F6 Amplifier

[palstanturhin]

F6 with a diamond BJT input buffer:

Black is the diamond buffer.
Red was the J-FET buffer.

I probably need to design a PCB for the diamond buffer version also...

BC546/556 was used in the diamond.

 

[palstanturhin]

Interestingly the cause of the high 3rd harmonic is the Hitachis.
So back to the IRFs then.

And now I got this:

...which I ADORE!

 

[Nelson Pass]

F6 with a diamond BJT input buffer

That there is only 1 dB difference is probably due to the resistance of the
primary winding.

 

[Soundhappy]

...which I ADORE!

Bravo

 

[aspringv]

Nearly there - F6 using cree SiC fets

Nearly there, Just a bit of chassis work and testing to go.

Twitchy to set the bias/offset. Wish I'd used multi turn trimpots now! currently biased up to about 1.6A, and the heatsinks are apparently at about 55C

Once I have it roughly set up I'll try an run it through a basic pc THD test.

 

[Zen Mod]

Geezers are havin' that sort of mileage , making them experienced enough to fiddle with standard trimpots

for us Greenhorns , multiturn ones are necessity , save us from palpitation and stress

 

[aspringv]

And I couldn't agree more; now I've made that mistake! Unfortunately, I'm stuck with them now, so I guess I'll be putting some mental miles on the clock and enduring (?) the stress.

 

[anilva]

I just noticed after many months of use of my F6, that it has the tendency for the output to swing little bit on offset, making my full ranger to go back in terms of cone movement and then settle back. Is it normal for F6 to behave like this, or did my power supply alter it's behavior off-late. Don't know what it is because, I did not notice before.

Thanks in advance.

 

[Zen Mod]

most probably mains fluctuation

 

[wdecho]

I have all my parts to start my point to point F6 build but I need to know where to set the bias and offset trim pots on startup before I install them on a board. This thread is quite large now and the information is hard find.

David

 

[Zen Mod]

set them to zero volts between wiper and end which is on JFet/Mosfet source

 

[wdecho]

I should be safe leaving them around half way 2500 ohms before starting up the amp?

 

[6L6]

What ZM said is best, but what you suggest will work, start with one channel at a time (Disconnect PSU from one channel), have a meter across a source resistor and don't be surprised if you need to turn it down quickly.

Bit it also depends on the Vgs of your specific Mosfet and the Zener voltage... I used 5.1V in the beginning and couldn't get enough bias, and then replaced them with 9.1V zener, and had tons. YMMV.

 

[wdecho]

Thanks, Zen and 6L6. I took your advice and bought 9.1 zeners. I just did not know if I should start the bias pot at a small resistance and bring it up slowly to begin with or start with a high resistance and bring it down.

David

 

[palstanturhin]

Hey!

Im going to make a factory order of my PCB!

Has also the possibility to use the Diamond Buffer in it.

Cost depends on the quantity but I am aiming to below 10$/pc.

Lets not pollute this thread, so better throw a private message if interested!

Thanks!

 

[CeeVee]

Hey!

Im going to make a factory order of my PCB!

Has also the possibility to use the Diamond Buffer in it.

Cost depends on the quantity but I am aiming to below 10$/pc.

Lets not pollute this thread, so better throw a private message if interested!

Thanks!

Where is this schematic with diamond buffer ?

 

[palstanturhin]

Where is this schematic with diamond buffer ?

You find the original diyAudio F6 circuit from http://www.diyaudio.com/forums/pass-labs/258613-diyaudio-firstwatt-f6.html thread.

On my PCB you have the option to replace the JFET buffer with a simple diamond buffer.
I used these components in my prototype (because that was what I had on hand), but feel free to experiment...

C3 was 1uF 50V X7R MLCC in the proto...

 

[6L6]

A preview of the diyAudio F6 build guide can be found here -- http://www.diyaudio.com/forums/pass-labs/258613-diyaudio-firstwatt-f6-10.html#post4341419

 

[tordnilsson]

What voltage rating for caps C1 & C2 ?

 

[6L6]

25V or more.