Small passive speakers for kitchen (or other solution)

[AnalogSteph]

Some MR3 measurements are in the "official" MR3 thread.

To complete this saga, the Onkyo T-405X tuner was delivered today. I was most worried about the glaringly obvious scuff in the display window, but thankfully a bit of Polywatch polishing paste and toilet paper (I couldn't find my usual polishing cloth / handkerchief) made quick work of it and removed it almost completely, to the point where other blemishes are more prominent now and may warrant addressing later. (I strongly suspect that the company selling Polywatch / Displex in tiny tubes for several Euros each is making a killing on the stuff, but you can't deny it's good for polishing acrylic.)

The topic of power consumption turns out to be dire as expected.
Standby ca. 7.3 W minimum, after the clock has been set (which the unit can do via RDS even when nominally powered off). Unit gets a bit warm to the touch, plus some faint transformer hum.
Operation ca. 8.8 W maximum. So the <9 W spec is in fact accurate.
Settings seem to be kept at least for a while when power is removed, so that's good.
Output is quite a bit hotter than my Clip+. Sound seems fine fo far, I'd have to do an A/B comparison with my KT-80 using something better than an old piece of wire.

It's quite a neat and nicely-designed unit, but now I am fully aware why the EU standby power regulations are what they are. There was just too much of these kinds of shenanigans going on around the turn of the century.

 

[AnalogSteph]

And now the part that absolutely nobody has been waiting for, the great tuner shootout: Kenwood KT-80 (1980) vs. Onkyo T-905X (1999). Both silver-faced and FM only (only the US version of the Onkyo has AM as well), but one a slimline analog normal-width model featuring a pulse count detector, the other a PLL synthesized micro affair sporting a regular ratio detector and RDS decoding. Both 4-gang tuners with 3 IF filters, neither featuring RF AGC.

They sound really, really similar. Even output levels are almost identical. The T-905X might be a bit leaner in the low end, but that's about it. I don't notice any noteworthy difference in distortion. The T-905X seems to have kept its alignment well - a sign of how mature FM tuner technology was by the late '90s.

Sensitivity wise, there doesn't seem to be much in it. I would have to have a proper antenna switch and all to tell for sure, which I don't. Physical location sems to have a greater effect on reception.

RDS on the Onkyo appears to work quite well and will dutifully display radio text when asked to. There are enough buttons on the unit for it to be fully usable even without a remote (it sports an Onkyo RI system connection for that). You can save a station to obtain the time from when in standby, and it will dutifully do so (along with the weekday) and display the time with dimmed brightness. (The weekday can be displayed when the unit is on.)

Selectivity is similar (neither being a thoroughbred DX machine) but it seems the Onkyo does slight better in 200 kHz separation as well as fending off the local flamethrowers over 400 kHz. You'd think that the Kenwood's combination of 1x 230 kHz GDT (MM) + 2x 180 kHz (MS3) should beat the Onkyo's 2x 280 kHz (MA5) + 1x 150 kHz GDT (MZ2K), but then the second IF amplifier stage in the Kenwood also is an IC limiter-amp and as such may be degrading performance when strong signals are involved.

Desperate times call for desperate measures, so I resorted to the method of listening to each others' LOs. The Kenwood's seems to be exceptionally clean, no hum, no signal modulation, no nothing (maybe not a surprise for an oldschool mechanically-tuned affair). The Onkyo's has some low-level hum and a hint of signal modulation from the currently-received station. Listening on the KT-80, the hum actually turns into a buzz (which is not present as such on my secondary receiver, a Sony ICF-SW7600, though that is a lot noisier), so looks like that's getting into the audio somewhere. I never noticed because volume is really cranked at this point, i.e. near max on low gain on my Atom Amp+ with HD600s... possibly 30-40 dB above normal.

In the schematic for the FE415-G02 schematic, I noticed that there is a higher than average 10k resistor feeding the tuning voltage to the FM LO, where in other models I've already seen 4.7k, 2.7k or even a 2.2 µH inductor. Mind you, noise level didn't strike me as problematic either way, and 10k had been good enough for a number of other tuners using the same LM7001 PLL synthesizer with the FD636U12 5-gang frontend (e.g. T-4670/4700, T-4670/4500, T-4850/407). The LM7001(J) is common as dirt in '90s tuners.

Overall, the Onkyo T-405X is a proper little tuner. The only thing I wish it was was a proper off switch. With the Euro spec model being a 4-gang tuner with 3 IF filters it would have some modding potential if you're after DX, I'm sure, but there's probably better candidates in terms of basic, inexpensive tuners to mod that are easier to work on (like maybe a T-4210R or T-4211, which already sport RF AGC; even the T-4310R with its 4 filters and IF bandwidth switching is not at all expensive). Either way it has rekindled my interest in tuners, and I might get another silved-faced model for the bedside table. The local radio landscape at night seems to have gotten pretty depressing though.

PS: Regarding the transformer hum - it seems to be majorly amplified by the case. It's hardly audible with the lid off, and none of the screws holding the transformer or transformer holder are loose in any way. That's thin sheet metal for ya, I guess. I may tap into my stock of bitumen mat. (And the T-405TX was even lighter?!) The transformer itself is a cute EI core job that doesn't look oversized one bit, which kind of is what you'd expect.

I've taken some "nudes" of the insides (will be posted in the teardown forum once developed, meanwhile you can get an impression of the Japanese model here). Not much going on in there. As small as the unit is, the PCB doesn't even fill it completely, close to 1/3 of real estate remaining empty. The frontend is quite tiny and standing up. There are some holes in the side wall to facilitate alignment, it still doesn't strike me as easy though.

 

[kurajber]