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Old 15th March 2004, 03:21 PM   #1
MaciekP is offline MaciekP  Poland
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Default Phono preamp- how to modify to get deeper LF?

Hello,
I have the Audio Note M3-8 preamp with good phono section. I like it's tone, but comparing to the other phono preamps connected to line input (my phono is in fact an independent phono preamp connected to the line input) it doesn't have a deep enough lower registers. All caps are AN CU PIO, all resistors are AN tantalums. Do you have any idea how to modify the circuit to get a better LF without destroying the rest of sound?
thanks
Maciej
http://diytriode.republika.pl/ANphonoschem.jpg
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Old 15th March 2004, 04:03 PM   #2
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The answer to your bass desires is most probably in the power supply. You may find a nice large low resistance choke and upgraded PS transformer very beneficial there. The heaters PS will also have some effect.

Generally, getting bass without destroying the midrange is not easy and i'd stay away from active regulators and excessive PS capacitance.
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Old 15th March 2004, 04:55 PM   #3
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Default Re: Phono preamp- how to modify to get deeper LF?

Konnichiwa,

Quote:
Originally posted by MaciekP
I have the Audio Note M3-8 preamp with good phono section. I like it's tone, but comparing to the other phono preamps connected to line input (my phono is in fact an independent phono preamp connected to the line input) it doesn't have a deep enough lower registers. All caps are AN CU PIO, all resistors are AN tantalums. Do you have any idea how to modify the circuit to get a better LF without destroying the rest of sound?
Hmmm. The -3db of the coupling into the RIAA EQ is around 15Hz, if you add all the other inevetible LF rolloff sources I'd think -3db @ 20Hz or worse is likely. One would also have to check the RIAA Accuracy, I hope you selected these AN PIO Cap's for 1% or better tolerance as they have a much wider rated production tolerance, which may cause the RIAA curve to be out of spec.

If the situation is as suggested, yo may wish to increase the size of the coupling cap to the RIAA. Kondo San uses 0.1uF in his circuit (which BTW is almost identical). An even better solution is completely re-design the RIAA EQ to be DC coupled to the Anode of the first stage and use a 47nF/1M coupling section to the second stage after the RIAA. But that would require a lot of (Resistor) Values in the RIAA Circuit to be adjusted.

Sayonara
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Old 15th March 2004, 09:27 PM   #4
MaciekP is offline MaciekP  Poland
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thanks Thorsten,
Do you mean C1 capacitor?
I have the spare AN silver 0.22uF, this should add more slam.

Maciej
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Old 15th March 2004, 11:13 PM   #5
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Konnichiwa,

Quote:
Originally posted by MaciekP
Do you mean C1 capacitor?
Yes and the other cap's in the RIAA (C7/C9?) - check their accuracy - they should be nominal +/-1%, assuming the RIAA EQ was correct per design.

Quote:
Originally posted by MaciekP

I have the spare AN silver 0.22uF, this should add more slam.
Maybe, first chec the accuracy of the other capacitors...

Sayonara
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