Psychtar Transformer Question

[Jamforthelamb]

Hey All,

I have all the parts bagged up for Tim E's Psychtar pedal, and I planned on using Torchy's layout for it found here: http://www.indyguitarist.com/torchy/

My question is this. I ordered a 42TM018 transformer from Mouser, and it has 6 leads coming out of it instead of 5. I've never used a transformer for anything before, and the layout shows the transformer having 5 leads not 6. Do I just use one of the center leads, and clip there other? If so, does it matter which one I use? One side of the transformer has a "P" stamped on it, don't know if that makes an difference.

Thanks for any, and all help.

God Bless,
JFTL

[Mark Hammer]

The P is the primary winding.  Since the transformer is a sort of isolation transformer without any sort of impedance change from primary to secondary, it probably doesn't matter which 10k side you stick where.  If it was one of those 1.3k:8R transformers, then the primary-vs-secondary distinction is clearly important, but in this instance much less so.  You can clip the centre lead on the side you use for primary, but a more conservative approach is simply to bend it out of the way and slip a piece of stripped wire insulation over the exposed lead.  That way if you ever need to use all 6 leads of such a transformer and have to cannibalize this one in an emergency, at least you'll be able to use it.

[Jamforthelamb]

Great! Thanks Mark!

I think I'll use the conservative approach like you said, but from the sound samples I've heard I think I'll be keeping this pedal. I plan on breadboarding it up first to see.

Thanks again!

God Bless,
JFTL

[Jamforthelamb]

Got it all breadboarded up, and fired up on the first try! Woot!

You really have to dial your guitar in to get the "sitar-ish" sounds huh ? I really didn't get much of an octave sound, but I'm wondering if part of my problem was that I was using a guitar with active pickups.

1 more quick question before I build it. I don't have a .002 cap, can I just put 2 .001 caps in serial to get the same value kinda like with resistors ?

God Bless,
JFTL

[Mark Hammer]

No.  Caps work opposite to resistors with respect to the series/parallel thing.  Resistors in series always make more resistance, but caps in series make less capacitance.  To make .002uf out of .001uf caps, place them in parallel.

Edit: Oh yeah, and congrats on getting it working.

[Jamforthelamb]

OH!!! OK.
I wonder if that's why the octave thing didn't seem to be working. Guess I'll find out after I build it 

Thanks again Mark!
You've been very helpful!

God Bless,
JFTL

[Jamforthelamb]

Got it all built. I need a stomp switch for it still, so I just have it wired up with no bypass for now.

Seems to be working, I don't have a guitar here to test it, only a keyboard and CD player. One thing I noticed is that the LED isn't lighting up. Shouldn't the LED light up when the input is louder ? It should be in there the right way. Do I need a different LED maybe ?

God Bless,
JFTL

[Jamforthelamb]

bumpage

[Mark Hammer]

Sometimes, LEDs are used in circuits for their particular forward voltage.  The LED will not necessarily light up if the current provided does not provide enough "oomph". 

Normally, we stick a current-limiting resistor in series with LEDs when we use them for status indicators.  That resistor assures that enough current is coming from the power supply (at the V+ voltage) to provide a visible illumination of the LED, but no *so* much current that the LED overheats and burns out.  The resistance used will be a function of the illumination you want, plus the brightness of the LED.  You can gets all sorts of brightness specs in "red" LEDs that have the same voltage drop (forward voltage).  In some instances the current level at voltage X which is sufficient to make one LED quite visible is much less than the current needed to make a different red LED visible, even though they both share the same voltage drop.

In some instances, LEDs WILL light up in response to audio signal, however in the majority they won't.  In the case of the Psychtar, the audio signal arriving at the LED is not of sufficient voltage or current to provide illumination for the vast majority of red LEDs.

Of course, in the "vast majority of cases", an LED also won't light up if it is accidentally reversed!