Topic: Stax SRM-002 amplifier mod (SRS-002 mod) (Read 1214 times)

Bill-p · « **on:** April 26, 2015, 09:54:30 PM »

Ravi will get my $300, so now I get to gut this little thing.

I like the SR-002 quite a lot, but I'm definitely not a fan of the stock SRM-002. Too mid-centric, not enough bass extension, and what's there is anemic at best due to attempts at conserving battery life and reducing part costs. But the amp section itself actually isn't half bad. So I thought... how about we slot in some higher quality components?

How to disassemble:

Flip the amp on its bottom, then unscrew 4 screws here. Highlighted for your viewing convenience since I know my phone pic sux.

Then plop open the bottom case. It should come right off easily, so don't apply lotsa force.

After that, pull the volume cap off. It should be easy and all.

See?

Then take the board out by lightly pulling on the ribbon to the side of the battery compartment

And this one should also be painless... see?

Next, slide off the plastic piece covering the connector here.

And it should come off easily, revealing the connector board

This thing is held on by... well, nothing! So yeah, that's why it breaks so easily. My solution to this is to simply pad the bottom side with foam, so that most of the force won't be so concentrated on the connector in the back. Well, you'll know what I mean when you get this far.

Anyway, due to the flimsy nature of this board, ya need to carefully use a flat tool around there (because I don't suppose anyone's finger can slide under there so easily?), and then your finger on the side to gently lift this up. Be careful!!

But it should come off pretty easily, too.

And here are the 2 electrolytic caps used for input. They are of high values (10uF IIRC?), but they are... freaking electrolytic, so they ain't that good. I put two polypropylene film capacitors i n parallel to them for some cool bypassin' action.

And that's it!

To do: roll op amps, replace PSU caps, bypass power management caps, replace and bypass output caps. <- basically a ton of work.

But this was the most glaring thing I saw when I opened the amp up, so I immediately did it. The improvement to soundstage, tightness, and detail extraction is quite amazing.

shipsupt · « **Reply #1 on:** April 26, 2015, 10:18:30 PM »

Very cool! Thanks for posting Bill. Encouraging results!

I've been wanting to mess with this amp for a while so this is good excuse as any to tear into it! The power side is a nightmare.

Making it rechargeable is must as well!

Bill-p · « **Reply #2 on:** April 26, 2015, 10:27:01 PM »

I've been thinking about that, too. There is quite a lot of room in here to play with. hell... I'm sure we can find an excuse to plop a 9V battery in with some cool power management tricks as well.

This one has been on my mind:
http://www.amazon.com/Maximal-9-Volts-Li-ion-Rechargeable-Battery/dp/B0051WZ516

9V with a power management board should take up about the same amount of space as the cradle for the 2 AA batteries. Maybe it'll be more cramped, but it's doable. And getting 3V (what the amp needs) out of 9V is easier than using 2 AAs.

shipsupt · « **Reply #3 on:** April 26, 2015, 10:32:10 PM »

Is there enough space for how thick the 9V is? If so, that may be a good option. I've kicked around some AA ideas without coming up with anything brilliant...

I need to dig back through the head-fi thread. There were a few guys trying a couple of battery options, will need to see how they made out.

Bill-p · « **Reply #4 on:** April 26, 2015, 10:41:15 PM »

Yeah. Once the battery compartment is removed, there is enough space for the 9V battery, and then a small surface mount board. I'm thinking that surface mount board will house a battery management unit to at least deal with regulating the 9V down to 3V, and then it should solve that problem (plus battery life) for us.

Rechargeable is a bigger problem, because I need to be able to boost the 3V power coming from the wall first... so that's the only drawback. If we're keeping the ol' AA batteries, then they can be easily recharged simply by ripping off the charging unit from another charger, but I'm not sure we'll have enough room to fit the board in, so... that's the problem. But I'm debating my options.

Making an external battery pack is easy. In fact, I'm sure I can also make a USB power adapter, so that the amp can be powered directly off of the USB port of a computer. This can potentially help transportability, but it won't solve portability, which I think is the main issue here.

shipsupt · « **Reply #5 on:** April 26, 2015, 10:48:42 PM »

Yeah, I'm kind of on the fence with portability with this amp... I typically end up using it in hotels and when working at remote locations. When I'm actually out and about or in transit I tend to grab my customs. So, I guess I could go external, but making it all fit inside is kind of the fun part.

I've got some ideas on 9V charging, let me do some research...

Bill-p · « **Reply #6 on:** April 26, 2015, 11:19:35 PM »

Sure thing.

The thing I like most about this is still that it's really high quality for what can potentially fit in my pockets. So I'm playing around with a lot of options for now to make it truly portable. It pairs amazingly well with my iPod after all. If only I could figure out how to improve its battery life.

CEE TEE · « **Reply #7 on:** April 27, 2015, 12:06:15 AM »

After you guys get the amps to where you like them and size specs/requirements are finalized, I would like to 3D print some cases for them.

I fired up Solidworks again and already ordered some parts from Shapeways...haven't gotten those parts back yet and am already thinking of additional tweaks.

Bill-p · « **Reply #8 on:** April 27, 2015, 12:12:51 AM »

Wow, that'd be perfect! Admittedly, I don't like the stock case design. It looks and feels like a toy.

And if we can print out custom cases, then we can take care of spacing issues, so I'm sure I can fit a 9V battery with charging circuits in now. In fact, I can probably add an extra small board to regulate USB instead of the horribad DC input of the stock amp, so this will be closer to the amp that Stax planned to release in 2014.

audiofrk · « **Reply #9 on:** April 27, 2015, 12:25:06 AM »

note to self: need to buy a soldering kit

Author Topic: Stax SRM-002 amplifier mod (SRS-002 mod) (Read 1214 times)

Bill-p

Stax SRM-002 amplifier mod (SRS-002 mod)

shipsupt

Re: Stax SRM-002 amplifier mod (SRS-002 mod)

Bill-p

Re: Stax SRM-002 amplifier mod (SRS-002 mod)

shipsupt

Re: Stax SRM-002 amplifier mod (SRS-002 mod)

Bill-p

Re: Stax SRM-002 amplifier mod (SRS-002 mod)

shipsupt

Re: Stax SRM-002 amplifier mod (SRS-002 mod)

Bill-p

Re: Stax SRM-002 amplifier mod (SRS-002 mod)

CEE TEE

Re: Stax SRM-002 amplifier mod (SRS-002 mod)

Bill-p

Re: Stax SRM-002 amplifier mod (SRS-002 mod)

audiofrk

Re: Stax SRM-002 amplifier mod (SRS-002 mod)

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Author Topic: Stax SRM-002 amplifier mod (SRS-002 mod) (Read 1214 times)