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The ultimate DIY? A Stax SRM-T2!


spritzer

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Reasonable minds differ on the 007 v 009 issue. biggrin.png

Best to try both if you can. They do sound quite different.

Arguing is half the fun... grin.gif My point really is that moar money isn't always better in this world so try before you buy. I also think the 009 would have been a whole lot better with slightly different voicing in the same way that the SR-007Mk1 is miles better than the Mk2. People also said I was nuts about that particular bit... laugh.png

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Good luck! You've been through the wringer a bit on your T2, although most of us have.

Mine (touch wood - as I do every time I change volume) hasn't missed a beat after multi silicon death through the dreaded counterfeit 2SC3675's.

It's been a painful birth but then again I get easily distracted and go work on something else. Too many projects, too little time and I'm always adding some random crap to the list. This week has been mostly spent finishing a preamp based on a 25$ ebay kit and buying parts for a Hiraga Class A amp to drive the LCD-2's. facepalm.png

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I am starting to build an ackodac, and will use twistedpears IVY-iii as an IV (as well as a "new take D1" later on).

http://www.twistedpearaudio.com/docs/linestages/ivy3_schematic_1_0.pdf

IVY-iii has 22R resistors on the balanced output from opa1632, to "help drive capacitive loads".

Does T2 count as a capacitive loads?? (due to C10/11)

peter

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  • 2 weeks later...

I finished the building of my T2 clone a week ago. The building process went very smoothly and the amp have played just wonderful until last evening when a “gunshot” was heard and there was just noise in the phones.

The PSU 60 Volts section measured almost 100 V, just a few volts less then unregulated voltage. May it be the TL783 that has given up for some reason?

I took a 60 V supply that was at hand to get all voltages correct from the PSU and connected the Amp. Left channel worked as it should – right channel was dead.

Right channels active batteries measure 523 V (-510 and +13 vs ground) and 546 V (-533 and +13 vs ground). All LEDs are lit except D10 and D11.

What could be the problem with the right channel?

HELP wanted and needed!

Joachim

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Thanks for your advice Kevin. I´ve changed tube and replaced all three transistors – Q11, Q12and Q25 but the problem is still there. The plate voltage is as you predicted +500 V.

What could next step be? I guess that the faulty 60 volt supply is due to something happened in the amp or could it be that a -300 V and -600V from the PSU have caused problem with the amp?

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Now I´ve done some measurements (I work slow - I´m just an uneducated amateur).

Output +: Anode -460 V, Cathode -500 V; LEDs D10, D11 no light

Output -. Anode +490 V, Cathode -318V

Batteries top voltage +10 V and bottom -500 V.

Input stage first tube cathode -27 V, second tube cathode -20 V and gate -19 V.

Current thru R9 15 mA and R10 6 mA.

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You probably have a few issues, but I agree, check why the batteries are not sitting at +200V on the top. Look at Q4 & Q5 to see the gate (~ 200V) and drain (~ 250V) voltages. If the gates are around 200V then Q4 / Q5 are likely at fault, if the gate is sitting near 10V then Q1 - Q3 are likely having issues and possibly D1 though the diode is is less likely.

Another thing you can try is to use a diode tester against all the combinations of the three pins per device. Check from the good channel to the bad channel. You will likely see differences (shorts, leakage or non-conductive issues) on the bad channel. If anything looks different between the good and bad channels, then replace that device in the bad channel.

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Thanks Kerry, yesterday I concentrated on the input stage and I replaced Q1,2,3 which didn´t solve a thing (trial and error, not so intelligent).

Top batteries voltage are at +10V and Q4/Q5 gates are at -15V. D1 gives the right base voltage and hopefully the Q1,2,3 are OK. What brings the U2 anode voltage down to -15V when it should be around +200V? What effect do Q34,35,36 have, the current thru R9 is 15 mA and R10 is 6mA.

edit: one more thing – will a faulty Q4/5 have effect on U2 anode voltage?

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Kerry,

I red your post at 7 in the morning Swedish time.

After a few hours of thinking and reading schematics and not getting any viser I did follow your advice to use a diode tester. And whips I found a K216 - Q26 - behaving different to the functional channel, replaced it with the very last spare I got. Now the T2 is playing just wonderful. That diode testing method will be my first choice next time, it´s like a Swiss army knife. When starting the diode test the whole process took less then one hour to get the amp playing.

Thank you very much. That goes to all you other people out there, no names, that have contributed to the forum. I´ve read posts forwards and backwards and that have made it possible for me to build the T2. Well, maybe one person should be remembered - Dr. Takeshi Hayashi. Dr. Kevin Gilmore – thanks for your GKSSHV it´s a lovely amplifier.

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Great news!

Also, just to answer your earlier question regarding the function of Q34 - Q36, they form a servo referencing the bottom of the batteries to set the where the input tubes sit. A defective Q26 can definitely have an impact on that servo. It's all one big system - very slick.

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