Amplifiers - What specs are important?

JStewart · Jan 30, 2019

I'm looking to purchase an outboard amp for 4 height channels only, but I'd like the option to re-purpose it to more critical listening in the future, just in case. Currently wavering between Outlaw 5000 and Parasound A52 (pre-owned most likely).

There seems to be a couple schools of thought on amps. One that they amplify without "coloring" the sound, i.e. an amp is an amp, and the other that they do impact sound quality. But then, there are large price differences between amps with similar output and there are a slew (pun intended) of specs that manufacturers provide. (Some of which don't seem to be standardized, which is annoying.) So one would think there are some quality differences worth paying for but what are they??

For anything that I can foresee 120watts per channel, all channels driven, would be sufficient power. And I think I'd want the amp to be able to handle 4ohm speaker loads in case I do re-purpose it in the future, so I guess I'd want something that can produce about 200watts into a 4ohm load, but that brings up a question... I've never seen any clear guideline indicating amp quality with respect to the the ratio of watts capable with 8 and 4ohm loads. Is there one? Or does it even matter?

Regarding the myriad of other specs are there any you think important and why? At what point does the number for the spec translate to audible differences? Or perhaps put another way, what spec numbers would you avoid?

Any insight into amp engineering mysteries will be much appreciated!

Tony V. · Jan 30, 2019

So your opening up a can of worms here as we had a poll running for some time and it was almost 50% saying yes they do have different sound qualities to them vs 50% saying no they did not.
In my opinion if the amp specifications are the same and they are all A or A/B switching amps they should be very similar. Tube amps do "color the sound" as do some off the wall designs. Class D amps are also different but should be very similar if the design is proven.

What is really important is that the power supply within the amp can power the amplification circuits properly. You always want headroom on a amp so that you dont run out of power before the speakers do causing distortion.

Staying away from those cheep brands that advertise crazy output numbers for $150 Pyle pro for example

JStewart · Jan 30, 2019

Tony V. said:
So your opening up a can of worms here as we had a poll running for some time and it was almost 50% saying yes they do have different sound qualities to them vs 50% saying no they did not.
In my opinion if the amp specifications are the same and they are all A or A/B switching amps they should be very similar. Tube amps do "color the sound" as do some off the wall designs. Class D amps are also different but should be very similar if the design is proven.

What is really important is that the power supply within the amp can power the amplification circuits properly. You always want headroom on a amp so that you dont run out of power before the speakers do causing distortion.

Thanks Tony. I figured a can of worms was possible. It just seems like there should be some reason for paying more for what on the surface looks like closely spec'd products from two reputable companies like Parasound and Outlaw.

I guess I'm one of those that thinks its possible there's a difference in sound quality depending on specs and related gear. If its dependent on your other gear how to figure it out? If it makes no difference why even test and publish some of the specs?

Regards the power supply, what would you look for? And how much head room (measured in dB?) makes sense?

Grayson Dere · Jan 30, 2019

Hi JStewart,

You are correct to think that amps do have differences based on pricing and features. I'm not too familiar with the current products offered by Outlaw but if memory serves right, you should have no issues with their amplifier quality (sound quality) in your application. Parasound is also a fantastic company that I would not hesitate to go with. Which speakers are you using and how large is your listening space? Listening distance from speakers?

120 Watts all channels driven is a lot of power and I would suspect that any major manufacturer with those specs for an amp would be fine to use. I really like THX certified amplifier products because they test their equipment for clipping and distortion at reference levels based on listener distance from the speakers and room size amongst other parameters. The Parasound A52 you mentioned is THX Ultra2 certified and will more than likely be fantastic since that is meant for a theater that is at least 3,000 cu/ft. playing reference levels. Your speaker's sensitivity will also play a great deal in determining how much power you'll require in your space. For example, THX Ultra2 main speakers made by MK Sound have a sensitivity of 92dB/w/m which is meant to mate with Ultra2 amps for no compromise in performance.

That being said, many experienced audiophiles would recommend you listen to an amplifier in your own specific case if possible because depending on the speakers you are using one amp may sound great while another might sound a bit underwhelming. Some audio dealers I have great ties with even go so far as to recommend not even looking at specs..I know it sounds a bit far fetched to think that way...even I still get caught up with wattage numbers. There are so many factors involved with amplifiers and speaker synergy that it's tough to look at specs alone and estimate sound quality.

