how reducing noise in guitar preamps?

[martin griffith]

a guitar distorsion box is commonly something that amplifies many times the
input signal,then changes it shape by a non linear stage,that could be an
op amp with antiparallel of diodes on feedback network,
even using an OP27,of course not the state of art in low noise,i 'm not able
to obtain the low noise of some pedals using less noble op amps as ne5532

even bigger is the difference with digitally controlled rack effects as
roctktron using HUSH super C noise reduction,i guess this is an example of
dynamic noise reduction,i.e. apparent but effective ,maybe an evolution of
noise gates

i'm not interested in noise gates that switch off completely the signal

under a certain threshold

anyone can help me in finding infos about how to obtain good results in
s/n?thank you

Diego,Italy

wavefront semiconductors, AL3101, should keep you busy for a day or
two


martin

 

[BobG]

What is the s/n of the pickup? Of the preamp? Of the amp? The end to
end system? If the system isnt any better than about 60dB, you will
need a gate if recording. If you are playing in a smoky honky tonk
where you cant hear yourself play over the rest of the noise, who cares.

 

[martin griffith]

What is the s/n of the pickup? Of the preamp? Of the amp? The end to
end system? If the system isnt any better than about 60dB, you will
need a gate if recording. If you are playing in a smoky honky tonk
where you cant hear yourself play over the rest of the noise, who cares.

No Ley Line detector?

But I did some geetar mods some 20 years ago, by putting in active
electronics in the guitar, very quite indeed. but pre surface mount .
Big XLR on the side, iso feeds of each pickup.

The muso couldnt cope, too clean!


martin

 

[blisca]

a guitar distorsion box is commonly something that amplifies many times the
input signal,then changes it shape by a non linear stage,that could be an
op amp with antiparallel of diodes on feedback network,
even using an OP27,of course not the state of art in low noise,i 'm not able
to obtain the low noise of some pedals using less noble op amps as ne5532

even bigger is the difference with digitally controlled rack effects as
roctktron using HUSH super C noise reduction,i guess this is an example of
dynamic noise reduction,i.e. apparent but effective ,maybe an evolution of
noise gates

i'm not interested in noise gates that switch off completely the signal
under a certain threshold

anyone can help me in finding infos about how to obtain good results in
s/n?thank you

Diego,Italy

 

[Eeyore]

What is the s/n of the pickup? Of the preamp? Of the amp? The end to
end system? If the system isnt any better than about 60dB, you will
need a gate if recording. If you are playing in a smoky honky tonk
where you cant hear yourself play over the rest of the noise, who cares.

The s/n of the pickup signal itself will depend hugely on the environment due to
the likely induction from stray magnetic fields and the like.

Acheiving ~ 100dB s/n from the elctronics is quite trivially simple though.

Graham

 

[Phil Allison]

"blisca"

a guitar distorsion box is commonly something that amplifies many times
the
input signal,then changes it shape by a non linear stage,that could be an
op amp with antiparallel of diodes on feedback network,
even using an OP27,of course not the state of art in low noise,i 'm not
able
to obtain the low noise of some pedals using less noble op amps as ne5532

anyone can help me in finding infos about how to obtain good results in
s/n?thank you

** The best input in terms of s/n ratio ( background hiss for electric
guitars is obtained with J-FET - types like the 2N5459, 2N5457 or 2SK30A
are suitable.

Use them as either a source follower or with the drain as the output with
gain set to around 3 to 5 times.

The input load should be 1 Mohm or greater with a series resistor of 4.7
kohms - resistor type does NOT matter here.

However, most guitar PUs produce significant buzzing and humming noise which
makes low noise pre-amps a waste of effort.





........ Phil

 

[blisca]

thank you all for interesting answers,
about the noise of the pick up
i would consider everything comes from pick up as signal for now,the hum
depends a lot by the environment (just if u change the angle of the guitar
relatively to the noise source the hum changes a lot)and changes if pick ups
are humbucking,active and so on
I would like focusize about how to reduce the "hiss",and that does'not
depends from the pickup ,i guess it depends more by topology,active
components and resistence thermal noise,(correct?)

