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The ultimate DIY? A Stax SRM-T2!


spritzer

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Years ago pedefede mentioned that replacing the 10k trimmers with some vishay PTF56 resistors (since they're 5ppm) did the trick. If it isn't the input tubes that's the next thing I'll try.

Anyone happen to have 9kOhm PTF56's lying around? :P

Edited by s_r
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Alright, I went ahead and did that. The current usage for each channel was close to identical, at about 47mA.

I also plugged in some headphones and each channel exhibits some weird behavior. Left only results in no audible noise, but the channel itself is much quieter. So maybe the noise is still there, just quieter since the whole channel is? Right only still gives the same noise, and the channel is about the right volume.

I'm starting to think this is where the black magic is required. :P

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Hm. If the battery voltages are on and offset is fine, LEDs are lit, the circuit pretty much has to be working. The reduced volume in one channel to me is very odd. I would perhaps continue to swap the easy stuff, input (assuming this is good) source and output tubes and even the two umbilicals. See if you can get that behavior to swap channels.

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I originally thought the left channel might not have all its LEDs lit or maybe the battery was out of whack, but it checks out fine. I also tried all the combinations under the sun and the channels don't swap their behavior.

Going to order some parts to try and swap in, mainly some PTF56s to replace the 10k trimmers in the battery. Would 10pf work as something to try in place of the 5pf cap?

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I think the trim pot is a good place to look.  I remember Inu looking at them as well as some other members needing to replace them to clean up the noise.  I think Inu did a full substitution with a fixed resistor at some point.  It's been a while so I don't completely remember.  For me, the noise was definitely coming from the resistors.  I used PRP and ended up replacing with everything in the batteries with Xicon, which did the trick.

Finicky thing these batteries. 

Speaking of trim pots, JoaMat, what trim pots are you using in your SMD battery above.  I'm just laying out my new boards and I wanted to size them properly.  Given that yours worked, I thought it would be a good source.

Lastly, I finally got to testing my new PS.  +/-500V, +250, -300, -60, +/-12V and 5V supplies.  Everything checked out. :D

One note is that the 47nF or .1uF bypassing the resistors going into the 20K resistors and feeding the error amp seem to increase any oscillations coming from the prior stage.  I've taken them out for now.  I'll post something about this in the carbon thread as well, since these new supplies are used there as well.  I'm seeing noise levels under 6mV, but there is likely noise coming from my room that I'm seeing. Also, I'm seeing some random spikes at around 50mV. 

EDIT: I'm going to try adding an EMI filter at the input to see if it cleans this up.

 

IMAG00322 2.jpg

Edited by Kerry
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