F4 questions - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Pass Labs This forum is dedicated to Pass Labs discussion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Thread Tools Search this Thread
Old 2nd May 2011, 11:50 AM   #1
diyAudio Member
Join Date: Mar 2004
Location: At the output stage
Send a message via Yahoo to mr_push_pull
Default F4 questions

Hi everyone,

I'm planning to switch from class D to class A and the F4 is my choice.

Quick q's:

- I'm using 86dB speakers and as per my measurements 30W is enough to reach levels above average but I have to ask: wouldn't the distortion reach inacceptable high levels when nearing max output on peaks?

- what preamp is most recommended? would a stepped transformer mate well with the F4?

Thanks in advance

Last edited by mr_push_pull; 2nd May 2011 at 11:55 AM.
  Reply With Quote
Old 2nd May 2011, 11:57 AM   #2
cjkpkg is offline cjkpkg  United States
diyAudio Member
Join Date: Aug 2008
Location: Roswell GA
I just completed an F4 and have a few comments/pointers:
1. F4 has no voltage gain so you will need a robust preamp with sufficient gain >20 probably. I am running a JFETBOZ and an Aikido both putting out about 15 which will drive the F4 loudly but there could be a little more.
2. My speakers are about 89dB which does not seem to be an issue
3. You may want to consider an F5 which is a slightly cheaper and simpler build - it has a gain of about 15 on its front end and would be happy with a simple preamp.

So far I am really happy with it but I am now going to revisit my preamp strategy...either tweak the JFETBOZ or possibly different input tubes on the aikido.

The Pumpkin Preamp is very highly recommended here especially for the F4. Search this forum for it.
  Reply With Quote
Old 2nd May 2011, 12:04 PM   #3
diyAudio Member
Join Date: Mar 2004
Location: At the output stage
Send a message via Yahoo to mr_push_pull
Thing is that someone has a ready built (not commercial but DIY mind you) on offer and the price is so attractive that I decided to buy it. Not to mention that it saves me all the hassle of sourcing the immense heatsinks, matched transistors etc.

I'm aware that with F4 the gain is 0dB but I want something that is the exact opposite of what I'm using now: brute force instead of complex circuitry, feedback and the like. I'm really not one of those religious guys scared of the mere ideea of feedback, I just want to experiment.
  Reply With Quote


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
scaling down F4 kalinowski Pass Labs 5 3rd March 2010 10:00 PM
Some beginner questions about B3 preamp and F4 power amp njepitt Pass Labs 32 28th June 2009 09:55 PM
first watt f4 help me!!!! mosfet1 Pass Labs 2 18th May 2008 06:44 AM
F4 and DAC? Flecko Pass Labs 9 23rd February 2008 09:57 PM
Possible F4 Heatsink Apex Jr Pass Labs 0 4th May 2007 04:21 PM

New To Site? Need Help?

All times are GMT. The time now is 10:24 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2