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Remove riaa stage from cheap phono pre
Remove riaa stage from cheap phono pre
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Old 26th August 2017, 12:41 PM   #11
DIP8 is offline DIP8  Italy
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VEry interesting for a newbie like me

The base formula is β = R1 / (R1+R2) = 0.0909 = 1 / 11

If I use an opamp'd phono preamp instad of the transistor one, is the same stuff?
I'm always lowering resistances in feedback loop ?
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Old 26th August 2017, 03:18 PM   #12
scottjoplin is offline scottjoplin  Wales
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Yes, lowering resistance of feedback resistor increases the amount of feedback and so lowers the gain. If you just remove the capacitors in your circuits you are left only with the resistors which on their own will set the feedback and the gain will be too high
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Old 26th August 2017, 04:28 PM   #13
DIP8 is offline DIP8  Italy
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Scott...
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Old 27th August 2017, 08:20 PM   #14
DRONE7 is offline DRONE7  New Zealand
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A very interesting discussion, I would like to try this..

For the attached circuit, if I follow correctly, I should disconnect C4 and C6 and short C5 and C7 then adjust gain by reducing the value of R14. Would that be right ?

http://www.pcb-audio.com/pcb-audio_c...mp-circuit.jpg
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Old 27th August 2017, 08:49 PM   #15
scottjoplin is offline scottjoplin  Wales
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Yes, but leave R14 and change R17 if required
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Old 28th August 2017, 12:28 AM   #16
DRONE7 is offline DRONE7  New Zealand
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Thanks for that Scott
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Old 28th August 2017, 12:56 AM   #17
scottjoplin is offline scottjoplin  Wales
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You're welcome
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Old 3rd September 2017, 10:05 PM   #18
DIP8 is offline DIP8  Italy
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Quote:
Originally Posted by DIP8 View Post
Hi Scottjoplin
thank for reply

In the tc750 that have discrete transistors, I have to remove c4,c5?
I've tried today.. but nothing to do if I remove c4 and short c5..no sound..

If I leave on board c5 and remove c4, there is an heavy equalization
if i remove c5 (without short it) there is a very boomy bass equalization

Last edited by DIP8; 3rd September 2017 at 10:08 PM.
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Old 3rd September 2017, 10:14 PM   #19
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by DIP8 View Post
I've tried today.. but nothing to do if I remove c4 and short c5..no sound..
Then you need to increase the gain by reducing the feedback
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Old 3rd September 2017, 10:18 PM   #20
DIP8 is offline DIP8  Italy
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can i try with a potentiometer? and then fixed the value, put a resistance?
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