Home |
Search |
Today's Posts |
#1
|
|||
|
|||
AWA transformer question
I recently picked up a couple of used transformers, AWA (Amalgamated
Wireless Association) model No 7XD1768. AWA was a respected Australian manufacturer, these were sold to me as microphone transformers. There's 3 pairs of wires, the multimeter shows one winding at 1.5kOhms, the other two at 8 Ohms. This seems WAY to low for a mic transformer, but what would a transformer with these windings be used for? Physically it's round, about 1" diameter, and about 1-1/4" high, so it's not a speaker transformer. Any clues? -- John Cafarella End Of the Road Studio Melbourne, Australia |
#2
|
|||
|
|||
AWA transformer question
There's 3 pairs of wires, the multimeter shows one winding at 1.5kOhms, the
other two at 8 Ohms. Thats @ DC what is the AC impedance. It might be say 5K and ?? Steve AllPro Electronics www.Allproelectronics.com Nashville, TN Phone: 615.833.1810 |
#3
|
|||
|
|||
AWA transformer question
In article ,
John Cafarella wrote: I recently picked up a couple of used transformers, AWA (Amalgamated Wireless Association) model No 7XD1768. AWA was a respected Australian manufacturer, these were sold to me as microphone transformers. There's 3 pairs of wires, the multimeter shows one winding at 1.5kOhms, the other two at 8 Ohms. This seems WAY to low for a mic transformer, but what would a transformer with these windings be used for? Physically it's round, about 1" diameter, and about 1-1/4" high, so it's not a speaker transformer. Any clues? Ribbon mikes? 8 ohms is kind of high for the primary on a ribbon but it might be a cheaper model. Maybe for some kind of moving coil dynamic with a very low number of turns on the coil? --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#4
|
|||
|
|||
AWA transformer question
In article ,
Stevaudio wrote: Well that's the _real_ question, ain't it! At what frequency do you measure at, is the next obvious question if you go down that path. 1k hz is good. Measure the voltage total and the drop across a ~5k resistor and then the current solve for R of the winding The standard measurements are normally done at 1KC. If you don't have a bench oscillator, though, a filament transformer can be a surprisingly useful source, and you can make measurements at 50 Hz which aren't going to be TOO far off if it's a wideband transformer. Be sure not to clip it, though! --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#5
|
|||
|
|||
AWA transformer question
On Tue, 5 Aug 2003 17:27:00 +1000, "John Cafarella"
wrote: Let me refine the question a bit: Are these DC resistances in the ballpark of what you'd expect from a mic transformer? Yes. For FET or vacuum tube loading. Can you measure turns ratio? Chris Hornbeck, guyville{at}aristotle{dot}net |
#6
|
|||
|
|||
AWA transformer question
Measure the voltage across the primary. Measure the open circuit voltage
across the secondary. Ep/Es = your turns ratio Ep / Es = square root of Zp / Zs You can then find the primary Z for any value of load on the seconday. This works for tightly coupled transformers. Stay away from frequency extremes and high levels. bg John Cafarella wrote in message ... I recently picked up a couple of used transformers, AWA (Amalgamated Wireless Association) model No 7XD1768. AWA was a respected Australian manufacturer, these were sold to me as microphone transformers. There's 3 pairs of wires, the multimeter shows one winding at 1.5kOhms, the other two at 8 Ohms. This seems WAY to low for a mic transformer, but what would a transformer with these windings be used for? Physically it's round, about 1" diameter, and about 1-1/4" high, so it's not a speaker transformer. Any clues? -- John Cafarella End Of the Road Studio Melbourne, Australia |
#7
|
|||
|
|||
AWA transformer question
The DC resistance will typcially be a quarter or a tenth of the AC
impedance (measure it at 1kHz) but it's really not something you can calculate like that. If they were sold to you as mic transformers, I'd guess the two "8-ohm" windings would be 150-ohms in parallel or 600 ohms in series, but they could also be 150-ohms in series and 38 ohms (for ribbon mics or MC phono cartridges) in parallel. Your best bet is to hook the primaries up to an oscillator, terminate the secondary with maybe a 10k or 50k resistor, and measure the gain. The amplification factor equals the turns ratio, and the impedance ratio is the square of that. So if you put in 100mV and get 1V out, then you've got 20dB gain, a turns ratio of 1:10, and an impedance ratio of 1:100 (which would mean 150:15k IF you actually are using a 150-ohm primary arrangement). Next measure the overload point (level at which a 50Hz tone visibly distorts on an oscilloscope) and the frequency response (at an operating level safely below the overload point). If either of these parameters look bad, try a different connection arrangement. You can also measure the phase response at high and low frequencies, and you can run a square wave through it and adjust the secondary loading for optimum square-wave output. ulysses John Cafarella wrote: I recently picked up a couple of used transformers, AWA (Amalgamated Wireless Association) model No 7XD1768. AWA was a respected Australian manufacturer, these were sold to me as microphone transformers. There's 3 pairs of wires, the multimeter shows one winding at 1.5kOhms, the other two at 8 Ohms. This seems WAY to low for a mic transformer, but what would a transformer with these windings be used for? Physically it's round, about 1" diameter, and about 1-1/4" high, so it's not a speaker transformer. Any clues? |
#8
|
|||
|
|||
AWA transformer question
John Cafarella wrote: I recently picked up a couple of used transformers, AWA (Amalgamated Wireless Association) model No 7XD1768. AWA was a respected Australian manufacturer, these were sold to me as microphone transformers. There's 3 pairs of wires, the multimeter shows one winding at 1.5kOhms, the other two at 8 Ohms. This seems WAY to low for a mic transformer, but what would a transformer with these windings be used for? Physically it's round, about 1" diameter, and about 1-1/4" high, so it's not a speaker transformer. Any clues? What are you planning to do with those transformers? If you decide that you have no use for them i know someone that may need them eventually. www.monsterisland.com |
#9
|
|||
|
|||
AWA transformer question
"Justin Ulysses Morse" wrote in message ... Any clues? Thanks to all for your assistance. Gotta say it again, what a great help this group is! Plenty of homework for me now. I bought them for use in a mic pre project I have in mind for the medium term future. Until then, I might put two back to back, and see if they sound nice as an pre-input to my mic pres. The only transformer input pre that I have at this time is the OpAmp labs unit, so it might be a nice flavour addition. -- John Cafarella End Of the Road Studio Melbourne, Australia |
Reply |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Moving Coil Transformer Question | High End Audio | |||
Serious question for "Michael McKelvy" | Audio Opinions | |||
RCA out and Speaker Question in 2004 Ranger Edge Question | Car Audio | |||
Step up transformer | High End Audio | |||
NEWBIE QUESTION: Need HELP With SOUNDCRAFT MIXER! | Pro Audio |