Grounding Eiclones

a DIY, modified Mullard 5-20 monoblock design

Grounding Eiclones

Postby SDS-PAGE » Tue May 01, 2012 9:47 am

How do you guys ground the board to the chassis? Do you ground J4-3,4, or 5 directly to the chassis? The standoffs are isolated, right?

FYI, I just got done building a stereo Eiclone, e.g. two boards sharing a power transformer. I get an audible buzzing through one of the speakers when hooked up to a CD player. The buzzing seems to follow the input wire from the CD player which suggests that it might be the source. However, I don't get such a buzzing from the CD player when hooked up to other amps using the same cable.

I have the two boards grounded at a single point on the chassis from J1-4 terminals. I also grounded the CT of the PT at the grounding point rather than connected to a board. Could the high current going through the grounding point cause this (I usually ground CTs along with the - term of the first filter cap with input grounds donwstream when I p2p wire)? Should I route the CT to the board?

Thanks for you thoughts,

Min
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Re: Grounding Eiclones

Postby Shannon Parks » Tue May 01, 2012 10:11 am

SDS-PAGE wrote:I have the two boards grounded at a single point on the chassis from J1-4 terminals. I also grounded the CT of the PT at the grounding point rather than connected to a board. Could the high current going through the grounding point cause this (I usually ground CTs along with the - term of the first filter cap with input grounds donwstream when I p2p wire)? Should I route the CT to the board?


Min, do you mean from J4-4 (instead of J1-4?)? Yes, J4-4 to the chassis from each board to a single location on the chassis sounds good. You can hook up your safety ground there, too.

Definitely change your center tap back to J4-5 (direct connect to PCB). That is probably the issue.

Shannon
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Postby SDS-PAGE » Tue May 01, 2012 7:09 pm

Thanks for the tip, Shannon. I did more troubleshooting and it seems that the buzzing seems to be somehow regulated by bias control. Do you see any potential impact on the noise level for using a single power transformer for the bias circuits for two boards? Should any modifications be made?

Thanks,

Min
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Postby Shannon Parks » Wed May 02, 2012 5:05 am

How do you have the power supply implemented? For example, do you have both boards fully stuffed and the power transformer running to both boards? If you have rectifiers in parallel, I think we will definitely have problems and will need to have one board be 'the slave' board. Can you post a pic or sketch?

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Postby SDS-PAGE » Wed May 02, 2012 9:07 am

Yes, I have the board fully stuffed and have the power trans going to both. How would I wire one of the board as a slave?

Thanks,

Min
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Postby Shannon Parks » Wed May 02, 2012 10:21 am

I've never done this before, and this will probably some tweaks but:

Slave Board Mods (with all caps drained)
1) Remove D1,D2, & D3.
2) Run jumper wire from Master at J5-1 to Slave J5-1 (or C9 +, or D1/D2 cathode). (Raw B+ jumper)
3) Run jumper wire from J4-4 Master to J4-4 Slave - this connects their grounds. Maybe solder this wire from the bottom lug to assure we never have a floating voltage. You'll still have the Master jumpered to chassis per your original post, but not the Slave (ground loop would then exist).
4) Remove Slave's R41 & R42. Probably remove the Master's R41 and R42 and use filament center tap instead.
5) Run jumper wire from Master at (C16-/D3 anode/R38 juntion) to Slave (C16-/D3 anode/R38 juntion). (Raw C-)
6) So now your power tranformer won't have the secondary connected to the slave at all.

This all seems like Phase One. So we have all the rectification happening on one board, but the filtering remains as two circuits. I think the bias scheme will handle the doubled current, but keep an eye on it and make sure you have all the range you need, else we need to adjust C18 on the Master.

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