JMP 50 replica

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Re: JMP 50 replica

Post by RockinRocket » Wed Jul 24, 2019 11:34 pm

wombat wrote:
Wed Jul 24, 2019 8:13 pm
RockinRocket wrote:
Tue Jul 23, 2019 9:02 pm
The whale tufnol is crap.. wonder if the carp is any good wombat?
Whale grade Tufnol is only recommended as electrical insulation in low voltage environments.

Carp grade has better electrical insulation properties due to it's finer weave (not as good as paper phenolic though). To my eyes it's finer than the weave Marshall used in their own fabric laminate boards back in the day. In practice I've been running this amp for 5 months with no issues whatsoever.

That being said, if you are concerned about moisture absorption then you should probably use something else.

Low voltage means diferent thing in different country's but in the UK low votage is good up to 900VDC.

All I konw for certain is the brown board and cream board Marshall used in the 70 dont have any small mA leakage in the amps I own.

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Re: JMP 50 replica

Post by Roe » Thu Jul 25, 2019 3:48 am

very nice build I must say. I personally like 50+50uf on the screens and phase inverter - it just gives that classical sound and response we've heard on so many records. I even like smaller screen resistors on low voltage amps. 1k takes avay some aggression on these amps, as does low preamp voltages. Finally, a switchable 5nf/100pf bright cap is a great idea (although switchable 2204 is not bad either). CTS makes a large 1ma pot with push-pull switching but they are expensive" onclick=";return false;" onclick=";return false;
Super 100 amps: 1202-119 & 1202-84
JTM45 RS OT JTM50 JMP50 1959/2203/34/39

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Re: JMP 50 replica

Post by wombat » Mon Jul 29, 2019 1:43 am

That's the cool thing about JMP 50s - there's a fairly broad spectrum of components and specifications that you can choose from depending on taste.

The specifications I chose were a matter of personal preference for me. The amp has a healthy amount of gain (more than I was expecting) but at the same time, it is quite pleasing on the ears and not too harsh. I can listen to it all day long without getting ear-fatigue and I guess that's the quality I like about it the most.

I think that the specs that I went with (including the lower filtering etc) went a long way to giving the amp it's "velvety" nature. Those specs got it almost there, but I also had to audition a lot of pre amp and power tubes before it went that little extra step where I was completely happy with it.

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