Using The Topping A30 PRO as a Reference Amplifier to test Headphones

[DualTriode]

Hello All,

On the bench I have an APx555 and GRAS 45CA-9 headphone test fixture. Also sitting here is a Topping A30 Pro headphone amplifier.

The goal is to select cords and plugs to extend the amplifier outputs across the room or across the hall away from the noise of the APx555 cooling fan on the bench.

Also I am thinking of using the A30 Pro amplifier to test Compression Drivers and horns for TS/P’s impedance curves and similar.

For this handful of pure Watts I am considering using Canare 4S6 20AWG Star Quad speaker cable and NUTRIK 4-pin XLR plugs

Similar to what I am doing with the Benchmark AHB2 reference amplifier I will test an assortment of cords and resistors to confirm the best performance of the A30 Pro.

Then armed with known quality test leads the tests of headphones will be a go.

Thanks DT



@JohnYang , do you have a idea of a quality output extension cord for the A30 Pro headphone amplifier?

 

[JohnYang1997]

Do it like this. Slipt the load and measuring point here. And for 16ohm load and above there would be no requirement for expensive load.

 

[DualTriode]

@JohnYang1997 ,

Thanks for the input.

I am going to test at the amplifier end of the cord and again at the headphone end of the cord in an effort to get the best possible performance from the "speaker cord".

Thanks DT

 

[DualTriode]

Hello All, Tomorrow there are a handful of NUTRIK 4-Pin XLR connectors arriving, there is already a roll of Canare 4S6 20AWG Star Quad speaker cable waiting.

The plan is to use separate lengths of Canare 4S6 20AWG Star Quad speaker cable, one cable for each channel.

That means that two separate speaker cables will attach to one 4-pin male XLR plug. Vishay Dale NH-50 Watt wire wound test load resistors will attach to the other ends of the speaker cables.

Looking around the ASR site I do see posts about headphone test loads. I do not see mention of Vishay Dale SH-50r wire wound resistors. I have a pairs of 33R, 72R and 300R resistors. I do not see mention of speaker cable used for headphone testing. We will see what voltage and thermal modulation looks like or not

If I can squeeze 2 speaker cables into the shell of a NUTRIK 4-pin plug I will run sum plots for dashboard, SINAD and FFT, then post the results here.

Thanks DT

 

[DualTriode]

Hello All,

This is the Topping A30 Pro, noise and distortion looks good;

Input is 4VAC, Output is 4VAC

Gain switch set at medium.

4-pin XLR Neutrik only L1 and L2 pins used

Canare 4S6 Quad Star Canare speaker cable all 4 conductors used for Left Chanel.

The test resistor was a Vishay 72R RH50 wire wound resistor. I used this resistor because it matches my LCD2 headphones measured impedance.



I am a bit disappointed with this setup. Only one speaker cable would fit in the 4-pin Nutrik cord end and that was a tight squeeze.

I wish that the Topping A30 Pro had two separate 3-pin XLR outputs or two separate SpeakOn outputs.



Thanks DT

 

[DualTriode]

Hello All,

The Topping A30 Pro is good to go.

The Vishay RH-50 50Watt wire wound resistors load Resistors work well across 20 to k22 BW.

The 4-pin Neutrik XLR with with 20AWG Canare speaker cable works well. The same speaker cable works well with the SpeakON and the ABH2 amplifier at 8 Ohms at 5 Watts.

We are good to go using this Topping A30 Pro and 20AWG speaker cable testing headphones, tweeters and CD/Horns.

Comments? Anyone!

Thanks DT

 

[Vini darko]

Look forward to seeing more measurements. I've been very intrested in Erin's compression and stability measurments for speakers. Is it possible to do that with headphones?

 

[DualTriode]

Look forward to seeing more measurements. I've been very intrested in Erin's compression and stability measurments for speakers. Is it possible to do that with headphones?

Hello,

If you will, point me in the direction of Erin's measurements.

Thanks DT

 

[Vini darko]

Hello,

If you will, point me in the direction of Erin's measurements.

Thanks DT

https://www.erinsaudiocorner.com/

 

[Roland68]

The goal is to select cords and plugs to extend the amplifier outputs across the room or across the hall away from the noise of the APx555 cooling fan on the bench.

I would basically avoid any unnecessary cable length when taking measurements.
Why not build an anechoic measuring room for headphone measurements, similar to what you would do with loudspeakers. A box with an inner edge length of 100-140cm square should be sufficient. You would have no external noise and reflections from the headphones would also largely be eliminated.

 

[DualTriode]

Hello,

For measurement purposes I am considering the speaker cable as an extension of the amplifier outputs. We now know the noise and distortion results of the test setup including the input and output connections. We are good to go with what we have.

If you look at testing done over at Head-Fi you will see a headphone test enclosure that rests on a 1300 pound vibration isolation table.

If you look around here at ASR, @amirm does his headphone testing with the GRAS 45CA test fixture in the same room with the APx555 cooling fan. The test fixture is across the room and at a different elevation than the AP analyzer. The analyzer with cooling fan is in an “enclosure” that attenuates the cooling fan noise to a degree.

The thinking is also that the headphones will isolate the test microphones from the ambient noise to a degree, closed back headphones even more.

I live in a quiet residential area out in the woods. There is a well stuffed linen closet across the hall, stuffed with blankets, pillows, sheets, towels and 2 years supply of toilet tissue.

I will do some noise level measurements in the same room as the APx555 with cooling fan, measurements across the room from the analyzer and measurements across the hall in the linen closet.

Perhaps the isolation chamber on the 1300 pound isolation platform is over kill.

For solid measurements we need to confirm that ambient noise is 10dB’s less than potential headphone 2nd and 3rd Harmonic Distortions.



Thanks DT