Amp for Acoustic Zen Crescendo 2 ?

Hi Bill,

Clever idea trying the 0.01 uf cap in parallel with the 0.47 uf.  That would presumably cause the filtering provided by the cap combo to become more effective at the RF frequencies corresponding to the switching that occurs in the output stage.  As you no doubt realize, as a general rule of thumb a smaller cap such as 0.01 uf will tend to act more purely like a capacitor at RF frequencies than a larger one such as 0.47 uf.

And I see no reason to doubt that the improvements you perceived were real.  Perhaps the reason is that the greater amount of RF garbage that was previously being put out by the amp had been finding its way to some other point in the system, or even some point earlier in the signal path within the same amp, resulting in effects at audible frequencies via intermodulation or AM demodulation or other such effects that can cause inaudible frequencies to have audible consequences.  Although I suppose it's also conceivable that the RF had been directly affecting the speaker's sonics in some manner.

Best regards,
-- Al

Hi Bill,

I’m one who certainly agrees that capacitors can sound different, to a greater or lesser degree depending on the circuit application, of course.

In this case I assume the cap is in parallel with the output, rather than in series, and therefore it may tend to be somewhat less critical than say a coupling cap that is in series with a signal. On the other hand, though, at 20 kHz a 0.47 uf cap would have an impedance of about 17 ohms (while having a proportionately higher impedance at lower frequencies), which means that within the audible frequency range its impedance is not high enough to be considered to be negligible in relation to the impedance the speaker presents to the amp.

So my speculative guess is that an upgrade stands a good chance of being worthwhile, but of course it’s hard to say with any kind of certainty.

Best regards,
-- Al

Wlutke 7-24-2017
I've researched the Lyngdorf and the idea of room correction is appealing.  God knows my room could use it.   On the other hand the idea of sending square waves to the speakers and having them do the smoothing curbs my enthusiasm.  No D/A conversion?  It could be the future.  I'll wait and see for now.

While Lyngdorf's writeups could be interpreted to mean that square waves are being sent to the speakers, I'm pretty certain that is not the case.  If it were the case the 2170's excellent THD numbers would be absurdly poor, not to mention that it would make most speakers decidedly unhappy :-)

Most likely the design uses a combination of an inductor and a capacitor at its output to filter out the high frequency (ultrasonic and RF) content of the pulse width modulated square waves, just as is done in pretty much all other class D amps.  That amounts to converting the square waves to sine waves, or in the case of a music signal, to a combination of sine waves at various frequencies.

Regards,
-- Al