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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Zen se-84cs question............

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Dave,

I checked Steve Bench's "Frequency Response Synthesis" article: http://members.aol.com/sbench/freqresp.html

The coupling cap/grid resistor combination does create a zero at DC and pole at 48Hz (for 0.01uF / 330K) - meaning the freqency response will be 3dB down at 48Hz (neglecting the OPT).

Of course, this may be a good thing if the amplifier is used as a tweeter amp, or the OPTs are small and saturation is to be avoided.


Icebear,

Do you find your amp lacking in low bass?
 
because the human ear naturally lacks bass response, and the -3dB point provided by the equation 1/(2*pi*C*R) for this case is 48Hz, you may not notice that much of a lack in bass seeing as from -3dB down point there is a -6dB rolloff per octave. this means by the time you get to 24Hz (1 octave lower than 48Hz) you are only down -9dB, and while this attenuation is noticeable at higher frequencies, considering the ears natural bass response you may not notice that much difference, unless this amp powers the sub, then you will definately 'feel' the difference, but you already said you have active subs.

cheers

by the way... it does not generally hurt to use a larger value cap in a coupling position unless it was placed there specifically to give a particular frequency response. HF response may suffer a little by using a larger value, but this can be overcome by placing another cap of 5% of the other caps value in parallel.
 
Icebear,

I assume you mean the Prometheus speakers available from DIY Hi Fi Supply? If you are driving the active sub from the speaker level inputs, it is almost certain that there will be an improvement found by increasing the coupling cap. However, if the active subs are driven by line level inputs from the source/preamp (a much better solution), it is probably better to leave the tube amp rolled off in the bass. The Zen amp doesn't need to make bass in this setup, so there's no need to get the OPT to pass low frequencies (which risks satuation if your OPT is small, which in turn results in distortion at all frequencies). Oh, and small-value high quality coupling caps are cheaper and generally have better performance than larger value ones :)


Benny,

Granted, the 1st order highpass created by the coupling cap/grid resistor isn't as significant as many other factors in affecting bass production (OPT size, speakers, etc...), but adding another mechanism by which bass is attenuated only makes things worse unless bass is not required (such as in a bi-amped arrangement, or with an active sub)

EDIT: By the way, I read in your DiyAudio profile that you are a high school student in Melbourne? VCE exams over! :D unless of course you do a language...
 
By the way, I read in your DiyAudio profile that you are a high school student in Melbourne? VCE exams over! unless of course you do a language...
yeah, all over - media on monday was the last... i wasn't really stressing though coz i haven't really taken school very seriously this year... i've been more focused on my music which is better and more fun... like about a month ago my band played a gig up at dizzys (maybe you know it?) and we were asked to come back and play regularly next year... so we were pretty stoked and all got paralytic and didn't get home till 4am... 9am i had a Physics SAC i hadn't studdied for, and i didn't care... it's kinda disapointin now schools over coz now i have to think about doing something with my life.

sorry, that was off topic
 
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