What's the best sound we can expect from internal amp?

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SimonH
Posts: 19
Joined: Sat Nov 12, 2011 10:41 pm

What's the best sound we can expect from internal amp?

Post by SimonH » Tue Jul 31, 2012 1:27 pm

Hi

I thought I posted something about speakers for the Joggler a good while back but can't find it now...

I have one of my Jogglers in the kitchen and would like to listen to speech radio (R4) on it mostly but the internal speakers are too tinny. What I would like to do, ideally, is connect an external speaker: either 1 or 2 way - mono would do.

The Joggler sound output according to the wiki and elsewhere appears to be provided by a STAC9202 chip (http://www.idt.com/products/audio-produ ... udio-codec). This has outputs for headphones and line out. Looking at the data sheet (http://www.idt.com/document/stac9202-da ... 92hd81-sta) p13 I think the headphone power output might be 50 mW peak per channel which doesn't sound enough for speakers.

So, basic questions:
1) The headphone output is presumably connected to the 3.5mm socket. Is the headphone output connected directly to the built-in speakers, or does the Joggler have some sort of other audio amp?
2) Has anyone found a good passive external speaker? Or am barking up the wrong tree here?!

Note: I could use powered 2-way PC speakers of course but I want to leave the Joggler on all the time and don't want (well, SWMBO won't want!) the extra wall wart, cables etc. I see Richer Sounds have some discontinued MINX10 speakers (8 ohm, 85 dB sensitity) for £30 (http://www.richersounds.com/product/boo ... -min10-blk) which I suspect would be wild overkill, but my Squeezebox Radio manages a fair sound from a 7.6cm woofer and it would be great to get something even half as good from the Joggler.

TIA!

Simon
SB Radio 7.7.2, SqueezePlayOS v1.09(SP v1.53) on O2 Joggler, SB Touch/Quad 606/Heybrook .5
LMS 7.7.2-r33893 on Syno DS213+ NAS. ~4000 tracks & mostly listen to BBC.
Prev: 7.6.1 SSODS(thanks flip!) on LS-XHL; 7.6 on Joggler/Ubuntu; 7.3.3 on LS-GL

SimonH
Posts: 19
Joined: Sat Nov 12, 2011 10:41 pm

Re: What's the best sound we can expect from internal amp?

Post by SimonH » Tue Jul 31, 2012 9:01 pm

Well, regarding headphone vs line-out http://techtalk.parts-express.com/showt ... difference suggests:
Line level outputs typically have a source impedance of 50 to a few hundred ohms. They are intended to drive loads that have a high input impedance, usually greater than 5k ohms. They are typically optimized for very low noise and low distortion when used with high impedance loads.

Headphone outputs typically have a source impedance less than a hundred ohms and the better ones have a source impedance of a few ohms or less. They are intended to drive the lower impedances presented by headphones which typically range from 16 ohms to 300 ohms. They are optimized for being able to drive higher current and for delivering reasonable distortion and noise with low impedance loads.
...
Headphone outputs can be used to drive line level loads and can provide good noise and distortion performance but are typically not as good as line level outputs.
This evening I've done a quick test by connecting one of the headphone channels to the passive speaker from a Creative Gigaworks T20 pair - these are 2 way, rated 14w per channel (when driven by the amp in the other speaker) and claimed response of 50Hz - 20kHz (the woofer is about 7cm I think) but I don't know their sensitivity. I'm running the excellent Squeezeplay OS and disabled the volume limiting feature (i.e. the OpenPeak one to stop the internal speakers distorting). The sound output was OK and certainly better than the internal speakers - probably fine for speech in a smallish room but the bass was fairly non-existent. This was from one channel of course - might be worth trying to make a stereo to mono circuit to double up the output though I suppose that would have to be active (i.e. more wires etc). :?
SB Radio 7.7.2, SqueezePlayOS v1.09(SP v1.53) on O2 Joggler, SB Touch/Quad 606/Heybrook .5
LMS 7.7.2-r33893 on Syno DS213+ NAS. ~4000 tracks & mostly listen to BBC.
Prev: 7.6.1 SSODS(thanks flip!) on LS-XHL; 7.6 on Joggler/Ubuntu; 7.3.3 on LS-GL

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