Marantz PM6007 Phono Input Capacitance

[Ian Knight]

I have a Marantz PM6007 amplifier. I want to use a EAT Prelude turntable with a Audio Technica VM95ML cartridge.
The supplied turntable cables look like Project E which have around 127pf / MTR. I am trying to find out what the phono input capacitance
Is on the Marantz PM6007. I can only find the 47k Ohm impedance figure in the manual.
Does anyone know if the Marantz has the usual 100pf capacitance input please?.

I may have to use a 0.5mtr cable to get the capacitance down in value anyway.

Cheers Ian.

 

[Raticosa]

Hello, I have same amplifier too.
No, the input capacitance is 220pF // 47kOhm and is too high for many MM cartridges, I know because I bought the PM6007 service manual (with schematics) and then dismounted the phono board (very easy to do, one connector and two screws) to replace the input capacitance with a smaller 47pF (WIMA red). The phono input board has a sort of "Pi greek" input filter, that is 220pF in parallel, then 33Ohm in series (with a ferrite bead to reduce ESD risk and RF noise), then another 220pF // 47kOhm in parallel, so input capacitance could be even more than 220pF. Some models are missing the first 220pF capacitor, mine has it. See attachments below, where you can see the schematics, the original board (with green capacitors) and after the mod (with WIMA red caps). I also replaced the 22uF / 25V decoupling electrolytic capacitor before the output connector (a good "RA2" ELNA one, but not the better "SILMIC" one you can find everywhere inside the PM6007 boards) with a better quality bipolar 22uF / 35V Nichicon ES Muse (the green one, circled) bypassed with a 0.47uF WIMA MKP2 to improve a bit the higher frequencies and lower the capacitor's ESR (is halved), and sounds a bit better (don't expect miracles). Anyway the phono preamp is a very good one, derived from the PM7000 one. Hope this helps.

 

[Ian Knight]

Hi,
Thanks for that brilliant and informative reply.

I have attached the reply from Marantz service.

Cheers Ian.

 

[Raticosa]

Hello Ian,
happy to help.

Just for sake of information, I tried to simulate with LTSpice the theoretical frequency response of my whole system (MM cartridge + turntable's inner cables + outer RCA cable + phono preamp input impedance) after the modification, with the parameters of my Audiotechnica MM cartridge, and now I'm very happy with it, only +1.8dB of peak at 13kHz (before, with 220pF, was an unacceptable +4.3dB at 9.5kHz, too bright sound) and with -1.8dB attenuation at 20kHz (before was an unacceptable -9.5dB).

It could be improved a bit more (see image 5) removing the first 47pF (before the 33 Ohm series resistor) lowering the peak response at +1.2dB and attenuation at 20kHz at -1.0dB, but I prefer to maintain the "Pi greek" configuration C - R - C of the input stage as originally designed by Marantz.

I used "only" 47pF because, even if my RCA cable (short and good quality one) has only 36pF capacitance, the turntable's inner cable has an high 120pF capacitance I cannot modify (is an old AKAI "tangential arm" automatic turntable with the best T4P cartridge I could find nowadays on the new-old-stock surplus market) so I put the smallest capacitance I can find from the WIMA FKP2 catalogue.

Best.
Gianluca

 

[Ian Knight]

HI Gianluca,

Really useful information...glad you sorted the peak out. I cheated and got myself a very low capacitance QED phono cable ( 40pf ) and run it on the 100pf input setting of a ifi Zen Phono 2 stage. This really does sound good with total capacitance including arm wiring of 150 pf for the Audio Tecnica cartride.

Regards.

Cheers, Ian.

 

[Nick_Sukhov]

Really useful information...glad you sorted the peak out. I cheated and got myself a very low capacitance QED phono cable ( 40pf ) and run it on the 100pf input setting of a ifi Zen Phono 2 stage. This really does sound good with total capacitance including arm wiring of 150 pf for the Audio Tecnica cartride..

Ian, try using less pF with more input resistance/ See my attach.

 

[Ian Knight]

Thanks for the tip Nick, very much appreciated.

Cheers, Ian.