Topic: Balanced Headphone Connection ADI 2 Pro FS

Hello,
I would like to connect my headphones to the ADI2 Pro FS in balanced mode.

I have Sennheiser HD660S headphones that has cables with 6.3mm  TRS unbalanced stereo jack or TRRS 4.4mm Balanced Jack.

Does anyone have experience or knowledge of what the optimum cable or adapter set up is to have a balanced headphone connection with the unit?

Thanks!

2 (edited by KaiS 2020-05-23 14:16:16)

Re: Balanced Headphone Connection ADI 2 Pro FS

I'd suggest to get a cable with 2 separate 6.3mm TRS jacks on one side and Sennheiser connection on the other.
An adapter would probably cost the same and often gives unreliable contact.

See manual page 43, the XLR in the diagram would be the Sennheiser connector.


If you or a friend has soldering skills you can use an original Sennheiser cable and mount the 2x 6.35 mm TRS jacks.
https://de-de.sennheiser.com/accessories--hd-650--cable
I'd suggest Neutrik 6.35 mm TRS, reasonable priced, high quality, unbreakable.
https://smile.amazon.de/Neutrik-NP3X-BA … amp;sr=8-9


I could not find any readily available cables on the market.


Technically the HD-660S doesn't benefit from balanced connection if used with RME ADI-2 Pro.
ADI-2 Pro single sided has more then enough power to drive them to earsplitting levels.
Soundwise, you won't notice a difference if you adjust to exact same audio-level.


But I do understand you like to try it.


Be careful not to accidentially break them.
Sennheiser HD 660S long-term input power is max. 500 mW into it's impedance of 150Ω.

Looking at the diagram page 88 in ADI-2 Pro's manual this fit quite well to the max. power of 600mW ADI-2 Pro can deliver.
With balanced this is almost quadrupled to 2000mW which can literaly fry your 'phones.

Re: Balanced Headphone Connection ADI 2 Pro FS

Thanks for the good tips!

If I understood correctly, the power from ADI2 Pro FS is enough without balanced connection.

I read in other forums about improvement in audio "quality" when a headphone is connected via balanced connection (4 pin XLR for example), but there seems to be mixed opinions.

Am I likely to hear an improvement in quality if I connect the HD660S with a balanced connection or is the improvement purely on a technical level, but in practically inaudible?

4 (edited by ramses 2020-05-23 17:34:38)

Re: Balanced Headphone Connection ADI 2 Pro FS

Look at the specs of the ADI .. can you hear a few dB SNR / Dynamik difference ? Surely not.
Also consider, if I remember right from forum, the ADI-2 Pro becomes warmer during balanced operation.

BR
Ramses
X10SRi-F, Win10 Pro 1909, Cubase, UFX+, Octamic XTC, ADI-2 Pro FS BE/R BE, RayDAT, ARC USB

Re: Balanced Headphone Connection ADI 2 Pro FS

Good point, I also read that it heats up in balanced operation.
If I find a way to make a split cable for the Sennnheiser phones I might try, but it does not sound like I'm going to hear the difference.

Re: Balanced Headphone Connection ADI 2 Pro FS

TBH .. balanced mode for phones is overrated... Simply use your good phones.

If you want better sound, then get better phones.

BR
Ramses
X10SRi-F, Win10 Pro 1909, Cubase, UFX+, Octamic XTC, ADI-2 Pro FS BE/R BE, RayDAT, ARC USB

7 (edited by KaiS 2020-05-24 08:38:08)

Re: Balanced Headphone Connection ADI 2 Pro FS

Misunderstanding on my side, read posting #14 below

ramses wrote:

Also consider, if I remember right from forum, the ADI-2 Pro becomes warmer during balanced operation.

costa wrote:

Good point, I also read that it heats up in balanced operation.


If a headphone heats up the related amp is broken and puts out DC.


Heat is energy, and energy does not come from nowhere.


Sennheiser HD 660S can stand just 0.5W at max, but not DC, only with music signal, which would be unbearable loud (~124 dB SPL).

0.5W DC does immediately kill the headphones, as the cooling effect of the moving diaphrag is missing, so DC needs to be significantly lower.


If someone is listening loud enough that headphones heats up, quality doesn't matter any more - the person is deaf.


An average human generates about 120W of heat.
A significant amount of this heat is released from the face and the ears, because there's no cover by cloth or hair.
In relation to this, the 0.5W a Sennheiser HD 660S can produce at max. is not very significant.


Looking at all these facts the heating up story can be regarded as a myth.


The myth might origin from the fact that, according to Ratings.com, The HD 660S is only half as "breathable" as it's anchestors, the 600 and 650.
The 660S was the first one to be delivered with a balanced cable.
People likely compare apples to oranges.

