F6 Amplifier - Page 336

buzzforb · 19th December 2012, 05:41 PM

dont you need a cap on secondary connection to prevent DC

DougL · 19th December 2012, 05:54 PM

The FET's are going to be in the Meg Ohm range, and there is no other path through the secondaries. So it isn't going to bother the transformer, if thats your concern.

It may be useful to have the upper JFET with an adjustable bias and AC coupled to the output, but I don't feel its necessary for operation.

flg · 19th December 2012, 06:05 PM

I think R1,2 and 3 and R1,2 and 3 need to be about 1 ohm not 2 ohm! And, that +23v on the top, needs to be about +60V

Of coarse you will need the appropriately sized sinks...
Otherwise, I like it!

DougL · 19th December 2012, 07:10 PM

Fig,
Can you explain why does the Vcc need to be +60?
In the F3, the extra voltage was there to bias the active load.

Doug

buzzforb · 19th December 2012, 07:13 PM

I like your sig and Monty python.

flg · 19th December 2012, 07:40 PM

More Vcc allows for more output voltage. More Iq allows for more output current

Gain might even increase slightly so you have the option of lowering F.B.

DougL · 19th December 2012, 09:10 PM

More is better!

With the Cascode, it shouldn't change much.

Antoinel · 19th December 2012, 09:14 PM

Quote:

Originally Posted by DougL

Fig,
Can you explain why does the Vcc need to be +60?
In the F3, the extra voltage was there to bias the active load.

Doug

DougL: Please refer to the upper cascode circuit. The idle voltage between the drain and gate of IRFP240 is Vdg ~16 Vdc. Suppose that a positive output signal peaks at 11 V. This transient state leaves a dynamic Vdg ~ 5V; which I am tentatively assuming to be needed for the proper operation of this MOSFET. The expected output power under this proposed condition is ~8 W(rms) into 8 Ohms. I reiterated in other words the response of flg above.

Best regards.

DougL · 19th December 2012, 09:56 PM

Antoinel,

Thanks for the explanation.

I am going to have to think about this some more.

Sounds like other topologies are more cascode suitable.

Antoinel · 20th December 2012, 12:29 AM

Quote:

Originally Posted by DougL

Antoinel,

Thanks for the explanation.

I am going to have to think about this some more.

Sounds like other topologies are more cascode suitable.

DougL, you are welcome. Your schematic is a functional design; noting that nobody complained about its topology. Suppose that the power rails you wish to use are +/-30 Vdc [flg] instead of +/-23 Vdc. The output voltage may then swing 36 Vp-p into an 8 Ohm load for an output power of ~20 W(rms). Please recall what Mr. Pass wrote in his F6 article [and his demo on the scope] that 1 Watt can be fully adequate with a sensistive loudspeaker; maybe of 93 dB SPL.

Best regards.

N.B. Will a darlington instead of a MOSFET be suitable? One may be able to getaway with a Vcb ~1.2 Vdc for more output power with lower power rails.

19th December 2012, 05:41 PM	#3351
buzzforb diyAudio Member Join Date: Oct 2010 Location: Burlington, NC	dont you need a cap on secondary connection to prevent DC __________________ \|F6 Kit/Trasnformer GB Sign up sheet Closed,\|Primrose GB Sign Up sheetClick Here ...Shape the sound , Man!

19th December 2012, 05:54 PM	#3352
DougL diyAudio Member Join Date: Feb 2004 Location: Wheaton IL. Blog Entries: 28	The FET's are going to be in the Meg Ohm range, and there is no other path through the secondaries. So it isn't going to bother the transformer, if thats your concern. It may be useful to have the upper JFET with an adjustable bias and AC coupled to the output, but I don't feel its necessary for operation. __________________ Scienta sine ars nihil est - Science without Art is nothing. (Implies the converse as well) Mater tua criceta fuit, et pater tuo redoluit bacarum sambucus

19th December 2012, 06:05 PM	#3353
flg diyAudio Member Join Date: Jul 2005 Location: North East	I think R1,2 and 3 and R1,2 and 3 need to be about 1 ohm not 2 ohm! And, that +23v on the top, needs to be about +60V Of coarse you will need the appropriately sized sinks... Otherwise, I like it! __________________ “Be who you are and say what you feel because those who mind don't matter and those who matter don't mind.” Dr. Seuss

19th December 2012, 07:10 PM	#3354
DougL diyAudio Member Join Date: Feb 2004 Location: Wheaton IL. Blog Entries: 28	Fig, Can you explain why does the Vcc need to be +60? In the F3, the extra voltage was there to bias the active load. Doug __________________ Scienta sine ars nihil est - Science without Art is nothing. (Implies the converse as well) Mater tua criceta fuit, et pater tuo redoluit bacarum sambucus

19th December 2012, 07:13 PM	#3355
buzzforb diyAudio Member Join Date: Oct 2010 Location: Burlington, NC	I like your sig and Monty python. __________________ \|F6 Kit/Trasnformer GB Sign up sheet Closed,\|Primrose GB Sign Up sheetClick Here ...Shape the sound , Man!


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19th December 2012, 07:40 PM	#3356
flg diyAudio Member Join Date: Jul 2005 Location: North East	More Vcc allows for more output voltage. More Iq allows for more output current Gain might even increase slightly so you have the option of lowering F.B. __________________ “Be who you are and say what you feel because those who mind don't matter and those who matter don't mind.” Dr. Seuss

19th December 2012, 09:10 PM	#3357
DougL diyAudio Member Join Date: Feb 2004 Location: Wheaton IL. Blog Entries: 28	More is better! With the Cascode, it shouldn't change much. __________________ Scienta sine ars nihil est - Science without Art is nothing. (Implies the converse as well) Mater tua criceta fuit, et pater tuo redoluit bacarum sambucus

19th December 2012, 09:56 PM	#3359
DougL diyAudio Member Join Date: Feb 2004 Location: Wheaton IL. Blog Entries: 28	Antoinel, Thanks for the explanation. I am going to have to think about this some more. Sounds like other topologies are more cascode suitable. __________________ Scienta sine ars nihil est - Science without Art is nothing. (Implies the converse as well) Mater tua criceta fuit, et pater tuo redoluit bacarum sambucus

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