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 Post subject: First SUT Build
PostPosted: Wed Oct 04, 2017 5:19 am 
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Joined: Tue Jun 21, 2011 1:18 pm
Posts: 850
Location: St. John's, NL, CA
Hey folks,

Recently acquired a DIY step up stransformer. I've solder the connections together. Have not drilled holes in the case work yet, as that may come a little later. But, I have a quick question about grounding. Currently, I have not used a ground connection in the SUT. Instead, I have my arm hooked directly up to the phono ground.

But, the kit includes a ground post and wire. So, I was wondering, do I use the ground pin, solder the ground wire output from the SUT to go from the ground pin on the casework to my phono, and hook my arm up to the ground on the SUT?

If so, does one ground out the negative leads on the output of the transformer as well? To test, I tried just holding the ground wire on to the negative output of the transformer, and just touched the case of my phono with the other hand. Resulting in slightly lower hum. With volume at moderate levels. As is, with just the ground going to the phono, while playing music, there is no audible hum. But, at a moderate level, with no music, there is a slight hum.

Just curious how this should work?

Also, I would imagine the metallic case would act as a connection from the negative RCA to the ground which is attached to the casework directly... Or should I leave well enough alone and have my tonearm ground directly to the phono...

I know, I should try all possible options to see which is the best. But, from your experience has anybody ever had better results with slightly lower hum?


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 Post subject: Re: First SUT Build
PostPosted: Wed Oct 04, 2017 5:31 am 
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Joined: Mon Jun 12, 2006 8:20 am
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Location: London, ON, CA
I use a Bryston TF-1 MC transformer and a Graham Slee Gram Amp 2SE phono preamp with an Ortofon MC20 Super. The Bryston has no ground connection, so I ground the tonearm to the Gram Amp. Try moving the transformer around a bit. You might find a spot that eliminates the hum.

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 Post subject: Re: First SUT Build
PostPosted: Wed Oct 04, 2017 6:01 am 
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Joined: Tue Jun 21, 2011 1:18 pm
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Location: St. John's, NL, CA
Thank you for your reply. I have moved it some. And it does change the hum. When I touch the casework, it seems to change the hum as well. I will most likely try with the ground going to the SUT and just the phono pre as it is now. But, I just wanted to know before I finish everything off, if it's worth going through the hassle, as my amp is kind of in an awkward spot due to wife approval factor! :P


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 Post subject: Re: First SUT Build
PostPosted: Wed Oct 04, 2017 6:43 am 
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Joined: Sun Dec 28, 2008 7:49 am
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Location: Fairport Beach (in Pickering), ON, CA
I don't have any hum problems whatsoever with mine:

Ground everything in the SUT chassis including the transformer shields to the input ground post. The - from the transformer should go to the - at the RCA then to the ground post. The ground post, transformer housing, and RCA's should be isolated from the chassis or try a plastic chassis.

If problems persistent, connect everything as above then connect the input ground to an output side ground post and connect that to your phono pre ground.

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Collecting vintage tube Pilot (Pilotone) HiFi gear.


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 Post subject: Re: First SUT Build
PostPosted: Wed Oct 04, 2017 2:59 pm 
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Joined: Mon Mar 31, 2008 9:17 am
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Location: Toronto, ON, CA
I would install the post, ensuring it's connected to the case, but float the RCA grounds. Daisy chain the ground wire from the deck, through the xformer case to the phono pre. Ground the xformer shield to the case as well. My preference may be due to the pseudo-balanced cables I use which incorporate a floating shield. This keeps audio ground separate from chassis ground, eliminates the possibility of a ground loop and ensures noise intrusion is kept to a minimum.

Don't forget to keep the internal leads short, in twisted pairs.

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 Post subject: Re: First SUT Build
PostPosted: Wed Oct 04, 2017 4:24 pm 
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Joined: Thu Jan 13, 2011 11:29 am
Posts: 425
Location: St.Catharines, ON, CA
Is this of any help.


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 Post subject: Re: First SUT Build
PostPosted: Wed Oct 04, 2017 4:35 pm 
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^ This is exactly how I do it. Notice the cable shield is only connected at the output side, as a floating shield should be.

BTW, pseudo-balanced with a floating shield is quite low capacitance, depending on the type of wire used. The 7 strand silver plated copper I use with the RB250 is only ~50pF total, from tags to RCA for 3ft external leads.

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 Post subject: Re: First SUT Build
PostPosted: Thu Oct 05, 2017 2:27 am 
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Thank you for the info! I'm not sure, but it seems my transformers only have 4 leads? 2 in 2 out? Does the schematic show two sets in and one out? Or, is it two sets, one for each side left and right?


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 Post subject: Re: First SUT Build
PostPosted: Thu Oct 05, 2017 3:16 am 
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Joined: Sun Dec 28, 2008 7:49 am
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Location: Fairport Beach (in Pickering), ON, CA
Here's another schematic. Still has two ratios so pretend you don't see connection 4 or 5. Not all transformers are shielded so ignore the dashed line too.

In summary just look at connection 5 (as +, not switched), 6, 7, 8 and ground as shown or get more complex if you have a hum problem. Cables can also induce hum so be sure to use shielded interconnect cables.


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Collecting vintage tube Pilot (Pilotone) HiFi gear.
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 Post subject: Re: First SUT Build
PostPosted: Thu Oct 05, 2017 5:24 am 
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Joined: Thu Jan 13, 2011 11:29 am
Posts: 425
Location: St.Catharines, ON, CA
And another.
From Sowter.


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