Rockford Fosgate Power 1501BD

[caraudioguy2100]

Got another one of these amps .

The voltage across the outputs is 0.03

As soon as I start turning up the gain the voltage across the outputs increases to 4 volts and jumps up and down when I turn the gain knob .

Any ideas what might cause this

 

[Perry Babin]

Leave the gain in one place. Does it still malfunction when you increase the level with the signal source?

What do you mean by 'across' the outputs?

 

[caraudioguy2100]

If I leave the gain in one spot and increase the signal it doesn’t do it .

If I touch the gain or the switches the voltage jumps up and down on the output terminals .


What I meant was DC on output terminals

 

[Perry Babin]

Did you try cleaning the controls?

Just barely touch the controls to see which one is most sensitive.

 

[caraudioguy2100]

Cleaned all switches and pots made no difference.

If I don’t touch anything and connect a test sub to it I get a loud hum out of the test sub .

When I leave everything alone and don’t touch anything the voltage remains at 0 bit get a loud hum thru the test sub

 

[Perry Babin]

With nothing plugged into the RCA jacks, what's the resistance from the input RCA shields to the main ground. Move the RCAs around to make sure the reading doesn't change.

 

[caraudioguy2100]

0.909K ohms

 

[Perry Babin]

Was the amp humming when you originally posted?

Is there any gain position that eliminates the humming?

 

[caraudioguy2100]

The humming was always present in the amp no matter where I have the gain position the test sub hums .

Out of the heatsink I noticed the Mesa board under the outputs gets hot is this normal or do I have a drive problem ?

 

[Perry Babin]

It would be normal if you had a speaker connected and the amp was humming.

Is the noise/humming present on the output of any of the preamp op-amps?

Did you have another thread on this amp?

 

[caraudioguy2100]

No speaker connected to the amp and the mesha board under outputs still gets hot .

All of the opamps show that hum on pin 5 and when the gain is messed with you can see it more on the op amps .

This is another amp the other thread is for another 1501 I have

 

[Perry Babin]

Starting at the RCA input and moving through the preamp, where is the first point where you see hum?

 

[caraudioguy2100]

I have 0.65 volts on pins 1 and 5 of every opamp in the preamp section .

I can’t seem to fond any hum on anything besides the opamps

 

[Perry Babin]

Do you mean 1 and 7?

Are you looking at it with a scope?

There should be no hum at the RCA jacks.

Is it a hum or a thumping?

Do you have a battery operated audio signal tracer?

 

[caraudioguy2100]

It’s a hum but if I flip the switches then the test sub thumps in and out .

I have a sine wave generator

 

[Perry Babin]

A signal tracer allows you to trace a signal while listening to it. It's battery powered so that nothing can interfere with what you're hearing.

The Radio Shack mini amp used to be a popular one. Now, I use bluetooth headphones with a transmitter.

With the black probe on the RCA shields, do you have ±10v on the power supply pins of the preamp op-amps?

 

[caraudioguy2100]

Yes I have + - 10 volts on the power supply pins of the opamps .

Can I use the rca ground to check the voltages on the other pins of the opamps or do I need to use main ground ?

 

[Perry Babin]

The preamp op-amps in most older rockford amps are referenced to the RCA shield (inverted triangle with an 'i' in it is the RCA shield ground). With an ungrounded signal source or no input signal, use the RCA shield.

 

[caraudioguy2100]

If I use the rca shield ground I get 12 volts on every pin of U2 and U3

Is this normal or do I have a problem with those opamps

 

[Perry Babin]

I would think you have a broken connection between the negative regulator and pin 4 of the op-amps U2 and U3.

I'm not sure where the 12v is coming from if the op-amp supply is 10v.

Since you didn't include U1, I'll assume that the voltages on it are 0v except for the power supply pins which are ±10v.