I apologize I don't have the necessary engineering background to provide hard evidence of electrical specs in real world application to sound quality. Beyond demo'ing amps in person the next best thing would be just to research reviews as much as possible and talk to knowledgeable dealers.

If you haven't already come across it here is a neat webpage courtesy of Acoustic Frontiers that has a downloadable calculator that may help with your amplifier power decisions:

http://www.acousticfrontiers.com/2013322spl-calculator/

The download is kind of buried in the article called, 'Max SPL Calculator.'

Anyone else have advice? : )

Grayson Dere · Jan 30, 2019

Tony V. said:
So your opening up a can of worms here as we had a poll running for some time and it was almost 50% saying yes they do have different sound qualities to them vs 50% saying no they did not.
In my opinion if the amp specifications are the same and they are all A or A/B switching amps they should be very similar. Tube amps do "color the sound" as do some off the wall designs. Class D amps are also different but should be very similar if the design is proven.

What is really important is that the power supply within the amp can power the amplification circuits properly. You always want headroom on a amp so that you dont run out of power before the speakers do causing distortion.

Staying away from those cheep brands that advertise crazy output numbers for $150 Pyle pro for example

Yes! the power supply can make huge differences. Thanks for pointing that out, Tony : )

Tony V. · Jan 30, 2019

Power supply size and weight is a good indication for A and A/B class amps. Toridal power supplies are really nice (the round donut shaped ones)

Noise floor can be a consideration as some pro amps used for big systems are a bit noisy with no signal output (slight hiss or hum) so thats often what separates the big guys and high end home theater amps.

Tony V. · Jan 30, 2019

As far as what headroom is acceptable it simply comes down to output and what your speakers are rated to handle. You want the amp to exceed the speaker normal power ratings by about 20% RMS and keeping in mind that most full range speakers with an efficiency rating of 90db will reach ear bleeding levels in a normal size space at about 125 watts

JStewart · Jan 30, 2019

Grayson Dere said:
I really like THX certified amplifier products because they test their equipment for clipping and distortion at reference levels based on listener distance from the speakers and room size amongst other parameters.

That's a good tip, thanks! It wouldn't mean another amp made by a company that doesn't pay for THX certification wouldn't be as good, but it would be some piece of mind for sure.

Grayson Dere said:
Some audio dealers I have great ties with even go so far as to recommend not even looking at specs..I know it sounds a bit far fetched to think that way...

Doesn't sound that far fetched at all from what I'm seeing!

Grayson Dere said:
If you haven't already come across it here is a neat webpage courtesy of Acoustic Frontiers that has a downloadable calculator that may help with your amplifier power decisions:

Thanks for this too. It was interesting to run the what ifs. Especially to see how much more wattage can be required for just a couple of dBs.

Tony V. said:
Noise floor can be a consideration as some pro amps used for big systems are a bit noisy with no signal output (slight hiss or hum) so thats often what separates the big guys and high end home theater amps.

Is noise floor different from or a part of signal to noise ratio? I wonder at what level might it become audible or interfere with low level details in the recording?

Tony V. said:
As far as what headroom is acceptable it simply comes down to output and what your speakers are rated to handle. You want the amp to exceed the speaker normal power ratings by about 20% RMS and keeping in mind that most full range speakers with an efficiency rating of 90db will reach ear bleeding levels in a normal size space at about 125 watts

The spreadsheet that Grayson linked seems to agree with this. Using the example of 90dB efficient 6ohm Chain A5rx and a listening distance of 9ft get you 85dB reference level with 20dB headroom with 162 watts.

Tony V. · Jan 30, 2019

Have a look at Emotiva as they have some very good amps that range from nonoblock to 7 channel

Grayson Dere · Jan 30, 2019

Tony V. said:
Have a look at Emotiva as they have some very good amps that range from nonoblock to 7 channel

The XPA-GEN 3 amps are very promising.

https://hometheaterhifi.com/reviews...fier/emotiva-xpa-gen3-power-amplifier-review/

Tony V. · Jan 30, 2019

Yes, class D amps

Grayson Dere · Jan 30, 2019

Currently I'm running a 'Class D Audio' brand amp for my mains and to me it sounds great!
I think class D amps have come a loooong way.

