Review and Measurements of Violectric HPA V281 HP Amp

[amirm]

Also your readings say there is no difference in output power between 1/4" and XLR4. However Violectric says output should be double on XLR4.

Where are you reading that? Here is their power table in the manual:

Notice that power peaks at 100 ohm and instead of continuing to rise with lower impedances, it actually drops. That says that there is current limiting going on. My balanced testing is at 50 ohm so it is very likely that it is current limited so doesn't matter which output you use.

There is so much power available here anyway through 1/4 that I don't see what the issue is.

 

[FourT6and2]

Where are you reading that? Here is their power table in the manual:

View attachment 35752

Notice that power peaks at 100 ohm and instead of continuing to rise with lower impedances, it actually drops. That says that there is current limiting going on. My balanced testing is at 50 ohm so it is very likely that it is current limited so doesn't matter which output you use.

There is so much power available here anyway through 1/4 that I don't see what the issue is.

It says these specs are for "balanced operation" and earlier in the manual it says balanced volume output is double that of single-ended.

And let's assume that SE and Bal out are the same power. The image you just posted says output should be 4,200mW at 50ohm! Your test showed only 2,900! That's way off. Doesn't seem normal to me, even if manufactures tend to overrate...

That, combined with the odd high-pass and ground lift, leads me to believe this specific unit either has a problem or the internal switches were messed with and not set for proper operation. Not intentionally or anything. But it's obvious the owner opened it up and played with the settings if he lifted the ground.

 

[amirm]

It says these specs are for "balanced operation" and earlier in the manual it says balanced volume output is double that of single-ended.

That may be at lower volumes or with high impedance headphones. But max power at 50 Ohm is no better than unbalanced as I measured.

 

[debunker]

Hmmm… Wasn´t there also an audio company from California
that went by the name "Lake People"? I think somewhere in
the late 70´s, early 80´s...

Valley People?

Being down 2dB at 20 Hz is kind of... terrible. I get their rationale for for not wanting to DC couple, but at least use a sufficiently high value for the input caps. We're talking about a $2500 device here. Also, I would bet money that this puts phase shift into the audible frequency range. Whether or not it's audible might be up for debate, but why even take the chance?

 

[JohnYang1997]

It says these specs are for "balanced operation" and earlier in the manual it says balanced volume output is double that of single-ended.

And let's assume that SE and Bal out are the same power. The image you just posted says output should be 4,200mW at 50ohm! Your test showed only 2,900! That's way off. Doesn't seem normal to me, even if manufactures tend to overrate...

That, combined with the odd high-pass and ground lift, leads me to believe this specific unit either has a problem or the internal switches were messed with and not set for proper operation. Not intentionally or anything. But it's obvious the owner opened it up and played with the settings if he lifted the ground.

You have to understand the nature of output power. Normally output power is rated at 1% which is -40db. If you go back to amir's graph it's pretty close to 4W.
Also if you do the calculation the output current is 290ma at 4.2W and it's 240ma at 2.9W. Very close.
It's the limited current output that inherently limits the power into 50ohm. If you test with 300 or 600ohm it will be much closer to the spec as distortion tend to be lower there and it's not current limited.

 

[FourT6and2]

You have to understand the nature of output power. Normally output power is rated at 1% which is -40db. If you go back to amir's graph it's pretty close to 4W.
Also if you do the calculation the output current is 290ma at 4.2W and it's 240ma at 2.9W. Very close.
It's the limited current output that inherently limits the power into 50ohm. If you test with 300 or 600ohm it will be much closer to the spec as distortion tend to be lower there and it's not current limited.

Honestly, I don't understand this stuff very well. I'm doing my best. I'll take your info at face value. But what about 1/4" and XLR4 being the same output? Again, Violectric (and owners of this amp) say volume and output should be louder on the XLR4 out. So what's up?

 

[JohnYang1997]

Honestly, I don't understand this stuff very well. I'm doing my best. I'll take your info at face value. But what about 1/4" and XLR4 being the same output? Again, Violectric (and owners of this amp) say volume and output should be louder on the XLR4 out. So what's up?

Because at 50ohm it's current limited. Take 240ma as the current output. The power into the load is 0.24*0.24*50 which is independent of the output voltage swing ability. Balanced output only doubles the voltage swing but has zero or a little bit negative effect in current output.
If amir takes measurements on 300 or 600ohm the output power will quadruple.

