Author Topic: Is the Phatbox DAC fully utilitized  (Read 12637 times)

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Offline A543

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Is the Phatbox DAC fully utilitized
« on: March 09, 2005, 12:59:56 am »
Just wondering if anyone know about this.
I read on the official forums that Phatnoise controls the audio's analog output voltage by how hard it drives the DACs or something like that.  It sounds to me like they might resample or digitally adjust the volume, to achieve the required output voltage for whatever head unit is attached.
Anyone know?

Offline rpm

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Re: Is the Phatbox DAC fully utilitized
« Reply #1 on: March 29, 2005, 12:54:11 am »
Yes, part of the DAC init is always volume level.  We adjust it to match the volume level of the CD-Changer we are emulating.

Most of the firmware's match their CD-Changer at around 80%-95% of our max volume.  Our op-amps and RCA outputs will not "clip" even at max volume, but most head units will "clip" if you are too much louder than the expected CD-Changer input.

Kenwood is set to 251 (out of 255 max).  At this volume, the peak-to-peak of a full scale signwave should be very, very close to that of an external Kenwood CD-Changer.

Offline EuroDriver

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Re: Is the Phatbox DAC fully utilitized
« Reply #2 on: April 21, 2005, 01:46:42 pm »
What is the volume / attenuation level for Audi 7.2 firmware feeding a Concert HU ?

Is the volume attenuation a possible reason for FLAC files sounding not as good as the original CD playing through the OEM Panasonic changer ?

Can this attenuation level be reset to full.  I would then install attenuating resistors to compensate

Thanks in advance for any info

Offline rpm

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Re: Is the Phatbox DAC fully utilitized
« Reply #3 on: April 22, 2005, 12:03:41 am »
VW/Audi (and newer universal PhatBoxes) use a different (better) DAC that has 0=Max volume.  It is set to 5 (which is a 2.5db attenuation).  You cannot change this setting (and you wouldn't want to as a setting of 4 will flatten the tops of a full-scale 1khz tone after it goes through a VW radio).

This attenuation will not hurt sound quality at all!  

A FLAC file should sound very close to an external CD-Changer playing the CD (the internal CD signal doesn't have to go over a 10-foot cable, so it may be cleaner).  The type of DAC and Op-Amp circuit used in each device may make a slight differance, but we use very high-quality products that are usually better than the ones used in most CD-Changers.

« Last Edit: April 22, 2005, 12:06:29 am by rpm »

Offline EuroDriver

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Re: Is the Phatbox DAC fully utilitized
« Reply #4 on: April 22, 2005, 07:08:14 am »
Thanks for the info.  

My Panasonic OEM CD changer is in the trunk where the Phatbox is, so they are running through the same cable to the head unit up front.

I am a bit of a HiFi freak and I can hear the difference between a digital volume control and an analog volume control, even different types of potentiometers !

I have used some Caig Pro Gold contact treatment fluid on the connectors, and it has helped the sound a bit.

Anyway the voice user interface is brilliant - Bravo to the Phatnoise team

How can I get the black face plate off without breaking it.  I need to ditch the heat sink in order to get the Phatbox to fit in the space on a Audi B5 Avant.  The unit is too long to allow one to close the door to the side cubby.

Offline Genesis

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Re: Is the Phatbox DAC fully utilitized
« Reply #5 on: June 04, 2005, 03:29:18 am »
Carefully insert a small jewlers screwdriver under the lip of the plastic front panel on the bottom of the case.  There are two catches, one on each side.

Once you release those, the panel will come off.

Behind the panel are two screws in the same place as they are on the rear of the unit.  Remove those four and the screws on the bottom of the chassis on the outside rail and the internal "guts" comes right out.

I had to do this to get mine to fit in the VW Changer cubby.  VW's idea of mounting it externally in the rear is idiotic, particularly for wagons (which I own) since that's the CARGO area and that makes the cable and unit prone to damage.