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Old 17th December 2009, 08:58 AM   #141
quan is offline quan  Australia
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Hi guys , just completed my phonostage-measured DC offset at 15/20mV-?any problem?
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Old 17th December 2009, 09:30 AM   #142
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Hello Peter, can you give some information about signal to noise ratio? Did you measure this ?
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Old 17th December 2009, 03:11 PM   #143
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I didn't measure it, but subjectively it's very quiet. You may check this review of the original circuit (I use different parts and completely different PS): H A L L O F F A M E


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Hi guys , just completed my phonostage-measured DC offset at 15/20mV-?any problem?
It shouldn't be a problem if your amp does not amplify DC. The simplified GC does, and coupling cap might be needed with such offset values.

The offset will depend on a particular OPA637 chip; some chips will produce much less offset.
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Old 17th December 2009, 08:49 PM   #144
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Sorry Peter, NOOB-GC?-what output coupling cap will be needed?
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Old 17th December 2009, 09:21 PM   #145
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Check the offset with the amp connected for different volume settings (speaker disconnected when testing). If it exceeds 100mV use 2.2 - 4.7uF coupling caps.
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Old 20th December 2009, 03:00 AM   #146
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Hi Peter, plugged in it today-the transformer humming and vibrating like crazy and feel as though not enough gain( compare with herron audio phonostage-66db)
The tranny was dropped onto the floor the other day!!! Likely to be faulty.
Please advise how to wire with dual secondaries toroidal transformer. NOOB question.
Thanks.
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Old 20th December 2009, 05:17 AM   #147
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I'm using 2 x 12V transformer, which unloaded produce approx 14V AC per secondary.

In attached pic, you can see 4 pads (on a left). Those pads are for external transformer connection: first two from the top are for one secondary, the other two for the other secondary. You will need approx 19V after rectification and 15V regulated. If you can get 15V because of too low voltage on secondaries, settle for lower regulated voltage, it will not affect anything (adjust with changing R7 and R8)
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Old 20th December 2009, 07:22 AM   #148
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Hi peter, do the secondaries need to be in phase?
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Old 20th December 2009, 03:16 PM   #149
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As both positive and negative regulator circuits are completely independent, the secondaries do not need to be in phase; you can also use two separate transformers with single secondaries.
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Old 20th December 2009, 07:13 PM   #150
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Thanks Peter.
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