Dummy Load / load vox for 45 w power amp

[heyveno]

hello, I have 16 ohm 100 w power resistors and an old computer ( with CPU ventirad).

I was thinking of making a power attenuator for an old silver faced bassman clone.

I 've seen quite a lot of dummy load loyout based on power resistor.

Is it possible to adapt them to make an attenuator with line out ?

The idea is to be able to choose between the line out and an attenuation ( /4 maybe) to connect to a cab. The transformer out in 12 ohm (made in italy), and my resistances as well as my cab are in 16 ohm.

I found this diagram as a starting point.

[Rob Strand]

If you want the line-out to represent what you hear from speaker there's many  technicalities.

Some of the main issues are:
- The speaker impedance isn't a constant resistance.
  If you load the output of an amp with a constant resistance the signal is duller/flatter.
- The speaker has a frequency response.   The signal you hear from the speaker
  is very different from the signal at the output of the amp.

A speaker sim circuit can address one or both of these issues to some degree.

Putting those issues aside if you want to add a means to attenuate the level to the loudspeaker
you can use one of the following attenuators.   The key point about these attenuators
is they all present a impedance of RL to the amplifier for any vaue of attenuation k.



The signal getting to the speaker isn't *exactly* what you hear when you connect the speaker directly
to the amp.   Each attenuator sounds a little different and they sound different depending on the amount of attenuation
used.

If you calculate the part values for an attenuation of k=1/4  you will see you need resistor values other than 16 ohm.

If you choose an attenuation of k=1/2 then some values end up as RL/2 and others RL.  For RL = 16 ohm you can make
a value of RL/2 with two 16 ohms in parallel.   In order to do that you need at least three 16 ohm resistors.

If you check out the many on-line attenuator schematics they tend to follow one of these circuits.
(Some use inductors which is a whole different way to go about things.)

[heyveno]

thanks.

I just want a attenuator for work, don't need to have a great sound that i have with my amp without, but if it can be better than at level 1 on amp it's nice ( it's a bassman)

[SatchmoeddieII]