 

[Kevin Aylward]

"blisca"


** The best input in terms of s/n ratio ( background hiss for
electric guitars is obtained with J-FET - types like the 2N5459,
2N5457 or 2SK30A are suitable.

Well, the 2n5459 has around 3nv/rthz at 1k, more at lower frequency, so
it is a poor choice compared to a 2sk162, which is around 0.6nV/sqrthz
(26 ohms noise resistance).

Use them as either a source follower or with the drain as the output
with gain set to around 3 to 5 times.

The input load should be 1 Mohm or greater with a series resistor of
4.7 kohms - resistor type does NOT matter here.

I wouldn't use more than a 1k series resister.

A typical pickup might be around 5k resistance, so where extraneous
noise happens to be low, a 5k extra resistance is around sqrt(2) more
noise than ideal. No point in adding noise when not necessary.

However, most guitar PUs produce significant buzzing and humming
noise which makes low noise pre-amps a waste of effort.

Not really. Do you actually have an amp and guitar? I do, in fact
several, and I just pluged one in to test, and I am afraid that your
information is a tad erroneous.

For the purposes of this test it was my Marshal AVT150 (the world leader
in guitar amp sales), and my John Connelly Maple Neck Les Paul, lovely
smooth neck indeed. The amp set clean, has very low noise indeed, you
have to be right up to the speaker to hear the noise. On inserting the
jack into and out of the guitar it is abundantly clear that the amp is
the dominant noise source. There is very little change in noise level,
well so long as the guitar is away from the amp by a couple of feet so
as to not pick up the transformer field.

I could of course try the same experiment with my Gibson Explorer, and
my Fender Twin, but the results will be the same.

Kevin Aylward B.Sc.
[email protected]
http://www.blonddee.co.uk

"There are none more ignorant and useless,than they that seek answers
on their knees, with their eyes closed"

 

[[email protected]]

Well, the 2n5459 has around 3nv/rthz at 1k, more at lower frequency, so
it is a poor choice compared to a 2sk162, which is around 0.6nV/sqrthz
(26 ohms noise resistance).


I wouldn't use more than a 1k series resister.

A typical pickup might be around 5k resistance, so where extraneous
noise happens to be low, a 5k extra resistance is around sqrt(2) more
noise than ideal. No point in adding noise when not necessary.

Why use a resistor in series with the input of the jfet, which is
already high impedance? What am I missing here?

 

[John Woodgate]

Why use a resistor in series with the input of the jfet, which is
already high impedance? What am I missing here?

I wondered as well; I thought it might be to make a crude r.f. filter.

 

[Phil Allison]

"Kevin Aylward"

Well, the 2n5459 has around 3nv/rthz at 1k, more at lower frequency, so it
is a poor choice compared to a 2sk162, which is around 0.6nV/sqrthz (26
ohms noise resistance).

** What insane BOLLOCKS !!

Electric guitar pickups are high impedance devices.

I wouldn't use more than a 1k series resister.

** 4.7 kohms is a better choice.

A typical pickup might be around 5k resistance, so where extraneous noise
happens to be low, a 5k extra resistance is around sqrt(2) more noise than
ideal. No point in adding noise when not necessary.

** More insane BOLLOCKS !!

Electric guitar pickups are high impedance, around 50 kohms to 100 kohms at
high frequencies .

Not really.

** Yes really - you fucking pompous ASS.

Do you actually have an amp and guitar?

** Seen and dealt with far more than YOU ever have - ARSEHOLE.

I do, in fact several, and I just pluged one in to test, and I am afraid
that your information is a tad erroneous.

** It is completely accurate.



....... Phil

 

[Phil Allison]

**Groper alert !

Why use a resistor in series with the input of the jfet, which is
already high impedance? What am I missing here?

** Protecting the J-FET from damage.

The outside world is a cruel place.



......... Phil

 

[Eeyore]

"Kevin Aylward"


** What insane BOLLOCKS !!

Electric guitar pickups are high impedance devices.

LOL !

Anyone would think Kevin was designing a low-Z mic amp.

Graham

 

[[email protected]]

**Groper alert !




** Protecting the J-FET from damage.

The outside world is a cruel place.



........ Phil

Is this protection when the circuit is not powered but still hooked up?

