Mic pre transformers

Tim Wyatt · 25th June 2006, 09:39 PM

Would a 1:10 ( Pri 500 CT / Sec 5K CT ) audio transformer work for a tube mic preamp? I have some Mil Spec Triad TF5S21ZZ I would like to use. I want to make a 4 channel tube pre mixer with a 6L6 outputstage. I have made many guitar amps and a clean power section is no problem but microphone preamps are new to me. Thanks for any help.

kevinkr · 25th June 2006, 10:48 PM

Hi Tim,
I assume by 1:10 you talking about the impedance transformation ratio, not the windings ratio. If so this equates to a ratio of about 3.33 or a little over 10dB voltage gain. Expect to make up required gain with a low noise amplifier circuit. Depending on the lossiness of the core this might work ok with a 600 ohm mic, at least it will provide a balanced input to unbalanced output and provide isolation which is a good reason for using a transformer. Worst case make provisions for replacing it with something else if it does not work well.

Tim Wyatt · 25th June 2006, 11:00 PM

Yes, Impedance ratio. It would feed a 12AX7 gain stage. I might just have to bread board one up and see how it goes.

25th June 2006, 09:39 PM	#1
Tim Wyatt diyAudio Member Join Date: Mar 2004 Location: Wichita,KS	Mic pre transformers Would a 1:10 ( Pri 500 CT / Sec 5K CT ) audio transformer work for a tube mic preamp? I have some Mil Spec Triad TF5S21ZZ I would like to use. I want to make a 4 channel tube pre mixer with a 6L6 outputstage. I have made many guitar amps and a clean power section is no problem but microphone preamps are new to me. Thanks for any help.

25th June 2006, 10:48 PM	#2
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Hi Tim, I assume by 1:10 you talking about the impedance transformation ratio, not the windings ratio. If so this equates to a ratio of about 3.33 or a little over 10dB voltage gain. Expect to make up required gain with a low noise amplifier circuit. Depending on the lossiness of the core this might work ok with a 600 ohm mic, at least it will provide a balanced input to unbalanced output and provide isolation which is a good reason for using a transformer. Worst case make provisions for replacing it with something else if it does not work well. __________________ www.kta-hifi.net

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25th June 2006, 11:00 PM	#3
Tim Wyatt diyAudio Member Join Date: Mar 2004 Location: Wichita,KS	Yes, Impedance ratio. It would feed a 12AX7 gain stage. I might just have to bread board one up and see how it goes.

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