SRM-T1 Mod Questions SE->Balanced?? TVC??
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sonicbath

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Hello everyone!

I am new here and would like to say HELLO!!


I have done some extensive searches of forums and gleaned some great information, but I still need some advise from you Stax Guru's.

Some History:

I've recently dug out my Lambda Pro Sigs/SRM-T1 combo out of the closet and quite frankly they sounded very bad. One earspeaker was about 6db down at the onset and got worse as time progressed (with eventual breakup). Swapping tubes and then elements determined it was a bad element so they were replaced with new 4040 elements (WOW... expensive!!)
. Problem fixed... or so I thought.

After some break in time they started to sound much better (imbalance gone) but not as great as I remembered. I found Dr. KG's instructions on differential & offset adjustment (wow do these drift during warmup). Helped a lot, THANKS!!

My next step is to replace the tubes (found some great advise here, thanks). I will then rewire.

Some Questions:

Is there a way to replace the stock potentiometer with a better unit? I have some S&B (silver) 102MkIII's lying around


Also, is there a way to convert the SRM-T1 into balanced inputs?? I see some empty pads on the PCB right next to the single ended input wires and thought, "can it be this easy"?? All my gear is balanced and it would be very nice if this can be done.

Any direction or advice would be GREATLY appreciated.

Thanks... Steen
 
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spritzer

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Welcome to the forum fellow Stax nut!


The volume pot can be replaced easily but you could also just bypass it and control the volume from a preamp. Space is a bit of an issue and the split volume knob is an extra convenience.

The circuit is basically the same as the T1S and T1W and they are both fully balanced with quad volume controls. I'm not sure whether or not Stax changed the PCB design and I haven't opened up the T1 in quite a while. If you see a "In -" somewhere that is connected to ground then the mod is easy. If there isn't then Stax might have included a phase splitter and that would have to be bypassed.

I might have some time over the weekend to open up my units and see how they are wired. I have both a T1 and a T1W.
 
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sonicbath

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Spritzer,

Thanks for the reply! Jes, I used to listen to my Stax rig all the time before I got myself a good speaker system but I am moving overseas soon and selling the speakers, amps, etc.

I had a sneaking suspicion this might be the case. Why go through the expense of designing and producing two seperate systems when you can manufacture just one and charge a premium for just adding XLR.

I would really appreciate it if you could check! I am assuming one of your systems is balanced in (T1W)??

I did see a jumper wire on the same trace next to the empty pad in the input section so maybe this is it? Common to ground out the negative side when using single ended inputs on a balanced system.

I guess if balanced is possible, I could just direct solder some flying XLR leeds and connect directly to my TVC pre.

Will take a picture of input area and post for comparison. Has anyone tried substituting TVC's in place of Potentiometer before??

Thanks again.

Steen
 
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sonicbath

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Just to get this straight:

SRM-T1: Single ended
Srm-T1S: Balanced??
SRM-T1W: ??
SRM-006tII: Very similar to T1??

Thanks again.
 
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spritzer

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The T1 was released in '87 while the T1S in '93 and the T1W in '94. The T1 continued in production after the others were introduced so they were a more upscale version with extra inputs.

I'm not using the T1W balanced. It is basically functioning as an input switcher now and the Blue Hawaii gets the XLR input. I'm moving away from the balanced topology in my next source and amp though.

Do post a picture. The Stax PCB's are semi transparent so it's easy to see the traces underneath. The cold part would be connected to ground and I'll check when I have time.

I haven't replaced the potentiometer but it's easy to do.

Quote:

Originally Posted by sonicbath /img/forum/go_quote.gif
Just to get this straight:

SRM-T1: Single ended
Srm-T1S: Balanced??
SRM-T1W: ??
SRM-006tII: Very similar to T1??

Thanks again.



T1 is SE, T1S and T1W are the same except the W has a passive preamp function, more inputs (one balanced), balanced outputs and variable bias on one output. 0067 and later versions are basically the same as the T1S though they have made some changes over the years. All these versions do not sound the same and I prefer the T1 over all of them.
 
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sonicbath

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Quote:

Originally Posted by spritzer /img/forum/go_quote.gif
The T1 was released in '87 while the T1S in '93 and the T1W in '94. The T1 continued in production after the others were introduced so they were a more upscale version with extra inputs.

