Jubilee 2550 clone - better grounding or hum reduction advice

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bxershrts
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Jubilee 2550 clone - better grounding or hum reduction advice

Post by bxershrts » Fri Oct 19, 2018 1:35 am

I have had a Marshall 2550 for some years now and decided to build a clone and sell the original.

While the clone sounds very similar to the original, it also exhibits many of the same nuances, of which are the same in the Marshall - and I would love to address and resolve them if possible!

Firstly the hum and noise. With all 3 (gain volume and master) set at 1oclock + both amps hum, badly. Its not the house power, as ever room I have gigged at is the same with this amp.

I have heard a few YouTube jubilee clones that are quite, quiet. How was the grounding done to minimize this? I have a ground buss and the preamp section is separate from the power and all come to one ground point. The input is shielded, but the fx loop is not. Could this be a source of big hum @ high gain levels?

The input gain pot is the biggest culprit of deep hum, most likely 60cyl.

Has anyone built one of these and gotten them quiet at high gain and high volume?

Next is the pot taper on the 1 meg push/pull pots. Both amps are the same. The pot had little movement in perceived volume from 0 to 12 o'clock. Is there a different pot value and taper that could have the volume coming up sooner driving the preamp section earlier?

I would really love some advice and wisdom on how to minimize the deep 60cyl hum in this amp and Change all 3 volume pots!

Thanks for your time and wisdom, I am ready to try anything out at the moment.

Stephen

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toner
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Re: Jubilee 2550 clone - better grounding or hum reduction advice

Post by toner » Sat Oct 20, 2018 8:42 pm

Having non-shielded wires on the fx loop can't be good but I doubt that would cause a 60Hz hum.

A member named "SDM" has some Jubilee layouts that may help with your grounding:
https://drive.google.com/drive/folders/ ... GI5bDZtRzg

You could also send him a private message through this site. His name is Steve and he knows more about amps than anyone I've ever talked to. :wink:

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