Marantz PM6006 phono stage

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Josem
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Marantz PM6006 phono stage

Post by Josem » 01 Dec 2016 17:55

Hi. I have purchased an integrated amplifier Marantz PM6006. Out of curiosity, someone knows if your phono preamplifier is passive; active; Discrete or with integrated circuits.
Curiosity arises, even though its performance is good, I think that it surpasses stages of phono DIY that I possess VSPS 300 dual mono and MUFFSY (active and passive resectively and both with IC.
Greetings.

Josem
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Re: Marantz PM6006 phono stage

Post by Josem » 30 Apr 2018 17:29

Hello everyone. I am building stages of DIY phono (or trying it) for some years.
I have read many articles about them, about RIAA, about power supplies, etc.
I have also built my first amplifiers and my first acoustic boxes.
But now I have come to have a modest audio system, consisting of acoustic boxes B & W dm602; Van den Hull cables; integrated amplifier Marantz PM6006; CD player Marantz CD 5400; direct turntable (1982) Aiwa AP2400 with AT440Mlb; Marantz ST6000 tuner.
Although the Marantz integrated amplifier has a phono stage, I am using the VSPS400 kit (for building the Emerald kit)
It's that its sound is more pleasant, less fatiguing.
I find that the phono stage of the Marantz, although it is good, has in my opinion an accentuation of treble that I estimate between 8 and 10 kHz which makes the music fatiguing.
I have not found the circuit of the phono stage of the Marantz PM6006, but I have seen that on the circuit board there are some inductors, one per channel at the phono input.
I found the circuit of the phono stage of the Marantz PM5004 and I see that these inductors are at the entrance of this stage. I also see cartridge loading capacitors. I think that if I remove them, using only the capacitance of the cable, it will improve that accentuation in treble
I would like someone to explain what function the inductors fulfill and what effect they have on the frequency response.
Greetings and thanks.
http://i67.tinypic.com/15yexlg.jpg
http://i65.tinypic.com/282hrk.jpg

Josem
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Re: Marantz PM6006 phono stage

Post by Josem » 10 May 2018 22:26

Nobody thinks?

DeepEnd
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Re: Marantz PM6006 phono stage

Post by DeepEnd » 11 May 2018 07:19

I not sure anyone other than the designer will be able to give the exact reason but I can try to “guesstimate” the answer.

The NJM2068 is a wideband opamp with reasonable slew rate and (up to 30mA) a reasonably symmetrical output with enough current to drive a capacitive feedback loop and is therefore a sensible choice for a phono stage.

In the classic era of phono that many of the designs people look (and use for kits etc) were generated that would be enough and a simple input stage used. The problem is current manufacturers now have to comply with stringent compliance testing. In particular we now have many radio sources around the home (WiFi, DECT phones, microwaves etc) and the current RFI testing regime is hard to pass.

Here the wide bandwidth of the IC becomes a liability as it will happily respond to these external signals. I suspect therefore that the rather strange double loading parallel resistors and capacitors AND the inductors are all to help with RF immunity.

The value is quite significant (320mH) given most MM/MI have internal inductance of about 500mH and at 20kHz it’s impedance is about 40K Ohms so will reduce the signal almost 3db at that point. Someone with better skills with simulation software may be able to plot out the full frequency response of the input circuit and the impact of the additional inductance with the capacitance.

I would think however with this front end you would not get the normal benefits of the lower inductance models (e.g. Grace and some AT units) that are considered “special” as their lower inductance would be swamped by the input inductance.

Josem
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Re: Marantz PM6006 phono stage

Post by Josem » 13 May 2018 17:35

Thanks DeepEnd.
I've seen hundreds of phono stage circuits; I've built a few kits and I've never seen this load configuration. (I clarify that the circuit I have published is Marantz PM 5005 and the one I have is Marantz PM 6006, which from what I have seen also has the inductors and double capacitors in the load).
I simulated in LTSpice with the values of AT 440 Mlb and as a result there is an accentuation around 8-10 khz and then a pronounced decotion.
I do not know if this actually happens, but listening seems a bit exhausting in the highs.
I am about to dismantle the amplifier, eliminate the inductors and load capacitors.
The issue is that the amplifier has only 1 year and a half purchased, and disarmament is somewhat complicated.
Meanwhile, I'm using the Phones stage of the RJM Audio VSPS 400 (kit) and occasionally the DIY Solidphono of TNT both very good.
Goodbye and thank you for your opinion.
If I make the modificacon I tell you

Spinner45
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Re: Marantz PM6006 phono stage

Post by Spinner45 » 13 May 2018 18:12

The inductors and associated parts are basically an RF interference filter.
The designers put that in place after extensive testing, to quell interference from nearby components.
Do not modify the circuit, as it's been designed in, and I'm sure the people who designed it know much more than you do.

