F5 power amplifier - Page 1021 - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

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
Reply
 
Thread Tools Search this Thread
Old 31st January 2011, 06:22 PM   #10201
anilva is offline anilva  India
diyAudio Member
 
Join Date: Mar 2004
Location: Bangalore
Quote:
Originally Posted by alazira View Post
Hi,
If you are planning on doing the 5ohm degeneration trick you need:
1) N-P matched mosfets for each channel.
2) 2SJ74 with an Idss about 1mA more than 2SK170
3) either add 5ohm resistor between the 2SJ74 source pin and the feedback node, or replace R with 15ohm and feedback of 75ohm.

All three steps are required.
I built a single ended F5 as above with one pair of Toshibas. I set the bias level much lower than irfs as I was not sure what is the recommended bias level. Any recommendations on what should be the bias level with Toshibas? My power rail is standard 24v.

Thanks.
__________________
DIY F5, F5T, F6, Aleph J, Fostex 206 based BLH, Altec Onken with 515B LF & 288H HF, Technics SP10 MKII & EMT938 turntables
  Reply With Quote
Old 31st January 2011, 06:50 PM   #10202
cviller is offline cviller  Denmark
diyAudio Member
 
cviller's Avatar
 
Join Date: Dec 2005
Location: Copenhagen
Blog Entries: 2
Quote:
Originally Posted by Marra View Post
Thanks for the responses.
I adjusted P1 almost fully upwards without any voltage reading across the source resistor; P2 slowly raised the voltage upwards. The right channel when connected with the left disconnected blew the fuse.
That is a sure way to burn the circuit - good thing you were saved by the fuse. Follow Zen Mods instructions and you'll get it right.
  Reply With Quote
Old 31st January 2011, 06:58 PM   #10203
diyAudio Member
 
bobodioulasso's Avatar
 
Join Date: May 2008
Quote:
I built a single ended F5 as above with one pair of Toshibas. I set the bias level much lower than irfs as I was not sure what is the recommended bias level. Any recommendations on what should be the bias level with Toshibas? My power rail is standard 24v.
Same as IRF
  Reply With Quote
Old 31st January 2011, 07:07 PM   #10204
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by anilva View Post
Just to clarify, I am asking if a 1uf mkp is a good capacitor value to block dc input to the f5. I am assuming 101k as the 'R' value of the input. I am not sure if 1/(2*pi*r*c) is the right way to calculate the high pass frequency for this setup.

TIA.
that's the correct formula.
I think 101k is the input impedance.
If you use 1uF (not 1uf) and 101k then F-3dB should be ~1.6Hz
The F-1dB should be ~3Hz. This allows the DC coupled amplifier to reproduce all the audio signal from 20Hz and up.
__________________
regards Andrew T.
  Reply With Quote
Old 1st February 2011, 04:22 AM   #10205
lhquam is offline lhquam  United States
diyAudio Member
 
Join Date: Mar 2010
Location: Olalla, Oregon: Land of the 100 Valleys
Default F5 cooling borrowing from Hafler DH500

Here is my new stereo F5 build, using a single HeatSinkUSA E007, cut in half and reassembled to make a heat tunnel. Airflow is provided by a Noctua NF-S12-B fan shown in the images. With this arrangement the heatsink temperature rise is only 30 degrees F (17C) with 12 volts to the fan. The MOSFETS are mounted with 1 mil thick mica and Thermalcote.

Since these fans are so quiet, especially at lower RPMs, it seems obvious to me that higher wattage class A designs should take advantage to the 3X increase of wattage for the same heatsink by using airflow from a quiet fans.

