Amp for Acoustic Zen Crescendo 2 ?

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
 

You are correct Al as usual.  

@almarg ,

I have a question for you. The Lyngdorf does use a very small inductor and .47uf cap on the output just before the speaker binding posts. How important do you think the quality, sound wise, of the cap is in this position? Since the entire signal, it is in the signal path, is going through the cap I would think this is not a place to skimp on a $2 cap? 

This assumes ones thinks caps sound different. I do 😁

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

Thanks Al.

Here is why I ask. I mod lots of gear and usually hear differences. I have modified this unit removing those Wima .47uf caps at the output. I replaced them with some decent Jupiter HT caps. I did hear an improvement and that is fine. However, I then decided to add the new Duelund silver foil bypass caps .01uf. Ok, now the improvement is VERY noticeable. So much so I had to ask you this question. The improvement across the board is very obvious and good. Trying to get an objective basis for my subjective experience.

I loved the unit before the mod and now I am smiling even bigger. We read a lot about expectation bias and I wonder sometimes. I felt I was open minded during this mod. Right now am hearing a considerably improved sound. It is very easy to hear the differences, but I have to wonder why the builder did not try and improve on that Wima part. I know it costs etc...I looked inside the unit and that particular part/position just stuck out.

It never ceases to surprise me of the level of sound refinement and improvement that can be had on highly regarded and reviewed gear with just a couple of nice upgrades. Or is it expectation bias? 😕 

I have completed mods that I did not like and many that I have.