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 1 
 on: Yesterday at 06:42:51 pm 
Started by wildplum - Last post by wildplum
I am in the market for a new shock mount for a Neumann U89. I am considering two very different designs.
Please see pictures below.

Shock mount A is of the standard design, using an elastic web to provide the protection.
Shock mount B is a newer design, using Rycote's Patented Lyre Technology for the shock absorption.
Shock mount B is about twice the cost of A.

Questions:
1. Which design will stand up to studio use longer (i.e. which design is more rugged)?

2. Which design is better at attenuating such things as shock, vibration, and handling noise?

Thank you.

 2 
 on: Yesterday at 04:56:19 pm 
Started by Mikeyod - Last post by Mikeyod
First thing I did when this problem started was send all three motors to Athan for rebuild.
So all new bearings and lube and spinning nice. Also replaced 8uf phase shift capacitor.
Just replaced 5.6v Zener D8 but haven't tried it yet. Will check voltage across that resistor. 

 3 
 on: Yesterday at 04:44:17 pm 
Started by Mikeyod - Last post by radardoug
One thing I hadn't considered is the motor being stiff from dried up bearings.

 4 
 on: Yesterday at 04:38:36 pm 
Started by Mikeyod - Last post by radardoug
So manual says it should drop to 3 volts. That indicates to me that it is not driving hard enough.
Also, check when it goes to 22 volts, whats the voltage across the R49, 10 ohm, If it is close to 22 volts, then thats the problem. You could try reducing this resistor to 8. 2 ohm. Does the motor spin freely?

If the voltage across R49 is lower than 22 volts, then  gain of the output or the driver transistor is the problem. I would try the Darlington driver which will give you more gain on the driver. Output transistors are generally a bit low gain anyway. Also there are a number of tantalums around the board, check them all for shorts. Its a bit fiddly, but also do a multimeter check on all the resistor values, watching for where they are in circuit.

 5 
 on: Yesterday at 12:01:48 pm 
Started by Mikeyod - Last post by Mikeyod
It does not go down to 3 V it drops to around 22.5. If when the machine is playing tape normally I grab the left reel hold down and stop the machine for a second it only goes down to around 25 v.
With the machine not playing, but tape loaded, if I manually pinch the capstan between my fingers it only drops to around 25. Also, on the schematic where it shows these voltages it says the nominal is 80 volts. I never see above 50 volts. Tape loaded, playing or not. Without tape loaded (capstan not spinning) it is at about 135 volts.

 6 
 on: April 26, 2017, 04:03:04 pm 
Started by MikeCheck - Last post by klaus
Before signing off on your diagnosis, I would remove the capacitor from the mic and put it on a capacitance tester.
KH

 7 
 on: April 26, 2017, 02:33:00 pm 
Started by MikeCheck - Last post by MikeCheck
Thanks Klaus,

I'm very positive. I was loosing my plate voltage after the 200K plate resistor. I swapped the cap out with 1.0uf MusiCap and everything was back to normal.
Honestly It was the last thing I expected myself. I'll triple check just to be sure, but I'm 100% at this point.


 8 
 on: April 26, 2017, 02:05:24 pm 
Started by fffaustino - Last post by fffaustino
Thanks for the info and your fast reply!

and best regards from Spain!

Alfredo

 9 
 on: April 26, 2017, 12:41:00 pm 
Started by MikeCheck - Last post by klaus
First,  I would like positive confirmation that this capacitor actually failed. In 30 years of dealing with them, both in M49 and U47/48 I have never had a single one fail.

But, if indeed the cap is shorted (?) your choice will audibly affect the sound of the mic: some swear by wet tantalums, others by oil-soaked contraptions. A very good film and foil (not metalized poly-prop!) will add a bit more clarity without thinning out the sound, while those film & foils made with other metal films typically sound more pointy in the mids and highs.

Contact me privately if you want to replace with original material-these days collectors collect everything...

 10 
 on: April 26, 2017, 12:31:31 pm 
Started by fffaustino - Last post by klaus
That is either  1974 or 1984- the appearance did not change much during that decade. Judging from the size of the hand writing, I guess 1974.
Best, KH

P.S.: I have assembled a good 100 different K67/87 capsule pictures on my desktop computer, which I will label and upload to my website, so these inquiries may become a bit easier in the future to answer.

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