Have I Fried my Fidelity Research Moving Coil Cartridge?

[ronaka]

Did a really dumb thing. I had my Marcof PPA-1h head amp out of my system, and when I put it back I plugged the cartridge cable into the output jacks instead of the input. There was a bit of a pop when I started it up and of course got no output. When I corrected the cable connections volume was near zero in the left channel. I did some testing as follows:

I unplugged the left input cable to the head amp. With the right input only I get full volume from the right channel, and zero volume from the left. When I plug the right channel only into the left head amp channel I get full volume out of the left and nothing from the right. Concluded the right channel of the cartridge and the head amp and my phone stage in the preamp are good. Also the left channel of the head amp and preamp also seem good.

Plugged the left channel only from the cartridge into the left channel of the head amp. I initially got nearly full volume from the left channel but it seemed to slowly drop down to 50%. I then shut of the head amp and volume went to zero. I switched the head amp back on and got nothing from the left or right channel. Thought there may be a battery problem in the head amp so I changed them. Tried same thing again and got nothing out of the left channel whether it was plugged into the left or right channel of the head amp.

I'm thinking I have a short in the windings of the left channel of the cartridge -- fried. Kind of sad as this is a recently rebuilt Fidelity Research cartridge FR1-MK3F. It has silver windings, and now has a ruby cantilever.

I'm thinking repair would not be possible. Your thoughts?

[JoeE SP9]

Have you tried measuring the coil windings with a meter? An infinite reading would indicate a blown coil.

[Ldg]

If I can ever get my head around the Marcof head amp, when you connected the cart incorrectly, the worst that could happen is two moderate electrolytic caps would charge/discharge once via the cart coil, from about 4.5V. You'd be unlucky to damage the coil that way, but the wire is typically super fine.........

I'd endorse JoE's advice, use a DVM. Shorted turns seems unlikely, open is far more likely. And be sure to try the cart without the headamp on another preamp before condeming it, asuming the winding is intact.

This is a floating headamp, so if the cart has intentional internal connections to ground that might muck things up, of course.

Good luck !

[josephazannieri]

Yo ronaka:

JoeE SP9 and I have same thought. perhaps your cartridge has opened up from too much current from output of preamp. I would suggest using a digital voltmeter with numbers, not an analog meter with a needle. Analog meters tend to shoot a fair amount of current through the cartridge while measuring it, putting fine coil wires at risk. Cartridge may have opened up from too much output from preamp, but no way to know unless you measure. Specified cartridge resistance may be listed in cartridge data base. Try looking it up. But, in a moving coil cartridge, there should be continuity between the outer shield of RCA plug and the center pin of same RCA plug. Chances are if it's infinite resistance, it's either an open coil or a break in wiring between RCA plug and the cartridge. To determine if it'a wiring or cartridge, take cartridge clips off the cart and measure between the right signal and right ground pin, and then measure between the left signal and left gound pin. Colors are red to green, and white to blue. If you get continuity through cartridge your problem is a wiring failure, which can be found by measuring between red wire and center pin of right RCA plug, Green wire and outer shield of right RCA plug,white wire and center pin of left RCA plug, and blue wire and outer shield of left RCA plug. Wires should measure 1 ohm or less.

And good luck from that colorful, yet digital, old guy,

Joe Z.

[ronaka]

If it helps here is a circuit drawing of the Marcof PPA-1h. I would have connected the cartridge to the audio out shown on the right ,

[josephazannieri]

Yo Ronaka:

You might not have applied any current to your cart. The preamp you show has a grounded input, which means that when there is nothing in the input, basically nothing other than a tiny amount of noise comes out the output. That might not be enough to hurt cartridge. Now if you were getting a sizable shot out of preamp, say if there was some sound or other stuff going in, then you may have fried the cart. But if there was nothing plugged into input when you plugged cart into output, you may have escaped, and your problem may be elsewhere. Use DVM on ohms scale and check carefully for cart resistance between the signal lead and ground lead on each channel. If that's OK, then check cart wires between headshell and the RCA plugs like I previously suggested.

