I'm working on a NC3015 build. It's all up and working so I've turned my attention to trying to reduce the noise.
The wiring diagram calls for a bus bar that is connected to the back of each pot. My understanding is it is better to have a single ground point for your bus bar. So i disconnected the bus from the pot and have it running from the 16uF cap to the input ground (point A to point B).
I'm wondering if it would be better to have the bus bar terminate at point C, thoughts?
2025-03-31 12_37_11-Window.png
Here's a pic of the actual amp. I've deleted the normal channel so it does look a little different.
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The buss runs from the input jack to the electrolytic cap. One end or the other should be extended to make a ground contact to the chassis. From what I gather, most folks like to ground the input jack end. I like to ground the e-cap end. Drill a hole, run a screw through it. Terminate the ground buss with a ring lug on the screw. Use toothed washers and, of course, a nut. Only one end, not both!
It looks like you have the HT center tap connected to chassis, but the filter cap for that stage is grounded via bus bar at the input. I would pick one or the other. Either ground the cap can to the chassis right at the CT ground point, or connect the CT to the cap can, not chassis, then to the PI cap on the bus bar.
might also want to ground the shorting contact of the tip of one of the output jacks to ground to protect against a no load situation. Probably not as much of a problem with no negative feedback, but still good practice. Make a note on the outside which jack has the shorted tip as the main speaker so you don't wonder why the amp is so quiet when you plug in the wrong one.
Looking at this again, it appears you have the neutral going to the fuse instead of the live. Mojotone diagrams aren't great with these kinda details... It's also a good idea to attach the live side of the fuse holder to the tip instead of the sleeve, so if the fuse holder is sitting open without a fuse and the amp is plugged in, you can't touch the live wire.
Another thing I didn't think to mention, you could "ground" the heater center tap (green/yellow) at the output tube cathodes to elevate it above ground. This can lower hum and might be a bit easier on the cathode follower tube.
maxkracht wrote: ↑Tue Apr 01, 2025 12:07 am
Looking at this again, it appears you have the neutral going to the fuse instead of the live. Mojotone diagrams aren't great with these kinda details... It's also a good idea to attach the live side of the fuse holder to the tip instead of the sleeve, so if the fuse holder is sitting open without a fuse and the amp is plugged in, you can't touch the live wire.
Another thing I didn't think to mention, you could "ground" the heater center tap (green/yellow) at the output tube cathodes to elevate it above ground. This can lower hum and might be a bit easier on the cathode follower tube.
So you're saying connect the green/yellow to pin 3 of the EL84 sockets?
_ej_ wrote: ↑Thu Apr 03, 2025 1:49 pm
So you're saying connect the green/yellow to pin 3 of the EL84 sockets?
Yes, though I would consider this the lowest priority of the things I mentioned.
If there is noise related to your ground scheme, I would suspect the HT centertap (red/yellow) first. It should be connected directly to that cap can one way or another.
_ej_ wrote: ↑Thu Apr 03, 2025 1:49 pm
So you're saying connect the green/yellow to pin 3 of the EL84 sockets?
Yes, though I would consider this the lowest priority of the things I mentioned.
If there is noise related to your ground scheme, I would suspect the HT centertap (red/yellow) first. It should be connected directly to that cap can one way or another.
Meaning I should ground it to the negative leg of the cap instead of the ground lug it's currently on?
Edit: sorry, I saw you explained that earlier. I'll try that. The amp sounds really good but just has a ground hum I'm really hoping I can get rid of.
maxkracht wrote: ↑Thu Apr 03, 2025 2:13 pm
Yes, like explained earlier. If it were mine, I would keep everything about the same, just move the two center tap wires.
Thanks man, I'll try that tonight. I appreciate it.
