F5 power amplifier

[eboleyn]

Originally Posted by Nelson Pass

...

Also, the use of different outputs, in your case, the IRFP9240 will
substantially alter the tone. Again, you may prefer it - some people do.

Thanks for the heads-up on this point!

I found the comments on the forum about output transistor choice and distortion. I'm a detail-nut (that's why I want an F5 derivative in the first place), so I'll probably try out either the Fairchild or Toshiba parts mentioned.

[lhquam]

Originally Posted by Nelson Pass

Hasn't this been around?

I finally added P3 as shown in post #10856 to my F5 channels which use Cviller V1.1 boards and matched Toshiba 2SK1530 and 2SJ201 MOSFETs. Left channel THD at 1 watt was reduced from .0077% to .0015%. Right channel THD at 1 watt was reduced from .018% to .0012%. WOW, what an improvement with such a small modification!

[Bksabath]

Hi Ihquam
Sorry if out of topic
Are screen shot from Virtinis + Audiohile 192?
Tried mine again and got similar peack on 200hZ but at -80dB (left most picture)
Made shure conections are fine 3 4 times most probably I got noise going in troug mother board.

I tried the P3 a while ago and burnt a cople of Jfets but now seiing this I worth having a second pop at it
Tanks for posting

[lhquam]

Bksabath:

The screen shots are from Sillanumsoft Visual Analyser with the M-Audio AP-192 sound card.

There should be be problem with adding P3, but be sure to turn P1 and P2 counter-clockwise to reduce the bias currents before turning on the amplifier. Make sure that P3 is adjusted at mid-position of 100 ohms. Then turn on the amplifier and adjust P1 and P2 as described in the "F5 Manual". Finally, adjust P3 to minimise distortion.

[Blues]

Originally Posted by lhquam

I finally added P3 as shown in post #10856 to my F5 channels which use Cviller V1.1 boards and matched Toshiba 2SK1530 and 2SJ201 MOSFETs. Left channel THD at 1 watt was reduced from .0077% to .0015%. Right channel THD at 1 watt was reduced from .018% to .0012%. WOW, what an improvement with such a small modification!

I see you're giving those mosfets a nice workout...thanks for posting your test results. That's a great objective improvement for a simple add-on...any before and after subjective impressions?

[Nelson Pass]

Originally Posted by lhquam

WOW, what an improvement with such a small modification!

Did it sound better?

[lhquam]

[QUOTE=Nelson Pass;2747623]Did it sound better?

[/QUOTE

It sounded very good before the mods. I believe it sounds better, the 2 channels being much better matched. Without doing a rigorous, blind A/B test, I cannot be sure.

[formula 22]

Hello all!
Since the big topic please give makes the final schematics and the PCB for this audio amplifier.
Thanks

[Bksabath]

Tanks wery much for chance to spare you comments such as go and read the tread from the beginning.

10856 has the SCH with P3
That is the new flawor and big bomb drop (in a good sense) Papa give us.
http://www.diyaudio.com/forums/attac...-f5-r1-sch.jpg

AS PCB goes not made so far?

[Botte]

Originally Posted by Nelson Pass

Did it sound better?

I added P3 to my F5’s and could dial in the null very easily. I didn’t like it that way though, so I made second harmonic dominant by 10 dB, its sounded better this way to me though I may go higher. The big change for me was the ability to get the phase of the second harmonic in phase with the test tone. The imaging seams more stable after the modification. It is fun to have a new tool, I find myself testing all my amps to look at the spectrum. Just a note: The BA-3 has much higher distortion and sounds great, so there is more to it than just the numbers.