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Old 11th February 2010, 07:03 PM   #1
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Default Phono preamp without confusing RIAA stuff

Hi.
I'm aware of the million threads on the famous RIAA phono preamp with all the re- de- pre-emphasis discussions, and I really got tired of searching the internet and not finding anything useful.
I just built one of those (google "PAiA - RIAA phono preamp kit" and the schematic pops up) and it works but it has the characteristic EQ curve with lots of treble and no bass.
I wonder if it is possible to built one of those preamps with a usable EQ curve that amplifies exactly the same sound that come off the record and converts it to line level or even a balanced line level as those used in professional mixing consoles?
Thanks in advance for any reply.
Phantombox
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Old 11th February 2010, 08:37 PM   #2
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Quote:
Originally Posted by PhantomBox View Post
Hi.
I'm aware of the million threads on the famous RIAA phono preamp with all the re- de- pre-emphasis discussions, and I really got tired of searching the internet and not finding anything useful.
I just built one of those (google "PAiA - RIAA phono preamp kit" and the schematic pops up) and it works but it has the characteristic EQ curve with lots of treble and no bass.
I wonder if it is possible to built one of those preamps with a usable EQ curve that amplifies exactly the same sound that come off the record and converts it to line level or even a balanced line level as those used in professional mixing consoles?
Thanks in advance for any reply.
Phantombox
What exactly is the problem? What do you mean by "it has the characteristic EQ curve with lots of treble and no bass"? Is the RIAA in error?

jd
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Old 11th February 2010, 09:16 PM   #3
AuroraB is offline AuroraB  Norway
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Just off the top of my head , I can't see anything wrong with that schematic...
If you built it , are you sure you didn't mix up some of the parts? I've built several 5532 based RIAA pre's to be used with radio mixers without any problems - sounds quite OK. Maybe not super-duper Hi End, but actually very much OK
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Old 11th February 2010, 09:16 PM   #4
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What I mean is that the preamp that I built is exactly to specifications according to the schematic, and unless I made the same mistake on both channels (L + R) and my preamp don't "de-emphasizes", then I'd say that the RIAA is in error.
Fortunately I'm not such a square-head... Let me check my design over again, see if I really missed something.
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Old 11th February 2010, 10:17 PM   #5
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Quote:
Originally Posted by PhantomBox View Post
What I mean is that the preamp that I built is exactly to specifications according to the schematic, and unless I made the same mistake on both channels (L + R) and my preamp don't "de-emphasizes", then I'd say that the RIAA is in error.
Fortunately I'm not such a square-head... Let me check my design over again, see if I really missed something.
But how do you know it is in error? Did you measure? Does is sound somehow wromg? What's the problem?

jd
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Old 11th February 2010, 10:22 PM   #6
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One little problem could be that this circuit has a rising response over 20kHz. A passive RC combination at the output can solve that. Another could be component tolerances. This DIY kit is dirt ceap so i do not expect close tolerance parts.
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Old 11th February 2010, 10:31 PM   #7
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This might seem like a silly question, but you are using a turntable with no preamp in it and an input on the power amp that's not a phono input, right? You might want to tell us the signal chain in any event.
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Old 11th February 2010, 10:46 PM   #8
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A phono preamp without the confusing RIAA stuff would not correctly reproduce the signal on the record.

RIAA equalization - Wikipedia, the free encyclopedia
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Old 11th February 2010, 11:20 PM   #9
PLB is offline PLB  United Kingdom
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Hi PhantomBox,

I just entered the "PAiA - RIAA phono preamp kit" schematic into a Spice simulation program and it shows that at 20Hz the response is about 4dB less than the RIAA curve and at 20KHz it's about 4dB higher than the RIAA curve.

Regards

Peter
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Old 11th February 2010, 11:23 PM   #10
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that whould explain the sound: no bass, too much treble. I expected the DC blocking cap to small and the circuit can not reduce the gain to zerro in the treble.
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