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Short circuit connecting preamp with amp (RCA)

Also I can try again to se the chassis to ground with the two wires grounded to the chassis.

It make sense to be grounded?
 
i will try and study this some more .
logic says the voltage on the chassis is coming from the centre tap of the transformer primary . i think this because its half of the supply voltage .
try checking ohms from the black-white white wires to chassis .

i cant see any other way the high voltage can get there to the chassis .

couple of tests to try ......
remove brown wires and check AC volts from chassis to mains socket earth ..
if still high volts remove brown/black wire and check AC volts chassis to mains socket earth ..
 
petehall347 said:
i will try and study this some more .
logic says the voltage on the chassis is coming from the centre tap of the transformer primary . i think this because its half of the supply voltage .
try checking ohms from the black-white white wires to chassis .

i cant see any other way the high voltage can get there to the chassis .

couple of tests to try ......
remove brown wires and check AC volts from chassis to mains socket earth ..
if still high volts remove brown/black wire and check AC volts chassis to mains socket earth ..
Click to expand...

Ok Peter

I will going to continue some time in the weekend or monday morning at least.

Family is arriving to the house for the weekend.

Thanks for your help.

Gonzalo
 
i may have some good news ...i just went to my workshop and i have an amplifier with a ground to the plug ...i removed the earth wire plugged it in and tested earth to chassis and got over 90v
so its looking like your is normal and would maybe be better to rewire it to have an earth wire to the plug socket .
and also adding safety capacitors .
you could try connecting chassis to earth and see what happens ..it can only make the trip switch trip if there is a fault ..
 
petehall347 said:
i may have some good news ...i just went to my workshop and i have an amplifier with a ground to the plug ...i removed the earth wire plugged it in and tested earth to chassis and got over 90v
so its looking like your is normal and would maybe be better to rewire it to have an earth wire to the plug socket .
and also adding safety capacitors .
you could try connecting chassis to earth and see what happens ..it can only make the trip switch trip if there is a fault ..
Click to expand...

So this design is with a hot chassis? maybe because its an old design?
So you think i have to modify the wires to have a grounded plug?
So you think then that white , and black /white wires need to go isolated or to ground?

Maybe you have info or a web page to do the rewiring safely?

BTW before the problem , I was using this amp with a pioneer pre amp, this pre amp also with a 2 wired not grounded plug. And didnt have any problem with it. The problem started when i tryed to use it with the Marantz 3200 pre amp , that has a 3 wire (grounded) plug.
 
leave them wires off the chassis .. it doesn't seem right to have them connected to me ... i will have a look at the internet and ask a friend who used to be an electrician .
 
petehall347 said:
leave them wires off the chassis .. it doesn't seem right to have them connected to me ... i will have a look at the internet and ask a friend who used to be an electrician .
Click to expand...

Hi Peter, today I pulled out the other amp, the marantz 250, just to try the AC between chassis and walls outlet earth. And ive got 89V AC no mater how I plugged the plug. Then just tu double check I conected the marantz 32 agian and mesured chassis to earth again and got 89V and 105V in the other way.

So do you think i need to rewired both? or its ok to have 89-105 V in tha chassis? My first baby its on the way( its coming in the next two weeks as much) and I need to be sure that its safe to have samething like this in the house.

Thanks a lot!
 
i would try and connect it to the earth at the wall plug . if there is a problem it will trip the mains trip .
if its ok then to be on the safe side rewire it properly so it has the earth connection .

like i said i tried an amp here minus the earth and got the same voltages as you have . it should have very little current .
also make sure live is going to the fuse .
 
petehall347 said:
i would try and connect it to the earth at the wall plug . if there is a problem it will trip the mains trip .
if its ok then to be on the safe side rewire it properly so it has the earth connection .

like i said i tried an amp here minus the earth and got the same voltages as you have . it should have very little current .
also make sure live is going to the fuse .
Click to expand...

