high current amp power delivery

[jdmccall]

Basic question here:

 

Let's assume we have two amplifiers, one rated at 100W @ 8 Ohms and 120W @ 4 Ohms, and a second amp rated 100 @ 8 Ohms and 200 @ 4 Ohms.  My question is can the first amplifier double it's power into 4 Ohm loads up to it's rated 120W or will its power into 4 Ohm loads always droop (not double).  For example, could the first amps power also be spec'd as 60W @ 8 Ohms and 120 @ 4 Ohms?  Or would it's power into 4 Ohms never be double it's 8 Ohm power, regardless of the power level?

 

Probably a dumb question, but there it is.

 

Thanks! 

[baron167]

This is an incomplete scenario. Please elaborate. The answer to the problem given is no.


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[JohnA]

OK, remember, these are ratings with an associated distortion spec, not necessarily max output at clipping.  In this simplistic situation, the power supply would appear to be limited to 5.5 amps and that is with a significant voltage sag. 

 

Following the formulas, Pwr = I x V and V = I x R the amp will deliver all the current (I) the Resistance (impedance) will allow, pushed by the Voltage set by the volume control, up to the 5.5 amp limit, regardless of the impedance.  At many points, it would certainly be 2x the power that the same voltage would push through 8 ohms, as long as you stayed below 5.5 amps.  That might even be 4x the power if you had a 2 ohm load (and stayed under thermal limits and 5.5 amps). 

 

Remember, voltage pushes, impedance restricts and current causes heat.  Kept within safe limits, any amp will almost double current into half the impedance.  No amp is so linear that it doubles when driven at its limits. 

[jdmccall]

OK, let me re-phrase: What I'm trying to determine is whether "high-current" amplifiers have real-world, audible advantages over other designs.  It makes sense to me that with reactive loads, as most all speakers are, the ideal amp should be able to double output power with every halving of impedance, in order to eliminate audible distortion and dynamic limiting when reproducing music or any other dynamic signal into varying impedances.  Of course, few amps are ideal!  So my question is...will my amp, even though it's not rated to double its power going from 8 to 4 Ohms, still be able to do just that...to a point?  In other words, let's say my amp is loafing along driving a pair of 8 Ohm rated speakers at a low volume level.  At some frequencies, these 8 Ohm speakers drop to 4 Ohms, though.  Would the amp double its power, thereby preserving accurate dynamics and low distortion...or will distortion rise and/or dynamics be limited, even though the power output is nowhere close to rated max?  Maybe another way to frame the question is this:  I used to own an NAD amp rated 150W into 8 Ohms or 4 Ohms.  Is such an amp still able to double its 4 Ohm power, relative to power into 8 Ohms...until 8 Ohm power output reached 75W, beyond which, 4 Ohm power would become increasingly distorted and dynamics increasingly limited?

[CECAA850]

10 hours ago, jdmccall said:

OK, let me re-phrase: What I'm trying to determine is whether "high-current" amplifiers have real-world, audible advantages over other designs.

Yes.  It's evident in the lower frequencies.

[Bubo]

Perhaps the question is: Is a more Robust Amplifier more desirable ?

 

A. Yes

It can handle a greater number of variances off of the ideal load.

Greater power reserves and the ability to deliver without distortion

The same goes for performance at higher and lower frequencies

When the Engineers design an Amp, they should and most likely Characterize it in the lab with a variety of load conditions, inputs and faults. To see how the Amp handles them, compared to the design.

"High Current" to me is more of a Marketing Slogan

I stumbled across the THX Lab tests they use to characterize Amps once, I wish I had saved it.

Might have been over 200 measurements under varying conditions to characterize the amp and determine if it was in tolerance to meet THX defined loads

 

Quote

 

We refer to the THX controller as both dedicated surround sound processor/preamplifiers, and the processing section of integrated receivers.

There are two distinct halves to the certification of a THX Controller. The first is the actual performance metrics, shown in the table at right. As you can see, it goes well beyond any review you’ve ever read, including our own best. What is absolutely key here is that these are not simply “minimums” a product must meet, but many are actually design considerations. For example, the line level outputs must not only meet a certain voltage capability, but their output voltage must be a certain level relative to an input signal, be it analog or digital.

https://hometheaterhifi.com/editorial/what-it-means-and-how-to-use-it/

 

 

The THX Controller

Metrics Tested on THX Controllers:

