You can pair the HDR 165, HDR 175 and HDR 185 headphones to any of the RS 1x5 transmitter. Up to two headphones may be paired to a transmitter.
As for the batteries, each product is supplied with high-quality, low self-discharge rechargeable batteries (AAA size, 1.2V, 820 mAh). And yes, upon a full charge, they can hold their charge for quite awhile.
Good info! Just to clarify, so an HDR 185 can be paired with a TR 175 transmitter and the functions and features are all supported by the controls on the headsets. An HDR 185 paired to TR 165 or 175, would NOT gain the bass boost or virtual surround sound functionality, but would retain its ability to control balance (the L/R buttons on the headset). The other differentiator of the RS 185 is the ALC/MLC feature…
Question on the ALC/MLC feature of the RS 185. From the manual (RS185 | p. 23): "The RS 185 headphone system offers two modes (Automatic Level Control ALC/Manual Level Control MLC) for controlling the input level of analog signals going through the system."
(Sorry if this is fairly newbie/ignorant question) Is this referring to the analog input via the RCA jacks on the back of the TR 185 unit (so not applicable to the digital S/PDIF input, controlled by internal DAC)? In MLC (manual mode), the instructions mentions "Use the MLC rotary knob to manually adjust the audio level." Does that mean this feature requires the TR 185 transmitter to function, as there no such dial on the TR 165/175/195. So an HDR 185 paired with a TR 165/175/195 would lose this functionality? How important is this function, since it's not on the other RS models — is it because the HDR 185 is open design and meant for music appreciation so *may* need finer adjustment of input levels? ALC mode can still function on HDR 185 when paired with a TR transmitter without this *knob*?
EDIT2: Went back to read Jude's CES 2015 Highlights (as suggested by Rosmadi a while back) and his thoughts on the RS 185; there is info about the ALC/MLC feature and that it's only needed for the analog input, if optical input is used it's not needed: "… Though (the RS 185) has an analog input from which one can choose automatic level control or manual level control, I use (as I do with the RS220) the optical digital input, feeding it from the optical output of a Fostex HP-A4 or Fostex HP-A8C. (From its optical input, the level is fixed, with volume only controlled by the headphone controls.)"
If the above case is true then cross-pairing the 175/185 units would yield:
• TR 175 + HDR 175 + HDR 185 = full RS 175 functionality, RS 185 functionality - balance buttons on headset, but MINUS the Manual Level Control, since knob only on TR 185.
• TR 185 + HDR 185 + HDR 175 = full RS 185 functionality, full RS 175 functionality - as all TR 175 buttons (VSS,BB) duplicated on the HDR 175 headset.
Is that the main difference, MLC functionality require TR 185? So if I stick to optical input on a TR 175, it won't be an issue with HDR 185; if using analog, I'd need to adjust the input levels before the signals arrive at the TR 175 transmitter unit.
(EDIT1: I see from marko2410's review images that the batteries are "GP ReCyko" AAA batteries, thank you for helpful review/images!)
On Batteries: Can I replace the factory batteries with eneloop NiMH AAA batteries and they'll charge in the RS 1x5 heaphones while on the cradle as expected? I remember watching a youtube review from 2014 that clearly showed the RS 170 to come with eneloop AAA batteries. I already have a few eneloop AAA NiMH batteries so I assume they will be interchangeable.
Thanks for starting this thread and answering these fairly focused/specific questions.
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EDIT1: Updated battery question after seeing marko2410's review/images. Checked on "GP ReCyko Batteries" saw 2010 review by "NLee the Engineer" on amazon, seems the batteries are of good quality.
EDIT2: Jude's CES 2015 Highlights as suggested by Rosmadi [http://www.head-fi.org/t/751094/head-fi-ces-2015-highlights/120#post_11336889].
There's some info around, but it's all in different places, pardon for editing my post as I find some answers to my questions.