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SanDisk Professor
Posts: 682
Registered: ‎04-18-2008

Re: DIY Line Out Cable - Works!


axon01 wrote: 

I'm curious about what you said about the line out. I'm new here and haven't found much information about the nature of the line out on the Fuze.  For instance, why does the line out need 3 volts?


 

The 3 volts is not on the line out itself, but is necessary to enable the line out.  Ordinarilly, the dock would supply the 3 volts on a certain pin.  This tells the Fuze it's connected to a dock and should enable it's line-out and disable it's headphone out.

 

As to the other comments about SQ through the dock, it will be interesting to see how much difference there is between a simple cable with no extra electronics versus the dock where the signal passes through another circuit board.

SanDisk Professor
Posts: 682
Registered: ‎04-18-2008

Re: DIY Line Out Cable - Works!


axon01 wrote:

14124all wrote:

NOTE: There has been much discussion about this not being a true line out signal, which is probably true. A true line out would be unaffected by volume or tone with constant output. It seems to be all we have to work with in the Fuze though. The volume needs to be at about 50% or greater (doesn't really increase much from that point on, like the griffin dock). The signal is noticeably stronger than using the headphone out and is still distortion free.



 

My understanding is that it's a true line-out.  The volume adjustment is applied digitally in the DSP before the analog output stage and the analog signal is not altered in any way.  The voltage on the line-out should be constant.

 

This is quite different from many (all?) ipods where the volume adjustment is applied to the analog signal, causing a variable output and poor sound quality.

 

 

SanDisk Guru
Posts: 5,822
Registered: ‎12-26-2007

Re: DIY Line Out Cable - Works!

Exactly.  The Sansa is doing the modifications in the digital domain, so it's not an old school issue of "more things in the signal path".  The gain of the output is variable, but it's the same device, not an added gain stage or rheostat.

 

Bob  Smiley Wink

SanDisk User
Posts: 49
Registered: ‎12-01-2008

Re: DIY Line Out Cable - Works!


Fifer wrote:

axon01 wrote: 
  • I thought the cleaner signal came out of the headphone jack on the Fuze, which makes sense considering the cheap electronics in the dock and the additional signal path.


The cleanest signal in any system should be the line out as, properly implemented, it is the 'earliest' analogue signal in the chain and thus not impacted by any additional signal path such as the Fuze's headphone amplifier stage. In the Fuze, it should be the signal which feeds the input of the headphone amp stage. The cheap electronics in the dock are irrelevant as they come after the line out stage and it's up to you what standard of electronics you feed it into.


 

I would tend to agree with you, but the Fuze appears to be implemented differently.

 

axon

SanDisk Fanatic
Posts: 363
Registered: ‎08-02-2008

Re: DIY Line Out Cable - Works!

I have to agree with Skinjob and neutron_bob. The Fuze is implementing the line out in it's own way. It should not be a concern about if it is a "true" line out or not. This was probably based on home stereo equipment with a 1volt peak signal. Are car stereos true line out with the 5volt pre-out signals?

The main thing is that there is a high quality, high impedance signal available to drive pre-in inputs harder than the headphone out. If I run the Fuze volume all the way to max, the signal is noticeably lower than with the Griffin Dock or the cable mod. The purpose of this project was to get a signal that is more useable with car stereos and line-in home equipment, as the headphone out does not drive them well. It seems to me that it works quite well without signal degradation, so I am happy with it.

If you are looking for audiophile quality, true to spec line out, you probably should not be using a compressed audio player anyway!

8GB Blue FUZE w/The Original DIY Lineout Cable and AT Button H-Phones Fitted To AT WM5 Headband:All Custom Built
Newbie
Posts: 8
Registered: ‎11-29-2008

Re: DIY Line Out Cable - Works!

Hey,

 

Great work!

 

Just had a thought - wouldn't it be nice to have a line in as well?

 

Pity you would have to muck with the firmware in order to get it to record.

 

Just an idea . . .

 

WR

SanDisk User
Posts: 49
Registered: ‎12-01-2008

Re: DIY Line Out Cable - Works!


Skinjob wrote:

axon01 wrote: 

I'm curious about what you said about the line out. I'm new here and haven't found much information about the nature of the line out on the Fuze.  For instance, why does the line out need 3 volts?


 

The 3 volts is not on the line out itself, but is necessary to enable the line out.  Ordinarily, the dock would supply the 3 volts on a certain pin.  This tells the Fuzz it's connected to a dock and should enable it's liniment and disable it's headphone out.

 

As to the other comments about SQ through the dock, it will be interesting to see how much difference there is between a simple cable with no extra electronics versus the dock where the signal passes through another circuit board.


Hi Skin and Neutron

 

It will also be interesting to compare the signals from a line out cable, a high quality dock and the headphone jack.

