[phthora]

Any reason not to use a power conditioner with the HPA4? I bought a Furman to eliminate some mains hum at my last house and have been continuing to use it as a glorified power strip. I don't think I have that issue anymore, but figured I'd use it anyway. Should be okay?

 

[jsiau]

Any reason not to use a power conditioner with the HPA4? I bought a Furman to eliminate some mains hum at my last house and have been continuing to use it as a glorified power strip. I don't think I have that issue anymore, but figured I'd use it anyway. Should be okay?

It is OK to use the power conditioner but it will not change the performance of the HPA4. The power supply in the HPA4 has two cascaded regulators and filters to isolate the audio circuits from AC line noise.

As a side note, the Benchmark AHB2 power amplifier should not be used with most power conditioners because it will overload the power conditioners on audio peaks.

 

[phthora]

It is OK to use the power conditioner but it will not change the performance of the HPA4. The power supply in the HPA4 has two cascaded regulators and filters to isolate the audio circuits from AC line noise.

As a side note, the Benchmark AHB2 power amplifier should not be used with most power conditioners because it will overload the power conditioners on audio peaks.

Thank you for the response! That situation you described with the AHB2 is exactly what I was concerned about with the HPA4. My Benchmark stack should arrive Thursday and I am nesting like an expectant mother over here!

 

[bimmer100]

I am a bit concerned with this comment. What amount does the ahb2 really draw to overload a power conditioner?
I briefly emailed about this a while back. But I have a 2000w O-type isolation transformer I’m using for our loud speaker system to power all our gear. And 20A dedicated circuits with 10g in wall wiring. It seems fine, but never figured it would be any issue. I do wonder the demands of the amp at peak. I can dig into the manual again if this is mentioned but don’t recall seeing this info.

 

[Articnoise]

If the amp would overload a good 16A power conditioner it would also overload the power line in many homes.

 

[jsiau]

If the amp would overload a good 16A power conditioner it would also overload the power line in many homes.

The AHB2 power amplifier will not overload the power line in homes, even if the circuit is a 120V 15 A circuit. The AHB2 has 8 A time delay fuses, and the average current is much less than 8 A. The problem is that many power conditioners cannot deliver high enough peak currents. The voltage output of may power conditioners will collapse when momentarily overloaded. The AHB2 can tolerate this voltage sag as long as the line voltage does not drop below 90 volts. A 16 A power conditioner may not be able to deliver a 20 A peak, but home wiring can deliver very high short-term peaks without tripping a breaker or blowing a fuse.

You have to ask why would you pay money to buy a "power conditioner" which will increase the voltage fluctuations at the input of the amplifier. The AHB2 can tolerate the bad AC power delivered by a power conditioner, but other connected devices may have problems. The AHB2 has regulated power supply rails and consequently the peak output power is always maintained even when the line voltage sags. In contrast, most audio power amplifiers have unregulated power supplies and the peak output power is directly related to the AC line voltage. A power conditioner will usually reduce the peak output power of a conventional power amplifier unless the output impedance of the conditioner is lower than the line impedance (very few power conditioners can meet this requirement, and they should not be used with power amplifiers).

Bottom line - don't use a single power conditioner to simultaneously supply AC power to an audio amplifier and low-power devices. Audio amplifiers should be connected to a separate power conditioner if the amplifier requires one, but in many cases amplifiers should not be connected to a power conditioner. The AHB2 does not need a power conditioner, so don't connect it to one!

 

[YooperAudio]

The AHB2 power amplifier will not overload the power line in homes, even if the circuit is a 120V 15 A circuit. The AHB2 has 8 A time delay fuses, and the average current is much less than 8 A. The problem is that many power conditioners cannot deliver high enough peak currents. The voltage output of may power conditioners will collapse when momentarily overloaded. The AHB2 can tolerate this voltage sag as long as the line voltage does not drop below 90 volts. A 16 A power conditioner may not be able to deliver a 20 A peak, but home wiring can deliver very high short-term peaks without tripping a breaker or blowing a fuse.

