F5 power amplifier

[TimS]

Originally posted by jameshillj


Anybody, looking for a 15H (not mH!)/ 350mA+/ <15R choke for the L-C supply - any ideas?

What is its rated voltage? It sounds like its for a valve B+ supply filter.

[TimS]

Originally posted by jameshillj
Yeah Tim,
Have rewired the 701s (Z=63R) and using an "unbal - bal" adapter that also includes the adjustable series resistors (varies with different amps unfortunately).
[Amazing sound connected directly to o/p of F3 (as unbal)]

Estimate about 350mA thru the 610/9610 fets, and about 5mA thru the Jfets.

Expecting some pcbs for a mini Babblefish J (from ZM) as an upgrade to Marchello Originals [also approx +/- 15v rails].

... Thanks.

Anybody, looking for a 15H (not mH!)/ 350mA+/ <15R choke for the L-C supply - any ideas?

Here is your amp, almost to your specs, I had to run the final bias a little higher (477mA) so it could drive its own feedback resistors and still keep the distortion low.

Now where shall I send the bill...

Cheers

Tim

[jameshillj]

Thanks Tim,
That sim program of yours saves an enormous amount of time, particularly with such an intriguing small "bunch o' bits"!

So, Rails of +/- 12volts, about 500 mA X 2 per channel = 24VA per channel - nice and solid, eh - no "toys"!
It will be interesting to hear how the different supplies effect the sound.

Should all those common connected Jfets have small isolation gate resistors?

Chokes: Most of the large size commercial ones that I've found are higher voltage units made for valve gear and the usual "large L, small C" designs have been for preamps and such - this load [1/2A X 2] doesn't fit into this category at all.
Is there such a thing as an "L multiplier"?!

About the bill - what do you need that we may have over here? [Apart from the AudioX which isn't available here, yet!]

Appreciate your time & effort - thanks again.

[Nicola]

Originally posted by Nelson Pass
If you Google "Fistwatt", you will get 9 references.

Argh, Freud you know.... but luckily i'm not the only one as googling FistWatt proves it...... ;-) Ant most of them are about YOUR product....

Anyway, did you get a free lunch with all of those more ??
There must be a price to it.

F1 rocks the bottom part of the sound spectrum, how does F5 compare to ? F3 is a close tube like sound, is F5 more classic Class A or more Class A like F3. Regards

[jacco vermeulen]

Originally posted by Nicola
Argh, Freud you know

Nicola,

speaking of Ziggy's-Mund, did you know your posts always come in matching pairs, and you are the Two-and-Only with this reaccuring phenomenon ?

[Nicola]

Originally posted by jacco vermeulen


Nicola,

speaking of Ziggy's-Mund, did you know your posts always come in matching pairs, and you are the Two-and-Only with this reaccuring phenomenon ?

Matching pairs but unfortunately not matched pairs ? Would have been rather nice in such forum. Wwell schizophrenia does not help. ;-). Seriously, never noted this phenomenon, unless that occurs only on some computers..... argh,,,,, (how many pairs of this now ??)

Regards

[Nelson Pass]

Originally posted by Nicola
is F5 more classic Class A or more Class A like F3. Regards

I would say not quite either.

[Brett]

Originally posted by TimS


Ma get me my gun..

Y'see, I'd only just finished watching the NZ movie masterpiece "The Devil Made Me Do It".

[TimS]

Originally posted by jameshillj
Thanks Tim,
That sim program of yours saves an enormous amount of time, particularly with such an intriguing small "bunch o' bits"!

So, Rails of +/- 12volts, about 500 mA X 2 per channel = 24VA per channel - nice and solid, eh - no "toys"!
It will be interesting to hear how the different supplies effect the sound.

Should all those common connected Jfets have small isolation gate resistors?

Chokes: Most of the large size commercial ones that I've found are higher voltage units made for valve gear and the usual "large L, small C" designs have been for preamps and such - this load [1/2A X 2] doesn't fit into this category at all.
Is there such a thing as an "L multiplier"?!

About the bill - what do you need that we may have over here? [Apart from the AudioX which isn't available here, yet!]

Appreciate your time & effort - thanks again.

You can add the small gate isolation resistor if you want.

Just a Biasing and Testing notes:
Test and bias each side with the the 15R resistors disconnected. when the sides are biased matched and tested then connect the 15R resistors.

You will have to tweak the biasing because your JFETs will be different from my sim JFETs. Make R134 R148 R102 R139 a 1k resistor in parallel with a 1K trim pot + 4k7 resistor.

Make sure the bias currents are identical between the left and right sides before connecting the 15R resistors.

Try to match the left to right sides of the amp as well as the top to bottom.

Don't worry about the the supply voltage will not effect the bias currents too much.

This amp is -3dB at 1MHz so be careful with your circuit layout and shielding.

If you want to change the gain, change R137 and R131. The circuit gain is (R150+R136)/R137.

[/NOTE]

If you could help me find some JFETs it would be much appreciated.

Cheers

Tim

[Tea-Bag]

I completed the AX article. I loved the intro about gates and drains and water pipe references.

I suspect the fistwhat F5 will become a very popular DIY project.
It's got a small parts count, less power fets, and reasonable gain and output. It's not as strange by design as the others IMO. The 25W RMS makes it a popular replacement for the GainClone crowd, assuming the sound is anything like the F4 from reviews.

If Nelson sticks to his word (or my interpretation of it), than the next few are repeats with more power as monoblock projects, and the cheapskates may be left behind, or at least listening in mono.