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Phase inverting problem

Hello,

I have a Conrad Johnson PV-12A pre-amp. It is phase correct for the phono stage, phase inverting for the line stage.

My power amplifier is a conrad johnson MF2100. It is phase correct.

So my first idea was to connect the speakers to the power amplifier the wrong way (black to red, red to black) and then connect the cartridge the wrong way around as well (R: + and - reversed, L: + and - reversed). Then the phase should be correct for everything.

But there lies the problem. When I switch the connections on the cartridge, I get a really loud hum, makes the music barely hearable. Perhaps it has something to do with the fact that R- is connected to the cartridge body, it is some kind of earth? Anyway, switching the connections on the cartridge is not an option. So, what to do?

My only idea so far is, seeing that I only have one line input (cd), is cutting open the RCA cable and switching + and - of the line, and connecting the speakers to the power amp the correct way. So, I'll do just that. But maybe there's a better solution that I'm missing. Any ideas?
swaf
magfan
1,583 posts
 
Can you REALLY tell? Most people can't, and given the way modern music is recorded, no wonder.
Modern music is a jumble of phase, sometimes recorded in different places days apart.
I doubt any recording engineer pays any attention to absolute phase coherency.
hifitime
715 posts
 
Swaf said the minus is tied to his cartridge body. So when he reverses them, the plus may be tied to the whole tonearm. That would explain the hum. Then if he grounded the whole arm with the cartridge wires reversed, it might short the signal (plus)to ground also.
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tonykay
1,301 posts
 
Phase inverting...whose idea was that? Clearly, I'm not an electrical engineer but who in their right mind wants to reverse leads on their cartridge or change the wires on their speakers just to play a record. If phase inversion can't be done with the flip of a switch, that component (no
matter how good) will never find it's way into my system.
unsound
7,329 posts
 
Tonykay, sometimes a manufacturer is trying to eliminate the source of extra potentially distorting circuitry from the inherent phase of the device. It's really no problem to reverse the speakers connections.
swaf OP
4 posts
 
Thanks for the responses.

Can I tell? No, actually I don't. But I just want to do it as correct as I can. You never know. i don't want to find out in five years I've been listening to a sound that could have been a lot better.

Almarg makes a god point - the phono stage does go through the line stage. I don't have a manual, and on the manufacturer's site it just says: "Line Stage phase inverting, Phono Stage phase correct" which sounds pretty ambiguous to me. I've sent them a mail. unless someone here knows the Conrad-Johnson PV12a and knows what it does?

Why does it hum when reversing the wires? No idea. I use a Technics SL1200MK2 with standard tonearm, if that helps. I see a black ground wire going in the bottom of the tonearm, but I don't know where it is connected to. I suspect the ground is connected to the inside of the tonearm (I can't check since the outside of the tonearm isn't conductive). The green wire (R-) is connected to the cartridge body, I can see that. But as far as I can make out, the cartridge body is not connected to the tonearm / ground. I can't figure out why switching the red/green and blue/white would cause a big hum, but it does.
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