UCD180 questions

[Yves Smolders]

I see a jaw-dropping Hans in his home theatre in the future?

Not many will be able to compare the improved modules vs the standard ones - but you can!

Listening tests are hard to do, if you have a positive mind about the modules and you disconnect your old amp, there's already the placebo effect.

I always thought well-built amps are all very close together, as long as they are not underpowered or rightout badly designed, they sound the same. I've learnt otherwise by reading just how many class AB designs are possible (feedback, bias level, current limiting, etc)

I can't say much yet, I've only done very limited single channel tests with b&w speakers and my old Philips speakers, the other speakers I tested don't have the resolution to show anything.

Both these speakers are larg(ish) floorstanders - The Philips I couldn't compare because I haven't heard them on my old system since october. The Philips did sound very tight in the bass, but it could be placebo effect or just the track being played (and they weren't in the same spot I'm used to hearing them)

The B&W Nautilus was in the same spot. It had a lot of authority playing a St. Germain track. The change was not subtle, it was even more revealing to switch back to my old amp. The difference is best described as "less tight"

I'm looking at the same soft start you are - the sound doesn't seem to be a concern, as long as the relay can handle the amps it should be fine - however, I wonder how long it takes for the caps before the relay will drain - if power cycles fast (like 5 seconds or so between off and on) the relay might still be engaged... maybe a resistor parallel over the relay?

About DC protection, i'm still thinking about the vellemans, they should do the job nicely, but it's a lot of stuff parallel on the speaker path, I'm afraid it will have sound - haven't seen any opinions on those in here - except on another forum, they are reported to "s*ck"

[richie00boy]

Originally posted by Jaka Racman
Hi richie00boy,

I am afraid that your assumption is incorrect. The point is that the current drawn from the power supply is average value of the waveform. I attach two waveforms, black one showing current drawn by classD amp and red one showing output (load) current of the same amp. Load current would be the same as current drawn by classB amp. In upper right corner you see calculated average values of both currents, 4.23A for classD and 6.26A for classB. (Average value is calculated as area of the waveform, so you must account for the voids between current pulses.) As you can see, there is 2A difference between both amps. Those 2A of current is transferred into heat in the classB amp, so this is why classD amp runs cooler: It draws less current from the power supply.

Best regards,

Jaka Racman

Jaka,

Thank you for that explanation, it was exactly what I was looking for. I guess the average current for the class-d amp will depend on the topology, or will all class-d amps have an average current that is x amount of the class-b average current?

[Jaka Racman]

Originally posted by richie00boy

I guess the average current for the class-d amp will depend on the topology, or will all class-d amps have an average current that is x amount of the class-b average current?

Hi richie00boy,

the answer is not very simple. In theory, Class D amplifier is a power conversion device and can theoretically be 100% efficient, that means that all the power from the source is transferred to the load without being wasted in the amplifier. That would be invariant of the topology of classD circuit.

In practice, for almost all comercially available classD amps only so called step-down (buck) topology is used. And because real devices are used as switches, there are also losses in those devices, which are subdivided into conduction and switching losses. So for comparing various classD implementations a factor of merit is used called efficiency

efficiency = power delivered to the load / power drawn from power supply

or

efficiency = power delivered to the load / (power dissipated in the amp + power delivered to the load)

For good classD amps, efficency is somewhere between 0.92 to 0.96 at full power, maybe even better for subwoofer amps. Sadly efficiency is not constant over the whole output power range (as Hugh has kindly noted) and is lower at low output powers because some losses are fixed and independant of output power level. On the good side, efficiency of classD is independant of the load phase angle.

Efficiency can equally well be applied to classB amplifiers. Here efficiency is is even more trickier to define over whole power range, since it depends on output power, shape of output waveform and load phase angle. In general, efficiency improves with output amplitude and reaches maximum of .78 (IIRC) for sinusoidal signal at full output power. It can be even grater with square wave signals.

Now your question was about dimensioning of power supply transformer. For continious output power, you dimension your transformer for load power + power dissipated in amp. Now this can simply be calculated as:

power required = maximum load power / efficiency

So for typical classD you need 1.06 times load power and for classB 1.28 times load power. As you can see, the difference is not that great, but it still exists.

Best regards,

Jaka Racman

[analogspiceman]

Originally posted by Jaka Racman
In theory, Class D amplifier is a power conversion device and can theoretically be 100% efficient, that means that all the power from the source is transferred to the load without being wasted in the amplifier. That would be invariant of the topology of class D circuit.

For good class D amps, efficiency is somewhere between 0.92 to 0.96 at full power, maybe even better for subwoofer amps. Sadly efficiency is not constant over the whole output power range (as Hugh has kindly noted) and is lower at low output powers because some losses are fixed and independent of output power level. On the good side, efficiency of class D is independent of the load phase angle.

