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Old 29th May 2003, 03:28 PM   #1
jkeny is offline jkeny  Ireland
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Default Lower feedback

J. Rasmussen uses 1m feedback resistor in his IGC - lower feedback - has anybody tried this? What results.?

John
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Old 29th May 2003, 03:40 PM   #2
Bricolo is offline Bricolo  France
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your amp will certainly clip with the same signal level

example: with a classical gainclone (gain=22), say 22V dc rails, your amp will clip with a 1v pp signal

with 1M (gain=100) it will clip with a 0.22V pp signal

your pot will always be between 0 and 10%



another thing; is that there are some optimal values for the resistor (not theyr ratio, tha values themselves)
these values have something to do with SNR I tkink
I can't explain you more, but I'd like to know more about this
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Old 29th May 2003, 04:36 PM   #3
jkeny is offline jkeny  Ireland
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Default Lower feedback

Bricolo,
I think J. rasmusen uses 22K resistor on input which sets gain at about 30 I think?

His Low pass filter and input buffer seem to make sonic improvements over the bare bones gainclone (as per Pedja's reports on his website) so I thought the lower feedback might also be a sonic improvement?

John
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Old 29th May 2003, 09:36 PM   #4
mikelm is offline mikelm  England
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Quote:
Originally posted by Bricolo


another thing; is that there are some optimal values for the resistor (not theyr ratio, tha values themselves)
these values have something to do with SNR I tkink
I can't explain you more, but I'd like to know more about this
This is my understanding,

lower value resistors ( with the same ratio ) will give lower noise, probably extended ( out of band ) HF response, less distortion at high frequencies but there could be less HF stability

I am quite interested to find out how this would sound but if running in inverted mode this will mean lowering the i/p resistance.

I intend to try 1K & 22K or 30K sometime but I have to build a LM6172 based stepped attenuator first to drive it.

cheers

mike
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Old 1st June 2003, 05:43 AM   #5
jkeny is offline jkeny  Ireland
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Default LM6172 based stepped attenuator

Mike,
Sounds interesting - do you have a schematic?
John
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