Reference Output Voltage
Voltage Gain
Input Impedance
Gain Control Range
Gain Tracking of the Master Gain Control
Overload Source Voltage
D.C. Bias Current at the Input
Maximum Output Voltage of Low-Level Outputs
Output Source Impedance
Polarity
D.C. Offset at the Output
Frequency Response Deviation
Signal Time Delay
Noise Output Voltage
Input Level Indicator (Clipping Indicator)
Video Path Switching
Video Level
Sync Level
Bar Tilt
Pulse/Bar Ration
K-Factor (K-2T)
Frequency Response Amplitude (0.5 to 4.2 MHz)
Group delay (0.5 to 4.2 MHz)
Chroma Gain
Chroma Delay
Differential Gain
Differential Phase
Noise
Video Conversion
Harmonic Distortion and Noise
Difference-Frequency Distortion
Dynamic Range
Digital Data Sampling Rate Support
Input Mode Control and User Interface Design
Input Mode Switching
Automatic Detection of Data Types
Output Modes and Post Processing
Equalization and Tone Controls
Signal Headroom
Bass Management
Filter Characteristics
LFE Channel Level Scaling
Loudspeaker Position Time Synchronization
Auto Calibration
Auto Setup
Output Levels
Dialogue Normalization

 

Another key element that THX requires for receivers and SSPs is the reference setting for volume control. When a system is calibrated according to the manufacturer’s instructions, “0.0 dB” on the volume control corresponds to reference level playback. In turning the volume down, the volume level is expressed in -dB, or how many dB below reference level you are.

Metrics Tested on THX Amplifiers:

Reference Output Voltage
Voltage Gain
Output Current
Output Source Impedance
Overload Restoring Time
Stability with Capacitive Load
Harmonic Distortion and Noise
Modulation Distortion
Difference-Frequency Distortion
Noise Output Voltage
Phase Response
D.C. Offset at the Output
Hum
Crosstalk
Acoustic Noise Level
Mechanical Noise
Input Sensitivity
Input Impedance
Output Impedance
Load Impedance Range
Voltage Output Capability
Current Output Capability
Transient Output Capability
Transient Overload Recovery Time
Asymmetrical Clipping
Frequency Response
Phase Response
Phase Margin
Time
Total Harmonic Distortion
Intermodulation Distortions
SMPTE IM Distortion
IHF IM Distortion
DIM 30 Distortion
Noise
Hum
Radiated Interference
Conducted Interference
Crosstalk

 

Make no mistake: THX Ultra power amplifiers tend to be very powerful. We’ve never seen one with less than 100 watts/channel continuous RMS, full band, all channels driven, BUT because of the “practical sum” THX has defined for themselves, even seemingly modest receivers under $1,000 can get THX Select2 certification and provide a satisfying experience for a lot of people who can’t afford a stack of THX Ultra power amps (we’ll talk about Select- vs. Ultra-Certification a little later).

 

Metrics Tested on THX Speakers:

 

Axial Frequency Response Analysis
Directional Characteristics
Sensitivity
Impedance
Harmonic Distortion
Low Frequency Cut Off
Phase Angle
Stray Magnetic Flux
Maximum Output Level
Acoustic Noise Level
Polarity

 

 

https://www.thx.com/aaa/

 

 

[Bubo]

This is a review of a headphone amp, not hard to extrapolate to an amp

Charts with the measurements

Review and Measurements of Massdrop THX AAA 789 Amp

https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-massdrop-thx-aaa-789-amp.5001/

 

[jdmccall]

In light of all preceding, which is "best":  an amp rated 70W into 8 Ohms / 140W into 4 Ohms, or an amp rated 275W into 8 Ohms and 400W into 4 Ohms?  Which, if either, would sound cleaner and more dynamic driving speakers that dip to 4 Ohms at some frequencies?  .....asking for a dumb guy I know.

 

[Bubo]

1 minute ago, jdmccall said:

In light of all preceding, which is "best":  an amp rated 70W into 8 Ohms / 140W into 4 Ohms, or an amp rated 275W into 8 Ohms and 400W into 4 Ohms?  Which, if either, would sound cleaner and more dynamic driving speakers that dip to 4 Ohms at some frequencies?  .....asking for a dumb guy I know.

 

The 75 W amp looks like a more robust design on one metric

 

The second amp may have problems with peaks

You also have to look at SN, THD etc....

YMMV

[ClaudeJ1]

22 minutes ago, jdmccall said:

In light of all preceding, which is "best":  an amp rated 70W into 8 Ohms / 140W into 4 Ohms, or an amp rated 275W into 8 Ohms and 400W into 4 Ohms?  Which, if either, would sound cleaner and more dynamic driving speakers that dip to 4 Ohms at some frequencies?  .....asking for a dumb guy I know.

 

Just buy a pair of Hypex NC-400 Monobloc Kits for about $1,600. It takes no soldering to build the kit, and is the easiest I've ever built. Be done with all this BS.

