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Old 8th August 2003, 01:56 PM   #11
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Sorry - I meant fdegrove, not fdgroove.
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Old 8th August 2003, 02:22 PM   #12
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Hi,

Quote:
And why is fdgroove so dismissive of impedence matching? Am I missing something?
Let me assure you that he's not dismissive of impedance matching.

What he means is that the "matching" in this case is usually understood as using a material that has the same mechanical impedance as the next or previous material.

In that case all we would have achieved is an increase in mass, not bad but not the ideal we want to achieve, namely provide an easy path for the spurious energy to go into the platter and dissipate as heat.

Ideally we should also provide for a difficult path for that energy to travel back into the vinyl record.
Using two materials with the same mechanical impedance would not provide that.

However, using a matrial with a slightly higher mechanical impedance than vinyl would, at least in theory.

Hope that clarifies it a little,
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Old 11th August 2003, 01:53 PM   #13
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Thanks for the clarification. I wouldn't have thought of the role of increased mass, but its and obvious issue. But it seems to me that if you want to make it easy for energy to be transported away from the record, and difficult to return, wouldn't you want lower mechanical impedence, not higher? If I am not wrong, its easier to go from high to low, so this would be benficial in both directions. I this correct? And what about the role of delay -- I assume that high impedence is related to quick transmission, whereas low impedence would be slower. Or am I using the terms incorrectly?

This is an interesting topic, and I appreciate your help thinking through it.
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Old 11th August 2003, 10:10 PM   #14
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All,

Thanks for the advice. I agree that impedance matching is important, but perhaps not something that we all agree upon as it is not an eaxct science, but neither is turntable building. As with anything it is a mix of theory, luck and experience.

Should a record clamp or weight be used? How does that affect impedance matching?

For convenience sake I have obatined a 2" thick disc of acrylic, approx 13" in diameter. I will add peripheral weights to it for inertia reasons, but they should not alter the impedance match.

I have the Teres bearing ready to fit the platter. I believe I will use a laminated MDF plinth with pockets for lead, oil, sand mix. This should add about 20lbs to the plinth and the whole assembly minus the motor pod should weigh about 60lbs or so.

I will try and veneer the plinth instead of paint, but it depends how well the veneer sticks down.

The motor pod will be an outboard unit weighing around 10lbs and made mainly of brass.

I will take photos as I go and post them, but this will take a couple of months to make any real progress.
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Old 11th August 2003, 10:10 PM   #15
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Hi,

Quote:
wouldn't you want lower mechanical impedence, not higher?
You could but; lower mechanical impedance material will also be softer materials.
Note also that the impedance "mismatch" between record vinyl and metacrylate is really small and there other reasons than just theoritical ones for chosing it that may not necessarily apply to DIY designs.

Putting a record on a softer than its own material will tend to diminish dynamic range and micro-detail.

An analogy I often use to allow people to picture what's going on is to compare writing on a solid fixed surface or writing on a cushion.

Viewed by the cartridge this would amount to the same.

There's alot more to tell and I'm trying to collect as much info as possible...

Cheers,
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Old 11th August 2003, 10:27 PM   #16
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Hi,

Quote:
Should a record clamp or weight be used? How does that affect impedance matching?
A record clamp is imperative IMO and the better ones apply the same principles as applied to platters with the added goals of keeping the record from slippling on the platter and flatten the record by applying pressure on the outer rim of the label.

One of the best I had was a Goldmund which was really well thought out.

Quote:
For convenience sake I have obatined a 2" thick disc of acrylic, approx 13" in diameter.
Be careful with oversized platters, some tonerams are really hard to put on those.

Quote:
I will add peripheral weights to it for inertia reasons, but they should not alter the impedance match.
If you insert them at the bottom of the platter they'll also help to absorb energy from the bearing.

Cheers and keep us posted,
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