Replacement soundcard S/PDIF for a laptop

[Vermes]

The device was designed in order to replace output circuits of the soundcard in a Dell laptop.



The laptop has place for two hard drives. There is a socket in the rear of the laptop, from which (from inside) S/PDIF signal can be downloaded. 5V voltage can be taken from power supply of the hard drive.



STA120D acts as a S/PDIF to I2S converter. It interprets correctly even 24bit/192kHz signal, but then jitter reaches such a high value, that it can be heard as an increase in noise. It is then converted to analog by CS4344, goes to the low-pass filter on operational amplifier TS952 (requires rail-to-rail), and then to the headphone amplifier on TS486 and speakers amplifiers, operating in bridge configuration. There is also a signal derived before the amplifiers as a line output. From the supply, you have a stabilizer system, which „cuts” noisy 5V to clean 4,8V. That voltage supplies the power amplifiers and filter. There is also a stabilizer LP2951 operating in the power supply, which produces the voltage +3,3V to power the systems CS4344 and STA120D. There is a lot of SMD chokes and decoupling capacitors, to make it possible to listen to music not interrupted by hard drive noise.

Jack sockets with some normally connected contactors are used to mute the speakers when connecting the headpdhones. Simple system on transistors and diodes controls the input /SHDN of systems TS4871, muting the signal when you insert the plug in any slot.

The card is directly controlled by Foobar2000 without system control, in the resolution of 88,2kHz/24bit. DAC introduces small noise, depending on the sampling frequency.

Effects:

• laptop is a good source when listening by headphones, it is silence without a signal
• output power is absolutely sufficient for the headphones – 4,8V from the supply
• speakers play slightly quieter than the original, but they can be used
• you can not notice the influence on the time of operation from the baterry

Link to original thread (useful attachment) - Zastępcza karta dźwiękowa S/PDIF do laptopa