psu w/out transformer

[hank reynolds 3rd]

hello,

http://sound.westhost.com/project05.htm

I've built/almost built a clone of the mutron octave,

http://matthias.grob.org/pEE/ppSchema/MutronOct.jpg
but i am trying to use this psu ,regulated at 12v,in place of one that uses a transformer..

http://sound.westhost.com/project05.htm
the only sound I'm getting is a loud humming sound ,I've checked the reg's are orientated correctly, and I'm at a loss... Any Idea's ??I've checked the circuit PCB layout is correct etc, but i'm not sure if it is worth hooking the v- to the output jack instead of the gnd.. the adadter/wallwart is 12v unregulated aswell...


Cheers

Sam





I

[puretube]

what`s the voltage @ the inputpins of your voltage-regulators?
(should be ~3V higher than their output rating...)

[Hal]

the way you said "without a transformer" scares me - it seems like the power supply you linked to DOES need a transformer, even though its not drawn.  You need 16vac on the front.

Obviously, the first thing to check is the power supply - are you getting correct voltages out of the power supply?  After this, its time to start debuging the rest of the circuit...

[puretube]

i was shocked too, firstly... but he mentions a wallwart ("12V unregulated")...

[niftydog]

qeh?

That mutron schematic DOES show a transformer. T1 in fact.

More info please, are you using a wallwart or something?

[walters]

1.) the Wallwart is the Transformer

       2.) What are u really trying to do you dont make
            sense


       3.) All effect pedals need a Transformer or a Battery
            A transformer either is a AC to AC  or a AC to DC
            the power supply in your pedal will either convert
            this to DC and filter it the AC

        4.) it sounds to me like u just hook the AC up straight to
             the regulator or something with no transformer

[walters]

but i'm not sure if it is worth hooking the v- to the output jack instead of the gnd? this was your question not mine

              1.) is the power supply Bipolar like V+, ground and V- ?

              2.) a Regulator and a Transformer is not the same thing

              3.) if your trying to make a pedal effect have more voltage
                   than it was made for you better be careful of the
                    power rates of the parts

[niftydog]

the Wallwart is the Transformer

this is a somewhat dangerous generalisation. Some wallwarts are just transformers, others are full DC power supplys.

What are u really trying to do you dont make
sense

biting my tongue.

A transformer either is a AC to AC or a AC to DC

just to clarify, all transformers are AC to AC.

Power supplys usually take AC and convert it to DC.

is the power supply Bipolar like V+, ground and V- ?

yes it is. That is shown in the link the OP gave.


Hank, I think you need to take a few steps back and do some basic reading on power supplies. You've made a few assumptions or errors that could be dangerous. I'm concerned that you may be fiddling with dangerous voltages without fully understanding what you're doing. Please tell us some more and we'll try to help you.

[hank reynolds 3rd]

hi all,
I've built a psu for another effect using this method
http://sound.westhost.com/project05.htm

and it worked fine w/out a transformer...
i did the same for the octave (but i only had a 9v ac adaptor,not 12v)
i built and got 2.8v from the +ve regulator input pin and nothing from the -ve one...
puretube, should this be higher
I'm guessing that the -ve regulator is dead..

I was guessing at the input of the -ve could go to the adaptor pin, but my hunch was to follow as is in the schematic ...
guess i'll try replacing the -ve regulator first...
I 'm pretty sure i can apply the above psu schem to this pedal as the phaser i used this method on works fine....

thanks for the help, i'll keep you posted

Cheers
Sam

[puretube]

as I assumed, and walters stated correctly: Your adapter/wallwart is the transformer, that transforms the mains AC down to a safe voltage.

First: disconnect your expensive/sensitive circuit from the power supply...

For a +/- 12V supply according to the westhost schem, you need a 12V AC
adapter/wallwart (like it says in the description...),
whose 12V is connected to where pins 1 & 2 are indicated at the Cannon male XLR connector.

You should get about +15V DC at the input pin (1) of the pos. regulator (7812), and about -15V DC at the input pin (2)of the neg. regulator (7912). Both voltages measured versus GND.

triple check the orientation of all diodes, and once again of the regulators (and verify the pin-out once again...).

find a 12V AC wallwart/adapter (=transformer) and measure again.
If both mentioned inputs get their respective plus/minus 15 volts,
their outputs ought to put out regulated +/- 12 volts...

[hank reynolds 3rd]

thanks for the reply...
the ac adaptor does provide the transformer,thats what got me thinking i could do this w/out another onboard the pedal...

I'm gonna get hold of a 12v ac adaptor ,replace the -ve reg ( i'm guessing this has died as nothing comes out of it), and maybe the diodes (i blew the 12ac i had last week through getting the pinouts of the -ve reg wrong!!! :oops:  )

thanks again

Sam