 

[amirm]

If amir takes measurements on 300 or 600ohm the output power will quadruple.

I plan to redo my headphone amp dummy load. What would be the most desired impedances for balanced output? My current one came about because I had two 25 ohm resistor that I could use to build a 50 ohm, not through any kind of research.

In other words, what are the most power hungry headphone impedances?

 

[JohnYang1997]

I plan to redo my headphone amp dummy load. What would be the most desired impedances for balanced output? My current one came about because I had two 25 ohm resistor that I could use to build a 50 ohm, not through any kind of research.

In other words, what are the most power hungry headphone impedances?

Just like the single ended loads I guess. 4*8ohm in series and 300ohm load would work just fine. The 50ohm load clearly showed current limiting for this amp. So it's not necessarily the load's fault, it just give less overall information vs two different loads. It would be even better to see 16ohm load in test. But that's a different story. The load impedances are just really arbitrary because the actual impedance of headphones varies a lot as well. So a low impedance load and a high impedance load (to see current limit and voltage swing limit) would work.

 

[deafenears]

I plan to redo my headphone amp dummy load. What would be the most desired impedances for balanced output? My current one came about because I had two 25 ohm resistor that I could use to build a 50 ohm, not through any kind of research.

In other words, what are the most power hungry headphone impedances?

@tomchr ? Any input here? I seem to recall reading somewhere where you posted your recommendations - 20ohm, 32ohm, 300ohm?

EDIT: Ah, found it - https://www.audiosciencereview.com/...pa4-headphone-amp-pre.8141/page-5#post-202101

 

[FourT6and2]

Decade box with a switch for multiple loads? Most headphone amps are rated at the same loads: 16, 32, 50, 100, 300, 600. Impossible to account for all the headphones out there, but it's easier to measure performance at what most amp companies list in their specs. You've already got 50ohms. So maybe add 16 and 300? Or just grab a multiposition switch and put a bunch on there.

 

[JohnYang1997]

One for current limit, one for rail limit is good enough. You can calculate everything in between with these two data points. So I second the idea of adding 16ohm and 300ohm.

TBH, there are countless iems that have very low and wobbly impedance curve. I would even suggest 8ohm load but only for 1Vrms or 100mW. The distortion will rise very quickly. It may seem harsh on the amplifiers but consider the actual use case it may not be too aggressive.

 

[amirm]

Decade box with a switch for multiple loads?

Decade box would not work due to too many contacts. And then there is the high cost of many high-power but low VCR resistors.

Mine has only one selector switch and that is too much with respect to measuring best in class amps. My plan is to build separate loads for each and hence the reason I am trying to keep the choices limited.

 

[Jimster480]

Glad to see that this actually performs well as a headphone amp. It's seems the trend for "audiophile" products at the price moves further past the $1000 mark is to actually decrease performance into scam territory. This actually performs very well. Having that low end roll off would actually help bass articulation since low end noise and distortion is one of the biggest enemies to dynamics and transient response for lower frequencies. A 2dB dip at 20Hz is not too bad, but the 5dB dip at 10Hz and below is actually helpful when listening to poorly produced music or recordings that may not have those lower frequencies trimmed away. A sharper roll-off that begins at 15Hz instead of 50Hz would have been better, but I think this is acceptable. The price really is not competitive though. This performance is really only worth somewhere around $500 in today's market. I do think the price was ok when this product was released, but the market has just changed so much with the advent of THX amplification technology.

I totally agree with you here.
I am glad that this product does have some actually decent performance.... but as you mentioned its just not competitive anymore with the THX amps on the market.
Now with literally 4 THX models on the market and the JDS Atom all being able to keep up with this for a fraction of the cost (or beat it by a country mile) it means that despite the "unique" nature of this amp.... there is no other selling point.

 

[solderdude]

@amirm :
Consider that the 50 Ohm is low LCR so it can handle MHz to GHz.
Headphones all will show a very high impedance at 1MHz so just using wirewound resistors for headphone loads is very realistic.
Of course, for e-stats it is different. I can understand you want the load to be resistive though over the entire spectrum but for headphones and speakers this is not realistic.

Honestly, I don't understand this stuff very well. I'm doing my best. I'll take your info at face value. But what about 1/4" and XLR4 being the same output? Again, Violectric (and owners of this amp) say volume and output should be louder on the XLR4 out. So what's up?

