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post #61 of 68

Hello! 

 

Some time ago I bought an SRM-727A amplifier and headphone SR-007 MKII. 

 

I already bought the resistors to perform Spritzer Mod and i want to make the service soon. 

 

So, I have a doubt: 

 

How do I adjust the balance DC? 

Where do the adjustments? In which components? 

How do the measurement? 

Could someone explain me step by pass, please? 

 

thank you

post #62 of 68
Quote:
Originally Posted by Furlan View Post
 

Hello! 

 

Some time ago I bought an SRM-727A amplifier and headphone SR-007 MKII. 

 

I already bought the resistors to perform Spritzer Mod and i want to make the service soon. 

 

So, I have a doubt: 

 

How do I adjust the balance DC? 

Where do the adjustments? In which components? 

How do the measurement? 

Could someone explain me step by pass, please? 

 

thank you

 

http://www.head-fi.org/a/adjusting-bias-on-stax-tube-amplifiers

http://gilmore.chem.northwestern.edu/dsc_1583mod.jpg

http://img829.imageshack.us/img829/2255/p1000579o.jpg

post #63 of 68

Dear jgazal, 

 

It was just what I needed. 

 

Thank you very much for your help.

 

Best regards:L3000:

post #64 of 68
Thread Starter 

Just a word to say I have added a stabilized  power supply using a mos-fet power transistor It is not an original design by me as there is a limit in the number of variations in solid-state design unless you make some specialized overload cut out. I used a constant current design which was pretty simple. Mos-fets are much more reliable in solid-state power supplies when used as pass transistors many normal transistors(BJT) need a lot of protection to stop them failing mos-fets dont and are used in millions of switch-mode power supplies World-wide. The result is a much reduced noise floor and power supply injected distortion products (cleaner -clearer sound ) as opposed to  simple power supply provided in a 717/727. I see many people upgrading the power supply capacitors while this is a positive thing it entails a good bit of time and work. While not a first glance looking any easier actually fitting a stabilized power supply is a good bit quicker and if you can read a circuit diagram no harder. It is easy enough to cut the pcb copper that runs to the two output fuses and solder flying leads to the power supply . It can be even simpler just fitting a pass mosfet and little more. I cut a section of the casing away next to the fuses  that allowed me to fit a small heatsink and mount the components directly onto the two mosfets. This kept the distances between components very short improving stability with no oscillation but you could make pcb to suite or even a strip board although that could introduce small amounts of capacitance. Active components must be at least 500 V working. The perceived fidelity when compared with just changing the caps is large . This is a mod you will hear right away making a large difference and will reward those with Omega 2 earspeakers with a large increase in detail due to decreased noise/distortion on the supply lines. Its no use having an amp with 0.001 thd when your power supply is outing large amounts of noise unless your amp has power supply rejection of the same amount.   


Edited by duncan1 - 5/23/14 at 11:33am
post #65 of 68

Hi guys,

I am entering the world of Electrostatics and am looking at the 717 for my solution.....

I have always loved playing with electronics and am confident to solder, replace resistors, caps etc but I really have no idea regarding how to test and measure circuits.

My question is can the 717 be easily converted from 110 to 240V?

Would it require a new transformer?

I note the caps are 400V so does that mean the circuitry would be fine with the change?

I would also like to thank you all for this thread...

As I said before I love to tinker and could see myself trying to perform the mods as described in this thread in the future .......

Thanks

post #66 of 68
Quote:
Originally Posted by Interben View Post
 

My question is can the 717 be easily converted from 110 to 240V?

 

Easily is a relative term. You can try the following posts: 

http://www.head-fi.org/t/223263/the-stax-thread-new/23625#post_9627206

http://www.head-fi.org/t/223263/the-stax-thread-new/21285#post_9223131

http://www.head-fi.org/t/679447/stax-727-voltage-conversion-100-to-117-help#post_9758538

 

Would it require a new transformer?

I note the caps are 400V so does that mean the circuitry would be fine with the change?

 

If your model allows, you can change how primaries are wired, so secundaries will hold the same voltage. You also need to change fuses (different ratings). Be careful. Even disconnected from the mains, capacitors may be charged. The voltages inside the amp are lethal.

post #67 of 68

Awesome... That was exactly the info I need....  Also thanks for the Heads up with the capacitors :).  When I was young I had a friends dad who would charge them up and throw them at us to catch... We obviously weren't that smart because we kept catching them :)

Thanks again jgazal....

post #68 of 68
Thread Starter 

I had forgotten to add that the feedback resistors total 300K OHMS in the unmodded version . If you check the circuit diagram you will see that it is a     version of a widely modded standard circuit. All the other versions show the series resistance as 200 K OHMS from the output to the input I had already reduced the series resistance to 200K OHMS using a parallel resistor across one of the 150KOHMS feedback resistors in the original circuit that means that 2 resistors are paralleled in each board. With the extra feedback it does make a positive difference I still stick by the fact that if you want a major positive difference to the 727 /11  then make the power supply stabilized or at least use a pass transistor or mosfet.Believe it or not its not hard to do a even a simple design  makes a world of a difference blocking a lot of  mains harmonics and noise and distortion. Many easy to follow designs are on the web.     

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