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Stax SRM-1/Mk2 Re-cap

post #1 of 49
Thread Starter 

Although I just recently created this account I've been lurking around on Head-Fi for the past 7 years now if the sticker on my Headroom Desktop amp is anything to go by. I've been curious about electrostatics for a very long time... almost as long as I've had good headphones but only after I heard an Orpheus at CES did I decide that I was going to make it happen. Money being what it is and Stax being what they are I decided that I was going to buy a new pair of headphones and a used amp. K_19 was good enough to sell me his SRM-1/MK II(a) and I am patiently awaiting its arrival. I've read that the SRM-1/MK II is a good starter amp for the money but I've also heard that many of these amps are nearly thirty years old and with that age can come capacitor deterioration. I have no access to any other electrostatics; In fact I am the only audiophile I know so unless something is clearly wrong like hissing I won't be able to tell if its just the Stax sound or the capacitors are on their way out. In that vein I am considering a re-cap. I have some limited experience with soldering but I have yet to take Blue Oyster Cult's advice and so I still fear the reaper. In light of that my questions are these...

 

1. Any advice on working with high voltage other than using a resistor to short the caps? 

2. What caps do you like? 

 

3. I've been using lead free Radio Shack solder. I imagine that this project is worthy of something a little better than what my keyboards get. What should I be using? 

4.Any other advice? Any tweaks I should be considering while I'm swapping out all of the capacitors anyway? 

 

Thanks in advance for your time... I know there are a lot of questions in there. I'm really looking forward to this system. 


Edited by spaceace1014 - 1/29/13 at 2:37am
post #2 of 49
Thread Starter 

How about:
What solder do you like to use and who makes good power supply caps? 

Looks like I'll need at least 3 400v 100uf caps. I can't read the others in Ken Rockwell's photo. 
http://kenrockwell.com/audio/stax/images/srm-1-mk-2/D3S_4907-inside-1200.jpg


Edited by spaceace1014 - 1/29/13 at 10:41am
post #3 of 49

Just let the amp sit for an hour unpowered and it should be fully drained.  You can always check with a volt meter just to be sure. 

 

Panasonic caps are what I use.  Nichicon and CDE are also nice. 

 

Use normal 60/40 Lead solder as that's what was used on the amp to begin with.  Mixing different types of solder isn't recommended. 

 

No other tweaks except adjust the offset and balance when you are done with the swap.  Remember the labels for the pots are swapped on the PCB so offset is balance etc. 

post #4 of 49
Thread Starter 

Thanks Spritzer I count two mistakes and a lot of time you've just saved me. 

post #5 of 49

Hope that you'll receive the amp soon! You won't need to worry about re-capping it right away out of the box IMO though as amp sounded great when I last used it. There was no imbalance, hiss, noise or anything with it that I can hear with my 007's. 

 

With that said, yeah, it's a 30 year old amp and can definitely use re-capping I'm sure. But do be careful and take your time with it... best of luck!

post #6 of 49
Thread Starter 
Quote:
Originally Posted by K_19 View Post

Hope that you'll receive the amp soon! You won't need to worry about re-capping it right away out of the box IMO though as amp sounded great when I last used it. There was no imbalance, hiss, noise or anything with it that I can hear with my 007's. 

 

With that said, yeah, it's a 30 year old amp and can definitely use re-capping I'm sure. But do be careful and take your time with it... best of luck!

I will and I'll definitely take some time to listen to it and enjoy it before I open it up. I wasn't worried about there being something out and out wrong with the amp and I fully expect it to run circles against what I have now or the 252s that I would have bought in its stead but I enjoy taking things apart, this seems like a fun challenge, and if I can improve its sound while learning some new things about electronics without breaking the bank then this project is a huge win in my book. 

post #7 of 49
Quote:
Originally Posted by spaceace1014 View Post

I will and I'll definitely take some time to listen to it and enjoy it before I open it up. I wasn't worried about there being something out and out wrong with the amp and I fully expect it to run circles against what I have now or the 252s that I would have bought in its stead but I enjoy taking things apart, this seems like a fun challenge, and if I can improve its sound while learning some new things about electronics without breaking the bank then this project is a huge win in my book. 

 

Let us know how it turns out.

post #8 of 49

I wouldn't worry about this particular amp (unless you want the project and the possible comfort that it is at its best). I had it before K-19 and it's sound is very clear and did an excellent job powering most Stax. I have used this very amp with 007 MKI, 009 and 404LE - and they all sounded very very good with it. Don't fret about doing anything with the amp unless/until you detect some problems. Others would know better than me, but I understood that capacitor deterioration was a somewhat gradual process - ie they don't sound fine one day and then exhibit noticable issues the next - but that heat and age will eventually take their toll.

post #9 of 49
Thread Starter 

It'll be fun and I plan to document the process when I finally do it for future noobs who might be getting their first Stax setup and are lucky enough to find an amp like this. I'm buying the entire signal chain from the USB cable out to the headphones from scratch and it represents quite a lot of money to me so I might as well go the extra mile and do everything I can to make it sound its best.

