F5 power amplifier - Page 781 - 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 25th April 2010, 06:07 PM   #7801
diyAudio Member
 
Join Date: Jan 2010
Default Opinions sought

Let's see if there are pitfalls I need to watch out for.

I have been assembling the parts to build Nelson's F5. The intended use is for direct driving the foil ribbons (24db L-R electronic crossover) on a pair of Magnapan 2.6's. I do not have the specifications for the driver but I think it looks something like this...

3.2 Ohms impedance. Essentially resistive.
750 Hz ~ 22kHz frequency range.
91 ~ 97 db efficiency (wild guess)

I feel comfortable that the rail voltages in an F5 is plenty for this driver. My only concern is for turn on/ turn off thumps and a friendly DC offset behavior. With the experience you have had with this amplifier I would like to ask...

1. Should I plan on an output relay for on/off transient protection?
2. Is the typical DC offset behavior of an F5 compatible with these ribbons?
  Reply With Quote
Old 29th April 2010, 08:01 PM   #7802
alazira is offline alazira  United States
diyAudio Member
 
alazira's Avatar
 
Join Date: Jun 2007
Location: Las Vegas
Blog Entries: 1
Quote:
Originally Posted by Macronaut View Post
My only concern is for turn on/ turn off thumps and a friendly DC offset behavior. With the experience you have had with this amplifier I would like to ask...

1. Should I plan on an output relay for on/off transient protection?
Hi Macronaut,

With the recommended power supply using the CL-60's, I've had absolutely no power-on thump. Dead quiet from the speakers. Others have reported the same.
  Reply With Quote
Old 29th April 2010, 08:57 PM   #7803
diyAudio Member
 
carlomar's Avatar
 
Join Date: Dec 2004
Location: lisbon
Quote:
Originally Posted by alazira View Post
Hi Macronaut,

With the recommended power supply using the CL-60's, I've had absolutely no power-on thump. Dead quiet from the speakers. Others have reported the same.
Thats right, and i dont have CL60.
  Reply With Quote
Old 29th April 2010, 09:10 PM   #7804
diyAudio Member
 
Join Date: Oct 2004
Default Blown fuse and mosfets

Wonder if any of you can provide any insight into the problem I have.

I got one channel up and running without a problem - the voltages across the output resistors are stable and the dc offset is around 22mV.

However when I was biasing the other channel this is what happened -
I got the v across the output resistors to about .575 volts. However the DC was around 200 mV. While I was pondering my next step suddenly the fuse blew. I was using a 3A fast fuse.
I replaced this with a 2A slow fuse(all I had), disconnected the other working channel to reduce the load, dialed the trim pots down a bit and turned it on again. This time there was crackling and smoke on the board before the fuse blew again.

I took the board down and went over it piece by piece. Two things to note. I could not find any trace of whatever burned on the board not even a smell of it and I am positive the smoke emanated from the board somewhere. More importantly I determined that both output mosfets were blown(dead short across the legs).

Now I have new transistors on the board and have checked everything else a few times over and compared it with the working channel and am ready to try again but I hesitate....

What could've caused these things to blow and why didn't the limiting circuit stop it? Is there anything in particular that I should double-check again that would have cause this?

Thanks
  Reply With Quote
Old 29th April 2010, 10:25 PM   #7805
diyAudio Member
 
Join Date: Jan 2010
Quote:
Originally Posted by alazira View Post
Hi Macronaut,

With the recommended power supply using the CL-60's, I've had absolutely no power-on thump. Dead quiet from the speakers. Others have reported the same.
Thank you, that is comforting to read. OK, I'll just use an appropriate fuse on the driver. Perhaps if I get really comfortable I'll try it without to see if there is any merit in that.
  Reply With Quote
Old 29th April 2010, 10:54 PM   #7806
awc is offline awc  New Zealand
diyAudio Member
 
