F-5 boards

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#62
i have the f5 rev 3.0 clone boards for the f5 amp. the store note that one of the differences between the rev 2.0 and 3.0 is the re-labeling of resistors to match schematics and makes reference to the schematic in the f5 turbo article. additionally, at the beginning of this thread there is a link to the v3 schematic (in the f5 turbo article). is the v3 schematic the one on the second page of the article?
thanks
k
 
#72
The challenge will be finding a suitable P channel device that matches an N channel you want to use. Filtering Mouser's offerings to Idss >8 mA and through hole mounting limits you to a dual P channel device that may be a compliment to another Interfet dual N channel.

I understand that the store's P channel pricing can be hard to swallow but you're getting a device that works in this circuit and has an N channel compliment. Not to mention that it still a small portion of the cost of a build if you use a decent power supply and build/buy an enclosure worthy of the amp's sound.

Also try member H_A - I think he may have some original Toshibas. Not sure if they will save you money, but you'll get Idss matched sets.
 
#75
I have a tube gain stage (John Broskie's CCDA) which I'd like to mate to a SS output, making a hybrid. The F5 has a little too much gain for this.

Would it be as simple as altering the feedback network resistors to reduce the gain to say, x3? Or are there some hidden consequences?
 
#78
No, that can make stability worse. When used correctly it can improve stability, but the range of correct is quite small.

More likely, but it's not an area I am any good at, is added capacitance across gate feed to the output device.
There should be others more qualified that could give better ideas on where to locate comp if it is required to restore the stability margins.
 
#79
#80
The 2sk170/j74 GR will require higher value drain load to turn on the output devices.

The Ebay jFETs will need to be measured against the datasheet parameters to prove they are jFETS and to find what Idss and what gm they are.
You may find thay are not jFETs, or are low gm types.
 
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