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Old 31st August 2004, 12:52 AM   #1
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Default Turntable / Phono Preamp Distortion

OK-- this thing has been driving me totally forking bananas for about a month now. I have a pair of Bottlehead Paramours and a Foreplay preamp (I know-- not real DIY] hooked up to a Hagerman Bugle SUPER SUPER CHEAPO preamp (but I really like it) and a Music Hall MMF 2.1 turntable (I know, not real hi-fi).

When I play jazz records that hit a certain frequency range (Monk's piano in Bemsha Swing, for example) I get this crackling on one channel for the duration of the tone. Its only in one channel and this happened when this particular TT and phono pre were hooked up to a GainClone, so I feel confident that its not the amps or the line stage.

Some records just sound great, while others hit this frequency rather hard and I JUST GO CUUURRAAZZEEEE when I hear this distortion. You know, I just had this idea that Miles Davis shoudn't make you want to kill indescriminantly-- that's what Micheal Bolton is for.

Anyway, before I take my preamp apart and start re-soldering, are there any of you geniuses out there who would like to play "Find and Fix Kofi's Distortion Problem" for a shot at a hand-knitted hat, scarf or mittens (your choice!) from Mrs. Annan?

Help me. For the sake of my marriage, help me.

Kofi
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Old 31st August 2004, 03:21 AM   #2
ashwin is offline ashwin  India
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This may be cartridge misallignment. See http://www.audioasylum.com/scripts/t.pl?f=vinyl&m=51464 for how to align cartridges.

- Ashwin
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Old 31st August 2004, 05:10 AM   #3
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First thing I'd do is look at it on a scope. But then you may not have access to one.
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Old 31st August 2004, 08:29 PM   #4
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From your problem description you probably have a stylus mistracking problem where the crackling is a symptom of the stylus bouncing in the groove. This can cause groove damage after repeated playings, with the crackling being permanently engraved into the groove.

You can increase the tracking force up to the maximum in grams recommended by the cartridge manufacturer while listening for improvement.

If the crackling is in the right channel only this may be corrected if your tonearm has antiskating adjustment, refer to the owner's manual for your tonearm or turntable for adjustment instructions. This is because as the disc rotates and the groove spirals from outer to inner disc area, more force is applied to the inner portion of the groove, which contains the left channel, and less is applied to the outer portion which contains the right channel. Mistracking occurs if too little force is applied to the right channel, antiskating adjustment applies a force towards the outer edge to compensate.

If the cartridge is incorrectly aligned I would expect both channels to have more distortion, and not a sudden increase in crackle in one channel. I notice a more grainy and gritty sound with bad overhang adjustment, about equal in both channels, but no gross mistracking.

You might even have a damaged cartridge, stylus or cantilever, particularly if the stylus has been dropped or scraped across the platter mat or platter edge. If this has happened, you may damage your records with repeated playing.

I think your preamp is the least likely cause of the problem, try swapping left and right channel on preamp inputs and outputs, if the problem moves to the left channel then something is wrong with the preamp.
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Old 31st August 2004, 08:41 PM   #5
fcel is offline fcel  United States
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Since I don't see too many TT post, let me interrupt this thread by asking a quick question. Hopefully someone has a quick answer ...

Assuming everything is working properly, if I want MORE bass, should I push the weight located at the back of the tonearm forward (towards the front of the TT) or push it backward (towards the rear of the TT)?

I understand that I have to change in it small increment to find the "sweet" spot - that I will experiment myself. I just wanted to make sure that I'm moving the tonearm weight in the right direction.
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Old 31st August 2004, 11:27 PM   #6
arnoldc is offline arnoldc  Philippines
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when you do that, you will change the tracking force. make sure you operate within the limits of the cartridge.
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Old 31st August 2004, 11:45 PM   #7
fcel is offline fcel  United States
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I understand that. So, what is the answer? Slide In or out?
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Old 31st August 2004, 11:53 PM   #8
arnoldc is offline arnoldc  Philippines
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ok, in my setup (Oracle Delphi, Eminent Technology ET 2.5, Clearaudio Sigma), i find that using the maximum tracking force is best.

you will need a tracking force gauge for this.
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Old 31st August 2004, 11:55 PM   #9
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Hi,

Koffi,

You could have a badly set anti-skating force pulling the stylus tip too much inwards.

Sometimes a combination of this + too little tracking force can do this as well.
The distortion is there all the time though, it's just you hear it more clearly on difficult to track material such as jazz piano (especially Mr. Thelonius Monk, ...kidding)....

fcel,

You don't adjust frequency repsonse by changing the tracking force, it should be well within the recommended settings of the cart manufacturer or you'll damage both record and stylus.

To increase tracking force move the counterweight forward, the assembly works like a lever.
Set the weight accordingly and if you're looking to set VTA for best imaging vary the tracking force by very small increments.

Cheers,
__________________
Frank
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Old 1st September 2004, 12:31 AM   #10
fcel is offline fcel  United States
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fdegrove (Frank?),

I forget to mention that I have set the tracking force per manufacturer recommendation and I'm not looking to improve imaging.

Based on your answer, adjusting tracking force is not the correct way to adjust bass response. What is the one single adjustment that I can make to adjust bass response - in my case, I want a little more bass? Thanks.
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