Another incredibly cheap Taobao toy
Posted 19th July 2015 at 10:00 AM by abraxalito
Updated 10th August 2015 at 10:44 AM by abraxalito (Listening report added; chip pinout added)
Updated 10th August 2015 at 10:44 AM by abraxalito (Listening report added; chip pinout added)
When browsing Taobao I can't resist the temptation to try the very cheap stuff. This little TFcard player really takes the biscuit for the lowest price of a digital audio source - 9.9rmb. So I ordered up three, I might just order more soon.
First powering up I tried some FLAC files, these don't work but wav and mp3 work fine and it even finds files below the root directory. Power supply is nominally 12V but its using an EF fed by a zener diode, not an IC reg so almost anything from 6V will probably work. I haven't managed to find the technical blurb for the chip so far so a little reverse engineering was needed. It incorporates a 3.3V regulator to power the IR receiver and the TFcard - I have fitted an additional regulator for the first mod because I wondered if the low-level noise I was hearing was due to interference from the flash card's power draw. Turns out no as when playing .wav files this noise disappears.
Incidentally the 9.9rmb cost includes the remote control and its lithium battery. Makes me wonder what the price of the main IC is...
Later on I'll post up results of my exploration into getting the best SQ from it.
Now I've had a chance to listen a bit more here's how it sounds. Surprisingly good, though not really hi-fi. I've improved the power supply by replacing the zener with a TL431 with its feedback wrapped around the EF. So now the 5V supply is stable. I've added extra caps across the 5V rail, notably two very low ESR Nichicon HMs (1800uF). It seems the HF dynamics are a bit limited by either the DSP or the DAC S-D processing or perhaps both. There's noticeable additional HF noise and some lispiness on vocals. These effects I notice on DSD too by the way (which is considered hi-fi by many), but more pronounced. As with DSD LF dynamics are really rather good so there's a nice jump factor, provided the outputs see very high impedances. I started out with about 68k as a load but this turns out to be too low for decent dynamics. I'm going to explore what the upper end is - I'd suggest no lower than 220k as a load for now.
Update - I've introduced a signal processing chain now - first a unity gain buffer (2.2Mohm input impedance) and reduced the player's output caps (they were 1uF X7Rs, now 22n NP0s) followed by a 4th order Chebyshev (designed with help from Simon Bramble's page here: https://www.simonbramble.co.uk/techar...ter_design.htm) with a -1dB point just above 17kHz. This has cleaned up the HF - one of its functions is as an analog apodizing filter - still timbres are incorrect though, strings too glassy, brass doesn't have the right bite when compared to multibit. However its good enough by far in terms of sheer enjoyment which is my main aim here - the sound's engaging and draws me in, plenty of extremely low-level details are revealed especially in the bass. I was listening to the Decca 'Misa Criolla' late last night and for the first time the very low, continuous bass note which appears in the first track had some identifiable texture to it, rather than sounding like mains hum as it has on all my previous amps. Together with my 'pocket rocket' headphone amp (based on my PSRR findings in earlier posts) this is potentially a winning mobile proposition.
Update2 - found a vendor on Taobao selling what looks to be the identical chip in this player, for 3RMB. I've attached the schematic they're showing which looks to be the same as the chip in my player even though the ID numbers are different on the top of the package.
First powering up I tried some FLAC files, these don't work but wav and mp3 work fine and it even finds files below the root directory. Power supply is nominally 12V but its using an EF fed by a zener diode, not an IC reg so almost anything from 6V will probably work. I haven't managed to find the technical blurb for the chip so far so a little reverse engineering was needed. It incorporates a 3.3V regulator to power the IR receiver and the TFcard - I have fitted an additional regulator for the first mod because I wondered if the low-level noise I was hearing was due to interference from the flash card's power draw. Turns out no as when playing .wav files this noise disappears.
Incidentally the 9.9rmb cost includes the remote control and its lithium battery. Makes me wonder what the price of the main IC is...
Later on I'll post up results of my exploration into getting the best SQ from it.
Now I've had a chance to listen a bit more here's how it sounds. Surprisingly good, though not really hi-fi. I've improved the power supply by replacing the zener with a TL431 with its feedback wrapped around the EF. So now the 5V supply is stable. I've added extra caps across the 5V rail, notably two very low ESR Nichicon HMs (1800uF). It seems the HF dynamics are a bit limited by either the DSP or the DAC S-D processing or perhaps both. There's noticeable additional HF noise and some lispiness on vocals. These effects I notice on DSD too by the way (which is considered hi-fi by many), but more pronounced. As with DSD LF dynamics are really rather good so there's a nice jump factor, provided the outputs see very high impedances. I started out with about 68k as a load but this turns out to be too low for decent dynamics. I'm going to explore what the upper end is - I'd suggest no lower than 220k as a load for now.
Update - I've introduced a signal processing chain now - first a unity gain buffer (2.2Mohm input impedance) and reduced the player's output caps (they were 1uF X7Rs, now 22n NP0s) followed by a 4th order Chebyshev (designed with help from Simon Bramble's page here: https://www.simonbramble.co.uk/techar...ter_design.htm) with a -1dB point just above 17kHz. This has cleaned up the HF - one of its functions is as an analog apodizing filter - still timbres are incorrect though, strings too glassy, brass doesn't have the right bite when compared to multibit. However its good enough by far in terms of sheer enjoyment which is my main aim here - the sound's engaging and draws me in, plenty of extremely low-level details are revealed especially in the bass. I was listening to the Decca 'Misa Criolla' late last night and for the first time the very low, continuous bass note which appears in the first track had some identifiable texture to it, rather than sounding like mains hum as it has on all my previous amps. Together with my 'pocket rocket' headphone amp (based on my PSRR findings in earlier posts) this is potentially a winning mobile proposition.
Update2 - found a vendor on Taobao selling what looks to be the identical chip in this player, for 3RMB. I've attached the schematic they're showing which looks to be the same as the chip in my player even though the ID numbers are different on the top of the package.
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