Phaedrus Audio: Spirit Tube U47 Circuit // Need help, please!

[Moby]

Hi Moby,
thank you for your good expanation and suggestion!
I will write to FAB about this. If it is an easy hack I iwll try to modify my V8 transformer. If not I will have to live with the decoupling resistors.
Thank you and all the best!
Simon

You welcome. It must be an easy task because as I can see the coils are connected internally and hopefully secondary winding is the top.one. (at least, geniune one has sec. as a top winding). If that's the situation you should just remove the top insulation and there is the CT. Cheers!

 

[grobaesthet]

I built many pc with this Phaedrus tube and I remember the schematics values are not really correct,some recalculations were needed. But the mics sounded good without the 2.2k phantom resistors or DC-DC converter.

Hi TLRT,
I just re-read the thread and saw that I misunderstood your post. You wrote that you did neither use the phantom resistors nor the DC-DC converter. Does this mean you used a center-tapped transformer? or did you do any other changes to the circuit to get the phantom power to the tube?
Thanks and best regards!
Simon

 

[RuudNL]

I don't think changing the two resistors to a center tap on the transformer will make a noticeable difference.

 

[TLRT]

Hi TLRT,
I just re-read the thread and saw that I misunderstood your post. You wrote that you did neither use the phantom resistors nor the DC-DC converter. Does this mean you used a center-tapped transformer? or did you do any other changes to the circuit to get the phantom power to the tube?
Thanks and best regards!
Simon

Yes I did not use phantom resistors or DC-DC converter. I used Moby BV8 and recalculated most of the resistors. The mics had high gain,low noise, overal a bit bright sound even with the better M7 capsules. Here is one example:

 

[rock soderstrom]

I used Moby BV8 and recalculated most of the resistors. The mics had high gain,low noise, overal a bit bright sound even with the better M7 capsules. Here is one example:

Yes, this works because your transformer has a center tap. The Fab V8 from the TO does not have that, he needs the resistors.

Nice video, great music!

 

[TLRT]

Yes, this works because your transformer has a center tap. The Fab V8 from the TO does not have that, he needs the resistors.

Nice video, great music!

I have to check my notes but I remember with the stock schematics values the "anode" and polarization voltages are too low, so the mic output was low too. It is easy to check with scope and electrometer.