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Old 14th October 2006, 02:25 PM   #1
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Default Gainclone kit passive pre configuration

I am going to build a compact system by integrating a Monica2 dac, stepped attenuator and lm3875 kit into one box.

I currently have a 100K attenuator that I'd like to use. Couple of questions:

1. Will 100K with >10cm connections to the amp board be ok? The capacitance of the short run will be minimal.....

2. Will the Monica2 be happy driving 100K? I think the dacs low output should prefer a higher attenuator input impedance.

3. Do I need the 22K resistor from input signal to ground on the ampboard if the 100K attenuator is hard wired and very close? This may be a stupid question, but it seems like we have two resistors doing a similar job... Put it another way, is 22K optimal after a 100K attenuator?
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Old 15th October 2006, 05:01 AM   #2
Leolabs is offline Leolabs  Malaysia
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Is the attenuator a log type???
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Old 15th October 2006, 11:27 AM   #3
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yes - 100k log attenuator
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Old 16th October 2006, 02:52 PM   #4
Nuuk is offline Nuuk  United Kingdom
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The best answer is to try it. You could also buy one of those 50K (and or 20K) 9mm Alps pots from Farnell or Jaycar and try that to see if you hear any difference.

I would personally want an active stage between pot and GC.
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Old 16th October 2006, 02:59 PM   #5
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Default Re: Gainclone kit passive pre configuration

Quote:
Originally posted by sharpi31
3. Do I need the 22K resistor from input signal to ground on the ampboard if the 100K attenuator is hard wired and very close? This may be a stupid question, but it seems like we have two resistors doing a similar job... Put it another way, is 22K optimal after a 100K attenuator?
If you are using minimized GC configuration, you need 22k shunt resistor, otherwise, with only a 100k pot you will get high DC offset at lower volume settings (shunt resistance >22k)

50k or 25k pot works better than 100k.

I obtained very good results with a pot directly at amp's input (you don't need an additional active stage here) and an active buffer at DAC's output.
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Old 16th October 2006, 07:05 PM   #6
keps is offline keps  Philippines
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Does it mean 10k pot works better than 50k or 25k pots?
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Old 16th October 2006, 07:13 PM   #7
Nuuk is offline Nuuk  United Kingdom
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Quote:
Does it mean 10k pot works better than 50k or 25k pots?
No! Remember that you must match the impedance right the way through the chain! Try Googling the subject.
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Old 16th October 2006, 07:15 PM   #8
keps is offline keps  Philippines
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roger that.
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