How can I volume match easily?

[nhatlam96]

Hello, I would like to compare two headphone amplifiers.
How do I volume match?
I have never done this and you can consider me an audio noob.
I have no idea about internals or technicalities of audio equipment.

My available equipment so far:
-DAC: SMSL Sanskrit 10th MK2
-Amplifiers: SMSL SP200 and Violectric V200
-Headphone: Focal Clear
PC connect to DAC via optical cable.
DAC connect to both amplifiers via 2x RCA Splitters.
Amplifier connect to headphone via unbalanced output. (I don't own a XLR cable for headphone).
-Digital Multimeter
-Huawei P20 Pro, I can download SPL app?
-Modmic Wireless

 

[Doodski]

Use a sine wave of ~3kHz to level match the amp outputs using the multimeter on AC voltage. Your multimeter has a 2V AC range and a unknown bandwidth specification. Perhaps you can check the owners manual and see if it has frequency bandwidth specifications for the multimeter on AC V. You can try the multimeter and see if it works at 1kHz or 3kHz. It should work. Then you can switch between the amps and compare using the headphones.

 

[Doodski]

Tone generator.

 

[3125b]

It's not a true-RMS meter. Well, shouldn't make too much of a difference if you use the same frequency for both amps. However measuring like that doesn't take output impedance into account (since the multimeter has something like 10Mohms input impedance in voltage mode).
Not much of an issue in this case since both amps have close to zero Z_out, just something to keep in mind when comparing to a device with high Z_out.

 

[Bob-23]

Hello, I would like to compare two headphone amplifiers.
How do I volume match?
I have never done this and you can consider me an audio noob.
I have no idea about internals or technicalities of audio equipment.

My available equipment so far:
-DAC: SMSL Sanskrit 10th MK2
-Amplifiers: SMSL SP200 and Violectric V200
-Headphone: Focal Clear
PC connect to DAC via optical cable.
DAC connect to both amplifiers via 2x RCA Splitters.
Amplifier connect to headphone via unbalanced output. (I don't own a XLR cable for headphone).
-Digital Multimeter
-Huawei P20 Pro, I can download SPL app?
-Modmic Wireless

In addition to what Doodski recommended:
For switching instantaneously (!) you need a A/B-switch-box. And measure/match the output voltages of the 2 amps with your headphones connected. There should be no more than 1 % difference between the voltages.
You can also use 400Hz.
This cheap - but astoundingly capable DMM does the job, too:

https://www.amazon.com/ANENG-AN8008...d=1&keywords=aneng+8008&qid=1608309704&sr=8-2

I woudn't go on mains with that DMM. (Look at Dave Jones' Test at EEV Blog).

EDIT: Switching instantaneously is an absolute necessity.

 

[nhatlam96]

true-RMS meter

This cheap - but astoundingly capable DMM does the job, too:
https://www.amazon.com/ANENG-AN8008...d=1&keywords=aneng+8008&qid=1608309704&sr=8-2

Is this better? It has true rms in the description.

a device with high Z_out

How do you know when sonething has high z_out and what should I with it?

a A/B-switch-box

This maybe?

measure/match the output voltages of the 2 amps with your headphones connected

How do I measure the output voltage of my amplifier?

 

[3125b]

It has true rms in the description.

Eh, what you have is probably fine. If you use the same frequency sine wave for both amps, the measurement error (well, calculation error done by the multimeter) with your meter is gonna be the same for both making the measurement comparable between the two but not to other measurements (wich is not your goal anyway).

How do you know when sonething has high z_out and what should I with it?

Z_out means output impedance. The amp and load create a voltage divider, so if one of the amps you were comparing had a higher output impedance than the other you couldn't level-match them this way (or you would have to do some calculations compensating for the error but that would requre some reliable measurements to be known in the first place) since the multimeter and the headphone do not have the same impedance.
Doesn't matter, works in your case anyway. You do not care about correctness, you only care about repeatablility.

How do I measure the output voltage of my amplifier?

You stick a cable in the jack and measure between a live and the ground wire (tip to shaft on a TRS plug for the left channel, ring for the right).

 

[Rock Rabbit]

 

[nhatlam96]

Hi, my english isnt the best. So im going to ask a lot, just to be safe. I would like to do this right.

Eh, what you have is probably fine.

If using the same sine wave for both amplifiers, then true rms is not needed. I can keep my multimeter. I think I got this right.

so if one of the amps you were comparing had a higher output impedance

SP200 outout impedance = 1.3 ohm
V200 output impedance = 0.0625 ohm
When is the output impedance too high? Or what can the output impedance difference be between the amplifiers?

View attachment 100071

I am so sorry, you provide a picture, but I still fail to understand. What is it that you plug into the amplifier output? It doesnt seem like a cable to me.

tip to shaft on a TRS plug for the left channel, ring for the right

Am I supposed to plug in my headphone cable into the jack? Because then I can not have access to the shaft and ring of the trs.

 

[3125b]

Am I supposed to plug in my headphone cable into the jack? Because then I can not have access to the shaft and ring of the trs.