Josem
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Re: Marantz PM6006 phono stage

Post by Josem » 14 May 2018 02:28

Thanks for the advice. I will not modify the circuit. I will leave it as designed.
You have reason, the engineers and designers of Marantz will know why they have done it.
But vinyl I like to listen to them with my DIY preamplifiers.
At least with the Audio Techica AT 440 Mlb.
Thanks again

chamaruco
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Re: Marantz PM6006 phono stage

Post by chamaruco » 24 Sep 2018 18:44

i'm trying to understand if the phono stage of my pm6006 is so bad or similar to pm8006 that i'am evaluating as upgrade.
someone knows more?
thanks

Coffee Phil
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Re: Marantz PM6006 phono stage

Post by Coffee Phil » 24 Sep 2018 21:02

Hi DeepEnd,

I believe you are correct in that the input network is for EMI attenuation. This issue is not unique to wide band op-amps. While lower bandwidth op-amps may not be able to follow an RF signal they will rectify it. That is what an AM detector is. This issue has been with us from the early days of modern magnetic cartridges. A 12AX7 is not typically what one would think of as a VHF amplifier yet RF signals can be detected by a 12AX7 phono stage if care is not taken.

Phil
DeepEnd wrote:I not sure anyone other than the designer will be able to give the exact reason but I can try to “guesstimate” the answer.

The NJM2068 is a wideband opamp with reasonable slew rate and (up to 30mA) a reasonably symmetrical output with enough current to drive a capacitive feedback loop and is therefore a sensible choice for a phono stage.

In the classic era of phono that many of the designs people look (and use for kits etc) were generated that would be enough and a simple input stage used. The problem is current manufacturers now have to comply with stringent compliance testing. In particular we now have many radio sources around the home (WiFi, DECT phones, microwaves etc) and the current RFI testing regime is hard to pass.

Here the wide bandwidth of the IC becomes a liability as it will happily respond to these external signals. I suspect therefore that the rather strange double loading parallel resistors and capacitors AND the inductors are all to help with RF immunity.

The value is quite significant (320mH) given most MM/MI have internal inductance of about 500mH and at 20kHz it’s impedance is about 40K Ohms so will reduce the signal almost 3db at that point. Someone with better skills with simulation software may be able to plot out the full frequency response of the input circuit and the impact of the additional inductance with the capacitance.

I would think however with this front end you would not get the normal benefits of the lower inductance models (e.g. Grace and some AT units) that are considered “special” as their lower inductance would be swamped by the input inductance.

combitek
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Re: Marantz PM6006 phono stage

Post by combitek » 13 May 2019 12:11

Hello Josem,

I also have the Marantz PM6006 integrated amplifier. I am not that experienced in phono stages but I would like to upgrade from the integrated one inside the PM6006. Please could you make me some recommendations based on your experience? I would like to do a DIY project, as I am capable with soldering and electrical assembly.

Many Thanks
Combitek

lini
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Re: Marantz PM6006 phono stage

Post by lini » 16 May 2019 15:27

Josem: Maybe the regulations have also changed elsewhere, but it might as well just be manufacturing simplification/unification.

Shall mean, if you study service manual/schematics, you might notice, that especially over here in Germany we already have a rather long history of "capacity-crippled" phono sections - due to comparatively strict FTZ/ZZF regulations regarding EMI. Quite a few years later that seemed to become more of EU-wide problem, probably foremost due to harmonised regulations. At roundabout the same time that capacity crippling was more and more perceived as problematic by both the hifi press and the users, probably also due to vinyl becoming more popular again, so more manufacturers have switched from purely capacitive to mixed inductive and capacitve low-pass filtering. And the most recent trend appears to be to move away from implementing that filtering in some countries/regions only in favour of generally implementing it instead. As already mentioned above, I'm not sure, whether that's due to regulations in (enough) other countries/regions having become more strict, too (so that not enough exceptions are left anymore to justify different versions for different countries/regions) - or rather due to the manufacturers simply striving for lowered cost by (more) unified production.

And hence I wouldn't quite agree with S45. Because, while the circuit designers might very well know, what they are or have been doing, they nevertheless may often enough only do/have done, what they do/have done, to comply with quite possibly (overly) strict regulations - which in case of more recent designs often enough may just not be easily visible from the service manuals/schematics anymore due to that unification. For example, roundabout 15 to 20 years ago, when you had noticed that the MM input on your EU-version Marantz PM7000/8000/7200 sounded rather odd, you just needed to check the service manual/schematic to see, that it had a 480 and a 670 pF cap installed instead of just a 150 pF cap in all other versions - whereas the service manual/schematic of a current Marantz model will most likely show no difference anymore, so that you're not getting a valuable, helpful hint anymore regarding a more reasonable degree of low-pass filtering.

Well, and while I'd concede, that there nowadays generally is more RF around, which may also include internal RF by modern, more digital designs (like for example modern digital surround receivers, but also stereo stuff with integrated DAC sections, USB ports, (W)LAN and Bluetooth et cetera...), it would seem pretty interesting, that separate phono stages typically have escaped all that crippling - without doing badly in our modern environments, just as most older, not yet (overly) crippled integrated phono sections also usually don't seem to have any problems to cope with modern-day EM radiation. Which in my view would appear to be a pretty strong indicator, that the corresponding regulations are unnecessarily strict - and that's why I wouldn't concur with S45, that modding such crippled designs would be bad idea.

And in addition I'd like to suggest to both fellow phono fans and the hifi press to excert a bit more pressure on the manufacturers to come up with phono section designs with user-selectable degrees of low-pass filtering/HF blocking. I.e., why not offer two or three settings, from which the user could choose according to his local requirements in his system environment? That would neither be hard to implement, nor cost all that much...

Greetings from Munich!

Manfred / lini

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