F2 Initial Listening Impressions

[john-china]

i think the output capacitor connects wrong place , it should touch the joint of 0.33 and 47K resistor

[Vix]

Thanks!

Yes, the output capacitor should connect on the other side of 47k resistor, on the joint with 0.33 ohm. I made a mistake while drawing the line

However, this is minor. What confuses me is the 470k resistor (marked red) I am not sure if it is needed if the mosfet is cascoded, as it is.

As I imagine, I hope this will work as a current amplifier, won't it?

Maybe somebody can clarify this.

Mr. Pass? Grey?

Thanks,

Vix

[stefanobilliani]

Originally posted by Vix

As I imagine, I hope this will work as a current amplifier, won't it?

Vix

My understanding , from some previous building tests , is that the buffer will put the gain of the amplifier at a much high level not suitable for this application, unless you use some ac feedback .

[Vix]

Hi Stefano!

As I understand, the buffer is there only to provide better impedance match, not a gain. Maybe I am wrong, that's why I am asking.

Thanks!

Vix

[Circlomanen]

I think the amp will work properly.
The 440 k resistor is needed to supply biasvoltage to the fet and a small amount of neg feedback at DC to stabilize the circuit.
You can adjust the gain by changing the 1,00 ohm resistor connecting the bottom fet with ground to higher values to decrese the gain and lower values to increse the gain of the amp.
Yes, the amp is a currentamp. It will have roughly the outputZ that you place in parralell with the output.

Mvh, Johannes.

[Circlomanen]

The top Fet should be a N chanel device. Not IRFP 9xxx.

[Circlomanen]

i think the output capacitor connects wrong place , it should touch the joint of 0.33 and 47K resistor

In the above drawing I think the output capacitors are connected too the right place.

[Vix]

Hi

Thanks for the replies!

IRFP9601 is a P channel fet, used as a buffer. The idea is "borrowed" from ZEN V4, except that I chose IRFP9610 instead of ZVP 3310, just because I have it "in stock"

I hope this should work well.

Regards,

Vix

[Vix]

Hi,

I meant IRF9610. Other three Fets are IRFP250N. The scanned schematic is not clear. Sorry.

Thanks,

Vix

[Circlomanen]

I would like to load the inputbuffer with a CCS instead. Any and all noise and hum that appear on the gate of Q1 will be amplified by the amp.

I would also suggest connecting 220 ohm between inputcap and 440 kohm/100kohmpot node.

Just a stabillity thing, it might not be needed but....

Johannes.