SDS-470CS
300w RMS @8ohm stereo / 600w RMS @4ohm stereo

JStewart · Jan 30, 2019

Tony V. said:
Have a look at Emotiva as they have some very good amps that range from nonoblock to 7 channel

I have an XPA-3 Gen2 I use for the front stage already. I've been happy with it because it's done it's job without me really noticing it one way or the other. The purchase decision then came down to watts/price/reputation.

JStewart said:
It just seems like there should be some reason for paying more for what on the surface looks like closely spec'd products from two reputable companies like Parasound and Outlaw.

So getting back to this question and looking at the specs for the two do you guys see any reason to choose one over the other? Or is the answer elsewhere.

Parasound A52

Continuous power output:
125 watts RMS x 5, 20 Hz - 20 kHz, 8 Ω, all channels driven
225 watts RMS x 5, 20 Hz - 20 kHz, 4 Ω, all channels driven

Current capacity:
30 amperes peak per channel

Power bandwidth:
5 Hz - 100 kHz, +0/-3 dB at 1 watt

Total harmonic distortion:
< 0.2 % at full power

IM distortion: balanced 16 V rms
< 0.04 %

Slew rate:
> 130 V/µsecond

Dynamic headroom:
> 1.5 dB

Interchannel crosstalk:
> 78 dB at 1 kHz;
> 63 dB at 20 kHz

Input sensitivity:
1 V for 28.28 V, THX Reference Level

Input impedance:
47 k Ω unbalanced; 94 k Ω balanced

S/N ratio:
113 dB, input shorted, IHF A-weighted

Damping factor:
> 1000 at 20 Hz

Voltage:
110V - 120V

Dimensions:
17-1/4" w x 5-7/8" h x 19-3/4 " d, 5-1/4 " h without feet

Net weight: 50 lb.

Outlaw 5000

Power output: 120 watts RMS x 5 (all channels driven simultaneously into 8 ohms from 20 Hz to 20 kHz with less than 0.02% total harmonic distortion, A-weight filter). 180 watts RMS x 5 (all channels driven simultaneously into 4 ohms from 20 Hz to 20 kHz with less than 0.03% total harmonic distortion, A-weight filter)

Frequency Response: 20Hz -20kHz +/- 0.5 dB at rated
output (120W)

Total Harmonic Distortion (THD): Less than 0.02% at rated output (120W), all frequencies, less than 0.01% at 1kHz

Intermodulation Distortion (IMD): Less than 0.05% from 250mV to output full rated output (120W)

Filter Capacitance: Four 6,800 μF Capacitors per Channel

Number of Output Devices: 4 per channel

Power Bandwidth: 5Hz - 54kHz +0/-3 dB

Damping Factor: Greater than 105 from 10Hz to 400Hz

Crosstalk: Greater than -70dB from 20Hz – 20kHz

Gain: Voltage gain of 29dB

Input Impedance: 40k ohms

Input Sensitivity: 1.00 Volt

Remote Trigger Voltage: 3 - 24 Volts DC at 5 milliamperes or greater

Power requirements: 120VAC, ±3%, 50Hz - 60Hz

Power consumption: 1,500 watts (maximum)

Dimensions including feet (H x W x D): 6.0" x 17.0" x 16.75"

Weight: 50 (lbs)

Tony V. · Jan 30, 2019

I would lean towards the Parasound

JStewart · Jan 31, 2019

Thanks again Tony. I was leaning that way too. Mostly on faith in the value of the brand.

ddude003 · Jan 31, 2019

There is no "Underwriters Laboratories" or a Industry Sponsored and Supported Independent Benchmark Lab that would ensure published specifications are measured the same or that all the specs that might matter are published or tested... It is pretty obvious that different amplifier designs and topologies with different parts and/or different quality parts will eventually sound different and have different specs...

Find some photos of the internals of these Amps (google is your frenemy)... Look for things like potted transformers, high quality parts, cables and wires (gauge, and routing) and layout of main components and heat sinks...

