Topping LA90 Discrete Amplifier Review

[antcollinet]

Hi all, I would like to have something cleared regarding gain and power.
I would like to know if there is a 'standard' gain that most amplifiers use.
Also I would like to know if the standard rule of 3db increase= double the power is valid when comparing different gains on the same amplifier or even different amplifiers: so an aplifier with 9db gain and 50w max power in 8ohms has the same spl of another amplifier with 12db gain and only 25w power into 8ohms?
Is the calculation a rough estimate or is it precise?
Thanks for any help on this.

There is no standard gain - although gain in the region of 25 to 30dB is common. However the topping PA5 for example has a gain of only 20dB (x10)

Gain simply multiplies the input voltage to output voltage.

It doesn't alter the maximum power or SPL of an amplifier. It only changes the input voltage needed to achieve the maximum power/SPL. The maximum power is limited by the output voltage or output current limits of the amp - not by the gain.

A very high power amp might need to have a higher gain in order to allow lower voltage sources to drive it to full power.

So for example if you have an amp with a gain of 26dB (x20) which is capable of 300w into 8 ohm (needing 48V), then a 2V (typical RCA) source would only be able to drive 40V to the output of the amp - which is only 200W into 8ohm. For this source you would need a gain of at least x25 (28dB) to drive it to full power. Or you would need a source capable of higher voltage.

 

[Michal]

Hi
I have a few questions for LA90D owners about how does this amplifier build the sound stage.
Where is the beginning of the soundstage - in front of the speaker line, on the speaker line or behind the speaker line?
Is the sound detached from the speakers and coming out to the sides?
Kind regards

 

[adLuke]

Thank you @antcollinet and @welwynnick for your help in clarifying the issue of gain.
I think I miss a lot of basic knowledge to understand how to interpret all the numbers.
I understand now that gain is one factor in the deliverable spl, and specifically it affects what the maximum power of the amp given the in voltage.
Now, I seem to understand that RCA and Balanced (TRS, XLR etc) have most often standard voltage: 2v for unbalanced and 4v for unbalanced (although there are exception, like Topping DM7 that can deliver 5v).
So in low gain mode, the LA90 has gain of 9.4db. I would like to know the math expression in order to calculate the multiplier mentioned by @antcollinet would that be roughly 3? So in low gain mode, LA90 would be able to reach 6v with RCA input and 12v with TRS imput. How do I convert that into W (power)?
I started with the understanding that Watts are given by Voltage*Ampere. But seems like we don't really need to know the current to determine the max power here. Am I wrong?
Sorry to bug with basic questions. Feel free to point me to a basic description of these concepts if you like.
Thanks again for your help.

 

[staticV3]

So in low gain mode, the LA90 has gain of 9.4db. I would like to know the math expression in order to calculate the multiplier

10^(dB ratio/20)=voltage ratio.
So 9.4dB gain is a voltage ratio of 10^(9.4/20)=2.95.

How do I convert that into W (power)?

Vrms^2/Ω=W
This doesn't account for current limits though, so keep that in mind.
How much voltage an Amp can output, depends on the load impedance.

Btw, here are some handy websites for converting units:
https://sengpielaudio.com/calculator-levelchange.htm
https://reference-audio-analyzer.pro/en/v-dbv-dbu.php#gsc.tab=0

 

[adLuke]

That is very clear and very good info. Thanks a lot @staticV3

 

[antcollinet]

I started with the understanding that Watts are given by Voltage*Ampere. But seems like we don't really need to know the current to determine the max power here. Am I wrong?

To add to @staticV3 's post.

Take a typical amp which can deliver (say) 200W into 4ohm, but perhaps 150W into 8ohm.

From Sv3's forumula: P = V^2/R also gives you V= sqrt (PxR).
You can also have P = IxV and P = I^2 x R and I = sqrt (P/R) (This are basically all the same equation with substitutions for I and V based on ohms law: V=IxR)

So for 200W into 4ohm, you need 28.3V AND you need 7.1A
For 150W into 8 ohm, you need 34.6V AND you need 4.33A

So you can see the amp is able to output 34.6V, and 7.1A. However, with a 4ohm speaker it is the maximum current that is reached first whereas with the 8ohm speaker it is the voltage limit that is reached first.

This is not an uncommon thing to happen. At the same voltage, if you half the impedance, then the power will double IF the amp is also capable of delivering double the current. This is often not the case, and the amp goes into current limit, thereby limiting the doubling of power.

