Mini report: High fidelity source on a budget. Part 1:
First of all yes it can be done and more importantly you don't need a PhD in theoretical physics or a jet set disposable income. Here's how i did it.
My normal usage is optical out of my late 2013 imac core which contains a 512 gb ssd and a quad core i5. The problem here is that even though it's an isolated source the computer is used for surfing, watching videos and so on. This made me uncomfortable having it directly connected to the HMS. It's still a relatively noisy machine and with ethernet wired in as it's the roon core we have the problem of the optical no longer being fully galvanically isolated due to capacitive coupling. I tried quite hard to find a better solution: one that improves on SQ with the imac having to remain wired in ethernet as roon core and a separate wifi endpoint. Funnily enough removing the ethernet connection eliminates the problem of capacitive coupling but then we have a roon core that's on wifi and amazingly a wired in imac did sound quite a lot better than on wifi as a roon core. I learnt the core communicates bidirectionally with my virgin router and roon endpoint which supplies an internet speed in excess of 200mps. Some very basic experiments (compared to some of the contraptions displayed here). If my imac does optical but needs to be wired in how do we deal with capacitive coupling? Surely optical is the reference so any attempt to improve on it would be in vain.
1) Mac mini optical out roon endpoint-impossible to manage on a daily basis without a monitor but would in theory do optical solving the catch 22 situation i found myself in with the core.
2) Google chromecast all problems solved? Core wired in with CCA emitting optical into HMS on wifi with no issues regarding capacitive coupling. Problem both with stock psu and ifi i power 5v it sounded like schitt. Compared to the core optical out wired or not the CCA presented itself as flat and totally 2D sounding.
3) Ipad air 2019 sounds exactly the same as core optical out. Nice true tone screen but with usb out to HMS no incentive to constantly charge/discharge with no increase in SQ.
4) Imac core usb to HMS no real gain in SQ plus the knowledge knowing the HMS is electrically connected to a mains powered computer.
5) Multi hundred/thousand pound streamers are all mains powered anyway plus out of my reach financially. I'm sure some of them sound excellent though. Pi's and Allo's present too much of a learning curve (Rob also mentioned how microrendu added RF noise) so i'm looking for plug and forget. Usb to optical hi end convertors (DDC's) are not really needed that contain precision femtoclocks as chord dacs and upscalers correct jitter up to 1000 times of magnitudes of error from optical sources. Just when i was about to give up i read about Rob and his excellent results using a simple motorola phone on battery as a perfect usb source. In conjunction with usb galvanic isolation which sounds very improved on usb HMS i had a new avenue to explore and i was reinvigorated. I want perfection on a budget remember. A battery powered source can't be beaten IMHO. Apparently even when a computer does optical out RF or stray currents can affect the ground plane of the dac or HMS as i understand. Another reason for me to search for a new source.
Part 2:
In effect i'm copying Rob. He designed the hardware so he must know the optimal implementations. An iphone/ipad/ipod touch as roon endpoint when using it's own internal dac (inbuilt speakers and headphone) maxes out at 48khz. Anything above that is downsampled. However with an Apple CCK 3 adaptor used with a lightning cable you can do up to 768 khz and DSD 256 with a maximum of 24 bits per sample rate. This means if you upsample in roon you don't get the purple lossless bit perfect signal however if you leave it at 44.1khz untouched and pass it through the apple ipad/iphone/ipod touch you do get a purple light lossless signal path which is bit perfect. You also get MQA to 96khz passing through to the HMS if you so want which the HMS does not need. Even better an ipod touch 32 gb which is basically an iphone with the cellular stripped out sells for £199 and after studying some roon users who had used it as a roon endpoint i clicked and collected one from Argos last Thursday.
Stunning little device but i quickly realised that on wifi i'm getting about 4.5 hours and not the 30-40 hours advertised which is with wifi off. Initial SQ on battery into HMS (using the Apple CCK3 adaptor connects the ipod touch to the HMS via usb) was stunning with stock usb cable. I deleted all but the most important apps, disabled passcode access, set screen to auto lock after 5 minutes (which means it plays with the screen off just totally dark conserving battery life). All notifications off and so on spending two hours studying again and eliminating anything and everything that consumed power so that only roon played nicely.
The roon remote app on the Apple app store clearly lists the ipod touch and took about a minute to load roon remote. The ipod has a lithium ion battery with a size of around 1000mAh and the screen is so small it becomes almost impossible to use your finger to select roon settings. No problem you just select private zone 'off' on the ipod and hey presto now i can control it using my imac as a dedicated audio zone. If it disconnects from roon (due to the screen effectively being turned off) when the music stops just press the home button and tap the roon app and you're reconnected in a few seconds.
The final step was that i needed a portable powerbank with a large capacity of 20,000mAh to give me enough juice to power up the ipod multiple times but one that recharges quickly. I settled on one by Energizer which recharges in just 2.5 hours and has a battery power percentage LED. By starting with a fully charged ipod touch (which gives 4.5 hours wifi and a fully charged powerbank) and rotating the charge/discharge cycles i calculated i can get an amazing 50 hours or so of playtime continuously on wifi on the stripped down ipod. Of course in practice you would never listen for 50 hours non-stop but 12 hours with short breaks is common for me. Incredible. Rob recommended low power sources and AFAIK there are very few transports or sources out there with such low power as with my set up. A low powered laptop on wifi as a roon bridge didn't really offer me much either as i had previously tried a lower end HP laptop bought new dedicated for that purpose which i later sold.
The ipod touch on battery gives three distinct advantages as far as SQ goes. 1) Micro/macro details magnified in the music equating to hearing new sounds in tracks i thought i knew well. 2) Amazing instrument separation and 3) A type of clarity and musicality in the overall presentation of the music which has improved my HMS/TT2 set up by at least 20% in SQ compared to optical from my imac. Finally i have an Anker power port 5 into which the powerbank and ipod touch are plugged into at the end of listening ensuring fully charged devices when i next listen to music. Both devices charge fully then go dormant with the powerport 5. Of course during listening everything is on battery (ipod/powerbank only).
As for audioscience giving the chromecast such high praise i find that hard to understand. Thankyou for reading about my search for a high performance source for HMS on a budget. (Three days straight on this mini project but paying off now though). Total cost £260 for the ipod touch 32GB and the powerbank and a certified usb cable being delivered from Germany as i could not find any in the UK. A new breath of life has found its way into my HMS/TT2 system. I hope other headfier's give this tiny magical minimum fuss source a try and implement it as i've done. Cheers MK.