You are comparing a ~$750.00 Amp to a ~$2,500.00 Amp... There is really no comparison... If you like your Emotiva XPA-3 why are you not looking for another Emotiva Amp, like the XPA-5?

JStewart · Jan 31, 2019

ddude003 said:
There is no "Underwriters Laboratories" or a Industry Sponsored and Supported Independent Benchmark Lab that would ensure published specifications are measured the same or that all the specs that might matter are published or tested... .

Thanks ddude003. You're absolutely right and that's become a frustration.

ddude003 said:
You are comparing a ~$750.00 Amp to a ~$2,500.00 Amp... There is really no comparison...

That's a bigger frustration and really the point because nothing in the published specs says one is worth more than the other or one might have audible differences from the other. How does a consumer compare and choose?

ddude003 said:
If you like your Emotiva XPA-3 why are you not looking for another Emotiva Amp, like the XPA-5?

I do like the Emotiva, but have two reasons. The additional watts aren't needed and if I understand input sensitivity correctly (which I may not and would appreciate a better understanding if that's the case) then likely better off with the lower input sensitivity offered by the outlaw and parasound when used with my AVR as a pre-amp. Parasound A52 is 1v Outlaw 1v Emotiva XPA-3 Gen2 1.1v (used now so I know it works well enough) Emotiva XPA-5 Gen2 1.7v Emotiva XPA-5 Gen3 1.5v and also a different topology.

ddude003 · Feb 2, 2019

I will just leave this here as food for thought... These are the things I think are important and I use for comparison purposes... I am sure others have other things they find important...

Power output in Watts… 10W is pretty loud for average listening and 100W to 150W is more than enough to damage your hearing… Often rated per Output Load Impedance 2, 4 or 8 ohms… Take Speaker sensitivity/efficiency into account… Driving larger speakers in larger spaces may need more Watts... A few Watts more or less is no big deal as the first Watts are the most important...

Total Harmonic Distortion + Noise (THD + N) is how much effect the audio amplifier has on the sound output. More distortion generally means more colouration to the sound. Lower numbers are better…

Dynamic Headroom is the ability of an audio amplifier to output power at a significantly higher level (while avoiding distortion) for short periods to accommodate sound peaks.

Frequency Response is the ability of a device (such as an audio amplifier) to handle the frequencies (a range) applied to it... 20Hz to 20KHz is the range of human hearing... What feelings may be gained with lower and higher numbers to a point...

Signal to Noise Ratio (SNR) is the comparison of the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in decibels... A ratio higher than 1:1 indicates more signal than noise... The goal is to make this background noise imperceptible, this means you hear more of the music and less of the noise... Bigger numbers are better...

Intermodulation Distortion / Crosstalk is a measure of how much undesirable left signal is mixed with right output... The more crosstalk there is, the harder it is to pick out the positions of the instruments/performers as stereo separation is affected (think sound stage)... Smaller numbers are better and the better the stereo channel separation.

Wide Band Damping Factor (DF) is defined as “the ratio of the load impedance (loudspeaker plus wire resistance) to the amplifier internal output impedance.” This basically indicates the amplifier's ability to control overshoot of the loudspeaker, i.e., to stop the cone from moving. Bigger numbers are better to a point... Greater than 40 or 100 is fine depending on audio amplifier design and speaker design and/or listeners preference...

Amplifier design and topology has some bearing on these specs... Tubed, Solid State class A, A/B, D and Hybrid implementations of Single Ended, Push Pull and Output Transformerless (OTL) audio amplifier... And things like feed back designs or the lack of them and how they interact with various speaker designs (think cones vs electrostatic).

bamtron · Mar 21, 2020

JStewart said:
I have an XPA-3 Gen2 I use for the front stage already. I've been happy with it because it's done it's job without me really noticing it one way or the other. The purchase decision then came down to watts/price/reputation.

So getting back to this question and looking at the specs for the two do you guys see any reason to choose one over the other? Or is the answer elsewhere.

