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Review and Measurements of iFi Ear Buddy (and iEMatch)

amirm

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#1
This is a review and measurements of iFi Ear Buddy which is the cheaper, non-configurable version of iEMatch. I purchased it for USD $20 from Amazon. The purpose of both devices is to reduce the output power of a headphone amplifier. This is needed often when the headphones are too sensitive relative to the amplifier power (or volume control range), not allowing precise control of volume. In addition, many headphone amplifiers have channel imbalances at very low volumes or hiss, both of which are annoying. The idea of Ear Buddy and iEMatch is to reduce the output of the amplifier and with it, eliminate these issues.

The Ear Buddy comes in consumer packaging, hoping to embellish what is ultimately a little cable/dongle:

ifi iematch package review.jpg

Strangely, it has a pair of ear plugs in there. For a moment I thought that was their solution to reducing gain. You stick the ear plugs in your ear and then wear your headphones over that! :D

Even more strange is the inclusion of a dual jack headphone adapter. I thought airlines eliminated those years ago.

There is also a case to put the little cable in there and presumably your IEMs. Pretty excessive packaging effort but likely demanded by retailers to stop shoplifters and make it more substantial.

Anyway, let's measure the thing and see how it does.

Measurements
The design here is simple and that of a voltage divider using two resistors. Stealing the graphics from this nice site, it looks like this:
1537816382330.png


I measured the male jack that connects to the headphone output of the amplifier (Vs above). It has a resistance of 18.7 ohms. The female socket where you connect your headphones measures at 3.4 ohms (Vout above). This means R1 is 18.7-3.4 = 15.3 ohms. That gives us a ratio of 15/3 or about 5:1 reduction of amplifier output voltage.

The iEMatch versions have selectable switches with different resistor and hence gain reduction.

I ran a test with Topping NX4 DSD DAC and headphone amp with and without Ear Buddy and at low gain:

ifi Ear Buddy iEMATCH distortion and noise measurement.png


The device functions as expected. It reduces the gain and as such, the amplifier clips much earlier as it is still running at full power. The amp actuallys sees a much more severe load because the source impedance of ear buddy is just 18 ohms.

Listening tests
Running the Sennheiser HD-650 or HiFIman HE-400i through Ear Buddy was quite disappointing. Sound went from anemic to hugely distorted while still not getting loud enough. I then switched to Arcam rHead headphone amplifier. Same results greeted us as with Topping NX4 DSD.

Searching through my stash of headphones, I pulled out the Sony MDRV6 which has much higher sensitivity than the above two. Finally the unit did what it was supposed to: no distortion and very nice range in the volume control.

For definitive test, I gave the Ear Buddy to my son Kamran, who has an Oppo HA-1 powering Audeze LCD-X headphones which he says are very efficient. Combined with his sensitive hearing, he was really suffering from problems I mentioned earlier, namely background hiss and poor channel balanced (aided by a volume control that has gone bad). This was happening in the low gain setting of HA-1. This is his setup:

ifi ear buddy and iematch review and measurements.jpg


The ifi Ear Buddy nailed his problem and made him a very happy camper! Prior to this, I was going to open the unit and modify the design to lower the gain. But he is so happy that there is no need to do that anymore.

Conclusions
The iFi Ear Buddy and iEMatch seem to do what they say and solve a real problem. They reduce the gain so that you are able to use more sensitive headphones with your headphone amplifier and thusly, reduce noise and improve channel balance. They need to be matched to the amplifier though so I suggest getting the iEMatch versions even though they are more expensive.

The only thing I am unhappy with is the very low source impedance that may load down amplifiers too much. For this reason, you want to use the setting/version that lets you use the amplifier well below its max level. Otherwise you may get more distortion.

Overall, given the low cost of Ear Buddy, and real problems it solves, I am happy to put it on my recommended list.

Of course if you can get an amplifier with flexible enough gain settings, that would be more ideal but that is not always possible.

-----
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maverickronin

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#2
Is the Oppo HA-1 that high gain?

As for IEMs, 3 ohms might still be too high. Based on typical impedance curves it would do better with DDs than BAs.
 

maverickronin

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#5
The more expensive IEMatch has 1 Ohm or less in its Ultra setting.
Looks like they updated their website. I checked on there before several months ago and couldn't figure out what the Z out was, but they have it up there now.

