quiet. lead dressing and the board is re arranged. btw, i used 12ay7 on all three, the amp has very nice clean sound but the distortion doesn't start untill i turn volume to 80%. i guess its because 12ay7 has less gain. thank you.