Portable supply for Stax SR-001 Mk 2
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AssafL

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As I am new to Head-fi, please forgive me if this issue has already been discussed.

I recently purchased the Stax In-the-earspeakers. Others have described the sound of these, which is remarkable (especially at this price range - see driftwood's detailed review elsewhere).
At first, I used alkaline batteries. Pretty soon (and with a pile of exhausted alkaline cells to show for it), this became too expensive so I tried 2 NiMH cells. Sound quality deteriorated considerably.
It became clear that the Stax driver unit needs a higher voltage for optimal performance. Performance at 4.5V (using a wall wart) was spectacular, 3V provided ample performance, but 2.4V was lacking.
Rummaging around the neighborhood Radio-Shack, I came across a unit called a "power bank - NiMH charger). The unit is a 4 cell NiMH charger, Wall-wart and DC-DC converter, all in one sleek unit. $39 was a bit steep but I ended up taking the unit home. 4 NiMH cells later, I set the power bank to 4.5 and plugged the Stax into the power bank.

The Stax started charging the internal voltage doublers (the power up "squeal"), and after a second or so the power bank abruptly shut itself down. I tried different combinations (DC-DC, wall wart mode), all with the same effect. Setting the voltage at 3V solved the problem, but I wanted 4.5V performance!

Radio-shack replaced the unit, but the new unit had the same problem. It was time to take out the test equipment. The problem became clear: at 4.5V, the power up current draw of the Stax driver, is a whopping 1.5A (for 2 seconds)! As the power bank has an automatic shut down at 1A, it would shut itself off.

I have identified two solutions (that work):
1. Start at 3V and switch to 4.5V (requires a screwdriver)
2. Pulse the power until the Stax has enough charge (unfortunately, the power bank does not have a power switch and the only way to reset the over-current sensor is to disconnect the DC cord).

The third option was to disable (or desensitize) the current overload sensing circuit so I opened the charger. Its construction, faithful to the brand, it is rather messy, with complicated switching circuitry (240/110AC, DC to DC, charging sensors), glued components, RFI shielding foil, all cramped in a small enclosure.

Does anyone have a schematic of the charger (or knows how to get one)?

Thanks,

AssafL.
 
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kajohndet

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I just used the walwart that I came with SL-CT570 PCDP and it worked just fine. It 's rated 4.5VDC 0.6A. Sorry if this is not answering your question at all.

Happy listening

John
 
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RickG

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Hi AssafL.....

You should send a private message (PM) to member setmenu. He has rigged a portable power supply for the baby Stax, and says he gets good results.

Happy Listening.....

 
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