[Peter Larsen[_3_]]

Scott Dorsey wrote:

Peter Larsen wrote:
Scott Dorsey wrote:

Null on the BM5 isn't bad but the output is very low.

I built a booster-amp for it with a Hitachi MC-preamp chip, works
fine with unbalanced input except for a bit of buzz from the upper
capsule. Some of the time I'm a coward, so I have NOT felt any
inclination to disassemble the mic-pair and investigate.

I would first rewire the mike for balanced output. The transformers
are inherently balanced; the only reason the output is unbalanced is
that one end is tied to ground.

My level of information is that the mic is balanced out, the preamp is
however not balanced in.

I might also try and replace them with Royer's new designs.

Could be that it is a better idea to build a trannybox, I have a
pair of Sennheiser TM005's that I used to use in reverse as input
transformers in my A77 with input board bypassed, ie. directly to
the rec-level pots. I should have thought of ripping the input
transformers from the becords that I had no room for keeping and not
only ripped the heads, but the TM005 is probably better as a step-up.

You need gain. Stepping up the voltage means stepping down the
impedance and that's not going to make the ribbon happy.

I am thinking 1:2

And that pristine BM5 which has just about done nothing - I did use
it to record a voice improvisation in 1985, great sound on vox if
not close, great space just recording in a reasonable listening-room
- but sleep in its fine wooden box for 50 years? - should I not
worry or stand the box on its end in the mic drawer? - mind you, its
precious, I paid DKK 250 for it and it is one of the products Bang &
Olufsen seemingly do not want to be reminded of having produced, no
info available from them.

I think they should be held upright so that the ribbons themselves are
vertical at all times.

I'll see if that can be implemented without a risk of the box falling over,
that probably would be bad.

B&O didn't actually make those, they just rebadged them. I don't
recall the whole story, but David Royer purchased the rights to the
original Speiden design which the B&O was adapted from and the
current Royer ribbons are mechanically very similar designs but with
much better transformers and magnets.

Ah, very interesting, thanks!

--scott

Kind regards

Peter Larsen