Hi everyone,
I have to replace the volume control in my Pioneer SA-1000 integrated amplifier. It is a dual 500k ohm pot. Can anyone tell me what wattage I should be looking for when I go shopping?
Sincerely,
Ralf
I have to replace the volume control in my Pioneer SA-1000 integrated amplifier. It is a dual 500k ohm pot. Can anyone tell me what wattage I should be looking for when I go shopping?
Sincerely,
Ralf
There will be such little power dissipated that anything would be fine. The main factor will be does it physically fit. It will be logarithmic type.
The original has a loudness tap, too. Cleaning is advised if at all possible.
500k - heavens, that thing must be noisy.
500k - heavens, that thing must be noisy.
Hi richie00boy
According to what you wrote about power dissipation, the volume control must be part of the preamplifier and not the poweramplifier?
I spent a day and a half on the internet trying to find a replacement to no avail. So I decided to take the existing pot apart to clean it. I had previously sprayed the pot with a cleaning fluid but it turned out to be a wasted effort. I discovered that the pot was permanently assembled by staking one of the wiper discs to the shaft. After removing the stakes by machining, I was able to disassemble the pot. I then cleaned all the slip rings and wipers with a very mild abrasive and I am now in the process of reassembling the pot. I replaced the stakes with a 1-72 machine screw and a .438"x.063 washer made from PCB material.
I'll let you know how it works out.
Thanks for the reply.
Sincerely,
Ralf
According to what you wrote about power dissipation, the volume control must be part of the preamplifier and not the poweramplifier?
I spent a day and a half on the internet trying to find a replacement to no avail. So I decided to take the existing pot apart to clean it. I had previously sprayed the pot with a cleaning fluid but it turned out to be a wasted effort. I discovered that the pot was permanently assembled by staking one of the wiper discs to the shaft. After removing the stakes by machining, I was able to disassemble the pot. I then cleaned all the slip rings and wipers with a very mild abrasive and I am now in the process of reassembling the pot. I replaced the stakes with a 1-72 machine screw and a .438"x.063 washer made from PCB material.
I'll let you know how it works out.
Thanks for the reply.
Sincerely,
Ralf
Hi sgrossklass,
When I unsoldered the pot I noticed the extra 2 taps but it never occurred to me what they were. Thanks for telling me.
I tried cleaning with a spray from the outside, but it didn't work.
I then decided to take the pot apart to clean it properly as explained in my post to "richie33boy".
I purchased the amplifier around 1972 and the sound was always beautiful. The volume control was never noisy. Sometime around 1994 I put it into storage and did not use it again until approx. 2010. I can't afford a new amplifier, so I'll have to fix what I have. It's worth it because it still sounds beautiful.
Thanks for the reply,
Ralf
When I unsoldered the pot I noticed the extra 2 taps but it never occurred to me what they were. Thanks for telling me.
I tried cleaning with a spray from the outside, but it didn't work.
I then decided to take the pot apart to clean it properly as explained in my post to "richie33boy".
I purchased the amplifier around 1972 and the sound was always beautiful. The volume control was never noisy. Sometime around 1994 I put it into storage and did not use it again until approx. 2010. I can't afford a new amplifier, so I'll have to fix what I have. It's worth it because it still sounds beautiful.
Thanks for the reply,
Ralf
The pot does not modulate power level signals, it attenuates the line level going into the amp.
Sounds like you did a great job cleaning it up there.
Sounds like you did a great job cleaning it up there.
Most vol pot (potentiometer) are power rated, but that actually puts a limit on the current capability. Check the maximum current and never exceed it at any vol pot rotation.
eg.
400mW 10k pot.
Vmax = sqrt(0.4W*10k) = 63Vac, or 89Vpk
Imax = sqrt(0.4W/10k) = 0.0063A = 6.3mAac, or 8.9mApk
The voltage applied across the track must not exceed 89Vpk,
The current into, or out, of any port (including the wiper) must not exceed 8.9mApk.
To improve longevity, I recommend you halve those peak values.
eg.
400mW 10k pot.
