Excessive low-frequency noise for some records (AMI G-120)

I'm re-condition an AMI G-120, and now that I have the mech all
working, I'm working on sound quality issues. I've bypassed the
internal original amp, but I'm still using the speakers in the juke.
So I can rule out an amplifier issue.

I've found that, for some records worse than others, there is an
inordinate amount of low-frequency "noise" while the records is
playing. When I EQ the bass all the way down, it goes away. When I
jack the volume up, I get low-frequency feedback.

Could this be due to the fact that the turntable no longer has the
fabric ring for insulation between the bottom of the record and the
metal? I know I need to replace that anyway, but it would be nice to
know if that is a good candidate for the causeso I can go on to other
things.

Thanks in advance,
Cory

On Dec 8, 10:11*am, wrote:
I'm re-condition an AMI G-120, and now that I have the mech all
working, I'm working on sound quality issues. I've bypassed the
internal original amp, but I'm still using the speakers in the juke.
So I can rule out an amplifier issue.

I've found that, for some records worse than others, there is an
inordinate amount of low-frequency "noise" while the records is
playing. When I EQ the bass all the way down, it goes away. When I
jack the volume up, I get low-frequency feedback.

Could this be due to the fact that the turntable no longer has the
fabric ring for insulation between the bottom of the record and the
metal? I know I need to replace that anyway, but it would be nice to
know if that is a good candidate for the causeso I can go on to other
things.

Thanks in advance,
Cory

The original ami cartridge is ceramic while most stereo receivers/amps
have a magnetic cart input. Usally when one is used on the other, the
differance is very noticable. Do you have the turntable grounded to
the amp?

wrote:
I'm re-condition an AMI G-120, and now that I have the mech all
working, I'm working on sound quality issues. I've bypassed the
internal original amp, but I'm still using the speakers in the juke.
So I can rule out an amplifier issue.

That is such an easy amp to rebuild, may as well do it and see what it
sounds like. Also check what indy-gus posted. Be sure the cartridge
matches the amp you are using. Sometimes an extra ground to the amp
will cause a ground loop (bad), that will give you a 60 cycle hum.
Sometimes things work better with an extra ground and sometimes they are
worse.


I've found that, for some records worse than others, there is an
inordinate amount of low-frequency "noise" while the records is
playing. When I EQ the bass all the way down, it goes away. When I
jack the volume up, I get low-frequency feedback.

Is this low freq feedback that starts the whole cabinet shaking? If so
first be sure the mech is floating on springs. Normally it is bolted
down tight for shipping then you loosen those bolts again. If it's
bolted tight find the shipping bolts and loosen them.

Next, is the turntable motor mounted to soft grommets? If they are
dried out replace them. Get the right kind, don't install something
found at home depot or lowes, they will be too stiff.

Try that before we go any further.

Tony



Could this be due to the fact that the turntable no longer has the
fabric ring for insulation between the bottom of the record and the
metal? I know I need to replace that anyway, but it would be nice to
know if that is a good candidate for the causeso I can go on to other
things.

Thanks in advance,
Cory

On Dec 8, 8:29*pm, Tony Miklos wrote:
That is such an easy amp to rebuild, may as well do it and see what it
sounds like. *Also check what indy-gus posted. *Be sure the cartridge
matches the amp you are using. *Sometimes an extra ground to the amp
will cause a ground loop (bad), that will give you a 60 cycle hum.
Sometimes things work better with an extra ground and sometimes they are
worse.

I was planning to re-build it anyway, I think I only need to replace a
couple of the tubes and probably have to re-cap it, since it was
sitting in storage for so long (27 years). I'll check the ground
issue. The amp is a 1990s era Pioneer stereo receiver I just had
lying around that happened to have a phono input. I'll try an extra
ground wire (thanks indy-gus) and see what happens. Right now, the
only thing connected to the amp is the speaker wire for one channel
and the phono input cable.

Is this low freq feedback that starts the whole cabinet shaking? *If so
first be sure the mech is floating on springs. *Normally it is bolted
down tight for shipping then you loosen those bolts again. *If it's
bolted tight find the shipping bolts and loosen them.

I already had loosened the shipping bolts, I figured those springs
were there for a reason!

Next, is the turntable motor mounted to soft grommets? *If they are
dried out replace them. *Get the right kind, don't install something
found at home depot or lowes, they will be too stiff.

I think the motor is, yes. I also don't think that is the problem,
since I don't hear the noise until a record is actually being played,
or sometimes when the armature/cam/records changer is moving records
around. When the turntable is spinning, it is quiet.

Thanks for the suggestions!
Cory

wrote:
I'm re-condition an AMI G-120, and now that I have the mech all
working, I'm working on sound quality issues. I've bypassed the
internal original amp, but I'm still using the speakers in the juke.
So I can rule out an amplifier issue.

I've found that, for some records worse than others, there is an
inordinate amount of low-frequency "noise" while the records is
playing. When I EQ the bass all the way down, it goes away. When I
jack the volume up, I get low-frequency feedback.

Could this be due to the fact that the turntable no longer has the
fabric ring for insulation between the bottom of the record and the
metal? I know I need to replace that anyway, but it would be nice to
know if that is a good candidate for the causeso I can go on to other
things.

Thanks in advance,
Cory

Have you loosened the shipping bolts so the mechanism is floating on the
spring suspension? This 'sounds' like acoustic feedback to me...

John :-#)#

--
(Please post followups or tech inquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

On Dec 9, 2:54*pm, John Robertson wrote:
Have you loosened the shipping bolts so the mechanism is floating on the
spring suspension? This 'sounds' like acoustic feedback to me...

Yep, did that a while back. I made sure they were as well.

I added an extra ground wire, and that didn't seem to help. It didn't
sound like 60-cycle hum anyway.

One thing that did help quite a bit was to put a few pieces of felt
between the record and the turntable itself. There is supposedly
supposed to be a piece of black velvet on the rim, apparently to
dampen vibration, and that was long since worn to nothing. The felt
really seemed to help, so I'm going to get a replacement turntable
fabric ring.

mrschmitz wrote:
On Dec 9, 2:54 pm, John Robertson wrote:
Have you loosened the shipping bolts so the mechanism is floating on the
spring suspension? This 'sounds' like acoustic feedback to me...

Yep, did that a while back. I made sure they were as well.

Have you confirmed no acoustic feedback by using external speakers only?

John :-#)#

--
(Please post followups or tech inquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

With that pioneer amp hooked up are you trying to run it real loud ?.
Turntables in general will do that if you try to get it loud with to
much bass

On Dec 9, 5:54*pm, John Robertson wrote:
Have you confirmed no acoustic feedback by using external speakers only?

Actually, I did, on accident. Before I had the amp removed, I just
used an old PA speaker (externally) and it sounded about the same. But
I do think there is a little bit of acoustic feedback, since it was
worse when I have it running through the internal speakers.

I have a feeling I was also trying to pump it too loud with the
external amp (as Ken G. said below), since at lower volumes it was
hardly noticeable.