What is a Digital Amplifier receiver (1 Viewer)

[Gabriela Mendez]

I use a dpr1001 as a preamp and a carver av505 as an amp. I hate the sound on the dpr1001. It also acted up from time to time with with weird sounds coming from the speakers, sounded like something taken out of TRON (no kidding)!

 

[Karl_Luph]

Gabriela, interesting you tell us this about the amp. A friend of mine had an early Line 6 amp that went wacky like this and was stuck in a loop making a weird oscillating sound, had to return it and get a new one.

 

[DarrylM]

If I recall, the biggest drawback to digital switching amps has been distortion. This is particularly true in the higher end of the spectrum, which requires digital switching frequencies up to 1,000 times greater than the low end (bass). Further, distortion in the low end is less noticeable in general. This is also why digital switching amps had been relegated to subwoofer amps for the past couple of decades until some recent advancements. However, I believe that even these newer ones still have some power stability problems with higher loads though (like 4 to 6 ohm speakers).

It's also not strictly true that they maintain a "purely digital" path from source to speaker. In fact, the digital amplifier, itself, acts as a kind of digital-to-analog converter, since your speakers (and, ultimately, sound waves) are analog. Whereas an analog amp converts a digital signal to analog and amplifies it, a digital switching amp converts a digital signal to analog during the amplification process. Moreover, the digital signal out of your CD or DVD player has little to do with the digital signal used by the switching amplifier (t's not like the switching amp is converting Dolby Digital signals directly to analog audio).

Digital switching amps are more efficient, and require smaller components (including heatsinks and power supplies), which makes them smaller and cheaper to build. I don't know that anyone has ever advertised an actual sonic advantage to digital switching amps, though Panasonic seems to have some fanboys out there who swear that their $200 receivers sound better than any other system in existence. With the push for smaller and more affordable consumer electronics, these amps will certainly have a big market. I believe the higher end digital switching amps (e.g., Evo) will remain boutique items for many years though.

 

[FeisalK]

This is not a receiver, but a stereo digital amplifier review by 6moons.com


it's hard to quantify a sonic advantage, maybe someone should do a head to head comparison between the $20 T-amp and a $20 Optimus, or Radio Shack analog amp.

 

[DarrylM]

I mean strictly theoretical performance: harmonic distortion, frequency response, output across various loads, signal to noise, et cetera.

If even newer digital switching amplifiers sounded inherently "better" than conventional analog amplifiers, it would stand to reason that manufacturers would all switch over immediately, particularly since most AV manufacturers have already experimented with the technology in their product lines and digital switching amplifiers are less expensive to make.

 

[David Judah]

Some are intrigued by the reltive simplicity of the design(like no need for negative feedback in some& no DACs in the traditional sense)and the lack of some of the problems inherent in analog. Of course, there are some similarities to analog designs, such as the need for a good power supply, and also other obstacles to overcome, such as EMI & oscillation control.

A recurring description is the amount of detail put out by even the inexpensive Panasonics you mentioned. If even the cheap Pannys can sound good under the right conditions(and IMO they do), imagine what kind of product you'd have if you could throw some more money into the design for better PCM/PWM converters, reconstruction filters, power supplies, decoupling capacitors, etc...

We are getting to the point now that with digital amps the money you sink in is considerably less than what you'd have to sink in to a traditional design to get the same level of performance.

DJ

 

[FeisalK]

Darryl,


sure.. what can you tell me about these amps?

Amp 1:
"Effective" power: 150W (no distortion percentage specified).
Frequency range: 20Hz-100kHz.
Input sensitivity: 1V.
Input impedance: 100k ohms.
Signal/noise ratio: >100dB (no reference level quoted).

