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schubert 12th March 2012 05:35 PM

Hifidiy clock part value
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I just bought a clock kit pcb from hifidiy - they used to offer kits, but now it's just the pcb. There's an inductor on the board next to the crystal for which no value is specified (see pic and schematic below). Candy at hifidiy, who is usually as helpful as her limited English allows, was no help this time, telling me to check for myself (?!). I installed one of the kits a few years ago (they work really well) but the inductor value wasn't specified on the part. Can anyone through experience or better brains than mine tell me what value I should use here? :confused:
Clock Kit PCB - $5.90 :

TheGimp 12th March 2012 05:51 PM

That is a ferrrite bead inductor.

They are normally specified by impedance (Ohms) at somefrequency (the Steward part kit I have in front of me specifies at 100MHz).

I'd go for a minimum of 50 Ohms, preferably 100. It looks like over 100 ohms may be a tight fit on that board so I suspect something around 50-70 Ohms is what they had in mind.

schubert 12th March 2012 06:07 PM

OK thanks - I'll see what Mouser has. So I assume there's probably some leeway allowable here?

schubert 12th March 2012 06:13 PM

Like this one? It has no value listed - maybe it's not important? It looks like it will fit.

BL01RN1A2A2B Murata EMI Filter Beads, Chokes & Arrays

TheGimp 12th March 2012 07:15 PM

That ought to work. It is specified to have 60 Ohms i mpedance at 100MHz. I had a heck of a time finding the catalog. The one linked at Mouser is for SM chips,not leaded beads.

schubert 12th March 2012 08:08 PM

OK I'll try it - thanks for your help :)

marce 13th March 2012 12:31 PM

Do these clocks have instructions for setting the value of the output resistor or is it one size fits all?
Curious as there is a chnace the line impedance (Zo) will vary depending on the coupling scheme to the PCB, or do they reccomend a specific co-axial cable for connecting the clock to the board.

schubert 13th March 2012 01:31 PM

One size fits all - the board sits on the player's board and is connected with short lengths of wire. At least that's the way I did it - it's only a problem if the clock doesn't fit in the case. Does impedance matching really matter in digital circuits?

TheGimp 13th March 2012 01:49 PM

That depends on the frequency, how far you are going, and what you are driving. You really need to look at the signal with a scope to see if you have ringing, or other distortion.

As a minimum I'd run twisted pair. I would not run it more than 2", and I'd switch to RG 174U (my do-all coax for audio) and scope the waveform.

schubert 13th March 2012 02:25 PM

Well, OK, does ringing/distortion really matter as long as it doesn't change a 1 into a 0 or vice-versa? I was curious because someone measured a bit of overshoot with this clock in another thread, but then said it sounded great. (He did measure it unloaded, however.)

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