What do you mean 317,337? You use them as a bench supply? 28.1 to 31.2 is not enough for the drop across the leds. If the buffer is working ok, then the Vout adjusts as without it. Else its a sign of oscillation. Presents a comb across bandwidth on FFT. I suggest you feed it from raw rectification and capacitor at 35V. Maybe the prereg is the problem. The bandwidth alters with the buffer. You did not tell us you got more electronics in the loop before.
I did not have anything but raw 34v in the first experiments.
My last post refers to this unique ocasion where I tried it on the bench... regulated +-15v and it was able to put out 28v from 31.
Unfortunatelly the issue persists.... I just installed it in the riaa and the output droped to 27.5v... the worst thing is that the whystle appeared again.
In the other channel I have a "normal" shunt and the input is 34.2v for 28.1v out.
Do I need more than 34v for this particular vout ?
My last post refers to this unique ocasion where I tried it on the bench... regulated +-15v and it was able to put out 28v from 31.
Unfortunatelly the issue persists.... I just installed it in the riaa and the output droped to 27.5v... the worst thing is that the whystle appeared again.
In the other channel I have a "normal" shunt and the input is 34.2v for 28.1v out.
Do I need more than 34v for this particular vout ?
I assume you didn't try base resistors as I suggested.
Can you please measure the current going through the shunt mosfet? There's a chance too much current sags the input voltage and that can also lead to oscillation. You may want to decrease R1 a little for testing purposes.
Edit: I just noticed your Vin. I think it's too low, you need a better margin of safety there.
Can you please measure the current going through the shunt mosfet? There's a chance too much current sags the input voltage and that can also lead to oscillation. You may want to decrease R1 a little for testing purposes.
Edit: I just noticed your Vin. I think it's too low, you need a better margin of safety there.
I did not have the oportunity to try the base resistor change.
The current is 190mA as I read 1.9v on R1 (10r).
If I decrease R1 can it not increase the current ?
Wait, don't decrease it yet. How much does your load draw? I just want to make sure your shunt mosfet has enough current to work with. You can use 38V from the supply, ONLY if your CCS mosfet has enough sink to dissipate 1A.
Ricardo,
In general:
The regulator needs a minimal input of 28.1 + 5.7 + 2V margin for unexpected drop = 36 volt. Don't go much higher for dissipation reasons.
If you know the current you can calculate the resistance value needed to drop any voltage you like to your needs. Terminate with a decent cap (1 milli Farad) and connect your regulator.
If you're unlucky (count on it) the bench supply makes your reg oscillate. Why don't you use the intended supply for your phono?
edit: Whoops, mustard after the meal
In general:
The regulator needs a minimal input of 28.1 + 5.7 + 2V margin for unexpected drop = 36 volt. Don't go much higher for dissipation reasons.
If you know the current you can calculate the resistance value needed to drop any voltage you like to your needs. Terminate with a decent cap (1 milli Farad) and connect your regulator.
If you're unlucky (count on it) the bench supply makes your reg oscillate. Why don't you use the intended supply for your phono?
edit: Whoops, mustard after the meal
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Hey, it's better, get a good night sleep and attack it with fresh forces next time. I'm sorry to see you taste some of this; to move from v1 to v1.5 and v2, all those versions in between, lots of failures, oscillation, and so on, I've tasted quite a bit of this. But you will prevail! 
A solution will be found.
A solution will be found.
Before I spend more in a new TX, I need to know If the lower input voltage might be responsible by the oscilation.
I am currently using a 25v TX + full wave rectifier + cap and should get +35v (I am reading 34,5v).
Next possibility would be a 30v TX that would provide +45vout.
I can not find a TX in between.
Is there a possibility that a low Vin should create oscilation ?
I am currently using a 25v TX + full wave rectifier + cap and should get +35v (I am reading 34,5v).
Next possibility would be a 30v TX that would provide +45vout.
I can not find a TX in between.
Is there a possibility that a low Vin should create oscilation ?
We can't put the finger. Beyond that we use buffers successfully, and the one that breaks your errr, nerves, works in 3-4 builds, we can know nothing more in a specific build that we can not physically examine. It surely can give some additional performance, but I suggest you go for remote sensing instead, in your case. Maybe it will compensate subjectively to enough degree for a notch better without the head busting part.
Universal Phono Shunt (aka v1.1) pcb
I'm trying to design a suitable pcb.... one question: should I refer Q7 & R8 in the same Vref loop? In particular, should I connect Q7 collector + Q2 drain + R 7 togheter, then to V+ and R8 + R5 + Q3 emitter togheter and then to the gnd point (star)?
I would like to prearrange the pcb for remote sensing if needed.
I'm trying to design a suitable pcb.... one question: should I refer Q7 & R8 in the same Vref loop? In particular, should I connect Q7 collector + Q2 drain + R 7 togheter, then to V+ and R8 + R5 + Q3 emitter togheter and then to the gnd point (star)?
I would like to prearrange the pcb for remote sensing if needed.
34.5Vdc @ what mains input voltage?
What are the minimum and maximum DC PSU voltages when mains supply is at minimum and at maximum?
Ok, thank you.
That was my first idea... and my pcb design, then a doubt arose.....
P2P: While I can draw nice pcbs (even for "porfessional") I'm a disaster with P2P....
My pcb design is based on "working examples" such as the drawings developed by James and Disco.... I'll cross my finger anyway!