BTW: With the addition of some insulated mountings, the 2 heatsinks can be electrically isolated from each other and ground, if you are inclined to mount your MOSFETS without any insulators.
Attached Images
File Type: jpg IMG_0934-cs.JPG (240.6 KB, 1402 views)
File Type: jpg IMG_0939-cs.JPG (184.1 KB, 1366 views)
File Type: jpg IMG_0937-cs.JPG (114.4 KB, 1316 views)
  Reply With Quote
Old 1st February 2011, 04:43 AM   #10206
lhquam is offline lhquam  United States
diyAudio Member
 
Join Date: Mar 2010
Location: Olalla, Oregon: Land of the 100 Valleys
Default Extra connections for bias adjustment

After smoking one of my F5 channels while performing bias adjustments, I decided to add some additional connections to the cviller PCB to make it easier and safer to make the adjustments. For each channel, five wires of a CAT5 cable were connected to the ends of R11, R12, and the output, each thru a 1k ohm resistor to minimize any effects do to the wiring. A 6th CAT5 wire is connected to ground. The 6 pairs from the two CAT5 cables are connected to a 2 pole x 6 position rotory switch whose 2 outputs are connected to a multimeter for bias adjustment.
Attached Images
File Type: jpg IMG_0946-cs.JPG (214.8 KB, 1898 views)
  Reply With Quote
Old 1st February 2011, 06:06 AM   #10207
lhquam is offline lhquam  United States
diyAudio Member
 
Join Date: Mar 2010
Location: Olalla, Oregon: Land of the 100 Valleys
Default F5 listening impressions

The last amp I built was a Hafler DH500 (250W/channel) in about 1986). I have loved its sound until I finished my Pass F5 yesterday and started to hear the differences. The DH500 at 1 watt listening levels is probably at its worst operating level for crossover distortion. The F5 definitely sounds more transparent, especially at the higher frequencies, where Miles Davis's Will O' the Wisp in Sketches of Spain could be very innoying.

One surprise was that low frequency (bass) output of the F5 appears to be higher than from the DH500. Hard to explain. Is this a damping factor issue?.
  Reply With Quote
Old 1st February 2011, 09:55 AM   #10208
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by lhquam View Post
One surprise was that low frequency (bass) output of the F5 appears to be higher than from the DH500. Hard to explain. Is this a damping factor issue?.
The F5 is DC coupled.
You have effectively removed two high pass filters from your system. You are now hearing the difference between a very slightly rolled off bass with a medium rolled off bass. And this with the same speakers that cannot reproduce those very low bass frequencies.
__________________
regards Andrew T.
  Reply With Quote
Old 1st February 2011, 10:08 AM   #10209
Marra is offline Marra  United Kingdom
diyAudio Member
 
Join Date: Nov 2009
Location: Near Lincoln
Aaargh; frustration riegns !. I think I must be one step back from a caveman. Connected up the right channel of my F5 first through the bulb and then without. This time the fuse did not blow. Again as per the left side adjusting P1 does not result in any voltage reading across the source resistor nor on the output whereas P2 I get an increase in mv reading across the output but no reading on the source resistor?? The amp has been powered up for 30 mins without the fuse blowing and no smoke. I connected the left channel, fuse did not blow but niether trimmer makes any adjustment.
  Reply With Quote
Old 1st February 2011, 10:30 AM   #10210
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
measure the voltage across the trimmer.
this voltage should change as you adjust the trimmer.
The group of resistors pass a current to the jFET.
This is nearly a constant current.
If the trimmer is set to 0r0 then Vrt=0v0
If the trimmer is set to 10r and 8mA flows to the jFET then Vrt~80mVdc ~0.080Vdc

Check the voltages across all the trimmers.

Check the voltages across the jFET source resistors.

Mark these on a schematic and post a pic of the marked up schematic.
__________________
regards Andrew T.
  Reply With Quote

Reply


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
Rockford Fosgate Power 20001 bd amplifier power rating?? pachoorion Car Audio 8 8th May 2011 11:49 PM
Power transformers versus amplifier output power..what is your option? destroyer X Solid State 38 9th May 2009 06:23 PM
McIntosh Power Amplifier Power Guard johnnyrt Solid State 2 23rd August 2007 11:22 PM
Output power for a power amplifier Progg70 Solid State 33 10th September 2006 09:44 AM
Amplifier 3000 Wats Rms Power + Smps Higcht Power Bestiality MARAVILLASAUDIO Class D 1 5th November 2004 05:06 PM


New To Site? Need Help?

All times are GMT. The time now is 03:08 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2