I'll try to explain to FourT6and2 the bit about balanced a bit more elaborate.

All amplifiers have a voltage limit and a current limit. voltage x current = power.
When one wants to double the voltage one can put those amplifiers in series.
This doubles the voltage but NOT the current.

When one wants to double the current one must put the amplifiers in parallel.
To illustrate look at the O2 schematic, it has op-amps in parallel to double the output current.
This, however, doesn't double the voltage only the current.

When an amplifier is bridged (used balanced) there basically are 2 amplifiers in series.
This means double the voltage but not double the output current.

When one takes a look at output voltages of balanced and RCA output DAC's as an example. The RCA out is 2V then the XLR is 4V. As there is as good as no load at line level these voltages always double.

NOTE: The example is not using actual values of the discussed Violectric amp but is an example.

Now comes the output power part, there is a lot of confusion about this.
Lets assume the amplifier in question has unlimited current (for argument sake) and can put out max 10V in SE and 20V in balanced.
some calculations for impedances.
'single ended' = 10V and 'balanced' = 20V

8 Ohm = 12.5W(1.25A) and 50W (2.5A)
16 Ohm = 6.25W(0.625A) and 25W (1.25A)
32 Ohm = 3.125W(0.313) and 12.5W (0.625A)
64 Ohm = 1.56W(0.156A) and 6.25W (0.313A)
128 Ohm = 0.78W(0.078A) and 3.125W (0.156A)
256 Ohm = 0.39W(0.039A) and 1.56W (0.078A)
512 Ohm = 0.19W (0.019A) and 0.78W(0.039A)

It is evident the output voltage is doubled and as a result of power = voltage x current (and current being voltage divided by resistance) is (voltage x voltage)/resistance. This means power is 4x higher in balanced mode.
What is also clear is that lower impedances require a lot more current than higher impedances.

Now comes the more difficult part in this story. The amplifiers are current limited. This means each amplifier can deliver 10V max and 250mA (0.25A).
In balanced mode these are in series so the output voltage can be double (and power quadrupled) as long as the current limit is not reached.

The amplifiers are in series so max. current remains the same in SE and balanced mode. Power = (current x current) x resistance.

same table but now current limited at 250mA = 0.25A (with infinite output voltage): ‘single ended’ and ‘balanced’
8 Ohm = 0.5W(2V) and 0.5W (2V)
16 Ohm = 1W(4V) and 1W (4V)
32 Ohm = 2W(8V) and 2W (8V)
64 Ohm = 4W(16V) and 4W (16V)
128 Ohm = 8W(32V) and 8W (32V)
256 Ohm = 16W(64V) and 16W (64V)
512 Ohm = 32W (128V) and 32W(128V)

As can be seen high voltages are needed when high power levels are needed in high impedances.

Now to figure out how much power there is when the amp is voltage and current limited all we have to do is look for the highest voltage the amp can put out (10V in single ended and 20V in balanced) in the above current table.

So for single ended (max 10V) and balanced (max 20V) we can see at certain impedances ,and 250mA current limit, voltages above 10V and 20V respectively are required but are not available.

8 Ohm = 0.5W(2V) and 0.5W (2V)
16 Ohm = 1W(4V) and 1W (4V)
32 Ohm = 2W(8V) and 2W (8V)
64 Ohm = 4W(16V) and 4W (16V)
128 Ohm = 8W(32V) and 8W (32V)
256 Ohm = 16W(64V) and 16W (64V)
512 Ohm = 32W (128V) and 32W(128V)

For voltages we can look in the table below that belong to the impedances and max currents (thus power). Here too there is a limit which in this case is 250mA both for single ended as well as balanced. Every level above 250mA (0.25A) thus is not possible.
This means we can strike out power levels requiring currents above 0.25A.

8 Ohm = 12.5W(1.25A) and 50W (2.5A)
16 Ohm = 6.25W(0.625A) and 25W (1.25A)
32 Ohm = 3.125W(0.313) and 12.5W (0.625A)
64 Ohm = 1.56W(0.156A) and 6.25W (0.313A)
128 Ohm = 0.78W(0.078A) and 3.125W (0.156A)
256 Ohm = 0.39W(0.039A) and 1.56W (0.078A)
512 Ohm = 0.19W (0.019A) and 0.78W(0.039A)

Now due to the impedances being stepped in factors of 2 the power levels that can be reached differ a bit in current and voltage.

