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Old 29th July 2006, 04:31 AM   #1
5150ed is offline 5150ed  Thailand
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Default Resistor Value on Inverted GC

I am using the inverted GC schematic on OPA541 chip.

Normall the schematic use 10K R in and 220K R feedback which give 22X gain.

But I want to reduce the gain to be around 6-4X, the problem is should I use the higher value R in to be around 47K or lower the value of R feedback to be 50K?

What the difference do they made?
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Old 29th July 2006, 04:44 AM   #2
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Lower the feedback resistor

47k resistor might add more noise.

In general,the higher the resistor value, the higher the noise

Are going to use a preamp or a buffer?
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Old 29th July 2006, 05:12 AM   #3
5150ed is offline 5150ed  Thailand
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You mean higher R in add more niose right?

How about R in =5.2K and R feedback = 22K, Is this seem better?
Or R in =220 ohms and R feed back = 1K, Is this too low?

Yep, I decide to have Tube preamp infront of my gainclone.
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Old 29th July 2006, 09:20 AM   #4
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Quote:
Originally posted by 5150ed
You mean higher R in add more niose right?
R or the feedback resistor

Quote:
Originally posted by 5150ed

How about R in =5.2K and R feedback = 22K, Is this seem better?
Or R in =220 ohms and R feed back = 1K, Is this too low?
How low you can go,depends on the output impedance of the component before the amp


Quote:
Originally posted by 5150ed

Yep, I decide to have Tube preamp infront of my gainclone.
Do you know the preamp's output impedance?
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Old 29th July 2006, 09:53 AM   #5
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If you have these op amp sockets, you can break off four pins and use them for resistor sockets. Just push the resistor leads until in snap into pins
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Old 29th July 2006, 01:03 PM   #6
5150ed is offline 5150ed  Thailand
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I do not know the preamp's output impedance, but I decide to use this schematic but with 6SN7 tube instate of 12AU7
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Old 29th July 2006, 03:35 PM   #7
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Have you done a search for 6SN7 srpp schematic?. I think the resistors values maybe difference from the 12au7. Voltage needs may also be differance
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Old 29th July 2006, 03:56 PM   #8
5150ed is offline 5150ed  Thailand
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From what I know 6SN7 and 12AU7 can be substituted. Moreover, 6SN7 and 12AU7 can do SRPP with 150R, 820R, 1.5K resistors with the voltage around 150V to 300V.

If am wrong please correct me .
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Old 29th July 2006, 06:26 PM   #9
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Yes, you are right they are similar.
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Old 2nd August 2006, 12:57 PM   #10
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As you topology, I suggest you build inverting amplifier with T network is better. Ri should not be low value.
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