Apollon NCx500ST Stereo Amplifier Review

[huba]

Hi. Possibly answered before, so I apologise in advance.

I have an Apollon NcX500 dual mono, with a minidsp SHD preamp/dac/dsp. I currently have the lowest gain settings for the Aplollon. The volume level is ok. The output on balanced is 4v. Should I change gain settings on the power amp or are these optimal settings?

From what I think I understand from the review, I should use next to highest gain to reach max power. But I'm not sure if I should? Or should I use lowest possible gain in power amp that let me reach desired listening levels?

 

[amper42]

Hi. Possibly answered before, so I apologise in advance.

I have an Apollon NcX500 dual mono, with a minidsp SHD preamp/dac/dsp. I currently have the lowest gain settings for the Aplollon. The volume level is ok. The output on balanced is 4v. Should I change gain settings on the power amp or are these optimal settings?

From what I think I understand from the review, I should use next to highest gain to reach max power. But I'm not sure if I should? Or should I use lowest possible gain in power amp that let me reach desired listening levels?

You don't mention the speakers used. If it was me I would try the various gain settings to see if you can hear any difference after level matching the volume. In my setup with Revel F328Be I found using the 27.5dB gain setting gave the system a bit more punch and dynamics than when the amp was setup with a 12.8 or even 20.5dB gain setting. Don't be afraid to try the various settings. You will likely find using a higher amp gain setting will bring extra life to your music collection without adding any audible distortion.

 

[huba]

You don't mention the speakers used. If it was me I would try the various gain settings to see if you can hear any difference after level matching the volume. In my setup with Revel F328Be I found using the 27.5dB gain setting gave the system a bit more punch and dynamics than when the amp was setup with a 12.8 or even 20.5dB gain setting. Don't be afraid to try the various settings. You will likely find using a higher amp gain setting will bring extra life to your music collection without adding any audible distortion.

Thank you for your reply I will test with a bit higher gain settings. My speakers are Pylon Jasper 23's:

Drivers: 2 x 15 cm (Scan-Speak 15W/8531K00), 1 x 26 mm (Scan-Speak D2608/913000)
Sensitivity: 88 dB
Impedance: 4 Ω
Frequency response: 35 Hz - 20 kHz

 

[antcollinet]

Or should I use lowest possible gain in power amp that let me reach desired listening levels?

This. There should be no audible benefit to higher gains - in fact lower gains will mean the amplifier self noise is lower.

Also using the upstream devices - eg your DAC - at higher output levels will maximise the SNR there also.

 

[amper42]

This. There should be no audible benefit to higher gains - in fact lower gains will mean the amplifier self noise is lower.

Also using the upstream devices - eg your DAC - at higher output levels will maximise the SNR there also.

And yet, you won't hear any difference in SNR with the Hypex amp set at any of the lower gain levels. You can certainly set the NCX500 at the lowest gain which causes the SHD preamp to be turned up much higher to obtain the same sound levels. You might detect a slight difference with an analyzer but nothing audible. On the other hand, I have detected more bass slam and improved dynamics with the Hypex gain set at 27.5 dB. You may notice no difference. But, I think it's worth trying it yourself.

 

[antcollinet]

And yet, you won't hear any difference in SNR with the Hypex amp set at any of the lower gain levels. You can certainly set the NCX500 at the lowest gain which causes the SHD preamp to be turned up much higher to obtain the same sound levels. You might detect a slight difference with an analyzer but nothing audible. On the other hand, I have detected more bass slam and improved dynamics with the Hypex gain set at 27.5 dB. You may notice no difference. But, I think it's worth trying it yourself.

I agree that the noise difference is unlikely to be audible - except perhaps with very high sensitivity speakers.

However the characteristics you describe for higher gain simply don't stack up with the engineering - except perhaps explained by
1 - insufficiently accurate level matching for the comparison (even a small level mismatch might be perceived as improved slam/dynamics).
2 - whatever source you have is unable to drive the needed voltage to get the volume you want with the low gain - and clips or otherwise distorts while trying.

Other than that - common or garden perceptive biases (which we are all subject to) must be at play.

Changing the gain only alters the output voltage - which is reversed when you turn down the input level to achieve the same volume.

 

[amper42]

I agree that the noise difference is unlikely to be audible - except perhaps with very high sensitivity speakers.

