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Old 27th July 2002, 05:57 PM   #11
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Location: Switzerland
Dear all

There are some things that I do personally not like about this amp.

1.
It is using an output filter of first order only, leaving all EMC issues to the user (they actually weave any liability in this respect).
I know that nowadays the output filter requirements of class-d amplifiers are usually not regarded as stringent anymore as they were about 10 years ago, allowing the least negative effect on the audio signal itself. But a first-order filter is definitely a NO-NO (apart from active speaker applications that are fully shielded) !!!!!
At least should this one be followed by an RF lowpass (2nd or 4th order) of reasonable cutoff frequency. I am a licensed HAM and can definitely confirm that you need a damnbloodylarge antenna of the correct physical layout to get an RF signal of some 100 kHz into the air. But for this signal's harmonics at a few MHz this looks quite different.
The fact that this amp's air-cored output coil is placed directly on the PCB is also ringing my PCB-layout-related EMC alarmbells !
In their datasheet they are talking of an upper cutoff frequency of 91 kHz into 8 Ohms and below there is a diagram showing an inductance of 80uH for the output filter coil. This is definitely a discrepancy because this filter would give a -3dB cutoff frequency of slightly below 16 kHz (I haven't heard of any serious manufacturer stating a -15 dB cutoff frequency !!!!!!!). I e-mailed them weeks ago regarding this discrepancy and haven't heard of them so far (maybe that says a lot).

2.
The price is quite high for just an ordinary PWM amplifier module !


Apart form that, a THD value of 0.07 % is nothing very famous anymore nowadys, not even for a swithing amplifier, specially when you don't know how it was measured (i.e. HOW was it bandwidth limited ?).

Regards

Charles
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Old 27th July 2002, 06:46 PM   #12
km is offline km
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hi.

eric , i suggest again you let magnus speak for himself (hopefully for the last time) is that a problem for you?

if you want to discuss things that are not written in the postings i suggest that you make a new thread for this , to discuss what you see between the lines goes beyond my capabilities im afraid.

charles i agree with you to a large extent , i did some time ago raise a few questions about lc audio and specs and facts , do you want to have a guess of the outcome?

would an amplifier like this in your opinion be legal to sell at all?

best regards - k madsen - cadaudio.dk
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Old 27th July 2002, 07:08 PM   #13
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Hi km

I think as long as you are honest regarding EMC issues, it is perfectly legal.

But I don't know where all the rave, about something that seems to be nothing more than just a very ordinary PWM amplifier, comes from.

A German HI-FI magazine even called it a digital amplifier. The most common misconception with switching amplifiers is the fact that most people think they were per se digital (and the marketing departments emphazize such things as well because to non-technical people everithing digital seems to be very cool).

Regards

Charles
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Old 27th July 2002, 11:54 PM   #14
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KM, If your product is so good, why don't you send an evaluation copy to Magnus so that he can compare your soloution and the Lc Audio soloution, in his home.
If your product wins then he can post an advert for your product on this forum.
Remember in your first post that you were screaming spam.
Then you "snip from dk.teknik.lyd" but won't translate it for English speakers.
Do you have links to reviews of your product so we can all learn more.

Eric.
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Old 28th July 2002, 04:03 AM   #15
swede is offline swede  Switzerland
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Default Hold your horses!

;=)

Hi all again,

Well, being VERY interested in the PWM technology, I have to apologize I was not aware that km (k madsen) had his own solution. I'm very interested in evaluating/listening to his solution as well.

I was not trying to promote a specific solution (as the LC Audio) when I started this thread. I am so sorry if I offended someone.

Though, I do not think k madsen was not after me in person, I think he got kind of upset that I got such a good impression with a (apearantly) concurrent technology.

I hope to get the opportunity to get to listen to km's solution. But I'm moving to Geneva on tuesday so for me going to Denmark in the next couple of months is not possible. If it would be possible to borrow a piece of km's gear I'd be more than pleased.

