about center tap transformers

[waky]

hi , im building a jawari, and i have the 10k:10k audio transformer 42tm018  ... the thing is that it has both primary side and secondary side center-taped, so...

* is it okay to omit the center tappering on the primary? (according to my little electronics knowledge it is, since voltage between the outer pins can be used without the tapper).

* at collegue my electronics class showed me that transformers have 3 uses:  increasing voltage, decreasing it, or as coupling devices, what does this transformer do?, if the impedance on both sides is 10k?)

* offtopic: what is exactly an effects loop?

*offtopic2: about the ic "4049ube", it says that it has six inverters. if an inverter is a device that turns dc into ac... how do you use that to get a distortion? if you are feeding it with an ac guitar signal anyways?.
  an example: http://www.runoffgroove.com/3leggeddog.html

*offtopic3: from what i've read   npn transistors use negative ground, and pnp positive ground. so how can some pedals feature both kinds of transistors? O.o

thx for any help !!!

[brett]

Hi

is it okay to omit the center tappering on the primary

It's not only OK, it's essential.

transformers have 3 uses:  increasing voltage, decreasing it, or as coupling devices,

It couples with a small voltage change.  All tranformers couple.  And they either raise or lower voltage and current by nothing, a little, or a lot.

I'll let someone else explain loops.

An inverter converts a positive signal into negative, and vice versa.  Some inverters can be used as amplifiers and for making amplified distortion.  The 4049 makes lovely amplified distortion.

npn transistors use negative ground, and pnp positive ground

Not true.  It's common (there's an electronics joke in there!) but not essential.

so how can some pedals feature both kinds of transistors?

Because the first statement isn't true.  See the RM Axis fuzz for an example of a PNP device used with emitter to the 9V supply.  Often, we want to connect the emitter to ground, and you don't usually do this with negative to ground and a PNP device.

cheers

[waky]

It's not only OK, it's essential.
It couples with a small voltage change.  All tranformers couple.  And they either raise or lower voltage and current by nothing, a little, or a lot.

so... besides rectifying, to get twice the frequency, it also changes the amplitude of the signal?

inverter converts a positive signal into negative, and vice versa.  Some inverters can be used as amplifiers and for making amplified distortion.  The 4049 makes lovely amplified distortion.

and the devices that turn dc into ac are also called inverters? how can i tell them appart?

[R.G.]

* at collegue my electronics class showed me that transformers have 3 uses:  increasing voltage, decreasing it, or as coupling devices, what does this transformer do?, if the impedance on both sides is 10k?)

They left one use out: isolation. A transformer can also simultaneously isolate primary side from secondary side for DC and low frequencies. In fact this is perhaps the most critical use of transformers in the world, as they isolate all equipment we touch from the AC power line and thereby prevent us from getting electrocuted. There is no conductive pathway between primary and secondary needed for a transformer to work.

*offtopic2: about the ic "4049ube", it says that it has six inverters. if an inverter is a device that turns dc into ac... how do you use that to get a distortion? if you are feeding it with an ac guitar signal anyways?.

In English, one word may have many meanings. This is what has you confused. In the context of power electronics circuits, "inverter" means "makes AC out of DC". In the context of logic circuits, "inverter" means "makes the opposite logical value on its output from what is on the input".

so... besides rectifying, to get twice the frequency, it also changes the amplitude of the signal?

Transformers establish a ratio between the voltage on the primary and the secondary. The ratio can be one to one, or an increase or decrease. They only work on AC. If you put rectifier diodes after a transformer, the DIODES make pulsating DC from the AC on the secondary. So a transformer makes a secondary voltage be some proportionate copy of the primary voltage (within limits of the frequency, voltage, etc. for which it's designed to work) but produces AC. Anything done after that is not the transformer's issue.

[waky]

oh, so in the circuit it prevents dc from reaching the output!!!! xD

thx guys ! ill get back to building it, ill try posting some soundclips later

[grapefruit]

oh, so in the circuit it prevents dc from reaching the output!!!! xD

It does, but the main reason for the transformer in this circuit is to provide two signals that are out of phase with each other, so that in combination with the two diodes you get a full wave rectified signal.

Stew.

[GibsonGM]

Check out some online tutorials, Waky, they really helped me out when I started this addictive hobby!  Google "basic electronics tutorial" or something like that.  DC and AC are a little different than each other.  In some places they are thought of as "the same" and in others, they are very much different.
   
Any transformer needs to have an AC input (now someone will come tell me cases where you don't, ha ha!).  They don't work at DC. The changing wave induces a magnetic field around the primary coil.  This cuts across the secondary coil, inducing a voltage (and current) in the secondary.  The secondary voltage is proportional to the turns ratio of the transformer.   That relationship determines if 120V at the primary will be, say, 12V at the secondary (a 10:1 ratio).   There is a trade-off...you can get less current out of the secondary if you boost the voltage, more if you drop it, to the limit of the primary's ability to deliver the current, and so on.   The AC can be line (wall) power, or a guitar signal, etc. etc., depending on the circuit and what you are doing.   For instance, an output transformer for an amp takes the voltage gain the amp provides and changes it into power (sort of) to drive a speaker using that trade-off mentioned above.   It also makes the amp 'see' an output load of several thousand ohms - for efficiency - yet still drive an 8, 16, 32 ohm speaker.   That's impedance matching.   So there are a few uses!  If you put a DC signal into a transformer, a voltage will only be induced in the primary at the moment the signal is switched off, resulting in a large 'pulse' or spike at the secondary, then nothing...like a capacitor.  This is why there are protection diodes on relays, BTW.     

This all involves some understanding of inductance and AC, and how it is different than DC.  So find a good tutorial, read up, and you'll be a pro at this!  )