Which chip and whatever happened to Mueta and UCD?

[JohnW]

Hi Sheriff,

I have one of Pauls very first system. This system is just as bad as the AP1 for RF IMD and DR.

My early version (1st?) uses the CS5327 on a National Instruments PC card, maybe his current units have pre-filtering in the external boxs.

I used to use it for Jitter testing, untill I discovered that most Jitter "components" below 100pS where due to ADC IMD products, and not Phase noise. Adding a 20KHz brickwall to the cards input removed about 100pS of Jitter!

John

[Bruno Putzeys]

Originally posted by JohnW
Below is an FFT of a TRUE digital amplifier, 118W 8Ohms 997Hz THD 0.0003% modulator and clock limited. Awtd dynamic range 114.5dB – again modulator limited.
118W 8Ohms 997Hz THD 0.0003% DR 114.5dB

How true is "true"?

There's a dane selling a "digital amplifier" that employs a secondary analogue feedback loop (pedec), which implies the loop considers the buffered "digital" signal as its analogue reference.

"true digital" should mean open loop - no correction of switch timing whatsoever because that would be a non time-discrete action (ie. analogue).

Waiting curiously, because the results surely look excellent (regardless of whether analogue processing was involved or not btw). THD vs frequency plots would be very welcome.

[Bruno Putzeys]

Originally posted by Sheriff
On a different topic to THD, Bruno mentions in an earlier post that UcD with the second integrator loop is unconditionally stable.

From this statement can i assume that it will drive any capacitive or inductive load, and give essentially loudspeaker independant performance?

If you tie a 1uF cap straight to the output without a speaker cable (=series impedance) and subsequently overdrive it you can make it go unstable.

This situation is fairly rare though. You can rest pretty assured the amp is left quite cold by the load.

[Jan-Peter]

Hi to All,

Some measurements at R&D when I am playing with an improvement on the UcD......

Measurement is with 4 Ohm and 8 Ohm load and by 1kHz.

Green is 8 Ohm and yellow is 4 Ohm.

Regards,

Jan-Peter

www.hypex.nl

[JohnW]

I don’t perform THD vs. Frequency sweeps as nothing annoys me more then seeing manufactures publishing THD sweeps to 20KHz with the AES17 filters enabled and the AP in 22KHz analyser Mode!!!

I perform 7.2KHz THD test (2nd & 3rd in audio band), but once again, the results are limited by the front-end reference modulator.

I do have 19KHz and 20KHz IMD results at 120W 8R – but these are limited by the R&S UPD05 having a near death experience. For dual tone IMD tests I cannot use the UPD’s “single frequency” notch filter, so what you see is the true resolution of the UPD’s ADC (i.e. without the benefit of the ~30dB dynamic range gain by using the internal notch filter) – the components you see at lower frequencies are the result of this near death encounter.

Despite this, the 3rd order IMD components of –115dB @ 120W 8ohms put most – if not all amplifiers to shame – the real level of these components could in reality be lower – who knows how much is due to the digitising ADC – and don’t forget that this is a total “replay” system result – ignoring speakers (i.e. no DAC or Pre-amp distortions to add).

In addition, although better then the AP1, the UPD has a real problem with “RF IMD”, unfortunately the UPD internal ADC’s sample at 48KHz, which “beat” with components of the 384KHz PWMFs (8fs).

The Amplifier is “TRUE” digital in the sense that the modulator is digital, continues time correction is applied around the OPS – which is not PEDEC.

John

19KHz and 20KHz IMD results at 120W 8R – once again results are UPD / modulator limited. They are identical to the modulators PWM reference node.

[Jan-Peter]

Again a measurement frequentie against THD in 4 and 8 Ohm with an outputvoltage of 13,5Vrms.

This are some mesaurements to see how shocking low a THD can be with a Class-D amplifier. Please notice this are really pre R&D measurements, where we only used some standard values for the Class-D modulator.......

I am really wondering how good will it be when the right components values are known ;-)

Regards,

Jan-Peter

www.hypex.nl

[Jan-Peter]

Hmm, this must be the picture.....

Regards,

Jan-Peter

[JohnW]

I REST MY CASE

I don’t perform THD vs. Frequency sweeps as nothing annoys me more then seeing manufactures publishing THD sweeps to 20KHz with the AES17 filters enabled and the AP in 22KHz analyser Mode!!!

If look at the above THD plot, you will notice the distortion drops off at higher frequencies, as increasingly less harmonics are in the measurement bandwidth - basically a meaningless graph above ~ 10KHz as even the second harmonic is now outside the 20Khz measurement bandwidth!

Pls. note that this is in no way a criticism of Jan-Peter, as 99% of manufactures perform & publish the same test!

But never the less, a very good result for such a simple design Bruno - how about calculating those optimised integrator component values for Jan?

[Jan-Peter]

John,

Ofcourse I agree with you. But measurement is also intepretating the graphs! You can increase the measurement bandwith of the AP, but the disadvantage will be the increasement of the noise.

So, In this case you woudn't see how good the amp performs at lower frequencies.

In a way you should measure with different bandwith settings of the AP.....

You have all the tools, can you show us your freq to thd graph?

BTW, I am VERY satisfied with AP Sys2 for R&D, we use the ATS2 for production (much cheaper).

Regards,

Jan-Peter

[Sheriff]

Hi John,

Looks like i am a pretty poor relative only having a AP sys 1 (sob).

The latest of Pauls stuff is really geared toward multichannel testing, so i guess (without speaking to him), that he has not had that many requests from manufacturers re class D apps. (well certainly not in the UK).

You have obviously spent a long time developing your amplifier, are you willing to share a little more about it?


Cheers

Sheriff