help diagnosing power issue with regulator.

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help diagnosing power issue with regulator.

Postby jkhuri44 » Wed Jan 01, 2014 12:56 am

hi guys, i have a power regulator (taking power from 12v AC 500mA plug pack) and spitting out 14-15V DC.
It for powering a headphone amp, and i need a bit of help diagnosing the issue.
i'm not getting any power on switch on....i cant see any shorts...

Im not really sure how to carry out a continuiyt test without clearly seeing the traces on the pcb....

The red wire is running from AC solder pad on PCB to the positive on the ac socket
Black is running to Ground on the PCB to ground on the ac socket
Green is running from an Earth location on the PCB, grounded to a make shift case (quality streets).

is anything obviously wrong with what i've done here...

http://imageshack.us/a/img42/9546/5xa7.jpg
http://imageshack.us/a/img845/7967/lw0o.jpg
http://imageshack.us/a/img36/3176/bp43.JPG
http://imageshack.us/a/img5/162/6n1q.jpg
http://imageshack.us/a/img707/7592/a4eh.jpg

The regulator is providing power to a light dependant resistor volume controller, and the amp itself (requiring max 100mA in its current class A config)


If any photos of specifics are required, let me know.
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Re: help diagnosing power issue with regulator.

Postby Alastair Reynolds » Wed Jan 01, 2014 7:34 am

Black wire is in the wrong place so you are only driving one side of the diode bridge.move it off the gnd pad and back to the empty hole next to the red wire that drives the other half of the bridge.you should then be in business.
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Re: help diagnosing power issue with regulator.

Postby jkhuri44 » Wed Jan 01, 2014 12:05 pm

hi alastair,
thanks for the quick response!
so, let me get this straight....
the wires on the AC socket ive pictured are ok??
i need to move black wire from ground (on the PCB) to the second available AC hole?
Do i then need to re solder what's on ground (on thE PCB) to another place on the AC socket?
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Re: help diagnosing power issue with regulator.

Postby Alastair Reynolds » Wed Jan 01, 2014 2:04 pm

No, the AC is floating (like balanced) and doesn't need the ground reference. Just move the black wire from the gnd pad to the ac pad between the 2 diodes and you should be in business. Do you have a schematic of the regulator ?
The gnd is virtual,created by the filter caps and maybe some resistors.
What voltage are you expecting from the + ve & -ve terminals ?
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Re: help diagnosing power issue with regulator.

Postby jkhuri44 » Wed Jan 01, 2014 2:07 pm

i have a schematic i can email you, just incase the designer gets the nannas with me...as i dont think he has it published. i'll pm it to you!
The DC output voltage is supposed to be 14-15 V
I will send you the pdf, thanks again alastair...grade A champ :-) hope this does work!
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Re: help diagnosing power issue with regulator.

Postby Alastair Reynolds » Wed Jan 01, 2014 2:38 pm

OK,a few questions
Is the amp you're driving with this a discrete class A transistor design using a single power rail and gnd or is it an IC type using +/- supplies and gnd or a push -pull transistor design using +/- supplies ?

If a single supply is it +15 V and gnd or -15V and gnd and what sort of transistor s is it using PNP or NPN ?

This power regulator is designed to be driven by a center tap transformer.in order for it to produce +/- 15V wrt gnd,you will need to use a 30V center tap transformer. A 12V AC plugpack will at best develop 16VDC when rectified and will only give about +/- 7V wrt gnd after the losses though the transistors etc.
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Re: help diagnosing power issue with regulator.

Postby jkhuri44 » Wed Jan 01, 2014 2:51 pm

HI alastair:

This is a write up of the amp....

While the topology is a proven complementary output buffer driven by a chip (all within a global feedback loop), great care has been taken to ensure no discontinuities occur in the forward path, rendering feedback ineffective. In addition the FET cascode OPA2134 op-amp has its output stage deliberately biased into Class A to obviate possible crossover and +Ve PSRR distortions. The discrete complementary output stage is also biased into Class A to 10mW @ 32 ohms or 200mW @ 600 ohms as standard, but this may be increased with a simple parts change. The area of Class A operation can also be reduced for low consumption portable operation - as low as 12V battery operation. The socketed chip can be rolled (changed) if another op-amp is preferred, or as improved op-amps reach the market.


-------------
i have selected the full class A option using 10ohm 1/4w m.f. resistors:

I believe the amplifier uses darlington pairs both PNP and NPN BD139s and 140s and op amp is used as well...,
I will send a schematic of the headphone amp as this power circuitry stuff and rails confuses me a little....
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Re: help diagnosing power issue with regulator.

Postby jkhuri44 » Wed Jan 01, 2014 2:57 pm

i should add, before purchasing the kits, i did ask whether it was possible to run the amp in full class A using a plug pack, i was advised it was possible....when reading the instructions for the regulator...didnt seem to be the case...
im completely appalled at the customer service provided and the instructions given for the projects....i do understand a lot of people understand electronics in depth, but for begineers, after some high quality gear at lower prices, this kind of vagueness is completely unhelpful.
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Re: help diagnosing power issue with regulator.

Postby Alastair Reynolds » Wed Jan 01, 2014 3:37 pm

Well, it is possible,but not ideal .It really needs a 30V ct transformer.
CT plugpacks are few and far between.
If you really want to use plugpacks ,use 2 of them the same and connect 1 lead from each to gnd and the other lead to the ac inputs( 1 to each) This effectively will give you a24V ct transformer to run the regulator.
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Re: help diagnosing power issue with regulator.

Postby jkhuri44 » Wed Jan 01, 2014 3:41 pm

i actually didnt want to use plug packs at all, as they dont represent quality to me...
but hwen i asked the guy if i could use them or not...he said you can, and didnt make mention of any quality loss...
from what i understand, having a transformer close to the electronics poses issues (noise wise?) so i thought having the transformer away was a good idea.....ohwell, live and learn.

I'll rewire the AC lines now....and give it a shot....there is also mounting the transformer in a seperate enclosure...thats an option too...let me see how good this amp is first hahaha.

Thanks heaps alastair, total champ!
Jamil Khuri
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Re: help diagnosing power issue with regulator.

Postby Alastair Reynolds » Wed Jan 01, 2014 8:22 pm

Use a toroidal transformer.they have a tightly contained electromagnetic field and ideal for audio circuits.
Jaycar have some nice little ones and not too expensive.
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Re: help diagnosing power issue with regulator.

Postby jkhuri44 » Wed Jan 01, 2014 9:30 pm

yeah, totoidal would be my choice for all audio for sure.
i've just tried fixing up the wires as per your instruction alastair, still no dice on the power up. :-(
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Re: help diagnosing power issue with regulator.

Postby Alastair Reynolds » Wed Jan 01, 2014 9:48 pm

Re-looking at the circuit,you will need a center tap transformer and at least 24V (12-0-12) to be worthwhile
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Re: help diagnosing power issue with regulator.

Postby jkhuri44 » Fri Jan 03, 2014 1:33 pm

so, where does one throw their money around here to get a project like this finished ? :-)
Jamil Khuri
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