Hi ! i would like to report a very strange situation
A friend of mine has lent me an old Electrocompaniet preamp.
Even with the volume completely turned down i hear a faint music from the speakers 😱 how is this possible ?
It has never happened to me before and it is very annoying
Do you have any explanation for this ?
Thank you All very much indeed.
Have a nice day, gino
A friend of mine has lent me an old Electrocompaniet preamp.
Even with the volume completely turned down i hear a faint music from the speakers 😱 how is this possible ?
It has never happened to me before and it is very annoying
Do you have any explanation for this ?
Thank you All very much indeed.
Have a nice day, gino
Perhaps the volume pot is old and misaligned, and wiper does not reach ground completely. Should be easy to measure with ohm meter.
Some circuits purposely have a low value resistor to lift the bottom leg of the control and so prevent 100% attenuation. I think the reason is to minimise the problem of poor tracking and less than perfect pot performance.
Examine the circuit to see if that is the case.
Examine the circuit to see if that is the case.
Hi thank you very much for the kind and helpful advice.
Could i bypass it in case ? or lower its value ? using a 100 ohm only resistor could cure the signal leakage ?
You need to first of all confirm whether such as resistor is fitted. If it is then yes, you can short it out. 100 ohm would be a very high in the scheme of things.
For a 10k pot adding a 100 ohm would allow 10 millivolts through for every volt applied... which is more than enough to be quite audible.
For a 10k pot adding a 100 ohm would allow 10 millivolts through for every volt applied... which is more than enough to be quite audible.
Hi thanks a lot for the very kind and helpful advice. I will check in the weekend with the meter. It is very possible because the pot is old.
To get a remote controlled efficient volume is not that easy. But i need a volume controllable by remote very much. 😱
Hi again and thank you very much. I wonder if shorting could generate noise.
Sometimes they use a resistor to isolate the input to the preamp circuit from the ground at zero volume ? i did this once in a preamp that was making some very bad noise when i raised the volume from zero, and the noise disappeared.
By the way i will measure everything in the weekend and take some pics. I like the fact that is remote controlled.
You got me 😱 my friend is me. I am sick for modding. I like to take old units and recapping them with new and better looking caps and resistors ... clean them ... replacing some trimmers with better ones.
I have no enough skills to building a unit from the scratch ... 😱 especially the metal work scares me ... i am even scared by just placing a iec socket on the back of an amp.
Now a preamp that with the volume at zero leaks sound is unaccettable ... 🙄
maybe the pot has gone bad and actually i hear some scratches when it turns.
I will take some pics to show the inside. i just need the weekend. I have already replaced the output caps ... i hate squared caps For me the caps must be cylindrical.
A low value resistor used to pad out the volume control would have no measurable impact on noise whether fitted or not. These are not used as ground isolating resistors which are something totally different.
And in the end it may not even use these... you have to look at the actual circuit and see.
And in the end it may not even use these... you have to look at the actual circuit and see.
I have actually manufactured potentiometers so I know them well.
1) it is not practical making pots which actually reach ZERO for mechanical reasons.
Track is resistive paint (finely ground graphite floating in a phenolic resin varnish) which is roller applied (for a thin and even coat) on a Pertinax (phenolic impregnated paper) strip and then baked in an oven.
It´s cut to shape and terminals are riveted at ends.
Terminals are metallic, wiper is also metallic, and it can not be allowed to touch the rivet, there is always a small resistive path between them, so a few ohm always remain.
There is a patch/kludge for that, but creates new problems.
2) If you NEED zero ohm between wiper and terminal, a small drop of silver paint (finely ground silver floating on similar phenolic varmish), it´s usually called "the silver patch", so when wiper touches it, wiper to rivet resistance is now "almost" zero.
Problem?
Electrical zero is now "outside" of "mechanical zero" and user complaint now is "hey , this pot is now mute between 0 and 1" or something similar.
So flip a coin, pick one problem or the other, we live in an imperfect World.
1) it is not practical making pots which actually reach ZERO for mechanical reasons.
Track is resistive paint (finely ground graphite floating in a phenolic resin varnish) which is roller applied (for a thin and even coat) on a Pertinax (phenolic impregnated paper) strip and then baked in an oven.
It´s cut to shape and terminals are riveted at ends.
Terminals are metallic, wiper is also metallic, and it can not be allowed to touch the rivet, there is always a small resistive path between them, so a few ohm always remain.
There is a patch/kludge for that, but creates new problems.
2) If you NEED zero ohm between wiper and terminal, a small drop of silver paint (finely ground silver floating on similar phenolic varmish), it´s usually called "the silver patch", so when wiper touches it, wiper to rivet resistance is now "almost" zero.
Problem?
Electrical zero is now "outside" of "mechanical zero" and user complaint now is "hey , this pot is now mute between 0 and 1" or something similar.
So flip a coin, pick one problem or the other, we live in an imperfect World.
Hi ! thanks a lot for the very helpful advice. I guess i have to live with that.
What leaves me puzzled is that i have never noticed this phenomenon with other equipment 😱... it is a first for me. 😱
Actually its fairly common for the ends of the carbon track(s) to be metalized, so that you get only milliohm levels of resistance at the end-stops. This should cure your problem, although it does depend on the resistance of the pot itself - its harder to get silence from 1k pot than from 100k pot as its a matter of ratios.
However its also common for a track to have no metallization, and thus no go fully to the end of the track where the metal is.
Careful examination of datasheets might pay off?
However its also common for a track to have no metallization, and thus no go fully to the end of the track where the metal is.
Careful examination of datasheets might pay off?
Hi ! thanks a lot for the very helpful advice. I have still to see under the lid ... i have got a flu now so i am not functional.
I will revert with pics of the inside from above and below the word possibly
In the wait i am attaching what i have found in the web ... not mine unit
http://www.electrocompaniet.ru/files/manuals/ec45.pdf
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