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Old 28th September 2013, 02:48 AM   #41
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Quote:
Originally Posted by sgrossklass View Post
Dynamic range can be shifted downwards as needed. Without this ability, source SNR requirements may become very strict.
Are you referring to an analog pot?

I hear talk about how digital attenuators (like on your computer) remove information from the signal unless they are set at 100%. I'm confused about this (I'm an analog guy from way back) and would appreciate some clarification on this topic, if possible.

Thank you.
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Old 28th September 2013, 12:31 PM   #42
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Quote:
Originally Posted by Fast Eddie D View Post
Are you referring to an analog pot?
All the time.
Quote:
Originally Posted by Fast Eddie D View Post
I hear talk about how digital attenuators (like on your computer) remove information from the signal unless they are set at 100%. I'm confused about this (I'm an analog guy from way back) and would appreciate some clarification on this topic, if possible.
That's a different story, but for one thing, a software-operated volume control does not necessarily mean digital attenuation. It may also control a PGA (programmable gain amplifier) in the analog stage. PGAs essentially are an electronic version of a stepped attenuator with gain-switchable amplifier, employing FETs as switches. I'd say your average onboard or MP3 player codec uses one. Fancy DACs typically rely on digital attenuation instead, as THD and SNR targets are hard to hit otherwise. PGAs allow for dynamic range management as outlined earlier, however, so they may have lower noise floor at low levels (unless their amplifiers are hissy MOS jobs).

If carried out at high enough precision, digital attenuation is absolutely nothing to worry about. A moderate amount usually is undetectable even when done straight in 16 bit, which is hardly ideal. Done in 24 bit or 32-bit float with 24-bit output or proper dithering to 16 bit, it's totally transparent. Obviously this only applies to PCM audio. A digital data stream like AC-3 or DTS audio would be corrupted when treated like that, as many people found out when trying to stream these things to their home theater receiver.

Many problems in digital audio today are related to high, not low levels. Overshoot in lossy codecs, intersample overs, stuff like that. A pinch of digital attenuation may mean that the following playback chain is safely kept out of clipping, without having to rely on graceful intersample over handling. If you are making use of ReplayGain, this usually introduces enough attenuation anyway.
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Old 28th September 2013, 01:45 PM   #43
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Thank you so much for clarifying that for me.
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Old 28th September 2013, 05:50 PM   #44
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@sgrossklass Good info!
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Old 25th April 2014, 10:40 PM   #45
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If anyone is still following this thread what was the DC offset if changing the original values of gain setting resistors to lower values . If someone has already said I apologies . Anyone got a theory about OK DC offset for headphones ? I was hoping 1 to 2 mV would be OK . A commercial headphone chip says absolute maximum 400 uV. One thread on a headphone site recommended something like 47 and 240 R as NJM 4556 has plenty of drive current .
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Old 28th April 2014, 04:16 AM   #46
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About DC offset-
DC offset will cause diaphragm to be slightly displaced "in" or "out" of its normal resting position consequently reducing max. excursions.Anything less than 20mV is acceptable, but if you are using very sensitive low impedance h/p than strive for offsets less than 5mV. Higher impedance/low sensitivity h/p are more immune to DC offsets.

As for gain resistors values I use this for reference(exhaustive details/comments but must read)-
NwAvGuy: Cmoy eBay Headphone Amp (with wrong value gain resistors)

NwAvGuy: Cmoy With Gain (with corrected gain resistors values)

If you are planning to build a simple CMOY, reduce the gain to as low value as possible(2X-4X range). I've achieved offsets < 2mV for JRC4556 based CMOYs.
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Last edited by availlyrics; 28th April 2014 at 04:24 AM.
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Old 28th April 2014, 05:24 AM   #47
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That was my hunch . Thank you .

Nigel
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Old 1st May 2014, 11:02 PM   #48
mr one is offline mr one  Lithuania
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I have this amp, and it lays in a drawer with zero usage i didnt liked it i dont know why
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