Parasound A52

Continuous power output:
125 watts RMS x 5, 20 Hz - 20 kHz, 8 Ω, all channels driven
225 watts RMS x 5, 20 Hz - 20 kHz, 4 Ω, all channels driven

Current capacity:
30 amperes peak per channel

Power bandwidth:
5 Hz - 100 kHz, +0/-3 dB at 1 watt

Total harmonic distortion:
< 0.2 % at full power

IM distortion: balanced 16 V rms
< 0.04 %

Slew rate:
> 130 V/µsecond

Dynamic headroom:
> 1.5 dB

Interchannel crosstalk:
> 78 dB at 1 kHz;
> 63 dB at 20 kHz

Input sensitivity:
1 V for 28.28 V, THX Reference Level

Input impedance:
47 k Ω unbalanced; 94 k Ω balanced

S/N ratio:
113 dB, input shorted, IHF A-weighted

Damping factor:
> 1000 at 20 Hz

Voltage:
110V - 120V

Dimensions:
17-1/4" w x 5-7/8" h x 19-3/4 " d, 5-1/4 " h without feet

Net weight: 50 lb.

Outlaw 5000

Power output: 120 watts RMS x 5 (all channels driven simultaneously into 8 ohms from 20 Hz to 20 kHz with less than 0.02% total harmonic distortion, A-weight filter). 180 watts RMS x 5 (all channels driven simultaneously into 4 ohms from 20 Hz to 20 kHz with less than 0.03% total harmonic distortion, A-weight filter)

Frequency Response: 20Hz -20kHz +/- 0.5 dB at rated
output (120W)

Total Harmonic Distortion (THD): Less than 0.02% at rated output (120W), all frequencies, less than 0.01% at 1kHz

Intermodulation Distortion (IMD): Less than 0.05% from 250mV to output full rated output (120W)

Filter Capacitance: Four 6,800 μF Capacitors per Channel

Number of Output Devices: 4 per channel

Power Bandwidth: 5Hz - 54kHz +0/-3 dB

Damping Factor: Greater than 105 from 10Hz to 400Hz

Crosstalk: Greater than -70dB from 20Hz – 20kHz

Gain: Voltage gain of 29dB

Input Impedance: 40k ohms

Input Sensitivity: 1.00 Volt

Remote Trigger Voltage: 3 - 24 Volts DC at 5 milliamperes or greater

Power requirements: 120VAC, ±3%, 50Hz - 60Hz

Power consumption: 1,500 watts (maximum)

Dimensions including feet (H x W x D): 6.0" x 17.0" x 16.75"

Weight: 50 (lbs)

0.2% distortion is not what I would call "HIFI". back in the late 90's through to 2012 I had a few amplifiers in an active crossover system each of which had 0.002% THD and IMD specs of 0.005% the bass amps at 350W per channel into 4 ohms, the mids at 220W per channel and the highs 150W per channel. (that's 3 stereo amps for 2 audio channels) 0.2% distortion would sound quite harsh. It could be that the marketing people have insisted on reporting the highest output power possible. It could well be that the distortion at 120W is only 0.02%. This is a graphic illustration of selective reporting. The best specification would be "less than ___% distortion at all levels below ____W which would tell you more about how it sounds at normal levels.
Bamtron.

bamtron · Mar 21, 2020

Most people don't understand distortion. THD (total harmonic distortion) is generated by non - linearity in semiconductors, and is reduced by the "negative feedback" circuitry. The products are new output signals at a multiple of the input. For example, 0.2% distortion is 0.2 Watts output of new, unwanted signals for 100W of wanted output. Sounds harsh and nasty. Further eg, 100W of 100Hz sound plus 0.2 W total of 300Hz plus 500Hz plus 700Hz etc. generated by the amp.
IMD (Intermodulation distortion) is worse. This is where 2 or more tones mix to get new output frequencies. eg 100hz plus 750hz wanted tones mix to give unwanted outputs of 850hz and 650hz. This is a simple 2 tone intermod. When you have 3 tones you get A + B, A + C, A + B + C, A - B, A - C, A - B - C, A + B - C, A - B + C. You can imagine how complex music can have an enormous number of new, unwanted signals. IMD = fuzzy, blurred, bad sound. These "simple" intermods are complicated by harmonics of ALL the above mentioned products. Bottom line is always look for the lowest amount of distortion you can find. By the way, these above mentioned distortion products are less than the products generated by most dynamic "hi-fi" loudspeakers, where distortion of 20%+ at certain frequencies can occur.
Bamtron

Amplifiers - What specs are important?

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