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The Stax SRM-002 mod thread - Page 3

post #31 of 33
Thread Starter 

the power supply section in 002 is different from the 001.


regulator for incoming power: 001 has a linear voltage regulator to drop the incoming voltage to around 2.8V, if the input is much higher than it will generate heat to burn off excessive input power (Q15 gets hot).  In the 002 the voltage regulation is done by a switch mode buck/boost chip, LTC3127, which takes whatever input voltage (supposedly anywhere from 1.8V to 5.5v is ok) and sends out regulated output voltage. It should have much higher efficiency than the linear regulator in the 001, so heat from this section of the circuit will not be a problem.


The step-up transformer in 002 is driven by a pair of SMD transistor (marked NAI, not sure what model # they are, looks very much like the Q11/Q12 transistors in the 001), these transistors are driven by two tiny three-lead SMD devices,  with "FQ 17" marking. Reference designators are Q9/Q10 so I assume they are transistors of some sort. There is not much else. (the circuit in 001 is much more complicated, involves a LM358 and a 74HC14, plus 6 tiny transistors).


I will try to find out where the 002 transformer driver system gets the switching signal from. Maybe from one of the pins of LTC3127 (which is a switch mode device after all).

post #32 of 33
Thread Starter 

For simplicity reasons I will only post a maxxed mod plan, it will be at a higher level than the SuperFatCat ++ mod I have done in the 001. It requires using an external power pack, which is not a problem now-a-days, since USB power banks are abundant, comes in all kind of sizes, and very inexpensive. Plus, the switch-mode regulator in 002's power input section can take wide range of input voltage and work just fine (at least in theory).



Input capacitor upgrades: these will stay in the space made available by removing the battery tray. Max size is 0.6" x 2.2". Two currently available options:

- DynamiCap (Loudspeaker) 1uf/310V.

- SoniCap 1.5uf/200V

Another possibility is VitaminQ 1uf/100V 96P. It is 0.5"x2" so will fit, but they are no longer commonly found on ebay. Might be avaiable locally. 


I have tried the SonicCap in the input section of 001 before, it has good clarity but tend to be a bit bright. ==> I will pick the DynamiCap here.



Power pigtail: Digikey has a right angle cable that can be use when modifiing a USB power pack (or external battery pack)


To be continued............

Edited by AudioCats - 7/24/15 at 6:36pm
post #33 of 33
Thread Starter 

002 mod experiments are back on track. Currently testing component combinations.



Might be able to post a few standard-level mods this weekend.

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