Bang and Olufsen Icepower tech support?

[glebert]

Got a reply back from Ashdown, he said that the added caps were done after if left the factory, as neither they nor B&O have done any mods on this module, and that they have had no problems with it at all. He suspects that someone blew the module and did a home repair on it and then had to add the caps to get it stable. There are no schematics available to see if the FETs match up with design, there definitely has been rework around the class D driver chips. His thought is that the module will have to be replaced. I think I may give it a bit of a torture test with a resistive load, and then just use it as a practice amp with an expendable bass cab. I'll be curious to see what kind of power I can get out of it into a resistive load, it has always felt a bit weak-kneed to me.

Thanks for inputs.

[J M Fahey]

Cool.
Please measure it, the old way, which matches "our" PA/Stage use.

I read Class D amp datasheets end to end and most say something like:

"500W RMS 1% distortion" ... cool.

"After 30 seconds 400W RMS"

After 5 minutes it may self turn off for thermal reasons

**Continuous** power available: 275W .

WTF?

As of the disposable speaker: no need to if you add a DC protection board with a relay or at least a TRIAC crowbar , Peavey style, between power module and speaker out terminals.

[glebert]

As an update, I ran this into my space heater load (10 ohm) and was able to maintain 50 vrms clean, maybe 53 at the onset of clipping, so it can put out full amplitude at some load (I haven't gotten around to making a second load to get down to 5 ohm). I ran a few different sine wave freqs and no stability issues or drop in power. I had it at that level for at least 5 minutes. Seems like it will be good enough for my use, as long as I am careful with my load and avoid cheap speakers.

[J M Fahey]

Cheap by itself is not the problem; but weird impedance is.

B&O, Ashdown, all other users are not fools and must have extensively tested the modules with all kinds of reasonable speakers.

Just guessing, but problem seems to be weird impedance, which must trigger all kinds of protections.

In any case, copy the Peavey Triac crowbar, cheap and simple.

Just thinking aloud, but since that is a bridged output amp and the crowbar does not really need reference to ground, I bet you can wire it "floating" across the speaker, so "just one" protects speaker from DC across terminals, no matter where that comes from, including two amplifiers driving it.

[glebert]

Was working on my latest class D bass amp, an Acoustic BN6210, and noticed that there was a small circuit board before the piezo tweeter. I did not verify if the amp module was B&O, but it looked very similar to their 500W Icepower module. I am guessing this board is to keep the class D amp from seeing the impedance of the piezo, which I think looks mostly like a capacitor. The Icepower module does have a capacitive load spec. I hadn't paid much attention to it since it said "purely capacitive" but maybe that means something different in German.

I think this would support Juan's assertion that cheap speakers with multiple piezo tweeters are inappropriate for class D amps. BTW, those speakers have been sent off to the thrift store in hopes of frustrating some garage band's dreams of stardom.

[J M Fahey]

Thanks.
Piezo being capacitive, typically .1 or .22uF and sometimes up to.35uF (depending on piezo disk diameter) and even worse in cheapie multi piezo PA/DJ cabs, I have seen some with 2 "midrange horns" and 5 round Tweeters ... all in parallel, just do the Math, they can make a MESS with Impedance.

Doubly so with Class D amps which even without signal in have a full rail to rail signal out at switching frequency ... anything from 33kHz to 500kHz ...... a perfect storm

So cheapest solution is to add a series resistor, most common value being 47 ohm ... I see 3 of them there plus a toroidal inductor and 2 caps.

If you still have it outside, please add a copper side picture so I try to draw the schematic; if not, donīt worry.

[glebert]

If you still have it outside, please add a copper side picture so I try to draw the schematic; if not, donīt worry.

flipped around horizontal axis, so inductor still towards the left.

[J M Fahey]

Thanks

[glebert]

BTW, the one cap you can see is labeled as .47u the other two are .33u.

[sheepdog]

Hi there - saw this old post looking for info on the Acoustic BN6210 that I have. My one works but makes farting noises so I opened it up. problem is with the power amp which is a class D. See a suspicious Cap that is slightly bulged but wonder if it makes sense to replace since the whole board is very tightly screwed in.
Any experiences? Sorry for highjacking this thread!