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Old 8th January 2009, 07:01 AM   #1
winner is offline winner  India
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Default how to make a low noise guitar preamp?

i made a guitar preamp using op amp tl074 with 1 mega ohm
impedance and voltage gain of 100 . but its too noisy and
also lot of hum? will using a voltage reg like 7812 help or
is it .coz of the opamp quality?
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Old 8th January 2009, 09:37 AM   #2
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I suggest you try posting the circuit for what you've built, but it sounds like it's your constructiion that's the problem (hum is usually poor construction).

Why did you use a quad opamp?.
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Old 8th January 2009, 01:54 PM   #3
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Default Re: how to make a low noise guitar preamp?

Ferrit beads on the power supply regulator legs always seems to help the automotive stuff I build. You would not belive how electrical noisy engines are.

Quote:
Originally posted by winner
i made a guitar preamp using op amp tl074 with 1 mega ohm
impedance and voltage gain of 100 . but its too noisy and
also lot of hum? will using a voltage reg like 7812 help or
is it .coz of the opamp quality?
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Old 8th January 2009, 04:12 PM   #4
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Guitar pickup pre-amps are tricky because they are so high impedance. I would have thought you'd have to go to a discrete JFET input to keep the noise down.

The 20KHz bandwidth thermal noise in a 100Kohm resistance is 5.8uV or 41nV/rt.Hz. The TL074 has a 1KHz noise figure of 18nV/rt.Hz which rises to more like 25nV/rt.Hz at 100Hz. Add a gain of 100 and the noise is getting pretty high.

The mains hum is due to leakage currents flowing in the high impedance input. A regulator won't help I'm afraid. Attention to grounding and use of shielded cable is the key.

Can you post the schematic? It's hard to guess exactly what the problem is.
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Old 8th January 2009, 06:07 PM   #5
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Hi winner - try this site for some tips.
http://www.geofex.com/tubeampfaq/tube_amp.htm
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