rockford fosgate 800a2

mike49504 · 2nd February 2010, 04:02 PM

I just got done putting new fets and new outputs in the left channel. Amp powers up fine. Left channel is distorted i checked the voltage across the emitter resistors in that channel i get 0 volts across all except 1. that one is measuring -.04 volts across it. Wondering if that could be where the problem is?

brandes.cm · 2nd February 2010, 04:13 PM

I would adjust bias pot ccw and turn gain completely down. Then look at the final stage of the preamp and see if it distorts there by adjusting the gain up.

mike49504 · 2nd February 2010, 04:26 PM

Already did that turned the bias pot fully counter clockwise and adjusted the gain in that channel still does the same thing (distorts)

Perry Babin · 2nd February 2010, 04:27 PM

With no power applied, does that resistor read 0.1 ohms (or whatever the others read on your meter)?

mike49504 · 2nd February 2010, 04:47 PM

Yes they all read the same

Perry Babin · 2nd February 2010, 04:53 PM

What transistor is it that's connected to that resistor?

mike49504 · 2nd February 2010, 05:21 PM

Ok more checking into this amp. I think i may have something shorted. When i first power on the amp it will draw 60 + amp of current for a sec then idle perfectly.

The orginal fets were MTP75N05HD I replaced them with IRF3205's Is this a good replacement?

I also replaced 1 gate resistor that was out of spec's (suppose to be 68 ohm)

More looking at the bottom of this amp there is some shady soldering from whoever worked on it before me. I will clean that up and resolder the parts.

So for right now is the 3205's a good replacement?

Perry Babin · 2nd February 2010, 05:25 PM

The 3205s have worked for me in the past.

mike49504 · 4th February 2010, 08:27 PM

I dont understand this amp. Left channel still distots.

Ive replaced the fets, all new outputs,all new emitter resistors,new a56's and 06's in that channel, also replaced a couple a2's and turned the bias pot all the way down and the stupid thing still distorts

Wondering if you have any ideas on where i should go from here maybe an op amp?

Perry Babin · 4th February 2010, 08:29 PM

It could be a protection circuit transistor that's shorted/leaking.

Did you get your scope back yet?

2nd February 2010, 04:02 PM	#1
mike49504 diyAudio Member Join Date: Sep 2006	rockford fosgate 800a2 I just got done putting new fets and new outputs in the left channel. Amp powers up fine. Left channel is distorted i checked the voltage across the emitter resistors in that channel i get 0 volts across all except 1. that one is measuring -.04 volts across it. Wondering if that could be where the problem is?

2nd February 2010, 04:27 PM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	With no power applied, does that resistor read 0.1 ohms (or whatever the others read on your meter)? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

2nd February 2010, 04:53 PM	#6
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	What transistor is it that's connected to that resistor? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

2nd February 2010, 05:25 PM	#8
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	The 3205s have worked for me in the past. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

4th February 2010, 08:29 PM	#10
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	It could be a protection circuit transistor that's shorted/leaking. Did you get your scope back yet? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links


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2nd February 2010, 04:13 PM	#2
brandes.cm diyAudio Member Join Date: Sep 2009 Location: Wisconsin	I would adjust bias pot ccw and turn gain completely down. Then look at the final stage of the preamp and see if it distorts there by adjusting the gain up.

2nd February 2010, 04:26 PM	#3
mike49504 diyAudio Member Join Date: Sep 2006	Already did that turned the bias pot fully counter clockwise and adjusted the gain in that channel still does the same thing (distorts)

2nd February 2010, 04:47 PM	#5
mike49504 diyAudio Member Join Date: Sep 2006	Yes they all read the same

2nd February 2010, 05:21 PM	#7
mike49504 diyAudio Member Join Date: Sep 2006	Ok more checking into this amp. I think i may have something shorted. When i first power on the amp it will draw 60 + amp of current for a sec then idle perfectly. The orginal fets were MTP75N05HD I replaced them with IRF3205's Is this a good replacement? I also replaced 1 gate resistor that was out of spec's (suppose to be 68 ohm) More looking at the bottom of this amp there is some shady soldering from whoever worked on it before me. I will clean that up and resolder the parts. So for right now is the 3205's a good replacement?

4th February 2010, 08:27 PM	#9
mike49504 diyAudio Member Join Date: Sep 2006	I dont understand this amp. Left channel still distots. Ive replaced the fets, all new outputs,all new emitter resistors,new a56's and 06's in that channel, also replaced a couple a2's and turned the bias pot all the way down and the stupid thing still distorts Wondering if you have any ideas on where i should go from here maybe an op amp?

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