You have to ask why would you pay money to buy a "power conditioner" which will increase the voltage fluctuations at the input of the amplifier. The AHB2 can tolerate the bad AC power delivered by a power conditioner, but other connected devices may have problems. The AHB2 has regulated power supply rails and consequently the peak output power is always maintained even when the line voltage sags. In contrast, most audio power amplifiers have unregulated power supplies and the peak output power is directly related to the AC line voltage. A power conditioner will usually reduce the peak output power of a conventional power amplifier unless the output impedance of the conditioner is lower than the line impedance (very few power conditioners can meet this requirement, and they should not be used with power amplifiers).

Bottom line - don't use a single power conditioner to simultaneously supply AC power to an audio amplifier and low-power devices. Audio amplifiers should be connected to a separate power conditioner if the amplifier requires one, but in many cases amplifiers should not be connected to a power conditioner. The AHB2 does not need a power conditioner, so don't connect it to one!

Oh great. Next you'll be telling me not to buy a $1000 power cable upgrade because I don't need that!

 

[jsiau]

Oh great. Next you'll be telling me not to buy a $1000 power cable upgrade because I don't need that!

We have been saying that for years!

 

[YooperAudio]

We have been saying that for years!

I know, and I like it a lot.

 

[jsiau]

I know, and I like it a lot.

Thanks!

BTW, I like your picture but you really need to do something about those yellow teeth!

You could look like this!

 

[Deftone]

Just got my dac3b and hpa4 setup yesterday. Do these benefit from burn in? Out of the box.. Very clean and detailed sound. Didn't think they were cold/dry as some have described.

Almost too clean a sound? I have a wooaudio 22 which I've been listening to past few weeks, and although it isn't the cleanest sound out there, it does have character..

So far.. Very good with the Meze Empy but a little harsh with Focal Utopia. I prefer the Utopia on the tube amp.

I've been thinking about this recently and from my experiences ultra low distortion doesn't mean cold or clinical sound it means tight, clean and fast. You're hearing the headphone at its best and not the equipment. When people say its analytical i think its them hearing just the headphone and they dont like what they hear if they have been used to colouration for a long time. Instead of admitting its the headphone they blame the other equipment.

 

[nordkapp]

I've been thinking about this recently and from my experiences ultra low distortion doesn't mean cold or clinical sound it means tight, clean and fast. You're hearing the headphone at its best and not the equipment. When people say its analytical i think its them hearing just the headphone and they dont like what they hear if they have been used to colouration for a long time. Instead of admitting its the headphone they blame the other equipment.

So true.

 

[jsiau]

I'm still unsure why you think the HPA4 won't do this?
The diff amp will sum the balanced phases (cancelling CM noise in the process) then post diff amp the negative phase for the balanced signal will have to be derived by some means.
An unbalaced signal applied to the diff amp would be converted to balanced after this process.
Unless Benchmark say otherwise, I'd assume the HPA4 does this - why don't you ask?

Tobes,
You describe the most common way of deriving a balanced signal from an unbalanced. We do this differently. In the topology you describe, the diffamp becomes the limiting factor from a noise standpoint. Our technique has a 9 dB to 19 dB SNR advantage over this common technique.

In the HPA4 we do the following:

• Send the + input to two independent voltage buffers.
• Send the output of one buffer to a low-impedance inverter that uses the isolated RCA ground as its signal reference (providing common mode rejection).
• Send the output of the second buffer to the inputs of two differential amplifiers that are wired in opposite polarity.
• Send the output of the inverter to the remaining inputs on the two differential amplifiers.
• One differential amplifier drives the +, the other drives the -, this balanced signal feeds the headphone amp or line output buffers.
• Placing the inverter in front of the diffamp gives us about a 6 dB SNR improvement.
• Using 2 diffamps gives us an additional 3 dB SNR improvement.
• The outputs of the diffamps are voltage balanced and common-mode interference has been removed from both balanced and unbalanced inputs.

