# Sensitive audio detector

I have a question about this transformer. I haven't been able to find an audio transformer or 120/6 ratio transformer. The only available transformer that I can buy is 220/6 V of 3.2 or 5 or 6 W. So, of course my question is will it work normally? Also I don't know anything regarding this transformer power because that isn't mentioned in parts description.

• What do the binding posts connect to? What audio signal are you trying to detect? Sep 16 '13 at 14:40
• Bit of a weird design; almost any transformer power is suitable, as the energy is tiny. I would just try it and see. Sep 16 '13 at 14:49
• I think it is about ratio's thus $120V:6V = 240V:\boxed{12V}$ Sep 16 '13 at 17:03
• Audio transformers for 70 volt PA systems often have their ratio specified in the watts of power that they will deliver to a speaker of typical impedance. Or perhaps AC line power transformers are being mistaken for signal transformers. What the poster probably wants is not either of those, but rather the kind of tiny transformer used as an output stage in older transistor radios: those are surprisingly hard to source today. Sep 16 '13 at 19:19
• Another possibility is using a pulse transformer (often used for MOSFET gate drive). These are extremely tightly coupled (low noise, excellent linearity) and available in similar winding ratios. Sep 28 '13 at 15:02

I don't know if they still do, but Radio Shack used to carry a tiny 500:8 audio transformer that'd work VERY well for this sort of project. I'm sure there are all sorts of similar transformers available still.

I think the Radio Shack ones were even center-tapped on the 500-ohm side so they could be used in experimental/prototype push-pull amplifiers.

EDIT: I'm NOT sure how available Radio Shack parts are in Montenegro, though. If all else fails, you COULD wind your own.

How's availability of mail-order electronic parts there? Can you freely buy things through eBay and Amazon?

You need a higher ratio an LP Pickup needle step up transformer but you need higher impedance phones or maybe sound powered phones.

A 220V to 6V transformer should be fine - it will give you a bit more sensitivity than the specified 120V to 6V transformer.
If you are buying a transformer, use the cheapest as the power ratings listed won't make (much) difference.
If the price is the same, use the transformer with the lowest watt rating. It might be (marginally) better than the others. The wattage rating would only be a problem if it were, say, 200W. The higher higher power transformer will have a lower impedance - with that behind the 1k resistor you might lose too much signal strength.

The transformer mentioned in the project page -- RadioShack catalog # 273-1365 -- is available on-line and may also be available in stores. It has a center-tapped winding, with voltage ratios of either 120/6 or 120/12.