 

[adLuke]

Thank you @antcollinet this is a very clear explanation

 

[adLuke]

Ok thanks to all that have helped, I have a newfound understanding that brings more questions:
Using the example of LA90: Low Gain Stereo 9.4dB, High Gain Stereo 19.4dB; Low Gain Mono 15.4dB, High Gain Mono 25.4
So using @staticV3 formula, the multipliers are (in order): 2.95, 9.33, 5.89, 18.62.
Given a standard balanced (say TRS) input voltage of 4Vrms, these multiplpiers (or ratio) imply maximum voltage deliverable by LA90 to be: 11.8V minimum, 74.5V maximum. Is all the math correct?
So, why do Topping choose a 64V power supply?

 

[antcollinet]

Ok thanks to all that have helped, I have a newfound understanding that brings more questions:
Using the example of LA90: Low Gain Stereo 9.4dB, High Gain Stereo 19.4dB; Low Gain Mono 15.4dB, High Gain Mono 25.4
So using @staticV3 formula, the multipliers are (in order): 2.95, 9.33, 5.89, 18.62.
Given a standard balanced (say TRS) input voltage of 4Vrms, these multiplpiers (or ratio) imply maximum voltage deliverable by LA90 to be: 11.8V minimum, 74.5V maximum. Is all the math correct?
So, why do Topping choose a 64V power supply?

The gain only works up to the maximum possible amplifier voltage. Once that is reached it doesn't matter how high the input voltage or gain is, the output voltage won't get bigger - it is a limit. Selectable gains simply allow you to match better based on the output voltage of your source.

Also consider - the PSU voltage sets a limit to the PEAK of the output voltage. For a sinewave, the peak voltage will be 1.4 times the RMS voltage.

Then in mono mode (BTL mode) the voltage applied to the speaker can be effectively doubled, by driving one side of the speaker with an inverted form of the other side.

 

[stereo coffee]

There is no standard gain - although gain in the region of 25 to 30dB is common. However the topping PA5 for example has a gain of only 20dB (x10)

Gain simply multiplies the input voltage to output voltage.

It doesn't alter the maximum power or SPL of an amplifier. It only changes the input voltage needed to achieve the maximum power/SPL. The maximum power is limited by the output voltage or output current limits of the amp - not by the gain.

A very high power amp might need to have a higher gain in order to allow lower voltage sources to drive it to full power.

So for example if you have an amp with a gain of 26dB (x20) which is capable of 300w into 8 ohm (needing 48V), then a 2V (typical RCA) source would only be able to drive 40V to the output of the amp - which is only 200W into 8ohm. For this source you would need a gain of at least x25 (28dB) to drive it to full power. Or you would need a source capable of higher voltage.

But conventional sources don't output 2V when playing conventional media,which includes streaming, rather is typically 6.32 times less. Before a thousand replies, the media controls the output level, and the media level which is 6.32 less than 2V is not the equipment capability. But if input sensitivity is the same or very similar to consumer line level , then there is no appreciable loss. A casual observation shows the majority of equipment is specified toward 0DbFs which in practical use is never achieved. To ascertain divide the input sensitivity stated by 0.316, this then gives you the amount of loss, where input sensitivity is stated related to output power.

This amplifier rated at 50W per channel https://www.hifiengine.com/manual_library/quad/306.shtml has as a result of equating to consumer line level, more available power than https://www.hifiengine.com/manual_library/parasound/halo-a23.shtml Or related to the OP the Topping amp achieves only 15.8 watts into 4 ohms per
https://addictedtoaudio.co.nz/products/topping-la90-power-amplifier so nothing to be excited about, which is 4.74 times worse than a Quad 306

 

[antcollinet]

But conventional sources don't output 2V when playing conventional media,

Well I've just put a loundess meter on the track I'm currently playing - and "true peak max" is showing as -0.2dB

So assuming 0dB represents full scale, this track outputs instantaneous peaks of essentially full scale - which is presumably 2V for a 2V output device.

Of course - on average it is going to be significantly lower than this - but that is not the point. We don't want our amp to be clipping on the peaks, either.

(Next track is half way through and has hit -2.1dB - this by the way is sedate female vocals) Ended at -1.3dB

Third track straight in at -3.5, now at -2 after 20seconds. After 1 minute, -0.9

 

[stereo coffee]

To give meaning the measurement of sensitivity for amplifiers, is usually stated as voltage Root Mean Square (V RMS ) , similarly a check of level of media using conventional source using Audacity can allow visualization of RMS, distinct from Peak Here is a graph of Mike Oldfields Amarok showing RMS in light blue and peak in dark. Streaming sources state level in LUFs where -14 LUFs happens to accord also with consumer line level. https://en.wikipedia.org/wiki/Line_level

 

[Mr_T]

I didn't find measurements of power in bridge mode for the LA90 discrete at 8 Ohms. Does anyone have this?
Topping on their website claims 180 watts at 1% THD. Really?

