Fixed resistor

[maddmaxxdrummer]

Hi I am a newbie hobbyist, just wondering if I can get some help here
I have pre amp with a 100k alps volume pot
I find that I have very little play on my volume control as its too loud at 1 setting
This only for late night listening where I can really go up on the volume position
I was thinking of placing 2 fixed resitors at the outputs of the volume pot to the outputs of the RCA's with a switch in the middle so I can select it for night time only.
But I don't know how to calculate what resistor values to use.
I would like to cut the volume pot by 3/4 which will give me a lot a headroom to turn the knob up.

Any help would be appreciated
Thanx

Maxx.

 

[merlin el mago]

Voltage divider - loaded and open-circuit dB calculator damping volts potentiometer circuit impedance damping pad decibel dB voltage attenuator impedance bridging matching - sengpielaudio Sengpiel Berlin

 

[AndrewT]

you probably have too much gain in your system.
You may not need a pre-amp at all.
Have you read?
http://www.diyaudio.com/forums/diyaudio-com-articles/186018-what-gain-structure.html

 

[rayma]

I have pre amp with a 100k alps volume pot I was thinking of placing 2 fixed resitors
\at the outputs of the volume pot to the outputs of the RCA's with a switch I would like to cut the volume pot by 3/4.

It's likely that you can use a series 10k and a shunt resistor from 1k-5k per channel. Start with around 3k and see how you like it.

 

[sesebe]

If you source can work on a lower impedance, I suggest you just to connect a resistor between output of the volume pot and gnd. The value of this resistor can be from 10K to 100K. The advantage will be that at maximum you will lose almost nothing from volume, but at lower level setting, the control will be more delicate.

 

[maddmaxxdrummer]

Thanks guys
lol.. Some stuff is too technical for me but I'll try the resistor approach by RAYMA.
How many watts for the 10K..?
Btw what is a shunt resistor.? Looked it up but get all kinds of weird looking things
Like I said.. Newbie.. Lol

 

[rayma]

How many watts for the 10K..? what is a shunt resistor.?

These resistors can be 1/2W size.

A shunt resistor just means that it goes to ground after the series 10k resistor.
Read the first part of this. (You don't need to match the impedances.)
http://www.electronics-tutorials.ws/attenuators/l-pad-attenuator.html

 

[maddmaxxdrummer]

Ok thanx, I'll try this out.

I found some Vishay S102K, 10K / 0.6 Watt, Bulk Metal Foil Resistor, 0.05% / 2ppm TCR,

On sale 3.95$ each on parts connex

Does this work for the series resistors ?

For the shunt resistors,

Shinkoh 3K0 / 0.5 (1/2) Watt, Tantalum Film Resistor, 1%

Am I making any sense in using these for my mod..?

Thanks again

 

[sesebe]

Ok thanx, I'll try this out.

I found some Vishay S102K, 10K / 0.6 Watt, Bulk Metal Foil Resistor, 0.05% / 2ppm TCR,

You don't need soo high precision. 1% or 0.5% metal film it is more that enought.

 

[AndrewT]

you stated you have a 100k vol pot.
adding a 10k series resistor in front of that will attenuate your output by about -0.83dB
Even adding 100k in series only attenuates the output by only ~-6dB.
You would need to add ~220k to get -10dB of attenuation.

Sort the excessive gain !

 

[JonSnell Electronic]

If you hang a 10k resistor between the slider and ground on each side of the pot, that will turn the pot into a more controllable range at the bottom end. You could use 5% 0.25W 10k with no issues. There is no point in lining the suppliers pocket at $## money prices!

 

[AndrewT]

The added "log faking" resistor has a much bigger effect during the upper 2/3rds of the wiper travel.
It has much less effect in the lower 1/3rd of wiper travle.

Look at the graph of output vs pot rotation for the log faked version.

 

[sesebe]

It is more easy with an image. My recommendation it is 10K for resistor...

 

[maddmaxxdrummer]

Hi guys
I was thinking of placing my resistors after the pot but at these posts which are at the back of the preamp so can place a toggle at the back of the chassis.
If would do it BEFORE the volume pot I would have to undo the whole PC board and it would make for longer wires to the toggle switch
I want the switch, so in the day time where volume is not an issue then there would be no extra resistors in the path..
See pics

 

[sesebe]

If you place the resistor like in previous photo you do not need to place a switch because the maximum gain/power it is not afected and during the day time you only need to use a higher volume setting.
For example, if you use durring the day usualy 30% of volume now, with a 22k resistor you will need to use 63% of volume. But if you need during the day usualy 60%, with resistor the setting will be 88%, or for 90% with resistor it is need 97% but still possible.

 

[maddmaxxdrummer]

thanks everyone for your help.