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+  MCI Console and Tape Machine Forum
|-+  MCI Tape Machines
| |-+  JH-110 (Moderator: brianroth)
| | |-+  JH110C 1/2" Conversion
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Author Topic: JH110C 1/2" Conversion  (Read 182 times)
TonesOnTail
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« on: March 24, 2018, 01:43:53 PM »

Hello all,

I know that this forum is largely dead, but I figured I would give it a try anyway.

I am assisting a colleague with installing 1/2" two track heads on a 110C. The heads are B/C heads, and the repro head has the same DCR as the 1/4" repro head of around 35.4 ohms. When running a brand new MRL IEC1 tape in repro, the 10khz response is -18dB down from the 1khz response. I did a test record as is on a new pad of RMGI 900 after boosting the input gain to set +4dB over bias, and swept tone from 1kHz and up, and discovered the -3dB corner to be at around 2800Hz.

Even though the heads measure the same DCR, and are manufactured for MCI B/C electronics it seems possible that an impedance mis-match is causing the 1/2" heads to act as a LPF filter above 2.8khz. Frequency response is flat up to that point.

So the question is, was there an errata or service bulletin dictating a component change on the audio electronics for conversion from 1/4" two track to 1/2" two track?
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'75 MCI JH16-24 w/ JH114 xport ----- '84 Sony/MCI JH110C-HP 1/4" 2trk ----- '82 MCI JH636-VU-AF
brianroth
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« Reply #1 on: March 24, 2018, 03:37:52 PM »

You might try contacting John French at JRF and see if he has any suggestions.

Bri

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Professional audio and video systems design/construction/service/common sense.

Now based in Salina, Kansas

http://www.BrianRoth.com
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