| Ahmad_tbp |
Hi all ...
i m tryin to build a balanced mic pre amp for a Behringer B1 Condenser type mic , it needs a phantom supply that i ll build separately ,
this preamp will use in a home studio as the mian Vocals/Instruments Preamp , so it so important for me that the pre be noiseless .. and one other thing :P i only have one 12ax7 for that :P ...... and it s almost impossible to find an input/output transformer here, so , do i have a choice ??? can i build a pre without any in/out transformer and only with one 12AX7 ?
any circuit ?any idea ??
thanks so much ... |
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| Eli Duttman |
You did say balanced and only a single 12AX7. Build a differential gain block around the 'X7. Set the grid leak resistor value consistent with the mic's loading requirements.
12AX7s exhibit a high O/P impedance and POOR drive capability. So, buffering is an absolute MUST. What's in your parts "stash"? Do you have a 12AU7 or some FETs? |
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| Ahmad_tbp |
| hi , i wish i had or i could find some more tubes , but there s nothin here , i only have one more 6av6 .. but i think i can find almost any FET , is bf245 ok ? |
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| Eli Duttman |
Look for the ZVN0545A. As stated previously, the 12AX7 has POOR drive capability. The ZVN0545A has low capacitances, which make it easy to drive. Read MOSFET Follies. You will DC couple a FET source follower to each 'X7 anode in the difference gain block.
While considerable better than the 'X7 in the drive dept, the ZVN0545A is not a "world beater". If you plan on driving a nasty downstream load, cascade followers and use the little FET to drive a big FET. |
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| Ahmad_tbp |
hi , thnx for replies ,
i m not an expert in electronic ,, do u think i can find a schematic ? |
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