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[kraftrourke]

Hi,

I recently acquired a 451E/ck2.  It had an intermittent wooshy crackle which ceased after cleaning the capsule/body contact but still has quite a high noise floor/low output.   It seems to be supplying only 1v to the capsule.   I've found a few schematics for both the 5 and 3 transistor version but none of them have component values.  Does one with values exist anywhere?

Thanks!
Adam Rourke

[klaus]

The 452E/EB is a 451 with phantom only, instead of 9-52 VDC supply requirements. Its schematic is closely related to that of the C414EB.

Email me privately if no one can upload a schematic here (I don't like the complication of this forum software in this regard), and I will scan one for you.
Likewise, if anyone can figure out the scanning of JPGs into this forum thread, that would be swell.

[kraftrourke]

Thank You for your help.   It seems there are a few versions of this mic which is why I was getting confused.  On the schematic I found at http://www.coutant.org/akgc460b/akgcms.pdf  the 451E I have looks to be the same exact circuit as the 451C (DIN connector)  It has 3 transistors.

[klaus]

The schematic with 7 transistors is the chipped re-issue (451B/452B). It cannot be converted as it does not contain discrete components.

[Jim Williams]

If only 1 volt the oscillator is down. Then again, if you don't test that before the large value resistors, the meter will not show that full voltage as the meter's input impedance will attenuate it. Check with a scope at the collector of T3. You should see about a 20 volt swing of a high frequency sine wave. If it's there and still no output, one of the coils in the head (transformer that is in the grey colored housing) is broken or you have a shorted out cap in the filter/zener diode DC converter stage or T3 is fried. The fix is a new tantalum cap or that grey transformer housing or transistor, available from AKG or Richard Land in Nashville.

[Kai]

As a temporary fix to test the capsule and mic you can move the + pin connection of Di1 to the center tap of Ü35.
This way phantom power is used as polarisation voltage.
The output will be about 6dB lower then normal, but for testing ...

Before doing so, measure the voltage at the - pin of Di1.
If it's something in the range of 40-60V DC (I don't know the exact value) the oscillator works.

Regards
Kai