The F6 Revisited

[birdbox]

"I'm ready for my closeup, Mr. Demille"

That amazing faceplate looks SO great! Love the LED position.
Did you machine that yourself, or is that a laser cutter?
"birdbox likee, birdbox wantee"

 

[jimk04]

Can someone explain the bias setting to me? I am measuring mv between R1 and R*. I am sitting at approx 700mv with about 4 or 5mv of dc offset.

I believe you should be measuring voltage over R2 (0r47). And so the maths would be 0.7v / 0r47 = 1.48A.
But I would be happy for someone much more experienced to confirm. The maths are correct however!

 

[TungstenAudio]

The math is correct. We read the voltage across either R1 or R2, then divide that by the value of the resistor. Simple and based on Ohm’s Law.

 

[Donaldspace]

The machining was done in stages with my CNC mill, a converted Bridgeport type bed-mill. I used a carbide engraving bit with an pencil grinder air spindle and went only a few thousandths of an inch deep to get a nice clean cut through the anodizing. Conveniently, the stop point for the diamond line operation ended with the cutter over the joint where the LED was placed. I spotted there and then drilled on a drill press to finish the LED hole. There is a "freeware" program called Desk Engrave that I used for the text.
Don

 

[zman01]

T.A. I have this HUGE spool from Boeing Surplus. Its AWM 105 degree C 16 Ga. I sometimes use a Sharpie to mark both ends of a wire to identify it when installing the wires. One black ring vs. 2 black rings, etc. I didn't do it on this build since it was a one wire at a time assembly.

I use one trick to change the color of the wire sheath - put a different color of heat shrink tube on it (and gently heat up the tubing so that it shrinks and sticks). Cheap and quite easy to do.

Nice work with the engraving!

 

[gsrchrisu]

My original diy f6 always buzzed so I thought I would try building with new boards a diamond version. It's early but so far not really digging this version. I ordered the jfet board version and might try building those to see if I can hear a difference.

 

[Mikerodrig27]

I am always up for listening impressions and comparisons. I hope you give it a shot!

 

[TungstenAudio]

It would be helpful to know what the source of the buzzing noise is. If it happens to be a power supply issue, then changing to one of the newer F6 versions will not correct this.

 

[poseidonsvoice]

New additions to the NPXP coming soon…

Best,
Anand.

 

[birdbox]

Very nice looking boards. Those red resistors look spiffy! What brand/model are those?

 

[TungstenAudio]

Going with the high nickel CineMags.. Should be fun.

 

[poseidonsvoice]

Very nice looking boards. Those red resistors look spiffy! What brand/model are those?

Those are PRP brand. Only went with them instead of my usual CMF 55 because all the values were available and come 1% stock.

Other resistors in the build include Takman metal film (gate resistors) and Mills (feedback, source) and AMRG (feedback).

The caps are Elna Cerafine.

All transistors are matched on a PeaK DCA75 with the exception to the large TO-247 N-channel on the outputs.

Best,
Anand.

 

[zman01]

Anand,

With reference to the images of your PCB in post # 509, I noticed that for the LEDs, there are 2 green LEDs and one clear LED in each row.

Why choose the clear LED?

 

[TungstenAudio]

I’m betting that clear is actually blue to help get a higher Vgs on the output FETs.

 

[poseidonsvoice]

Anand,

With reference to the images of your PCB in post # 509, I noticed that for the LEDs, there are 2 green LEDs and one clear LED in each row.

Why choose the clear LED?

https://www.diyaudio.com/community/threads/the-f6-revisited.405444/page-24#post-7605416

Tungsten beat me to it! You need an extra volt with FETS I’m using (IXTQ75N10P). As always, the devil is in the details .

Best,
Anand.

 

[TungstenAudio]

This is an F6 Diamond with premium parts!

 

[Vunce]

Sweet F6D boards Anand! 😉

What is the part number for the 3-position screw terminal header you used?

 

[poseidonsvoice]

Well, at the end of the day, it’s the design topology that really counts. Let’s see:

• Austin Buffer
• Cinemag CMOQ transformer (high nickel version)
• Choice of FET (i.e. IXTQ75N10P)
• Amount of Bias (more the better)
• Provision for output degeneration done with Q1, the top FET

The choice of passive parts for me is just eye candy. The constellation of colors looks pretty and it makes amp building less like dialysis.

I do have a QuantAsylum unit that I will press into use to measure the various harmonics. Should be fun.

Thanks again Tungsten for sharing your work.

Best,
Anand.

 

[poseidonsvoice]

Sweet F6D boards Anand! 😉

What is the part number for the 3-position screw terminal header you used?

Thanks Vunce for sending me the boards!

https://www.mouser.com/ProductDetail/651-1988118

Best,
Anand.

 

[Vunce]

No prob and thanks for the link.