F5 power amplifier

[jackinnj]

Folks might be interested in this -- I had some PCB's made to accomodate different JFETs. With a pair each of 2N5460/2N5457 I can get the THD+N% below 1% Idss of the pairs was around 7mA.

 

[6L6]

That's awesome! Will you sell the PCB and parts kits?

 

[jackinnj]

Folks might be interested in this -- I had some PCB's made to accomodate different JFETs. With a pair each of 2N5460/2N5457 I can get the THD+N% below 1% Idss of the pairs was around 7mA.

Shoulda said -- the TDH+N% is well below 0.01%

2SK170 in GR and BL are generally available which is better than the 2n5457 (suddenly in short supply) -- and it may make sense to use 3x matched 2n5460.

 

[noSmoking]

Hi,
I ordered 10 of 2n5460 and see how they sound,Found a test circuit for them.
Cheers,
NS

 

[jackinnj]

2N5460 is DSG, (not that it should matter).

Below is Erno Borbely's "Simple JFET Tester" -- of course it's set up for N-Channel devices, but just change the polarities, and reverse the direction of the current sources (you can use JFETs for the current sources since the diodes are rather hard to get.)

Engaging the first position of the switch gives the pinch-off voltage Vp, read by the volt meter. Shorting the source to gate (ground) gives Idss. Thus you can calculate gm.

 

[noSmoking]

Hi Jackinnj,
Thanks for the pinouts I'll be sure to check those parts when they get here ,I got that circuit from their site, pins are different !
Thanks for the schematic it looks like it's easier to use
NS

 

[jackinnj]

This is with some patience -- a matched pair of 2N5460 and 2N5457 -- the source resistor on the IRFP240 was reduced from 0.68 ohms to 0.40 by placing 1R in parallel. (Every time you change the source resistors, you have to rebias the amplifier). The output transistors in this case are badly matched.

The scale is dBV and the output @2.83V=1.0W=9.0dBV

An externally hosted image should be here but it was not working when we last tested it.

 

[ArthurDK]

HiJack

Do you still sell F4 kits ?

And what about BA-2 front end kits ?

There is allmost nothing listed on your Pass page anymore.

It could be because you dont have any kits anymore, or it could be a fault on the website.

Could you entlighten me ?


Best regards
Arthur.

 

[noSmoking]

Hi JackinNj,
Is that a software FET tester? what interface?
Where can I get one?
My fets are on the way,,,,
I have a bunch of 170's in the gr region and all about 10 sj 74 are BL,Ive been stacking the 170 to a close match,I read that the P really needs to be about a ma or two more than the n do you know ?
Thanks ,
Board or kit news from you?
Cheers,
NoSmoking

An externally hosted image should be here but it was not working when we last tested it.

[/QUOTE]

 

[jackinnj]

Do you still sell F4 kits ?
And what about BA-2 front end kits ?

Nope and nope

But now you know that with a little effort you can substitute for the 2SJ74.

 

[Rush]

Shoulda said -- the TDH+N% is well below 0.01%

2SK170 in GR and BL are generally available which is better than the 2n5457 (suddenly in short supply) -- and it may make sense to use 3x matched 2n5460.

Are you suggesting using 2SK170 GR or BL with a pair or 3 matched 2N5460? I assume you want to equal the idss of the 2SK170 with what ever number of 2N5460 it takes?

Rush

 

[doolav]

Hi, it likely has been discussed here, but searching through about a half of this thread I still cannot find it, so can anybody advise/point to: what has to be changed on cviller's boards (v.2 - not the current one rev.2) in order to build F5 Rev.1?

 

[Zen Mod]

Cviller's Blog

 

[Marra]

Here's the link

http://www.diyaudio.com/forums/blogs/cviller/191-gb-f5-guide-pcb-version-2.html

 

[doolav]

thanks, will try.

 

[jackinnj]

Are you suggesting using 2SK170 GR or BL with a pair or 3 matched 2N5460? I assume you want to equal the idss of the 2SK170 with what ever number of 2N5460 it takes?

Rush

I substituted one 2SK170GR with Idss of 6.1mA, and the THD was equal to the paired 2N5457. Interesting, however, the 2nd harmonic was a bit higher, but the 3rd was lower and the 4th way down in the weeds.

 

[Russellc]

I substituted one 2SK170GR with Idss of 6.1mA, and the THD was equal to the paired 2N5457. Interesting, however, the 2nd harmonic was a bit higher, but the 3rd was lower and the 4th way down in the weeds.

shouldnt hurt, should it? I like a little second harmonic...

Russellc

 

[jackinnj]

Some more numbers -- using a matched J74GR/K170GR the THD% was 0.0018% 1W, 1kHz. With the 2N5460/2N5457 the best that I could do was 0.0029% -- either number is very respectable. The noise of the J74/K170 seemed to be -135dBV just as in the article while the 5460/5457 was -128dBV.

 

[alazira]

My fets are on the way,,,,
I have a bunch of 170's in the gr region and all about 10 sj 74 are BL,Ive been stacking the 170 to a close match,I read that the P really needs to be about a ma or two more than the n do you know ?

I believe you are referring to EUVL's source degeneration matching trick.
http://www.diyaudio.com/forums/atta...48-f5-power-amplifier-input-jfet-variants.pdf
Although I think it would mostly be useful with complementary output mosfets like the Toshiba 2SJ201/2SK1530.

 

[jackinnj]

I believe you are referring to EUVL's source degeneration matching trick.

This is what P3 in the F5-R1 does.

I set up the amplifier bias @1.3A, and output of 2.83V in to 8R and then let the FFT run while adjusting P3. Even with a 25 turn trimpot you find that only a small fraction of a turn will knock the 2nd harmonic down by several dB. As I said previously, be patient, let the beast warm up for a while before making the adjustment --