Where to get 220 M.ohm resistors?

[Ruud]

220 M.ohm is used in the U47 FET for example. In that situation it is part of an R-C combination.

 

[Bo Deadly]

220 M.ohm is used in the U47 FET for example.

Ok. So this is a case where IMO you should follow the schematic. You could tweak values to account for parts costs / availability. Manufacturers do that all the time. But if you're re-creating an existing circuit you should copy the circuit as closely as is reasonably possible. I'm not sure if I would use 250 Mohm in this particular case. I think I might actually parallel 400 || 500.

 

[abbey road d enfer]

There are two RC circuits R2/C2 and R3/C3. their product defines the low frequency point where the capacitive effect slowly gives way to the resistive effect.
In normal gain, this frequency is 40 Hz. When the pad is engaged, the frequency is 48Hz. Neumann's engineers have considered that this difference is not very important.
I would not hesitate to fit a 250Meg resistor there, unless you think that the mic is too sensitive to LF noises.

 

[RuudNL]

250 M was already my alternative.

 

[TLRT]

I have many old NOS Allen Bradley 100meg carbon resistors, they have usually 10-20% tolerance so easy to put them in series for 220meg. Otherwise 250meg should be just fine for that u47 filter circuit.

 

[ubxf]

Would you like carbon comp or metal film ?

 

[RuudNL]

At the moment I am waiting for a reply from my contact in Taiwan.
As soon as I know more, I will let you know!

 

[ZHAOMENG]

At the moment I am waiting for a reply from my contact in Taiwan.
As soon as I know more, I will let you know!

Chinese e-commerce companies generally have the specifications of 200M and 300M, 220M and 250M, which are not normal. If you need a large number of products, you can customize the specifications you need from the manufacturer. For example, Neumann has many non-standard customized components. In China, the specification of 200M and 300M for 10 pieces only costs 6RMB, That's less than a dollar，and the postage is free. It takes 3 days at most from your order to the receipt of the goods

 

[Trouble Report]

Have you checked Mouser? They have quite a few in that range.

 

[RuudNL]

Yes, Mouser has some values that are close to what I need, but pretty expensive. (For a single resistor!)

 

[Diabolical Artificer]

Could have sworn I posted the other day..... I have some 120M resistors, NOS blue high voltage jobbies,your welcome to 10 for the price of postage, drop me a PM if any use, Andy.

 

[FIX]

For biasing mic elements, the high ohm resistors can really effect the tonal qualities of the mic. You may want to get several from different places and listen. A carbon one will yield a bit of nice 2nd harmonic distortion, as thats that a carbon resistor does well, as it has some non linear qualities.

Making high ohm resistors bus be hard, like maybe they blow resistive steam on them and then seal them... I used a Gohm once on a mic design.

This is why hot breath on a good mic kills the gain. The recover time is basically the charge time of the resistor to the element in relation to the humidity of the room.

 

[RuudNL]

Problem solved! (With thanks to my friends in China!)