Neurochrome HP-LOAD Review (Headphone Dummy Load)

[tomchr]

If they added a 100MOhm option with 100pF load you could even create a dummy electrostatic. Easy mod I suspect...

Nothing 100 MΩ related is easy. It doesn't take much of a leakage path to blow that 100 MΩ. A little humidity. A few specs of dust... There's also the "little detail" that the input impedance of the AP (100 kΩ) is in parallel with the load impedance.

From what I have read, headphones become capacitive in very high frequencies where instability may occur.

Amplifiers tend to have a much harder time driving capacitive loads, which is why everybody and their dog have been testing them that way for ages. And it's worth noting that it is possible to have 'holes' in the capacitive load coverage. I.e., spots where the amp will be unstable even if it is stable with higher and lower capacitance loads. The Neurochrome HP-1 was that way. It would happily oscillate with 200-500 pF load capacitance, but not with 100 pF and not with 1 nF or above. My 2.1 GHz spectrum analyzer came in handy for debugging that.

Tom

 

[tomchr]

All I bought were four resistors, a switch and a cable, used an old lunch box for the case. Works well for casual measurements and costs <10€/$.

Great. The keyword here is casual. Nothing I do is casual. I run a business. As does Amir. We both got tired of fiddling with individual resistors. Obviously I'm not making this product with the hobbyist in mind. I'm making it for those who have an AP and have gotten tired of dinking around with stuff that can't be automated and has bad connections and whatnot.

I did consider just hacking it and have a few resistors on a board with a rotary switch, but I wanted the remote control feature. It also turns out there's nothing else like it in the market, so I turned it into a product. $1500 it the test equipment world is cheap. It's 1/10th the cost of a base model APx525. ~4% the cost of a base model APx555B.

*Edit: well, using individual conductors for the return you could make it balanced, but I'm not sure if that makes sense given the kind of accuracy you'd want to measure a higher end amp/system like that?

The HP-LOAD is indeed set up like that. I use Kelvin sensing and sense the voltage at the output connector of the amp under test. This means that if you use the HP-LOAD for measurements of output impedance, you will see the true output impedance of the amp (and its output connector), not the impedance at the end of some length of cable.

Tom

 

[DualTriode]

200 Watts 150Ohms $15

Thanks DT

https://www.ebay.com/itm/254807286542?hash=item3b53b2a30e:g:VbgAAOSwBG9cdOya

 

[tomchr]

Great! Now make it remote controllable from 12 Ω to 600 Ω with an 8-bit TTL input.

Tom

 

[amirm]

200 Watts 150Ohms $15

Thanks DT

https://www.ebay.com/itm/254807286542?hash=item3b53b2a30e:g:VbgAAOSwBG9cdOya

Those things are terrible. I have a few and their VCR is poor resulting in excess measured distortion of power amps. You have to use top brand name load resistors which unfortunately can set you back hundreds of dollars. Vishay/Dale and Arcol are the two brands to go with. Arcol is cheaper but can't handle as much power. The Visahay 250 watt ones cost $160 each! You need four for stereo load at 4 ohm so you are in for $600 just for that!

 

[DualTriode]

Great! Now make it remote controllable from 12 Ω to 600 Ω with an 8-bit TTL input.

Tom

Your automated factory floor quality control may need a $1500 solution. My APX555 on the bench only needs a pair of Mills Vishay precision wire-wound resistors.

Thanks DT

 

[DualTriode]

Those things are terrible. I have a few and their VCR is poor resulting in excess measured distortion of power amps. You have to use top brand name load resistors which unfortunately can set you back hundreds of dollars. Vishay/Dale and Arcol are the two brands to go with. Arcol is cheaper but can't handle as much power. The Visahay 250 watt ones cost $160 each! You need four for stereo load at 4 ohm so you are in for $600 just for that!

