Will an impedance adapter improve matching of low impedance headphones to old EMU 0404 USB Audio interface?

[OK1]

I have a USB audio interface, a beloved EMU0404 USB. It's a bit dated, and the specs are not exactly top of the line, compared to today's best, but it's acceptable, and should save me having to shell out more money, in the short term, for the latest greatest USB DAC.

I've been following Julian Krause, who is a member of ASR, and also a Youtuber who reviews consumer and professional audio interfaces aimed for the project studio market. Search for the Julian Krause channel on Youtube.

Julian Krause

www.audiosciencereview.com

In so many of his reviews, he would highlight any headphone outputs on audio interfaces, with output impedances above about 10 ohms, as being a worrisome issue when driving low impedance headphones in the region of 32 ohms. One consistent example are the Audient ID audio interfaces., which have an output impedance of 22 ohms.

I have read somewhere, a long time ago, that output impedances of headphone amps should be in the order of 1/8th of the headphone's nominal input impedance.

My EMU 0404 USB audio interface has a similar output impedance of 22 ohms. But I wish to use IEMS with nominal impedance of between 16 and 32 ohms.

Can I solve this challenge by using an impedance adapter to, for example bump up the IEM's presented impedance to at least 80 or 100 ohms, or even higher, say 150 ohms? What impedance adaptor values should I be purchasing to achieve this.

I've been on a journey with inexpensive dongle DAC's, (see link below) which work great with the inexpensive low impedance IEM's I've acquired, and while wishing to upgrade more modern DAC's which measure better, at the end of the day, the only compelling reason for such an upgrade would be to take advantage of their low impedance headphone outputs (typically below 2 ohms, and more often than not, below 1 ohm)

Here's a link to an example of such an impedance adapter.

https://www.amazon.co.uk/Impedance-Cancelling-Resistance-75-ohm/dp/B0CVVPQFR3/ref=sr_1_4?crid=1SCWG9A49JPQ7&dib=eyJ2IjoiMSJ9.07bXe_Va1QsuDr2qnwycZf3w0eO000RXBPsTyfCIZynL9NaMvZ1E1eIkgnyyuPcHQdqXWmsYwPYalpPwrRtmt--piNuNmy-9q4wP-josCfhpO_GP-Uvt8IvL3DoIvcEPpD28PpHOdY7NkoxxwhuoqfCU1AFUVOnNYvqEihXQww-WsrVemgiLl0lZ5vd6gi1KjuPWZdCgsWfmnJ-aUf5ki5nfTzSM9I0ks3mQMo1jW1w.UczsfN1BZUlhaNICPLbqThbeAojPSto2tmc9DIOfsCo&dib_tag=se&keywords=headphone%2Bimpedance%2Badapter&qid=1716385867&sprefix=headphone%2Bimpedance%2B%2Caps%2C747&sr=8-4&th=1

Thanks for sharing your opinions.

 

[Dunring]

I would just get an Apple 3.5mm to USB adapter for $9. I keep one around for travel and they can power a lot of things with low output impedance.

 

[PuX]

you could use it as a DAC and attach it to an external amp...
headphone amp stage of 0404 USB has never been its strong point.

 

[oleg87]

No, that is just effectively adding more output impedance.

It’s only an issue if your IEM’s impedance over frequency varies significantly enough to cause frequency response shifts, single-driver IEMs usually have pretty constant impedances.

 

[AnalogSteph]

Can I solve this challenge by using an impedance adapter to, for example bump up the IEM's presented impedance to at least 80 or 100 ohms, or even higher, say 150 ohms?

Impedance adapters generally are just series resistors. From the IEM's perspective, you will merely be adding to internal output impedance, exactly the opposite of what you want. This may still be helpful if e.g. the output has to contend with high ground return resistance or smallish coupling capacitors or distortion performance is affected by low-impedance loads. If you need to reduce source impedance, an attenuator with an actual resistor divider stands a better chance of getting the job done, assuming resistor values are chosen accordingly.

Also keep in mind that a rule of thumb is just that. You may want even less for multi-driver BA IEMs, while typical dynamic driver jobs often have near-flat impedance responses and as such are not awfully impressed by much anything.

 

[DVDdoug]

A transformer can be an "impedance adapter" but I don't know of any transformers made for that purpose. And it would reduce the voltage as well as the impedance.

An active solution (a different DAC or an additional headphone amp) would be best.