I'm not using the T1W balanced. It is basically functioning as an input switcher now and the Blue Hawaii gets the XLR input. I'm moving away from the balanced topology in my next source and amp though.

Do post a picture. The Stax PCB's are semi transparent so it's easy to see the traces underneath. The cold part would be connected to ground and I'll check when I have time.

I haven't replaced the potentiometer but it's easy to do.



T1 is SE, T1S and T1W are the same except the W has a passive preamp function, more inputs (one balanced), balanced outputs and variable bias on one output. 0067 and later versions are basically the same as the T1S though they have made some changes over the years. All these versions do not sound the same and I prefer the T1 over all of them.



Thanks again Spritzer!

Took some pics & will post once I figure out how


There is definitely a provision for balanced in on the T1. I also removed the bottom plate revealing the resistors (look to be early smd). The resistors on the empty pad side seem to be 100 ohm.. would have thought they would be 0 ohm.

I also noticed that the pot is a 3 pole with the 4th missing. No big since thinking of TVC.


The top of the board, where the signal wires attach, has a capacitor and what may be a resistor (or a zener diode for over voltage protection?) encased in clear shrink tube. Also what looks like provisions to go to a switch (S003). Does anyone know the values for these components? It would save me some soldering work to check the values. A schematic would be even better.

Thanks!

Steen.

PS. After leaving the unit running with a source on repeat, the unit is really starting to sound great
Guess it is taking longer for the new elements to break in than I originally thought it would. How long does it usually take for elements to break in?
 
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spritzer

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Quote:

Originally Posted by sonicbath /img/forum/go_quote.gif
Thanks again Spritzer!

Took some pics & will post once I figure out how


There is definitely a provision for balanced in on the T1. I also removed the bottom plate revealing the resistors (look to be early smd). The resistors on the empty pad side seem to be 100 ohm.. would have thought they would be 0 ohm.

I also noticed that the pot is a 3 pole with the 4th missing. No big since thinking of TVC.


The top of the board, where the signal wires attach, has a capacitor and what may be a resistor (or a zener diode for over voltage protection?) encased in clear shrink tube. Also what looks like provisions to go to a switch (S003). Does anyone know the values for these components? It would save me some soldering work to check the values. A schematic would be even better.

Thanks!

Steen.

PS. After leaving the unit running with a source on repeat, the unit is really starting to sound great
Guess it is taking longer for the new elements to break in than I originally thought it would. How long does it usually take for elements to break in?



You can upload the pictures here and either post the URL or use the insert image function to insert it into the post.

It's too bad we do not have the schematic but I'll try and open up my amps soon ASAP but until then here are pictures of every Stax amp ever made and internal pictures of all of the T1's. It's in Japanese but the pictures speak for them selfs.

The elements need about 40 hours to break in as the mylar gets smoother and smoother. It might even improve some more.
 
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sonicbath

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Quote:

Originally Posted by spritzer /img/forum/go_quote.gif
You can upload the pictures here and either post the URL or use the insert image function to insert it into the post.

It's too bad we do not have the schematic but I'll try and open up my amps soon ASAP but until then here are pictures of every Stax amp ever made and internal pictures of all of the T1's. It's in Japanese but the pictures speak for them selfs.

The elements need about 40 hours to break in as the mylar gets smoother and smoother. It might even improve some more.



Heeloo Spritzer,

Thanks for the Stax pics link. With all the pages of Google I searched, I didn't find that one.

I looked at the SRM-T1S, and it is the same main circuit board as mine right down to the part # http://earsp.web.fc2.com/kako-d/srm-...5_jpg_view.htm (PB-201)!!
The daughter boards seem to be interface and switching for inputs. Cant be absolute due to resolution though.

I think this is doable


It looks like the only difference is an extra set of coupling caps and they've moved the zener (?) over to the negative side. The only question now is what are the values of the resistors on the bottom of the PCB


I look forward to your findings on your T1S. The resistor values at the input section is my real need.

Thanks again for your help. This is a great forum for earspeaker nutz!
I am just starting to realize what a fool I've been leaving the Stax in the closet for all these years.

