DIY Mic Pre Kits, Lunchbox Mic Preamp Kits, Power Supply Kits

Hello,
so I got the 2448 psu built. With the transfo kit I wired up the ac according to the post on the forum. Dialed up the dc voltages ..things seemed to be good. I switched the meter to ac and from ground to the psu board I get 60 vac! I've checked the board for solder bridges and it looks fine. I've doubled checked the tranformer wiring and it is the same as the instruction post so im unplugging and could use some help on where do I start on tracking this down?
Thanks all for for your help.

i un wired the box and re-did it today. SAME. I left it on for about 10 minutes and had no problems but still wonder if its correct?
IS what im reading(60vac from chassis to psu board) just from the CT or do i have a short?

Other than fixing shit when it breaks and rebuilding a couple tube guitar amps I'm entirely new to this and am learning on the way. This is my first go at racking up some micpre's so i'm trying not to muck it up too much!

thanks for your help.
steve

You said you bought a different transformer than the one I supplied in the kit. But you followed the wiring diagram for my transformer. Is the wiring configuration for my transformer and the one you bought compatible?




At WHICH POINT in the circuit board are you measuring 60VAC? The PSU board takes AC voltage from the transformer secondary and converts it to DC.

So there will be areas in the PC Board that will have AC voltages (i.e. coming from the transformer secondary).

You said you were using a 25-0-25 vac transformer. So you could be measuring 50+VAC from the transformer secondary.

You need to be more specific at which 2 points you're measuring.

** I know this is rare but it happened to a few customers.... is your METER working properly?

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Thanks,
yes the other transformer had the same wiring as yours but currently im using the one from your kit. Im getting the 60vac if I measure from my chassis ground to any of the dc out pads (+ - 48 gnd ) and the board mounting holes. As far as my meter goes........its not the best but does seem to work to measure my mains. Also im making sure the psu is not Manny contact to the case. And like I said above it is working im just wondering about that measurement.....also if it matters my mains voltage is about 118. And im getting 20 vac out of the transformer. Hope that helps.

The transformer I supplied is 18-0-18. The highest secondary AC you could measure there is about 36-40VAC (measured between 18 and 18 wires).



I duplicated the test you did, set my meter to AC, and measured the output voltage... and I'm reading 0 volts AC.

I think your meter is screwy.
You mean to say between GND and V+,
OR between GND and V-
OR between GND and +48V output,
your meter is measuring 60 volts AC on any of these combination?

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I will see if I can borrow a meter from work today and re check.
no....if I measure any of the dc outs its all good....I get 0ac and the correct dc volts. If go between chassis( earth) to one of those points on the board(dc power solder pads or PCB mounting holes) I get the 60 vac. Am I high? Don't answer that! I will check with a different meter and get back at cha. I appreciate your help.

If you said you measure 0volts AC between GND and V+, why would you get 60vac between case and V+?

The case is also the same as GND, so it's the same as measuring between GND and V+

Do you see what I'm saying? The case and GND are connected. So you should also get 0vac between the case and V+ (same reading between GND and V+)

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Right! That's why I thought it was strange. Question: how is the psu connected to ground? As I said before im lacking in electronic therory and I really am thankful f
or your input.

In the projects I do, I have the Safety Ground from the mains line connected to the case.

Then I solder/bridge pin1 of the XLRs to it's metal case (I'm using Neutrik jacks). This metal case then makes contact with the rack case. Then XLR pin 1, 2, 3 is wired to the preamp board.

No noise, no ground loops.

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Just shoot me now!
Ruel, i seriously need your help here!

Now i have two meters telling me i have 60vac from the pcb to earth so i think we can safely rule out the meter being wacky.
I'm thinking the transformer is wacky.

On the secondaries of the transformer here's what i get with 122vac from the wall:
black/red=20vac
black/yellow=21vac
black/orange= 0vac
red/orange =20vac
red/yellow= 0vac
orange/yellow=21vac

secondaries to ground:
yellow=52vac
red =52
black =68
orange=68

I really would like to help you but the meter readings you're giving me don't make sense.


Huh? Red and Orange are connected/shorted together at the PCB.
These two wires are essentially the same as the GND terminal.


From the transformer manufacturer:


The RED/ORNG wires above are connected together at the PCB.
(see photo below)
Terminal #2 and #3 (RED/ORG) wires is also the same as the GND terminal on the output.


How can you measure 20V across two GROUND terminals?


Red and Yellow are the two terminals of the secondary wiring. You should measure 18-20Vac here.
Not 0 Vac.

If you think the transformer is wacky, return it. I'll return it to the factory and let them have a look at it. I can send you another one.

But again, I want to know how you can measure something across RED and ORANGE when these wires are connected together/shorted together. You're telling me you're getting 20Vac across two wires that are basically electrically connected.



The RED/ORNG wires are ALSO the GND Terminals.
Now you say, you measure 52Vac between the RED and GND terminal?
and measure 68Vac between the ORG and GND terminal?

How could that be?.... when the RED and ORG wires are connected together, and basically is the GND terminal.

earlier you told me "red/orange =20vac"
now you're telling me "RED/GND" is 52Vac, and ORG/GND is 68Vac.

I don't get it. RED and ORNG are connected together and are both the GND terminal on the PCB.
How can you measure "20Vac" and "52Vac" and "68Vac" across the same two GND terminals?



As I said, RED/ORNG wires are connected together and is the same as the GND terminal.

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Man i know its totally crazy. Am i not measuring correctly? ? How should it be done?
Those reading were taken with transformer not connected to the PSU.

When i say "Secondaries to ground" i mean from the transfo 2nd's(not connected to the psu) to the chassis or safety ground.
NOT the pcb terminals on the psu.

the psu was not connected during those tests.
----------------------------

Connecting the 2nd's to the psu.
blk=ac1 terminal
orange/red= ct
yellow= ac2

It works and puts out the correct dc volts. BUT i still get the 60vac from the psu terminals to the chassis. Now this is with out any preamps wired up to it or the case. Just transformer and psu and case.

I took some pics but was having trouble getting them off the phone to up load.

IF it the PSU is working should i just say fuck my crazy readings and move on?

Ahhh, You should have told me that.

Okay, But I still think you should NOT be getting those kind of high voltage readings. I duplicated the tests you did, and I'm only getting about less than a volt AC between the trafo SECONDARY and the Safety GROUND wire.

What you're reading is basically HALF of your 120V ac input.

I don't think the problem is with the transformer. Because the transformer is outputing the correct voltage.

I think the problem is with your Ground HOUSE WIRING. Are you living in an older house?
Maybe the Ground wire in your house is not connected to earth, or not good?

I was able to come close to your readings (but only 20Vac) by measuring between the secondary transformer terminal, and connecting my other probe to the LIVE or NEUTRAL line. In this case, I got readings of 15 to 20Vac.

So it looks like a house wiring/ground issue. This is beyond my expertise, I think you should have an electrician look at your house wiring and that Safety Ground line.

** If you want to return the trafo, I'll send you a replacement just to rule out the trafo is the problem. (I don't think it is, but for your peace of mind.)

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Thanks so much for your help. I feel like I owe you money for customer support. The house is not that old but you've reminded me that I have had problems in the past to that regard.
Today I brought it to work and am going to check it here with our broadcast engineer.......will keep you posted.