 

[Kevin Aylward]

LOL !

Anyone would think Kevin was designing a low-Z mic amp.

Oh...


Kevin Aylward B.Sc.
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

"There are none more ignorant and useless,than they that seek answers
on their knees, with their eyes closed"

 

[Kevin Aylward]

"Kevin Aylward"



** What insane BOLLOCKS !!

Electric guitar pickups are high impedance devices.

And your point would be?

** 4.7 kohms is a better choice.




** More insane BOLLOCKS !!

Electric guitar pickups are high impedance, around 50 kohms to 100
kohms at high frequencies .

And your point would be?

A typical model of a guitar pickup is around 5k in series with 1H. At
1khz, this would be 6kohms inductive + 5k resistive.

Secondly, this impedance dose not generate thermal noise, as would a 50k
resister. The impedance of the guitar pickup is irrelevant as far as its
thermal noise is concerned. So, what is your actual point about the high
impedance, other than higher impedance are more susceptible to external
interference?

I shall point out though, because there is an erroneous implication in
your comments, fets are not used because the have high input impedance.
It is of course, trivial to design a high impedance amplifier with a
bipoler devices. The reason is that fets have very low shot
(current)noise. This means that the current noise dropped across the
large inductive impedance is much reduced compared to bipolars.

** Yes really - you fucking pompous ASS.

No, not really.

** Seen and dealt with far more than YOU ever have - ARSEHOLE.

Your kidding right?

Been playing sone I was 11 years old mate. Been through one or two
guitars in the time, although I currently only have 4.

** It is completely accurate.

Yeah, sure...

Kevin Aylward B.Sc.
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

"There are none more ignorant and useless,than they that seek answers
on their knees, with their eyes closed"

 

[Kevin Aylward]

I wondered as well; I thought it might be to make a crude r.f. filter.

Yes, and gate protection. Its not nice to send inputs naked into the
world.


Kevin Aylward B.Sc.
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

"There are none more ignorant and useless,than they that seek answers
on their knees, with their eyes closed"

 

[Eeyore]

A typical model of a guitar pickup is around 5k in series with 1H. At
1khz, this would be 6kohms inductive + 5k resistive.

And after the guitar's 'volume' control ? What then ?

Graham

 

[Eeyore]

Yes, and gate protection. Its not nice to send inputs naked into the
world.

Very wise advice.

Graham

 

[Phil Allison]

"Kevin Aylward"

And your point would be?

** Obvious to anyone who is not mentally ill - like YOU are.

And your point would be?

** Obvious to anyone who is not mentally ill - like YOU are.

A typical model of a guitar pickup is around 5k in series with 1H. At
1khz, this would be 6kohms inductive + 5k resistive.

** Why stop at 1 kHz ?

The noise is mostly above that frequency.

Secondly, this impedance dose not generate thermal noise, as would a 50k
resister.

** Shame about the ** 500 kohm** volume pot on most electric guitars and
the 1 Mohm resistor on the J-FET gate.

The high source impedance of the guitar PU does NOT attenuate their
thermal noise like a 5 k ohms resistor !!

DAMN SHAME what happens when the guitar's volume pot is turned down
slightly from its max position - instantly making the source impedance
very high and resistive ( 100 -200 kohms typical).

Kinda swamps the tiny noise contribution of a 4.7 k series resistor !!

No, not really.

** Giant YAWN .....

Aylward is totally INSANE .

He plainly cannot even see the crucial word "most" in my para above.

He has also ignored the obvious fact that the word " which " connects my
final comment TO the previous fact.

Standard ASININE performance for someone who has bi-polar disorder and ASD.

Your kidding right?

** Not at all.

Been playing sone I was 11 years old mate. Been through one or two guitars
in the time, although I currently only have 4.

** Have built over 100 SS guitar amps (my own design & with J-FET inputs)
and serviced around 6000 valve and SS guitar amps over the last 36 years.

Seen, played and repaired most types of electric guitar too - Les Pauls,
SGs, Strats, Teles etc.

Yeah, sure...

** Absolutely for sure.

Most electric guitar PUs in common use DO generate lots of buzz and hum.

Only a small fraction are relatively immune.





......... Phil