DIY Line Out Cable - Works!

@sansafix wrote:
Next release of Fuze firmware will output fixed line level when connect to the Dock.

Hi sansafix

If the firmware is just going to eliminate the ability to control the volume of the dock from the Fuze, my suggestion is to leave it as is.  It’s a nice feature to have and since the signal is being controlled digitally, the end result sound quality will remain the same as it is now, whether we can change the volume or not. 

If the headphone lead from the DAC chip goes to the headphone jack and the lineout lead from the DAC goes to the docking plug, there is no reason to remove the ability to adjust the volume on the dock.  However, from my experience with the Fuze, I don’t believe that is the case.  ‘To simplify the construction,’ and the fact that firmware can alter this feature, leads me to think there is just one lead from the DAC that goes to the volume control and then either to the headphone jack or the docking plug, allowing the Fuze to control the volume of the headphone and the dock. 

This is not a bad thing, however, and my advice to SanDisk is to leave it alone.  Firmware is not going to change the source of the sound or the sound quality.  The Dockable Fuze is a winner just the way it is!  There is no reason to remove the volume feature just to make the Fuze have a fixed line level when connected to a dock.   That would be a downgrade rather than an upgrade.

axon

Message Edited by axon01 on 12-08-2008 08:53 PM

@neutron_bob wrote:

I like aspects of either configuration, as one could tweak the volume while docked.

 

The advantage of fixed becomes apparent when I use the e200v2 on the dock: the volume setting for the headphone is retained, and restored when I pull the device from the dock.  Quite convenient!

 

Bob  :smileyvery-happy:

Hi N_B

I don’t see the advantage of a fixed lineout.   Right now I can leave my headphone setting right where it is, dock the Fuze and get a line level signal for my office stereo, but I also can lower the line level out to the dock should I want to plug a sensitive headphone into it for listening at home.   And should I need to balance the line out level with my other components (which I don’t, it’s as loud as my tuner), I have the ability to, as you said above, tweak the volume while docked.

axon

axon, Now I’m confused! In 2 of your posts you say the headphone out seems cleaner than the dock out and the volume level is near equal. I thought your dock lineout level was low, maybe I misunderstood. So why bother with the dock? Just use a cable on the headphone out since the level is the same and the quality is better or equal and you retain full volume control. The dock also kills FM reception so why bother with it?

The general problem with applying the volume completely digital is the signal to noise ratio of the DAC. For example on a 16 bit DAC with a 16 bit signal the volume setting 25% would require to drop the signals lowest two bits making it in fact a 14 bit signal and so increasing its quantization noise (relative to the full signal).

If I read correctly the Fuze’s DAC has 18 bit, while all audio played has 16 bit. So if you would like to amplify as much as possible in software (digital) without introducing additional noise, then you would do the lower 25% of the amplification by leaving the digital signal untouched and just amplifying it with an analogue circuit. Beyond this point you can do the amplification in software by multiplying the signal with a factor of up to 4 without overflow and without introducing errors bigger than 0.5 digit.

This also relieves the hardware developer mostly of the burden of creating an analogue amplification circuit that is neutral in sound all the way from lowest to highest amplification. You just have to assure that the highest amplification is perfect, then 75% of the volume range is always perfect.

So what seems to happen in the current firmware when line out is activated is that the digital amplification is set to max, while analogue amplification still depends on the volume setting as before.

calv, Thanks for the excellent explanation! I have only dealt with DAC operation on industrial motor control and was not aware of the audio amp workings. What you have presented explains why the Griffin Dock output will increase from the Fuze volume control to about 25 or 30 percent and then sits at that peak with no more increase all the way up. My lineout cable is probably overdriving the pin7 input and that is why I get a noticeable volume increase over the dock. I’m not hearing audio distortion on a Klipsch Promedia (did hear some clicks at times which may be clipping), but it probably is there and would be heard on axon’s DT880s. I’ll drop the voltage feed to pin7 with a resistor instead of a straight jumper.

@14124all wrote:
calv, Thanks for the excellent explanation! I have only dealt with DAC operation on industrial motor control and was not aware of the audio amp workings.

Well, to be honest I have no practical experience with DAC or analogue circuits at all. Its just composed of what I think to have learned at university. Now I’m more of a computer scientist :slight_smile: so someone who actually knows the matter from real experience might correct me in one or the other thing.

