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stax srm717/srm727-11 - Page 5

post #61 of 64

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 64
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 64

Dear jgazal, 

 

It was just what I needed. 

 

Thank you very much for your help.

 

Best regards:L3000:

post #64 of 64
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
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