rockford power 250m p/s cycling. - 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 5th February 2012, 01:44 PM   #1
diyAudio Member
 
Join Date: Apr 2011
Location: Anchorage AK
Default rockford power 250m p/s cycling.

so, i have this amp that i was just fixing the broken rca shield board connections. powered it up and went to test it, and noticed that it would cycle the music on and of. looked at my amp gauge on the poser supply, and noticed that the idle current bounces in an odd fashion... kind of reminds me of hitting one of those hanging punching bags. one spike, followed by bouncing current fluctuations that taper before the next spike.
  Reply With Quote
Old 5th February 2012, 02:02 PM   #2
diyAudio Member
 
Join Date: Sep 2009
Location: Wisconsin
What happens if you pull the rca's, will it idle fine with no source?
  Reply With Quote
Old 5th February 2012, 02:15 PM   #3
diyAudio Member
 
Join Date: Apr 2011
Location: Anchorage AK
nope, makes no difference
  Reply With Quote
Old 5th February 2012, 06:55 PM   #4
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Bias set too high?

If you set the bias to fully counter-clockwise, do you read anything more than 0.000v DC across the 0.1 ohm source resistors as it attempts to power up?
  Reply With Quote
Old 5th February 2012, 08:45 PM   #5
diyAudio Member
 
seankane's Avatar
 
Join Date: May 2010
Location: Washington State
Which 250M is this the old one or the newer one?

Can you post a photo of the board?
__________________
Pyramid 52 Amp Power Supply----Fluke 787 Processmeter----Tektronix 465 Scope----Velleman HPS40 Scope----Soldering Iron----Desoldering Iron----Hejet HJ 500-S Heatgun----DM4070 Digital LCR Meter----Propane Torch
  Reply With Quote
Old 6th February 2012, 08:48 AM   #6
diyAudio Member
 
Join Date: Apr 2011
Location: Anchorage AK
I think it is the "newer" one. About 2k "waffle" design. i will try to post a picture of the board soon.

The bias adjustment was too high. Once I turned it down, it did idle just fine. Rail voltages rose back to +/-36v with 0.000v across the source resistors. I never touched the bias pot before this, but perhaps the previous owner attempted to adjust it because of the broken rca jacks.
What is the rail voltage supposed to be on this amp?
Thanks,
-Heath H-
  Reply With Quote
Old 7th February 2012, 12:54 PM   #7
diyAudio Member
 
Join Date: Apr 2011
Location: Anchorage AK
So, i'm wondering if i adjusted the bias correctly. I started full ccw, then adjusted it cw to the point that it started to draw current, and backed it off a tad. I was watching the current meter on my power supply and measuring rail voltage on the source resistors (both sides of the resistor). I did this several times until i was sure of the adjustment. 37.82 and -37.94 @ 14vsupply. The adjustment left it 0.17v less.
The issues:
1-it does play clean audio and all preamp functions operate, but efficiency seems low. I did not set up the amp clamp, but i did measure the output ac voltage on both 4ohm and 2ohm sub loads, and, without knowing imp. rise, it is putting out roughly 50watts rms, while pulling 100 from the power supply.
is this normal at the lower power level for this amp? i cannot feed it 30a, like i would like to.
Should i re-adjust the bias so that there is no rail voltage drop?

2- It seems to require higher input signal to get a decent level of power out of it, even with the gain pot adjusted to max. I remember reading somewhere that there are a couple resistors, or caps that tend to be damaged sometimes when the rca shield legs break. which components are those, or should i be looking at something else.
3- is q110 supposed to be attached to the thermal board, or free-standing? It came free-standing, but i see the copper pad for it. I also have a rf punch75.2 that has the same thing, and the one on each side is bent over touching flush, but not glued down. The 75.2 looks to have been repaired, though.
  Reply With Quote
Old 7th February 2012, 10:17 PM   #8
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
That rail voltage drop is absolutely insignificant.

Class B and Class AB amps are very inefficient at low output levels.

Why can't you get 30 amps to it?

Drive a sine wave into it and measure the AC voltage at the RCA jacks and across the speaker terminals. Post the voltages.

I don't have any information on this amp but if this is the bias transistor, it's supposed to be in contact or in close proximity to the MEHSA insulator.
  Reply With Quote
Old 8th February 2012, 11:19 AM   #9
diyAudio Member
 
Join Date: Apr 2011
Location: Anchorage AK
I suspected the rail voltage drop was unimportant, but I figured I would throw it up just in case. It did show more finitely the current draw, vs, my current meter, though.

All my other amps a/b/d seem to have significantly higher output with the same drain, even high current us amps, soundstreams, and just about every mainstream brand in between.

The power supply i built only has a 10a cb installed in it, which is pretty close to what it will currently sustain. i am about to order the rest of the parts to re-wire it with a 317-based adjustable regulator, and build another 75a+@12.5vsupply. This last spring, I think, tossed out 12 optimas, and then later, my 2 yellow tops that i had for benching higher power.
at 12.4v unloaded, i got +36/-36.25 at the rails, for reference.
198mvac input = 20vac output
400mv ac input= 29.98vac output
loaded:
200mvac input= 9.5vac output
could not drive it to 400mvinput due to the current draw
shouldn't this amp be 200mv sensitive?

thanks-
-Heath H-
  Reply With Quote
Old 8th February 2012, 05:39 PM   #10
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
A couple of problems...

With only 36v of rail, you cannot get more than 36v of rail without clipping. After it begins to clip, the voltage readings are inaccurate.

The output vs input should not change loaded/unloaded unless the output is clipped badly.

The only voltages usable here are the 198mv vs 20v. That's 40dB of gain which is more than some of the older Rockford amps, which had up to 36dB of gain (if I remember correctly).
  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
Marantz 250M Repair PB2 Solid State 49 11th January 2012 06:09 AM
RF 250M or 200M schematic brandes.cm Car Audio 9 30th January 2010 11:04 PM
Source follower thermal cycling? wildswan Solid State 2 26th October 2009 03:39 PM
Blown Rockford Fosgate 250M, help a newb =-) mkfosgate Car Audio 11 26th July 2009 08:23 PM


New To Site? Need Help?

All times are GMT. The time now is 01:32 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