To anyone who can answer this question:

I have an Audio Research LS3 preamplifier. It is supposed to be one of
the best preamplifiers of all time. One thing I noticed immediately when
replacing my Sony TA-E1000ESD with it was the noise floor. When the
preamplifier is on, there is a very low level, but constant hiss, even
with no inputs connected at all and the gain all the way down. My
hearing is extremely sensitive and I can hear it from 10 feet away. Most
other people need to come close to the speakers, however. My Sony did
not have this problem. What causes this excessive noise floor? I know it
is supposed to be from "random electron movement" but I mean what
specifically, the transistors, resistors, capacitors, circuit design,
what? Also, is there any cure for it?

Many Thanks,
Eitan Adut

"Eitan Adut" wrote in message
news:hO0Za.103174$YN5.72738@sccrnsc01...
To anyone who can answer this question:

I have an Audio Research LS3 preamplifier. It is supposed to be one of
the best preamplifiers of all time. One thing I noticed immediately when
replacing my Sony TA-E1000ESD with it was the noise floor. When the
preamplifier is on, there is a very low level, but constant hiss, even
with no inputs connected at all and the gain all the way down. My
hearing is extremely sensitive and I can hear it from 10 feet away. Most
other people need to come close to the speakers, however. My Sony did
not have this problem. What causes this excessive noise floor? I know it
is supposed to be from "random electron movement" but I mean what
specifically, the transistors, resistors, capacitors, circuit design,
what? Also, is there any cure for it?

Ten feet away from the ribbons of a pair of Tympani IVa, with the gain down
AND the treble turned all the way up, I don't hear "tube rush" from a ARC
SP-3-a-1. As expected the noise floor is greatest from the phono source. If
your pre-amp is excessively noisy, perhaps it might be worth you while to
aquire a different set of tubes. I obtained 2 sets, (one to serve as a
back-up, or repalcement) from Triode Electronics Online, 6-"12ax7tesla" and
2-"12ax7eielite" for positions V1 and V4 in the above pre-amp, phono gain?,
all for a grand total of $70.90 including a very speedy securely packaged $6
shipment. (Go to www.triodeelectronics.com, IMO a great source for all tube
needs. I have absolutely no relation to them.)

"Eitan Adut" wrote in message
news:hO0Za.103174$YN5.72738@sccrnsc01...
To anyone who can answer this question:

I have an Audio Research LS3 preamplifier. It is supposed to be one of
the best preamplifiers of all time. One thing I noticed immediately when
replacing my Sony TA-E1000ESD with it was the noise floor. When the
preamplifier is on, there is a very low level, but constant hiss, even
with no inputs connected at all and the gain all the way down. My
hearing is extremely sensitive and I can hear it from 10 feet away. Most
other people need to come close to the speakers, however. My Sony did
not have this problem. What causes this excessive noise floor? I know it
is supposed to be from "random electron movement" but I mean what
specifically, the transistors, resistors, capacitors, circuit design,
what? Also, is there any cure for it?

Many Thanks,
Eitan Adut


Its almost probably not electron noise etc as this is very low down sub -130
to -160db.

The 1st thing to check is the noise, is it pickup? ie is it external to the
preamp ? the best way to check this is to short out the inputs (buy some
cheap plugs and short out the inputs, only becarefull only the inputs) if
the noise floor decreases then you know its external to the preamp ie some
sort of emi pickup. If however it remains the same then its either the
preamp or the connections between the pre and main amp. - try some other
leads, check the earth (grounding) plan (probably the most likely call) is
it correct?, and if that don't fix it -get the preamp checked out by someone
else (this eliminates your possible configuration problems in one hit) it
could be faulty.
If its the preamp -- look at the cap's first, then the resistors high values
going open circuit, then the transistors or equivalents.

