Hi
I just got hold of a 15 steps Plessey make before break rotary switch and intend to use it as a stepped potentiometer for volume control of my passive pre-amp.
I am seeking advice on the resistor value required.
Using the HiFi Collective 50K Shunt 46 steps as a guide, I decided to skip every 2 steps on their 46 steps, and used the remaining for mine. Is this the correct way?
(Number rounded)
1 - 0R
2 - 18R
3 - 50R
4 - 100R
5 - 200R
6 - 400R
7 - 800R
8 - 1K5
9 - 3K
10 - 7K
11 - 11K
12 - 17K
13 - 27K
14 - 50K
15 - 121K
Thanks!
I just got hold of a 15 steps Plessey make before break rotary switch and intend to use it as a stepped potentiometer for volume control of my passive pre-amp.
I am seeking advice on the resistor value required.
Using the HiFi Collective 50K Shunt 46 steps as a guide, I decided to skip every 2 steps on their 46 steps, and used the remaining for mine. Is this the correct way?
(Number rounded)
1 - 0R
2 - 18R
3 - 50R
4 - 100R
5 - 200R
6 - 400R
7 - 800R
8 - 1K5
9 - 3K
10 - 7K
11 - 11K
12 - 17K
13 - 27K
14 - 50K
15 - 121K
Thanks!
1) What is the series resistance?
Do not understand your question, I am trying to build a 50K (or there about) shunt stepped potentiometer if that was your question. It starts at about 9 dB step attenuation and gradually reduced to 3 dB attenuation per step.
2) what circuitry and components are before the volume control?
CD/DAC output, it connects to power amp. Intend to use it as passive preamp initially and may use it for volume control of active preamp later.
3) Is this a make-before-break switch? Yes
Do not understand your question, I am trying to build a 50K (or there about) shunt stepped potentiometer if that was your question. It starts at about 9 dB step attenuation and gradually reduced to 3 dB attenuation per step.
2) what circuitry and components are before the volume control?
CD/DAC output, it connects to power amp. Intend to use it as passive preamp initially and may use it for volume control of active preamp later.
3) Is this a make-before-break switch? Yes
Here is a good explanation of the various attenuator types.
https://www.goldpt.com/attenuator_types.html
The series attenuator behaves pretty much like a regular potentiometer with detents, while a shunt type presents a variable impedance to the circuit preceding it. My preference would be the series attenuator, especially when used as a volume control in a passive preamp.
Note that Goldpoint no longer offers ladder and shunt attenuators, but you can of course build one yourself if that is what you want.
https://www.goldpt.com/attenuator_types.html
The series attenuator behaves pretty much like a regular potentiometer with detents, while a shunt type presents a variable impedance to the circuit preceding it. My preference would be the series attenuator, especially when used as a volume control in a passive preamp.
Note that Goldpoint no longer offers ladder and shunt attenuators, but you can of course build one yourself if that is what you want.
You can't just delete steps that way. You can select the steps you want and add all the resistors between them. That is a very substantial switch. It looks like its for high current. Hopefully those are silver contacts.
Another possible resource is the John Broskie dual stereo control where ladder and shunt are mixed together producing an incredible amount of steps. In that design, you have 'coarse' volume control in concert with a 'fine' volume control. You can still use your type of switch instead of his if yours is better quality.
Actually, you can do this with a shunt type attenuator, which was described in the original post. That type has one large series resistor (50k in this case), and an arbitrary number of additional resistors that form the other resistor of the voltage divider. So the OP could take the design he has and use every other resistor value if he wants, and that will work as I think he intends.
See the Goldpoint description of the shunt type attenuator in the link below.
https://www.goldpt.com/attenuator_types.html
After reading the article I decided to use series instead of shunt. Thank you
Thank you, I was going with a shunt initially but decided to change to a series…
My understandings is that with the shunt I could just jump and omit those between, but with series I will have to add the value of the omitted resistors, as confirmed by another contributor.
The switch is a NOS Plessey Type 72
An R/nR Resistor ladder like a R/2R ladder allows you to use only a couple resistor values. In any case, with only 15 steps, you need to choose the steps carefully and the last step to "off" is a big one. For a 50K "pot" with about 2dB steps, you need 10K series and 200K shunt resistors, terminated with 40K. (Somebody check my calculations? -2dB~=40K/50K and 1/40K-1/50K=1/200K)
Note that the "Goldpoint" article does not actually cover a ladder circuit??? Not Invented Here? What they call a ladder circuit is not. See R/2R ladders:
https://en.wikipedia.org/wiki/Resistor_ladder
Also, a more convenient resistor values simply gives slightly different attenuation per step, which may be a better solution.
Personally, I'd go for a digital solution. 4 relays is 16 steps, 5 relays is 32 steps...
https://en.wikipedia.org/wiki/Logarithmic_resistor_ladder
https://en.wikipedia.org/wiki/Resistor_ladder
Also, a more convenient resistor values simply gives slightly different attenuation per step, which may be a better solution.
Personally, I'd go for a digital solution. 4 relays is 16 steps, 5 relays is 32 steps...
https://en.wikipedia.org/wiki/Logarithmic_resistor_ladder
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I think one of the questions you have to answer will be how to define the curve you want.
I agree that if you have 15 steps, a particular curve will suit you best. An averaged curve is not what would give you the most control. In fact, I wonder if things were set up to actually use more of the curve by starting with zero volume actually being low volume, thereby allowing 1 or more resistors to be used at a higher attenuation.