F6 Amplifier

[2 picoDumbs]

I'm not following... what revision would you like to see?

Better spacing of the mosfet (move it to next standard spacing hole) so it doesn't sit right on the edge of the heatsink. It will make labjr and I very happy.

 

[2 picoDumbs]

More to the point, does that lab supply really need a cushion for a hat? Maybe it's running too cool? 🙂

(I know you probably just wanted to shade the meters for a better photo)

I like to sleep with my lab power supply. Hahahaha

 

[labjr]

Better spacing of the mosfet (move it to next standard spacing hole) so it doesn't sit right on the edge of the heatsink. It will make labjr and I very happy.

Outputs should have symmetrical spacing like the F5 Boards. If need be, make the PCB longer to accommodate the transformer.

 

[2 picoDumbs]

Outputs should have symmetrical spacing like the F5 Boards. If need be, make the PCB longer to accommodate the transformer.

That would be the ideal scenario but moving mosfet to next spacing hole would definitely be a huge improvement without any modification to pcb dimensions.

 

[labjr]

It appears they tried to keep the PCB the same length as the F5 Board but needed room for the transformer so the MOSFET was moved over. I say just make the PCB longer and the MOSFETS can be equally spaced.

 

[oreo382]

hi oreo, don´t know about how the cap is involved soundwise, but my F6 seems to developed to a little more bright/right side for me. Wait at least two days. Maybe it´s my woodoo thinking and because of tweaking the speakers a little i lost reference somehow.
for the resistors, i changed the feedback (a second 100 ohm to make it 50 ohm) what made it a bit more foreward but also a little more tight, less lush. i went back to the original.
For the source R´s, i changed R2 from .56 to .47 and one could say it was clearer, but for me the soundstage, depth, was more flattend. So i went back to original too.

i like it better now 🙂

I have been playing around with a sim and found that the most effect on distortion ratio is the capacitor. Specifically reducing the value from 1000 to 220uF increases the 2nd harmonic from -102db to -88db. The 3rd stays the same, I think its a function of the transformer. This is 1 watt into 8 ohms, 1khz sine wave. 1st harmonic at +9.5db. Changing the resistors from 0.56 to 0.47 didn't do anything in that respect. Upping the bias reduces overall distortion across the board. I don't know if -88 from -102 would be audible. I know some people claim more 2nd is agreeable. I simmed my Aleph J and found it has more 2nd than 3rd at 1 watt and I like its sound a lot.
Thats my 2 cents worth.

 

[buzzforb]

I settled at 470uF, organic polymer. Changing the resistors affects harmonics as well as the phase of the harmonics.

 

[2 picoDumbs]

Changing the resistors from 0.56 to 0.47 didn't do anything in that respect. Upping the bias reduces overall distortion across the board. I don't know if -88 from -102 would be audible. I know some people claim more 2nd is agreeable. I simmed my Aleph J and found it has more 2nd than 3rd at 1 watt and I like its sound a lot.
Thats my 2 cents worth.

If changing resistors doesn't affect harmonic distortion profile you must be doing something wrong.

 

[oreo382]

I'm curious what you have found with your sims?

 

[oreo382]

I settled at 470uF, organic polymer. Changing the resistors affects harmonics as well as the phase of the harmonics.

The phase of the 2nd went from 21 to 25 deg. The db level was essentially the same. What have you found with your sim?

 

[2 picoDumbs]

I'm curious what you have found with your sims?

Can you post a picture of your circuit with 0.56 source resistor.

 

[needtubes]

Changing the resistor value does seem to have a less pronounced effect than lowering the cap value.

 

[oreo382]

Here is my sim.

 

[oreo382]

Here is my sim.

And a pdf of the schematic.

 

[2 picoDumbs]

Here is my sim.

That is the circuit, not sim result.

 

[oreo382]

That is the circuit, not sim result.

You asked for the circuit. You can run the sim and see for yourself.

 

[2 picoDumbs]

You asked for the circuit. You can run the sim and see for yourself.

I don't use those jfet models, if you provide the models then yes I can run the sim. Are these models matched for Idss?

 

[2 picoDumbs]

If you're not getting a dominant 2nd harmonic with 0.57 and 0.47 source resistors there is something wrong with the jfet models (most likely not matched)

 

[needtubes]

Which models do you use?

And, speaking of input JFETs, can one use GR grade JFETs on the inputs? I can't seem to find record of this anywhere, but I am sure it must have been discussed...

 

[2 picoDumbs]

Which models do you use?

And, speaking of input JFETs, can one use GR grade JFETs on the inputs? I can't seem to find record of this anywhere, but I am sure it must have been discussed...

I developed my own to get matched Idss devices.