how to make a low noise guitar preamp?

winner · 8th January 2009, 07:01 AM

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?

Nigel Goodwin · 8th January 2009, 09:37 AM

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?.

Kramerguy · 8th January 2009, 01:54 PM

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?

Iain McNeill · 8th January 2009, 04:12 PM

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.

c2cthomas · 8th January 2009, 06:07 PM

Hi winner - try this site for some tips.
http://www.geofex.com/tubeampfaq/tube_amp.htm

8th January 2009, 07:01 AM	#1
winner diyAudio Member Join Date: Jan 2009	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?

8th January 2009, 09:37 AM	#2
Nigel Goodwin diyAudio Member Join Date: Jul 2005 Location: North Derbyshire	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?. __________________ Nigel Goodwin

8th January 2009, 06:07 PM	#5
c2cthomas 49 - for the 16th time diyAudio Member Join Date: Oct 2006 Location: Near "Music City" (Nashville Tennessee)	Hi winner - try this site for some tips. http://www.geofex.com/tubeampfaq/tube_amp.htm __________________ "You can't always get what you want" K. Richards/M. Jagger *** "Next time I will know some things better" Zen Mod

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8th January 2009, 04:12 PM	#4
Iain McNeill diyAudio Moderator Join Date: Oct 2007 Location: Santa Cruz, California	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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