Total Domination VFET (TDV) Amp (using 2SK2087C)

[codyt]

Congrats! Just make sure to keep an eye on R3. If you can measure across it, might be worth calculating how much it’s dissipating. Want to say it’s 3-4W

 

[von Ah]

R3, 1R: One side is 1.62V, other is 1.48V

 

[von Ah]

2.7 and 2.6 A across R3, respectively to previous voltages.
So… 4.4 and 3.9 Watts? I need to research Ohm’s Law.
While I’m educating myself, test speakers are singing sweetly! Sounds LOVELY. And it has an absolutely pitch black background of nothingness.

After about an hour of on-time, it’s warm, but not F5 warm. Definitely under 50C on the sinks.

I’m enthralled! It’s my newest and simplest amp! Thank you all!

 

[codyt]

Your calculations sound right to me.

Well done on the build!

 

[von Ah]

Thanks, Cody!

I have it playing in the main system now, with ACP+ and Manzanita speakers. Good times. Cheers.

 

[ra7]

R3, 1R: One side is 1.62V, other is 1.48V

You want to measure across R3. Are thise measurements on two legs of R3 with other side of multimeter at ground? And what about R4?

 

[von Ah]

Those were measured across R3. ”Side” in this case meant the R3 on one side of the amplifier.

 

[e_fortier]

R3, 1R: One side is 1.62V, other is 1.48V

If this is directly across R3 and it’s a 1 ohm then 1.62V - 1.48V = 0.14V therefore 140mA bias going through 2SK2087C

Something is odd since you also said that you’re getting 1.1Vdc across the inductor. These 159ZC are 0.7 ohm therefore the current going through them to generate 1.1Vdc would be 1.1/0.7 ~ 1.6A

For now enjoy the music but later on I’d be curious to know your bias...😀

 

[von Ah]

As I tried to describe before, my measurements were done across the two pins of R3. DVM leads only on the legs of one R3 resistor. I measured across R3 on one board, then R3 on the other board. I measured for voltage first, then current. It seems I’m in the ballpark because the amp was warm and playing music nicely. I will repeat my measurements tomorrow after the amp has warmed up again.

 

[e_fortier]

I think I got it, when you wrote “one side is 1.62 the other is 1.48” you meant your 2 voltages across each R3 for your 2 channels and NOT your DVM leads for 1 channel. Sorry if I misunderstood, looks like you’re all set 👍

 

[von Ah]

One R3 had 1.62V going through it. The other R3 (other amplifier channel entirely) had 1.48V going through it. Two separate measurements for two different resistors.

😆 “…Third base.”

 

[Zen Mod]

change that output cap, if you have offset

 

[von Ah]

No offset to speak of. No power on or off thump, either.

 

[ra7]

R4 open?

 

[von Ah]

Yes, because there is no R4 printed on my CYOF boards.

J1 is jumpered for self-bias. I have the speaker terminal resistor on the back of the board.

 

[ra7]

Okay, so if you measured 1.6V across 1R then the bias is 1.6A. You could go higher if your heatsinks allow. How does it sound?

 

[von Ah]

It sounds FANTASTIC! Thank you for bringing the design to the forum!

My 3U300 heatsinks have 53C at the hottest part of each sink. Everything works wonderfully, so I don't think I will press my luck just yet.

I could use a little more gain with it in my system, but I expect that is just part of the source follower topology. It won't get very loud, but it has just enough grunt to satisfy my listening environment.

 

[e_fortier]

What are you driving your amp with?

 

[von Ah]

What are you driving your amp with?

ACP+, Topping E30 DAC.

 

[ra7]

Glad to hear you are enjoying it. Yeah, the gain is slightly less than 1, so the preamp has to provide all of it. I also think it sounds better after temps have stabilized… about an hour.