 

https://www.diyclassd.com/product/nc400-mono-kit/24

[jdmccall]

3 hours ago, ClaudeJ1 said:

Just buy a pair of Hypex NC-400 Monobloc Kits for about $1,600. It takes no soldering to build the kit, and is the easiest I've ever built. Be done with all this BS.

 

https://www.diyclassd.com/product/nc400-mono-kit/24

Hmmm...interesting.

 

 

[ClaudeJ1]

7 hours ago, jdmccall said:

275W into 8 Ohms and 400W into 4 Ohms?  Which, if either, would sound cleaner and more dynamic driving speakers that dip to 4 Ohms at some frequencies?  .....asking for a dumb guy I know.

the Hypexes doe this and never gets hot, so I leave them on all the time.

[Chief bonehead]

If distortion limits are the same.....the second amp

[jdmccall]

My Parasound runs really cool, too, and it's a class AB (...I think).  I like it real well and have no complaints but I've just been cipherin' on amplifiers and power ratings and current delivery and low-impedance drive capability....you know, important stuff like that.   Primary motivation, I suppose is the Denon PMA-1600NE integrated that I'm thinking would sure look nice with my Denon CD player.  The Denon is rated 70W into 8 and 140W into 4 Ohms.  Probably more than enough for my Cornwalls...but is it?  My Parasound 2250 v.2 is rated 275W into 8 and 400W into 4 Ohms.  So I'm wondering if I would actually miss the power, SQ-wise, or could the Denon actually sound better because of it's ability to double it's 8 Ohm power into 4 Ohm loads.  I don't recall seeing an impedance plot of a Cornwall IV, so I don't know how low their impedance may go.  I should check into that.

[willland]

If the newer Denon integrated amps are even close to the build and sound quality of the 80’s/90’s PMA amps, then I don’t think you are missing out by going with the Denon.  I have owned at minimum 4 of these older Denon PMA integrated and they have been nothing short of spectacular with any speakers I threw at them, especially Heresy’s, Fortes, and Quartets.  Bass drive galore with a very natural sound with great detail.

 

The Denon’s “70w/channel” will feel like double that.

 

Bill

[ClaudeJ1]

20 hours ago, Chief bonehead said:

If distortion limits are the same.....the second amp

Yep. This what the Hypex NC-400 does so well.

[JefDC]

On 1/5/2021 at 5:29 PM, jdmccall said:

In light of all preceding, which is "best":  an amp rated 70W into 8 Ohms / 140W into 4 Ohms, or an amp rated 275W into 8 Ohms and 400W into 4 Ohms?  Which, if either, would sound cleaner and more dynamic driving speakers that dip to 4 Ohms at some frequencies?  .....asking for a dumb guy I know.

 

 

 

 

 

Your reasoning is correct, amplifiers which can double their power when halving the load are better able to drive difficult loads. (other parameters must be considered as well off course).

In your question the 70W one is more stable 

The Hypex is an excellent amplifier, an alternative is an XTZ Edge A2-300 amplifier @ about 500$ (you can easily google the site and specs).

Here the link to the specs of the used Integrated Power Circuit; it goes in great detail: https://icepower.dk/download/2420/

 

Example for 4 and 8 Ohm figures below:

 

Edi: forgot Power specs:

2 x 460 W (1% THD, 2.7 Ω)
2 x 300 W (1% THD, 4 Ω)
2 x 150 W (1% THD, 8 Ω)

[DirtyErnie]

Ultimately, the only thing that matters is what sounds best with your speakers, room, and ears.

 

"If it measures good, and sounds good, it is good. If it measures good, and sounds bad, you've measured the wrong thing." ~ H.H. Scott

[ClaudeJ1]

10 minutes ago, DirtyErnie said:

Ultimately, the only thing that matters is what sounds best with your speakers, room, and ears.

 

"If it measures good, and sounds good, it is good. If it measures good, and sounds bad, you've measured the wrong thing." ~ H.H. Scott

It measures better than any other amplifier. It's only bettered by a slight margin by the newer version designed by Bruno Putzey and the THX AAA amplifier from Benchmark, but with that one, it's limited to about 100 watts rather than 400.

 

https://purifi-audio.com/eigentakt/

 

[DirtyErnie]

3 minutes ago, ClaudeJ1 said:

It measures better than any other amplifier. It's only bettered by a slight margin by the newer version designed by Bruno Putzey and the THX AAA amplifier from Benchmark, but with that one, it's limited to about 100 watts rather than 400.

 

https://purifi-audio.com/eigentakt/

 

 

But how does it SOUND?