 

From what I am beginning to understand, the Fuzz is applying it's amplification (or attenuation), digitally, through the chip, (thank you Neutron).  It makes sense then, that when the dock is deployed, the headphone jack is not, because the signal from the chip is routed to either the jack or the line out. 

 

The fact that you are able to get a signal from either the line out or headphone jack but not both and the position SanDisk placed the headphone jack, (intentionally precluding use while docking), seems to bear out that there are not two amplifiers, as I have read. 

 

The digital concept makes further sense because there is no distortion regardless of the volume level.  The interesting thing is that if Neutron's supposition is correct,  that the gain is being applied digitally by the chip, the exact same signal would be available through the jack or the line out.  This, btw, agrees with what I heard when comparing the Griffin dock to the headphone jack.  The headphone jack, having less to go through, had the cleaner signal. 

 

More digital evidence might be when someone reported that when they used the remote on the sansa dock to change the volume, it did so by changing the volume on the Fuze.

 

axon

SanDisk User
Posts: 49
Registered: ‎12-01-2008

Re: DIY Line Out Cable - Works!

[ Edited ]

14124all wrote:

I have to agree with Skinjob and neutron_bob. The Fuze is implementing the line out in it's own way. It should not be a concern about if it is a "true" line out or not. This was probably based on home stereo equipment with a 1volt peak signal. Are car stereos true line out with the 5volt pre-out signals?

The main thing is that there is a high quality, high impedance signal available to drive pre-in inputs harder than the headphone out. If I run the Fuze volume all the way to max, the signal is noticeably lower than with the Griffin Dock or the cable mod. The purpose of this project was to get a signal that is more useable with car stereos and line-in home equipment, as the headphone out does not drive them well. It seems to me that it works quite well without signal degradation, so I am happy with it.

If you are looking for audiophile quality, true to spec line out, you probably should not be using a compressed audio player anyway!


Hi 14

 

This is really strange.  I don't know why this was not what I found?  Fuze volume set to 100% gave me the same volume from the Griffin dock and the headphone jack.  I used an 18" Zu  Pivot (mini to RCA) to my M^3 and DT880s for the comparison.  

 

axon

 

Edit to add link:  What I used 

Message Edited by axon01 on 12-02-2008 11:29 AM
SanDisk Professor
Posts: 682
Registered: ‎04-18-2008

Re: DIY Line Out Cable - Works!


axon01 wrote:

14124all wrote:

I have to agree with Skinjob and neutron_bob. The Fuze is implementing the line out in it's own way. It should not be a concern about if it is a "true" line out or not. This was probably based on home stereo equipment with a 1volt peak signal. Are car stereos true line out with the 5volt pre-out signals?

The main thing is that there is a high quality, high impedance signal available to drive pre-in inputs harder than the headphone out. If I run the Fuze volume all the way to max, the signal is noticeably lower than with the Griffin Dock or the cable mod. The purpose of this project was to get a signal that is more useable with car stereos and line-in home equipment, as the headphone out does not drive them well. It seems to me that it works quite well without signal degradation, so I am happy with it.

If you are looking for audiophile quality, true to spec line out, you probably should not be using a compressed audio player anyway!


Hi 14

 

This is really strange.  I don't know why this was not what I found?  Fuze volume set to 100% gave me the same volume from the Griffin dock and the headphone jack.  I used an 18" Zu  Pivot (mini to RCA) to my M^3 and DT880s for the comparison.  

 

axon

 

Edit to add link:  What I used 

Message Edited by axon01 on 12-02-2008 11:29 AM

 

Hmm, not sure why you're not hearing a noticable difference.  It's fully expected that a headphone-out connected to a normal line-in will result in a low level.  The difference is usually very obvious.  Is it possible the line device you are plugging into has some kind of auto-sensing jack and is compensating for the headphone input?  A lot of newer devices that were designed with portable gear in mind handle headphone input better than devices designed for traditional home a/v gear.

SanDisk Fanatic
Posts: 363
Registered: ‎08-02-2008

Re: DIY Line Out Cable - Works!

axon01, take a look at the block diagram for the AMS AS3525 SOC. It may answer some of your questions. The system chip has 3 independent audio outputs on chip: headphone amp, line out and speaker amp. All of their inputs are driven by a common signal with the DAC and AGC limiter upstream. Easily manipulated digitally before the DAC output. Note that the line out output does not feed the headphone out input. This may clear up some confusion.

Google for AustriaMicrosystems AS3525 to find the function sheet and block diagram. Sorry, I do not have a URL handy.

8GB Blue FUZE w/The Original DIY Lineout Cable and AT Button H-Phones Fitted To AT WM5 Headband:All Custom Built