Rock ola 474 amp

[Dave N.]

I just pick up two Rockola 474's and the one I'm working on has stati
in the right speaker all the time sometimes you can hear it over th
music. I have replaced most all of the electrolytic capacitors on th
driver board, the pre amp and the power board with no change in th
noise. has any one ever had this before.

Thank you for your help

Dave Niccum
Georgetown, Il US


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Dave N.

[John Robertson]

I just pick up two Rockola 474's and the one I'm working on has static
in the right speaker all the time sometimes you can hear it over the
music. I have replaced most all of the electrolytic capacitors on the
driver board, the pre amp and the power board with no change in the
noise. has any one ever had this before.
Thank you for your help
Dave Niccum
Georgetown, Il USA

Unlikely to be a capacitor, more likely a resistor or transistor or even
a noisy electrical connection.

First, try unplugging the input to the amp. If that solves the noise
then check the cartridge and wiring.

When you adjust the volume does the noise go up/down with it?

If yes, then the problem is either the volume control or in the pre-amp.

If it doesn't change then the problem is most likely in the power amp
section.

An audio signal tracer is what you want to track that down!

John :-#)#

[Dave N.]

On 2020/08/10 12:37 p.m., Dave N. wrote:-
I just pick up two Rockola 474's and the one I'm working on has static
in the right speaker all the time sometimes you can hear it over the
music. I have replaced most all of the electrolytic capacitors on the
driver board, the pre amp and the power board with no change in the
noise. has any one ever had this before.
Thank you for your help
Dave Niccum
Georgetown, Il USA
-
Unlikely to be a capacitor, more likely a resistor or transistor or eve
a noisy electrical connection.
First, try unplugging the input to the amp. If that solves the noise
then check the cartridge and wiring.
When you adjust the volume does the noise go up/down with it?
If yes, then the problem is either the volume control or in th
pre-amp.
If it doesn't change then the problem is most likely in the power amp
section.
An audio signal tracer is what you want to track that down!
John :-#)#
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Thank You I will check it ou


--
Dave N.

[John Robertson]

On 2020/08/10 12:37 p.m., Dave N. wrote:-
I just pick up two Rockola 474's and the one I'm working on has static
in the right speaker all the time sometimes you can hear it over the
music. I have replaced most all of the electrolytic capacitors on the
driver board, the pre amp and the power board with no change in the
noise. has any one ever had this before.
Thank you for your help
Dave Niccum
Georgetown, Il USA
-
Unlikely to be a capacitor, more likely a resistor or transistor or even
a noisy electrical connection.
First, try unplugging the input to the amp. If that solves the noise
then check the cartridge and wiring.
When you adjust the volume does the noise go up/down with it?
If yes, then the problem is either the volume control or in the pre-amp.
If it doesn't change then the problem is most likely in the power amp
section.
An audio signal tracer is what you want to track that down!
John :-#)#

Thank You I will check it out

Hi Dave,

These tests are done when the machine is playing a record and you are
hearing the noise...

John :-#)#

[Jay Hennigan]

I just pick up two Rockola 474's and the one I'm working on has static
in the right speaker all the time sometimes you can hear it over the
music. I have replaced most all of the electrolytic capacitors on the
driver board, the pre amp and the power board with no change in the
noise. has any one ever had this before.

If you have an oscilloscope you can probe the same points on both
channels looking for the noise.

Otherwise you can narrow it down, does the volume of the static vary
with the volume control or is it always at the same volume? Does it go
away during scan when the box is muted?

It's most likely a transistor. Without test equipment you can often
narrow it down by temperature. Most noisy components are noisier when
warm. Get a can of freeze spray (or computer duster, just turn it
upside-down) and give a light spray to each transistor during operation.
The one that causes the noise to go away or drop substantially is the
culprit.