Hum in Chubby Clementine

sweet & juicy SE amp for 1626 Darlings and the 6L6 family

Hum in Chubby Clementine

Postby patrick1962 » Fri Mar 20, 2015 12:34 pm

I have a noticeable hum coming from my chubby clementine and I am not sure how to resolve the issue. I have checked for cold solder joints, probed the wiring to see if that changes the audible hum. I am running the amp with a pair of Fostex 206 horns.
Here are some gut shots, maybe I have missed something.
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Re: Hum in Chubby Clementine

Postby patrick1962 » Fri Mar 20, 2015 3:43 pm

It is definitely a 60 Hertz and the volume control effects the hum. Any ideas as to where to start troubleshooting?
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Re: Hum in Chubby Clementine

Postby miker » Sat Mar 21, 2015 4:58 am

Try a ground connection from the circuit board ground to the chassis ground. I like to ground the speaker negative jacks to the chassis also.

The other usual suspect is the input jack wiring. I can't tell if you are using shielded cable.
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Re: Hum in Chubby Clementine

Postby patrick1962 » Sat Mar 28, 2015 4:06 pm

So where the center tap from the PT is soldered to the PCB, run another ground wire to the chassis?

The input wiring is shielded and the grounding for the input and output, to the board, are at the volume pot.

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Re: Hum in Chubby Clementine

Postby EWBrown » Sat Mar 28, 2015 7:09 pm

I don't see any connection between he PC board's ground and the chassis, so the PC board would be "floating" in reference to the chassis plate.
Take a continuity check between the chassis and the "GND" pad on the PC board. If it reads "open" or a very high resistance, then there is no ground connection between the circuitry and the chassis. That could create a 60 Hz hum issue (not to be confused with 10Hz ripple).
It would need a single point ground (multiple grounding points to the chassis will cause ground loops and hum issues)
I'd use the same point where the black/red center tap lead from the power transformer connects to the board's "Ground" pad.

Do you have the silver "drain" wire connected to the black wire at one end of each the shielded twisted pairs?
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Re: Hum in Chubby Clementine

Postby patrick1962 » Sun Mar 29, 2015 11:44 am

I don't see any connection between he PC board's ground and the chassis, so the PC board would be "floating" in reference to the chassis plate.


The only ground points I have are the earth ground for the IEC and the black/red wire from the PT to the PCB, between J5 and J7. Did I miss where the PCB is supposed to be grounded to the chassis in the instructions?

So I need to run a ground from where the PT is grounded, pin 1, to my top plate to ground the PCB?

Also the silver drain wires are connected to the black wires from the input and output to the board at the volume pot.

On the OPT side I have the white with blue stripe wires soldered together for later use.

Thanks.
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Re: Hum in Chubby Clementine

Postby EWBrown » Sun Mar 29, 2015 1:35 pm

On the OPT side I have the white with blue stripe wires soldered together for later use.


The OPT's blue /white wires are for the ultralinear screen grid connections, they should not be soldered together.
This would create all sorts of "weird" problems...
Separate them, and tape over, or use shrink tubing over the ends of these leads.

Your shielded twisted pair (STP) is good, with the drain soldered to the black wire.

A good convenient grounding point on the board would be either(feedback) J10 or J11, pin 2. Those connect directly to the board's signal ground.
Just connect either one to the chassis plate, that should do the trick. The board mounting screws on either side of V1 ( and very close to J10 / J11) would be a good, direct connection.
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Re: Hum in Chubby Clementine

Postby patrick1962 » Sun Mar 29, 2015 3:27 pm

Grounding at J10 pin 2 resolved the hum issue andseparated the ultralinear wires.

Did I miss the grounding the board to the chassis in the schematic or connection chart, or it is assumed that I would know to do that?
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Re: Hum in Chubby Clementine

Postby Shannon Parks » Wed Apr 08, 2015 6:34 pm

patrick1962 wrote:Did I miss the grounding the board to the chassis in the schematic or connection chart, or it is assumed that I would know to do that?


You didn't miss anything. It's not documented other than here in the forums, and I need to update the docs. Glad you sorted it out.

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