@14124all wrote:

axon, Now I’m confused! In 2 of your posts you say the headphone out seems cleaner than the dock out and the volume level is near equal. I thought your dock lineout level was low, maybe I misunderstood. So why bother with the dock? Just use a cable on the headphone out since the level is the same and the quality is better or equal and you retain full volume control. The dock also kills FM reception so why bother with it?

Yeah, that was my point exactly.  Plus, my main use for a line-out would be in the car, so the dock is less than ideal.

@14124all wrote:
calv, Thanks for the excellent explanation! I have only dealt with DAC operation on industrial motor control and was not aware of the audio amp workings. What you have presented explains why the Griffin Dock output will increase from the Fuze volume control to about 25 or 30 percent and then sits at that peak with no more increase all the way up. My lineout cable is probably overdriving the pin7 input and that is why I get a noticeable volume increase over the dock. I’m not hearing audio distortion on a Klipsch Promedia (did hear some clicks at times which may be clipping), but it probably is there and would be heard on axon’s DT880s. I’ll drop the voltage feed to pin7 with a resistor instead of a straight jumper.

Interesting.  What is the voltage you’re getting on the line-out?  Is it the same as whatever you feed pin-7?

Line out is clearly specified as a 700 mv RMS P-P signal.

When you connect to the dock,  it should drive this level and you adjust the volume on your stereo.  When you remove the device from the dock,  the headphone setting is restored.

This is the way it works with the other Sansa Devices,  and docks,  including View… 

There are two different outputs one for Line out and one for Headphone,  but they share the same DAC.  VOlume adjustment is done in the analog domain,  and digital attenuation at lower levels.

So generally speaking,  fixed line out will offer the best SNR signal for your stereo.

Using the Sansa Base station,  you can adjust the gain of the preamp using the remote,  but the line level should be unchanged.

If you want to use a variable output,  you can connect the headphone output directly to your stereo.

Message Edited by sansafix on 12-09-2008 08:55 AM

So will fixed line-out apply to just the Sansa Base Station, or the Griffin Dock as well?

And if someone sells a cable (like the one mentioned in this thread), it might also apply there? (really I wish Sansa would sell that cable; a lot of people want to use these in cars where docking stations are just ridiculous).

I’m glad to hear Sandisk is fixing this, and returning the headphone output to its previous level is icing on the cake! Pretty much everything else in the audio world (besides speakers and headphones) use a specific line-level.

Its really too bad that people outside this forum aren’t all that aware of the features that Sansa has been adding in firmware. I’ve seen vendors promise this for years, but very few follow through.

Fixed line out will apply to all Docks, including the Griffin.

As for the Cable,  you’ll have to make you own.

sansafix, Thank you very much for the info!

skinjob, The voltage applied to pin7 is DC. It is an enabling input which seems to very the audio output based on it’s level. The lineout level is analog AC, so the voltages are not comparable. The Sansa Dock remote probably varies the DC level on pin7 to control output level. The Griffin Dock applies a fixed DC voltage of approx. 1volt to pin7. My original cable jump puts approx. 3volt DC on pin7. It is clear to me now that it is too much and driving the output too hard. The output is louder, but is most likely distorting or clipping. The ideal signal will be with 1volt DC on pin7. I will determine what resistor value to use as a jumper to get the DC voltage down to 1volt from 3volts. This should produce the same level as the Griffin Dock which should be a true 1v p-p AC (.7v p-p rms AC) on the lineout. Sansafix has said that the firmware will set the lineout level as fixed. This is how most lineout devices apply it. If you need a varied output, the headphone out can be used as it is a very clean signal as is even at 100% volume.

The output signal has nothing to do with the voltage on Pin 7.  That just enables the line out.

Message Edited by sansafix on 12-09-2008 10:44 AM

Wow! Than there is more involved. My straight jumped cable increases the output more than the Griffin Dock output. I’ll have to keep digging!

@14124all wrote:

axon, Now I’m confused! In 2 of your posts you say the headphone out seems cleaner than the dock out and the volume level is near equal. I thought your dock lineout level was low, maybe I misunderstood. So why bother with the dock? Just use a cable on the headphone out since the level is the same and the quality is better or equal and you retain full volume control. The dock also kills FM reception so why bother with it?

Hey 1412 

The dock is only for convenience.  I’m basically using the Fuze as a transportable music player that replaces a CD player in my office system.  All I have to do is plug the Fuze into the dock at my office and I’m good to go.  At the end of the day, I lift the Fuze out of the dock and go home.  The dock is just easier, provides a secure place to hold the Fuze while it’s playing and keeps the screen aimed at an effective angle.

