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Old 11th February 2012, 03:53 PM   #1
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Red face New amplifier????? Help please

Hello all,

I'm very new to all this & could do with a bit of advice please.

I currently have an hitachi HA-5700 amp with marantz cd6002 & kef concord IV

Speakers & usinc sonic link cable with Cambridge audio interconnects.

I'm looking at buying a 2nd hand marantz pm7200 amp & wondered if it will

much better than the hitachi??

Any help would be greatly appreciated.

Thanks in advance.
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Old 11th February 2012, 05:41 PM   #2
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The quality of amplifiers is hard to quantify on a linear scale, so you'd have to be a little more specific as to what "much better" would mean.

The Hitachi is a 50 wpc unit and weighs 10.8 kg? That thing must be built like the proverbial tank. The only larger weakness appears to be quiescent current pots troubled by oxidation, so having those cleaned and readjusted seems like a good idea. Otherwise MOSFET amps like that are pretty hard to kill. The use of contact pairs in the protection relays keeps contact resistance low, too, though how well they might do under a fault condition is anyone's guess. Overall, a decent middle-class vintage amp.

The PM7200 is 20 years its junior, so one would expect some progress. It has a good bit less hiss (about 6 dB), and is more powerful while exhibiting less distortion, too. (Not as little as I'd want to see, but about 6..10 dB less nonetheless.) It is the better unit overall. Note, however, that you'd be losing the ability to use MC cartridges.
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Old 12th February 2012, 01:06 AM   #3
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by mafia1976 View Post
I'm looking at buying a 2nd hand marantz pm7200 amp & wondered if it will
much better than the hitachi??
My intuition says that you will much prefer the Marantz for some reasons:

1) You have a "cheap" speaker that will like class-A amp. I don't believe the Marantz can go 25W class-A, but even 5W class-A is good enough.

2) The Hitachi is an old design. The problem is, IC technology was poor back then. Many old amp had good output stage but used terrible IC (and the power supply) for the preamp, and worse without "main amp input" to bypass the IC/preamp. The output stage and the transistor of the Hitachi is preferable, but the preamp I'm sure will kill the quality of the amp.

A simple DIY idea that you might want to try is: bypass the preamp of the Hitachi and add a much better preamp. Op-amp based preamp but with modern IC will be acceptable. Or even the B1. You just need to find out how to get this preamp
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Old 12th February 2012, 01:35 PM   #4
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Thanks for the replies. The marantz sounds good & then a bit of DIY on the hitachi is a great idea. I must admit although old the hitachi sounds pretty nice to me but an upgrade inside can't hurt. Just need to find the workings etc now of the hitachi tank amp & then start looking in to taking it to bits.
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Old 12th February 2012, 03:25 PM   #5
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While there are about 3 ICs inside the Hitachi (service docs are on HiFiEngine), none of them are standard opamps. Two of them are HA12017s, which is a purpose-built low-noise amplifier IC with what seems to be rather good performance (the datasheet isn't exactly in the best quality I've seen). I wonder what happened to these Hitachi parts, you rarely see any past the mid-'80s.

The problems I can see with the circuit are topological in nature. Impedances around the tone amp in particular seem quite high, and that one determines output noise. A 200k volume pot, crazy. But try finding a replacement with a loudness tap, no chance - these are custom jobs. When redimensioning the whole shebang, a 6 dB reduction in noise should be feasible (but that really is best left to those who know what they're doing).

Back in those days, the big German manufacturers (e.g. Grundig, Braun) generally had smarter gain distribution and paid more attention to noise than their Japanese colleagues.

Whatever you do, don't ruin "ye olde faithful" Hitachi. You may want to look into how to clean all the switch contacts properly. Some of the small electrolytics may have become leaky, too, though I am not an advocate of mindless bulk recapping.
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Old 12th February 2012, 05:41 PM   #6
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Thank you sgrossklass i appreciate your comments. I think I'll dust off my other hitachi amp & look in to cleaning all the pots etc & with the diagrams check for any imperfections inside. While I'm very new to all this I am very keen to improve what I have already with the least amount of money being spent. :0)
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