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Class D Switching Power Amplifiers and Power D/A conversion

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Old 15th June 2011, 09:39 AM   #61
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Join Date: Apr 2004
Location: BE/NL/RW/ZA
Originally Posted by eclectic2k View Post
uh, unless it ends up costing as much as a small car, then I'm out
OK how about a motorcycle then? J/K :P

Originally Posted by Trevor White View Post
Have you considered an all in one power amp/power supply combination similar to the ice power modules for driving subwoofers ??
Given the ease with which an SMPS and amp can be wired together I've never understood the fascination with combos, but the demand is there and UcD + SMPS projects are being started. With all the aux supplies and whatnot.
Old 15th June 2011, 09:55 AM   #62
deandob is offline deandob  Australia
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What about a well tuned discrete input stage? Or use a top notch opamp like the LM4562 biased into class A.

Use of high quality components (eg. low ESR caps for power supply decoupling).

Its also a bit painful to get the earth's right on the UCD's (at least for the original models I use) when using non balanced connections, so better grounding arrangements for unbalanced inputs would help.

As I have an amp using the first generation UCD's (standard not HG) with OPA627's biased for class A, I'm considering swapping out the modules for these latest ones. What changes to the sound should I expect comparing the old UCD400 with these new modules (note I didn't say better - I'm pretty happy with the old UCDs but still interested in what has changed)?

Last edited by deandob; 15th June 2011 at 10:06 AM.
Old 15th June 2011, 10:12 AM   #63
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Originally Posted by deandob View Post
Its also a bit painful to get the earth's right on the UCD's (at least for the original models I use) when using non balanced connections, so better grounding arrangements for unbalanced inputs would help.
It can't get any easier than it is. If you have two ground paths, for instance your supply is grounded to chassis and so is your RCA input, just don't connect your RCA ground to the ground pin of the amplifier module as well because then you get current flowing through the RCA cable. Use the "cold" input as ground instead and for Pete's sake don't connect the cold pin to the amplifier ground directly. Once you get your head around how differential inputs work you'll realise that it already does exactly what you want, that is solve ground loop problems for you. There used to be an app note on the site for this, I'll have a look round where it went and put it back.
Old 15th June 2011, 01:40 PM   #64
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Default RCA to Balanced - Hypex AppNote

Here is the "old" wiring appnote from hypex site. I think for quite a few of us it will still take trial-error approaches.
My "gut-feel" is that right approach is the one on right hand side (power supply/amp/grounded to the amp-chasis). Balanced input connector has ground connected to the amp input (and from there it is grounded to amp-chasis)). Unbalanced input, you build a cable as per the picture (unbalanced ground/negative goes into the "cold" in balanced input, and shield also connects to the unbalanced source ground/negative at the source, and at the balanced input on the amp gets effectively connected to chasis).
Hope i got it right ?

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File Type: pdf wiring.pdf (95.5 KB, 486 views)
Old 15th June 2011, 09:09 PM   #65
deandob is offline deandob  Australia
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Its the bit about not connecting power ground to the chassis, for DIY implementation I'm not comfortable with a metal chassis (which also provides good EMI shielding) not connected to power ground. I ended up with the arrangement you suggested, where the chassis was connected to power ground and the module grounds including RCA ground were isolated from the chassis ground. I did find, as suggested, that the earth loop was eliminated by connecting the RCA ground to the amp cold input, not amp earth.
Old 15th June 2011, 09:31 PM   #66
AP2 is offline AP2  Italy
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Location: Italy
These connections are governed by the rules.(depend upon the class of the psu and the class of the product).
chassis must be connected to the earthing.
(this requires that the SMPS (if using an EMI filter balanced), must have the central pole in the chassis (earth) and not on output gnd.
Therefore, in the case of RCA, must be isolated from the chassis.


Roberto P.

Last edited by AP2; 15th June 2011 at 09:34 PM.
Old 16th June 2011, 07:18 AM   #67
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IMNSHO the word "ground" should be forcefully removed from the school curriculum. The conflation of "chassis potential", "earth potential", "power supply return" and "reference potential" into that one little sneaky cowardly word "ground" is the source of an absolutely incredible array of engineering problems the world over. Conversely, the simple act of not using the same galvanically connected network for both reference potential and any combination of the other three solves all problems. Chassis, earth and PSU null may be interconnected in any way you like provided that actual signals are accompanied by another wire carrying the reference potential of the source. The receiver, of course, should be capable of subtracting the voltages between the two wires, not attempt to take a shortcut by forcing one of the two to its own "ground" (or to try and force its own "ground" to follow the potential of the reference wire).

Class I equipment needs direct earthing of the chassis for safety, class II equipment does not. However, in the latter case you may not use earthed mains inlets. You may have noticed that mass market consumer audio gear has class II wiring and a 2-prong mains cord. This is because unbalanced connections simply do not mix easily with earthing.

If you cannot construct per class II, floating the secondary ground is a commonly used and very bad practice. Very bad because it requires star connections which are a source of HF problems. It is much better to use a differential input to float the reference terminal ie the RCA shell and sense between the shell and center pin without making a direct connection to chassis or any other of the irrelevant "grounds". One would place a cap and perhaps a resistor to chassis to limit the voltage between the two and stop the connection from becoming an antenna.

That way the differential input acts like an input transformer: only the voltage between two input pins matters, not the voltage with respect to whatever one may think is "ground". There is always an easy solution that does not require fancy floating schemes if you have a differential input at your disposal. There is neither a simpler nor a better solution than the one already in place in the UcD modules. The only thing we can do is write a very long and detailed document explaining the operation of differential inputs. Trust me, once the penny drops you'll bang your head and say "if only I knew it was that obvious". One thing you're guaranteed to do, for instance, is immediately adopt the scheme on the right hand side of the wiring application note. This is much better than any floating secondary or differential RCA connection you can dream of.

So let's move back to the topic of what the Ncore DIY module is going to look like.

Last edited by Bruno Putzeys; 16th June 2011 at 07:27 AM.
Old 16th June 2011, 08:28 AM   #68
jmbulg is offline jmbulg  Belgium
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From a practical point of view, maybe a heatsink which can be acessed (screwed) from both sides? On the UcD400 you have to drill across the chassis; or add a second, larger, plate before being able to fix it from the inside onto the chassis or thick external heatsink.
Old 16th June 2011, 08:32 AM   #69
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Originally Posted by Bruno Putzeys View Post
So let's move back to the topic of what the Ncore DIY module is going to look like.
I thought we had solved that. More power than the UcD400 (ideally at NC1200 levels), premium components (where it matters) and the best discrete input you can design (aka world class).
Old 16th June 2011, 08:34 AM   #70
brubeck is offline brubeck  Netherlands
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For home hifi i builded and played with Hypex UCD180 with HXR modules. I remember with these modules that the control was really impressing. Though, i couldn't get used to the overall sound of class D. There was a lack of liveness, warmth, involving character of the sound comparing to modern class A/B amps. Not to say that the modules where bad, i suppose that the effect has to do with the absence of (harmonic) distortion? I don't know.

What can be said about the sound of the new Ncore amp in this area?


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