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Old 3rd December 2011, 03:55 PM   #11
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Start at post 3139.
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Old 4th December 2011, 03:34 PM   #12
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The Audio Radio Handbook contains a description of the equalization required by a crystal cartridge. The crystal cartridge is also displacement device so the equalization might be the same for a strain gauge cartridge.

National Semiconductor Audio/Radio Handbook - Circuit Cellar, Inc.

Ray
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Old 4th December 2011, 03:50 PM   #13
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In my thread you find the response of the Panasonic.
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Old 4th December 2011, 03:52 PM   #14
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Here it is ....
Attached Images
File Type: png Pannasonic Straig Gauge FRD FFT JL.png (106.1 KB, 285 views)
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Old 4th December 2011, 09:37 PM   #15
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Thanks Joachim!
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Old 7th December 2011, 10:49 AM   #16
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And here..:
Turntable Forum • View topic - Preamp for EPC-450CII and semiconductor / strain-gauge carts

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Old 7th December 2011, 09:18 PM   #17
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Cobra2, thanks! Interesting.

It looks fairly easy to correct the frequency deviation on the panasonic strain gauge carts. The Sound Smith cart should be easy too given others comments.

Anyway, I hope do this soon but got a speaker project to finish, and don't have have the funds right now.
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Old 2nd January 2012, 11:36 PM   #18
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Quote:
Originally Posted by Joachim Gerhard View Post
In my thread you find the response of the Panasonic.
Hi Joachim and all,

You may want to read all the pages on the Vinylengine thread called "preamp for strain gauge" or something like that.

I've done two circuits, one is proven, the other (the new one) you should ignore for now.

Basically to do a Panasonic SG cartridge preamp is extremely simple: The catridge measures 800 ohms. Use a battery to get +9V, connect this in series with a 2.2K resistor and the strain gauge. Total resistance = 3Kohm. Then 9V/3Kohm = 3mA which is within the 2-6mA desired current for powering up the strain gauge.

The output, obviously, will have a DC bias, you will have to use a capacitor as a High Pass filter to remove it. Then add about 32-38dB of gain to bring the out to AUX/LINE levels.

Now, equalization is another thing... The cartrige doesn't have a flat response. It has a slight peak around 100-300Hz of about +2dB, and then a pronounced valley of about -3dB from 2KHz-6KHz (i'm recalling this from my head, don't take these figures as exact). But the real thing is that response from 15KHz-20KHz goes up to the sky (+6dB).

I find that the most important thing is to correct the highs using a standard low pass filter with cutoff at 10 to 13KHz (to suit your taste). The 2KHz-6KHz valley is better not to correct since IMHO it gives a 'pleasing' sound.

I do have an EQ circuit on the Vinylengine thread that in theory would give a flat response, but i haven't tested it due to lack of time. However, i think that the most important thing is to filter those extreme highs.

Greetings,
Flavio81
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Old 2nd January 2012, 11:39 PM   #19
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I forgot to add, you need to invert one of the two outputs. I do this by connecting one strain gauge to +9V and the other one to -9V, so one is inverted (relative to the other).

Another way is to use an inverting op-amp.

Another way is to swap the polarity of one of your speakers.
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Old 6th January 2012, 04:12 AM   #20
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Hi Flavio81,

Thanks, I'll check out Vinyl Engine. Where can you get the panasonic cart?

Though, I plan on using the Sound Smith SG cart, probably the cheaper on to start with since I don't know much about SG, and I'm not sure how it will work out.
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