Opinions on the Conrad Johnson MV75 amplifier please. - diyAudio
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Old 26th September 2006, 10:50 PM   #1
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Default Opinions on the Conrad Johnson MV75 amplifier please.

I saw a Conrad Johnson MV75 amplifier on ebay this week and it got thinking about buying one. I was wondering if any members own, have owned the MV75 amplifier. What were the sonic impressions of this amplifier and your thoughts.

There are some in this forum that would blast me because I am NOT a believer that a small cathode resistor vers/ a direct path to ground in the bias circuit is going to effect the sound quality. This amplifier has a 20ohm 2 watt resistor from cathode to ground for each output tube. Another interesting feature is the bias circuit that you adjust until a led turns on then you back it off a hair.

Anyone have anything to offer?
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Old 26th September 2006, 11:36 PM   #2
5u4 is offline 5u4  United States
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Had a MV-75a almost 20 years ago. Thought it was an okay amp. Passed it around amongst all my hi-fi buddies at the time and everyone thought it was okay. I'd take a Citation II over one of these any day.

Called up Conrad-Johnson on the phone and asked if I could use Chinese power tubes in this amp and they said definately not. Well, like a dope I put them in anyway and in a few days the amp quit working. Burned out a resistor and the LED bias thingy didn't work right anymore. Got it working and sold it.

One of my favorite amps of that time was an Audio Research. Don't remember the model anymore, but it had a boatload of tubes and all balanced circuitry.
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Old 27th September 2006, 02:15 AM   #3
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From looking at the schematic its running the 6550's plates at 590 volts. This might be a tad hot for the chinese tubes.
The led circuit is primative and very easy to repair. Can't say that I have heard a Citation II yet.
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Old 27th September 2006, 10:37 AM   #4
SY is offline SY  United States
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That amp has very good iron and rather mediocre circuitry. It's a variant of the Mullard 5-20 with an unneccesary cathode follower in it just so they could feel creative. If the price is good, buy it, strip it down, and build a better amp in that good-looking box.

edit: Correction, this was the version without the CF. They saved that for their more expensive unit.
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Old 27th September 2006, 10:41 AM   #5
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Sy,

I haven't had my first cup of coffee yet so my eyes aren't really open yet but where do you find the cathode follower?

Maybe I'm mistaken here so correct me if I am. Cathode followers
have output on the cathode end of the tube?

This has the coupling caps off of both plates of the 6CG7/6fq7 tube.
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Old 27th September 2006, 11:04 AM   #6
SY is offline SY  United States
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Coffee is on me- note my edit just a few minutes later.

In the Premier line, they inserted a cathode follower between the input tube and the diff amp. This is intended to get rid of the pole formed between the input stage and the LTP from the latter's input capacitance. Since this isn't even close to the dominant pole, it's unclear why they would do that, other than my earlier speculation. My reccommendation still stands- you can do much better for an input stage.
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Old 27th September 2006, 11:13 AM   #7
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Sy,

The amp is in Hungry and the last time I looked it hadn't met reserve at $331.00 Shipping would be expensive on it so I am looking here in the US for one with a reasonable price tag. As pointed out in a prior post these don't appreciate fragile output valves. The plate voltage seems a bit higher than I have seen before and that is probably how they wring out 75 watts a channel.

I have never been fond of the Audio Research's workmanship on their amps.

Maybe a good candidate for the SYclone front end.

Would you say its better than a Quicksilver 8417 conversion?
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Old 27th September 2006, 11:44 AM   #8
SY is offline SY  United States
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I haven't compared the iron side by side, but I've used CJ's supplier in the past with excellent results.
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Old 19th May 2007, 10:32 PM   #9
caoauto is offline caoauto  United States
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Hi, I have the same amp here. Just replace all the zeners and all transitors in the power supply. Got the amp back to sing very good sound. The B+ is 610V, B1 is 550V, B2 is 350V. Look like abid high to me? and the power trans is getting hot (touchable, I would say about 110 degree F) after 2.5 hours playing time. The question is any one know how hot is call too hot?, I don't want to have the power tranni smoke up. Thanks ahead for all your input.
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Old 4th June 2010, 09:54 PM   #10
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im thinking of a CJ clone. what supplyer dose cj use and could i order from them?
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