Yes, even on its low gain for his specific headphones.
That's nuts. Is it a balance issue on the pot? The LCD-X might be efficient for a planar but there are plenty of more efficient full size models.

Cool that you found an easier solution that opening it up and swapping in different feedback resistors though.
 

amirm

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#6
That's nuts. Is it a balance issue on the pot? The LCD-X might be efficient for a planar but there are plenty of more efficient full size models.
Do they have the same low impedance of 18 ohms?
 

garbulky

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#7
Doesn't the resistor mess with the output impedance? I know the dropping resistor in the Emotiva A-100 used to attenuate its large power output for sensitive headphones increased the output impedance of the amp from less than 1 to 220 ohms. This increased output impedance also produces changes in the way the amp interacts with the speaker.
 

maverickronin

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#8
Do they have the same low impedance of 18 ohms?
There are plenty which get just as loud from less voltage, even though they are higher impedance. I'll just list a few examples from Ty'lls measurements on IF.

Volts RMS required to reach 90dB SPL
Impedance @ 1kHz:
Power Needed for 90dB SPL

LCD-X
0.065 Vrms
15 Ohms
0.28 mW

Audio Technica AD2000X
(Pretty much all ATs except for their new ~400ohm flagship are cluster around here)
0.034 Vrms
43 Ohms
0.03 mW

Fostex TH-900
(There is a huge family of headphones based around this driver which Fostex OEMs for Denon, Massdrop, and E-MU)
0.062 Vrms
26 Ohms
0.15 mW

AudioQuest NightOwl
0.043 Vrms
27 Ohms
0.07 mW

Final Audio Pandora IV
0.022 Vrms
11 Ohms
0.04 mW

Ultrasone Edition 8
0.065 Vrms
33 Ohms
0.13 mW
 

amirm

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#9
Doesn't the resistor mess with the output impedance? I know the dropping resistor in the Emotiva A-100 used to attenuate its large power output for sensitive headphones increased the output impedance of the amp from less than 1 to 220 ohms. This increased output impedance also produces changes in the way the amp interacts with the speaker.
A single resistor would do that. Here there is a pair of them so the only worry would be the the lower, 3 ohm or so.
 

garbulky

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#11
A single resistor would do that. Here there is a pair of them so the only worry would be the the lower, 3 ohm or so.
The A-100 has two dropping resistors - one per channel. Is that what you mean by one?
 
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#14
As Amir said: A single resistor would do that. Here there is a pair of them so the only worry would be the the lower, 3 ohm or so.

The lower R2 would essentially be the output resistance. In the IEMatch you can select this, going down to 1Ohm. This version has an output impedance of around 3Ohms.
 

Jimster480

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#15
A single resistor would do that. Here there is a pair of them so the only worry would be the the lower, 3 ohm or so.
So your headphones would be seeing 18ohm?
So for example, would that mean that if you plugged this into the Topping A30, your headphones would see only 3ohm output impedance?
So would this fix the output impedance of 30 on the 3.5mm by reducing it to 3ohm (while at the same time causing high load?).
 

amirm

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#16
So your headphones would be seeing 18ohm?
So for example, would that mean that if you plugged this into the Topping A30, your headphones would see only 3ohm output impedance?
So would this fix the output impedance of 30 on the 3.5mm by reducing it to 3ohm (while at the same time causing high load?).
The headphone sees the smaller resistor. The amp sees the sum of the two or about 18 ohms. Is this what you were asking?
 

Jimster480

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#17
The headphone sees the smaller resistor. The amp sees the sum of the two or about 18 ohms. Is this what you were asking?
Yes, so basically the headphones would be seeing 3ohm output impedance. While the Amp sees 18 ohm output impedance.

Meaning that if you plugged it into an amp with a high output impedance, you could reduce that impedance to fix your headphones impedance mismatch. Correct?
 

amirm

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#19
To be very accurate, what the headphone sees is the 3 ohm in parallel with the (15.3+amp impedance). Let's say the amp is 15 ohms too. In that case, the impedance that the headphone sees is 2.7 ohms.
 
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