If you want name brand quality I can help you out with some hospital grade VFD braking resistor recommendations.

https://www.galco.com/buy/ABB/P1449...n6fDE_5PpZSMwxEG-5njOrl3jXJyv1ehoCrbAQAvD_BwE

 

[IVX]

Here is mine Please note, 32 steps from 10 to 300ohm L/R independent and balanced/unbalanced 3.5/2.5mm supported. No cables to reduce residual rig impedance i.e. you can measure 50mOhm output and see .05ohm. Also possible to off all resistive load to use real headphones instead. $20 retail ))

 

[restorer-john]

Your automated factory floor quality control may need a $1500 solution. My APX555 on the bench only needs a pair of Mills Vishay precision wire-wound resistors.

You are either missing the point completely, or just being obtuse.

You know full well the dodgy Chinese resistors are absolute garbage for ultra low THD measurements. You also know full well the requirements for HPAs are extreme precision at low powers- something you cannot achieve with the types of loads you are advocating.

 

[jfree77]

that box is beautiful. amazing piece of craftmanship!

 

[wwenze]

While we're on the topic of distortion due to load, how much distortion does real headphones add to the amp? If we are trying to emulate a real headphone, would low electrical distortion matter? Or would the ability of the amp to absorb the distortion be a figure of merit?

 

[DualTriode]

You are either missing the point completely, or just being obtuse.

You know full well the dodgy Chinese resistors are absolute garbage for ultra low THD measurements. You also know full well the requirements for HPAs are extreme precision at low powers- something you cannot achieve with the types of loads you are advocating.

This is a $1500.00 solution looking for a $20.00 problem, and you know it.

There is a baggie with several R values of 12 watt precision Wire-wound Mills Vishay resistors in the bin near my bench that does just fine testing HPA's.

 

[JohnYang1997]

This is a $1500.00 solution looking for a $20.00 problem, and you know it.

There is a baggie with several R values of 12 watt precision Wire-wound Mills Vishay resistors in the bin near my bench that does just fine testing HPA's.

Come on. Firstly what's the exact problem?

Also $1500 is the price of a product made by someone by hand from a small company. The cost of components would be way less. And what's the cost for 14 (7 values and 2 channels) of the resistors you mentioned?

And then what do you get for as few resistors? Can you do automtion? How reliable?

I don't understand your perspective being any relevant to the use case.

 

[David_M]

@tomchr ... Thanks for making this device as it'll standardize all HP measurements worldwide. I hope the global HP audio community embraces your device as they've done with the APx instruments. May it be the next "it" device testers everywhere use to measure their devices. Amen and Amen!

Now, PLEASE, PLEASE, PLEASE (seriously!) ... can you make a reactive speaker load box, able to handle up to 1kW (or more) up to 8-Channels of amplification? This would handle stereo and all MCH amp types out there.

I have no doubt it will be a bit more expensive and even more challenging to design and build but we need a consistent reactive load device able to simulate the different types of speaker technologies on the market. Resistive loads are ok, but they don't stress the amplifier as much as a reactive load. As you well know, current/voltage are in phase with a resistive load but their relative frequency-dependent phase angles come into play once the load becomes reactive. This prevents the amp from providing rated power to the speaker, and depending on the reactive load, could cause the amplifier to oscillate. An amp could measure fine/superb with static loads but have serious trouble performing with complex reactive loads.

The following is a partial list of speaker load types out there, that your new box could test for:

1. Electrostatics (with their decreasing impedance with increasing frequency, up to 0.2 ohms at 20 kHz like the MartinLogan Spires I had for years). Examples are Martin-Logan and Quad Electroacoustics.

2. Purely resistive loads (Yes, that's right!) like most Magnepan speakers (4-ohms)... add in the obligatory low distortion 8, 4, and 2 ohms standard resistive loads.

3. Sealed enclosure and bass reflex loads with their resonance peaks (due to the woofers, mids, and tweeters) and their dips around their crossover regions.

You could make the new test box expandable, where for example, a user could parallel 2 boxes to handle 2kW amplifiers, 3 boxes to handle 3kW amplifiers, OR simulate loads for 16- channels amplifiers ... just an idea.

The box should be able to send its results to the APx that in turn calculates true amplifier distortion curves for a given reactive load. This truly can reveal an amplifier's true performance. I believe this will instill the fear of God in all amplifier designers as they see how their amps whimper terribly under the test.

