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Review and Measurements of Violectric HPA V281 HP Amp

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amirm

amirm

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Just use some 20W 8ohm resistors to make some loads.
Nope. I tested a bunch I have and only one of them was good. The rest all had issues. Had to buy very special and expensive resistors to remove the problem.

You have to have an amp like the Benchmark to see and measure the problem.
 

typericey

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I have a V280 which is about half the size of the V281 and FWIW:

- Subjectively neutral. Doesn't add, subtract, change anything to the sound
- Power seems infinite. It can drive my 6XX to painful and harmful levels with ease and poise.
- I can't perceive any noise (at full volume, no signal), nor distortion. No scratchy volume control, no power on/off pop.
- Awesome build quality and engineering
*Note: all observations made using unbalanced inputs and outputs
- Overall, I can't complain about anything except that it may not be the best value with the THX AAA, etc. in existence. We have to take into consideration German labor costs and that they're overbuilt. Also, I got mine used.
 

JohnYang1997

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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.
I use 8ohm 20W resistor never had any issue. Only 3.5mm contacts are not very reliable. I only measure down to -130dBFS.
 

JohnYang1997

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Load having effect on performance for voltage amplifier just doesn't make sense. Output impedance is the only possible issue. I include x7r capacitor at output and no problem either. Down to -130db.
 

fdg

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This is Fried Reim from Lake People / Violectric.

V281 offers not only a "convenience" 4-pin XLR socket but a true balanced output.
There are 4 amps inside !! It is a BTL or push-pull arrangement.
The balanced headphone output should be measured in a differencial way and never related to ground.
Otherwise the inverting amp will be tied to ground - causing distortions.
Assuming the same input signals and the same load the balanced output is double as loud (+6 dB) as the SE outputs
and the amp will deliver about 4 times the power.
Also, each of the 4 amps has its own current limiter, so 2 amps will really deliver 4 times the power.
Concerning the output voltage swing HPA V281 is the most powerful headphone amp delivering up to 40 Veff into 600 ohms = 2700 mW !!
The technical data from the manual are no cheats but true:

RLoad (Ohm) 600 => Ua (dB) 34,4 = Ua (V) 40,2 => Pa (mW) 2700
RLoad (Ohm) 300 => Ua (dB) 32,8 = Ua (V) 33,8 => Pa (mW) 3800
RLoad (Ohm) 100 => Ua (dB) 29,7 = Ua (V) 23,7 => Pa (mW) 5600
RLoad (Ohm) 50 => Ua (dB) 25,4 = Ua (V) 14,5 => Pa (mW) 4200
RLoad (Ohm) 32 => Ua (dB) 21,7 = Ua (V) 9,5 => Pa (mW) 2800
RLoad (Ohm) 16 => Ua (dB) 16,0 = Ua (V) 4,9 => Pa (mW) 1500

The peak is at 100 Ohm load impedance, for lower loads the internal current protection will act.

The output voltage @600 Ohms may suffer a bit due to poor US AC supply !
The above data was taken with European 230 V AC.

The low frequeny roll-off is due to the low impedance input from the relay attenuator circuitry.
This is not "nice" but normally not to hear.
With the "standard" volume control the frequency range is ruler flat down to 5 Hz (-3dB).

About the loose knob.
The shaft from the potentiometer is made of steel while the massive knob is made from aluminum.
Unfortunately this mix of materials sometime causes a loose knob.
Normally a 1,5 mm allen key is supplied with the unit to fix the knob.
To come out of this trouble we could use a smaller knob or one with a plastic insert - but we don´t want to ;-)

Best regards, Fried Reim
 
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fdg

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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...

That was Valley People.
And, indeed, when Lake People started in 1986 any "accidential" correlation was appreciated from our side ;-)
Those guys had been the gods of sophisticated analog design !!
 
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This is Fried Reim from Lake People / Violectric.
Warm welcome to the forum. It is always great when company designers or representatives join the discussion.
 
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The technical data from the manual are no cheats but true:

RLoad (Ohm) 600 => Ua (dB) 34,4 = Ua (V) 40,2 => Pa (mW) 2700
RLoad (Ohm) 300 => Ua (dB) 32,8 = Ua (V) 33,8 => Pa (mW) 3800
RLoad (Ohm) 100 => Ua (dB) 29,7 = Ua (V) 23,7 => Pa (mW) 5600
RLoad (Ohm) 50 => Ua (dB) 25,4 = Ua (V) 14,5 => Pa (mW) 4200
RLoad (Ohm) 32 => Ua (dB) 21,7 = Ua (V) 9,5 => Pa (mW) 2800
RLoad (Ohm) 16 => Ua (dB) 16,0 = Ua (V) 4,9 => Pa (mW) 1500
Unfortunately they don't have specifications with respect to distortion. As you know, if you allow more distortion you can report higher power levels. My standard is to pick onset of clipping which is usually lower than what manufacturers use.
 