Good hunting Chris

He Renaud
I understand your point, however as their seems to be an ethos on this forum
of "arrogant bigheads with personal agendas" desiring to make arguments by
provocatively seizing on some word or phase in reply, and trying to make an
argument about it, therefore I think my reply is a valid one ! Unless you
and the other moderators are trying going to do something about this whole
issue ?
It does nothing to forward the cause of highend audio, understanding, wisdom
and knowledge, it just encourages those with affective and other disorders
to propagate themselves and prevent real discussions on subjects. I am
rapidly becoming disenchanted with this forum

----- Original Message -----
From: "Renaud Dreyer"
To: "chris"
Cc: "Bath David"
Sent: Tuesday, August 12, 2003 5:53 AM
Subject: preamplifier noise floor problems

Le lundi, 11 aoû 2003, Ã* 11:33 US/Pacific, chris a écrit :

No if you want to you can find enough about it on the Web.

"chung" wrote in message
...
chris wrote:
"Eitan Adut" wrote in message
news:hO0Za.103174$YN5.72738@sccrnsc01...
To anyone who can answer this question:

I have an Audio Research LS3 preamplifier. It is supposed to be one
of
the best preamplifiers of all time. One thing I noticed immediately
when
replacing my Sony TA-E1000ESD with it was the noise floor. When the
preamplifier is on, there is a very low level, but constant hiss,
even
with no inputs connected at all and the gain all the way down. My
hearing is extremely sensitive and I can hear it from 10 feet away.
Most
other people need to come close to the speakers, however. My Sony
did
not have this problem. What causes this excessive noise floor? I
know
it
is supposed to be from "random electron movement" but I mean what
specifically, the transistors, resistors, capacitors, circuit
design,
what? Also, is there any cure for it?

Many Thanks,
Eitan Adut


Its almost probably not electron noise etc as this is very low down
sub -130
to -160db.


Care to provide some calculations/measurements to back that up?



Dear r.a.h-e contributor,

Thank you for submitting your post to the newsgroup. However, your
article was a response to one particular individual and of little
interest to the entire r.a.h-e readership. Private e_mail might be
more appropriate. This violates the posting guidelines, meaning that I
have to reject your post. Regards,

Renaud Dreyer
r-a.h-e moderating team

"Eitan Adut" wrote in message
news:hO0Za.103174$YN5.72738@sccrnsc01...
To anyone who can answer this question:

I have an Audio Research LS3 preamplifier. It is supposed to be one of
the best preamplifiers of all time. One thing I noticed immediately when
replacing my Sony TA-E1000ESD with it was the noise floor. When the
preamplifier is on, there is a very low level, but constant hiss, even
with no inputs connected at all and the gain all the way down. My
hearing is extremely sensitive and I can hear it from 10 feet away. Most
other people need to come close to the speakers, however. My Sony did
not have this problem. What causes this excessive noise floor? I know it
is supposed to be from "random electron movement" but I mean what
specifically, the transistors, resistors, capacitors, circuit design,
what? Also, is there any cure for it?

Many Thanks,
Eitan Adut


Eitan,

The noise you are referring to is thermal noise and is defined by the
equation:

V = ?KTBR

Where K is Boltzman's constant, T is temp in Deg K, B is bandwidth and R is
resistance. Transposing the equation gives

V2/R = KTB

This works about at 300 deg K (27C) to be -204 dBW/Hz. With a 20kHz
bandwidth this is -161dBW, i.e. 161 dB below 1 watt.

This is the theoretical minimum, and all components will add a certain
amount of additional noise albeit very small. Some components are better
than others e.g. wirewound resistors are better than metal film which in
turn are better than carbon film. Active components are much noisier,
especially valves.

Hope this helps.

Pete Brown

On Tue, 12 Aug 2003 14:59:40 GMT, "PeteB" wrote:

"Eitan Adut" wrote in message
news:hO0Za.103174$YN5.72738@sccrnsc01...
To anyone who can answer this question:

I have an Audio Research LS3 preamplifier. It is supposed to be one of
the best preamplifiers of all time. One thing I noticed immediately when
replacing my Sony TA-E1000ESD with it was the noise floor. When the
preamplifier is on, there is a very low level, but constant hiss, even
with no inputs connected at all and the gain all the way down. My
hearing is extremely sensitive and I can hear it from 10 feet away. Most
other people need to come close to the speakers, however. My Sony did
not have this problem. What causes this excessive noise floor? I know it
is supposed to be from "random electron movement" but I mean what
specifically, the transistors, resistors, capacitors, circuit design,
what? Also, is there any cure for it?

