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Old 4th December 2010, 04:10 PM   #61
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nice alternative Kevin ! similar 100$ 47k
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Old 4th December 2010, 04:14 PM   #62
Salas is offline Salas  Greece
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Quote:
Originally Posted by kevinkr View Post
If not common mode it will buzz..
I hope the SUT will appear decently balanced then. Will try that first chance. Is it explainable it loses gain from expected x10 (20dB) in this configuration? I.e. floating cart and primary, grounded secondary feeding single ended phono. Lost 6 dB within experimental error figure. The number is fishy there is a plausible electrical explanation.
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Old 4th December 2010, 07:30 PM   #63
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by Salas View Post
I hope the SUT will appear decently balanced then. Will try that first chance. Is it explainable it loses gain from expected x10 (20dB) in this configuration? I.e. floating cart and primary, grounded secondary feeding single ended phono. Lost 6 dB within experimental error figure. The number is fishy there is a plausible electrical explanation.
Hi Salas,
Yes something is very fishy, grounded primary or not should make no difference, just be sure that the cartridge returns (-) are not common somewhere, but again this would just tend to unbalance things from the standpoint of CMRR and should not result in any change in gain.

I would be very suspicious of any SU transformer whose maker insists must have a ground on the primary side as it is almost impossible to guarantee sufficient symmetry for balanced operation without substantially degrading CMRR. A transformer that was not specifically designed for balanced operation might have substantially more capacitance from winding to core at one end than the other, but even this should not be a significant issue at 50Hz.

A pair of resistors creating a pseudo center tap matched to 0.1% will in an otherwise perfect set up degrade your CMRR to just 60dB, a correctly designed transformer in a "perfectly" balanced set up can do much better than this at 50Hz. (Maybe as much as 30 - 50dB better..)

A lack of capacitive symmetry between the phases may start to degrade CMRR above few kHz or so, but in this application that is not really so important as long as HF response isn't impacted.

Regardless of connection scheme as long as the same taps are used gain should not change.

Are you certain that the cold ends of both windings are completely isolated from each other?
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Last edited by kevinkr; 4th December 2010 at 07:32 PM.
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Old 4th December 2010, 07:47 PM   #64
Salas is offline Salas  Greece
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Kevin:

Will have to investigate soon. Its a double SUT in a common case.
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Old 10th January 2011, 01:44 PM   #65
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I like the look of this as a project. Not sure I have completely got my head around it yet though. Interested in others experiences and difficulties encountered in building this.
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Old 11th January 2011, 10:04 PM   #66
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You will not find more info than from those two builds that my friend Michael made and I presented here. Nobody else made another one till now as far as I know. About the losing some SUT ratio VS nominal, we saw (thanking jackinnj for feedback on his HMN experience and measurements) that a much less secondary resistance Sowter loses some dB (half than mine) but still does, so it must be impedance matching and reflection to secondary/division thing. Wired the other way around it just hummed, so it wasn't wired sub optimal.
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Old 12th January 2011, 03:51 PM   #67
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Quote "so it wasn't wired sub optimal."

Can you explain ?

Do you mean you had hum when earthing the primary ?
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Old 12th January 2011, 05:04 PM   #68
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I meant that it wasn't wired in wrong polarity or something. If it was wrong polarity and the primary was earthed then hum was apparent. It also plays best and louder when seeing 47k secondary load no matter the particular cart can work down to 120 Ohm reflected load. The specific SUT feels better with 47k on its secondary. It has 1.7k secondary resistance and I haven't looked in its pulse behaviour with RC compensation.
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Old 21st January 2011, 03:47 PM   #69
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Quote:
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Went to Mikvous's place today to examine another Itch he made. With my Rev1 changes included.
Salas

Is this the latest version or are there any other mods to this you would care to share? Being a relative novice compared to the wise and esteemed members of this forum I have lots of questions most of which I can solve with a bit of research others I may have to ask if anyone can stomach answering them.
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Old 21st January 2011, 03:52 PM   #70
Salas is offline Salas  Greece
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That is revision 1 and it measured and played better enough. It utilised the SSHV regulator also. There are no further changes done than those posted.
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