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 Post subject: Hum
PostPosted: Thu Sep 28, 2023 1:08 am 
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Joined: Thu Sep 28, 2023 12:14 am
Posts: 5
Hi all! I've had everything stitched together for a while now, and have even used it for a few shows.

However, there's a pretty loud hum that's happening. Here are some notes:
- Trafo wires routed pretty much as in build guide
- Double checked & traced all circuits
- Tested all capacitors
- Hum pot is adjusted for as little hum as possible
- Hum is the same volume regardless of where the volume knobs are
- Hum is non-existent when only the power tubes/rectifier are installed
- Hum appears when the phase inverter (3rd tube) + power section are installed. First two preamp tubes are not installed at this point.

Have ruled out other interference by hearing the same hum in 5 locations.

Has anyone else experienced something similar and can point me where to look?

THANK YOU!


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 Post subject: Re: Hum
PostPosted: Tue Oct 10, 2023 3:27 pm 
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Joined: Thu Sep 28, 2023 12:14 am
Posts: 5
Hello - has anyone covered this ground before or need any more info? Really appreciate the help!


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 Post subject: Re: Hum
PostPosted: Wed Oct 11, 2023 9:52 pm 
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Joined: Wed Oct 11, 2023 9:45 pm
Posts: 1
You may want to check the connections and wiring for these components to see if there are any issues there. Additionally, you could try swapping out the tubes to see if that makes a difference. If you continue to experience the same issue, it may be worth consulting with a professional technician who can offer additional guidance and support.

Immaculate Grid


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 Post subject: Re: Hum
PostPosted: Mon Oct 16, 2023 7:42 pm 
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Joined: Thu Sep 28, 2023 12:14 am
Posts: 5
Ive traced everything point to point, and against ground to ensure I wasn't grounding anything I shouldn't. Also have verified component values along the way, and verified with two sets of tubes.

Even compared it with a friend's triptop he bought secondhand.

Driving me nuts!


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 Post subject: Re: Hum
PostPosted: Sat Oct 28, 2023 7:55 am 
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Joined: Tue Sep 21, 2021 5:45 am
Posts: 6
The first step is to determine if it's 60Hz or 120 Hz hum.

If 60Hz, you may be dealing with a ground loop somewhere in the circuit. Even gear connected outside the amp can be an issue. My HiFi system had a nasty ground loop when I had the pre amp and power amps connected to the same AC power source, all with three prong plugs. Adding cheater plugs (lifting the ground) on the PAs, leaving only the pre amp grounded, cured that issue. Possibly filament AC is getting on to the signal path. Check the way you have your heater / filament wires run.

If 120Hz, you are likely getting AC on B+ coming off the power supply. In that case you will find it is normally a filter or coupling capacitor. Since you say it doesn't happen until you install the PI tube, I'd start in the preamp. You may have a bad coupling cap there. Or it could be that you don't hear the 120Hz hum until the preamp is in the circuit as it is the most sensitive.

Have you tried new tubes?

In either case the best course of action is to get in there with a scope and trace the circuit to find where the noise originates.

I recently had a loud 120Hz hum coming from my HiFi tube pre amp. I knew it was 120Hz because I put a scope on B+ and saw it had a nasty 120Hz riding on it coming off the power supply. This pre has regulated B+ and DC filament voltage. The DC is normally absurdly clean out of the power supply. I tried the filter caps with no luck. It ended up being the lr8n3 regulator. A new regulator fixed it up. We don't have a B+ regulator in our Trip Tops, just trying to illustrate that that going forward, you'd be better off having test equipment in use.


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 Post subject: Re: Hum
PostPosted: Mon Dec 04, 2023 10:49 pm 
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Joined: Thu Sep 28, 2023 12:14 am
Posts: 5
Hey all, wanted to follow up here...

I took it to an amp doctor, turns out it just needed the output jacks mounted with isolating washers. https://www.talkbass.com/threads/b15-ra ... st-5186112

I'm now chasing down tube cage rattles at volume, going to make rubber "feet" with sugru (moldable rubber glue).

The only other rattle I have at volume is the transformers, certain notes just send those flying. The bolts are as tight as they possibly can be, but it doesn't take much. How have others approached this problem?


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 Post subject: Re: Hum
PostPosted: Thu Dec 07, 2023 6:56 pm 
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Joined: Thu Sep 28, 2023 12:14 am
Posts: 5
Figured out a solve for the transformers. The feet had bent been during shipping - I tried to bend them back as best I could but there was still like a micron of space below them, when I'm playing at volume it would rattle, really loud though they were tightened as tight as tight can be. Wound up cutting a 1mm neoprene mat to make pads for mounting. Worked perfectly.

This fliptop is DONE!!! (and sounds great) :happydance:


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