Squeezebox Duet
First we'll start with the external psu, supplied with the Duet comes a cheap plug in SMPS , I decided to try a well filtered linear based PSU using LM1086 to see if it offered any performance boost in this particular application, I found it slightly improved SPDIF and analogue output, because I felt the move from SMPS to linear improved performance I decided to go a little further.
Apart from Paul Hynes I don't know of any other alternative upgraded psu's in the UK for the SB's so I tried one of his PR3 modules, this required a small 12v transformer which I already had , other bits needed like the case, cable etc came from Maplin
Heres the PR3 installed in the Maplin case
If you don't want to go the diy route Paul sells complete Squeezebox and Duet Receiver upgraded psu's called SR1 which can be found here http://www.paulhynesdesign.com/page7.html
So how does the PR3 compare against my diy linear? In all honesty it was noticeably better! What was very interesting is that the Receivers analogue out didn't sound bad at all now! Its quite surprising what influence psu's have on a units performance , I'd say the analogue out was on par with most decent mid priced cdps I've heard where as before with the SMPS it was more like a cheap DVD player
The next stage was some internal mods, the first round is going to be basic stuff easy for most to try if they wish, nothing new here
Heres the standard Duet pcb
First thing was to replace the filter cap on the input DC socket, the standard one is a general purpose SMD type which is probably next to useless especially if using the external SMPS, I replaced it with a Oscon , any low ESR should be ok here, stability using low ESR in this position was fine
The 74HCU04D is part of the SPDIF and XO circuit , its supply comes from the onboard 3v3 switcher used to supply other various bits and bobs, ideally you want a clean supply here so separating the line and giving it its own regulator is worthwhile ,for now I fitted a basic VBE supplying a 3v3 reg, this will be upgraded to something better later (I'll post results) .
I may also try using separate Hex inverters instead of the one shared for XO and SPDIF but the reg mod alone is certainly worthwhile for both analogue and mostly SPDIF out
Instead of butchering the track I lifted the supply leg and ran the new regulator straight to it
Warning, this is fiddly, its very easy to snap off the leg
With reg installed
The Receiver also uses SMD ferrites on both the SPDIF out and analogue out, probably there to help filter possible noise because of the SMPS, A guy called ART posted some interesting measurements on Audiocircle about these ferrites used in the SB3 (only used in the SPDIF output for the SB3) , the SPDIF measured better without it so I also decided to bypass both the SPDIF one and also the pair on the analogue out
What I intend to do later is make use of the internal I2S lines in the Receiver but for now I wanted to see what improvements could be done to both the SPDIF out and the internal dac
The dac is a cheap WM8501 , not exactly state of the art , these don't even require an additional active output stage
Datasheet can be found here http://www.wolfsonmicro.com/uploads/.../en/WM8501.pdf
I next changed the output coupling caps which was a pair of general purpose 10uf SMD's, you can use what you like here as long as theres room in the case, I just used what I had to hand, a pair of Panasonic for audio (metallic blue sleeve) with a Wima film cap strapped across them, I'll faff about comparing alternatives later
Theres a small 5v SMD reg for the WM8501 dac, this would certainly be worth upgrading too if your using the Duets analogue outs, I'll change this later along with decoupling caps and post results.
Theres more to try yet so will update as soon as I can, this will mainly be internal regulation.
I'm currently running in the Receiver but initial impressions are very promising
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Originally Posted by Covenant
