Rockford Fosgate Power 650 - diyAudio
Go Back   Home > Forums > General Interest > Car Audio

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 29th January 2013, 02:49 PM   #1
shawnk is offline shawnk  United States
diyAudio Member
 
Join Date: Dec 2009
Default Rockford Fosgate Power 650

I've got another of these 650's here. I'm having issues with the bias/feedback circuit for the the "low frequency" channels (orange/black & yellow brown)

This amp has previously been worked on before and D41D8 + D40D8 have been replaced with 2n6491 + 2n6488 (installed by shifting the transistor over one slot and using a jumper for the emitter)

There were a lot of issues with these two channels, and I have already replaced the majority of the components for them. ie, output fets, drivers biasing pots, several resistors, both op amps, and all zeners.

I'm getting ~ -1.5v dc on the outputs for these two channels and I just can't seem to track it down. This is with the bias pot at minimum (fully counter clockwise), but I can actually get rid of the dc voltage on the outputs by adjusting the bias The problem with this however, is that the output fets are heating up excessively. I'm obviously missing something, but like I've said I just can't track it down. I'm wondering if the 2n6491 + 2n6488 are causing more problems than not?

Thanks in advance

Last edited by shawnk; 29th January 2013 at 02:51 PM.
  Reply With Quote
Old 29th January 2013, 04:13 PM   #2
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Post the voltage on the op-amp for those channels.
  Reply With Quote
Old 29th January 2013, 04:39 PM   #3
shawnk is offline shawnk  United States
diyAudio Member
 
Join Date: Dec 2009
Hi Perry,

These are the two op-amps for the feedback circuit (I hope that's what you're looking for?)

Op-amp 1 (blue/white & Orange/black)

Pin
1) .029
2) -.066
3) 0
4) -17.6
5) 0
6) -.055
7) -.061
8) 18.2

Op-amp 2 (gray/green & yellow brown)

1) .012
2) -.068
3) 0
4) -17.8
5) 0
6) 0
7) -3.4
8) 18.4

Please note that currently there are no output fets installed for one of the low side channels (yellow/brown)

Thanks
  Reply With Quote
Old 29th January 2013, 04:44 PM   #4
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
It's strange that pin 7 and pin 6 on op-amp 1 are both negative. Is that one of the channels with excessive offset?
  Reply With Quote
Old 29th January 2013, 04:47 PM   #5
shawnk is offline shawnk  United States
diyAudio Member
 
Join Date: Dec 2009
I noticed that as well.. Yes, this is one of the channels with dc present (orange/black)
  Reply With Quote
Old 29th January 2013, 05:22 PM   #6
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
It would appear that the op-amp is defective. If you haven't done so, replace it.
  Reply With Quote
Old 29th January 2013, 05:32 PM   #7
shawnk is offline shawnk  United States
diyAudio Member
 
Join Date: Dec 2009
I have swapped them out a couple of times. I just swapped them again and I'm getting the same results

Thanks
  Reply With Quote
Old 29th January 2013, 05:38 PM   #8
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
If you clamp everything down and drive that channel to full power (4 ohm load good enough), Does it produce clean audio all the way up to the point where it clips?
  Reply With Quote
Old 29th January 2013, 05:43 PM   #9
shawnk is offline shawnk  United States
diyAudio Member
 
Join Date: Dec 2009
I will try and let you know.... Should I adjust the bias to the point where offset is minimum, or leave the bias pot where it is (lowest setting)?
  Reply With Quote
Old 29th January 2013, 05:49 PM   #10
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
The bias shouldn't matter but since it only takes a minute to check both ways, do so.
  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 650 seankane Car Audio 82 6th February 2013 09:38 AM
Rockford Fosgate Power 650 Mosfet "rejuvification" pgerry Car Audio 16 20th October 2012 02:25 PM
Rockford Power 650 Mosfet seankane Car Audio 16 7th September 2011 07:17 PM
rockford fosgate power 650 mosfet mike49504 Car Audio 43 24th March 2011 10:21 PM
Help with Rockford Fosgate Power 650 shawnk Car Audio 31 14th July 2010 08:11 PM


New To Site? Need Help?

All times are GMT. The time now is 10:14 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