 

[antcollinet]

I didn't find measurements of power in bridge mode for the LA90 discrete at 8 Ohms. Does anyone have this?
Topping on their website claims 180 watts at 1% THD. Really?

It's plausible. If you look at the normal 8 ohm power at 1% (-40dB) from the chart it is around 55W. If you double the voltage in bridged mode, you'd get 4x the power (220W). Take into account hitting current limit, and it drops down to 180W

Or take the 4ohm power unbridged. The chart doesn't go as far as -40dB (probably due to current limit) but is heading towards 90W. Put that same current into 8ohm at double the voltage and you are at or around 180W

Plus topping tend not to lie - they expect their devices to be measured.

 

[stereo coffee]

But the Topping like all amplifiers responds to input signal, which is not being measured properly.

 

[antcollinet]

But the Topping like all amplifiers responds to input signal, which is not being measured properly.

Say what? Was that a reply to me? If so I'm not sure what you are meaning.

If not, it'd. be better to quote what you *are* replying to.

 

[terryforsythe]

Hi
I have a few questions for LA90D owners about how does this amplifier build the sound stage.
Where is the beginning of the soundstage - in front of the speaker line, on the speaker line or behind the speaker line?
Is the sound detached from the speakers and coming out to the sides?
Kind regards

My setup is a little different. I have two LA90D amplifiers and a Hypex Nilai stereo amplifier. The Nilai powers the woofers in the left and right speakers (Elac Uni-Fi Reference bookshelfs with the passive crossovers removed). Each speaker also has a dedicated LA90D, with one channel powering the midrange and the other channel powering the tweeter. I have a Velodyne HGS 18 subwoofer handling frequencies below 100 Hz. Crossovers and DSP are provided by a miniDSP HTx.

The soundstage is large and extends well beyond the speaker placements in all directions. The speakers disappear on good recordings - if wearing a blindfold you would not be able to pinpoint where the speakers are located. The imaging also is superb.

With that noted, the biggest limitations to overcome are due to the room, the speakers and speaker placement. Due to aesthetic considerations, I don't have any room treatment beyond normal furnishings, but the room is in an open floor plan and the shape of the room is complex. The only significantly large parallel surfaces are the floor and ceiling, which is 20 ft. high. Also, a table prevents me from pulling the right speaker away from the front wall further than 27" when I setup for my listening position. Nonetheless, even with those constraints, I have been able to tune the system to get what I consider to be excellent soundstaging.

My biggest gains in soundstaging have resulted from tuning the speakers - I have addressed cabinet resonances with additional internal bracing and damping material, I have plugged the ports, I have tuned the active crossover frequencies, and I have tuned the parametric EQs. Adjusting the midrange/tweeter crossover frequency to optimize the directivity index as best as I can has benefited the size of the soundstage.

I am still tuning, but so far the system sounds very good. After I finish tuning (it takes time to make adjustments, listen for a few days, and repeat), I am going to drag my KEF LS60 speakers to the family room to compare. I suspect that the KEF coaxial drivers will soundstage even better than my Elacs' coaxial drivers, but we will see.

 

[Mr_T]

It's plausible.

Thank you for your detailed answer. Do you have any info on what the performance is at 0.1% THD at 8 Ohm?

 

[antcollinet]

Thank you for your detailed answer. Do you have any info on what the performance is at 0.1% THD at 8 Ohm?

Look at the chart here for 8ohm not bridged at 0.1% (-60dB) and multiply by four. You'll be there or thereabouts.


EDIT = that is about 50x4 = 200 - more than the 1%, which is not realistic. So probably still around 180W or slightly less. Or perhaps reduce by 20% (as we do for 1%) - so 160W

 

[stereo coffee]

Say what? Was that a reply to me? If so I'm not sure what you are meaning.

If not, it'd. be better to quote what you *are* replying to.

Amplifiers respond to input signal , if the input signal is substantially less than the sensitivity manufacturers state, ( being only 0.316V RMS from conventional sources, which is the media being played restricting , and not the devices capability ), then figures of output power are also less. Not factoring that in is what I am meaning.