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Firestone Audio GreenKey Review

post #1 of 4
Thread Starter 

Firestone Audio GreenKey Review

 

Thanks to Firestone Audio for the sample.

 

 

 

First Impressions:  Well the GreenKey looks just like its siblings and comes in the same box.  I still don’t get what the cap is for other than for aesthetic reasons.  Anyway what the green key does I’m rather interested in.  You see when I use my FiiO A1 for witching TV stuff I have to crank the volume rather a bit and I can hear interference.  I’m pretty sure it’s being generated by the computer as in my experience, Dell don’t tend to seem to shield things well.  (Granted I’ve still mostly used Dell’s for other reasons.)  Still the interference is at times annoying and hopefully the GreenKey will solve it.

 

 

 

Eagerly, I pull out the USB plug from the computer and add the GreenKey.  Nothing happens.  No sound.  Okay, well it is then going into a USB hub so maybe it needs to be after that.  Nope.  Okay lets just unplug it and go directly to the computer and the GreenKey.  Success!  But hold on, there is noise, a lot of noise.  Like when you don’t have an input plugged into anything and its picking up static form your fingers.  What?

 

I don’t know what the incompatibility is but the GreenKey does not like my FiiO E7/E9 to A1 set up.  I note that the GreenKey does specify it will not allow high current draw through it so I presume that’s got something to do with it.

 

 

 

Time to give other things a go then.  Since I have sitting next to me the Firestone Audio BlackKey it’s the obvious option.  So I plug it into the GreenKey and then that into an USB extension cable then into the computer.  The output from the BlackKey goes into 3.5mm to phono cable and into the back of the FiiO A1.  Like magic music appears.  Huzza!  Muting the music and cranking the volume there appears to be no digital noise. No cracks and buzzing.  Trying the same set up sans the GreenKey and it returns, woo hoo, clearly the GreenKey is doing something then.  It’s dead silent and I can turn the volume to full before a slight hiss appears.

 

 

 

So it would appear that the GreenKey does what it is supposed to, sometimes anyway.  I think it may be time to rip out all the cables and to start from scratch.  I would really rather it worked with the FiiO setup as it lives permanently on my desk.  So we have a clean start and suddenly seems to be working as they ought to and now I seem to be able to max out the volume with no extraneous noise appearing.  YEY!!!  So the GreenKey does what it says on the tin.  It’s a bit finicky about it but it works and it has to me made a difference. 

 

 

 

Value:  Its available for 59 Euro’s which just now is  £49.  So that seems a fair amount given the cost of things like the rather excellent BlackKey.  It’s really going to depend on what you already use, should you be using a very pricey DAC and find your getting some extraneous noise then the GreenKey may be just what you need to remove it.  If indeed the USB connection is the source of that noise.  £49 is a hell of a lot cheaper than buying a new computer.

 

 

 

Conclusion:  The GreenKey right from the get go is a pretty niche device.  It does what it claims to provide the USB socket is the source of the background noise you want rid of.  If that something that is causing you some real bother then it could be a very worthwhile upgrade for you.  For most people though I suspect it’s not going the best upgrade money spent.  I mean for my own use I rather wanted one to see if it would remove the irritating noise that was audible in my TV watching with the volume turned up high.  In music listening though with its greatly lower dynamic range didn’t need the volume turned up anything like as much and hence was to me inaudible.

 

 

 

Of course if your one of those people who loves upgrading everything and you already have an awesome DAC and amp and you are getting this sort of USB static and interference then it’s a vastly cheaper way to clean up the signal path than a new computer or DAC that might filter  it.  In grander audiophile setups £49 isn’t even new interconnect money and I would personally much sooner but the GreeKey than spend the same on an interconnect.

post #2 of 4

I have just purchased the HiFimeDiy USB Isolator for 29$, it will have the same limitation, as it only provides a 200mA output:

 

Features:
* Signal Isolation 5kV
* Voltage Isolation 3kV
* 200mA power supply from USB bus (no external power supply required)
* Power supply LC filter
* Copper ground
* ADUM4160 Support USB full speed USB 1.1, but not "high speed" USB 2.0

 

Does E7 allow to turn off USB charging like E17 does? Then you may use it while battery lasts.

post #3 of 4

Yeah, USB Isolators in generally are either affordable but limited in one way or another, or capable but quite expensive.

post #4 of 4

I wonder if iFi's iPurifier has the same current limitation...

 

Anyway, I think the key is to have manufacturers build the USB isolation chips (e.g. http://www.ti.com/lsds/ti/interface/digital-isolator-products.page) into the USB-to-SPDIF stage itself effectively galvanically isolating the stage; it's more important that the SPDIF signal is passed cleanly to the DAC chip. This is what Firestone's Custom Cute DAC does, I believe: http://www.imagebam.com/image/4d71dc253147054

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