Vmax = sqrt(0.4W*10k) = 63Vac, or 89Vpk
Imax = sqrt(0.4W/10k) = 0.0063A = 6.3mAac, or 8.9mApk
The voltage applied across the track must not exceed 89Vpk,
The current into, or out, of any port (including the wiper) must not exceed 8.9mApk.
To improve longevity, I recommend you halve those peak values.
Would those dissipation figures (or rather the max voltages derived from those) be applicable to the track of a non linear pot such as those having a B or C taper ?
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Hello everyone
Thank you for the additional replies. I learned a lot about potentiometers.
Today, I reassembled the potentiometer and soldered it back into my power amplifier. To my dismay I discovered that, the intermittent operation of the right speaker is still a problem. Tomorrow I'll continue to solve the problem, by inspecting other mechanical switches and relays.
Sincerely,
Ralf
Thank you for the additional replies. I learned a lot about potentiometers.
Today, I reassembled the potentiometer and soldered it back into my power amplifier. To my dismay I discovered that, the intermittent operation of the right speaker is still a problem. Tomorrow I'll continue to solve the problem, by inspecting other mechanical switches and relays.
Sincerely,
Ralf
Good question.
The taper must change the relative proportions of resistance to track area. That probably has an effect on the dissipation capabilities of the track.
If a lot of the track resistance is in the upper half (as it is in a log law pot) then much of the dissipation will also be in the upper half.
Could that result in a lower current capability for the track?
I don't know.
One would think it would lead to a reduced capability. I couldn't really turn much up on this.
Omeg show some graphs here. I suppose by inference of these being from the same product range that the log pots have a lower dissipation. I couldn't find any reference to wiper currents either.
Omeg ECO potentiometer data
Omeg show some graphs here. I suppose by inference of these being from the same product range that the log pots have a lower dissipation. I couldn't find any reference to wiper currents either.
Omeg ECO potentiometer data
volume control is usually done with log law pots, whereas variable resistor duty is by linear pots.
Vol pot rarely if ever see the high voltages that even a tiny ¼W could survive with, so maybe log law don't actually have a problem. The Vmax of a ¼W 50k log law is theoretically ~111Vac. No one would ever think of applying that level of Signal across the vol pot track.
It's the variable resistor type that can use just a part of the track that can run into the current limit. So here power dissipation is very much our concern.
Running a lin law pot as a variable resistor and keeping the current @ less than 50% of Imax is surely safe. I have recommended to some that one never exceed the half power current, i.e. 70% of Imax.
eg. use a 1k ½W trimmer in parallel to 470r to set a CCS to the required current.
One could (by mistake) set the VR to 10r. The applied voltage will be ~600mV, the wiper current will be ~60mAdc. The max power for this current is 3.6W, that requires a power rheostat, not a 400mW pot.
Vol pot rarely if ever see the high voltages that even a tiny ¼W could survive with, so maybe log law don't actually have a problem. The Vmax of a ¼W 50k log law is theoretically ~111Vac. No one would ever think of applying that level of Signal across the vol pot track.
It's the variable resistor type that can use just a part of the track that can run into the current limit. So here power dissipation is very much our concern.
Running a lin law pot as a variable resistor and keeping the current @ less than 50% of Imax is surely safe. I have recommended to some that one never exceed the half power current, i.e. 70% of Imax.
eg. use a 1k ½W trimmer in parallel to 470r to set a CCS to the required current.
One could (by mistake) set the VR to 10r. The applied voltage will be ~600mV, the wiper current will be ~60mAdc. The max power for this current is 3.6W, that requires a power rheostat, not a 400mW pot.
This reminds me of the potentiometers I acidentally set fire to back in school, as I used them as regular resistors. 😉 😉 Literal flames, and not a very pleasant smell. However, you could just blow out the fire and keep using them afterward.
Quite a few fires were (acidentally, or ignorantly) started back then. Of course, nobody ever told the teacher. Although, by the final year, he implied that he knew all along. 😉 Fun memories...
Quite a few fires were (acidentally, or ignorantly) started back then. Of course, nobody ever told the teacher. Although, by the final year, he implied that he knew all along. 😉 Fun memories...
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