Bass Boost at low volume level

A

Andy

Guest
Im looking to build myself a pre-amp whose characteristics are such
that its amplification factor decreases as the level of input
increases. Its so that I get a higher level of bass when my music is
turned down low but it doesnt then cause my woofers to distort when i
crank the master volume contol up.

The pre-amps input will be fed from my amplifiers line out, the
tweeters and mid range are driven from the amplifiers power out.

The woofers are driven from a separate power amp, this is where my
pre-amps out put will be connected, the power amp has a built in low
pass filter so my design doesnt need to include a lpf.

My current design is basically an opamp with the usual Rf/Rin setup
and a couple of diodes in opposite directions each in series with a
resistor to get some sort of clamping that isnt too squared off as the
input increases.

Does any one have any suggestions? agc maybe?
 
maccyd10@hotmail.com (Andy) wrote:

Im looking to build myself a pre-amp whose characteristics are such
that its amplification factor decreases as the level of input
increases. Its so that I get a higher level of bass when my music is
turned down low but it doesnt then cause my woofers to distort when i
crank the master volume contol up.

Does any one have any suggestions? agc maybe?
Click to expand...
What you are asking for is known as "loudness" control.
Search for "loudness schematic" or "loudness circuit".

There are several technical solutions to the problem.
The old type used a special volume pot with an extra connection.
Some designs use a microphone to sample the volume in the room.
But most modern designs simply change the bass and treble content at higher
sound volumes.



--
Roger J. (No Emails)
 
I read in sci.electronics.design that Andy <maccyd10@hotmail.com> wrote
(in <f2bcd835.0403230706.4eb317ab@posting.google.com>) about 'Bass Boost
at low volume level', on Tue, 23 Mar 2004:
Im looking to build myself a pre-amp whose characteristics are such that
its amplification factor decreases as the level of input increases. Its
so that I get a higher level of bass when my music is turned down low
but it doesnt then cause my woofers to distort when i crank the master
volume contol up.

[snip]
My current design is basically an opamp with the usual Rf/Rin setup and
a couple of diodes in opposite directions each in series with a resistor
to get some sort of clamping that isnt too squared off as the input
increases.
Click to expand...
You will get violent distortion if the circuit actually does limit your
signal amplitude. It's quite the wrong approach.
Does any one have any suggestions? agc maybe?
Click to expand...
No, AGC will simply stop you turning up the level.

The solution was invented over 60 years ago (in Germany?). It's called
'loudness control'. When it was incorporated in almost every radio and
amplifier designed in Continental Europe (it wasn't all that popular in
Britain), you could get 10% log-law volume control pots with centre-
tapped tracks, used in a circuit like this:

Use Courier font; R is about 10% of the pot resistance; C is chosen to
give about 3 dB boost at 250 to 400 Hz:

-------------+
|
| Centre-
+++ tapped log pot
| |
Input | |<---------
+----| |
R | |
| +++ Output
C |
| |
-------+-----+-----------

You won't be able to get a tapped pot, probably. You can simulate one
with a 12-position rotary switch (more poles if you can get them) and
fixed resistors. The calculation of the resistor values is left as an
exercise for the student. (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
Andy,
Here is something crude that might work.
1. Have a normal volume control.
2. Now tap off some of the signal ahead of the pot, and pass it through an
RC low pass filter (say ~100 Hz).
3.Combine the low pass filter output with the pot output. You will need to
combine the two signal in an opamp to prevent interaction.

Normally, in a loudness control both the bass and treble are boosted at low
volume. Surprisingly, I did not see "loudness control" listed in the index
of the Radiatron Designers Handbook.

Tam
"Andy" <maccyd10@hotmail.com> wrote in message
news:f2bcd835.0403230706.4eb317ab@posting.google.com...
Im looking to build myself a pre-amp whose characteristics are such
that its amplification factor decreases as the level of input
increases. Its so that I get a higher level of bass when my music is
turned down low but it doesnt then cause my woofers to distort when i
crank the master volume contol up.

