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rs1026 20th May 2005 02:44 PM

Line level volume control
 
What is line level volume control? Is it controlling the volume from line out port?

I have a dvd player.I have built a lm3886 based GC but the player cannot control the volume and GC has a fixed gain.So the music level is quite high.Can I connect a pot from line out of the dvd player to input of the GC to reduce this level. Is this good idea??
I want to keep it as simple as possible without a preamp.

tobias_svensk 20th May 2005 03:03 PM

Just use like a 10-20k pot and your fine, look Here on page 14.

youyoung21147 21st May 2005 08:04 AM

I plan to build a stepped attenuator, so I will get only two pins.
Does anyone know howto cable this ?

h_andree 21st May 2005 01:17 PM

You will need 3 pins. You always need an input impedance
and a connection to ground.

I had vey good results with a 5 kOhm reistor in the
signal path and then using a 100k pot as variable
resistor to ground.

Although the stepped relay attenuator I made is better
it's also much more expensive. It does give me
remote volume though.

Harry

youyoung21147 21st May 2005 02:01 PM

You mean that, contrary to a pot, the stepped attenuator must be connected after the input resistor ?

h_andree 22nd May 2005 01:43 PM

No.

Think of a pot as a voltage divider. One part of the
signal goes through a resistive value. Then it's
weakened by connecting it to ground.

What I'm proposing is to use a 5k fixed resistor
for the signal and a variable 100k resistor to shunt
to ground. The actual impedance your sources
see would vary between 5 k and whatever your
input impedance is.

Harry

youyoung21147 22nd May 2005 03:05 PM

In fact it may look like this :

In ----> 5k resistor ----> stepped attenuator -----> amplifier
??????????????????????????????????????????|
??????????????????????????????????????????|
??????????????????????????????????ground impedance resistor
??????????????????????????????????????????|
??????????????????????????????????????????|
???????????????????????????????????????ground

or this ? :

In ----> 5k resistor -------------------------------------> amplifier
????????????????????|??????????????????????|
????????????????????|??????????????????????|
????????????stepped attenuator ground impedance resistor
????????????????????|??????????????????????|
????????????????????|??????????????????????|
-----------------------ground----------------------ground

h_andree 22nd May 2005 05:36 PM

Attenuator
 
This is about it:


|---5K--|--300--OpAmp
| |
| Var100K
| |
| GND

youyoung21147 22nd May 2005 05:53 PM

Thanks a lot, that will help me build my future gainclone ! :D

I suppose the 5K resistor helps keeping a high input impedance in order to limit distorsion, unlike driving a low impedance headphone that can be as low as 16 Ohms

h_andree 22nd May 2005 06:18 PM

Yes.

You may try lower but may get in trouble with some sources.
I heard these low impedances may cause problems with
some tube output stages.

I think the noise level of a 5kOhm resistolr is much better
then a 50 or 100kOhm resistor. I feel that this is one
of the reasons why amps do not sound as good at low
volume. I'm using the Visky s102k ($15 a piece). If you
do not wnat to spend that much I would recommend
Holco H8.

I'm switching 15 resistors from signal to ground. I'm using
relays switched by a micro controller. This gives me
60 dB attenuation in 1 dB steps.

Then I've added Carlos's Opamp amplifier.

I've heard many pre-amps but this is one of the most detailed
ones possible. Switching from a Alps 100k pot to this
volume control made a hugh improvement.

Harry


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