Amp 2:
Rated output: 160-watts / 4 ohm, 100-watts / 8 ohm
Frequency Response: 5Hz-25kHz / 4 ohm, 5Hz-50kHz / 8 ohm
Distortion rate (THD): 0.03% (8 ohm, 1kHz, 50watts), 0.05% (4 ohm, 1kHz, 50watts)
S-N ratio: 120dB(400Hz-3kHz BPF)
Input Sensitivity: (Input Impedance) 1V/10k ohm
Residual noise: 25µV(400Hz to 30kHz at BPF)
Damping Factor: 200(8 ohm,1kHz)

Amp 3:
Rated Output: 100-Watts (6 ohm)
Frequency Response: 4Hz-88kHz,±3dB
Distortion rate: 0.09% (6 ohm)
Input Sensitivity: 85dB (103dB, IHF’66)

Amp 4:
• 200W @ 0.2% THD+N, 10Hz – 20kHz, 4 ohm
• 230W @ 1% THD+N, 10Hz – 20kHz, 4 ohm
• 290W @ 10% THD+N, 10Hz – 20kHz, 4 ohm
• 100W @ 0.2% THD+N, 10Hz – 20kHz, 8 ohm
• 130W @ 1% THD+N, 10Hz – 20kHz, 8 ohm
• 110dBA dynamic range, 200W @ 4 ohm
• THD+N = 0.006% @ 1W, 8.,1kHz
• THD+N < 0.2%, 0.1W – 200W, 4 ohm.
• Input Impedance = 11 kOhm.
• 79 % total efficiency @ 200W, 4 ohm.
• Upper bandwidth limit (-3dB): 65kHz @ 8 ohm, 45kHz @ 4 ohm
• Lower bandwidth limit (-3dB): 3,5 Hz
• Abs. output impedance: 10 mOhm
• CCIF Intermodulation distortion: 0.0005%, 10W/4ohm 14kHz/15kHz
• Transient intermodulation (TIM): 0.004%
• Damping factor: 4000, 100Hz, 8 ohm
• Minimum load impedance: 3 ohm
• Gain: 27 dB
• Output referenced idle noise: 90 µV
• Stand-by power consumption: 0.5 Watt per channel

Amp 5:
Output Power: 100W (20 dBW)
Damping Factor: >110
Input Impedance: 10k Ohms
THD: 0.07%
Frequency Response: DC - 250kHz (±3dB)

In no particular order the amps are: Panasonic XR50 ($300, digital), Wavac SH833 ($350,000, analog, tubes), eAR202 ($499, digital), NAD S300 (price unknown, analog, solid state), Flying Mole (about $800?, Digital)

 

[DarrylM]

You've provided several different arbitrary measurements for each amp (actually, it looks like you've provided manufacturer specifications), as opposed to a set of test results from the same series of measurements for each amp. Provide a standardized set of test measurements for all five amps, and I'll be happy to throw in my two cents worth.

 

[FeisalK]

It's really amazing.. every so often someone comes in here and lays down a bunch of specs of two receivers and asks "which one is better?" The most common response he will get is "Have you listened to either of them? which one do you like better?" Now we've got a whole bunch of subjective listening reports, and what do you want?

Well Darryl.. they are manufacturer specs except the first. I don't think anyone has done a standardized test for all five amps, so these are the best figures we have at the moment.

Just for the purposes of this discussion, can we just say hypothetically that the manufacturers are honest and publish specs that conform to an acceptable standard in the audio/hifi world. What then? I mean, for all we know these could be THE specs when we line them up anyways.

Furthermore if you have two amps with the exact same specs (standardized test) do they both sound the same?

 

[DarrylM]

I'm sure you could still have slight differences in timbre and such with real signals passing through them. This also assumes that everything is equal, including the sub output and roll-off. And, of course, the quality of the pre-amp section shouldn't be overlooked.

Obviously, certain measurements are indicative of performance, including the output at clipping, distortion, and noise. The difference between its output at 4 and 8 ohms is also an item worth noting, since it provides a good indication of current handling ability.

Subjective opinions about receivers (or anything else, for that matter) aren't particularly meaningful to me, personally -- particularly when different room acoustics, different speakers, or different sources are involved (not to mention any psychological factors). Frankly, my girlfriend thinks her $30 clock radio sounds great. I'd rather see some good bench measurements from a reliable source.

Keep in mind that just because someone likes the sound of a particular receiver doesn't mean that it performs well or even that it accurately reproduces the signal. (Certain Bose speakers have been an example of this effect.)

Anyway, to each his own.

 

[Peter Fallon]

PWM in not really digital. While the voltage only has two discrete states, the pulse width is actually continuous not discrete. There's no quantization involved, PWM lets you represent continuous voltage with continuous pulse width. This is the same reason the video and original audio channels on a laserdisc are considered analogue. The pits and lands can only represent two states, but the length was continuous.

PCM on the other hand represents discrete values at discrete intervals of time.