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Class D Switching Power Amplifiers and Power D/A conversion

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Old 2nd July 2013, 09:00 PM   #421
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True. And the SystemD 2k4 offers symmetric input.
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Old 5th August 2013, 08:24 PM   #422
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..Dimitri's comments pushed my brain to the right direction.

I am sticking to my I-want-it-all requirements and consequently will get an undesired GND loop somewhere.
But when you wire both signal grounds to a star right at the RCA sockets, then the input amp will always automatically compensate the undesired voltage drops on the GND, no matter if used asymmetric (one RCA of each channel shorted) or symmetric.

The attached schematic shows the simplified principle without EMI filtering.
Attached Images
File Type: jpg LoopCompensationWiring.JPG (80.0 KB, 845 views)
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Old 7th August 2013, 06:52 PM   #423
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...did I say unavoidable loop?
Nobody heavily complaining?

My brain blanked out the option as attached here, because I generally dislike a large geometric separation of signal wires and signal GND.

...and it messes my geometric separation of power GND and signal GND.
Fortunately my signal GND is close to the speaker power GND on the PCB and the PSU GND is not inbetween.

It will also suffer from adding to the signal the voltage drop of the GND connection between both amps, but will also benefit from the compensating effect of the input stage.

Nevertheless I am starting to think of this as a viable option, when routing the signal wires geometrically close to the GND connection.
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File Type: jpg LoopCompensationWiring2.JPG (81.4 KB, 802 views)
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Old 2nd September 2013, 08:31 PM   #424
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Default V1dot5

Here an update on V1dot5, which is going to be the version for my living room.

- Speed:
In the first two pictures you can see the amp reproducing a 12kHz rectangle with +/-10V. First without load, then with 2R load.
==> No overshoot. Sloping times of approx. 3us
Voltage scale: 5V/div
Time scale: 10us/div

- Distortion / IMD:
See THD and IMD vs power in the table.
THD vs frequency in the graph (10W).

- Ability to reproduce complex signals with high fidelity:
AP2 often is pointing to complex music signals. Even when I doubt that you need unaffordable measurement equipment to analyse the amp with real music program - I am convinced that optimizing an amp for more complex signals pays back during listening.
A simple combination of a large triangular signal (1kHz) with superimposed rectangular signal (10kHz) can open your eyes on short comings in your design. V1dot5 showed good fidelity already from the beginning. After another analysis of the loop gain including all options to control dv/dt - the behavior of the amp brought a smile on my face.
Voltage scale: 20V/div
Time scale: 100us/div
Attached Images
File Type: jpg 12kHz_10V_noload.jpg (167.1 KB, 702 views)
File Type: jpg 12kHz_10V_2R.jpg (157.9 KB, 656 views)
File Type: jpg Distortion1kHz.JPG (40.5 KB, 548 views)
File Type: jpg THDvsFreq_10W.JPG (47.7 KB, 120 views)
File Type: jpg TriRect_50V.jpg (150.2 KB, 131 views)

Last edited by ChocoHolic; 2nd September 2013 at 08:46 PM. Reason: Typo
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Old 7th September 2013, 02:48 PM   #425
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Triggered by another thread I analysed the noise and noticed that V1dot5 was wasting about 10db SNR, just by the symmetric input stage.

Unnecessary high impedances combined with LT1364 and unnecessary high gain.
So I changed to the AD8620 and reduced the impedances and the gain.
AD8620 gives one OP amp to the symmetric input gain stage and the second for the power amp itself.
Fortunately AD8620 is fast enough and provides mostly identical perfection in control, also the signal shaping for low THD remained fine.

The output noise is now 63uVrms (still dominated by the symmetric input gain stage), a value which is fully up to the mark with class AB amps.
Attached a screen shot of the spectral noise distributions at 1W and 1000W.

Also THD vs. frequency remained fine.
Attached a screen shot which displays K2+K3 in comparison to THD+noise. Power was 10W into 2R.
Attached Images
File Type: jpg noise.JPG (56.4 KB, 129 views)
File Type: jpg THD+Noise_vs_k2k3.JPG (50.0 KB, 103 views)

Last edited by ChocoHolic; 7th September 2013 at 02:49 PM. Reason: typos
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Old 7th September 2013, 05:49 PM   #426
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I am sticking to your thread as it raises the bar........Nice measurements and tweaks.
Congrats Choco.
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Old 8th September 2013, 06:32 AM   #427
Baldin is offline Baldin  Denmark
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Amazing .....
..... I subscribe to this thread just to learn
.... cool work Choco
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Old 10th September 2013, 04:30 AM   #428
soc15 is offline soc15  Thailand
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Default dymamic hysterisis

u can use limit input like
EP 1071215A1
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Old 12th September 2013, 03:53 PM   #429
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by ChocoHolic View Post
The output noise is now 63uVrms (still dominated by the symmetric input gain stage), a value which is fully up to the mark with class AB amps.
Attached a screen shot of the spectral noise distributions at 1W and 1000W.

Also THD vs. frequency remained fine.
Attached a screen shot which displays K2+K3 in comparison to THD+noise. Power was 10W into 2R.
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Old 26th September 2013, 07:02 PM   #430
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Default Dual mono in experimental enclosure

Why experimental?
-Heat sinks are larger than necessary.
-It is 2 units high, but 1.5 units would be sufficient.
-Wiring suffered from experimenting.
-A friend is considering to build the amp as well and go for a special enclosure, I kept the supply wiring longer than necessary in order to stay flexible for a potential transfer in a different enclosure.

Nevertheless, the set up is performing very well.
I tested both wirings (posting #422 & posting #423).
Both showed no issues with HF interactions between both channels.
The first wiring showed a slightly superior behavior in case of strong external magnetic fields. This can become relevant, when stacked directly on top of an ancient amp with monster transformers. So the wiring like in posting #422 is my final choice.

Even without top cover you can run the amp at full power without interfering a FM reciever close by.
Distortions and complex signal handling remained unchanged after implanting the amps into the housing.

You will notice four RCAs for each chanel, two for AC coupling and two for DC coupling.
For AC coupling I am using the Panasonic ECW series. Definitely one of the better choices, when staying with non audisoteric types. The Mundorfs which I used earlier where fine as well, but with 4u7 they would simply be to large for the PCB - while the Panasonics easily compete in sound and come at attractive size.

This allows all considerable input choices:
-DC coupled symmetric inverting, DC coupled symmetric non inverting DC coupled inverting, DC coupled non inverting, DC coupled bridged.
-AC coupled symmetric inverting, AC coupled symmetric inverting, AC coupled inverting, AC coupled non inverting, AC coupled bridged.

The sound? Detailed and decent at the same time. Unmatched bass control. ...and sound stage!!
Sound stage always is a hard to meet design goal. The design variations with this amp gave me some more insights - still no bullet proof recipe.
My friend must hurry up, the more I am listening to this amp the less I want to disassemble it...

Attached some photos of the nice guy.
Attached Images
File Type: jpg backview.jpg (96.8 KB, 223 views)
File Type: jpg sideview_r.jpg (93.4 KB, 226 views)
File Type: jpg back_closed.jpg (61.1 KB, 149 views)
File Type: jpg back_closed1.jpg (48.8 KB, 121 views)
File Type: jpg Set.jpg (71.4 KB, 142 views)
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