Squeezebox Duet

[leo]

Behind again

How you going with the Receiver John? did you manage to get it working?

I got itchy fingers last night, after searching about in my stash I found one of those Burson clocks, I removed the onboard cheap oscillator and replaced it with a Guido Tent, supply was tapped into the main Paul Hynes PR3 , its a 5v XO so a 100R resistor was added from the out of the clocks inverter to ground because of the Receivers Xilnix is 3.3v.
The Receivers stock onboard XO was removed and the new clocks output ran straight to the Xilnix

Seriously this made one hell of a difference! everything just locks into place and that bass it trounces the modded Musiland for 44.1 material
Obviously this lash up is not ideal but was mainly as a test and gives me an idea how a better clock affects this unit, i wasn't actually expecting this much of an improvement with the Receiver , this was clearly heard with all three dacs

Amazes me those who claim all spdif sources are the same, I read some total crap on another forum from one of the ex members on here , that guy must have huge amounts of fur growing in his ears

[leo]

What do you think of this reply from Wolfson about how to supply an external 2.5V - I think it's piffle

Hmm, it does seem like piffle doesn't it? so if the Enable pin is disabled it turns the whole device off not just the voltage bias doesn't seem to say that in the datasheet unless I'm missing something

[jkeny]

Behind again

How you going with the Receiver John? did you manage to get it working?

I got itchy fingers last night, after searching about in my stash I found one of those Burson clocks, I removed the onboard cheap oscillator and replaced it with a Guido Tent, supply was tapped into the main Paul Hynes PR3 , its a 5v XO so a 100R resistor was added from the out of the clocks inverter to ground because of the Receivers Xilnix is 3.3v.
The Receivers stock onboard XO was removed and the new clocks output ran straight to the Xilnix

Seriously this made one hell of a difference! everything just locks into place and that bass it trounces the modded Musiland for 44.1 material
Obviously this lash up is not ideal but was mainly as a test and gives me an idea how a better clock affects this unit, i wasn't actually expecting this much of an improvement with the Receiver , this was clearly heard with all three dacs

Amazes me those who claim all spdif sources are the same, I read some total crap on another forum from one of the ex members on here , that guy must have huge amounts of fur growing in his ears

Great Leo, I have found exactly the same sound with my modded hiFace (clean PS to on-board low-jitter clocks) - the bass is deep, tight, musical & has texture as well as the rest of the frequency range just being so much clearer - the sound of low jitter = very good analogue

[jkeny]

Hmm, it does seem like piffle doesn't it? so if the Enable pin is disabled it turns the whole device off not just the voltage bias doesn't seem to say that in the datasheet unless I'm missing something

Yes, that's what I thought! The communication with Wolfson has gone dark - no reply to my last email which questioned what he said above & asked him to explain exactly how an external 2.5V could be provided to the VMID pin - hopefully he's off checking with colleagues

[leo]

Yes, that's what I thought! The communication with Wolfson has gone dark - no reply to my last email which questioned what he said above & asked him to explain exactly how an external 2.5V could be provided to the VMID pin - hopefully he's off checking with colleagues

I'd have thought it would be in their interest to help you mainly because people like us diyers post results and opinions on the net which works out in their favour especially if your happy with the performance.

Anyway keep at em John nobody is going to know more than their own engineers, if they don't want folks like us hassling, the online datasheets should be more detailed

[jkeny]

Here's a application note on the use of external supply to VMID (sent to me by Wolfson)

Edit: Sorry, i see that the PDF didn't upload - zipped it

So here's what it says:

The WM8501 is designed to generate an internal VMID reference voltage however due to the internal architecture of the device any voltage applied to the VMID pin will be accepted as the internal reference of the device. Figure 3a and 3b show the connections to the external supplies required for DC and AC voltage supplies to the VMID pin of the WM8501.

OK, so it seems to say that the DAC chip will turn off the internally generated 2.5V when an external supply is connected - fine! Why the mention of an AC supply connection to VMID?

[Dan Giovanni]

The internal reference won't be so much turned off as over-ridden. It used to be pretty common to provide external references to some DAC chips to improve performance.

I'm scratching my head why an AC signal would be used though - obviously it will modulate the output of the DAC. Perhaps there's some non-hifi application for it.

[jkeny]

The internal reference won't be so much turned off as over-ridden. It used to be pretty common to provide external references to some DAC chips to improve performance.

Improving performance is exactly the object here! Surely though the internal generation of 2.5V on VMID pin has to be turned off in order to feed an external 2.5V supply into this pin? if there still is 2.5V being generated internally then external supply is meaningless, no?

I suppose one way of testing this would be to provide a 2V external supply & measure the voltage on VMID. If still 2.5V then internal supply is on & not over-ridden.

I'm scratching my head why an AC signal would be used though - obviously it will modulate the output of the DAC. Perhaps there's some non-hifi application for it.

I agree, the more info I get the more I'm confused

[Dan Giovanni]

Surely though the internal generation of 2.5V on VMID pin has to be turned off in order to feed an external 2.5V supply into this pin? if there still is 2.5V being generated internally then external supply is meaningless, no?

The internal reference is formed using a potential divider - two resistors between another voltage supply. Hence it is a high impedance point. Supplying a low impedance Vref will "take charge" of this node.

In other news .... found this kit for USB isolation:

http://www.circuitsathome.com/produc...usb-interfaces

Thought you might be interested - I am! Someone has already used it with a USB DAC and claimed it improves sound quality ....

[jkeny]

The internal reference is formed using a potential divider - two resistors between another voltage supply. Hence it is a high impedance point. Supplying a low impedance Vref will "take charge" of this node.

Cool, thanks - I just needed an explanation that makes sense (I don't have the E'ee background to work it out myself Now any idea why they would also show the possibility of an AC supply feeding VMID - what possible use could it serve?

In other news .... found this kit for USB isolation:

http://www.circuitsathome.com/produc...usb-interfaces

Thought you might be interested - I am! Someone has already used it with a USB DAC and claimed it improves sound quality ....

Sorry, but it won't work on hi-speed USB2 - 480Mbps which is what the HiFace (& Musiland use)!