When I want to go portable, I use the Clip.

I ran it the other way before the dock came.  1st I had to plug in the AC power connector, then I had to plug in the headphone jack, then I had to set the volume at 100%, and do the reverse at the end of the day.  Couldn’t see the screen, and I had to make sure it was laying on something that wouldn’t scratch the back or fall off the shelf it was on. 

You don’t really need the dock, but it’s so inexpensive, there was no reason not to get one or two… depending on how you want to use it.  :slight_smile:

axon

@sansafix wrote:

Line out is clearly specified as a 700 mv RMS P-P signal.

 

When you connect to the dock,  it should drive this level and you adjust the volume on your stereo.  When you remove the device from the dock,  the headphone setting is restored.

 

This is the way it works with the other Sansa Devices,  and docks,  including View… 

 

There are two different outputs one for Line out and one for Headphone,  but they share the same DAC.  VOlume adjustment is done in the analog domain,  and digital attenuation at lower levels.

 

So generally speaking,  fixed line out will offer the best SNR signal for your stereo.

 

Using the Sansa Base station,  you can adjust the gain of the preamp using the remote,  but the line level should be unchanged.

 

If you want to use a variable output,  you can connect the headphone output directly to your stereo.

Message Edited by sansafix on 12-09-2008 08:55 AM

Hi sansafix

I don’t understand how the volume is adjusted. 

In my Fuze, at 100%, the volume out of the headphone jack = the volume out of the line out dock.

Where is the analog amplification applied and where is the digital attenuation applied?

axon

Digital attenuation is before the DAC.

Each amplifier,  HP or Line out has adjustable Analog gain.

At full scale,  the HP out will be the same level as line out assuming you use the Volume “High” setting.

@sansafix wrote:

The output signal has nothing to do with the voltage on Pin 7.  That just enables the line out.

@14124all wrote:
Wow! Than there is more involved. My straight jumped cable increases the output more than the Griffin Dock output. I’ll have to keep digging!

So what what the heck is going on then?  I assume this means 14124all’s cable is fine “as is” and doesn’t need a resistor.  But, what’s up with the dock then?  I guess the dock must be doing something to reduce the output level coming from the Fuze?  Weird…

In any case, just to be clear, the jumped cable should be supplying the correct line-out voltage and there shouldn’t be any problem with overdriving, right?

This is great info, and its good to be able to get this much technical information on the inner workings of these devices.  Even better to hear that Sandisk is addressing this further for us.  I do, however, have two simple questions:

  1. Would it be possible to enable line-out without requiring voltage to pin 7?  If so, what are the chances Sansa would allow this with a future FW upgrade, and what (if anything) would be their reasons for not doing so?

  2. Why doesn’t SanDisk want to make a cable?  Seems like it would be a great way to make some extra money, as well as increasing sales to people who buy Ipods instead due to the much greater accessory market.  I can understand that they want to sell their docks for home use, but it would be great for cars, as well as for the portability factor.  Seems like they’d be missing out NOT to make a cable, so what are the reasons against them doing this? 

@skinjob wrote:


@sansafix wrote:

The output signal has nothing to do with the voltage on Pin 7.  That just enables the line out.


 


@14124all wrote:
Wow! Than there is more involved. My straight jumped cable increases the output more than the Griffin Dock output. I’ll have to keep digging!


 

So what what the heck is going on then?  I assume this means 14124all’s cable is fine “as is” and doesn’t need a resistor.  But, what’s up with the dock then?  I guess the dock must be doing something to reduce the output level coming from the Fuze?  Weird…

 

In any case, just to be clear, the jumped cable should be supplying the correct line-out voltage and there shouldn’t be any problem with overdriving, right?

That is strange. 

  • Why do we think the dock reduces the volume? 

  • sansafix said the volumes of the lineout and the headphone jack are the same at 100%.

  • The dock and the headphone jack sound the same to me volume at 100%, therefore one might assume that the dock does not reduce the volume below the level of the headphone jack.

  • Why does 1412’s lineout cable increase the volume above the levels produced by the dock and the headphone jack?  How does it do that?

  • And why does the Fuze need two amplifiers to send the exact same signal to either the lineout or the headphone jack?  Especially if only one output is operational at a time.

I  don’t think I understand what’s going on yet.

axon