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Hi everybody,

I just finished a BYOC Tweed Royal. The amp works and sounds fine with two exceptions:

1. There is a humming noise only in single-ended mode regardless if an instrument cable is plugged in or not. The hum is present regardless of whether the channel volume is high or low. There is no unusual or excessive hum in standby-mode or push-pull-mode.

2. The guitar input signal becomes becomes quieter with the cut-knob past 2 o'clock in single-ended AND push-pull-mode. The hum in single-ended mode becomes quieter as well.

Could be something in the power amp section or could there be some grounding issues?

Single ended power supplies do not reject hum as well as push pull sections do. It could have to do with wire layout. You should post photos of your wiring.


This is quite normal. As you turn the cut knob clockwise, more and more feedback from the output section is being introduced and cancelling more and more signal out.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

Maybe you have the start and finish of the SE transformer primary swapped. Pics would help.

The cut knob reduces the negative feedback resistance as you turn it clockwise, which reduces gain. Turning it full turn counter clockwise activates the switch which removes it completely, for infinite resistance, which is maximum gain.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

I was not really aware that a Champ has a kind of a general basic hum problem because of its single-ended construction.

I did some research about the hum of a Champ, but I did not find some evidence about what is an usual or acceptable hum of the Champ and what is an unacceptable hum which requires action to solve a problem. So I can offer two ways for a possible evaluation of the amplifier’s hum level:

First of all, I can describe the noise level of single coil pickups in comparison with the single-ended hum of the Champ mode. I use a Fender Telecaster with Don Mare Hot Bakelite single-coil pickups which have a little higher output on the bridge pickup with 6.7K. When I use the Telecaster one yard in front of the amp, the single coil hum of the bridge pickup with volume on 10 becomes a little louder than the hum from the amp.

Secondly, I measured the sound volume pressure in dB with my mobile phone Samsung s10. I used a tweed cabinet with a WGS G12C-speaker which has a sound pressure level of 99.48 db. So, this speaker has an average loudness.

I measured one yard in front of the speaker in a very quiet environment, no lights or other electronic devices switched on and no guitar cable plugged in the amp inputs:

• Usual sound pressure in my room: 18dB.
• BYOC Tweed Royal in standby-mode: 22dB.
• BYOC Tweed Royal in push-pull 5E3-mode: 52dB.
• BYOC Tweed Royal in single-ended Champ-mode: 56dB.

Do you think this could be the usual hum level of a Champ?

I wasn't saying that you should expect the SE mode to hum more than the PP mode (mine doesn't really do that), I was saying that SE amps can be more susceptible to hum and you should post some photos of your wiring in case we might be able to help with that.

+4dB is a pretty noticeable increase and that's not normal for this circuit. I suspect you may have an issue somewhere.

One question on your testing - did you have the guitar facing the amp one yard away when you measured the dB increases? If you did, wouldn't it make more sense to do that measuring in a normal playing position (i.e. not right in front of the amp)?

_________________
MasterDelayer/Reverbrador/Ampaholic/TopJacker

1. Pics please.

2. Check the orange and blue wires of OT2 to make sure you don't have them flipped around.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

The orange and blue wires of OT2 are not flipped around.

Meanwhile I changed the speaker from the WGS G12C to a Jensen P12Q which has a 5dB-reduced sound pressure level in comparison with the WGS. This reduced the basic hum level a lot (which is no real surprise).

I also have to admit that I did a lot of mods which might be responsible for some hum in single-ended operation. I am preparing a detailed description of the amp in Facebook which includes pictures as well.