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Old 4th September 2004, 06:13 PM   #31
mikeks is offline mikeks  United Kingdom
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Quote:
Originally posted by Bruno Putzeys
....Lower THD figures (-110dB) are readily realised......

You'll forgive me for taking this with a vast pinch of salt...

....at what frequency is this figure quoted?

...and of even greater importance, what was the measurement bandwidth?

.....If the measurement bandwidth was the typical 80KHz used for linear amps., and we assume you mean -110db at 1KHz, then this class-d amp. outperforms the majority of linear class-ab designs...

Even assuming that residual carrier signal at the class-d amp's output did not cause the input stages of of the distortion analyzer to slew limit, this figure is unlikely in the extreme....
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Old 4th September 2004, 07:16 PM   #32
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Mikeks,

Hereby a measurement of a UcD Class-D amplifier with an extra integrator loop. Measurement bandwith was 22kHz.

This is not implemented in a product, but a test to take a look how low we can get the THD......

Regards,

Jan-Peter

www.hypex.nl
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Old 4th September 2004, 08:16 PM   #33
mikeks is offline mikeks  United Kingdom
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A schematic of the class-d amp. to which this performance is attributed would not be remiss....?
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Old 4th September 2004, 08:27 PM   #34
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Quote:
Originally posted by mikeks
You'll forgive me for taking this with a vast pinch of salt...

....at what frequency is this figure quoted?

...and of even greater importance, what was the measurement bandwidth?

.....If the measurement bandwidth was the typical 80KHz used for linear amps., and we assume you mean -110db at 1KHz, then this class-d amp. outperforms the majority of linear class-ab designs...

Even assuming that residual carrier signal at the class-d amp's output did not cause the input stages of of the distortion analyzer to slew limit, this figure is unlikely in the extreme....
This figure was quoted at 1kHz. Measurement BW is 22kHz, but you will recognise that going to 80kHz would make noise dominate the measurement, but not add any further harmonics to the measurement. In fact, for this reason, the 110dB pertained to THD, not THD+N.

Concerning slew-rate limiting on distortion analyser inputs, you will understand that this would require a very large residual.

The AP analyser will analyse at least up to 200kHz full-scale audio signals, The carrier is at 400kHz. It should not elicit any slew rate problems as long as it is better than 6dB suppressed. It is suppressed by better than 40dB.

AP's do potentially have a problem with the presence of a carrier, in that the autoranging circuits base their decisions on the full-bandwidth signal. At low amplitudes the carrier will force an unnecessarily high gain setting, adversely affecting the device's resolution at low signal levels. The AES17 pre-filter used to measure D/A converters (most of which have large outband noise levels causing similar problems) remedies this.

On the AP2 this problem is not overly dramatic. JP's plot was made without the use of an AES17 filter.
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Old 4th September 2004, 08:30 PM   #35
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Quote:
Originally posted by mikeks
A schematic of this class-d amp. to which this performance is attributed would not be remiss....?
You can find the basic "UcD" schematic by looking up the patent application. Add 2 orders of integration. You should not find this hard to do.
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Old 4th September 2004, 09:10 PM   #36
IVX is offline IVX  Russian Federation
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Quote:
You can find the basic "UcD" schematic by looking up the patent application. Add 2 orders of integration. You should not find this hard to do.
Bruno,
however basic UcD is sounding better yet?
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Old 4th September 2004, 10:47 PM   #37
JohnW is offline JohnW  Hong Kong
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mikeks,

You seem to doubt that Class D amps can perform technically if not sonically. I’ve posted FFT’s on the UCD180 thread and others, that show the performance of both my Digital and Analogue Class D designs that are limited by the performance of the AP2 and R&S UPD05 test systems.

I’m in the process of designing a new measurement system that should allow me to measure the full performance of my designs.

John
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Old 13th October 2004, 11:42 AM   #38
skippy is offline skippy  United Kingdom
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Jan-Peter,

You say: "At the moment we have no plans for a SMPS. SMPS are still less reliable as with a traditional toroidel transformer and not to forget the price is much higher."

If this is the case, why do all the 300-500W Class D DVD receivers coming out of China have SMPS? Or are you only considering the case of low-volume home build?

Regards,

Skippy.
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Old 13th October 2004, 11:46 AM   #39
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Skippy,

The volume of this products is >100.000 or even >1.000.000.

I am happy with a traditional transformer...

Regards,

Jan-Peter

www.hypex.nl
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Old 13th October 2004, 12:34 PM   #40
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Quote:
Originally posted by skippy
Jan-Peter,

You say: "At the moment we have no plans for a SMPS. SMPS are still less reliable as with a traditional toroidel transformer and not to forget the price is much higher."

If this is the case, why do all the 300-500W Class D DVD receivers coming out of China have SMPS? Or are you only considering the case of low-volume home build?

Regards,

Skippy.
We've had tons of these over here for analysis. If you run all channels at full power, they shut down within seconds. Some of them will deliver 2 channels of full power for prolonged periods of time, but not all.
Therefore, a 6x50W receiver is not a 300W device, far from it.
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