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Old 24th March 2005, 03:37 PM   #1
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Default RIAA stage, with certain requirements..

Am in the process of building a phono stage like Gary Pimm has made...in the meantime I want to throw together a little op amp RIAA amp, just for kicks but also as a reality check.

The requirements are..
I have 2 TLE2027 AI opamps that I want to use, I'm not going to buy OPA627's or any other opamp.

So I found attached schematic in some datasheet. Any suggestions for improvement/alterations?
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Old 24th March 2005, 07:15 PM   #2
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The op amp sees a 100 ohm load at high frequencies with your schematic, which may or may not be a problem depending on the op amp.

Look at VSPS for a solution to this.
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Old 24th March 2005, 07:28 PM   #3
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Nuvistor! What a great link...it even has a low z option for Grado...I happen to have a Grado!

Thanks so much... I also have a pair of 5532...would that be better than an TLE2027 (OP27) in the application for a Grado cartridge?
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Old 24th March 2005, 07:36 PM   #4
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I have used a buffer for this type of low load but if your requitrements are "medium" I think the circuit you have shown will work but it's good to use a rather fast opamp because you want to apply some feedback also.

100 ohm pure resistive load isn't a problem to most opamps. You haven't got exactly any voltage over it in normal frequencies.

Bas, if you haven't seen my two RIAA amps you may check them out.
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Old 24th March 2005, 07:42 PM   #5
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Quote:
Bas, if you haven't seen my two RIAA amps you may check them out.
Hi Per, I have...but they are too complicated for me!

Regards,
Bas
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Old 24th March 2005, 08:56 PM   #6
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The Xc of 0.03uf and 0.01uf in series is 100 ohms at 133kHz, so all is well for audio, I'm more concerned about what happens if incidental pickup from an AM radio station gets amplified. The 100 ohms is high enough to prevent op amp instability due to the feedback network capacitive load.

This thread is a discussion of the VSPS.
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Old 24th March 2005, 09:07 PM   #7
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Quote:
Originally posted by Bas Horneman
Hi Per, I have...but they are too complicated for me!
You can remove the "complicated" stuff and take the rest. I'll recommend you to download the datasheet for the LT1115. There you have a passive RIAA, almost the same as Mr. Jung has present in his very thick and good book from Analog Devices.
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Old 24th March 2005, 09:10 PM   #8
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Quote:
Originally posted by nuvistor
I'm more concerned about what happens if incidental pickup from an AM radio station gets amplified.
I good pcb will help. Both my pcb's with groundplanes have also place holders for RF filters.
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Old 24th March 2005, 09:31 PM   #9
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I am using the VSPS and can highly recommend it, don't know how it compares to other circuits, but for such a simple circuit it produces excellent results. I am using OPA627's (free samples). I added switchable loading network to the front end.

Shoog
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Old 24th March 2005, 11:14 PM   #10
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The simplest RIAA op amp circuit uses 1 OPA, active RIAA is the best approach using 1 modern OPA. Passive RIAA requires at least 2 and perhaps 3 OPAs for enough gain to overcome RIAA network insertion loss with good overload margin. Simplest is best for someone who just wants to throw something together.

A comparison between a VSPS-type and the Pimm would be interesting, my wager is on the Pimm having more low-level detail and better perceived dynamics, and the VSPS measuring better for noise and distortion, assuming both are built carefully and with good quality passive components.
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