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Old 15th November 2004, 02:01 AM   #1
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Default Zen se-84cs question............

O.K., is that a .01uf or .1uf coupling cap in the schematic?? Also, am I really loooking at a 1k ohm 50W resistor in the p.s.?? The reason I'm asking is because the online schematics are fuzzy and hard to read. Anybody??
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Old 15th November 2004, 02:59 AM   #2
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Default Re: Zen se-84cs question............

Quote:
Originally posted by cadaverdog
is that a .01uf or .1uf coupling cap in the schematic??
The schema i was reading yesterday said 0.1 uF -- it really doesn't need to be that big. (0.1 uF x 330k = 0.033 Hz?).

dave

BTW: a bogus ZEN (ie ZENclone) is called a Mulligan
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Old 15th November 2004, 10:27 PM   #3
icebear is offline icebear  Norway
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Mine is 0,01 uF. Is it ok? I was also confused by the different values on their site.

b
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Old 16th November 2004, 04:58 AM   #4
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Quote:
Originally posted by icebear
Mine is 0,01 uF. Is it ok?
Still gives a 0.33 Hz LF cutoff... if your OPT is small, even smaller would likely be better.

dave
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Old 16th November 2004, 08:51 AM   #5
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Quote:
Originally posted by planet10
Still gives a 0.33 Hz LF cutoff... if your OPT is small, even smaller would likely be better.
Dave,
Feel free to correct me if I'm wrong, but doesn't a 0.01uF coupling cap into a 330K grid resistor create a pole at:

1/(2*pi*0.01uF*330K) = 48Hz?
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Old 16th November 2004, 08:58 AM   #6
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Quote:
Originally posted by audiousername
eel free to correct me if I'm wrong, but doesn't a 0.01uF coupling cap into a 330K grid resistor create a pole at:

1/(2*pi*0.01uF*330K) = 48Hz?
In my 1st post with a cutoff i put a question mark because i wasn't sure of the formula and being away couldn't look it up... you could well be right...

dave
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Old 16th November 2004, 09:17 AM   #7
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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?
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Old 16th November 2004, 11:06 AM   #8
icebear is offline icebear  Norway
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I run the amp on Prometheus dipoles, and have active subs from 100Hz and down so I can not say I'm lacking any bass. I got it up and running yesterday, so I'm not familar with is yet :-)
But I think I'll change the cap to the correct value anyway.

b
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Old 16th November 2004, 01:43 PM   #9
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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.
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Old 17th November 2004, 05:58 AM   #10
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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! unless of course you do a language...
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