Pimp your sound card!
How to get more bass under a heavy headphone load
I recently acquired some headphones so I could listen to the delicate sounds of squirrels making love on my office PC. While the HD650s were certainly a step up from my old Aiwas, I still felt a bit disappointed with the sound quality. Some Afrofans told me I needed an external headphone amp because a soundcard just cant handle the headphones, so I built one. There are various guides on the internet to show you how to do this. The first thing that I noticed was that the bass sounded vastly better. It sounded deeper, punchier, and just great overall. I wasn't the only one to notice this. In fact, if you ignore the large increase in sound volume, the sound quality didn't seem much better at all except for the improved bass response. So this got me thinking... why would adding an amplifier improve the quality of the bass and only the bass?
The problem is that under heavy loads, the soundcard's output high pass filter can't cut it.
When you
connect a headphone amp, you effectively make the load a bajillion
ohms, so the high pass filter cutoff becomes almost 0Hz, and you get
excellent bass response. Here is a simplified diagram.
When
you connect the headphones directly to the soundcard, you have a simple
RC high pass filter. With 300Ohm headphones like the HD650s, and a 10uF
cap, the cutoff is around 54Hz, meaning that a significant amount of
audible bass will be lost. It's a complete waste of good technology -
just like Optimus Prime giving the Matrix to Hot Rod.
Here is a scope shot of my soundcard (Chaintech AV-710) trying to directly drive a 330Ohm resistor at 2 different frequencies. I used some tone generator
software to do it. You can see a 50Hz trace on top of a 300Hz trace.
Both were coming out of the soundcard at the same volume, but the low
frequency signal was attenuated by a whopping 20%.
Now it is time for graphs because Dilbert told me that if you show people graphs they will think you are smarter than MacGyver.
To
simulate a 'normal' loading situation, I used a 6.8k resistor and
recorded amplitude versus frequency on my scope. Most amps will have
input impedances a little higher than this. As expected, the frequency
response was reasonably flat.
When
I used a well made external headphone amplifier, the response was
perfectly flat because it placed a very high impedance load on the
sound card.
Now what happens when you connect a 330Ohm resistor to simulate Sennheiser headphones? Holy crap everything goes to hell!
So
what is the solution? Simply increase the value of the capacitor, and
the high pass cutoff will shift closer to DC! (No not that ghetto place, 0Hz).
I used my continuity meter to trace the path from the DAC to the card's
output to find out which capacitors were the high pass ones. As
expected, they were the ones right next to the output jack. They were
10uF 16V electrolytic caps, one for each channel.
I modded one channel at first to do
subjective listening tests. I just took a 330uF capacitor and soldered
it in parallel with one of the high pass caps on the card. I made sure
that the polarity was the same.
There
was definitely a difference - I was able to hear certain frequencies
that were nearly inaudible on the unmodded channel. I went ahead and
modded the other one.
Benchmark results:
Not
bad! The response curve wasn't as flat as with a headphone amp, but it
came pretty close. For 30 cents worth of capacitors and a minute of
soldering, this is the best way to get more bass on the cheap.
This mod certainly can't replace the increased gain a real headphone amp will give you, but it is extremely useful for listening to music at moderate volumes on multiple machines. It is a huge pain in the ass to carry an amp around with you between multiple computers at home and work, and building/buying several amps is just Petarded. I intend to mod the sound cards of all my machines in this way. The beauty of this mod is that it is nearly impossible to screw up. Adding more capacitance to any of the electrolytic caps on a sound card will, at worst, do nothing. Just like that last gram of baking soda I bought.
OMG TESTIMONIAL!!!!!!
Hey,
I'm not sure why, but I decided to try pimping my sound card based off your guide. The main reason why I hesitated to was that the last time I tried anything off the site (increasing the power to a case fan), I ended up blowing up the fan.
But, my headphones do sound a lot better, and thanks for the info on how to do this. The only problem is that the capacitors I chose were too large to fit into my external SB Live, so I had to make a few changes to the case. I've attached a picture.
Thanks,
Rob
OMG TESTIMONIAL OF TESTIMONIAL!!!!!!
hahaha that is awesome
-scalded
