I have a series attenuator that I traded for many years ago, and I can't remember what the value is.
How do you measure the value of a pot or attenuator?
How do you measure the value of a pot or attenuator?
Hi, in to ground disregarding the wiper. If switched it may vary. rgds, sreten.
That input impedance. Output is wiper to ground with the input near shorted.
That input impedance. Output is wiper to ground with the input near shorted.
It's that easy? The resistance between in 'in' and 'ground' ? Wow, I didn't know it was that simple! Thanks!
Impedence is the measure of reactance and resistance combined and so because there isn't any reactance in a pot your left measuring the resistance!
Aha! That makes sense - I was probably getting hung up on the semantics... a pot is referred to as having a 50K impedance.
Yes. But the item that I do not know the value is an Attenuator made from a 24 pole switch and a bunch of resistors. Hence why I need to ask! 🙂
Hi,
check the resistance from input to common for all switch positions.
It may vary.
Check also if it is make before break or break before make.
A break before make may go open circuit on the output when very slowly operating the switch between positions.
A make before break may read a little low on the output, during the switch over between positions.
check the resistance from input to common for all switch positions.
It may vary.
Check also if it is make before break or break before make.
A break before make may go open circuit on the output when very slowly operating the switch between positions.
A make before break may read a little low on the output, during the switch over between positions.
It is a Make Before Break.
I also have a switch in my junk box that is Break Before Make. Other than the obvious clicking that this would have as you move between each pole, are there any other disadvantages to a BBM?
Hi,
the high impedance of a break before make presented to the power amp may do lots.
It could just be a touch of extra wideband noise while the contacts are open.
Or
Slightly worse would be slight instability and RF breakthrough.
Or
The fuses blow because the amp goes into full oscillation when not loaded with a low source impedance.
the high impedance of a break before make presented to the power amp may do lots.
It could just be a touch of extra wideband noise while the contacts are open.
Or
Slightly worse would be slight instability and RF breakthrough.
Or
The fuses blow because the amp goes into full oscillation when not loaded with a low source impedance.
Youch! That has the potential of being quite bad. I think I will discount using that switch in that way...
Hi,
but you said you had a make before break switch.
That can be tested and proved.
It's safe to use a MBB at the input of a Power Amp, even when longish cables are used in between.
but you said you had a make before break switch.
That can be tested and proved.
It's safe to use a MBB at the input of a Power Amp, even when longish cables are used in between.
I have a series-stepped attenuator that is all wired up and ready to go, it is built on an ELNA MBB.
I also have another, different switch in my box, just sitting there, kinda dirty, that is BBM. That's what leaded me to ask about the problems with BBM... 😀
BBM can leave a valve grid floating, if used straight onto the grid. At the very least this could cause loud clicks when switching. Cheap solution is a 1M from grid to ground. Better solution is a coupling capacitor and then a 1M to ground.
If you trust your switch this is not necessary with MBM. It is necessary with a normal pot, as pots cannot be trusted, but most people don't bother.
If you trust your switch this is not necessary with MBM. It is necessary with a normal pot, as pots cannot be trusted, but most people don't bother.
Last edited:
- Status
- Not open for further replies.