Build Your Own Clone Message Board

Hello all! I finished my Champlifier build, worked first time and sounds great. However there is a pretty bad 60 hz. hum present that does not change with volume settings. The hum occurs with or without the 12Ax7, it seems to me it originates with the power section not the preamp. I've checked all my ground connections for continuity, everything seems ok. I've read that an artificial center tap may work, but I believe the transformer has a center tap... the green/yellow wire that goes to the chassis ground, right? I've also read that the preamp and power section should have their own separate ground. Would cutting the ground connection between C6 and C7 separate the pre and power grounds and help this issue? Here is a pic. I think my heater wires are ok and are not the problem. I've tried moving wires and poking around with a chop stick when the amp is running, nothing has any effect on this hum. Any thoughts? Btw... I currently have a 5V4 and 6L6 installed (15 watt OT), the hum is present with 5Y3 and 6V6 as well. No change...

a simple try would be to tuck the heater wires up against the chassis .. having them hovering right over the input area of the circuit possibly causing it..... good luck !!!

Here is how I run them...

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Great looking build and nice job troubleshooting so far!

Correct. Sometimes, disconnecting the center tap and adding an artificial tap can improve things, but not always.


This may or may not help, but I have had this clear up ground issues on one two of my builds. After you cut the ground between those 2 caps, you need to run a new wire from the preamp filter cap over to the board ground connection (not the chassis connection) for the 12AX7 25uf cathode bypass cap.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

Thanks Morgan, that's what I was thinking... cut the ground between C6 & C7, then ground C7 to board... but wanted someone to confirm as a possible fix before I tied it.

I tried cutting the ground between C6 & C7, then ran a wire from C7 to 12AX7 25uf cathode bypass cap. No change! I really thought this would help. I'll try the artificial center tap next...

Verify the ground on the 6V6 25u cathode bypass cap. If that is tied to the preamp filter cap ground (now going to the the preamp ground) it should be moved over to the power amp ground with the first filter cap. Also, while you’re rearranging grounds, make sure the volume pot ground is also tied to the pre amp ground.

So, basically, you want power transformer and 6V6 grounds in one spot near the PT; and 12AX7, pot, and input jack grounds in one spot on the other end of the chassis.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

could you put up an audio of the noise? reason i as is i have built four of these amps and i have not had any issue with noise. they are really quiet... even the three that have no metal chassis.. i do get a little 60 hz buzz when i have the led lights that i have inside the enclosure on but its not really too bad... have you tried moving the amp to a different area or on a different power source? that can have a huge impact on noise... also try a ground lift...... good luck !!

So... I grounded power transformer and 6V6 to the chassis at the solder terminal/lock washer on the PT. 12AX7, pot and input jacks grounded together at the other end, the 25uf cap. Same hum, no change. If I try the artificial center tap I have to disconnect the green/yellow wire that is currently grounded at the solder terminal/lock washer on the PT... right?

Correct

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

Thanks for your help Morgan. Disconnected the green/yellow center tap, installed the artificial center tap with 2 100 ohm resistors on the pilot light, tied them together and grounded them at the solder terminal/lock washer with the 6v6 grounds. No change! It's exactly the same. I don't know where to go from here...

did you try anything i suggested? i have built four of these and havnt had an issue.... can you post a short audio ?

here is a video of one the ones i built.... this amp is super quiet even without a chassis..... https://www.youtube.com/watch?v=727lIY0_CUs&t=52s

Okay, let's back up a bit:
- Working Champlifier with a pretty bad 60 hz. hum present that does not change with volume settings.
- The hum occurs with or without the 12Ax7.
- Currently has a 5V4 and 6L6 installed (15 watt OT), the hum is present with 5Y3 and 6V6 as well.

So, we know the tubes are not the issue. You changed the grounding scheme and that did not affect the hum. You tried an artificial center tap and that did not change the hum.

Here are more things you can try:
- like mblemmy said, you can try bending over the heaters and try the amp in a different part of the house.
- How about pulling the 12AX7 and 6V6? Hum still present but not as loud?
- No tubes - hum still present?

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

Hey there TommyD! Just wanted to touch base as I just finished work on someone else’s 5F1 build that had a nasty hum. This one did not match your symptoms exactly, as the hum changed with the volume control. But there may be something here that helps.

First, mostly as an exercise, I went through the same steps you did. I rewired the ground scheme to separate the pre amp grounds - no change. I floated the heater center tap ground to the 6V6 cathode - no change. Then I rewired the heater wires to tuck in the corner of the chassis instead of flying over the top - no change. I’m guessing it wasn’t heater noise.

Next, I started disconnecting components at the input jacks until the hum ceased. When I disconnected the white wire that connects to the two 68K input resistors to the 12AX7, the hum stopped. I pulled the resistors off the board, removed the wiring on each end of them, wired them directly to the input jacks, and ran a shielded cable to the tube socket. At that point, I had a pretty quiet champ. I then replaced the wire from the 12AX7 to the volume control with a shielded cable and had an extremely quiet champ. The shields of each cable are only grounded on one end of each cable.

You might try those last steps. Running the input resistors right off the input jacks made the most difference. Hope this helps!

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

I've run the long wires with shielded cable since i built it and have never had noise issues either. This was gonna be my suggestion. Hope it works!

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i hope you get it figured out,,, i did want to point out one thing, although your build looks perfect with all the straight wires and component leads i can tell you as it relates to the component leads its not a good way to do it.... yeah ,,, lots of folks are doing it and it does look cool and all.... but from a reliability standpoint it is not a good idea at all... let me explain why, as with any material it expands and contracts with temperature changes . when you have component leads that straight it is just a matter of time before you have a failure.. usually a cap. it will not fail at your soldered end it will fail due to constant expansion and contraction on the end of the lead that goes into the component. just some food for thought......... good luck !!!

This is why I glue (RTV) the power filtering caps to the board. "Specially F&T's. Great caps but those leads...

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Everyone likes sausage. Nobody wants to see how it's made.

yes, a silicone base sealant helps with vibration issues to prevent movement but does little to none for expansion and contraction. and with stiff straight leads its just a matter of time before a failure occurs.....