MPI4.

62caddy

Trust but verify
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Latest addition (and last) to my "stack of Mc". Had wanted one of these for some time - had to move the CR7 and CD player to a side table so the main rack is a tower of black glass (except for the power controller).

Purchased from Audio Classics it's in great condition.

Very handy tool for multipath detection, testing of cartridge performance, stereo spread/balance, output monitoring and more.

Owner's Manual specifies special RCA cables - originally supplied with the MPI4, now long gone - must be used for making connections from the MPI4 to tuner and preamplifier. I checked with Ryan and he said modern shielded type RCA cable should suffice. Shielded cabling being less commonly available back in the mid '70s when the MPI4 was being produced.

All functions seem to work fine with the cables I'm using.

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Dual trace mode. Upper trace is left channel.

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Stereo Mode below.

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I think you would want to use the video type RCA terminated cables. That is 75 ohm typically with yellow ends. I think the wording of the owners manual slipped by the proof reader....ie.....low capacity was supposed to read low capacitance.
 
Yes there are quite a few proof errors in the MPI4 manual I noticed.

Would that type of cable be necessary for both the tuner and preamplifier connections? I'll see if I can locate that type.
 
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No just as part of the RF circuit from TP1 and TP2. I think most coax digital cable are speced at 75 ohms also and do need to care digital at RF like frequencies.
 
Last? ROTFLMFAO!!!!

Nice acquisition caddy - time to put it to use to dial in the cartridge on that tt.
 
Last? ROTFLMFAO!!!!

Nice acquisition caddy - time to put it to use to dial in the cartridge on that tt.

lol! Last for the main rig anyway. Rack is completely filled.

*Different test record is needed than the one I have for anti skating adjustments. Adjustments have to be made by ear with the Stereo Review test record I have now. I'll have to pick up a CBS test record to use the MPI4 for making those adjustments.

The MPI4 confirmed very respectable performance of the AT 440MLa cartridge. When I get a chance, I'll post some traces of the tone burst & square wave tests.
 
Looks great, congratulations.

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Love those later knobs on the MQ101. How'd you pull that off???

The large ones are 2205 I believe. They were on one of my 2125 when I got it.

The small one for the (L) 20Hz shaft was a "throw in" that came along with the package of some other Mc knobs I got. Had no idea what it was for but I decided to see if I could get it on the MQ101 and amazingly, fit right on along with the 2205 knobs I had laying around after I got the proper knobs for the 2125.

The MQ looks right at home with the other pieces now.
 
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Lookin' good, nice one 'caddy.

You can now use your Nortronics AT-210B alignment tape and get into the cassette repair business.
 
To measure crosstalk you need two double pole double throw switches, a triple throw double throw, or just unplug one turntable lead at a time. Ultimately you are measuring how much signal is leaking into the unhooked channel.

Crosstalk is the most important parameter for stereo image vs. a mono image.

You need a series of hotly cut tracks to monitor the channel breakup on the scope for anti skate.
 
Here are some scope readings.

Square wave test.
*Explanations from test record accompanying literature.

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Tone burst test.


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Intermodulation distortion pattern.


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Multipath reading.

(Multipath Polarity switch needs to be in (+) with the MR80.)


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Does your test record have a cartridge resonance test?

I have not yet received the HiFiNews test record but from what I have read review wise I think it might be the best currently available.
 
No cartridge resonance test. Might the tone burst pattern reveal anything along those lines or is resonance an entirely different matter?

I'll have to check into that test record. McIntosh cites the CBS test record pretty regularly so I figured that would be the best but if the HiFiNews (or any others) are better, I'm open to any recommendations.

My SR12 is 1969 issue and fairly worn so an updated record is probably a good idea anyway.
 
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Nice find! It looks as though you've got one with a good healthy trace.
I once had one, but due to the horizontal config of my Mac components and turntable, I simply ran out of room.
Not that I couldn't have came up with a workable solution though. Bottom line is that I rarely used it anymore, and the resale value was enough to justify selling it.

I must admit, seeing yours in your system, I occasionally question that decision. Very impressive!
 
No cartridge resonance test. Might the tone burst pattern reveal anything along those lines or is resonance an entirely different matter?

I'll have to check into that test record. McIntosh cites the CBS test record pretty regularly so I figured that would be the best but if the HiFiNews (or any others) are better, I'm open to any recommendations.

My SR12 is 1969 issue and fairly worn so an updated record is probably a good idea anyway.

The only test records I ever used with Gordon or Dirk were the " for the trade" test records from Shure, AT, and Ortofon. ( DOB though was fascinated watching the Sota Stapphire suck down flat a CTI potatochip record)

A resonance track will have a 6-20 hz tone imbedded in a higher frequency. The low tone will excite the tonearm/stylus system causing a possible physical and audible indications of the systems resonant frequency. These test frequencies are announced by a narrator ( the female Scandinavian on the Ortofon record was far superior to the dry engineer on the Shure records.) you want to increase, decreasing is expensive, the mass of the arm to get it to resonate in the 10-12 hz range. Above record warp, 8 hz and below, and below a 32 foot organ pedal at 16 hz.

Time consuming, yes, but if you want to do it right it has to be done.

Sanding down a lead spacer plate to affect the azimuth, a trick I showed Gordon with his prototype MCs, is all part of details.

Pushing these details to the limit allow you to get channel separation up into the high thirtys even up over 40dB with the best exotic cartridges. A typical microridge like the 440 would come in at 26-28, the AT32 MC, the first microridge, vintage 1982 or so, could achieve 33 dB. A typical cartridge would be in the 20-22 range.
 
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