Rockford Fosgate Power 1501BD

[caraudioguy2100]

Someone tried repairing this amp before .

They have 10 ohm gate resistors with 3205’S installed are the 10 ohm gate resistors fine or should I use the 47 ohm ?


Also does anyone know what value C60 is ?

It sits behind the LM337 regulator

Also the value of R44 ?

It sits next to the transformer

 

[Perry Babin]

I leave the 10 ohm gate resistors. Some use 47. Either will work. All need to be the same value.

C60 is the same as C59, 100uF@25.

R44 is 10 ohms.

 

[caraudioguy2100]

Do you know what the value is of the gate resistors for the outputs ?

Someone switched them all and I don’t think they are the correct value

 

[seankane]

If memory serves I believe they are 15 ohm

 

[caraudioguy2100]

That’s what I thought but wasn’t sure .

They have 27 ohm in there now

 

[seankane]

I have also seen 22 ohm in there from the factory as well, I have also seen a mix of 15 ohm and 22 ohm from the factory.

 

[caraudioguy2100]

Anyone have a schematic for this amp ?

amprepairguy@hotmail.com

I noticed someone has switched other caps in here to the wrong value and other parts as well so I’m in need of a schematic to figure this amp out since there are a lot of wrong values

 

[seankane]

Here are some documents that may help.

 

[caraudioguy2100]

In the schematic half the outputs have 15 ohm gate resistors the other half have 22 ohm gate resistors .

Can I use 15 ohm resistors for all of the outputs ?

 

[Perry Babin]

I'd suggest that you use the original values but it should be OK with all 15 ohm resistors.

 

[caraudioguy2100]

The 27 ohm gate resistors we’re wrong someone switched them out .

So you would suggest using 15 ohm for half the outputs and 22 ohm for the other half like the schematic says ?

 

[Perry Babin]

The loading of the drive circuit is different between the 3415s and the 6215s. Maybe the engineers had a reason to use different values... maybe it's just what the modeling told them to use. I'd use what's in the diagram unless someone has a valid reason to use something else.

 

[caraudioguy2100]

Ok got the amp all back together .

Powers up and idles fine .

I get +- 12 volts on opamps and get 125 volts of rail measured directly across the black and red wires .

Amp has very low output

Any ideas on what to check ?

 

[Perry Babin]

Have you operated all pots and switches through their entire range to see if that helped?

Do you have rail-rail oscillation on the outputs?

With the gain and crossover controls fully clockwise and a low frequency drive signal (50-100Hz) of about .25v AC at the RCA jacks, what is the AC voltage at pin 1 of U4?

 

[caraudioguy2100]

Yes I operated all switches and pots through the entire range .

I have rail to rail oscillation on the outputs .

On pin 1 of U4 I get 0.80 volts ac

 

[Perry Babin]

This is what I have on an amp here.

At 0.23v at the RCAs...

0.419v AC at pin 1 of U4
4.32v AC on pin 6 of U17
4.18v AC on pin 2 of U8

All of the above are audio, approximately RMS

On pin 3 of U8...

The 91k triangle waveform that swings about ±5.2v.

This gets a BD1000 just to clipping, no load.

 

[caraudioguy2100]

I see the problem .

The whole preamp section has to be rebuilt .

Someone switched all of the values of the resistors in it so none of them match the schematic

 

[caraudioguy2100]

Anyone have a high res pic of the preamp section in this amp ?

Wanna make sure the schematic is right since there are different value resistors and there are caps missing in this amp

 

[Perry Babin]

Are you sure? The voltage out of your preamp section was higher than mine and this amp clipped at the speaker terminals at about 1/4v in.

Sorry about the quality but they're mostly in focus.

 

[caraudioguy2100]

So I’m gonna have to rebuild it off of your pics since the schematic doesn’t match your photos