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amirm

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The peak is at 100 Ohm load impedance, for lower loads the internal current protection will act.
That is what I explained earlier. Because my balanced load is at 50 ohm, it did not result in more power than unbalanced and hence my comment about it being a convenience feature.
 
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The balanced headphone output should be measured in a differencial way and never related to ground.
Otherwise the inverting amp will be tied to ground - causing distortions.
It always is in my testing. I have a special load I use just for this purpose. It is differential all the way through to the analyzer.
 

tomchr

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@tomchr ? Any input here? I seem to recall reading somewhere where you posted your recommendations - 20ohm, 32ohm, 300ohm?
P = V^2/R --> lower R <==> higher P.

The most common impedances seem to be: 32, 50, 300 Ω, though some make it down to 16-20 Ω. I'm considering building a load with built-in relays that can be controlled by the APx525 for automated testing. I'll probably do something like 16-20-32-50-150-300 Ω, likely with some capacitances in parallel as well. I usually test 100 pF - 10 nF in 2-3 steps per decade.

Tom
 
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The most common impedances seem to be: 32, 50, 300 Ω, though some make it down to 16-20 Ω. I'm considering building a load with built-in relays that can be controlled by the APx525 for automated testing. I'll probably do something like 16-20-32-50-150-300 Ω, likely with some capacitances in parallel as well. I usually test 100 pF - 10 nF in 2-3 steps per decade.
I will buy one from you if you build it. I am just out of time to build one myself. I even have the relay board and have prototyped the control but no time to build the rest.
 

solderdude

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Had some trouble with correct wiring of my switchbox (4W max.) to get the channel separation to be at least decent.
30,60,120, 300, 600 Ohm and open. 1nF or 10nF can be paralleled.
 

fdg

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I had a sleepless night because of the graphs and so we made some this morning.
Please note:
1. the scaling of the axis are different to those of Amir. X-axis 10mW to 5W, Y-axis -120 dB to -70 dB
2. We are using "Prism Sound Dscope III" which obviously has a worse analog output compared to the AP system.
So our graphs go hardly beyond -100 dB
For THD relevant measurment during circuit design we stock an old R+S UPL

V281_THD_vs_P_32R_BAL_0dB.png
V281_THD_vs_P_32R_UNBAL_0dB.png
V281_THD_vs_P_50R_BAL_0dB.png
V281_THD_vs_P_50R_UNBAL_0dB.png
V281_THD_vs_P_300R_BAL.png
V281_THD_vs_P_300R_UNBAL_0dB.png
V281_THD_vs_P_600R_BAL 0dB.png
V281_THD_vs_P_600R_UNBAL 6dB.png
 

tomchr

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I will buy one from you if you build it. I am just out of time to build one myself. I even have the relay board and have prototyped the control but no time to build the rest.
I'll toss you an email. I can push on this project pretty easily once we settle on the specs.

Tom
 
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amirm

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I had a sleepless night because of the graphs and so we made some this morning.
Didn't mean to cause this kind of worry. :) Your amp is already so powerful that it doesn't need to produce more power with balanced.

Regardless, I updated the review to indicate that lack of extra power was due to low impedance load I used/current limiting.

Thanks for the additional info.
 

JJB70

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This is Fried Reim from Lake People / Violectric.
About the loose knob.
The shaft from the potentiometer is made of steel while the massive knob is made from aluminum.
Unfortunately this mix of materials sometime causes a loose knob.
Normally a 1,5 mm allen key is supplied with the unit to fix the knob.
To come out of this trouble we could use a smaller knob or one with a plastic insert - but we don´t want to ;-)

To be honest I find this very disappointing, it is rationalising poor design, given that the sole reason to buy a product of this nature when SOTA headphone amp performance can be bought for peanuts is premium build and engineering it seems crazy to design the main touch point badly. A loose knob is infuriating and there is no reason at all not to just design it better. The rest of the amplifier does appear to be excellently designs=ed and manufactured to a very high standard (as it should be), I just can't see any sense in not doing the volume knob right too.
 

FourT6and2

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To be honest I find this very disappointing, it is rationalising poor design, given that the sole reason to buy a product of this nature when SOTA headphone amp performance can be bought for peanuts is premium build and engineering it seems crazy to design the main touch point badly. A loose knob is infuriating and there is no reason at all not to just design it better. The rest of the amplifier does appear to be excellently designs=ed and manufactured to a very high standard (as it should be), I just can't see any sense in not doing the volume knob right too.

Or one could just tighten the set screw? Or maybe Violectric can just put some Loctite on it. Or even a very thin bit of heat shrink on the pot's shaft to give the set screw something to grab. Doesn't require a total re-design of a knob lol.
 

wadec22

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