Originally posted by Old House Scott:
I was wondering if anyone had any thoughts about retrofitting them with maybe Burr-Brown OPA(2)134's or OPA627's?

It looks like the 2134 would work okay, although the current draw can get up to 10 mA which is about 2mA higher than the 55 series will pull. This could stress the power supply. It looks like the 627 is better in this respect, it will draw up to 7.5mA. I can't comment on the sound quality of either of these opamps since I haven't used either of them.

I redid my JH24 with analog device OP275 (duals) and OP176 (single). They have the nice advantage of drawing far less current (~5mA). And made a nice improvement in the sound overall.

Mark Plancke [url="((deadlink))[/url]

I replaced some of the 5534s in my MCI board with burr-brown op134s and the 5532s with analog devices op275s and was quite please and didn't have to otherwise mod the circuit.

I don't know what the "chip change" will do to the audio as I've always left them 'stock' (and quite like the way they sound). I will pass along one major maintenance tip...

On the first of each month, turn off the machine, pull out both power supplies. Undo the 4 fasteners that hold the "fan plate" on and carefully remove that plate. Now, vacuum the inside of the power supply. Get it as clean and dust free as possible. Now reassemble, and reinstall.

JH-24's have a bit of a bad rap for being unreliable, dust buildup not permitting proper cooling of the power transistors is the usual cause of these failures. If you take proper steps and keep the supplies clean, you should find the deck to be rather reliable indeed.

Best of luck, the JH-24 is without a doubt one of my favorite machines ever built!!

Originally posted by Fletcher:
On the first of each month, turn off the machine, pull out both power supplies. Undo the 4 fasteners that hold the "fan plate" on and carefully remove that plate. Now, vacuum the inside of the power supply. Get it as clean and dust free as possible. Now reassemble, and reinstall.

I also found a fan which is installed above the power supplies on the frame itself that benefited from cleaning. If you pull the supplies it should be in the middle above where the supplies sit. Mine is a '87 JH24 so I'm not sure if this applies to all machines.

Also, when you get the machine make sure to go through, pull all the transport boards and clean all the molex connectors (I used deoxit) it doesn't hurt to touch up the solder joints either. I found that most of the problems that crop up can be traced to these connectors. Do the same in the remote.

Rock on!

Mark Plancke

the JH-24 is without a doubt one of my favorite machines ever built!!
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No arguement from me regarding sound quality or reliability. But am I the only one who thinks that MCI recorders take the prize for ugliest pro multi tracks ever sold? Maybe I just hate fake woodgrain, but MCI machines always remind me of my neighbors Country Squire wagon circa '71. When industrial design students look back on the 1970s, they are going to laugh their asses off wondering why manufacturers glued fake woodgrain contact paper on items that had NEVER been made out of wood. My favorite was my woodgrain Norelco shaver I got in high school. sorry, waaaay off topic......