Conrad Johnson PV10A--Classe CA 100

mcnaget

Member
2013-02-23 5:37 pm
A little help from you guys , when i connect preamp to power amp , classe ca100 begins to hum and there is also noise from speakers , when disonected from preamp it is quiet is there some ground problems?I have pluged each component to different wall socket.
THX

Best regards
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
.....I have pluged each component to different wall socket....
That is almost never a good idea as it usually means a bigger ground loop, not a smaller one - that's what you are looking for to minimize hum from mains wiring.

You don't say anything else about your system, whether it is all recently purchased, unknown condition, untested with other gear etc, what source you have connected or if you just have open inputs. That makes it hard to identify any problem. However, you seem to be saying that the amplifier itself emits a hum noise when you connect the preamp. That suggests either or both the preamp and amplifier are wrongly (probably dangerously) earthed. Possibly, they have been messed with before? :confused:
 

mcnaget

Member
2013-02-23 5:37 pm
That is almost never a good idea as it usually means a bigger ground loop, not a smaller one - that's what you are looking for to minimize hum from mains wiring.

You don't say anything else about your system, whether it is all recently purchased, unknown condition, untested with other gear etc, what source you have connected or if you just have open inputs. That makes it hard to identify any problem. However, you seem to be saying that the amplifier itself emits a hum noise when you connect the preamp. That suggests either or both the preamp and amplifier are wrongly (probably dangerously) earthed. Possibly, they have been messed with before? :confused:

THX Ian for sharing your thoughts , equpiment is used but in overall good condition yesterday was cleaned and just few minutes ago i turned on to a one power and as you said no hum . Lesson learned.

Thanks again for help

Best regards Zoran
 

mcnaget

Member
2013-02-23 5:37 pm
Rca connectors - resistor

Id like to ask why there are two resistors atached one on left and the other on the right side of amplifier rca connectors , in the original photos of classe ca-100 amplifier there is no resistors?

THX

Regards
 

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mcnaget

Member
2013-02-23 5:37 pm
check your power amp output noise without interconnects and then with interconnects and finally with the interconnects shorted together at the barrels.
These 6 measurements should show deficiencies in the power amp wiring.

I did that but not with speaker connected and there is no difference with or without cables and even if i shorted togheter at the barrels i look closer and there is one positive cable to rca , one negative or ground is connected from xlr connector below the rca and between these two cables are resistor.

Regards
 

mcnaget

Member
2013-02-23 5:37 pm
If you measure output @ 0.0mVac for all six test arrangements, then the Power Amplifier has been wired to be tolerant to the way the interconnects are wired.

That means the wiring fault is inside the Source.

THX Andrew for help i did check again and it is 0 mV , if i connect speaker cable and interconnects to power amp still ok but if i touch the tip of IC the middle pin on rca from power amp i hear a poping sound from speakers .
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
The line-out connectors from the tube preamplifier are not balanced for use with XLR connectors and I assume the input sockets on the CA100 amplifier have not been properly modified to accept a balanced input either, so what part of your system uses XLR connectors, which usually means a balanced line?

I guess the amplifier has been modified, since you say there are additional resistors between an XLR socket and original RCA input sockets on the amplifier but it would not make sense to change to a proper balanced 600 ohm line, just for the sake of it. I'm guessing XLR cables are for looks or for when the amplifier perhaps was used with another preamp. that did have balanced outputs.

Personally, I would remove the XLR adaptor wiring and use both units as designed, with RCA connectors. You probably wouldn't like to pay ($$$) for a transformer to adapt the PV10 to a real balanced line anyway.

pv10a.jpg
 

mcnaget

Member
2013-02-23 5:37 pm
The line-out connectors from the tube preamplifier are not balanced for use with XLR connectors and I assume the input sockets on the CA100 amplifier have not been properly modified to accept a balanced input either, so what part of your system uses XLR connectors, which usually means a balanced line?

I guess the amplifier has been modified, since you say there are additional resistors between an XLR socket and original RCA input sockets on the amplifier but it would not make sense to change to a proper balanced 600 ohm line, just for the sake of it. I'm guessing XLR cables are for looks or for when the amplifier perhaps was used with another preamp. that did have balanced outputs.

Personally, I would remove the XLR adaptor wiring and use both units as designed, with RCA connectors. You probably wouldn't like to pay ($$$) for a transformer to adapt the PV10 to a real balanced line anyway.

pv10a.jpg

Thanks Ian for replay my sistem is cec cd player tl5100z , conrad johnson pv10a and power amp classe ca100 , those resistors where removed no i will leave as is.

THX

regards