Green pre woes....

[Ptownkid]

So i got two of my four channels built this weeknd, fired em up and all I got was hummmmmmmmmmmmmmm

Then the 10R resistors on both channels between the 33k res and the 47uf cap started smoking, what the hell is happening? It's the one just below and to he left of the ne5532

 

[tmbg]

a short!

 

[Ptownkid]

ok, now process of eliminations, i hooked up each channel one at a time.

The only constants were the Lorlin switch and the psu so I'm assuming it's on one of those things right?

 

[Mbira]

unless you stuffed both boards at the same time and put an incorrect value sumthin-sumthin in there or maybe a cap the wrong direction? Check voltages.

Joel

 

[Ptownkid]

Yeah, I cleaned up a trace on the power board and now no resistor smoke, but I still getting nuthing but hummmmmmmmmmmm

 

[matta]

Check your grounding!!!!! I had a similar issue, mine became more prominent with phantom power on and worse when you filliped the phase switch. And it did it before they were racked, I moved the XLR inputs/outputs around and away from the input trafo and it went away, then when I racked them the hum came back, again I just made sure the XLR inputs and outputs were away from the power and grounded to the earth and now all seems to be well.

Cheers

Matt

 

[peterc]

Before putting your IC's in their sockets, did you check the voltages on the pins using the Voltages doc? Would have shown up a short.

How are you PSU voltages?

It's important not to dive in head first but to approach the switch on methodically. For instance, put an ohmmeter between GND & the power rails to check for shorts.

 

[Ptownkid]

Yeah, so I'm a total douche, I completely forgot to insert the 200k resistors.

I couldn't believe it when I finally noticed, everything went too well, there had to be something missing. Gonna put them in tonite and run some tests.

Peter - on your setup document it says to use a signal generator, what if I don't have one of those?

 

[Ptownkid]

This is probably a dumb question, but why are there only two wires for the xlr out? Also, to put a power switch in the circuit, where would I put it? Does it just go on one of the primary wires to break the circuit?

 

[tmbg]

use the same ground as the input ground for the output.

I would use a mains rated switch to break the power going to the power transformer.

 

[Ptownkid]

[quote author="tmbg"]use the same ground as the input ground for the output.

I would use a mains rated switch to break the power going to the power transformer.[/quote]

Can you be a little more descriptive on these two answers...

I'm not sure if your're answering one or both of my questions, thanks

 

[OddHarmonic]

He was answering both, in regards to the lack of three connections for the output XLR, the same ground point for the input XLR is used for the output XLR.

The power switch you asked about is indeed placed between the power inlet and the transformer primary. (just make sure it is mains rated switch as suggested...)

Andrew

 

[Ptownkid]

Ok, so the output xlr connector will not have a wire running to it then?

Also, I assumed that that was the case, but pin one on an xlr is the ground, and pin one on the diagrams have a wire going to it, so is something incorrect then?

 

[OddHarmonic]

Not sure which diagram you mean, but looking at the V14 PCB, the input XLR connector does indeed have three connections, labeling XLR IN Pin 1/2/3. Those are obvious. The output is a two pin connector, labeled XLR OUT Pin 2/3. Those of course go to pins 2/3. Pin 1 is ground, as you said, and should be connected to the star ground of your entire system. Often, folks will put a buss wire directly connecting Pin 1 of the Input XLR to Pin 1 of the Output XLR.

hope that helps,
andrew

 

[Ptownkid]

Yeah, on the diagram with the pcb traces/parts/both together it says pin 1 and 2.

I knew that had to be wrong.

And yes, that does help, thanks andrew
o now that i know that marking is wrong, can someone put up a quick diagram of the proper pin outs for the in and output xlrs.

 

[OddHarmonic]

what's your email? I'll send it on your way

andrew

 

[Ptownkid]

[email protected]

Thanks alot

 

[peterc]

now that i know that marking is wrong, can someone put up a quick diagram of the proper pin outs for the in and output xlrs.

Well the marking is NOT actually wrong, the 1 & 2 refer to the numbers of the Molex connector, NOT the XLR.

There is no GND connection on the output connector so as not encourage an earth loop.

There is a thread here somewhere that discusses the best grounding techniques.

 

[Ptownkid]

Yeah, i realized that a minute later, it's just confusing because when i read pin 1 and pin 2 I assumed hat it meant on the xlr connector.

You know what happens when I assume...i make an ass outta myself.

haha, thanks everyone.

 

[Ptownkid]

Alright, so peter said they markings on the drawing refer to the actual pins of the molex, so on the xlr in, what is the order, 213 like it says or pins 123 from top to bottom, and to be clear, i'm referring to the xlr pins