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Pass HPA-1, what do we know?
Pass HPA-1, what do we know?
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Old 7th December 2016, 02:24 PM   #31
jam is offline jam  United States
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Hi Dennis,

You could probably get more than 30v peak to peak which is far more than you would need for normal use.

The output impedance in preamp mode is about 50 ohms so it is able to drive fairly long runs of cable. In preamp mode the headphones are disconnected as a safety feature.
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Old 7th December 2016, 02:48 PM   #32
Dennis Hui is offline Dennis Hui  Canada
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Pass HPA-1, what do we know?
Hi Jam,

Thanks for the info. Us greedy boyz are always interested if something can drive an F4.

Cheers,
Dennis
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Old 7th December 2016, 02:59 PM   #33
jam is offline jam  United States
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Just be sure there there is enough gain to drive your speakers.
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Old 21st December 2017, 11:29 AM   #34
JeffYoung is offline JeffYoung  Ireland
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What opamp is used for the servo? The Stereophile article says the Burr Brown OPA2804, but they also talk about the "cascade" so who knows.

I would have thought the OPA2604 more likely?

Cheers,
Jeff.
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Old 21st December 2017, 02:49 PM   #35
wayne is offline wayne  United States
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We only have 2604 in the stock room.
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Old 21st December 2017, 02:58 PM   #36
JeffYoung is offline JeffYoung  Ireland
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He he... you missed your calling as a diplomat.
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Old 11th October 2018, 10:33 AM   #37
JeffYoung is offline JeffYoung  Ireland
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A question for you guys:

If there's a servo to null out the DC offset, then why are the coupling caps needed on the pre-amp out?

Does a servo work differently with a current feedback design? (My go-to book only covers voltage feedback, so I'm a little out of my depth here.) Or is there something else in play on the pre-amp side of things?

Thanks,
Jeff
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Old Yesterday, 03:52 AM   #38
Hikari1 is offline Hikari1  United States
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Quote:
Originally Posted by JeffYoung View Post
A question for you guys:

If there's a servo to null out the DC offset, then why are the coupling caps needed on the pre-amp out?

Does a servo work differently with a current feedback design? (My go-to book only covers voltage feedback, so I'm a little out of my depth here.) Or is there something else in play on the pre-amp side of things?

Thanks,
Jeff
Servo works same for current feedback. Perhaps the preamp amp output is before the heavy biased mosfet output stage...less drive needed for line amp duty than headphones. And since headphone impedances are so low compared to power amp input impedances...servo makes more sense than cap.

Maybe?
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