am9 preamp (b*b*c*)

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A very kind soul has scanned the schematic and related documents (testing documents) for me
pm me with your email for me to pass it on

It's a broadcast preamp
Input -20db to -75db in 10db steps
output -20db 0db
can include a 15.625hz notch filter to get rid of picture noise from a 625 line screen (-40db cut)
bass cut filter
output muting (>80 db)
+/-12v 25mA
BCY71, BC109, Input (1:3.5) /Output (1:2) transformers

the next bits are stuff I don;t understand but I will include it for those cleverer than me
noise figure >4db at 300 ohm load at maximum gain
distortion 0.1% with output of 16db into 12kohm load at 1Khz
 
For all you lurkers
You are missing a great circuit.

Can I say a 7 transistor mic pre (discrete that is).

Place LK2 in circuit so the notch is not there.
Delete the whole muting circuit.
Remove C13 and connect to C16.
Add a 20 dB pad and Phantm circuit to Xformer primary.
The L1 input circuit is not needed unless you live beside a radio station.
Raise the rail voltage a little.
I guess the transistor connected to C16 is a BC109?


And this thing will smoke all the commercial junk made today.

And no it will NOT sound like a plug-in.
 
Great! I have 4 of those... :green:

Just a copple of questions Adrianh:

Just placing LK2 get rid of the notch in the "B" version? no need for remove the filter components?

I think a 40dB pad would be better for use the preamps with line level signals, what impedance want to see in input trafo?

And finally, using +-15V would be better than +-12?

Thanks!

Synthi.

PS: I`m making a front panel in FPD for two AM9 preamps in a 2U rack, if anyone is interested just ask me for the .fpd file! :wink:
 
synthi

Yes placing LK2 in circuit will get rid of the notch.

Just use the standard U pad.
two 680 resistors and a 150 ohm across them.
http://www.uneeda-audio.com/pads/

If you want a 40 db pad in front great add one.

I like plenty of voltage headroom.
I personally think even +/- 15 volts is too low.
So pushing the circuit to 15 or 24 I think would be great.
But you will need to scale the resistors up in value
and make sure the transistors are still biased correctly.
And make sure nothing is running to hot or needs a heatsink.

I would build it as +/-12V and then do futher engineering work for +/-15V
or higher when you have time.

Robert;
rlaury or Northsiderap will send it to you.
 
OK, I'm dying to see the schematic! Somebody email it to me and I'll post it.

<my user name> at yahoo.com, or hit the email button at the bottom of this post.

Peace,
Al.
 
Thanks Robert! :grin:

Al: I jst emailed the schematics and description, please post them if you have web space for sharing! :thumb:

Synthi.
 
bbcam9.jpg
 

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