BUT... Is there REALLY a problem with the sound? You might prefer the way it sounds now! And is it THAT important? ...Typically, you are using an interface with in-ears or headphones for monitoring while recording and the sound quality isn't super-critical at that stage of the production process.

 

[OK1]

I would just get an Apple 3.5mm to USB adapter for $9. I keep one around for travel and they can power a lot of things with low output impedance.

My dongle search rabbit hole

Where do I start? 1st I'm on Windows 10, which could be part of the challenge. Those on Apple devices appear to have a more seamless experience. I have an EMU 0404 USB, audio interface which I use with an AKG K702 headphone - but this is not a very portable solution. So most of the time I...

www.audiosciencereview.com

Thank you.

I've a bit of a recent, not too exhaustive journey with dongles already. Quite a bit of what I do is mixing music, am on Windows 10 or 11, so need reliable ASIO drivers. I had high hopes for the Apple dongle, having read the measurements based reviews. Took the trouble to order the North America version of the Apple dongle, had it shipped to the UK, paid customs and handling which cost almost twice the $9, I paid for the dongle, only to be disappointed with the sound, when compared with Samsung's dongle. No regrets. Some things one has to learn, by trial and error, and personal experience.

The Apple dongle also does not have ASIO drivers (well neither does the Samsung, which is used via WASAPI). Which is part of the reason, I'm seeking to go back to familiar territory, with professional or prosumer audio interfaces, which always come with an ASIO driver, if they are compatible with Windows.

 

[OK1]

you could use it as a DAC and attach it to an external amp...
headphone amp stage of 0404 USB has never been its strong point.

I do not have anything "serious", or "professional", to compare the headphone output of the EMU 0404 with, well except the Apple and Samsung USB-C dongles, and the onboard headphone outs of Windows laptops and desktops. So far - with my AKG K702's (impedance 62 Ohms, sensitivity 105dB/1mW), I've been satisfied (maybe cos I have not heard any better yet), with the headphone output of the EMU 0404 USB's. Also I do not listen too loud.

Can imagine that the EMU 0404 USB's output is specced at 20mW(without any mention of the load and if this 20mW is per channel!), and is likely to pale comparison to almost anything out there today. When I was researching dongle options, the minimum specs I came across @ 32 Ohms, was 55mW per channel.

Impedance adapters generally are just series resistors. From the IEM's perspective, you will merely be adding to internal output impedance, exactly the opposite of what you want. This may still be helpful if e.g. the output has to contend with high ground return resistance or smallish coupling capacitors or distortion performance is affected by low-impedance loads. If you need to reduce source impedance, an attenuator with an actual resistor divider stands a better chance of getting the job done, assuming resistor values are chosen accordingly.

Also keep in mind that a rule of thumb is just that. You may want even less for multi-driver BA IEMs, while typical dynamic driver jobs often have near-flat impedance responses and as such are not awfully impressed by much anything.

While I'll still continue to use it, purely out of nostalgia, and to avoid turning it into another landfill item (I'll never get rid of it cos it has too much sentimental value), I've decided on second thoughts, time to get a new modern dongle or desktop DAC, with low output impedance., and ample power, for most of the kinds of headphones, I'll be using. With ASIO drivers for Windows. About time. The EMU 0404 USB has served me well, with massive return on investment, time to get a replacement.

Only reason I will be stepping away from the EMU is, while there is a workaround for installing a driver for Windows 10, it's unsupported, unofficial and prone to break every time there is another Windows Update. And the Windows/ASIO drivers are probably nowhere near as efficient as modern devices, leading to higher CPU usage than is optimal.

Will follow up my journey discussion on this other thread.

My dongle search rabbit hole

Where do I start? 1st I'm on Windows 10, which could be part of the challenge. Those on Apple devices appear to have a more seamless experience. I have an EMU 0404 USB, audio interface which I use with an AKG K702 headphone - but this is not a very portable solution. So most of the time I...

www.audiosciencereview.com

 

[OK1]

A transformer can be an "impedance adapter" but I don't know of any transformers made for that purpose. And it would reduce the voltage as well as the impedance.

An active solution (a different DAC or an additional headphone amp) would be best.

BUT... Is there REALLY a problem with the sound? You might prefer the way it sounds now! And is it THAT important? ...Typically, you are using an interface with in-ears or headphones for monitoring while recording and the sound quality isn't super-critical at that stage of the production process.

That has been my line of action. Have a dedicated headphone amp purchased, should be delivered anytime soon.

 

[solderdude]

That is the only proper solution.
Fortunately, these days, good ones can be had cheap.