MOD OR NOT?

johancraftech · 30th July 2011, 09:49 AM

While waiting for my new TT (Pro-Ject RPM 1.3), I need some guidance whether to mod my existing phono-preamp (old B & O) for the Ortofon 2M (Red) cartridge or should I go ahead and diy the famous J-Fet phono-preamp?

Skorpio · 30th July 2011, 11:49 AM

Keep the old and try with input capacitance...you might like it?

johancraftech · 30th July 2011, 11:53 AM

Quote:

Originally Posted by Skorpio

Keep the old and try with input capacitance...you might like it?

Thanks Scorpio

merlin el mago · 30th July 2011, 01:06 PM

Also try 100K trimmer instead R3 fixed 56K so can get best input load for your MM cartridge.

johancraftech · 31st July 2011, 06:36 AM

So far: (1)Will experiment with different values for C1, (2)Replace R3 with 100k multi-turn pot and (3)Insert 100pF capacitor across R1.

merlin el mago · 10:42 AM

Pay attention load input capacitance in parallel with R3 (try manufacturer suggestions something between 150-300pf if possible type silver mica), I suppose C1 it's to avoid input DC so if you don't use a MC pre-pre you can get off.

johancraftech · 31st July 2011, 10:41 AM

Typo on my side, suppose to be 100pF across R3. Do you mean remove C1? (cartridge MM)

merlin el mago · 31st July 2011, 10:45 AM

If you will use only MM cart or you are sure that MC pre-pre don't have DC output, yes I remove C1

johancraftech · 31st July 2011, 10:50 AM

I get it, will short out C1 after measuring if any dc exists.

merlin el mago · 31st July 2011, 10:54 AM

Quote:

Originally Posted by johancraftech

I get it, will short out C1 after measuring if any dc exists.

Attention If you connect directly the MM cart don't measure, for sure you don't have DC!!!!! it's only if you will use a MC pre-pre.

31st July 2011, 10:38 AM	#6
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Blanes - Costa Brava	Pay attention load input capacitance in parallel with R3 (try manufacturer suggestions something between 150-300pf if possible type silver mica), I suppose C1 it's to avoid input DC so if you don't use a MC pre-pre you can get off. Last edited by merlin el mago; 31st July 2011 at 10:42 AM.

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30th July 2011, 11:49 AM	#2
Skorpio diyAudio Member Join Date: Mar 2004 Location: Denmark	Keep the old and try with input capacitance...you might like it?

30th July 2011, 01:06 PM	#4
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Blanes - Costa Brava	Also try 100K trimmer instead R3 fixed 56K so can get best input load for your MM cartridge.

31st July 2011, 06:36 AM	#5
johancraftech diyAudio Member Join Date: Dec 2010 Location: South Afica	So far: (1)Will experiment with different values for C1, (2)Replace R3 with 100k multi-turn pot and (3)Insert 100pF capacitor across R1.

31st July 2011, 10:41 AM	#7
johancraftech diyAudio Member Join Date: Dec 2010 Location: South Afica	Typo on my side, suppose to be 100pF across R3. Do you mean remove C1? (cartridge MM)

31st July 2011, 10:45 AM	#8
merlin el mago diyAudio Member Join Date: Sep 2009 Location: Blanes - Costa Brava	If you will use only MM cart or you are sure that MC pre-pre don't have DC output, yes I remove C1

31st July 2011, 10:50 AM	#9
johancraftech diyAudio Member Join Date: Dec 2010 Location: South Afica	I get it, will short out C1 after measuring if any dc exists.

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