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Vintage amplifiers that could challenge or approach current state of the art amplifiers

SirPaulGerman

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what do you make of the matching amp the rotel rb-870bx ?

3234888956_baef8bb881.jpg
 

SirPaulGerman

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They are an excellent preamplifier with little to criticise about the design. What I love about them is the complete left/right separate power supplies right back to the transformer and very careful layout.

The ALPs bowden cable linked switches can get noisy/intermittent in their old age and it is a big job to properly fix. (I'll post up a link to yesterday's rainy day Rotel project).

Enjoy. :)
I got it on ebay for $50 with the original box and in mint condition

How do you feel about replacing the op amp 5534 for this
OPA-604 biased with a FET transistor into class A? that the mods that people from the fm tuner group does to the tuner 990BX
 
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restorer-john

restorer-john

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I got it on ebay for $50 with the original box and in mint condition

How do you feel about replacing the op amp 5534 for this
OPA-604 biased with a FET transistor into class A? that the mods that people from the fm tuner group does to the tuner 990BX

What a bargain.

Just leave the 5534. It's likely a low noise version and carefully selected by Rotel from batches of already low noise ICs.

Look at the suffix on the 5534.
 
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restorer-john

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The medium power rotel dual mono amplifiers are again, fabulous products. Very reliable and sound great. They can sometimes have a little too much mains noise (hum/buzz) but on the whole, I would pick them many brands.
 
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restorer-john

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what about the 2134 op amp ?

Leave it alone too.

Test the preamplifier thoroughly before doing anything. No replacement caps or ICs, OK? It's extremely unlikely you will improve the design and may make it a lot worse by messing with it.

Run some basic frequency response checks on all the paths, check the controls for functionality/noise. Look for any DC noise on switches which can point to leaky coupling caps upstream, test residual noise levels and THD. Look for symmetrical clipping etc.

What test gear do you have?
 

SirPaulGerman

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The medium power rotel dual mono amplifiers are again, fabulous products. Very reliable and sound great. They can sometimes have a little too much mains noise (hum/buzz) but on the whole, I would pick them many brands.
Do you have the model numbers for those ?
 

Steven Holt

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The MCS 3265 (distributed by JC Penny) was made by NEC and had dual amps, one on each side, and, from what I understand spec'd out pretty decent. I don't believe NEC ever sold their gear in the US, you had to go thru Penny. These come up every now and then.
 

sarumbear

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Interesting Don, thanks for digging in the back shed of your brain for me. So they were only a 3.5A Ic rated transistor, massively paralleled. High voltage, lowish current, lowish selected gain and massively stacked. I think I prefer the modern way...
When you need high instantaneous power you need high voltage specced transistors. I think at the time there was not much choice.
 

Doodski

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Is the yamaha MX-55 any good ?
I remember this stuff now. It was in the Titanium Series of Yamaha. Very nice gear. I sold it when it was new and it was flying off the shelves because peeps loved the titanium finish. It's a nice amp, not heavy duty like some but for home use it's ample and should sound justtt fine. :D
 
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restorer-john

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I found a Yamaha MX-55, I like the specs for distortion, the power is not that bad

The MX-55 is a useful amplifier and quite nicely made. I bought an MX-55 and an MX-35 in Titanium back in the day when Yamaha was throwing out all the Ti coloured gear, along with a few DSP units to match. They are still buried in my storeroom in their sealed cartons...
 
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restorer-john

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You should test those, what do you make of the specs ?
I am going to use it as a 2 channel amp

They are great little amps. The MX-55 is a proper amplifier, whereas the MX-35 has a pair of stereo STK amplifier hybrids run in 4/2channel mode.

At the time (about 1992 IIRC) I was into 6 channel DSP and Yamaha had the DSP-1, the DSP-3000 and the DSP-100 processors. The amps you used were the M-35, then the MX-35/55. Titanium was a short lived and disastrous colour for Yamaha- it didn't match anything and it all ended up cleared within a year or two at about 1/3 of its original dealer cost.

I couldn't resist the Ti coloured MX-55, I think it cost me about AU$120 or so back then.

Then I decided DSP was too noisy and it's all been sealed up for 30 years.
 

Doodski

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when Yamaha was throwing out all the Ti coloured gear
It's interesting that in Canada the titanium finish was very popular and we depleted the supply. Staff was buying it too and customers where getting into it. It was like the fancy woodgrain MB Quart speakers that we got huge amounts of inventory of. It took a few weeks and then the people started coming in and buying it. What a visual combo with titanium Yamaha with some African wood or other exotics finish for the speakers. I really dug the titanium stuff. :D
 

SirPaulGerman

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Does anyone have the service manual for the Yamaha MX-55 ? I don’t want to spend $20 on a paper copy
 
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