Wednesday, February 24, 2010

B-Tech BT928 headphone amp

I was looking for a headphone amplifier on the cheap, very cheap. I needed an amp with two stereo channels, or two amps. The amps are going to be looked up via rca to a playstation cable, for my co-op gaming setup.
At first I found the Millenium HP4 which provides 4-channels for 61 €. A very nice price and good looking product I thought, and bought it. Bad idea. The build quality is top notch, it looks and feels like a pro product. The sound is another story though, it's very thin and hollow, with little or no dynamics. In fact it was so bad I almost considered it unplayable. Remember we are simply talking about solving a connectivity problem with PS3's and headphones.
Clearly I needed to find another solution.

A quick search at a national retailer revealed the B-Tech BT928, which was retailing at 80 €. It can be found at Amazon for 32 €, which puts it within my budget. Even after factoring in the UK-to-DK plug adaptors.

My BT928s above, after modification, (see more below).

The BT928 is dirt cheap, simple, ok looking device with nice connectors. The tone pot is a piece of crap though, no matter what neutral setting I attempted it produced a distorted sound with badly boomy bass and/or scratchy treble. So I decided to remove it as suggested by a thread. I got a budget soldering iron, and desoldering pump, and went to work.

BT928, pcb only, with tone potentiometer on the left still attached.

In order to remove it, I simply desoldered the 6 connections for the tone pot, and as suggested by the thread also the green and orange capacitors marked 101 and 472.
Desolder these components to greatly improve the sound quality.

BT928, pcb and lower case. After tone pot removal.

The difference was like night and day. I did it with only one of them at first, so I could compare before/after easily. As a side effect the volume knob very quickly rises (exponentially) to loud levels, so it requires some more fine tuning, but is still very usable.

The sound quality after tone pot removal is more than acceptable for gaming. I wouldn't recommend it for a HiFi setup though. For that you'll need a higher quality amp, or make some serious mods like they did at Rock Grotto.

I used a Cambridge Audio DacMagic, and Sennheiser HD 25-1 for testing.