'64 Vox AC-30/6 with Top Boost add-on
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'64 Vox AC-30/6 with Top Boost add-on
I just put together this top boost add-on for my '64 AC-30/6, it sounds awesome but there is a bit of increased hum and noise, I assume it is to be expected with an extra gain stage, but maybe there's a better way. I tried to keep all leads as short as possible, both in and out from the module are shielded on the pot side.
Should have I placed the 33uF el. cap on the chassis, next to the dual 8uF, sharing the same ground like on the original Vox instructions? What can I do to improve the signal/noise ratio? And yes, I am getting correct knobs next week.
Should have I placed the 33uF el. cap on the chassis, next to the dual 8uF, sharing the same ground like on the original Vox instructions? What can I do to improve the signal/noise ratio? And yes, I am getting correct knobs next week.
Re: '64 Vox AC-30/6 with Top Boost add-on
I suggest that you lift the cathode bypass off the tb common cathode stage and re-assess. With it in place, there’s too much gain, which raises the noise floor and makes the other nasties apparent.
My band:- http://www.youtube.com/user/RedwingBand
Re: '64 Vox AC-30/6 with Top Boost add-on
Your hum, no doubt, comes from your multiple ground points. I see the middle lug of your three-position standoff is grounded to the chassis, and at least two wires are grounded there: red and brown. That same brown wire appears to be grounded to the main strip board, true?
Where are the new 12AX7's cathodes grounded?
Where are the new 12AX7's cathodes grounded?
I build and repair tube amps. http://amps.monkeymatic.com
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Re: '64 Vox AC-30/6 with Top Boost add-on
You mean the 25uF cap (22uF, that’s what I had) on the TB unit?
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Re: '64 Vox AC-30/6 with Top Boost add-on
Everything on the TB unit is grounded on the middle lug of the strip there, and a wire connects that strip to the ground star next to v1 on the chassis (to a short wire coming out of it, there's no room anymore). The TB unit is also in contact with the chassis where it is fastened: could that create a ground loop?xtian wrote: ↑Fri Feb 05, 2021 12:16 am Your hum, no doubt, comes from your multiple ground points. I see the middle lug of your three-position standoff is grounded to the chassis, and at least two wires are grounded there: red and brown. That same brown wire appears to be grounded to the main strip board, true?
Where are the new 12AX7's cathodes grounded?
Re: '64 Vox AC-30/6 with Top Boost add-on
YesLaurent Brondel wrote: ↑Fri Feb 05, 2021 11:17 amYou mean the 25uF cap (22uF, that’s what I had) on the TB unit?
To avoid a hum loop, it’s better to leave the mounting tag unused; obviously that will increment the numbers of tags necessary.Laurent Brondel wrote: ↑Fri Feb 05, 2021 11:22 am...Everything on the TB unit is grounded on the middle lug of the strip there, and a wire connects that strip to the ground star next to v1 on the chassis...
My band:- http://www.youtube.com/user/RedwingBand
Re: '64 Vox AC-30/6 with Top Boost add-on
Yes, that is exactly a ground loop.Laurent Brondel wrote: ↑Fri Feb 05, 2021 11:22 amEverything on the TB unit is grounded on the middle lug of the strip there, and a wire connects that strip to the ground star next to v1 on the chassis (to a short wire coming out of it, there's no room anymore). The TB unit is also in contact with the chassis where it is fastened: could that create a ground loop?
I build and repair tube amps. http://amps.monkeymatic.com
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Re: '64 Vox AC-30/6 with Top Boost add-on
Thank you for the responses, I removed the bypass cap and wire going to ground on the chassis and it helped a good bit with the noise.
Now the TB is grounded solely from its bracket to the chassis, is that OK?
Now the TB is grounded solely from its bracket to the chassis, is that OK?
Re: '64 Vox AC-30/6 with Top Boost add-on
If it works then it works. And I guess many originals got done that way.
But personally I’d fit a 4way tagstrip try to control the 0V return path by using a dedicated wire.
But personally I’d fit a 4way tagstrip try to control the 0V return path by using a dedicated wire.
My band:- http://www.youtube.com/user/RedwingBand
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