Need A Resistor Value - 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 10th April 2006, 11:44 PM   #1
diyAudio Member
 
Join Date: Jan 2005
Location: The Great Lakes
Default Need A Resistor Value

I received this amp, mtx 8100d. The problem was that it had both power supply resistors are shot. I replace them with 68ohms, but i think the value are wrong. Because i get a hissing sounding coming from the transformer. I know rockfords have this problem, but usually mtx are very quiet amps.


Click the image to open in full size.

there r435 and r436
  Reply With Quote
Old 11th April 2006, 05:02 PM   #2
niteowl is offline niteowl  Canada
diyAudio Member
 
Join Date: Sep 2005
Hi swordfish689

That value should work fine. You can almost use any value from 10 to 100 ohms. try pressing your finger on the transformer in differant spots and see if the sound go's away. I've had to do this with rockfords then if it quiets down, I would put some glue on the windings to suppress it. Does the amp work?

Martin
  Reply With Quote
Old 11th April 2006, 06:00 PM   #3
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
In the 1501 that I have here, they are 39.2 ohms.The board layouts look the same and the resistors have the same designations so the value should be right.

Some of those amplifiers are extremely noisy. After repairing it, run it hard. The power supply and the output FETs should all operate at roughly the same temperature. If either set of FETs is running significantly hotter than the other, you may want to check it a little more thoroughly.
  Reply With Quote
Old 12th April 2006, 12:07 AM   #4
lndm is offline lndm  Australia
diyAudio Member
 
Join Date: Mar 2006
Location: nsw
Not sure from the picture, but it looks as if the capacitor has expanded. Bad capacitors can hiss (not sure if this is what you meant).
  Reply With Quote
Old 12th April 2006, 05:34 PM   #5
diyAudio Member
 
Join Date: Jan 2005
Location: The Great Lakes
Thanks for the replies. The only thing that i replaced were the 8 power fets, 2 resistors near the fets, and one diode that seemed to be overheated, it still worked, but i didn't want to take any chances. It turns on and works, the only thing i don't like is the sound of the transformer, making a loud hissing sounding. Also it has no gain, its full all the time, the first time i connected it to my sub it rattled the windows. Scared the **** out of me. I need to check the op-amps. Thanks again.
  Reply With Quote
Old 12th April 2006, 06:34 PM   #6
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
If the RCA jack shield 'bell' isn't soldered to the RCA jack 'frame', solder them together. Apply heat from the outside of the frame and apply solder to the inside of the frame. If the shield ground is not solidly connected, the amp will oscillate at ~100hz at full power. The newer RCAs are soldered.

The amps do have problems with failing op-amps that cause low frequency oscillation but I've never seen a failed op-amp cause full power oscillation.
  Reply With Quote
Old 12th April 2006, 10:38 PM   #7
lndm is offline lndm  Australia
diyAudio Member
 
Join Date: Mar 2006
Location: nsw
Did you say it was the transformer making the sound? Is it a buzzing sound? If so, this is probably not a problem, many xfmrs buzz a little.
  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
Which resistor type for emitter resistor? sajti Parts 25 8th April 2009 06:12 AM
What resistor should I use? Rob11966 Tubes / Valves 1 2nd March 2009 09:52 AM
Why this resistor? Shel-e-bean Everything Else 28 4th August 2006 04:57 AM
Help with Resistor Please saabie22 Parts 5 2nd February 2005 09:39 PM
screen-plate resistor and grid leak resistor metebalci Tubes / Valves 4 26th February 2004 03:18 AM


New To Site? Need Help?

All times are GMT. The time now is 03:20 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