Poor sound quality from BantamDAC

[TriHFH]

Hey guys, I'm new here and I'm also a newbie to audio equipment in general, so forgive me if the solution to this problem is only due to my ignorance, but..

I'm an EE student and I decided to build two BantamDAC's this past week. I built one with VitaminQ output coupling capacitors and the other with the standard Vishnay-Roaderstein caps. I built both and tested them with my Audioengine A2's, and found the quality to be better than the internal sound on my MacBook Air.

Anyways, I was happy with my results until today, when I plugged in my Shure SE310's for the first time. To my surprise, the audio coming from the BantamDAC was "tinny" sounding... it sounded like the sound was coming out of a $0.99 pair of headphones from wal-mart. This happens on both of my builds of the BantamDAC. Yet, the Audioengine A2's still sound as good as the first day.

Is this behavior normal? My first thought was that it was a grounding issue, but after some testing I found that didn't change anything.

Is it because the Audioengine A2's have a built in amplifier? Must I use a headphone amp in conjunction with the BantamDAC to listen with my headphones, or did I make a mistake somewhere along both builds?

Any help is appreciated, thanks

[cetoole]

Yes, the BantamDAC is about the worst choice to use to drive IEMs directly, and I must enjoin you not to try it, because it could actually damage the DAC. You absolutely need a headphone amp in conjunction with it. The reason it sounded good with the Audioengine A2 is because those have an integrated amp. Even a cmoy would be a huge improvement over the BantamDAC to drive headphones with.

[TriHFH]

Originally Posted by cetoole

Yes, the BantamDAC is about the worst choice to use to drive IEMs directly, and I must enjoin you not to try it, because it could actually damage the DAC. You absolutely need a headphone amp in conjunction with it. The reason it sounded good with the Audioengine A2 is because those have an integrated amp. Even a cmoy would be a huge improvement over the BantamDAC to drive headphones with.

Ah, just what I suspected.. Thank you for confirming this . I legitimately tried multiple searches but couldn't find a definite answer. Your help is much appreciated, I'll look into building a headphone amp of my own

[JamesL]

It may be due to a different reason, but driving 28ohm IEMs with a low value coupling capacitor creates a high pass filter with a very high cutoff frequency, which is probably why it lacks in bass and sounds tinny.
The A2's on the other hand have an integrated amp with a much much higher input impedance of 10k ohms.

[Hayduke]

Originally Posted by TriHFH

Ah, just what I suspected.. Thank you for confirming this . I legitimately tried multiple searches but couldn't find a definite answer. Your help is much appreciated, I'll look into building a headphone amp of my own

I was going to point you to Tangent's site and recommend building a Cmoy amp, but tangentsoft seems to be having trouble today

I still recommend a cmoy though. Decent sound, fairly easy to build, and cheap! You can try lots of different opamps too until you find the one that suits you.

Since you built a Bantam already, you are obviously interested in DIY. I'm curious what you're gonna build after your cmoy. If you get interested in tubes, my apologies to your wallet :P

[TriHFH]

Thanks for the tips guys . I'm not quite sure what to make of the theory of the low impedance creating a high-pass filter (I'm only a beginner EE student ), but I'll definitely look into the cmoy and hopefully I'll be building one soon. Can't wait to start tackling another project

[tomb]

Originally Posted by TriHFH

Thanks for the tips guys . I'm not quite sure what to make of the theory of the low impedance creating a high-pass filter (I'm only a beginner EE student ), but I'll definitely look into the cmoy and hopefully I'll be building one soon. Can't wait to start tackling another project

"the theory of the low impedance creating a high-pass filter " - not a theory - it's a fact. Whatever you connect the BantamDAC to is a load (resistance - R) that forms a series-RC circuit with the output capacitors (C) of the Bantam.

If you connect your headphones to the BantamDAC directly - as already mentioned to you, this is a BIG NO NO and could damage your DAC - the impedance (resistance) of the headphones becomes R, typically something between 32 to 300 ohms, depending on your headphone. The BantamDAC is designed to connect to an amplifier, where the input impedance (resistance) of the amplifier is 10,000 ohms to 100,000 ohms. That's a difference of 3 or 4 magnitudes, at least.

Quite simply, an RC circuit has a varying response to a signal at frequency.. At certain values of the product "RxC", the frequency response drops off like a cliff. For series RC circuits, these are bass frequencies. This is a natural order logarithmic function that can be reduced to the following equation at the -3dB point (sound power down by half):



If we plug in the values for your headphone impedance and the output capacitance of the BantamDAC we have:

f = 1/(2 * PI * 32 * 0.000001) = 4973 Hz. As you can see, that's almost 3000 Hz above midrange. So, you won't even have midrange, much less any bass - which both disappear into nothingness.

f for an amplifier connected to the BantamDAC is 3 Hz (assuming a 50K input impedance on the amplifier, which is typical). That's well below the level of audibility of any bass note your ear could even hear. IOW, full frequency response - OK.

So you see, besides being dangerous to your BantamDAC, connecting it directly to a pair of headphones means that the circuit can't even produce most of the audio spectrum. Yes, it would sound very bad, indeed.

Please don't do it.