Join Date: Aug 2009
1. Should I plan on an output relay for on/off transient protection?
[/QUOTE]
Yes, even if you only use 2 on / off switches on you speaker outs, leave in off position till amps powered on, (there are worse things than thumps), use cheep speakers first, any ohms or wattage rating (PC speakers) your just listening for any unwanted noises before hooking up good speakers.
  Reply With Quote
Old 29th April 2010, 11:03 PM   #7807
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
Seems dutch Amplimo got the message....they now sell this thermistor/fuse kit along with their toroids

Inrush Current Protection 500VA 230V
__________________
sometimes we know very little, and sometimes we know too much
  Reply With Quote
Old 29th April 2010, 11:04 PM   #7808
udailey is offline udailey  United States
diyAudio Member
 
Join Date: Mar 2008
The relay could be made to take care of DC offset if its high enough to trip your circuit but transients are going to come through before the relay opens. Thats my guess, could be wrong.
Uriah
__________________
purchase LDRs anytime Also try my Resistor Replacers or LDR based Input Selector Email me. diyldr@gmail.com
  Reply With Quote
Old 29th April 2010, 11:07 PM   #7809
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Quote:
Originally Posted by udailey View Post
The relay could be made to take care of DC offset if its high enough to trip your circuit but transients are going to come through before the relay opens. Thats my guess, could be wrong.
Uriah
I use a PIC micro to look for DC conditions.
If it sees DC for more than 500mS it trips teh relay.
It also holds off the output to the speakers for 3 seconds on power up.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 30th April 2010, 03:24 PM   #7810
Renron is offline Renron  United States
diyAudio Member
 
Renron's Avatar
 
Join Date: Jan 2007
Location: Sacramento
I've been turning on my F5 in the morning, off when I go to bed for about 5 weeks now. Just to "burn in" the components and let them settle to their stabilized values. Never had any turn-on thump, ever!
Interesting note; when I turn off the amp, with no speakers connected to the outputs the DCV offset jumps to .620 then settles down to 0 very quickly. Hmmmmm. When speakers are connected, no turn off thump or cone excursion noticed.
I disconnected the speaker output cables and connected the multimeters (2) to ascertain how far things have drifted since the original build settings. Very happy to say that one channel's bias V was off by .11V and the other was even less. Now both set at 6.00V, drifts ~.03V. DC offset had wandered on one channel to .014 , very tolorable IMO. Reset to .000 - .002 (drifts a little) , put the screws in the top and closed her up!
Thank you Papa for a wonderful amp. I couldn't be happier.

I had previously taken some temperature measurements at idle after a warm up of a few hours, this was with Silpads as insulators. I ordered the correct size Mica insulators and swapped the Silpads for the Mica a few days ago. Let it go through about 10 thermal cycles to "set" the thermal grease and checked the temps at Idle last night. The difference? Not too much surprisingly, the house is set at 66*F so that did not change. Which is hotter running / more efficient? The Mica by about 1.5*F, taken at the hottest spot on the exterior of the case with an infrared temperature gun. Big Whoop. Both work very well. Using the giant Conrad heatsinks, I can leave my hand on the amp all day and it's very comfortable, never hot.
Very happy F5 owner.
Thanks to Steve Eddy, who diagnosed my shorted capacitor problem (and others),
Thanks to Christian (Cviller) for selling me enough beautiful boards to finally get it right. and offering to help me in person.

Mostly, Thanks to Nelson Pass for his extreme graciousness and love of quality audio to share the design of his amp(s) (and others components) with us. (For FREE!!!)

Most grateful,
Ron
__________________
"If it doesn't work properly, hope it catches on fire"- Nelson Pass @ BA3
"I fired up the prototype. Literally." The Prophet Pass.
  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 10:49 PM
Power transformers versus amplifier output power..what is your option? destroyer X Solid State 38 9th May 2009 05:23 PM
McIntosh Power Amplifier Power Guard johnnyrt Solid State 2 23rd August 2007 10:22 PM
Output power for a power amplifier Progg70 Solid State 33 10th September 2006 08:44 AM
Amplifier 3000 Wats Rms Power + Smps Higcht Power Bestiality MARAVILLASAUDIO Class D 1 5th November 2004 04:06 PM


New To Site? Need Help?

All times are GMT. The time now is 03:01 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