However the characteristics you describe for higher gain simply don't stack up with the engineering - except perhaps explained by
1 - insufficiently accurate level matching for the comparison (even a small level mismatch might be perceived as improved slam/dynamics).
2 - whatever source you have is unable to drive the needed voltage to get the volume you want with the low gain - and clips or otherwise distorts while trying.

Other than that - common or garden perceptive biases (which we are all subject to) must be at play.

Changing the gain only alters the output voltage - which is reversed when you turn down the input level to achieve the same volume.

When you run the NCx500 at low gain with 12.8 or even 20.5dB settings it causes the remote on the pre-amp (in my case the RME ADI-2 DAC FS) to be less impactful with each move up than with the 27.5dB amp gain setting. That difference can make adjusting volumes between tunes/albums less responsive. If you spend time with 27.5dB for a while and then go back to 12.8 or 20.5dB you may feel the difference. My Revel F328Be are sensitive to it. I would suggest NCx500 owners spend time with the various gain setting rather than simply start at low gain and turn up the preamp to see if it offers enough volume.

With no audible difference in amp SNR between the settings even with sensitive speakers it's worth trying the higher gain settings. Your pre-amp might not offer sufficient gain to make up for a gain starved amp or your remote volume control may be less responsive with a super low gain amp setup. The suggestion to run the amp at the lowest possible gain certainly wasn't the optimal choice for my setup.

 

[huba]

When you run the NCx500 at low gain with 12.8 or even 20.5dB settings it causes the remote on the pre-amp (in my case the RME ADI-2 DAC FS) to be less impactful with each move up than with the 27.5dB amp gain setting. That difference can make adjusting volumes between tunes/albums less responsive. If you spend time with 27.5dB for a while and then go back to 12.8 or 20.5dB you may feel the difference. My Revel F328Be are sensitive to it. I would suggest NCx500 owners spend time with the various gain setting rather than simply start at low gain and turn up the preamp to see if it offers enough volume.

With no audible difference in amp SNR between the settings even with sensitive speakers it's worth trying the higher gain settings. Your pre-amp might not offer sufficient gain to make up for a gain starved amp or your remote volume control may be less responsive with a super low gain amp setup. The suggestion to run the amp at the lowest possible gain certainly wasn't the optimal choice for my setup.

I have played around with the gain some, and I tend to agree that there is more punch in the mids/upper bass. But my ears are deceptive so need to fine tune sub level etc. and listen over a couple of days.

 

[antcollinet]

I have played around with the gain some, and I tend to agree that there is more punch in the mids/upper bass. But my ears are deceptive so need to fine tune sub level etc. and listen over a couple of days.

You were told that is what you would hear - and so you did.

This is exactly how perceptive biases work.

it causes the remote on the pre-amp (in my case the RME ADI-2 DAC FS) to be less impactful with each move up

Can you come up with any explanation as to why that might be, when the engineering would say that sound quality will be optimised (albeit inaudibly) at maximum output of the DAC? I find this especially difficult to reconcile, with a DAC as well regarded as the RME. What you are describing is suggesting it might be faulty.

 

[amper42]

Can you come up with any explanation as to why that might be, when the engineering would say that sound quality will be optimised (albeit inaudibly) at maximum output of the DAC? I find this especially difficult to reconcile, with a DAC as well regarded as the RME. What you are describing is suggesting it might be faulty.

Here's an example, if you normally listen to music on the ADI-2 DAC FS at -34dBr with the NCx500 gain set at 27.5dB, you will need to turn up the ADI-2 to -19dBr in an attempt to compensate for an NCx500 amp set at 12.8dB gain. That can reduce headroom, potentially leading to clipping if pushed too far on peaks. It also doesn't seem to have the same punch as a NCx500 setup with a 27.5 gain setting.

Once you've done the test with music you are familiar with it's easy to see a gain starved amp doesn't always offer a positive outcome. Especially, when there is no audible benefit to running the amp with a 12.8dB setting. When you spend thousands trying to maximize the sound of your music it's important to actually try the various setting to see which one works best for you. I think it's great to have the option to run the NCx500 with 27.5dB gain or higher. AND it's really helpful if you are using it with other AB amps on an AVR.