Will post my pics as soon as I get a chance.

Steen.
 
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spritzer

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Quote:

Originally Posted by sonicbath /img/forum/go_quote.gif
Heeloo Spritzer,

Thanks for the Stax pics link. With all the pages of Google I searched, I didn't find that one.

I looked at the SRM-T1S, and it is the same main circuit board as mine right down to the part # http://earsp.web.fc2.com/kako-d/srm-...5_jpg_view.htm (PB-201)!!
The daughter boards seem to be interface and switching for inputs. Cant be absolute due to resolution though.

I think this is doable


It looks like the only difference is an extra set of coupling caps and they've moved the zener (?) over to the negative side. The only question now is what are the values of the resistors on the bottom of the PCB


I look forward to your findings on your T1S. The resistor values at the input section is my real need.

Thanks again for your help. This is a great forum for earspeaker nutz!
I am just starting to realize what a fool I've been leaving the Stax in the closet for all these years.

Will post my pics as soon as I get a chance.

Steen.



There is a whole goldmine of Stax stuff closed to us by the language barrier. It's a shame really as there is a whole lot of good amp designs and other projects.

They could very well have used the same PCB as they were made at the same time. Do you remember when you bought the Signature/T1 setup?

We are a crazy bunch here but we need to step it up a notch by building some amps.
Stax has no place sitting in a closet as while they won't beat a speaker setup, they can do some things better and bring the listener closer to the music.

I'll open them up tonight and take some pics of the input stage.
 
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spritzer

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Here are some pictures of the inside of the T1W. It uses the same PCB as my T1 with only a few minor mods, mostly to do with the delay on the PSU. Just click the pictures for a much bigger version. Sorry about them net being very sharp but I had to this with camera in hand and no flash.







 
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sonicbath

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Hi Spritzer,

Thanks much for the pics! Not many people would take apart there beloved audio gear for a stranger on the net.

So in input section I see two symmetrical sets of resistors. Brwn-Blk-Blk-Brwn (10 ohm) in series, and Org-Blk-Brwn, 300 ohm in parallel (followed by maybe a white band tolerance, I can't tell)?

This looks good. Can you get a value off the coupling caps? Mine seem to be 240 uf.

Thanks again!

Steen.
 
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spritzer

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Quote:

Originally Posted by sonicbath /img/forum/go_quote.gif
Hi Spritzer,

Thanks much for the pics! Not many people would take apart there beloved audio gear for a stranger on the net.

So in input section I see two symmetrical sets of resistors. Brwn-Blk-Blk-Brwn (10 ohm) in series, and Org-Blk-Brwn, 300 ohm in parallel (followed by maybe a white band tolerance, I can't tell)?

This looks good. Can you get a value off the coupling caps? Mine seem to be 240 uf.

Thanks again!

Steen.



I'm always happy to help out a fellow Stax enthusiast. This research might help many users later on that want to add a XLR input to their T1 amps.

There seems to be a line in the parallel resistor but I can't make it out even with my nose dangerously close to the board. The colors and values are right.

The caps have 240J written on them so they should be 24pF. A 240uF cap would be much larger. I'm guessing it is some form of a mica cap or something similar.

The input stage seems to be a mirror image of the other channels (as it should be) so just copying it should work. The weird part is the color coding for the input wiring as Stax obviously designed the amp to have a XLR input form the start as the SE wiring was color coded.
 
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Spritzer, when you said you prefer the T1 over the T1W, did you mean the stock model or your modded one? >_>
 
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spritzer

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Quote:

Originally Posted by Tachikoma /img/forum/go_quote.gif
Spritzer, when you said you prefer the T1 over the T1W, did you mean the stock model or your modded one? >_>


The stock T1 doesn't have this "etched" feeling that covers every bit of music in the T1W. It isn't a huge difference but it's there. The modded one is miles and miles ahead.
 
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Hi Spritzer,

Thanks. I'll see if I can dig up four BP caps in near enough value and do some soldering on Sunday.

Just curiosity, but the switch at the back grounds out the cold (-) side of the inputs when using single ended (rca)??

I can see what you mean about the stock T1 vs T1W. With all that extra switching gear , wiring, and baby boards, on the T1W it's no wonder...

Steen.
 
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