DIY mic splitter using Carnhill VTB2281 question

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paulrichards7
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DIY mic splitter using Carnhill VTB2281 question

Post by paulrichards7 » Sat Sep 13, 2014 5:47 am

Well, Im kind of new to all this electronics stuff and don't seem to grasp most of it really
And unfortunately, there dont seem to be any audio electronics courses in the South West of the UK
So, I just do the best I can and use my ears really

I have been experimenting with using transformers patched into line level signals to add certain mojo/characteristics to various sounds
To a lot of success may I add

Anyway, I picked up a couple of Carnhill VTB2281 to add to my Triad, Lundalhl, BBC and others transformer box
It wasnt until I got them, that I realized i could use them as a two in two out device

This got me thinking ?
Well, I have a spare transformer now
So I wondered if I could use it as a microphone splitter ?

The idea was to connect pins 1 & 4 and 2 & 3 on the primary side, then connect signal positive/hot to pin 1 and signal negative/cold to pin 3
The on the secondaries, could have 2 outs(pin 5 positive/hot and pin 6 negative/cold, also pin 7 positive/hot and pin 8 negative/cold)
These 2 outs would go to two different mic pres
Hope this is making sense so far
Anyway I basically rigged up this on an insert of a mic pre to test
Yes it worked fine, except the two outputs were 3dB down compared to input, which I kind of had a feeling there would be a loss
And the impedance of the two outputs was double that of the input impedance

Ive looked at the Carnhill spec sheet and its says that if you have the primaries configured as series and secondaries configured to parallel, you should be seeing a 6dB loss and a quarter of the impedance ?
Any ideas or insight ?

Also, what would i use as earth ?
The case that the transformer is bolted to ?

Im not sure if any of this makes sense to you electronics Gurus !

Thanks
Paul

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floid
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Post by floid » Sat Sep 13, 2014 7:13 pm

it might be useful to think of a tx with multiple primaries and secondaries as an electronic gearbox. setting aside mostly minor losses in real world, rather than ideal, situations, power in equals power out. but a big gear mated to a smaller one yeilds higher rpm (amperage) with less torque (voltage) to factor out to that 'same' power (wattage) figure. think of impedance as a specifically tuned combo of these factors. different wiring combos allow you to change gears, as it were. one primary to dual secondaries might be analogous to shifting into 4wd.
more wheels, less power per.

in and out can usually share a ground, perhaps add a lug in your mounting scheme if you don't have one on the case itself.
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floid
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Post by floid » Sat Sep 13, 2014 7:33 pm

also, i think you've confused parallel secondaries with split secondaries.
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Post by The Scum » Sat Sep 13, 2014 9:33 pm

Does it help any if you think about the transformer as having four independent windings, each of 300 Ohms?

It could be one primary and three secondaries. A 3 way split.

Or three primaries and one secondary - it could perform as a 3 input mixer.

In series, a pair gives you 600 Ohms. In parallel, 150. The ratios between the input and output give you the step up.
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paulrichards7
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Post by paulrichards7 » Sun Sep 14, 2014 2:29 pm

Thanks for all that guys
Now Im really confused lol
Ill just wire it up and see how it goes
Thanks again
Paul

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