JessJackson
Well-known member
I set out to build a u67 inside a u87ai body,
I have the untouched genuine modern k67 which came with the u87ai, I have a very low noise NOS telefunken ef86 and Olivers bv12,
I am utilizing the yellow Vishay 1813 0.01uf caps throughout the circuit as I couldn’t source the Wima Tripofols and the metal oxide in the high impedance section under the head basket.
As for resistors I used all carbon film 1/2 watts with the exception of the 60meg and 400megs which were metal oxide dales
Its all 100% point to point, SUPER quiet mic!! and SO MUCH gain.
The 40hz jumper is running shorter distance across the top circular perfboard section and there was no need to run the traces down into the bottom board for coupling cap as I mounted it next to the tube for easy access to swap out.
Based on Klaus and a few other guys I decided not to include the bottom board which holds the passthrough filter caps. The 2000pf filter caps don't serve much purpose in this design. "These caps were put in so the mics could comply with German public broadcast specs. Neumann complied with all requirements, but the broadcasters still rejected the model, because it used the "wrong" tube."
Im using Dany's PSU. perfect voltages across entire mic. Bias / plate / grid, output etc...
Things left to do.
Find a couple screws and bolts small enough to travel through transformer and drill holes.
Source Truchel mount.
Powder coat glossy like original u67
design print labels for transformer and outer casing bell.
Source 0.01 wima tfm's and some wire wound high impedance resistors as per original.
This is the best mic I've built.
I have the untouched genuine modern k67 which came with the u87ai, I have a very low noise NOS telefunken ef86 and Olivers bv12,
I am utilizing the yellow Vishay 1813 0.01uf caps throughout the circuit as I couldn’t source the Wima Tripofols and the metal oxide in the high impedance section under the head basket.
As for resistors I used all carbon film 1/2 watts with the exception of the 60meg and 400megs which were metal oxide dales
Its all 100% point to point, SUPER quiet mic!! and SO MUCH gain.
The 40hz jumper is running shorter distance across the top circular perfboard section and there was no need to run the traces down into the bottom board for coupling cap as I mounted it next to the tube for easy access to swap out.
Based on Klaus and a few other guys I decided not to include the bottom board which holds the passthrough filter caps. The 2000pf filter caps don't serve much purpose in this design. "These caps were put in so the mics could comply with German public broadcast specs. Neumann complied with all requirements, but the broadcasters still rejected the model, because it used the "wrong" tube."
Im using Dany's PSU. perfect voltages across entire mic. Bias / plate / grid, output etc...
Things left to do.
Find a couple screws and bolts small enough to travel through transformer and drill holes.
Source Truchel mount.
Powder coat glossy like original u67
design print labels for transformer and outer casing bell.
Source 0.01 wima tfm's and some wire wound high impedance resistors as per original.
This is the best mic I've built.