[Tiagahsong]

With trans 10k : 600, 6sn7 tube What preamp can I build.?
One option is ultrapath, I have big problem with noise.
Can parallel the triode to achieve lower impedance?
Recommedations and suggestions please
Thanks
Goh

[Ian Bell[_2_]]

TiaGahSong wrote:
With trans 10k : 600, 6sn7 tube What preamp can I build.?
One option is ultrapath, I have big problem with noise.
Can parallel the triode to achieve lower impedance?
Recommedations and suggestions please
Thanks
Goh




You could build a mu follower line stage. A 6SN7 will give you 25 to
26dB gain in a mu follower so taking out the 12dB loss in the op
transformer you have an overall gain of around 12dB. Output noise will
be better than -90dBV.

Cheers

Ian

[Tiagahsong]

Ian
Thank you for your suggestion.
I will be glad if you can describe the schematic. I have say B+ 260V, pot
100K, so what should be the cathode resistor value and single triode or two
in parallel.
What should be the idle current etc
Thanks

Goh
"Ian Bell" wrote in message
...
TiaGahSong wrote:
With trans 10k : 600, 6sn7 tube What preamp can I build.?
One option is ultrapath, I have big problem with noise.
Can parallel the triode to achieve lower impedance?
Recommedations and suggestions please
Thanks
Goh


You could build a mu follower line stage. A 6SN7 will give you 25 to 26dB
gain in a mu follower so taking out the 12dB loss in the op transformer
you have an overall gain of around 12dB. Output noise will be better
than -90dBV.

Cheers

Ian

[Ian Bell[_2_]]

First I suggest you do an internet search for mu follower so you know
how the two triodes are basically connected. Then with a 6SN7 I would
recommend aiming for an idle current of about 5mA. Choose the cathode
and intermediate resistors based on your supply voltage, a suitable
operating point and the idle current.

Cheers

Ian

TiaGahSong wrote:
Ian
Thank you for your suggestion.
I will be glad if you can describe the schematic. I have say B+ 260V, pot
100K, so what should be the cathode resistor value and single triode or two
in parallel.
What should be the idle current etc
Thanks

Goh
"Ian Bell" wrote in message
...
TiaGahSong wrote:
With trans 10k : 600, 6sn7 tube What preamp can I build.?
One option is ultrapath, I have big problem with noise.
Can parallel the triode to achieve lower impedance?
Recommedations and suggestions please
Thanks
Goh

You could build a mu follower line stage. A 6SN7 will give you 25 to 26dB
gain in a mu follower so taking out the 12dB loss in the op transformer
you have an overall gain of around 12dB. Output noise will be better
than -90dBV.

Cheers

Ian

[Patrick Turner]

TiaGahSong wrote:

With trans 10k : 600, 6sn7 tube What preamp can I build.?
One option is ultrapath, I have big problem with noise.
Can parallel the triode to achieve lower impedance?
Recommedations and suggestions please
Thanks
Goh


With a 10k:600 OPT, the voltage ratio is 4:1.

So if you have a 6SN7 with voltage gain of 16, then the preamp gain will
be 16 / 4 = 4x, or +12dB.

If you have a paralleled 6SN7 with Ia = 5mA for both halves, then Ra
will be about 5k total.

The OPT will reduce this Ra by the factor of 1 / impedance ratio =
1/16.66 so that Rout at the sec is 300 ohms.

If you used 1/2 a 6SN7, Ra would be about 10k and Rout becomes 600 ohms.

If you had an RC coupled gain 1/2 6SN7 triode direct coupled to a second
1/2 6SN7 connected as a cathode follower, and then coupled to an OPT,
the CF Rout of about 500 ohms is reduced to 30 ohms by the OPT.

But to the Rout figures I quote you have also to add the "reflected"
primary wire resistance and the secondary resistance.

For more on preamps see

http://turneraudio.com.au/preamplifiers.htm

I have never seen any need to use an OPT on a preamp, and where I want
to reduce the gain of a 6SN7 or 6CG7 from say 16 down to a typical 4,
then I would use a shunt NFB loop.

OPT for preamps with a 10k:600 ratio are OK if there is plenty of
voltage headroom.
Some are available with input to the 10k primary which is limited to
less than 2Vrms, which is a bit low.
So you need to have a 20Vrms capability at 10Hz without core saturation
and a HF cut off at above 30kHz.
And low THD produced by the iron.
And then there is the issue of having the right air gap for SE
operation.
I hence concluded there were easier and cheaper ways to build a preamp
than using an OPT, and yet still have excellent sound.


Patrick Turner.