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Old 26th July 2011, 07:04 PM   #1
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Default IMPEDANCE MATCHING FOR I/V TRANSFORMER

I am about to carry out the usual updating of a Quad 34 preamp and wish to customise the tape input for use with the I/V transformer in my DAC.
The transformer secondary has a dc resistance of 900r and an impedance of 5K.

I intend to directly couple this to the non- inverting input of the buffer opamp and change the input resistor which is currently 10K. (ie removing the input cap and series resistor)

Am I correct in thinking that 5K is the optimum value - ie equal to the transformer output impedance?

I can't decide which op amp to use in place of the existing TL072 - a biploar NE5532 or a FET OPA2134. In view of the low impedances, might the NE5532 be better choice?
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Old 26th July 2011, 07:29 PM   #2
kevinkr is offline kevinkr  United States
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Consider the LM4562, but do look for signs of oscillation on the output of any op-amp you swap in there. The TL072 is very forgiving of layout issues compared to many more modern devices and also has rather good EMI resistance as well.

You may need to experiment with loading on the secondary of the transformer to find the optimum load to reflect back to the DAC..
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