 

[Chagall]

Here's an example, if you normally listen to music on the ADI-2 DAC FS at -34dBr with the NCx500 gain set at 27.5dB, you will need to turn up the ADI-2 to -19dBr in an attempt to compensate for an NCx500 amp set at 12.8dB gain. That can reduce headroom, potentially leading to clipping if pushed too far on peaks. It also doesn't seem to have the same punch as a NCx500 setup with a 27.5 gain setting.

Once you've done the test with music you are familiar with it's easy to see a gain starved amp doesn't always offer a positive outcome. Especially, when there is no audible benefit to running the amp with a 12.8dB setting. When you spend thousands trying to maximize the sound of your music it's important to actually try the various setting to see which one works best for you. I think it's great to have the option to run the NCx500 with 27.5dB gain or higher. AND it's really helpful if you are using it with other AB amps on an AVR.

Gain starved amp, why should the amp care?

The rule has always been to use the lowest gain setting that gets loud enough depending on your speakers/headphones for the lowest noise on the amp and the lowest signal attenuation on the preamp. This also helps if there is a preamp channel imbalance.

Don't know why would it be any different with this amp/preamp except louder equals better.

 

[antcollinet]

That can reduce headroom, potentially leading to clipping if pushed too far on peaks

That's not how it works. When the RME is set to 0dB (Full - and what is used in DAC mode or whatever they call the equivalent in RME land) the maximum peak will not clip, since the DAC is designed to output 0dB FS (0dB Full scale). The maximum value of the digital file will then output the maximum voltage on the output of the DAC. And most music isn't encoded to use those maximum values in any case.

The only exception to this would be the possibility of inter-sample overs - but you only need to be at most 3dB down from 0dB to completely eliminate them. And even if they occur at 0dB they are not normally an audible issue - and don't happen in any case with properly mastered music.

Once you've done the test with music you are familiar with it's easy to see a gain starved amp doesn't always offer a positive outcome.

Only if you test in a properly controlled way - and then I suspect your perceived differences would evaporate because they simply make no sense.

And gain "starvation" is not a thing. There is only the question "Can the amp with the supplied input volts deliver the needed output volts for the volume required. Because if it can, then the amp is not starved.

Finally

Especially, when there is no audible benefit to running the amp with a 12.8dB setting

One non audible benefit of using the lowest gain setting you need - is if your source (DAC, preamp, whatever) shits the bed and decides to set volume to full** - at a lower gain your speakers and ears are far more likely to survive the experience.

**or even a child - or clueless adult - cranks the volume.

 

[amper42]

There are a few reasons why someone might want to set the Hypex NCx500 amplifier at a higher gain setting of 27.5 dB versus the lower 12.8 dB option:
1. Increased output power: The higher gain setting allows the amplifier to produce more output power for a given input signal level. This can be beneficial if you appreciate more volume or are driving less sensitive speakers.

2. The volume control may seem sluggish with a 12.8dB gain compared to a 27.5dB gain setting. This is a result of .5 gain increments offering less volume difference per click with 12.8 than a 27.5dB gain setup. However, if you need finer volume adjustments the 12.8dB setting might be just what you want.

3. Better matching with source components: The 27.5 dB gain may provide better matching with typical preamplifier or source component output levels. It will allow you to utilize more of the amplifier's power while keeping the volume control of your preamp in an optimal range.

4. Improved signal-to-noise ratio: In some cases, running at higher gain can improve the overall signal-to-noise ratio of the audio system, as source components operate at lower output levels.

5. At a higher 27.5dB gain setting, the amplifier boosts the input signal significantly, which can lead to:
Higher output power: The amplifier can deliver more power to the speakers, especially in the lower frequencies that require more energy to reproduce.
Improved dynamic range: A stronger signal allows for better reproduction of sudden changes in volume, which is particularly noticeable in bass-heavy music.

6. The NCx500's design and performance at different gain settings contribute to the perceived bass impact:
Damping factor: The NCx500 has an ultra-high damping factor, which helps control speaker movement more effectively at higher output levels, potentially leading to tighter and more impactful bass.
Current output: With a high current output capability (max 28A), the amplifier can better handle the demands of low-frequency reproduction at higher gain settings.

7. The perception of more impactful bass at higher gain settings may also be influenced by:
Loudness sensation: Higher gain typically results in higher overall volume, and human hearing tends to perceive louder sounds as having more bass due to the Fletcher-Munson curves.

