ZXCD1000: Any good?

[theAnonymous1]

There are completed boards for sale on ebay that use this chip. Price is OK, though the off board inductors scare me a bit.

http://cgi.ebay.com/Class-D-digital-...QQcmdZViewItem

[BWRX]

Originally posted by theAnonymous1
though the off board inductors scare me a bit.

The type, location, and wiring of those scare me Not very good at all...

Note that Zetex uses gapped toroids on their demo board in the ZXCD1000 datasheet.

[Gyula]

The Crown I-Tech series prof. amps also use outboard inductors.

[BWRX]

90% of computer users use Windows but that doesn't make it right

Also, the coils in the Crown I Tech amps are huge compared to the ones used in that ebay amp and the I Tech amps are cramped for space!

Page 3 of this brochure shows the insides of an I Tech http://www.crownaudio.com/pdf/amps/137231.pdf

[Gyula]

And what is the correlation between I-Tech and Windows?

[DcibeL]

He's just saying that just because someone else does it doesn't necessarily make it a good idea.

[Gyula]

Yes, but think about n*100 A motor control circuits in power conversion. The motors can't be placed on board, however it works!

[BWRX]

Originally posted by Gyula
Yes, but think about n*100 A motor control circuits in power conversion. The motors can't be placed on board, however it works!

Yes they do work, but that's way out of context. Look at what some reputable class d amps of similar output power use for the output inductors. They generally aren't off board and they aren't simple, cheap ferrite bar core inductors. EMI performance is one of the main driving factors behind inductor choice, and both the type of inductor and the way they were wired/mounted for that ebay amp is pretty poor. You can obviously see that they were looking for the cheapest solution that worked.

[Gyula]

Yes, the FM and PWM spectrum is similar. So if you design the wires for lambda/4 belongs to k*Fs, your broadcast can be received with an FM radio too. And the coupling of the coils can scramble the music on the speakers. So you get an FM broadcast and an analog mixer for one price. The wires should be measured to find out what Zetex was indeed to make this set-up. I think the left side should be sized to k*Fs, and the right side is to (k+1)*Fs for channel separation. An interesting thing could be the realization of a stereo FM.

[BWRX]

Originally posted by Gyula
Yes, the FM and PWM spectrum is similar. So if you design the wires for lambda/4 belongs to k*Fs, your broadcast can be received with an FM radio too.

It works the other way as well. I used some surface mount shielded bobbin coils (they're lifted off the PCB with 8mm lengths of wire used to connect the coil to the circuit) in place of through hole mount toroids on my little class d amps and if I get their position just right and use myself as an antenna I get some faint radio stations coming through my speakers. Not local stuff either, as far as I can tell. One night it sounded like I had intercepted a secret Chinese military broadcast. Crazy stuff