8 (edited by ramses 2020-05-23 20:11:25)

Re: Balanced Headphone Connection ADI 2 Pro FS

> If a headphone heats up the related amp is broken and puts out DC.

The ADI-2 Pro becomes a little bit warmer, how much I can not tell. This has nothing to do with something being broken.

I told it only proactively, as some user in the past were already concerned about the normal operating
temperature of the device.

BR
Ramses
X10SRi-F, Win10 Pro 1909, Cubase, UFX+, Octamic XTC, ADI-2 Pro FS BE/R BE, RayDAT, ARC USB

9 (edited by KaiS 2020-05-23 20:16:35)

Re: Balanced Headphone Connection ADI 2 Pro FS

ramses wrote:

> If a headphone heats up the related amp is broken and puts out DC.

The ADI-2 Pro becomes a little bit warmer, how much I can not tell.
This has nothing to do with something being broken.

This is simply explained by the fact that in balanced operation the current stays the same, but the amp's supply voltage virtually doubles, meaning two times more losses.

Re: Balanced Headphone Connection ADI 2 Pro FS

And why you wrote this before ?

> If a headphone heats up the related amp is broken and puts out DC.

BR
Ramses
X10SRi-F, Win10 Pro 1909, Cubase, UFX+, Octamic XTC, ADI-2 Pro FS BE/R BE, RayDAT, ARC USB

Re: Balanced Headphone Connection ADI 2 Pro FS

Because pure music that heats up headphones would be too loud to stand.

So an inaudible signal like DC must be involved.

BTW: The usual PET diphrags can stand about 150°C before they permanently deform.
The neodym magnets loose their magnetism above 80°C.
Just to give some figures.

Re: Balanced Headphone Connection ADI 2 Pro FS

I didn't want to make a big story out of this.
All I wanted to share with the forum is, that the ADI becomes warmer when using balanced phones.
Whether its worth it for only a few dB SNR more .. try it out .. I have doubts and prefer to run the device cooler.
Thats all.

BR
Ramses
X10SRi-F, Win10 Pro 1909, Cubase, UFX+, Octamic XTC, ADI-2 Pro FS BE/R BE, RayDAT, ARC USB

13

Re: Balanced Headphone Connection ADI 2 Pro FS

Confused me too. KaiS seemed to have misread these two comments and discussed heated up headphones - nobody talked about that.

Regards
Matthias Carstens
RME

14 (edited by KaiS 2020-05-24 21:54:50)

Re: Balanced Headphone Connection ADI 2 Pro FS

costa wrote:

Good point, I also read that it heats up in balanced operation.

A misunderstanding on my side, I thought "it" meant the Sennheiser HD-660S gets warmer if used balanced.

You both meant ADI-2 Pro gets warmer, thanx Mr. Freud, I didn't realize as it's so unlikely!


Heating up ADI-2 Pro is only possible if one maxes out ADI-2 Pro's headphones amps by listening loud enough with headphones with very low efficiency (think HiFiman Susvara).



HD-660S is quite efficient, there would be a difference in the heat generated by ADI-2 Pro, but very, very minor, noticable only under labaratory conditions.



Let's do some math:

• Sennheiser HD-660S has a sensitivity/efficiency of 104dB at 1V input.
• Assume you won't listen too far beyond the healthy long term listening limit of 82dBA SPL (A-filtered):
http://www.sengpielaudio.com/Zulaessige … gszeit.htm
• dBA's A-filter removes the bass, with music, measured full range, you end up about 10dB higher, at ~92dB linear.
• This is 12dB or 0.25x lower than Sennheiser's 104dB at 1V.
So, to drive HD660S we need 0.25V on each cup.
0.25V into 150Ω results in a current of 0.0017A (0.25V divided by 150Ω).
• ADI-2 Pro's headphones amp has a power supply voltage of 15V.
Volt x Ampere equals Watt (Power).
15V x 0.0017A = 0.025W each channel, = 0.05W total, unbalanced.
• Now double that if you use both of ADI-2's headphone amps in balanced configuration to deliver the same current (Ampere, A), you end up with 0.1W balanced.

• ADI-2 Pro, idle state, consumes about 12W total that heats it up significantly.

Do you think additional 0.05W makes a difference?




I just did some measurement to verify my calculation:
With my power meter's resolution of 0.1W ADI-2 Pro's power consumption does jump up 0.1W if I feed 0.5V into an Sennheiser HD-58X (150Ω).
0.2W ADI-2 Pro consumption at 1V into the HD-58X.

Due to the power meters resolution this is more like an estimate than a real measurement, but still some kind of confirmation.


To do "real measuements" I'd feed 8.3V into the 2x150Ω power resistors (not to break the headphone).
Then measured the rise of ADI-2s power consumption:
2.0W unbalanced.
3.7W balanced.