While higher gain settings can potentially offer benefits, they may also reduce headroom. The optimal gain setting will depend on the specific audio system components, room acoustics, and personal preferences. The NCx500's selectable gain settings enables users to find the best balance for their setup. That actually requires trying the various settings to determine your desired favorite. You may notice more impactful bass with 27.5dB and a remote volume control that's more responsive. But if you don't notice these differences or don't care about them the 12.8dB gain setting may be the optimal choice as long as volume levels meet your needs. It's important to note, running at higher gain does not inherently impact the audible quality in terms of distortion or frequency response. The Hypex NCx500 is designed to maintain its excellent performance characteristics across its gain range. Choice is nice!

 

[Chagall]

There are a few reasons why someone might want to set the Hypex NCx500 amplifier at a higher gain setting of 27.5 dB versus the lower 12.8 dB option:
1. Increased output power: The higher gain setting allows the amplifier to produce more output power for a given input signal level. This can be beneficial if you appreciate more volume or are driving less sensitive speakers.

2. The volume control may seem sluggish with a 12.8dB gain compared to a 27.5dB gain setting. This is a result of .5 gain increments offering less volume difference per click with 12.8 than a 27.5dB gain setup. However, if you need finer volume adjustments the 12.8dB setting might be just what you want.

3. Better matching with source components: The 27.5 dB gain may provide better matching with typical preamplifier or source component output levels. It will allow you to utilize more of the amplifier's power while keeping the volume control of your preamp in an optimal range.

4. Improved signal-to-noise ratio: In some cases, running at higher gain can improve the overall signal-to-noise ratio of the audio system, as source components operate at lower output levels.

5. At a higher 27.5dB gain setting, the amplifier boosts the input signal significantly, which can lead to:
Higher output power: The amplifier can deliver more power to the speakers, especially in the lower frequencies that require more energy to reproduce.
Improved dynamic range: A stronger signal allows for better reproduction of sudden changes in volume, which is particularly noticeable in bass-heavy music.

6. The NCx500's design and performance at different gain settings contribute to the perceived bass impact:
Damping factor: The NCx500 has an ultra-high damping factor, which helps control speaker movement more effectively at higher output levels, potentially leading to tighter and more impactful bass.
Current output: With a high current output capability (max 28A), the amplifier can better handle the demands of low-frequency reproduction at higher gain settings.

7. The perception of more impactful bass at higher gain settings may also be influenced by:
Loudness sensation: Higher gain typically results in higher overall volume, and human hearing tends to perceive louder sounds as having more bass due to the Fletcher-Munson curves.

While higher gain settings can potentially offer benefits, they may also reduce headroom. The optimal gain setting will depend on the specific audio system components, room acoustics, and personal preferences. The NCx500's selectable gain settings enables users to find the best balance for their setup. That actually requires trying the various settings to determine your desired favorite. You may notice more impactful bass with 27.5dB and a remote volume control that's more responsive. But if you don't notice these differences or don't care about them the 12.8dB gain setting may be the optimal choice as long as volume levels meet your needs. It's important to note, running at higher gain does not inherently impact the audible quality in terms of distortion or frequency response. The Hypex NCx500 is designed to maintain its excellent performance characteristics across its gain range. Choice is nice!

1. Sure. Conversely, you wouldn't go up a gain level if you have high-sensitivity towers that reach the desired SPL with less power.

2. Correct

3. Correct

4. Sure, some integrated amps or AVR pre-outs clip at higher output levels, but high-quality preamps usually work best at max level and power amps can reach their max output power in low gain.

5. Higher output power is the same point as 1.
Example: If speakers need 15W to reach 85dB SPL (the preferred listening level at the listening distance). To get 90dB SPL 31W is needed with the same speakers. Capping the amp's power to 100W by staying in low gain is fine. Improved dynamic range: Modern music has a 10 dB dynamic range and 100W (with the same speaker) will be enough for 15dB of amplifier headroom. Of course, if the speaker is low sensitivity then, by all means, go up a gain setting.

6. Not sure about this whole point and what it has to do with gain setting? The damping factor varies with frequency and the current is dependent on the speaker impedance dips and desired SPL.

7. Yes, louder equals better

Selectable gain levels are super useful, but what gain to set has more to do with the preamp output level, speaker sensitivity, and desired SPL at a listening position. Level-matched Ncx500 should sound the same in all gains, but low gain has the lowest noise.

