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New high-Z 1:1 input transformer from Hammond (10k:10k)

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rongon

rongon

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Joined 2009
#1
I just saw this in the New at Mouser category...

Hammond 140UEX 1:1 input transformer

140QEX_B.jpg


It's kind of expensive at $67.50 in ones and twos. Very close to Jensen and Cinemag pricing. Hammond says 20Hz-20kHz within 1dB. 882k impedance and 36.5H pri and sec at 1kHz, 1V. Only 5mW max (?). Still, looks interesting...

Datasheet: http://www.hammondmfg.com/pdf/140UEX.pdf

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#4
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#8
JLH said:
Isn't (10dBm) 10mW equal to only 0.7071 Vrms? If so, then that is pretty useless for most audio amp inputs.

http://www.markimicrowave.com/menus/data/power to voltage.pdf
Click to expand...


0dBm is 1 milliwatt, usually into a load of 600 ohms which equates to the usual 0.775 volts. 10dBm is 10 milliwatss which is 2.45 volts rms - typical hi fi maximum level.

Unfortunately, Hammond fail to specify the impedance for their 10dBm measurement and where just a voltage level is meant it is more usual to use dBu. +10dBu is 2.45V rms whatever the impedance.

This is a 10K:10K transformer so maybe they mean 10dBm into 10K. Now 10V rms across a 10K resistor gives 1mA current and 10mW power. So +10dBm into 10K is 10V rms which is +22dBu, rather closer to the Jensen spec.

It really disappoints me when manufacturers are so woolly in their definitions.

Cheers

Ian
 
#12
Ok, someone tighten me up on this. What's so special or useful about a high impedance 1 to 1 input transformer. Is it just for isolation? If so, why not just go in through a quality capacitor? Every mike input transformer I ever wanted or needed was low in and high out.
 
#15
My understanding is that it's much easier to get good bandwidth and low distortion from a 1:1 xfmr than from a step-up or step-down xfmr.

I was hoping to use it as a phase splitter on the input of a power amp, unbalanced in -> balanced out to the driver stage push-pull grids. It would be driven by a separate line amp based on a common cathode low-mu triode, maybe with a cathode follower output to lower the line stage's output impedance. Is that a reasonable idea? Or (as usual) am I missing something?

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#16
rongon said:
I was hoping to use it as a phase splitter on the input of a power amp, unbalanced in -> balanced out to the driver stage push-pull grids. Is that a reasonable idea? Or (as usual) am I missing something?

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Click to expand...

To use it as a phase splitter it really needs a centre tapped secondary. You could use a pair of resistors across the secondary with the centre point grounded instead. It would need to feed a pre-driver stage but otherwise the basic idea seems sound to me.

Cheers

Ian
 
#17
rongon said:
My understanding is that it's much easier to get good bandwidth and low distortion from a 1:1 xfmr than from a step-up or step-down xfmr.

I was hoping to use it as a phase splitter on the input of a power amp, unbalanced in -> balanced out to the driver stage push-pull grids. It would be driven by a separate line amp based on a common cathode low-mu triode, maybe with a cathode follower output to lower the line stage's output impedance. Is that a reasonable idea? Or (as usual) am I missing something?

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Click to expand...

you may just be able to do that as per above post...
look here...Power Amps
i hope SY chimes in and post his cyclotron amp...😉
 
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