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In Reply to: Re: Fantastic! posted by danlaudionut on April 10, 2007 at 09:02:47:
2.7uF seems really small, have you considered something about 10x larger?
Follow Ups:
A 2.7uFd gives an F3 of 88Hz.
I want to limit the bass because
my speakers are only 90dB and
with only about 5W to play with.
Keeping the amp from doing bass seems to me a way
of efficient use of limited amount of wattage.
I just tried some VA EL34s in it but blew the fuse.
I think the VA EL34 has a short.
Made my GZ34 flash I hope it's OK.
Now I need to get fuses though 8^(
With increasing cathode impedance at that 88 Hz though comes reduced damping factor. I tried a small cathode bypass once (5K:8 SE OPT) and ended up with a damping factor that dropped from about 4 mid-band to about 0.8 at the lowest frequencies. Bass was ... funny in a ha-ha way.
But I am not doing any frequency near that frequency.
The speakers have a half power point of 200Hz.
The amps half power point of 62Hz.
That's two octave difference seems plenty.
I believe that it just needs to break in.
One octave isn't that far away. In the case I mentioned the cathode bypass was sized for maximum sub-bass flatness into an 8 ohm resistor. At one watt is was dead on to 10 Hz. The damping factor however was degrading a decade higher. 2.7uF will still have significant impedance at 200 Hz.
Thermionically addicted.
Thermionically addictedI don't know if you know this but
the lower a drivers Qes the less the
dampening factor it needs to function.
My 5.5" driver has a Qes of .32 and
I have it open back design so
there is no box to increase the Qts.
Dampening factor is not an issue for me
in my design as well as phase shift due to
the fact I have a plate amp driving the woofers
and it has a phase adjust to compensate.
Only gain level is a concern which
I am tending to think it is adequate
because the more it plays the more
it is filling in.
Only about 3 hours of play right now.
Even so, damping factor is just output impedance referenced to a particular load. In my amp's case a sub- 1 DF meant the amp's output impedance was around than 10 ohms at those frequencies. At 200 Hz your 5.5" driver's impedance on open baffle is almost certainly near its minimum (5 ohms?) and your amp's output impedance near it max. It also looks like you didn't account for the KT66's cathode impedance in calculating the roll over point, it's likely much higher than ~90 Hz. That and the voltage divider ratio caused by the two is a possible explanation for your lack of bass.I share your distaste for large, or any, electrolytics. In this app I'ld consider fixed bias and a small high quality coupling cap to set the roll-off.
Thermionically addicted.
Thermionically Addicted> > It also looks like you didn't account for the KT66's
> > cathode impedance in calculating the roll over point,
> > it's likely much higher than ~90 Hz.Yes I did.
The composite impedance is 698 ohms when
the cathode imedance is added to the OPT impedance
in parallel with the 750R cathode resistor.> > In this app I'd consider fixed bias
No room in the inn!
It is pretty cramped in there right now.
6 GE Motor Run Caps are room consuming 8^D
But they sure are worth it !!!I am running Svetlana (Flying C) 6550s right now.
I had them around so I figured I try them.
MUCH better 200Hz transition and the treble is
better suited to the Dynaudio D260 Tweeters.
The KT66 was a bit piercing after about 100 hrs
of break in I'll try them again and see.I tried some VA EL34s but
one shorted and popped the fuses.
So I don't want to try them again.
I might get some JJ KT77s to try too.
Ok ok, uncle! Glad it's working out with the new tubes.
;)
Thermionically addicted.
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