 

[huba]

There are a few reasons why someone might want to set the Hypex NCx500 amplifier at a higher gain setting of 27.5 dB versus the lower 12.8 dB option:
1. Increased output power: The higher gain setting allows the amplifier to produce more output power for a given input signal level. This can be beneficial if you appreciate more volume or are driving less sensitive speakers.

2. The volume control may seem sluggish with a 12.8dB gain compared to a 27.5dB gain setting. This is a result of .5 gain increments offering less volume difference per click with 12.8 than a 27.5dB gain setup. However, if you need finer volume adjustments the 12.8dB setting might be just what you want.

3. Better matching with source components: The 27.5 dB gain may provide better matching with typical preamplifier or source component output levels. It will allow you to utilize more of the amplifier's power while keeping the volume control of your preamp in an optimal range.

4. Improved signal-to-noise ratio: In some cases, running at higher gain can improve the overall signal-to-noise ratio of the audio system, as source components operate at lower output levels.

5. At a higher 27.5dB gain setting, the amplifier boosts the input signal significantly, which can lead to:
Higher output power: The amplifier can deliver more power to the speakers, especially in the lower frequencies that require more energy to reproduce.
Improved dynamic range: A stronger signal allows for better reproduction of sudden changes in volume, which is particularly noticeable in bass-heavy music.

6. The NCx500's design and performance at different gain settings contribute to the perceived bass impact:
Damping factor: The NCx500 has an ultra-high damping factor, which helps control speaker movement more effectively at higher output levels, potentially leading to tighter and more impactful bass.
Current output: With a high current output capability (max 28A), the amplifier can better handle the demands of low-frequency reproduction at higher gain settings.

7. The perception of more impactful bass at higher gain settings may also be influenced by:
Loudness sensation: Higher gain typically results in higher overall volume, and human hearing tends to perceive louder sounds as having more bass due to the Fletcher-Munson curves.

While higher gain settings can potentially offer benefits, they may also reduce headroom. The optimal gain setting will depend on the specific audio system components, room acoustics, and personal preferences. The NCx500's selectable gain settings enables users to find the best balance for their setup. That actually requires trying the various settings to determine your desired favorite. You may notice more impactful bass with 27.5dB and a remote volume control that's more responsive. But if you don't notice these differences or don't care about them the 12.8dB gain setting may be the optimal choice as long as volume levels meet your needs. It's important to note, running at higher gain does not inherently impact the audible quality in terms of distortion or frequency response. The Hypex NCx500 is designed to maintain its excellent performance characteristics across its gain range. Choice is nice!

After adjustinggain to 27,5 I went through rew alignment of subwoofer/speakers and dirac live. Bass was good before, but what stands out is the mids. More energy, and not subtle. I correct only up to 350hz in dirac. I may be fooling myself, and it may well be more of a matching case against the preamp. Time to crawl uo of the rabbit hole for now and listen to some music

 

[amper42]

1. Sure. Conversely, you wouldn't go up a gain level if you have high-sensitivity towers that reach the desired SPL with less power.

You might think that, but my Revel F328Be Towers with 91dB sensitivity offer more punch with the amp set at 27.5dB gain instead of 12.8db even when level matched. An amp configuration with more output power for a given input signal can make an audible difference even with sensitive speakers.

 

[Meshuggener75]

Hello
Did anyone tried different rolling opamp om this amp? How much does it really effect?
I have OPA 1656 but thinking of try different.

 

[GiBo61]

A few questions for those who use a Wiim Pro Plus/Ultra as a preamp directely connected to this Apollon NCx500ST power amp:
1) what gain level do you set on the Apollon?
2) What output level do you set on the Wiim?
3) Is the connection with RCA cables or do you use an RCA-to-XLR converter to use the Apollon's balanced input?

T H A N K S

 

[kchap]

A few questions for those who use a Wiim Pro Plus/Ultra as a preamp directely connected to this Apollon NCx500ST power amp:

I assisted my sister with the purchase and setup of a Wiim Pro Plus and and a pair of Apollon NCx500M monoblocks

1) what gain level do you set on the Apollon?

After trying a few options we went for the max gain of 29dB. She listens to Spotify etc, but her main source of music is CDs. She has around 3000. The CD player is connected to the line in of the Pro Plus.