The noise you are referring to is thermal noise and is defined by the
equation:

V = ?KTBR

Where K is Boltzman's constant, T is temp in Deg K, B is bandwidth and R is
resistance. Transposing the equation gives

V2/R = KTB

This works about at 300 deg K (27C) to be -204 dBW/Hz. With a 20kHz
bandwidth this is -161dBW, i.e. 161 dB below 1 watt.

This is the theoretical minimum, and all components will add a certain
amount of additional noise albeit very small. Some components are better
than others e.g. wirewound resistors are better than metal film which in
turn are better than carbon film. Active components are much noisier,
especially valves.

While the above is certainly all correct, it might be worth noting
that in this particular case, the most likely cause is excessive gain
after the volume control. This improves overload tolerance, but leads
to an increase in the noise floor which can not be mitigated by
turning down the volume.

The only practical solution is a fixed 'L-pad' attenuator at the input
to the power amplifier, probably in the 10-20dB range.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

PeteB wrote:
"Eitan Adut" wrote in message
news:hO0Za.103174$YN5.72738@sccrnsc01...
To anyone who can answer this question:

I have an Audio Research LS3 preamplifier. It is supposed to be one of
the best preamplifiers of all time. One thing I noticed immediately when
replacing my Sony TA-E1000ESD with it was the noise floor. When the
preamplifier is on, there is a very low level, but constant hiss, even
with no inputs connected at all and the gain all the way down. My
hearing is extremely sensitive and I can hear it from 10 feet away. Most
other people need to come close to the speakers, however. My Sony did
not have this problem. What causes this excessive noise floor? I know it
is supposed to be from "random electron movement" but I mean what
specifically, the transistors, resistors, capacitors, circuit design,
what? Also, is there any cure for it?

Many Thanks,
Eitan Adut


Eitan,

The noise you are referring to is thermal noise and is defined by the
equation:

V = ?KTBR

Where K is Boltzman's constant, T is temp in Deg K, B is bandwidth and R is
resistance. Transposing the equation gives

V2/R = KTB

This works about at 300 deg K (27C) to be -204 dBW/Hz. With a 20kHz
bandwidth this is -161dBW, i.e. 161 dB below 1 watt.

This is the theoretical minimum, and all components will add a certain
amount of additional noise albeit very small. Some components are better
than others e.g. wirewound resistors are better than metal film which in
turn are better than carbon film. Active components are much noisier,
especially valves.

Hope this helps.

Pete Brown


What you are showing here is the *available noise power* from a
resistor. This is very different than the noise floor of an audio
amplifier. An audio amp is not a matched impedance system. An audio amp
provides finite voltage gain and almost infinite power gain.

To calculate the noise floor contribution from the preamp, you have to
measure/compute the equivalent noise voltage at the input of the preamp.
For instance, if there is a 1K resistance to ground at the input of the
preamp, that resistance will generate a 4nV/sq.rt(Hz) voltage noise
density, assuming for the time being that the noise currents of the
active input devices are negligible. That gets amplified by the gain of
the system from the preamp and the power amp, and also multiplied by the
frequency response of the system (which is not flat if the preamp is
used as a phono-preamp). Clearly, a line level preamp contibutes much
less to output noise floor because there is much less gain.

Then you have to calculate the equivalent noise voltage of the active
devices, in particular the input transistors/op-amp/tubes of the preamp.
In most cases, this is the dominant noise source.

The original poster said that the hiss stays the same even when the gain
control is all the way down. That indicates that the noise is not at the
very front end of the preamp, but coming from the output stages, or the
power amp. Wonder what is the noise spec. of that pre-amp.