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Old 3rd December 2008, 07:41 PM   #41
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Lars,

"but the sensitivity is very high at 100mV rms"

could you elaborate please. Input sensitivity? Thanks
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Old 4th December 2008, 05:51 AM   #42
poynton is offline poynton  United Kingdom
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Quote:
Originally posted by desperateaudio
Lars,

"but the sensitivity is very high at 100mV rms"

could you elaborate please. Input sensitivity? Thanks

Input voltage required to give full output.
CD player gives 2.00v !!
Usual input sensitivity is around 0.75v for maximum output.


Remember
With 6080, apply filament ( heater ) supply for at least 2 minutes before applying the high voltage........



Andy
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Old 4th December 2008, 06:04 AM   #43
Klimon is offline Klimon  Belgium
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Why not swap the 6sn7 cascode for a ccs'ed 5842 or 6c45 for lower distortion (see pete millets research) and better drive capability?

@fuling: at how much do you estimate the material costs for the chokes you winded?

Simon
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Old 4th December 2008, 06:40 AM   #44
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Klimon: The 6SN7 is not connected as cascode. Desperateaudio had allready breadboarded the 6SN7 cascaded driver so I just checked it for him. Wouldn´t recommend it either!

Your recommendations are great!

Without NFB 6C45 is the best choice, albeit it normally sounds better with a high B+ 400V and anoderesistor. Remember Milletts measurements are without load! 5842 is a nice sounding, descent tube but suffers from limited swing capability compared to 6C45.

One could even add a small amount of NFB to the 6C45 and still get an acceptable senstivity.

If one decide to use NFB a cascaded 6H30 would be the obvious choice. My idea is that the feedback shouldn´t be over the whole configuration, the input tube should be left outside the loop.
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Old 4th December 2008, 08:07 AM   #45
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Klimon,
Think you will like this simple one .

It sims 2W at 8ohm with 1% THD and a DF of 3. Sensitivity is 1Vrms. NFB in the ballpark of 10dB.
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Old 4th December 2008, 08:14 AM   #46
Klimon is offline Klimon  Belgium
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I do

Please don't stop

Simon
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Old 4th December 2008, 08:24 AM   #47
Klimon is offline Klimon  Belgium
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The feedback loop goes to the grid of the input tube?
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Old 4th December 2008, 08:29 AM   #48
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This is called "shunt feedback". The grid will be virtual zero and Zin 22k. When feeding you must use a lowZ source, so it won´t work with an input pot.
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Old 4th December 2008, 10:13 AM   #49
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If you want high Zin and possibility to add a volume pot this could be the solution. One more tube and some sand is needed though. Negative supply is same as DC heater-voltage. Another advantage is that effects of "Mr. Miller" is less pronounced.
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Old 4th December 2008, 10:55 AM   #50
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Just finished breadboarding the original design last night. Plugged the CD Player into a passive preamp volume control (50K) and then directly into amp. Sensitivity is an issue as previously discussed as I cannot get volume to go above a few clicks before distortion. The orginal design cannot be good for more then a few watts. Keep volume in check and she sound like she has potential.
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