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Old 4th January 2003, 06:29 PM   #1
Chris is offline Chris  Norway
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Smile Just another RIAA......

Some time ago I posted a thread where I asked if anybody had any opamp based riaa design to recomend. I got a few answers and paulb gave me the following webadress:

http://www.national.com/an/AN/AN-346.pdf

I decided to use the design described in this application note. This design is a two stage riaa phono preamplifier.
Currently I use BB opa 37 in the first gainstge an BB opa 606 in the second gainstage. The result is shown in the following pictures.
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Old 4th January 2003, 06:30 PM   #2
Chris is offline Chris  Norway
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Another picture,.....
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Old 4th January 2003, 06:31 PM   #3
Chris is offline Chris  Norway
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Last one .......
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Old 4th January 2003, 08:58 PM   #4
mlloyd1 is offline mlloyd1  United States
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Looks nice; great job! How do you like the sound?
mlloyd1
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Old 4th January 2003, 10:22 PM   #5
Chris is offline Chris  Norway
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The sound is nice. Good soundstage, relaxed but dynamic..
However it has a somewhat enhanced s-sound. I wonder why ?
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Old 4th January 2003, 11:07 PM   #6
Cobra2 is offline Cobra2  Norway
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Default RIAA...

Quote:
However it has a somewhat enhanced s-sound. I wonder why ?

Did you try other op-amps? Or (DC-blocking) caps?

I have just finished off another "Bugle", running it in now, and it sounds fine w. RIFA caps & AD825 op-amps in and out, and a "cost-saving" OPA2134 inbetween.

Arne K
NORWAY
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Old 4th January 2003, 11:20 PM   #7
Chris is offline Chris  Norway
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Hi Cobra2

I`m not using any DC blocking caps. There is no DC at the outputs.

Could it be the load capacitance ?
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Old 5th January 2003, 07:09 AM   #8
Electrons are yellow and more is better!
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Quote:
Originally posted by Chris
The sound is nice. Good soundstage, relaxed but dynamic..
However it has a somewhat enhanced s-sound. I wonder why ?
Have you been able to eliminate the vinyl itself? Is it the new amp or is it the LP?

Have you checked the input capacitance? Maybe you need a trim? Some pickups needs up to 400 pF.
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Old 5th January 2003, 09:53 AM   #9
Chris is offline Chris  Norway
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Originally posted by peranders


Have you been able to eliminate the vinyl itself? Is it the new amp or is it the LP?

Have you checked the input capacitance? Maybe you need a trim? Some pickups needs up to 400 pF.

Hi

The pickup i use (ortofon om 10) should be loaded with about 100 - 200pF. I have tried both values with no real improvment IMHO. Currently I have no load capacitance and it`s better I think.
Could it be that the cable I use introduce enough capacitance ?
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Old 5th January 2003, 04:27 PM   #10
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Normal TT cable has approx. 100 pF per meter and must of course be included.

If you connect the TT to an another RIAA amp, do you get the same S-sounds?

I salute you also to your achievement (I can feel the joy you feel) but unfortunately your wiring doesn't get any high score. NEMKO had their heads. Think tidyness. Separate 230 volts from the rest. NO unisolated parts!

Which circiut have you built? The last one in the application note?
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