Below the ‘borders’ once more.

32 Ohm = 2W(8V) and 2W (8V) versus 3.125W(0.313A) and 12.5W (0.625A)
64 Ohm = 4W(16V) and 4W (16V) versus 1.56W(0.156A) and 6.25W (0.313A)
128 Ohm = 8W(32V) and 8W (32V) versus 0.78W(0.078A) and 3.125W (0.156A)

So the limits are somewhere between these values because there is current and voltage limiting in these amps.

For low impedance headphones the power is limited by current (which is the same for both amps so below a certain impedance the max. power is the same as shown in the current table BUT the voltages associated with that voltage can not be reached.

For high impedance the max power is determined by the output voltage so above a certain impedance the output voltage can be up to 2x higher in the balanced (20V) version.

8 Ohm = 0.5W(2V) and 0.5W (2V) = current limited
16 Ohm = 0.5W(2V) and 0.5W (2V) = current limited
32 Ohm = 2W(8V) and 2W (8V) = current limited
64 Ohm = 1.56W(10V) = voltage limited and 4W (16V) = current limited
128 Ohm = 0.78W(10V) and 3.125W (20V) = voltage limited
256 Ohm = 0.39W(10V) and 1.56W (20V) = voltage limited
512 Ohm = 0.19W (10V) and 0.78W(20V) = voltage limited

As can be seen above a certain impedance the power quadruples and below a certain impedance the power is actually the same with a small transition between same power and quadruple power between 32 Ohm and 128 Ohm and peaking somewhere around 64 Ohm in this case.

At 10V and 250mA one can calculate the maximum power as being 2.5W for which one needs 40 Ohm.
At 20V and 250mA the max power is 5W for which one needs 80 Ohm.

Again... these are NOT the numbers for the Violectric.

 

[Herbert]

Herbert said: Hmmm… Wasn´t there also an audio company from California
that went by the name "Lake People"? I think somewhere in
the late 70´s, early 80´s...
Valley People?

Ouch, I was waaay off!! There was not even people or any lake in the name:
Soundcraftsmen!
https://web.archive.org/web/20061219035423/http://www.soundcraftsmen.com/

 

[amirm]

@amirm :
Consider that the 50 Ohm is low LCR so it can handle MHz to GHz.
Headphones all will show a very high impedance at 1MHz so just using wirewound resistors for headphone loads is very realistic.
Of course, for e-stats it is different. I can understand you want the load to be resistive though over the entire spectrum but for headphones and speakers this is not realistic.

Inductance is not a concern for me. The concern is that resistors modulate their values based on voltage across them. This causes non-linearities of their own, in the form of third harmonic. In power amplifiers, this limits the SINAD to 105 dB if the damping factor of the amp is not very high. This is called VCR or voltage coefficient resistance and sadly is not documented by resistor companies.

Likewise, even the connectors used make a difference.

With so many amps and headphone amps now getting to exceedingly small distortion values, I need to keep my setup very optimal.

 

[JohnYang1997]

Inductance is not a concern for me. The concern is that resistors modulate their values based on voltage across them. This causes non-linearities of their own, in the form of third harmonic. In power amplifiers, this limits the SINAD to 105 dB if the damping factor of the amp is not very high. This is called VCR or voltage coefficient resistance and sadly is not documented by resistor companies.

Likewise, even the connectors used make a difference.

With so many amps and headphone amps now getting to exceedingly small distortion values, I need to keep my setup very optimal.

It won't cause any issue if you place the resistor to the output close enough. Output impedance will play the role here. If output impedance is low enough and enough amount of feedback is present there will be no extra distortion. We can place a ceramic capacitor at output and still have low distortion. So no resistor is not the problem. Just use some 20W 8ohm resistors to make some loads.
The real issue is the contact. The bad contact will cause a lot of issue, with enough current flow the distortion can rise 10 times. Just be sure the resistor is at the closest to the amplifier and it will be good.

 

[JohnYang1997]

Resistor at feedback loop can cause distortion if high voltage applies across it. But it won't matter at output.

 

[amirm]

It won't cause any issue if you place the resistor to the output close enough. Output impedance will play the role here.

I tested that and it makes no difference. It is the resistor itself which heats up and changes characteristics. The physics of it are quite complex actually. So much so that it is not well understood. The wire temp doesn't change so doesn't change its make up enough to matter.