And good luck from that now hopeful old guy,

Joe Z.

[Ldg]

It's not inuitive, so need to be on form to interpret. But methinks it can't be worse than already posted.

BTW, don't know -ve Vbe specs for those transistors, but maybe some power up protection is in order anyways ? It must be tight.

And if each headamp channel still works seperately, as I think you posted, all can't be too bad for the head amp. It must be working ?

[steve195527]

don't measure your cartridge with an analogue meter:-that will def blow it!

[ronaka]

And if each headamp channel still works seperately, as I think you posted, all can't be too bad for the head amp. It must be working ?

Yes, if I use the cartridge right channel output cable and connect it to either the right or left channel of the pre preamp I get normal output. I think that proves the pre preamp and the rest of the system is good. However, when I plug the left channel into either channel of the pre preamp I get nothing. Seems to strongly suggest the left channel of the cartridge has died.

I have a digital multi meter, but am still working on the nerve to check the DC resistance of the cartridge channels. I don't even know for sure what it is supposed to be. My Fidelity Research manual says it has a load impedance of 10 ohms. I'm assuming that it wants to see a load impedance of 10 ohms, and that is not a spec on what the winding DC resistance is.

[josephazannieri]

Yo Ronaka:

I believe that you are saying that when you plug your turntable into right channel of pre preamp amp and plug pre preamp into play you get normal sound. If that is the case, then your problem is on one side. Use your DVM, (NOT an analog meter with a needle) and measure both sides of cart. If right side of cart works, then you may assume that it is good. The resistance of the right channel will be your benchmark. Just compare right and left channels. If they are the exactly the same, say 100 ohms and 100 ohms, the cart should be OK. If they are close, say 100 ohms and 92 ohms, cart is probably still OK. If they are WAY different, say 100 ohms and no measurement (open circuit) or 100 ohms and 3 ohms, (pretty much dead short)then you may have a problem. The farther apart the cart sides are, the more likely that you have a problem. If you have a problem, go to Fidelity Research and ask them if it's fixable, and what it will cost. It might be doable.

The general rule in stereo gear is, if one channel works and other doesn't, you can use the good channel's measurements to get an idea how the bad channel should be reading. Just fixed my Dyna PAS-3x by comparing bad channel with good channel. Problem was a dirty switch.

And good luck from the old comparator,


Joe Z.

[MR F]

Sorry I can't help with your question, but I have one of my own.

How good is this cartridge? I have one that came on a used turntable, and the cantilever is completely demolished. It seems like a seriously high-end cart, I figure it's worth trying to get it repaired (and buy an appropriate SUT). Anyone have any comments on the MK3F?

[ronaka]

OK some good news and bad news. The good news is that I think my cartridge may be OK. I pulled the pre preamp out and connected all the cables where I can see and work with some room, and one at a time wiggled them. I'm now convinced I have a bad RCA phono plug on the left channel cable from the cartridge.

The bad news is that it appears to be a special cable for the Grace G-707 tonearm. I belive Grace is out of business, but non OEM replacements are available on the internet, but for prices ranging from $120 to double that. I'm thinking I will just buy a couple of gold plated RCA plugs (originals were not) and replace them. Should work I think?? Here is what the tonearm end plug looks like - the beige one. It also says Grace on it.

[MR F]

Looks like a standard 5 pin DIN, but most arms have the pins in the arm and the receptacle in the cable. I guess this arm is reverse?

You could replace the phono plugs, but the continuity problem could be in the cables themselves. You could de-solder the DIN and attach a new set of cables.

[ronaka]

Looks like a standard 5 pin DIN, but most arms have the pins in the arm and the receptacle in the cable. I guess this arm is reverse?

You could replace the phono plugs, but the continuity problem could be in the cables themselves. You could de-solder the DIN and attach a new set of cables.

Just going by feel, I think the issue is right at the connector. But yes it could be in the cable. The center conductor is stranded and very small. I'm working on soldering the new connectors now.

Yes, this cable seems to be the reverse of the standard. Male pins on the end of the extension cable, and female on the tonearm part.