I'm going to build a Pass XOno.

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#101
With 90mV on 22 ohm resistor current is 4mA. Four jfets with 4mA is 16mA. If you remove jumper for 4db gain, voltage on R66+R40 is 16V. With this voltage transistor Q14 in this case not work properly. Decrease drain voltage on jfets decreasing value R16, Q14 will have enough voltage to work correctly. In my preamp i put drain voltage at 10V and about 4-5 voltage across Q14 and 73mV across source resistors.
 
#102
impuls said:
With 90mV on 22 ohm resistor current is 4mA. Four jfets with 4mA is 16mA. If you remove jumper for 4db gain, voltage on R66+R40 is 16V. With this voltage transistor Q14 in this case not work properly. Decrease drain voltage on jfets decreasing value R16, Q14 will have enough voltage to work correctly. In my preamp i put drain voltage at 10V and about 4-5 voltage across Q14 and 73mV across source resistors.
Click to expand...

Pass X-Ono clone designed by Nagard(Dragan) which you probably have , has the following measured results in his instruction manual: 91mv across 22 ohm, 11.50V drain voltage ,
R16 and R18 both 10K and total gain of 70.12db. As you can see, accurate full gain with Q14 working properly, with both jumpers removed.
Input J-Fets have Idss of about 6.5ma, close to BL group as in original X-Ono as its designer told us.
 
#105
The values we ended up using are the ones that gave the sound we liked and kept all the parts in power rating. After that the curves reproduced quite consistently on the AP. Since this is DIY you can have as much fun as you want with values and parts. Thats what I am doing right now for the XS phonostage.
 
#107
wayne said:
Since this is DIY you can have as much fun as you want with values and parts. Thats what I am doing right now for the XS phonostage.
Click to expand...

I hope so this will be a SUSY-like fully balanced thing.😎
You know, I really like balanced circuits, because these are like ying-yang.🙂

I have paralleled a 27.4k with R18, according to your advice.
Input JFET drain now at about 13.8V.
I have changed LED, so R67 and R53 at 1.09V.

I'm decided to work now with chassis.
I have made some progress.
Pictures will follow.

Gyuri
 

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#112
Somehow I progress slowly with chassis.
But the power supply is ready.
How can I places the two boxes?
Can I put them on each other?
In this case power supply cable can be short between boxes.
And I think, it would be prettier.
Or make a longer PS cable, so I can put them farther?
I welcome any advice!
 
#113
For more thoughts:
PS box metal frame must be on safety ground.
It is not a question.
Can I use a thermistor for ground lifting? (between box and PS board ground)
Safety ground must be on separate preamp box?


I ask so many stupid things, because I want this thing it is to be safe and possible hum-free.
 
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#115
I think distance between the power supply box and the main circuit is very good. I know that if I move my PSU close to the circuit I get hum picked up. I put the transformers and PSU in one box (Salas shunt) and then just the circuit in the other box.

Yes, you should earth the PSU box to ground - I used back to back diodes paralleled with a 15R power resistor and low value capacitor.

BTW, russian MBGT caps sound very good in this amp.


Fran

Fran
 
#116
Thank you for your answer Fran,
I think we know all tomorrow.
I just want one cable sets to be constructed.
I think I stacked the boxes first, and connecting them temporarily.
Then we shall see. (hear, let's be more precise)
Just like that, when it was on the table, there was a little hum.
It depended mostly, on how I put the cables.
See you later!

Gyuri
 
#118
If you use two separate enclosures, forget about any isolation devices like thermistors, diode bridges etc. Original X-Ono had thermistors since it used sub D -25 connectors which shells are grounded to both enclosures, to separate safety earth from signal ground.
Just tie green/yellow earth wire to PS enclosure( do not connect raw PS ground to it!) and use 2 meters of screened cable and multicore connectors between cases. Connect cable screen at audio circuit enclosure only.
Audio circuit enclosure should be grounded to signal ground in one point at the back plate which is also turntable ground by suitable binding post.It must have shakeproof washer. GND side of output connectors go to that point.
Input RCA sockets should be insulated from the enclosure.
It is very important that power amp or headphone amp have direct connection
between safety earth and signal ground. Only one component in audio chain!
All others must not have direct connection.
Thermistors and isolation devices are suitable only for single enclosure approach .
 
#120
It's just a little bit like when I asked my mother, asking her advice, she replied to me:

If you listen to me, son, you can do whatever you want.😉

So now the power supply and the amplifier are in the boxes.
I tried to implement cabling as it was on the table.
Because it was not really humming.

Boxes don't have any GND connection.
Boxes isolated of each other galvanically.
Turntable also doesn't have any GND connection.
Safety ground attached to GND of PS board only.
I know it's against safety regulations.
But there isn't any hum induced by XOno.
Very low hiss was also reduced further, when I set R18 to 7.3k according to Wayne's advice.
It is amazingly quiet.
So now I know what it's capable of.
But now, before I go further direction to the security, I need to listen to some music.

Kind regards,
Gyuri
 
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