Phonoland

I installed a really good phone pre amp and also switched out the Sonotone AT8 cartridge to a Pickering V15 with a NP/AC needle from Kabusa, but the dissapointment was great when I started a play records.
It seems like noice is picked up by the new needle/cartridge and the pre amplifier then amplifies the noice.
The oscillating sound is very high (sound like a WW2 Spitfire engine) and you can bearly here the music when the noice starts.
It can appear anytime on any record, the noice wasn't there before the "upgrade".

Any ideas what to do?
Maby go back to the Sonotone AT8 or....?

Phono pre amplifer:
http://artproaudio.com/turntable_preamp ... /djpre_ii/

Listen to the oscillating noice here, it's the first 3 seconds even before the music starts to play.
http://s236.photobucket.com/user/gbak/m ... 9.mp4.html

I can't get the audio to play, but guessing from your description, you are loosing the ground (earth)--somewhere--??
Ron Rich

I was thinking the same so I have have new (grounded) shielded cables from tonearm to pre amp.
I have also checked for ground loops and tried different groundings without any luck!

Is the shield touching ground AND the tone arm, or cartridge??--If I recall correctly, that model should not have a shield from the plug to the cartridge-- Ron Rich

Shield is not conected to the tonearm or cartridge itself.
I connected the shield as it was when I got the jukebox, to the connector on the plate behind the arc.

Photo is not from my jukebox but I have done the same connection.

With (the other side of ) that plug removed, measure all lugs on the cartridge to the tone arm frame, or an un-painted portion of the mechanism--there should be NO reading !

From what little was recorded, I have never heard a noise like that resulting from ground fault. This may be a new one for me.

Does the noise persist if the one and then both pickup leads going into the preamp are removed?

Does it persist if the tonearm is held away from the record?

What happens when the output of the pre is connected to an external amp and record is played through it?

Rob-NYC

I'm quite shure it's a oscillating sound!
I can heare the noice very low when it starts, and within a few seconds the noice increases
Then as heard on my recording it dissapeares when the music is starting to play.

It's always on the same place on the record I play.
And the noice suddenly dissapears to comes back 1 minute later again!
If I remove the needle from the track it stops!
If I push hard on the blue large back plate the noice gets weeker or stops!
If playing the record on low volume there is no noice!

Just a thought:
Can the blue back plate (or something else??) act as a large microphone on some specific frequenses and transfer the vibrations to the tonearm/cartridge?

Havn't got the time to try the the other ideas yet.....

Gbak wrote:I'm quite shure it's a oscillating sound!
It's always on the same place on the record I play.
And the noice suddenly dissapears to comes back 1 minute later again!
If I remove the needle from the track it stops!
If I push hard on the blue large back plate the noice gets weeker or stops!
If playing the record on low volume there is no noice!

Just a thought:
Can the blue back plate (or something else??) act as a large microphone and transfer vibrations to the tonearm/cartridge?

Havn't got the time to try the the other ideas yet.....

Due to the Pickering's extended frequency response, sensitivity of the magnetic cartridge, and compliance, it's apparent that this "modification" is not a wise choice for this particular machine.
Mechanical feedback, overall design of the machine, and other things all contribute to this problem.
Not all machines can "handle" such modifications, and quite possibly more extensive modifications to the whole system would be required, including low frequency filtering/limiting in the amplifier itself.

Best to stick with "original" design sometimes.

Matt and all, before we jump to conclusions, I modded just over 20 of these carousel Wurlitzers with Pickering DAT/NPAC magnetic carts and this has never been a problem. though I agree that with the mach and speakers in the same acoustic environment the potential exists for feedback.

Does turning down the volume cause the feedback to stop? If so, it seems to be a form of acoustic-mechanical feedback, check:

1) That the mechanism is floating on the springs and does not directly touch the cabinet at any point, this is crucial. BTW: The springs w/red stripe are supposed to go at the rear of the mech. They are stronger though I never found it to make much difference.

2) Try strapping the two inputs (to make them mono) either at the plug on the arch or in the amp and see if the feedback goes away. Since there is no separation with the speakers so close you might as well leave it mono anyway.

Make sure that the turntable motor and it's mounting plate are suspended by the rubber mounts and not sagged and touching the drip pan or anything else.

It is possible that the preamp is overloading the input of the amp as it was designed for a low output ceramic. This would not cause feedback directly, but would make the machine more prone to picking up rumble on quiet records and possibly distorting with loud records. As a clue; an average record should start out a bit low and slowly rise in up to an average level. Wurlitzer used a too-long time constant on their amps, but that is another matter.

Rob

If strapping the input leads at the connector the noice gets much lower!
So what does this mean?
Should I use shielded cable all the way to the cartridge?

Essentially, a mono pickup will generate electricity only from lateral (side-to-side) movement. A stereo pickup also responds to slight upward movement at approx 45º on either side. The effect of this is to make the pickup somewhat more sensitive to rumble and feedback because it can generate electricity from vibrations going in more directions. It is also much more sensitive to surface noise such as clicks and pops.

Wiring the two channels in parallel thus making them mono causes a cancellation of these effects and lowers the noise, rumble and feedback susceptibility.

If removing the pickup from the record causes the noise to go away, the problem will not be fixed by using different tonearm cable. Poor tonearm cable shielding would cause a steady hum of 50Hz in your country and 60Hz here in America.

This is a mechanical-acoustical problem. Wiring to mono will reduce or eliminate it....and the stereo effect

Rob

I tightend the transportation vingscrews and as I did it the noice incresed dramatically!
So I added cork "washers" over and under the "floating" springs just to see if the noice was changing and it seems like it is much lower now or almost gone!

Still there are two different noice (hum/rumble) left that needed to be taken care of!
One comes from the turntable motor (rumble) itself, it stops when I unplug the motor connector and picks up by the cartridge. This is not so high and I can live with it.
And the other one is a what I think a grounding issue and is quite disturbing and should be fixed! I hope a shielded cable from the pre amp directly to the cartridge will do it!

Unfortunately did something happend, so now is the same record playing over and over again
The magazine motor dosent reverse, might be some relay issue or switch.

I'm tired of troubleshooting and all my power just faded away!
Will look at this when the motivation is back......

And the other one [hum] is a what I think a grounding issue and is quite disturbing and should be fixed! I hope a shielded cable from the pre amp directly to the cartridge will do it!

Did you remove the tiny copper strap that goes from a pin on the cart to it's shell? If not it creates a ground loop which causes hum of the 50-60Hz type. Also. keep the grounds shields from amp to cart separate. On some Wurlitzers the shield leads are soldered together at the plug on the arch, this too causes a loop and hum.

Rob

Guyz,
Rob has "jogged"my memory here--
I have run into a couple of these "conversions" where the female four pin, socket, mounted behind the tone arm has been shorted to ground. I just replaced it with a loose hanging socket, to solve this problem.
As for the grounding clip, or lack of--that's why I said to measure to ground (earth) in an earlier post ---as I suspected a clip is there !!
Ron Rich