Just a cable. And measure it like that (it's easier if you don't have to take a photo):

When is the output impedance too high? Or what can the output impedance difference be between the amplifiers?

Depends on the load (headphone) impedance. In this case it doesen't matter.
There is always gonna be a difference between the measurement from Amir and the manufacturers spec, both amps areactually gonna be fairly close.

If you don't understand certain things I could explain them in German of course, write me a pm.

 

[nhatlam96]

Just a cable. And measure it like that (it's easier if you don't have to take a photo):

I use this cable? With this cable I have two TRS. I can plug in one TRS into the amplifier and then just measure the other TRS?

 

[3125b]

Yes. Just plug it in and measure the voltage between a channel and ground.

 

[nhatlam96]

Can anyone recommend me a reliable stereo switcher? A switch box? It's like my last puzzle. I have found two so far: this and this. Anyone have experience with those? Which one is better? I fear that they degrade sound quality?

 

[Bob-23]

Can anyone recommend me a reliable stereo switcher? A switch box? It's like my last puzzle. I have found two so far: this and this. Anyone have experience with those? Which one is better? I fear that they degrade sound quality?

It should be something with a single switch, so that you can switch between the sources - back and forth - immediately. (Toggle switch/push button)...

Hallo noch! Ich sehe erst jetzt, daß Sie aus Mannheim kommen - und ich erinnere mich: wir hatten schon einmal auf diesem Wege 'korrespondiert'. Also: Kippschalter wäre optimal.

EDIT:
DPDT-Switch (Double Pole Double Throw)
should be one without 'middle Position'!

 

[Bob-23]

Just remembered another member who A/Bed by a switch box, he also used one of the nobsound boxes.
You may read the thread:
https://www.audiosciencereview.com/...ld-i-a-b-test-headphone-amps.8186/post-203887

 

[Rock Rabbit]

You need 1/4 TRS plug to measure output voltage on pre. Buy one or scrap some plug and cable from some obsolete device...some headphones have detachable cables with connectors (like HE4XX). Or use a cable with RCA plugs and stereo plug

Beware to make a shortcircuit when measuring

 

[nhatlam96]

Can someone have a look on my volume matching write up? It worked for me. Switching between the amps was flawless. No differences.

Volume match SP200 and V200:
1. Connect headphones to SP200 and set Windows Audio to 50%. Adjust the volume knob for pleasant listening level. I had my SP200 set to ~3 o’clock.
I chose 50% volume for Windows Audio, because 50% is enough for Spotify tracks, but there are some flac files where I need to go up to 100%.
2. Disconnected headphone from SP200 and set Windows Audio to 100%.
3. Get this cable and use this 3.5 to 6.3mm adapter on it.
Picture: First this and then this.
4. Plug either side into either amplifier and then lay the other side of the cable like shown.
Use something heavy to fixate the cable.
5. Play 3khz tone from online tone generator.
6. Set multimeter to AC voltage like shown.
Press “SEL” button to change to frequency, like here.
7. Put the red side at the tip area and the black side at the sleeve area.
It will look like this. Here are the areas for reference.
8. The multimeter should show 3000hz, because the online tone generator was set to 3000hz.
9. Press SEL button again to change back to AC voltage.
Measure again and write down the voltage value. Mine was exactly 1.045 Volts.
10. Do the same thing with the other amplifier V200 now. Check frequency, it should be 3000hz. Then set volume knob to 1.045 Volts, like SP200.
11. Check again, if both amplifiers have 1.045 Volts.
Here is a picture after I have set the same output voltage for both amps.
12. Stop the tone generator and set Windows Audio back to 50%.
This way I don’t damage the headphone.
13. Connect both amps and the headphone to AB switcher box.
I can connect both amplifiers to ab switcher box with two of these cables.


That’s it. I basically matched the output voltage of the amplifiers. I did not have to worry about the output impedance here, because of the following reasons:
SP200: 1.3 Ohm.
V200: 0.06 Ohm.
Both values do not audibly impact the headphone, because those values are very low.
The ohm impedance values have to be a lot higher to have an audible impact.
Here you can see the Focal Clear (which is the headphone used in this test) driven by 120 Ohm source.
Another example with Focal Utopia.
HD599 and HD800 with different ohm impedances.
As you can see, something like 10ohm is needed to maybe have 1dB impact.
That’s why 1.3 ohm is humanly audibly indistinguishable to 0.06 ohm.

Both amps sounded exactly the same on this method.

 

[Blumlein 88]

Yes, good procedure, your volumes are matched just fine this way.

 

[nhatlam96]

Yes, good procedure, your volumes are matched just fine this way.

Seriously, have you read everything?... Sorry for being sceptic, this is important for me. I usually get critized most of the time. Therefore it seems unreal to me, that everything was correct.

 

[Blumlein 88]

Seriously, have you read everything?... Sorry for being sceptic, this is important for me. I usually get critized most of the time. Therefore it seems unreal to me, that everything was correct.

While one could have used slightly different steps or connectors, everything you have done is fine. You'll have volumes matched. You did a good job. I did indeed read everything and make sure I understood the connections and adjustments.