This confirms my calculations above.

15 (edited by ning 2020-05-24 20:14:47)

Re: Balanced Headphone Connection ADI 2 Pro FS

IMHO:

1. '15V x 0.0017A = 0.025W each channel, = 0.05W total, unbalanced.' sounds unreasonable. The output power is 0.25v x 0.0017A which is a lot smaller. The opamps themselves is not ideal so they generates heat, but they are not linear regulators, so the calculation is not output current * power supply voltage.  Also, ADI-2 is using +-15V rail for the opamps, not +15V and 0V. so the total voltage is 30V.

2. I think for fair comparison the test should be done based on same output loudness(power), not same onscreen volume as that has +6db gain, nor " to deliver the same current (Ampere, A)". In this case, the actual current and  amplitude of vpp should all be 1/sqrt(2) of the original value.

3. Balanced HP mode may use a little bit more heat as now  HP 1/2 is working rather than shutdown by a relay, which may generate a little bit more heat... but in this case, each HP outs consumes less energy, which makes the heat better distributed, and as a result should make the caps last longer.

16 (edited by KaiS 2020-05-25 06:30:25)

Re: Balanced Headphone Connection ADI 2 Pro FS

ning wrote:

IMHO:

1. '15V x 0.0017A = 0.025W each channel, = 0.05W total, unbalanced.' sounds unreasonable. The output power is 0.25v x 0.0017A which is a lot smaller. The opamps themselves is not ideal so they generates heat, but they are not linear regulators, so the calculation is not output current * power supply voltage.  Also, ADI-2 is using +-15V rail for the opamps, not +15V and 0V. so the total voltage is 30V.

2. I think for fair comparison the test should be done based on same output loudness(power), not same onscreen volume as that has +6db gain, nor " to deliver the same current (Ampere, A)". In this case, the actual current and  amplitude of vpp should all be 1/sqrt(2) of the original value.

3. Balanced HP mode may use a little bit more heat as now  HP 1/2 is working rather than shutdown by a relay, which may generate a little bit more heat... but in this case, each HP outs consumes less energy, which makes the heat better distributed, and as a result should make the caps last longer.

@ 1.:
0.05W is the power that generates heat inside ADI-2 due to voltage drop x current.
Unbalanced only one power rail against ground delivers current at a time.
The other path is idle until the signal polarity reverses, so 15V.
Only in balanced mode current flows from +15V rail to the other, -15V.

For simplification, I did not take into account the OPA1688's 0.0016A idle current.
The result would have added to what I wanted to show anyway:
even less extra heat generated with the Sennheiser HD-660S at reasonable listeng levels.

0.25v x 0.0017A is ADI-2 Pro's output power to the headphone, not heat inside ADI-2 Pro.
This was to calculate the current needed to generate 96dB SPL at the headphones.


@ 2.:
It is - same current through the 2x150Ω resistors = same voltage = same power = same loudness. Ohm's law.
All voltages RMS BTW.


@3.:
As my calculation shows, CONFIRMED BY my 2nd measurement (for the same voltage at the same resistor) balanced consumes almost double the power from ADI-2 Pro's PSU for the same level at the headphones:
Same current now flowing from rail to rail, 30V, instead of rail to ground, 15V.

Both headphones amps are located close together on the board, almost double heat, more stress to the caps.
One set of caps is located between the 2 HP-Amp's BTW.
I have measured up to 95°C on the chips under heavy load.


BUT: Significantly more heat balanced only if you really need permanent high power.
Few headphones do, usually no problem.

Re: Balanced Headphone Connection ADI 2 Pro FS

I read your original post again and found you are right! Sorry I misread for the first time.

18 (edited by KaiS 2020-05-25 08:31:55)

Re: Balanced Headphone Connection ADI 2 Pro FS

Always good to clear up things, you're welcome.

Dependencies are sometimes not obvious.
To explain everything from the scratch would result in unreadable long postings.
I mostly end up long enough anyway.



Some might stumble across the relative low voltage of 0.25V needed for the average loudness of 92dB SPL (linear) on the Sennheiser HD-660S.
0.25V is the long term average RMS, the value relevant for heat generation.


There may well be much higher peaks with music listening.
In the studio we leave an ample headroom of 20dB above that level to deal with sounds in their original dynamic range.

This would mean peaks of up to 2.5V or 112dB SPL with the Sennheiser HD-660S.
Remember, we started wit 82dBA SPL (A-filterd) long term average to end up there!


Summary:
With music of natural dynamic range you can get:
82dBA RMS average = 92dB RMS linear average = 112dB Peak short term.

The importance about this level of 82dBA is, it's the maximum allowed level for continuous exposure without hearing damage:
http://www.sengpielaudio.com/Zulaessige … gszeit.htm