i know this has been done to death but here goes again 
at the moment i have the negative from the phono input going to the ground tap on the attenuator then onto the negative input of the amp. but i have just discovered that the attenuator is also grounded via the case.
my question is should i divert the negative from the phono input straight to the input of the amp and remove it from the ground of the attenuator?
this
or this
if none of the two above then which way should i do it?
Thanks
at the moment i have the negative from the phono input going to the ground tap on the attenuator then onto the negative input of the amp. but i have just discovered that the attenuator is also grounded via the case.
my question is should i divert the negative from the phono input straight to the input of the amp and remove it from the ground of the attenuator?
this
An externally hosted image should be here but it was not working when we last tested it.
or this
An externally hosted image should be here but it was not working when we last tested it.
if none of the two above then which way should i do it?
Thanks
What you definitely do not want is a noisy bottom end of your pot because then you lose dynamics as the volume setting goes down. Noise comes via the screens of your connecting cables. Better to give the pot its own dedicated ground, not one which is contaminated with common-mode currents. The latter would be the case if you wire the bottom of the pot to the input ground directly.
think about it as a "connecting modules" problem.
You need a two wire connection from Source to Receiver every time you want to transfer a signal.
The vol pot is one of your modules.
Use a two wire connection between Source and vol pot.
Use a two wire connection between vol pot and Receiver.
In the first the vol pot is acting as the Receiver module.
In the second the vol pot is acting as the Source module.
There is one final problem.
You said the vol pot is connected to Chassis.
Show us why you think that.
You need a two wire connection from Source to Receiver every time you want to transfer a signal.
The vol pot is one of your modules.
Use a two wire connection between Source and vol pot.
Use a two wire connection between vol pot and Receiver.
In the first the vol pot is acting as the Receiver module.
In the second the vol pot is acting as the Source module.
There is one final problem.
You said the vol pot is connected to Chassis.
Show us why you think that.
thanks Andrew.
i was checking the ground on the case as i had removed a source switch in the signal path. while checking the ground i checked the ground ring of the stepped ladder attenuator to case and it showed a path i then checked the ground ring to the fixing nut and it showed a path so i got confused. of course its grounded its connected to the case, my brain was not working properly like it never does.. lol. i removed the stepped ladder attenuator from the case to isolate it and checked the ground ring to the case fixing thread and there was no path.
i'm using the ground tap on the stepped ladder attenuator as the connection from source (phono plug -) then out to receiver (headphone amp in -). the case is grounded via the headphone socket.
i was checking the ground on the case as i had removed a source switch in the signal path. while checking the ground i checked the ground ring of the stepped ladder attenuator to case and it showed a path i then checked the ground ring to the fixing nut and it showed a path so i got confused. of course its grounded its connected to the case, my brain was not working properly like it never does.. lol. i removed the stepped ladder attenuator from the case to isolate it and checked the ground ring to the case fixing thread and there was no path.
i'm using the ground tap on the stepped ladder attenuator as the connection from source (phono plug -) then out to receiver (headphone amp in -). the case is grounded via the headphone socket.
Considerations like that come in when you have to pass audio between multiple modules powered by the same power supply. DIY boomboxes, for example, are very commonly plagued by ground loops since there tend to be two ground connections, one via the audio cable and another via the power supply.
Classic hi-fi with unbalanced interconnects assumes all devices floating, or at least no more than one per setup being grounded. This rule is commonly violated these days though. Ungrounded devices with larger switch-mode power supplies (like TVs) can also be pretty nasty, however, due to mains filter leakage currents. The odd HDMI input and output has been wrecked this way.
Classic hi-fi with unbalanced interconnects assumes all devices floating, or at least no more than one per setup being grounded. This rule is commonly violated these days though. Ungrounded devices with larger switch-mode power supplies (like TVs) can also be pretty nasty, however, due to mains filter leakage currents. The odd HDMI input and output has been wrecked this way.
This philosophy breaks the two wire connection rule.
You MUST make the interconnection using two wires. Either a twisted pair, or a screened twisted pair, or a coaxial cable.
I've never seen an attenuator where the threaded mounting was part of the circuit, its good practice to ground the body of regular pots with a metal shell as it acts as a shield, but there will be no direct connection to the three terminals of the pot.
You also cannot assume the ground is at the same level on all equipment, hence the need to carry the ground with the signal. Infact most consumer grade hifi components don't even have an earth wire so the entire circuit is floating.
Best way to think of it is the volume pot acts as a voltage divider between the signal + and signal return -. Therefore to do its job properly it needs to be connected between the signal + and signal return of the source device..
You also cannot assume the ground is at the same level on all equipment, hence the need to carry the ground with the signal. Infact most consumer grade hifi components don't even have an earth wire so the entire circuit is floating.
Best way to think of it is the volume pot acts as a voltage divider between the signal + and signal return -. Therefore to do its job properly it needs to be connected between the signal + and signal return of the source device..
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If you did not refer to the signal return wire as "ground" there would be less confusion.
i like +(hot), -(cold), COM(common) for audio. i usually refer to ground/earth as household mains safety ground/earth but very very few people do it that way and i suppose its because a fair few country's dont have one. i work on 12v motorcycle electrics a fair bit and everyone i know refers to the negative as ground or earth when in fact there is no ground/earth on a vehicle as its not connected to the 'ground' due to the rubber tyres acting as insulators, there is only positive and negative.
anyway, thanks for all the help.
anyway, thanks for all the help.
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