Hi Peater , i will try that , but im not sure with a little thing. The plug on the marantz 32 has both leads of the same form and size. So ita unpolarized. I just need to test with diode mode what lead goes to the fuse and just plug that lead to live in the outlet?

And can i put chasis to earth with a aligator wire or this is unsafe?

thanks very much!

Gonzalo
 
you will need to pull the fuse out to see which wire goes to it or you will also measure the transformer .

you could go straight to earth at plug or to some other equipment that has an earth already and is plugged in and turned off . it shouldn't do any harm either way .

you might want to put a resistor in series with the earthing wire .highest value you have 1/4 watt should be fine . its better this way in case there is current behind the voltage .
then try volts to earth from chassis again
 
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petehall347 said:
you will need to pull the fuse out to see which wire goes to it or you will also measure the transformer .

you could go straight to earth at plug or to some other equipment that has an earth already and is plugged in and turned off . it shouldn't do any harm either way .

you might want to put a resistor in series with the earthing wire .highest value you have 1/4 watt should be fine . its better this way in case there is current behind the voltage .
then try volts to earth from chassis again
Click to expand...

Peter, you are going to kill me.

I think i found the problem ,( im ashamed with it but...)

I retested the power bar where i was connecting the amp and preamp. And realised that the polarised was inverses indeed.

I took out the power bar and test it into another outlet (a good outlet) and the power bar was OK . (polarized good) .

Tho problem I think it s that the Power bar was conected to the wall outlet via a n ac splitter (I dont know if thats the real name) and this spliter had one outelet with good polarisation , and the other one (unfortunately the one where the power bar was connected) had inversed polarity.

I am uploading a photo of the M@$F#@$!

Tomorrow Im going to try without this splitter and connect the preamp with the amp and see if the box doesnt trips.

Im pretty sure that was the stupid problem. I didnt realised it first because I tried it before with another power bar , and y think in that time it was pluged in the right (polarised) side of the splitter. So it work good. But when i rearranged
The shelves to make it neat , i think i could change the place of the power bar to the inversed polarised one.

I feel so stupid!

But I hope at last that this was the problem.

Tomorrow we will know for sure.

Thanks for the help
 

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petehall347 said:
i don't think that's the problem ..
did you try it yet ?
Click to expand...

Yes , tried it today, and half good news.

The preamp & power amp combo , power up connected with the Rcas without triping the box. The relay in both (pre amp & power amp) kicks .

The problem now is that right channel is down ( it plays but realy low volume)

Tomorrow i will make more tests to be sure that is not a bad conecttion or somthing stupid.

BTW , i could adjust bias in two channels to 4.5mV, and DC offset around 0.6 mV in both sides. I think thats preatty good. The only thing to check tomorrow is why right channel is giving this problem.

Thanks a lot and tomorrow I will update.

Its possible that after having a good bias setting and good DC settings , one channel gives this symptom? Maybe a bad power transistor ? or output transistor?
 
petehall347 said:
good luck .. maybe its just a loose wire
Click to expand...

Hey Peter!!!!!

Now its working fine!!!

I found the problem with the right channel. I tried listenig the amp with the right heatsink laid a side, and the problem was gone. So I thought it was somthing in the board that was touching the amp board. After cheking and cheking I found ( a miracle) that the toriod that is attached to the heat sink was making that contact so y took it aout and put a plastic washer between the head of the bolt and the toroid. The tested with the DMM and Voila.

Testet again conected and no problem!

Enjoying now the realy nice sound of this to marantz! way better than the pioneer pre amp match!

The only thing is that the chassis is with the same 89V , but i think that is the way it works.

Thank you very much for your time and patience, I will try to recor a small video and put the link so You can see how its working.

Thanks a lot again! this site is awsome!

Gonzalo
 
Nothing really to add but I just want to say I'm glad you, Mr Grillo, got your mystery solved. Just like a good mini-series, I've been following this drama faithfully and was fascinated with the steps taken to resolve this problem.

This might be one of the best threads ever on this site. Good show by all, particularly Mr Hall.
 
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