Tycobrahe Octavia - Transformer Requirments

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ilcaccillo
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Post by ilcaccillo »

Hello,
I read a lot of threads here on the Octavia circuit, also I read most of the relevant info online,
one thing that I still don't understand quite well are the general specifications of what should be required for a transformer to work well on this circuit.

It seems all the DIY Octavia projects online list the Xicon small transformers (42TM022 or 42Tu011) or the LT-44 for this task,
But I guess the reason for these transformers being recommended comes down to the small price and wide availability.
Seeing these transformer specs, they are in fact quite really crude, which might be good or not, but a 300 Hz to 3.4 kHz freq response seems quite narrow to me, even for a guitar.

I know the recommended ratio for an Octavia transformer is 3:1, and how about input impedance and output impedance? what would be the range necessary for a transformer to be useful in this circuit?
Also does DC resistance of primary and secondary matter also?

The Xicon 42TM22 has 1.5K primary impedance and 600 ohms secondary impedance
http://eu.mouser.com/ProductDetail/Xico ... UAwdFkk%3d

The Xicon 42TMU11 has 1.5K primary impedance and 500 ohms secondary impedance
http://eu.mouser.com/ProductDetail/Xico ... UUpQ%3d%3d

LT-44 has a 20K primary and 1K secondary
http://www.maplin.co.uk/p/miniature-aud ... 00mw-hx82d

Checking this info it's easy to see that the Ratio of the transformers is not the same, also the primary impedance is mch higher on the LT44.

I would like to know the rough requirements so I could try some builds with other transformers besides the usual Xicon.

OEP and Edcor both make a nice range of transformers (much better than the small Xicon) that are not too expensive but have much better performance.
It could probably be possible knowing the requirements for the circuit to find something in their catalog that could work well in this application.

I also have a stock of quite a few transformers from Jensen, Sowter, Cinemag, UTC, Triad that I could try in the circuit just for the sake of experimenting and fun.


Thank

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ivan H
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Post by ivan H »

Hi, I cant really help with the tx requirements, but from memory (I built a ggg tycobrahe kit some time back), the transformer is hooked up in reverse, or the secondry is used as the primary. Cheers

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ilcaccillo
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Post by ilcaccillo »

Been thinking about this and actually I think the ratio shouldn't be that important,
I think an 1:1 transformer would be fine or any other small ratio. The important thing here I suppose is having a center taped secondary so that a signal split can be made, and two signals with oposite polarity are created.

What Im always really confused is about transformer impedances of input and output.
So in terms of impedances what would this circuit like to see?

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ilcaccillo
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Post by ilcaccillo »

What Im always really confused is about transformer impedances of input and output.
So in terms of impedances what would this circuit like to see?

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