2) What output level do you set on the Wiim?

I'm not sure, my sister is far more familiar with the Wiim App than I am.. She controls it via her iPhone and seems very happy with the results.

3) Is the connection with RCA cables or do you use an RCA-to-XLR converter to use the Apollon's balanced input?

We used RCA cables.

 

[Descartes]

This is a review and detailed measurements of the Apollon NCx500ST stereo class D amplifier based on Hypex NCOREx NCx500 modules. It was kindly drop shipped from the member and costs 1,090.00€ (US $1,168) with standard opamp.

View attachment 310220
While the case is stamped aluminum, it is a heavily customized one with attractive side vents. You get to select your color of choice. The back panel is where you notice the high value add:

View attachment 310221
You have no less than four gain settings and even an LED brightness switch! FYI, I will have to confirm which op-amp is included with this sample.
EDIT: the default TI OPA1612 op-amp was in this sample.
EDIT 2: turns the amp used Sonic Imagery op-amps (by mistake).

To make sure I didn't go mad given the combination of input types and four gain settings, I stayed with XLR testing.

If you are not familiar with the tests that are about to follow, please watch my video on understanding amplifier measurements.

Edit: just realized I left out the "n" out of the name on all the notations.

Apollon NCx500ST Amplifier Measurement
I started with the lowest gain setting:
View attachment 310222
While just a couple of dBs shy of the reference design, performance is good enough to easily land in our top 10 best amplifiers tested:
View attachment 310223
You need a ton of input voltage to get max power in this low gain setting so let's step up through the gain settings:
View attachment 310224

View attachment 310225
View attachment 310226

You can see the benefit of low gain in am amplifier for best noise performance especially since the dynamic range of the DAC improves as well with higher output.

Here are two SNR measurements:
View attachment 310227

I picked next to highest gain because it lets you drive it to max power with less than 4 volts on XLR:
View attachment 310228

In that reward, it would have been nice to have a different gain level optimized for 4 volts output from the source (here, we jump from 2.1 to 5 volts).

Notice how channel separation is also gain sensitive:
View attachment 310230

Frequency response is expectedly excellent and load independent:
View attachment 310229

Intermodulation is kept to very low levels:
View attachment 310231
View attachment 310232

This is one powerful amplifier:
View attachment 310233
View attachment 310234

View attachment 310235

The amp has a very robust protection circuit and did not mind at all being pushed way beyond clipping. This made it easy to measure with PowerCube:
View attachment 310236

An ideal amp would keep its voltage constant regardless of load. We almost have that at 4 ohm but at 2 ohms, the required current goes through the roof and output droops. Lest you get depressed about that, check out the amount of power you are getting:
View attachment 310237

For a moment, it produced 2.2 Killowatts on my 20 amp circuit! I should mention that I have modified these tests for burst rather than continuous power. With continues output, it is very easy to push the Powercube beyond its specs. The burst nature is the reason so much power was to be had at that 2 ohm load setting.

Anyway, the amplifier is extremely robust and doesn't care how difficult the load is.

Distortion is kept at a minimum at or below 1 kHz:
View attachment 310238
BTW, this test is also updated to have more frequencies represented than before (addition of 200 Hz).

Amplifier is stable on power up:
View attachment 310239

And is extremely quiet on power on/off:
View attachment 310240

Conclusions
The Apollon NCx500ST is a clear value added class D amplifier with lots of features compared to reference design. It gives up just a few dBs of noise performance but still manages to rank #6 in our list giving you confidence of transparency while producing copious amount of power. It is also easily sourced in Europe which is a benefit for many of our readers.

I am happy to put the Apollon NCx500ST amplifier on my recommended list.

Manufacturer Specifications:

Frequency Response: 0 – 70k Hz +0/-3dB
Low Distortion: THD+N – – 0.0002 % 20Hz-20kHz
High Input Impedance 50K
Signal to noise ratio: 137dB
Gain (dB) 12,8/20,5/27,5/29
Ultra High Damping Factor
High Current Output
Power rating: 675W @ 2ohm | 650W @ 4ohm | 380W @ 8ohm
Case Dimensions: 350mm depth x 90mm height (with feet) x 280 mm width
Weight: 2.9 kg

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Which amplifiers keep its voltage constant regardless of load?