• We use a relay to remove the inverter when feeding from a balanced XLR input.
• The dual diffamps are integrated into our active relay-controlled stepped gain/attenuation volume control stage to optimize the noise performance of the diffamps.
• The fully-balanced stepped gain/attenuation controls the gain of two buffer amplifiers that are in front of the diff amps in order to optimize the balanced signal level into the dual diffamps.
• This optimization is important because balanced inputs are often 16 dB higher than unbalanced inputs.
• This optimization can provide a 10 dB SNR improvement for unbalanced inputs (above and beyond the 9 dB described above).
• The result is that the system SNR is largely independent of the input signal level.
• The SNR for a 2 Vrms (8.2 dBu) unbalanced input is almost as good as it is with a +24 dBu (12.28 Vrms) studio-level balanced input.

• The line and headphone outputs have entirely separate relay-controlled gain/attenuation stages.
• The line and headphone outputs are derived from two separate sets of dual diffamps.

In total there are 8 diffamps in the HPA4 allocated as follows:

• 2 for L input driving balanced line bus
• 2 for R input driving balanced line bus
• 2 for L input driving balanced headphone bus
• 2 for R input driving balanced headphone bus

I am using "bus" to refer to the internal balanced signal distribution paths that follow the fully balanced volume controls.
The line bus drives the balanced and unbalanced output buffers.
The headphone bus drives the balanced inputs on the THX-888 headphone amplifier.

While this may sound complicated on paper, the parallel structure shortens the individual signal paths and allows the use of lower impedances in critical parts of the signal path.

 

[Tobes]

Thanks for the thorough explanation John.

 

[YooperAudio]

Tobes,
You describe the most common way of deriving a balanced signal from an unbalanced. We do this differently. In the topology you describe, the diffamp becomes the limiting factor from a noise standpoint. Our technique has a 9 dB to 19 dB SNR advantage over this common technique.

In the HPA4 we do the following:

• Send the + input to two independent voltage buffers.
• Send the output of one buffer to a low-impedance inverter that uses the isolated RCA ground as its signal reference (providing common mode rejection).
• Send the output of the second buffer to the inputs of two differential amplifiers that are wired in opposite polarity.
• Send the output of the inverter to the remaining inputs on the two differential amplifiers.
• One differential amplifier drives the +, the other drives the -, this balanced signal feeds the headphone amp or line output buffers.
• Placing the inverter in front of the diffamp gives us about a 6 dB SNR improvement.
• Using 2 diffamps gives us an additional 3 dB SNR improvement.
• The outputs of the diffamps are voltage balanced and common-mode interference has been removed from both balanced and unbalanced inputs.

• We use a relay to remove the inverter when feeding from a balanced XLR input.
• The dual diffamps are integrated into our active relay-controlled stepped gain/attenuation volume control stage to optimize the noise performance of the diffamps.
• The fully-balanced stepped gain/attenuation controls the gain of two buffer amplifiers that are in front of the diff amps in order to optimize the balanced signal level into the dual diffamps.
• This optimization is important because balanced inputs are often 16 dB higher than unbalanced inputs.
• This optimization can provide a 10 dB SNR improvement for unbalanced inputs (above and beyond the 9 dB described above).
• The result is that the system SNR is largely independent of the input signal level.
• The SNR for a 2 Vrms (8.2 dBu) unbalanced input is almost as good as it is with a +24 dBu (12.28 Vrms) studio-level balanced input.

• The line and headphone outputs have entirely separate relay-controlled gain/attenuation stages.
• The line and headphone outputs are derived from two separate sets of dual diffamps.

In total there are 8 diffamps in the HPA4 allocated as follows:

• 2 for L input driving balanced line bus
• 2 for R input driving balanced line bus
• 2 for L input driving balanced headphone bus
• 2 for R input driving balanced headphone bus

I am using "bus" to refer to the internal balanced signal distribution paths that follow the fully balanced volume controls.
The line bus drives the balanced and unbalanced output buffers.
The headphone bus drives the balanced inputs on the THX-888 headphone amplifier.

While this may sound complicated on paper, the parallel structure shortens the individual signal paths and allows the use of lower impedances in critical parts of the signal path.

This is pretty amazing.

If I did this with some of the proprietary processes we've invented and/or implemented at software companies I've worked at, I'd be in big trouble.

Just putting it out there like this in such a transparent way is really something.