Hi,


first post on this forum, i hope this is the right place to ask this.

while searching for a small (portable) wideband (below 15hz) preamp i found one but alas no details on the components values (probably have everything to build it, but i have no infos on these transistors)

The specs:



Operating Voltage: 12- 30 V/DC

Super Wideband: 10Hz - 150KHz (approx)

Input Sensitivity: 2 - 20mV (approx)

Output: 200 mV - 2 V

Structure: 2 - Stage


Datasheet:

http://www.kemo-electronic.de/datasheets/b073.pdf


Any ideas on those values, especially the transistors!


I'll really appreciate any help!


Johnsy.

 

There are 1000 ways to build a microphone preamp.
If you are interested in the circuit you have presented why not purchase the kit?

 

Thanks for your reply!

There are 1000 ways to build a microphone preamp.

Yes i know, but i didn't find any schematics for a preamp with those specs (10hz is required up to 100khz)

If you are interested in the circuit you have presented why not purchase the kit?

I first contacted both the vendor and ebay sellers but the shipping charges are very high (three to four times the price of product) which is absurd.

Knowing that i might have the components already here, it makes sense to ask if someone might help on this.

 

Only a guess - 2N3904.

 

D1: Don't connect the power backwards and you can leave this out. Other way use a 1N4001...1N4007

Reading the color code.
R1: 560
R2: Mystery 160k?
R3: 47k
R4: 560
R5: 560
R6: 100
R7: 2.7k

Guessing at the capacitors:
C1: 100 uf
C2: 22 uf
C3: 22 uf
C4: Maybe 47 uf

T1, T2: Low noise audio NPN such as 2SC3199, BC414, BC549, 2SA1048, or KTC3200

 

Only a guess - 2N3904.

Thanks ronv for your reply (personally i thought of the bc549)



Thanks a lot DickCappels!

R2: Mystery 160k?

Are you sure?

I couldn't find R2 in the color codes (not really sure about that one)

C3: 22 uf

Really? it seems to me that "47.." can be read on the side (i might very well be mistaken)

T1, T2: Low noise audio NPN such as 2SC3199, BC414, BC549, 2SA1048, or KTC3200

Ah! i have everything then, this is great!


I wonder why this schematic isn't very popular (might need to reduce gain but not much beyond that)

 

About R2: No not sure, but 160k is a reasonable value based on how its used in the circuit. 150k should work fine as well.

About c3: Its the power supply bypass capacitor so not critical. Generally, using the larger capacitor is more conservative.

As Mrchips pointed out, there are a thousand ways to make a preamp, and this is merely one of them.