In case anyone was wondering the signal chain is this:

PC ->  Audioquest Forest USB -> AQVOX Linear USB power supply -> April Music Stello U3 -> Moon Audio Black dragon 75ohm Coax -> Schiit Bifrost -> DH Labs BL-1 -> SRM-1/Mk II -> SR-507


Edited by spaceace1014 - 2/1/13 at 3:22pm
post #10 of 49
Thread Starter 

here are some photos I took of the inside of the SRM-1/MKII

 

From the top. The front is on the right.

 

 

Here are the four power supply capacitors. By my measurement there are:
3 400v 100uf capacitors that are 60mm high and 30mm in diameter. 

1 35v 470uf capacitor that is 31mm high and 15mm in diameter.
None of the capacitors can be any wider but the small capacitor could be taller.  

 

This is the bottom of the unit the front is now on the left. You can see where the power caps go on the upper right hand side.

 

Close up of the power capacitor section from the bottom. 

 

Balance and offset adjustment points from afar

 

Closeup of balance and offset.

 

Alps Potentiometer from the back.

post #11 of 49
Thread Starter 

I'm going to attempt to spell things out from here on out both so that I can be corrected If I'm about to make a mistake and so that future lurkers lacking in experience can easily read and understand this.

 

----------------------------------------------------New caps on post 13
For the 400v 100uf Caps I found these: Nichicon UPW2G101MRD

Mouser Link: http://www.mouser.com/ProductDetail/Nichicon/UPW2G101MRD/?qs=sGAEpiMZZMsh%252b1woXyUXj%2f8AO0m74dJ9b%2fPy1%2fXLQbg%3d

 

For the 35v 470uf Cap I found this: Nichicon UKA1V471MPD1TD
http://www.mouser.com/Search/ProductDetail.aspx?R=UKA1V471MPD1TDvirtualkey64700000virtualkey647-UKA1V471MPD1TD

----------------------------------------------------

Both of these caps are physically smaller than the original capacitors in the unit. I'm given to understand that this isn't a problem and that I just need to float the capacitors off the board a little bit so that the leads can be spread out to fit through the original capacitors larger holes. Am I missing anything and are both of those capacitors appropriate for this task? before I order this is there something better that I should be using?
 

 

 

 


Edited by spaceace1014 - 2/2/13 at 11:28pm
post #12 of 49

You can safely use 220uf/400V caps in this amp, it is what Stax would put in there if they were doing the refurb (only value they have in stock).  For the low voltage caps I'd use Panasonic FM or FC series.  Not a big difference but these caps have excellent specs. 

post #13 of 49
Thread Starter 

Ok, Changing the three 400v 100uf caps to 400v 220uf caps and changing the 35v 470uf cap to a Panasonic FM.

 

----------------------Turns out I need a snap in cap. See Spritzer's next post.
For the 400v 220uf caps I found these: Nichicon UPW2G101MRD

http://www.mouser.com/ProductDetail/Nichicon/UPW2G101MRD/?qs=sGAEpiMZZMsh%252b1woXyUXj%2F8AO0m74dJ9b%2FPy1%2FXLQbg%3D
----------------------


For the 35v 470uf caps I found this: Panasonic FM EEU-FM1V471

http://www.mouser.com/ProductDetail/Panasonic/EEU-FM1V471/?qs=4F1vP4lJYtGxZCTadysVhQ%3d%3d#AB

Remarkably these are $.30 where the nichicons were $1.22USD

 

These caps are still smaller than the originals even though the 400v caps have been uprated to 220uf

 

I'll probably place the order on Monday unless I've made poor choices on the above caps and I'll hold on to them for a couple of weeks until my new gear has been broken in a bit and I have a good feel for its sound signature.

 

Thanks again for all the help.  


Edited by spaceace1014 - 2/3/13 at 1:01am
post #14 of 49

You need snap in caps for the HV so something like this:

 

http://www2.mouser.com/ProductDetail/Panasonic-Electronic-Components/EET-ED2G221CA/?qs=sGAEpiMZZMtZ1n0r9vR22QqzopUJ6WFXd%252bC8iva6%252bdg%3d

 

Any cap you put in there will be much smaller than what Stax used 25-30 years ago. 

post #15 of 49
Thread Starter 

Yeah I feel like a noob. Thanks Spritzer.

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