M2 Macbook Pro’s Low Impedance Power Output Problem

[emresarii]

Macbook provided 1.25 volts rms under 150 ohms and 3 volts rms over 150 ohms. However, planar headphones generally have low impedance and sense, regarding that they are hard to drive. The question is how can I get 3 rms with planar headphones like he400se on M2 MacBook pro?

 

[staticV3]

Macbook provided 1.25 volts rms under 150 ohms and 3 volts rms over 150 ohms. However, planar headphones generally have low impedance and sense, regarding that they are hard to drive. The question is how can I get 3 rms with planar headphones like he400se on M2 MacBook pro?

If it's anything like Cirrus' DACs (which AFAIK Apple contracted to design their own DACs), then you can defeat the impedance sensing auto gain with a regular old extension cable.

Plug the extension cable into the MacBook, then your headphones into the extension cable, and it should give you full beans regardless of headphone impedance.

Be aware though that that'll allow the Amp to clip when you push volume too far.

You can get short extension cables that won't get in the way:


Though sadly you'll have to repeat that ritual (Cable->MacBook, then Headphone->Cable) every time you plug it in.

Also, welcome to ASR!

 

[Basic Channel]

If it's anything like Cirrus' DACs (which AFAIK Apple contracted to design their own DACs), then you can defeat the impedance sensing auto gain with a regular old extension cable.

Plug the extension cable into the MacBook, then your headphones into the extension cable, and it should give you full beans regardless of headphone impedance.

Be aware though that that'll allow the Amp to clip when you push volume too far.

Also, welcome to ASR!

You just mean an audio extension cable, right?

My friend has a MacBook and says the HE400se are not loud enough, whereas I can plug them in and EQ them with -6db preamp. So thank you OP

 

[staticV3]

You just mean an audio extension cable, right?

Yup, see the image I added above.

 

[Basic Channel]

Yup, see the image I added above.

Thank you, I responded before you edited. Just for my understanding, the MacBook is seeing the HE400se with normal cable as higher impedance than it is?

 

[staticV3]

Thank you, I responded before you edited. Just for my understanding, the MacBook is seeing the HE400se with normal cable as higher impedance than it is?

If you just plug the 400se in like normal then the MacBook correctly senses the 25Ω impedance and adjusts gain accordingly, limiting volume.

If instead you plug in an extension cable with nothing plugged into the other end, then the DAC will sense that something was plugged in, but can't actually measure an impedance since there's nothing plugged into the other end, so the gain is left at max.

After that you can plug your headphone into the cable and enjoy max gain.

At least, that's how Cirrus' DACs function.

 

[emresarii]

If it's anything like Cirrus' DACs (which AFAIK Apple contracted to design their own DACs), then you can defeat the impedance sensing auto gain with a regular old extension cable.

Plug the extension cable into the MacBook, then your headphones into the extension cable, and it should give you full beans regardless of headphone impedance.

Be aware though that that'll allow the Amp to clip when you push volume too far.

You can get short extension cables that won't get in the way:
View attachment 365950

Though sadly you'll have to repeat that ritual (Cable->MacBook, then Headphone->Cable) every time you plug it in.

Also, welcome to ASR!

I saw your comment on another post, so I tried to plug It in cable first and headphones after that and I'm using this cable. And it didn't change the volume. Should I go for another pair of this extension? Or am I doing something wrong?

 

[staticV3]

I saw your comment on another post, so I tried to plug It in cable first and headphones after that and I'm using this cable. And it didn't change the volume. Should I go for another pair of this extension? Or am I doing something wrong?

Hm doesn't look like another extension cable would make a difference.

It's definitely possible that Apple changed the behavior of the impedance sensing function to patch this workaround.

If you're curious, you can use a basic multimeter to measure your MacBook's output voltage yourself under different scenarios.

If it turns out that there's no way to trick the auto gain, then maybe consider buying a Topping DX1. It can output about 2.9Vrms at 25Ω.

 

[emresarii]

Hm doesn't look like another extension cable would make a difference.

It's definitely possible that Apple changed the behavior of the impedance sensing function to patch this workaround.