The pre-amps input will be fed from my amplifiers line out, the
tweeters and mid range are driven from the amplifiers power out.

The woofers are driven from a separate power amp, this is where my
pre-amps out put will be connected, the power amp has a built in low
pass filter so my design doesnt need to include a lpf.

My current design is basically an opamp with the usual Rf/Rin setup
and a couple of diodes in opposite directions each in series with a
resistor to get some sort of clamping that isnt too squared off as the
input increases.

Does any one have any suggestions? agc maybe?
Click to expand...
 
I read in sci.electronics.design that Tam/WB2TT <t-tammaru@c0mca$t.net>
wrote (in <2qadncgZluC9A_3dRVn-sA@comcast.com>) about 'Bass Boost at low
volume level', on Tue, 23 Mar 2004:

Normally, in a loudness control both the bass and treble are boosted at
low volume. Surprisingly, I did not see "loudness control" listed in the
index of the Radiatron Designers Handbook.
Click to expand...
That's because it's called 'Automatic frequency-compensated volume
control'. Section 15.10.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
On Tue, 23 Mar 2004 15:29:26 -0500, "Tam/WB2TT"
<t-tammaru@c0mca$t.net> wrote:

Andy,
Here is something crude that might work.
1. Have a normal volume control.
2. Now tap off some of the signal ahead of the pot, and pass it through an
RC low pass filter (say ~100 Hz).
3.Combine the low pass filter output with the pot output. You will need to
combine the two signal in an opamp to prevent interaction.

Normally, in a loudness control both the bass and treble are boosted at low
volume. Surprisingly, I did not see "loudness control" listed in the index
of the Radiatron Designers Handbook.

IIRC those vilume pots had a fixed tap for that?
Click to expand...
 
"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:VapwgBIQTKYAFw4s@jmwa.demon.co.uk...
I read in sci.electronics.design that Tam/WB2TT <t-tammaru@c0mca$t.net
wrote (in <2qadncgZluC9A_3dRVn-sA@comcast.com>) about 'Bass Boost at low
volume level', on Tue, 23 Mar 2004:

Normally, in a loudness control both the bass and treble are boosted at
low volume. Surprisingly, I did not see "loudness control" listed in the
index of the Radiatron Designers Handbook.

That's because it's called 'Automatic frequency-compensated volume
control'. Section 15.10.
Click to expand...
Thanks. The book must predate the term loudness control.

Tam
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Click to expand...
 
I read in sci.electronics.design that Tam/WB2TT <t-tammaru@c0mca$t.net>
wrote (in <7eqdna2rR8vmff3d4p2dnA@comcast.com>) about 'Bass Boost at low
volume level', on Tue, 23 Mar 2004:
"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:VapwgBIQTKYAFw4s@jmwa.demon.co.uk...
I read in sci.electronics.design that Tam/WB2TT <t-tammaru@c0mca$t.net
wrote (in <2qadncgZluC9A_3dRVn-sA@comcast.com>) about 'Bass Boost at low
volume level', on Tue, 23 Mar 2004:

Normally, in a loudness control both the bass and treble are boosted at
low volume. Surprisingly, I did not see "loudness control" listed in the
index of the Radiatron Designers Handbook.

That's because it's called 'Automatic frequency-compensated volume
control'. Section 15.10.

Thanks. The book must predate the term loudness control.
Click to expand...
Not really. The term and technique weren't popular in Britain, and at
that time technical opinions in Australia were very much influenced by
opinions in Britain. Not that people like FLS couldn't form their own
opinions, but the often cam to the same conclusions as their British
colleagues.

One objection to the technique is that it makes assumptions about the
incoming signal voltage, the loudspeaker sensitivity and the room size.
For a radio, only the latter is variable (unless you are listening to a
really weak station), but for a separate amplifier all three quantities
vary, so you don't know where the volume control will be set. With a
strong input signal you may get the bass lift appropriate for 60 dB SPL
when you are listening at 80 dB SPL.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
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