BTW ... I foresee that marketing departments will hate you with a passion as they'll be forced to temper their often questionable and enthusiastic advertising claims quite a bit to match the amps' true measured performance.

Thanks for listening!

 

[DualTriode]

Come on. Firstly what's the exact problem?

Also $1500 is the price of a product made by someone by hand from a small company. The cost of components would be way less. And what's the cost for 14 (7 values and 2 channels) of the resistors you mentioned?

And then what do you get for as few resistors? Can you do automtion? How reliable?

I don't understand your perspective being any relevant to the use case.

Okay a little perspective.

Looking back through the HPA reviews here at ASR I do see sequence automation steps for HPA input voltage and output power measurements, The AP APx500 software and APx555 hardware “sequence mode” increments through each step of the test sequence except the switching of the test loads.

I also see two typical test loads; 300 Ohms and 32 Ohms. I do not see any complex impendence loads in the ASR reviews. I do not see any evidence of automated switching between the test loads.

So what we do have is a $1500 solution looking for a problem to solve.

How is that for relevance?

Thanks

 

[restorer-john]

@tomchr ... Thanks for making this device as it'll standardize all HP measurements worldwide. I hope the global HP audio community embraces your device as they've done with the APx instruments. May it be the next "it" device testers everywhere use to measure their devices. Amen and Amen!

Now, PLEASE, PLEASE, PLEASE (seriously!) ... can you make a reactive speaker load box, able to handle up to 1kW (or more) up to 8-Channels of amplification? This would handle stereo and all MCH amp types out there.

I have no doubt it will be a bit more expensive and even more challenging to design and build but we need a consistent reactive load device able to simulate the different types of speaker technologies on the market. Resistive loads are ok, but they don't stress the amplifier as much as a reactive load. As you well know, current/voltage are in phase with a resistive load but their relative frequency-dependent phase angles come into play once the load becomes reactive. This prevents the amp from providing rated power to the speaker, and depending on the reactive load, could cause the amplifier to oscillate. An amp could measure fine/superb with static loads but have serious trouble performing with complex reactive loads.

The following is a partial list of speaker load types out there, that your new box could test for:

1. Electrostatics (with their decreasing impedance with increasing frequency, up to 0.2 ohms at 20 kHz like the MartinLogan Spires I had for years). Examples are Martin-Logan and Quad Electroacoustics.

2. Purely resistive loads (Yes, that's right!) like most Magnepan speakers (4-ohms)... add in the obligatory low distortion 8, 4, and 2 ohms standard resistive loads.

3. Sealed enclosure and bass reflex loads with their resonance peaks (due to the woofers, mids, and tweeters) and their dips around their crossover regions.

You could make the new test box expandable, where for example, a user could parallel 2 boxes to handle 2kW amplifiers, 3 boxes to handle 3kW amplifiers, OR simulate loads for 16- channels amplifiers ... just an idea.

The box should be able to send its results to the APx that in turn calculates true amplifier distortion curves for a given reactive load. This truly can reveal an amplifier's true performance. I believe this will instill the fear of God in all amplifier designers as they see how their amps whimper terribly under the test.

BTW ... I foresee that marketing departments will hate you with a passion as they'll be forced to temper their often questionable and enthusiastic advertising claims quite a bit to match the amps' true measured performance.

Thanks for listening!

It already exists. About $16k last time I checked.

https://www.audiograph.se/

 

[staticV3]

A quick market survey reveals headphones ranging in impedance from 12 to 600 Ω. I choose those end points deliberately. I bet if you made a histogram of headphone impedances, you'd find three modes: 32 Ω, 300 Ω, and a smattering around the 50-80 Ω mark

Here are 589 IEMs measured by ReferenceAudioAnalyzer:

Here are 572 headphones:

And combined:

 

[Doodski]

It already exists. About $16k last time I checked.

https://www.audiograph.se/

They also have a water cooled version.

 

[David_M]

It already exists. About $16k last time I checked.

https://www.audiograph.se/

The swedes have done it again .... first with Purifi(?), then this? Anyways, competition is good. The more options the better.

 

[tomchr]

Um... The Purifi is designed in Roskilde, Denmark. About 20 km from the town I grew up in. The lead designer is from Holland.

Tom