Efficiency can equally well be applied to class B amplifiers. Here efficiency is is even more trickier to define over whole power range, since it depends on output power, shape of output waveform and load phase angle. In general, efficiency improves with output amplitude and reaches maximum of .78 (IIRC) for sinusoidal signal at full output power. It can be even grater with square wave signals.

So for typical class D you need 1.06 times load power and for class B 1.28 times load power. As you can see, the difference is not that great, but it still exists.

Hi Jaka,

A few points: 1) I admire your knowledge and gentle patience; 2) in the ear of my mind your name has a soft "J" (like the German "Ja") and a hard "c" (like a "k") - am I "hearing" that correctly?; 3) perhaps your diplomatic nature is leading you to understate the efficiency difference between the B and D classes of amplifiers. Your estimation of the efficiency of a typical class D design seems correct, but, in my experience, a typical class B amp will be lucky to achieve fifty percent (near forty is more likely) when operating with best case real music (highly compressed techno) into a real load (at least thirty degrees inductive) at maximum listenable output (ten percent clipping). So the size ratio of the transformers will be closer to 2:1. And the ratio for heat sinks will more like 10:1.

Regards, analogspiceman (note: the "spice" is sharp)

[Jaka Racman]

Hi anlogspiceman,

Your pronunciation is correct and I agree with everything you have writen. I forgot to mention that my figures would be correct if the transformer would be dimensioned in an industrial way (for continious operation with maximum output power and sinusoidal signal). Class B has worst efficiency at half output power (only 0.5), and given dynamic nature of music signal it will most likely operate around this point when pushed to the limit. For anyone interested, here is link to the Rod Elliot's page discussing classB efficiency.

On the other hand classD should maintain high efficiency over much broader range (over 0.9 above 20 or 30% of output power) so it's heatsink (and transformer) can be considerably smaller.

Since Bruno gave some insight how transformers in audio are dimensioned nowadays (FTC testing at only 1/8th of rated output power), your figure would seem correct for transformers that are dimensioned for music signals.

Best regards,

Jaka Racman

[Hans L]

While I'm not getting any answers to my questions and you are having a blast with differenct classes of amps, I might as well go back to meta communication...

Since when is taking a cheap stab at one person and opening the next post with an insult towards two ppl considered gentle patience and of diplomatic nature??? There are some funny social rules going on here. Since analogies are in, try this one: 'If you are One-eye in the land of the blind, you get to smack anyone you meet and still be praised for you peaceloving nature.'

[Yves Smolders]

Hans,

I've posted a listening test on Ucd400AD's in the UcD400 thread. Of course, keep in mind it's highly subjective and compared to 2*90W/8 ohm channels of a receiver. The dynamics I experienced could be due to the double power UcD400 provides (quite a few db's headroom extra)

Yves

[classd4sure]

Hi Hans,

Question one, Since you cling to what Bruno say's, you'll notice he's spoken of that op amp rather highly, may as well go with that opinion.

Question 2: How is that different from the LCaudio one? I've never seen an actual schematic of it.

That simple one though, leaves nothing in the path of the signal other than the relay contacts, even if there were any noise induced by that (doubtfull I think), it still goes through your power supply and all the amps local bypassing, so I think it's safe to say it would have zero audible effects.

Regards,
Chris

[Hans L]

Thank you Yves (and for your previous reply). I will look up your review of the UcD400AD. The 400 is supposed to sound pretty much the same as the 180 so I'm sure the difference you describe should be what I may expect.

Classd4sure, I don't have a schematic of the LCaudio module either. Was hoping someone could shedsome light on it, but I think it's safe to say they are rather expensive and might not be fundamentally different at all.

I don't have enough understanding of electronics to judge what a 'loose hanging' capacitor or other parts, once the relais is closed, may invoke on a circuit. Thanks for clearing that up. It seems to be a superb diy choice, it's simple and cheap and does exactly what one needs. I guess the only thing worth spending a few bucks more on would be the relais (solid contact over the years). One thing I would think of doing is use multiple resistors in parallel (instead of the series resistors) across the relais for better power handling and aim for a higher total resistance just to be on the safe side.

[richie00boy]

IMO a soft start using a relay will not have any influence on the sound as it's far too removed from the audio, firstly by a transformer then by a bank of smoothing caps. Be wary of using parallel resistors instead of series as they will need to be rated for the full mains voltage which will not be easy to find; that's why people use series.

Series will still have the same power handling. Also beware of increasing the resistance, if you increase it too much the PSU caps will barely have charged during the soft start period so when the relay closes you get another surge.

If you fancy making your own board I have designed one that uses a very simple circuit, which I am just finalising. You are welcome to the layout if you want it.