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Need to do some work...


Marvel

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Well put, both of you... I won't be able to delve deeper into this until tomorrow afternoon. We're preparing for a Philippine Indepwnddnce day celebration tonight and my birthday is tomorrow. Fixing/dianosing the amp is secondary to the weekend.

 

What I have been able to do:

Swapped all tubes to rule out a tube issue, including the single triode in the JMA Merlin preamp.

 

Swapped speakers to make sure it wasn't something in these old Sansui SP-2000 speakers.

 

Used a different source (you never know...)

 

I would feel pretty stupid if I founf out it wasn't the amp.

 

Have a great weekend, gentlemen. I get back to this after I get to spend more time with it.

 

I'll be 68, btw, can't believe it.

 

Bruce

 

 

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I am certanly not criticizing anyone for liking what they like. A lot of the vintage gear I like was built with extremely poor components but had nice iron, decent circuits, and well executed layouts. The latter is more of my gripe with certain amps.

 

The Moondog 2A3 amp circuit particulary isn't terrible at all and I can attest to the cascading 6SN7 triodes driving a 2A3 to be a beautiful combination. Staying well below grid current all is well, everyting behaves and the amp does it's job just fine. But with a 2 watt amp it is easy to get over zealous and turn the volume up to where you may encounter some blocking distortion and depending on variables within the circuit it could take a while to recover and stabilize, this will effect the sound. This isn't an opinion it is fact. Does the amp need direct coupling to sound good? Not at all. It is my opinion that low powered amps can benefit from it as a precautionary measure because they often run near max output.

 

In a power supply filter where no signal is present (C1/C2)  only see 120Hz. The cap reactance will be much larger at this frequency regardless of ESR which is in series and sums with the reactance i.e. When the reactance is 132 ohms (10uF at 120Hz) the impedance difference between film and electrlytic is moot. Now with higher frequencies where reactance drops the ESR can begin to dominate. This isn't opnion, it's fact. I figure since he may be going through the amps in the near future and possibly buying new caps or fixing things up I can express my opinion on the matter and he can weigh them at his own accord. It is just as easy for him  to say as he did, I like the amp the way it is and I don't want to change them but thank you for input. Which is fine and I am no way offended. Somebody on the other hand may have done the opposite and say, let me try using this here as suggested, it will only cost me a couple bucks extra and a little bit of soldering time (some people like soldering). Then they listen, they either notice a difference or don't, the latter no worries either way and the former if results are good it's a benefit, if it's a negative improvement then it only take a little more time to undo. I was not suggesting the current owner go ahead and do major modifications, maybe some cap choice and value changes at most.  Whether the original designer is offended that I said to DC couple things? Not sure, I doubt it, different ways to skin a cat they say. 

 

Layout Layout Layout.

 

What I don't budge on is layout. So we have a good circuit that sounds good and is well recieved. My bone to pick would be mainly with component choice and layout. Engineering is tradeoffs. I like p2p a lot but large film caps just hanging on by their leads randomly placed is a recipe for disaster, and may be part of why he is having issues. Fourth owner and the amp is being shipped around and vibrated, something may have come loose and made a bad connection.

 

I guess I just see a lot of audio related gear with huge film caps shoe horned in places where they don't belong. I can see in some places where the signal is present like as a cathode bypass or C3, but other places like in the power supply it's of no real benefit sonically. I would love to see sombody be able to audibly discern the difference between a film or lytic' cap in C1 position. Or, I am all ears if someone can explain to me why a film cap in this position is of any use. If you are worried about RF you can bypass the lytic' with a small film cap.

 

At the end of the day I think it's a great excersise to discuss these technical matters openly. Nothing is better for progress than peer reviews and nobody has to act upon what is discussed if they don't think it has any merit. 

 

Thanks for listening to this old bugger. I love audio gear and discussing how they work.  No offense intended.

 

 

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Happy birthday, Bruce!

 

Erik, I still have these; they are amongst my favorite flea amps. If I ever sell them, you will get the first call.

 

And while Ron had a penchant for good design, his penchant for felonious behavior has driven him from the US, from what I understand. Interstate fraud is a very, very bad thing.

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2 hours ago, sheltie dave said:

And while Ron had a penchant for good design, his penchant for felonious behavior has driven him from the US, from what I understand. Interstate fraud is a very, very bad thing.

 

When it went downhill, it went quickly...

 

Didn't have a chance to get a deeper look into the amps today. It was my birthday, slept in from a huge Filipino party last night (with all the appropriate food...), went to Mass and had a great lunch with aFilipino couple we're close to. Got home late, all tuckered out.

 

Bruce

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13 hours ago, Marvel said:

 

When it went downhill, it went quickly...

 

Didn't have a chance to get a deeper look into the amps today. It was my birthday, slept in from a huge Filipino party last night (with all the appropriate food...), went to Mass and had a great lunch with aFilipino couple we're close to. Got home late, all tuckered out.

 

Bruce

 

 

Yea he stuck me for a few bucks for parts on order on his way out. 

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