Aleph P Finished (Well at least 99% done)

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Wuffwaff,

After looking at the article it appears that this attenuator arrangement can only be used on the input, the caveat of this configuration is that any switch noise (click etc.) will be amplified and definately heard. That is why I chose to attenuate the output of my preamp instead of the input. Very good article. Thank you for the link to it.
 
Thanks guys for discussing volume controls...I am learning what and where to look in deciding for my future Aleph P. I've done preliminary work on the circuit board design with a common heatsink for all 6 fets/ch so I can keep it warm but not toasty 24/7.
 
Hi,

it is sort of logarithmic. I took 2k2 output resistors and calculated the others to give ca. 3dB steps. You will need 22 resistors. The first step is closed (0 ohm) the last open.
The others are:
5600, 2200, 1200, 720, 470, 330, 220, 150, 100, 68, 47, 33, 25, 18, 12,
8,8
6,2
4,4
3,1
2,2
1,5
1,2
some values are not available so you´ll have to take the nearest one. Output impedance will be very low for most of the range. Only the highest leves have a bit more . Here´s the range from -0dB to infinity:
2195, 1579, 1100, 776, 542, 387, 287, 200, 140, 96, 66, 46, 33, 25, 18, 12, 9, 6, 4, 3, 2, 1, 1, 0 (all in ohms)

hope this helps,

William
 
Audio signal amplitudes are measured in deciBells (dB). The range of loudness which can be perceived by the human ear varies over 6 orders of magnitude making linear measurements of loudness difficult to deal with. Therefore a logarithmic scale of loudness, the deciBel scale, has been adopted.

This logarithmic measurement of signal intensity describes the amplitude of a signal relative to a standard referrence amplitude. Therefore the dB scale is said to be a relative, not an absolute scale of measurement. The referrence used for 0dB varies according to the circumstances for which the signal is being measured.

To calculate dB for amplitude, the formula the is dB=20 Log(Amp / RefAmp). To calculate dB for power, the formula is dB=10 Log(Power / RefPower).
 
Thanks for the information William, i think it will help.

As i see a 10k stereo Poti could also be used. I`m thinking of a Thel guidance plastics potentiometer (as Systran translated it) cause i like attenuators with fine adjustability.

Regards, illusionxx.
 
Hi Illusion,

you can´t use the Thel (or any other pot) :no: :no: I tried both Thel and an Alps. They are way too coarse in the lower region so you can´t regulate the lower volumes and one channel will be louder than the other.

William
 
Nbaula,

it should work for every balanced output preamp. You must choose the output resistors (1k-2k) and then calculate the shunt resistor to get the desired attenuation. I´ve got a small excel sheet attached. Here you can calculate the neccesarry resistor values, look at the output impedance and the errors you get when choosing real world resistors.

William
 

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Hi Arne,

yes that´s the way I use it for unbalanced output. The dB steps will change though. I wouldn´t use it for an unbalanced only amp and you have to be shure that the preamp has no problem when it sees an impedance of 1k or so at the output

William
 
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