[scootsit]

So is 15V for the FM the best?

 

[tomb]

Quote:

So is 15V for the FM the best?

Yes, I think so.

 

[scootsit]

Do you think so for all the Millett tubes? I'll try biasing mine higher soon!

 

[tomb]

Quote:

Do you think so for all the Millett tubes? I'll try biasing mine higher soon!

It's possible, but I'm not as certain as I am with the 12FM6's.  Plus, tube biasing on the Millett Hybrid series is not too far off from "adjusting" the volume knob.  It's something you should be checking on a regular basis and perhaps experimenting with a great deal.  JMHO ...

 

[fmlfml]

Is there any other diy balanced headphone amp except beta 22 

 

[tomb]

Quote:

Is there any other diy balanced headphone amp except beta 22 

A B22 will only be balanced if you build it that way.  Same for the Millett MAX - Head-Fi user pabbi built one.  A balanced M3 has been built and sold many times - I believe Rockhopper onced offered them commercially.  There are plenty of other examples as well.

 

[KimLaroux]

As tomb said, any DIY amplifier can be built for balanced operation. basically, you just have to build a 4 channel amplifier, and bridge the outputs.
 
The only limitation is you can't buy a full kit and turn it into a balanced amplifier. You'll need a custom enclosure around twice the size of the normal amp.

 

[ModMax]

My MOSFET-MAX is complete, pics below:
 
 
1.  The innards.  Integrated grubDAC in upper left corner.  Also, VitQs (Beezar.com) and Elna Silmic II's as part of the build.  Most of the wiring is routed under the PCB.
 

 
 
2.  Rear view.  Black=GND, Red=V+, Green=L/R Tube Bias, Blue=L/R MOSFET Bias.  RCAs (Beezar.com) and USB for grubDAC.  Square opening took a long while and was started with a 1/4" hole and squared off with a metal file.
 
 

 
3.  Front View.  Center toggle for power, side toggle for input select (DAC vs RCA).  Both 1/4" and 1/8" TRS plug sockets.  Knob is KILO ML-90-3-6MM from
DigiKey (Part #226-3028-ND).
 
 

 
 
4.  Input select toggle.  Down (RED) for grubDAC, Up (GREEN) for RCA.
 
 

 

 
 
Oh, and did I mention, it sounds amazing!!!  My ears have never been happier especially with my HE-400s.  Current setup:  V+=27 V, 12AE6 Tubes=14 V, MOSFETs=230 mV
 
 
 

 

[dustinsterk]

Quote:

My MOSFET-MAX is complete, pics below:
 
 
1.  The innards.  Integrated grubDAC in upper left corner.  Also, VitQs (Beezar.com) and Elna Silmic II's as part of the build.  Most of the wiring is routed under the PCB.
 

 
 
2.  Rear view.  Black=GND, Red=V+, Green=L/R Tube Bias, Blue=L/R MOSFET Bias.  RCAs (Beezar.com) and USB for grubDAC.  Square opening took a long while and was started with a 1/4" hole and squared off with a metal file.
 
 

 
3.  Front View.  Center toggle for power, side toggle for input select (DAC vs RCA).  Both 1/4" and 1/8" TRS plug sockets.  Knob is KILO ML-90-3-6MM from
DigiKey (Part #226-3028-ND).
 
 

 
 
4.  Input select toggle.  Down (RED) for grubDAC, Up (GREEN) for RCA.
 
 

 

 
 
Oh, and did I mention, it sounds amazing!!!  My ears have never been happier especially with my HE-400s.  Current setup:  V+=27 V, 12AE6 Tubes=14 V, MOSFETs=230 mV
 
 
 

 
Wow...look amazing!  Do you mind me asking what the total spend was?

 

[ModMax]

Quote:

 
Wow...look amazing!  Do you mind me asking what the total spend was?

 
Thanks!
 
Not sure... I do plan on putting a final BOM together with all parts I used... I can get back to you then with some up-to-date pricing on the components for this build.

 

[tomb]

Quote:

 
Thanks!
 
Not sure... I do plan on putting a final BOM together with all parts I used... I can get back to you then with some up-to-date pricing on the components for this build.

That's gorgeous!  Great job!!!

 

[jdkJake]

Nice work ModMax.

I especially like the color-coded bias jacks.

 

[scootsit]

When you mentioned biasing the tubes to 15V, you leave the supply voltage at 27, right?

 

[tomb]

Quote:

When you mentioned biasing the tubes to 15V, you leave the supply voltage at 27, right?

Yes.  That seems to be the limit with a typical 24VAC walwart.  You might can get it up to 28V, but at some point, you push the voltage out of regulation and things end up a lot noisier.  This can depend a bit on your house's line voltage, too - is it 120V or close to 115 or 110V?  All of that led us to the decision to just tell everyone to set the power supply at 27VDC.  That takes care of 99% of the situations while guaranteeing that the regulation is still active.
 
As for the tubes at 27VDC, the center point of the signal wave would theoretically still be at 13.5V.  So, biasing at 15V means you would lose the tops of the waves at 27-15V = 12V signals, instead of 13.5V signals.  All that means is that you may not be able to turn the volume up as loud without clipping.  Since with most headphones you never even get close to this point, biasing at 15V has a very small effect.  Yet, the tubes seem to run with less distortion at the higher voltage.

 

[scootsit]

Quote:

Quote:

When you mentioned biasing the tubes to 15V, you leave the supply voltage at 27, right?

Yes.  That seems to be the limit with a typical 24VAC walwart.  You might can get it up to 28V, but at some point, you push the voltage out of regulation and things end up a lot noisier.  This can depend a bit on your house's line voltage, too - is it 120V or close to 115 or 110V?  All of that led us to the decision to just tell everyone to set the power supply at 27VDC.  That takes care of 99% of the situations while guaranteeing that the regulation is still active.
 
As for the tubes at 27VDC, the center point of the signal wave would theoretically still be at 13.5V.  So, biasing at 15V means you would lose the tops of the waves at 27-15V = 12V signals, instead of 13.5V signals.  All that means is that you may not be able to turn the volume up as loud without clipping.  Since with most headphones you never even get close to this point, biasing at 15V has a very small effect.  Yet, the tubes seem to run with less distortion at the higher voltage.

Perfect. I've never even gotten to 12 o'clock on the volume. Thanks, Tomb.