I have one old German directional dynamic microphone "SEL BST 205-1" and I remove everything inside it and pack 2 condenser microphones from mobile phones "Nokia 5130".

Like preamp I use this shematic: enter image description here

My problem is that any voice recorded via those microphones sounds like output from a can. I know that these microphones can record better sound and I think my preamp need some tweaks or some special filters.

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    \$\begingroup\$ You appear to be confusing the word "datasheet" with "schematic" or "circuit". \$\endgroup\$ – Tut Aug 15 '17 at 11:00
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    \$\begingroup\$ Unlikely that a preamp made to work with dynamic microphones and electret microphones will sound good with either. For starters, you need much more amplification for a dynamic microphone than for an electret. If the preamp has enough gain for the dynamic, it will have too much when used with the electret. \$\endgroup\$ – JRE Aug 15 '17 at 11:29
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    \$\begingroup\$ Try putting 1 kohm in series with the 100 uF capacitor across R3 to lower the gain and linearize the circuit and reduce distortion. \$\endgroup\$ – Andy aka Aug 15 '17 at 17:17
  • \$\begingroup\$ Generaly I remove dynamic mycrophone from case and instand of it place electret mycrophones. But my problem is sound quality. \$\endgroup\$ – Ivijan Stefan Stipić Aug 15 '17 at 17:17
  • \$\begingroup\$ @Andyaka you mean to repace R3 with 1k ? That can work. \$\endgroup\$ – Ivijan Stefan Stipić Aug 15 '17 at 17:18

Add a resistor in series with the 100 uF capacitor across R3 as shown below: -

enter image description here

Without that resistor there is nothing that defines the AC gain of the amplifier and the effect of the 100 uF without the 1 kohm resistor will make the input impedance very low and significantly distort the signal from the microphone.

With the 1 kohm resistor I've added, the circuit AC gain will be around 22 and the input impedance will be around 10 kohm.

  • \$\begingroup\$ You are totaly right. This is the right answer. Now sound is clear and loder. Is almost perfect but equalizer reduce that. THANKS! \$\endgroup\$ – Ivijan Stefan Stipić Jan 10 '18 at 10:57
  • \$\begingroup\$ @Andy aka, As per the last comment, your suggestion solved the problem. Now, I have a doubt, the circuits working voltage is 6V to 30V. But, R1 is only 1K. Is it a printing mistake.....? In many other circuits I have seen R1 value is 10K. If R1's value printed is wrong, what should be it's value for 9VDC and 12VDC powersupply....? \$\endgroup\$ – Anil Kumar. K Dec 17 '19 at 13:18
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    \$\begingroup\$ R1 is dependent on the electret microphone used and I used the circuit diagram posted by the OP because R1 wasn't the problem here. Indeed much higher values are sometimes used and typically I've seen 3k3 used a few times and 2k2 and 6k8. R1 is chosen for the microphone specifically used. There is no set rule @AnilKumar.K \$\endgroup\$ – Andy aka Dec 17 '19 at 14:25

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