If you're curious, you can use a basic multimeter to measure your MacBook's output voltage yourself under different scenarios.

If it turns out that there's no way to trick the auto gain, then maybe consider buying a Topping DX1. It can output about 2.9Vrms at 25Ω.

I'm going to buy Magni+, but I was curious about this situation. I asked about the extension cable because the extension cable you mentioned has a "non-resistance" tag on it. I didn't find anything related to that. I don't know what the problem is but sticking into 1.25 rms when you were able to provide 3 is kinda suck. I tried HE400SE with an old Marant P700 amp and loved it. So I'm trying to enjoy it while getting the Magni+ (it will come to me around a month).

 

[staticV3]

@emresarii
Just to make sure: You first plugged to cable into the MacBook, then the headphone into the cable?

Not Headphone->Cable, then Headphone+Cable->MacBook?

The order is important.

Edit: Sorry I read your post again and sure enough you did.

 

[emresarii]

@emresarii
Just to make sure: You first plugged to cable into the MacBook, then the headphones into the cable?

Not Headphone->Cable, then Headphone+Cable->MacBook?

The order is important.

Yes, I plugged the cable into the Macbook and then plugged the headphones into the extension cable. I didn’t update macOS for a while. Can it be related to that? Also using eqMac, don’t know if it makes any difference.

 

[staticV3]

Yes, I plugged the cable into the Macbook and then plugged the headphones into the extension cable. I didn’t update macOS for a while. Can it be related to that? Also using eqMac, don’t know if it makes any difference.

On Cirrus hardware this function is hard coded and can't be firmware updated.

It's possible that Apple can update their solution but it would be somewhat surprising.

eqMac can change frequency response and software volume but can't affect the auto gain afaik.

 

[emresarii]

On Cirrus hardware this function is hard coded and can't be firmware updated.

It's possible that Apple can update their solution but it would be somewhat surprising.

eqMac can change frequency response and software volume but can't affect the auto gain afaik.

Removing this trick is meaningless to me (if they really removed that) because you can drive planars like 400se. And I don't understand the logic behind the ohm detection, there are too many headphones that require power on low ohms. I am confused now.

 

[staticV3]

Removing this trick is meaningless to me (if they really removed that) because you can drive planars like 400se. And I don't understand the logic behind the ohm detection, there are too many headphones that require power on low ohms. I am confused now.

The lower the headphone impedance gets, the less voltage a Headphone Amp can output before it clips (sudden rise in distortion).

Apple doesn't want their headphone jack to ever distort because that would make their products look cheap and unrefined.

So they built in an impedance sensing function that limits the Amp's output so that it's guaranteed to never hit its limits.

 

[emresarii]

The lower the headphone impedance gets, the less voltage a Headphone Amp can output before it clips (sudden rise in distortion).

Apple doesn't want their headphone jack to ever distort because that would make their products look cheap and unrefined.

So they built in an impedance sensing function that limits the Amp's output so that it's guaranteed to never hit its limits.

Even If a simple javascript website can calculate RMS output, I think they can provide something similar on their product. Do you have a Macbook or extension cable to try this method?

 

[staticV3]

Even If a simple javascript website can calculate RMS output, I think they can provide something similar on their product. Do you have a Macbook or extension cable to try this method?

I don't have one with the new headphone amp. Would have to borrow one from a friend to test.

 

[emresarii]

I don't have one with the new headphone amp. Would have to borrow one from a friend to test.

I have the m2 pro model, If you are going to test that could you please inform me?

 

[staticV3]

I have the m2 pro model, If you are going to test that could you please inform me?

Sure.

Just know that you can test output voltage yourself with about $35 worth of parts.
A basic multimeter and this board is all that you need: https://www.aliexpress.com/item/3256803497862592.html

It's really simple.

 

[emresarii]

Sure.

Just know that you can test output voltage yourself with about $35 worth of parts.
A basic multimeter and this board is all that you need: https://www.aliexpress.com/item/3256803497862592.html

It's really simple.

It will come to me around june if I buy that ‍️. I’m just try to get juice out of Macbook’s dac/amp. But don’t know how…