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Old 6th February 2013, 05:59 PM   #51
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And with 500pF/47k as cart load (the high end of the recommended capacitance)

With RF filt:
4.7dB @ 8.7k

Without RF filt:
4.1dB @ 9.3k

Hmmm....

PS I was trying to isolate the input circuitry and see what it does ... and unfortunately TINA doesn't have an LT1010 model :-(

Last edited by AudioLapDance; 6th February 2013 at 06:08 PM.
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Old 6th February 2013, 06:03 PM   #52
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Do not add any capacitance. Please see that additional input capacitor is zero in the BOM. Keep only C2, indexed as per my schematics. Your different indexes are confusing the issue and may be misleading for other readers. Please do not modify the part values if building the preamp.
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Last edited by PMA; 6th February 2013 at 06:07 PM.
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Old 6th February 2013, 06:41 PM   #53
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Just two pics:
Attached Images
File Type: png openamp_sch.PNG (29.2 KB, 296 views)
File Type: png openamp_fch.PNG (52.7 KB, 291 views)
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Old 6th February 2013, 06:52 PM   #54
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Sorry Pavel, you were right.


Simming the rest of circuit isolated the RF filter from loading the cartridge.

Ok, no C1 capacitor and just assume 150pF as the value to account for cable capacitance. I've updated my circuit.

With the RF filt (R2=150ohm, C2=100pF) there's a difference at 50MHz:

With RF filt
PMA riaa w RF filt.png
5MHz @ -195dB

Without RF filt
PMA riaa no RF filt.png
5MHz @ -180dB

TINA didn't have LT1010 but it did have BUF634 so I used that just to see the basic frequency response. Here's the TINA circuit with the BUF634.
PMA riaa no DC servo.png
And the TINA file:
PMA riaa OPA627 BUF634.zip


Anyone know where to get a LT1010 TINA model? I think there's a LTspice4 model of the 1010 ... how to import ...

PS Sorry for screwing up your thread, I've corrected all the typos I think ...

Last edited by AudioLapDance; 6th February 2013 at 07:22 PM.
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Old 6th February 2013, 07:16 PM   #55
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You will get the same sim results for buf634 and lt1010 regarding freq response. Please keep C1 = 0 and C2 = 100p, as written in the manual and the bom.
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Old 6th February 2013, 09:00 PM   #56
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Linear Technology had a similar circuit many years ago for their LT1115. I was surprised it is still on the LT website. Here it is. LT1115 - Ultra-Low Noise, Low Distortion, Audio Op Amp - Linear Technology

Ray
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Old 7th February 2013, 02:48 AM   #57
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Here's the TINA circuit with 627, BUF634, OP07:
PMA riaa w BUF634 w servo.png

And the TINA file:
PMA riaa OPA627 BUF634 wservo.zip

I found a LT1010 spice model and tried to import it but it peaked the freq response?!?

http://cds.linear.com/docs/en/softwa...ion/LT1010.txt
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Old 7th February 2013, 03:07 AM   #58
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I think I got it! I successfully imported the LT1010 spice file and assigned some pins ...

OPENAMP1 TINA schematic
PMA riaa OPA627 LT1010 OP07.png

Frequency Response 20-30k
PMA riaa OPA627 LT1010 OP07 freq resp.png

And TINA file
PMA riaa OPA627 LT1010 OP07.zip

Last edited by AudioLapDance; 7th February 2013 at 03:35 AM.
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Old 7th February 2013, 07:32 AM   #59
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Looks good!
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Old 7th February 2013, 07:36 AM   #60
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Quote:
Originally Posted by rayfutrell View Post
Linear Technology had a similar circuit many years ago for their LT1115. I was surprised it is still on the LT website. Here it is. LT1115 - Ultra-Low Noise, Low Distortion, Audio Op Amp - Linear Technology

Ray
Yes it is similar, but for MM we preferably use JFET input opamps with reasonably low voltage noise, for the reason of almost no current noise added. Remember that above 1kHz the noise in MM preamp is dominated by the 47k standardized load resistor (just one comment here, reducing load resistance below 47k increases resulting noise!!!!!!! - for the reason of character of MM cartridge impedance). BJT opamps like AD797 are definitely the choice for MC preamps.
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