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Author Topic: JH110 revisions audio electronics/head compatibility question  (Read 3054 times)

BobSchwenkler

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At the studio we've got a couple JH110 machines and a whole boatload of spare parts. Many of the spares we have are from JH110As and the machines we have are a B and C (8 channel rev. of the B). Among the spares we have are 6 channels of JH110A audio electronics.

The once I tried swapping (I think) an A repro card (though it might have been a record card) into the B or C it didn't work very well, severe high end rolloff. Are the audio electronics/heads of these two revisions straight up not compatible or am I missing something? There's not much else on the switching cards that would affect how the repro cards are responding to the heads.

Greg Reierson

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Re: JH110 revisions audio electronics/head compatibility question
« Reply #1 on: April 14, 2011, 02:15:24 pm »

Randy is the MCI guru.

http://www.blevinsaudio.com/


GR
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Greg Reierson
Rare Form Mastering

BobSchwenkler

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Re: JH110 revisions audio electronics/head compatibility question
« Reply #2 on: April 14, 2011, 09:12:45 pm »

I've talked to him about a thing or two over the phone before, thanks. I don't feel comfortable calling with the expectation of having him answer a tech question though.

mbrebes

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Re: JH110 revisions audio electronics/head compatibility question
« Reply #3 on: April 15, 2011, 02:25:54 pm »

The A version had a transformer output with the transformers on the motherboard, while the B was transformerless.  The Repro card on the A version was single-ended out.  Can't remember whether it had transformerless input on the A version.  Would need to pull out my manual when I get home.
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Jim Williams

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Re: JH110 revisions audio electronics/head compatibility question
« Reply #4 on: April 16, 2011, 11:36:30 am »

I'm not sure even the pinouts are similar. I wouldn't try that as it might "let the smoke out".
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BobSchwenkler

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Re: JH110 revisions audio electronics/head compatibility question
« Reply #5 on: April 16, 2011, 01:37:15 pm »

Pinouts do match.

BobSchwenkler

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Re: JH110 revisions audio electronics/head compatibility question
« Reply #6 on: April 16, 2011, 01:41:39 pm »

The A version had a transformer output with the transformers on the motherboard, while the B was transformerless.  The Repro card on the A version was single-ended out.  Can't remember whether it had transformerless input on the A version.  Would need to pull out my manual when I get home.

I'm pretty sure all the repro revs are single ended outs, our B has electronically balanced ins and outs, while the C has transformers on at least the outputs. The B docs list transformer and transformerless as separate options.

The thing I feel like is more likely the issue has to do with the record head drivers or the repro head receivers, rather than the line outputs.

If nobody knows off the top of their head, don't worry about it too much. I can do some more testing and swapping at the studio, just thought I'd see if it was an easy answer for anyone before I put too much time into it.

Time Tech

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Re: JH110 revisions audio electronics/head compatibility question
« Reply #7 on: April 17, 2011, 03:11:00 am »

I believe the "A" series PB heads were Low Impedance heads, hence the need for the tape head transformer. Also the "front end" PB pre is discrete while the EQ section is IC based. Also I believe the PSU voltage is different on the "A" series (+/- 24vdc vs +/- 15vdc of the later models) Severe HF roll off would suggest that the PB head is being loaded by a too small impedence. Probably the Z and DCR of the tape head transformer.
I may be interested in some "A" series spare parts. Plz contact me offline if interested.
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BobSchwenkler

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Re: JH110 revisions audio electronics/head compatibility question
« Reply #8 on: April 17, 2011, 11:20:15 am »

Thanks. I'll take a little more of a look into those with our machines to verify. We have a bunch of spares including PSUs, audio electronics, transport, basically two whole machines worth. I'll PM you when I've looked at our machines. Anyone else passing who has interest in parts feel free to contact me also. I don't want to get rid of them all, but we have more than we need of some things.
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