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Old 3rd December 2009, 08:53 PM   #11
godfrey is online now godfrey  South Africa
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Location: Cape Town
"Spitty" distortion could also be caused by a damaged stylus (needle/whatever) on the cartridge. Maybe try your turntable with another phono pre-amp to check that?
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Old 4th December 2009, 12:32 AM   #12
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ah, very good recommendation, thank you! I didn't know that type of distortion could come from the needle but it does make sense. I was thinking about buying a new needle anyway..
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Old 23rd December 2009, 09:47 PM   #13
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okay so a friend let me borrow his great Stanton needle but the distortion is still there...so it is definitely the preamp.

I am using this preamp: RIAA Preamp

I'm using a +-5v supply with 4 OPA211 opamps.

I noticed the design is almost exactly the same as the one here:
- DIY Phono Preamp : Recording Magazine -

minus changes in the "rumble" filter settings for R3 and C3 and the input filter (R6 and C6) and the resistor (R12) instead of a 4.7uf cap on output.

I attached a picture using wave splitter to see if clipping is occuring and it looks like it clearly is (30k to -30k) and I'm wondering, would this account for the distortion?

Also, since i am using a split supply I put 100k resistors between each voltage and the opamp input (substituting for R1 and R2 in the first schem) however, since I am using a dual supply I don't know how to change the values without messing up the RIAA curve. The first link says:

"To adjust the gain of the amplifier without sacrificing the RIAA equalization response, scale both R1 and C4 together as a set, and R3, R5, C2, and C3 together as a set, remembering that a capacitor's impedance is inversely proportional to its capacitance, at any given frequency. For instance, if you needed to halve the gain, you could double R4 to 3k (2.7k or 3.3k are practical values), and halve C4 to 11 uF (10 uF). Or, you could halve both R3 and R5, while doubling C2 and C3. "


This confuses me though since he says I can just double R4 and halve C4 after saying I need to scale much more than that.

So I have a couple questions:
1) could the 'lower' +-5v supply be causing the clipping?
2) should I just change the circuit to the second schem (is it better)?
3) do the input bias 100ks have anything to do with the clipping?
4) should doubling R4 and C4 fix the problem per his suggestion (since I am biasing differently)?


Thanks for any help on this! I'd be glad to upload an audio clip for anyone to listen to the distortion I am talking about if it would help (I would need to find a site for it too since I cannot attach it here).
Attached Images
File Type: png wave splitter.PNG (20.2 KB, 223 views)

Last edited by audiomodder; 23rd December 2009 at 09:49 PM.
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Old 6th November 2012, 04:15 PM   #14
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I am sure this is too late to help but using a split supply you do not need the 100K resistors, this is probably the source of your problem.
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