As for the translation, here is a decent try:

Quote:
> > Hej,
> > Jag köpte en LC Audio pulse samplifier, som jag håller på att
> > utvärdera.
> > Det vore intressant att höra någon annans värdering av den!
> >
> > Antowo

Jeg har da hørt den engang.. Som forstærker syntes jeg ikke den imponerede..
Men den var en udemærket modtager af AM radio på sine store spoler.. Den
hylede og pev. Så kunne man vippe spolerne lidt og så modtage forskellige
stationer
[Translation]
>> Hi,
>> I bought a LC Audio pulse amplifier, which I'm evaluating.
>> It woult be interresting to hear someone else's evaluation of it!
>>
>> Antowo

I hav heard it once.. As an amplifier I don't find it impressive..
But it was an excellent reciever for AM radio by it's large inductors.. It [hylede og pev. ??? no translation]. If you moved the coils a bit it recieved different stations
[/Translation]

Well, I don't see why this translation would do much to end your confusion.

As I said, I don't favor any solution just because of it's name. I just said that I would most likely buy an evaluation kit from LC Autio, because of the impression I got. I would probably try to get an evaluation kit from km if possible, though my financial status is questionable at the moment.

Hope to hear from you ks.

Best regards,
//magnus
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Old 28th July 2002, 08:15 AM   #16
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Default Commenting on your competition when he is not here?

KM: Your products may be great, but I think you might benefit from a more hands off approach on informing us about how bad your competitors are and/or your opinion of their claims -- be they true or false.

I think it is great that there are several people doing cool things with digital amplification in our part of the world. Sooner or later customers will figure out what products offer the best value. The field of digital amplification is in great motion (but not as great as I would prefer ...) and will likely provide us with excellent products at low prices at some point in the future.

I know that both Tripath and LC audio initially promised true digital amps (from digital source), but neither have managed to deliver on that promise to date (even though Tripath are supposed to be doing something about this soonish). I personally find the Tripath modulation scheme very interesting but that is beside the point.

Good luck with your product developments and sales.

Petter

Reference: lc audio the end and thd
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Old 29th July 2002, 02:02 AM   #17
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Quote:
Originally posted by km
....you for one allready read things "betweeen the lines" in magnus´ posting and read motives in my posting that are shall we say a bit far fetched.
....ps. i think i will limit myself to repplying to things that are in the postings and not "between the lines" , may i suggest that you do the same....
Quote:
Well, being VERY interested in the PWM technology, I have to apologize I was not aware that km (k madsen) had his own solution. I'm very interested in evaluating/listening to his solution as well. Magnus.

Km, SEE, I TOLD YOU SO !.

Eric.

- Still waiting for reviews of your product.
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Old 29th July 2002, 02:43 AM   #18
jleaman is offline jleaman  Belgium
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has any one gotten one of these and have it working

id like to get one my self they look awsome..

Jason
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Old 1st August 2002, 09:03 AM   #19
km is offline km
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hi.

ok to sum it up a bit ;

if lc audio gives correct and honest specs they can sell the zappulse amplifier and kit
(hmm wasnt there something on this subject a little back?)

if magnus is not related to lc audio he can post adds with pictures, link to producer and lots of praise.
(cheap form of advertising if you ask me)

if eric can decide we should have a kind of war/contest bewteeen differend pwm amplifiers and magnus shall be the judge.
(wonder if thats gonna happen)

regards to all - k madsen - cadaudio.dk
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Old 1st August 2002, 07:21 PM   #20
swede is offline swede  Switzerland
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Default Competition

Hi

Quote:
if eric can decide we should have a kind of war/contest bewteeen differend pwm amplifiers and magnus shall be the judge.
(wonder if thats gonna happen)
Well, if there is a cheap way for me to compare different PWM solutions, I'll be more than glad to do so.

//magnus
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