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In the Forum: Melquiades Amplifier
In the Thread: Super Melquiades Amplifier.
Post Subject: Re: OK, ok, I did it!Posted by cv on: 7/20/2005

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Interesting Romy, particularly the "echo" affect and weird overtones with the aircap. I wonder if the thing is picking up resonances and if the impedance issue is responsible for the overtones... signal being modulated by the varying input capacitance of the 6C33. If the latter is true, it shoud all start to sound a bit like bad solid state...

How does the aircap sound compare to the silver mica? If it's an impedance issue, they should probably sound more similiar than different. If it's a mechanical resonance/signal pickup issue, they should sound quite different. I notice the vanes are near some signal wiring - wondering if there picking up the high level OPT primary signal? I guess the 1nF Cube will help solve the puzzle.

let me just point out 2 or 3 things, from an engineering standpoint:
1) If you want to hear what the aircap can really do, the high Zout filter might be buffered by a cathode follower (maybe pentode based), direct coupled to the output stage. This will drive the 6C33 properly but may or may not introduce other sonic issues, depending on implementation etc. Obviously a pain in the cloaca given the amp's built so forget this one for now.

2) In some ways, the best place for the filter is ahead of the amp, so the driver stage will not be trying to reproduce LF - cleaner drive to the output valve. But it may not work with the Melquiades input stage (impedances again). OTOH, you could try the filter ahead of the amp and apply battery bias to the first stage since you have a blocking cap at the input.

3) Don't be afraid to increase the cap value and reduce the resistor at the 6C33 grid. The only issue is that you will start to load down the driver, but if it is happy dealing with it, then the 6C33 can only benefit from the lowerd driving impedance and the smaller grid resistor (the smaller the better from the point of view of keeping the grid locked down).

(3) ain't difficult to try, same with (2) really. Just depends on how happy you are with the small 950 when it arrives...


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