R/E/P Community
R/E/P => Klaus Heyne's Mic Lab => Topic started by: klaus on April 17, 2011, 10:23:10 PM
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Originally Posted By: Glenn (Jakeandthephatman) on Sun, 08 October 2006
Hey All- here is my ordeal...
I acquired this mic about 3 months ago. It's a Fairchild Syncron AU7A. I never knew that Fairchild produced a condenser, so I was more than excited to get it. (It's in mint condition mind you, looks brand new.)
The only issue is that it takes batteries? AA batteries wont fit, and AAA are too small...
After doing some research on my own I found out that a few of the first solid state microphones (pre-phantom power) used batteries; there are a few Neumann models, however I'm not sure exactly which ones.
At any rate, does anyone have an idea of whom I can get to modify the mic and get it working (with a power supply?)
Thanks in advance guys!
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Contact Dan Zellman
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http://www.coutant.org/syncron/index.html
Lot's of info here.
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Hello
I have two consecutively numbered Syncron AU7a mics that I purchased in the 1970s. They were in good working order when purchased and the batteries were available. The mic uses two 22.5 volt batteries in series for the polarizing voltage and two 4.2 volts batteries in series for the FET head amp. The mercury batteries originally specified were later deemed environmentally unfriendly and discontinued.
The 22.5 volt batteries are readily available but are slightly wider than the original and will not fit in this mic. The 4.2 volt batteries are not available but there are 4.5 and 3.6 volt models that can be used to get very close to 8.4 volts and they will fit perfectly inside the mic.
I became interested in these mics again after seeing some posts on the web and dug them out to see if they still worked. I decided that building a power supply was out of the question and chose going the battery route. After some carefully study of the circuit boards I drew a simple schematic of the battery section and realized I could use the existing mic connector with a 5-conductor cable to get 45 volts to it and balanced audio from it. Radio Shack had a battery holder for two AA battereies that worked perfect for the two 22.5 volt units.
After some extensive cleaning of the internal connections (with the head basket safely covered) I soldered up a test rig that fed the polarizing voltage and teminated the audio to an XLR cable. Both mics still work, so building a proper power supply is probably the way to go. I actually have a schematic for the Syncron-designed AC power supply somewhere. I never built it because the technology looked too old school at the time, but maybe the Syncron schematic deserves another look.
I used my Syncrons for recording vocals and horn parts for years until we got a U47 and U67. By then the batteries were impossible to get and the Syncrons were shelved. While certainly nothing like a healthy U47 or U67, the Syncrons don't sound that bad. For me they sit somewhere between a FET condensor and a large element dynamic, like a U87 and a RE20. They have a very simple single FET amplifier that seems to suit the capsule and output transformer. They have a sound that is honest and fairly even. The bottom is full, the midrange is punchy and the top end is clear without being sizzly.
If mine were dead due to a bad capsule or something like that I don't think I would spend a whole lot of time messing around with them. If the problem with your mic is simply not being able to power them up for a test, you can get the necessary batteries and other odds and ends for less than $50.
The 7-pin connector on the bottom of the mic is a custom-made part that was whittled down from an off-the-shelf Amphnol part. If you don't have the male half then you are probably going to encounter a huge headache just trying to power up the mic. I have read posts from others who have sucessfully replaced the bottom connector with something different and rewired the innards to accept phantom power. Mine are stock and they are going to stay that way.
Jamie Goldsmith
om recording