problem with zen line stage

supernet · 20th January 2002, 06:28 PM

I have built Zen line stage some days ago. The preamp is working and the all voltages are fine. The problem is that I want it used as unbalanced preamp( I got unbalanced power amp and CD player) so I put at the input of preamp -OUT to ground and +IN to signal. At the output I put +OUT to power amp and
-IN to ground.

It is right to do like this?

The main problem is that I get too much gain at the output. For R15 I used 430 ohm and at the input, I put 10k log, but I get too much gain for my Leach power amp.

Thank you for any ideas!!!!!

tschrama · 20th January 2002, 08:41 PM

As far as I understand, you should not groud one of the outputs!
You could ground one of the inputs but it is not nessecery.

Just use one input and one output, this should work fine. Try both outputs, and use the one you like best if there's any dtecteble difference.

the gain determining resistor can be set according to the gain you need. You might not even need any gain so a passive 10K log pot would be just fine.. Or increase the resistor from 120R to 330 or even higher..

goodluck,
Thijs

Nelson Pass · 21st January 2002, 06:30 PM

You can ground the outputs of the BOZ or Balanced
Line Stage as you like.

tschrama · 22nd January 2002, 08:41 AM

hmmmmmm .well Pass. oke.. that leaves me stupid

:-(

greetings

Nelson Pass · 22nd January 2002, 05:53 PM

No, it's really pretty simple. The output of the
BOZ or BSOZ comes off the Drain of the gain
device, and this is just a current source, not a
voltage source. To turn it into some kind of
voltage source, we load it with some resistance,
in this case the resistances which go off to the
positive supply and any load that we happen to
attach to the output.

On the BSOZ, the resistance to the positive supply
is 750 ohms, so the voltage is developed across this
and the output impedance is 750 ohms. You can
attach the output to additional resistance, all the way
to 0 (ground) and the current source of the transistor
will still happily send the same amount of current through
the output, although the voltage developed gets lower
and lower with decreasing load impedance.

tschrama · 22nd January 2002, 06:57 PM

Thanks Pass!

but I always thought that the MOSFET performs better with higher Drain-Gate voltages and less current swing (more lineair, more gain, more feedback ?)....

Isn't that why the Aleph P (and the X-series amps?) uses active current sources at the drain of the input device ?

Wouldn't a ground or low resistance to ground to the output of the BOZ or BOSOZ create a filter with a too high corner frequency?

Maybe that doesn't matter since it doesn't effect the other output connection in the BOSOZ.

Hi Supernet,

you got your anwser too... just lower the resistance which the preamp is using to create a voltage.. lower resistance means lower voltage, thus lower gain..

greetings,
thijs

Nelson Pass · 23rd January 2002, 07:23 PM

Yes, the P maximized the voltage by using current
sources, however when you do this you must come
up with another mechanism for determining the
DC voltage on the Drains. With the resistors for
loads, you don't have to deal with this.

As you approach 0 ohms loading, the hi pass
cutoff becomes the cap and the Drain + output
resistor, which is 221 + 750 = 971 ohms.

20th January 2002, 06:28 PM	#1
supernet diyAudio Member Join Date: Dec 2001 Location: Europe	problem with zen line stage I have built Zen line stage some days ago. The preamp is working and the all voltages are fine. The problem is that I want it used as unbalanced preamp( I got unbalanced power amp and CD player) so I put at the input of preamp -OUT to ground and +IN to signal. At the output I put +OUT to power amp and -IN to ground. It is right to do like this? The main problem is that I get too much gain at the output. For R15 I used 430 ohm and at the input, I put 10k log, but I get too much gain for my Leach power amp. Thank you for any ideas!!!!!

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20th January 2002, 08:41 PM	#2
tschrama diyAudio Member Join Date: Jul 2001 Location: The Netherlands	As far as I understand, you should not groud one of the outputs! You could ground one of the inputs but it is not nessecery. Just use one input and one output, this should work fine. Try both outputs, and use the one you like best if there's any dtecteble difference. the gain determining resistor can be set according to the gain you need. You might not even need any gain so a passive 10K log pot would be just fine.. Or increase the resistor from 120R to 330 or even higher.. goodluck, Thijs

21st January 2002, 06:30 PM	#3
Nelson Pass The one and only Join Date: Mar 2001	You can ground the outputs of the BOZ or Balanced Line Stage as you like.

22nd January 2002, 08:41 AM	#4
tschrama diyAudio Member Join Date: Jul 2001 Location: The Netherlands	hmmmmmm .well Pass. oke.. that leaves me stupid :-( greetings

22nd January 2002, 05:53 PM	#5
Nelson Pass The one and only Join Date: Mar 2001	No, it's really pretty simple. The output of the BOZ or BSOZ comes off the Drain of the gain device, and this is just a current source, not a voltage source. To turn it into some kind of voltage source, we load it with some resistance, in this case the resistances which go off to the positive supply and any load that we happen to attach to the output. On the BSOZ, the resistance to the positive supply is 750 ohms, so the voltage is developed across this and the output impedance is 750 ohms. You can attach the output to additional resistance, all the way to 0 (ground) and the current source of the transistor will still happily send the same amount of current through the output, although the voltage developed gets lower and lower with decreasing load impedance.

22nd January 2002, 06:57 PM	#6
tschrama diyAudio Member Join Date: Jul 2001 Location: The Netherlands	Thanks Pass! but I always thought that the MOSFET performs better with higher Drain-Gate voltages and less current swing (more lineair, more gain, more feedback ?).... Isn't that why the Aleph P (and the X-series amps?) uses active current sources at the drain of the input device ? Wouldn't a ground or low resistance to ground to the output of the BOZ or BOSOZ create a filter with a too high corner frequency? Maybe that doesn't matter since it doesn't effect the other output connection in the BOSOZ. Hi Supernet, you got your anwser too... just lower the resistance which the preamp is using to create a voltage.. lower resistance means lower voltage, thus lower gain.. greetings, thijs

23rd January 2002, 07:23 PM	#7
Nelson Pass The one and only Join Date: Mar 2001	Yes, the P maximized the voltage by using current sources, however when you do this you must come up with another mechanism for determining the DC voltage on the Drains. With the resistors for loads, you don't have to deal with this. As you approach 0 ohms loading, the hi pass cutoff becomes the cap and the Drain + output resistor, which is 221 + 750 = 971 ohms.

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