The STAX SRM-252S comes with small and handy 500 mA wall adapter but thankfully non switch mode power supply (SMPS). It is considerably good but not the best for high quality audio application. In this mod project, the wall adapter will be replace by the suitable battery. But one things should be consider is the DC jack polarity is reverse. Means the body is (+) positive and the center is negative (-). It is stated on the label in the STAX wall adapter or the DC input marking on the STAX amplifier.
On hands, I got this brand new Yuasa NP7-12 lead acid battery. This 12 volt/ 7 Ah battery commonly use for UPS or motorcycle battery. The good point of this battery is you don't have to worry for the battery position. The liquid inside won't spill out. It is just like a dry battery.
It is still brand new, never been charged. The voltage reading here is also indicate the battery still in workable voltage rating.
I make simple battery connector to DC jack. Nothing fancy here, as long as it is work, then I will go for it.
This battery powered using the same type DC jack connector just like the OEM STAX amplifier. So I can make an A-B comparison in quite short time.
The result with the battery powered is improving the sound quality with no subjective feeling at all. I know the STAX amplifier is very good at mid to high frequency. It is god like voice and wider sound stage you would hear with the stock STAX wall adapter. Compare with the battery powered, you will hear the less noise back-ground sound with no edgy on high frequency. The overall music presentation is more reveal and the bass are noticeably give more impact.
I completely can live the sound of this STAX amplifier with the wall adapter, but once I changed to the battery, I know now how further is the better sound of the STAX amplifier can be. You can also try this little easy mod and have your own experience with this battery powered STAX amplifier by your own. It is quite easy to follow but once again I warn you to check the reverse polarity of the DC jack. It can be check with multi meter for the DC jack polarity body for positive (+) and DC jack center hole is negative (-).
Disclaimer: Any statement and photos in this article are not allowed to copy or publish without written permission from the writer. Any injury or loss from following tips in this article is not under writer responsibility.
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I'm trying to find a suitable smaller battery to possibly use the 252 as portable in the future.
ReplyDeleteLithium battery for sure
DeleteQuestion: Do you face distortion at high volumes (past 2-3 o'clock)? Specially on busy tracks or with deep beats?
ReplyDeleteI tend to EQ +1-4 dB for bass and mid bass region frequencies and lower the overall gain... so to listen to "high" volume (nowhere near deafening) I have to crank up the volume on my SRM-252S to 2-3 o'clock.
Does changing the wall wart or using a battery increase the power available in the SRM-252S? I have read in several places that the wall wart is 500mA which is not enough power for the SRM-252S so it was recommended to use the 0.7A to 1A 12V power supply instead.
Is there any mod that could be applied to increase the available power delivery?
The Stax amp has lower gain compare to other amp I’ve experianced before, but it is really depends on what source you put in it. Mostly I listen at 11 to 15 but never facing the distortion. Perhaps because the music I played is not too much beat. If the distortion you mentioned is like each instrument become less focus at high volume, I guess it the limit of the amp.
DeleteIt can be also effected by the EQ you’ve adjust on the source, try it FLAT, it sound good.
I do not find using battery gives higher power. It is more quiter.
Hello Orronoco!
ReplyDeleteI found your blog when I surfed the internet looking for an SRM-252 mod (don't have the amp yet).
As a fellow Indonesian, I found your projects were very well done and nicely documented.
Regarding this post, would you consider reversing the polarity of the DC jack of the amp?
This youtuber here reviewed a polarity-changed SRS-252 and it works just fine with any normal 12v adapter https://www.youtube.com/watch?v=8_pLxnkdMmc
I am curious about your impression on this matter.
Thank you beforehand!
Hi, thank you for your support in this blog.
DeleteI’ve watch the link you shared above and the reason why he reversed the polarity because he is now using commercial available smps which has the common polarity on the DC jack is the center positive.
Stax amplifier quite weird when set the DC jack is center negative, that is why others common power supply use with it require to reverse the polarity first before plugin to the amp unit.
I personally try to avoid as much as possible using any smps to the amplifier unit. I prefer the transformer type power supply with the regulator in it.
Hello Orronoco.
ReplyDeleteYou are welcome, I enjoyed reading your blog.
I did not notice your replies since you are using an anonymous account on the comment.
I understand the context of the reversing polarity, you can use almost any 12v adaptor from it.
What I don't understand is why STAX went to reverse the polarity in the first place?
Is there anything that they wanted to achieve from doing this?
From my POV, seems like they wanted to make their system a closed ecosystem.
On using linear power supply, are you interested in making a separate external PSU unit for the amp?
Thank you.
By default I only can reply using anonymous, I don’t know why🤔
DeleteAnyway, to anwer your question, the reason STAX reverse the DC socket polarity is nothing to do with the performance. I see this method on vintage electronic which start to changed the DC jack to center positive on early 90’s
Hello Orronoco, sorry for the late reply.
ReplyDeleteI have read that it is Japanese custom for electronics DC jack to be reversed relative to global custom.
May I ask what is the best way to reverse the polarity of the amp DC jack?
Thank you!
Hmn.. if the amp socket need to reverse then the pcb trace should be cut and connect them crossing each others. It is not elegant approach I think.
DeleteMaybe the best way is build a converter from dc jack in to dc jack out in reverse.
Thank you for the suggestion!
ReplyDelete