Re: Audio pre-amplifier for microphone?

Ian Reeve

Hi Arv,


Thankyou for your advice. As it stands using the stock electret element wired as shown in the instructions produces a very poor ssb output. The equivalent output on cw is around 10 watts depending on the band, so I know the mic amp and modulator are being well under-driven.

I will experiment and use the information you have kindly supplied to achieve a workable solution. Ideally I would like a solution where normal speech levels produce a ssb power of over 80% of available rf output as compared to cw on the same rig,same band.


My Kenwood TS590SG effortlessly achieves that,so that will be my aim!


Best 73




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From: <> on behalf of Arv Evans <arvid.evans@...>
Sent: Thursday, August 22, 2019 4:47:35 PM
To: <>
Subject: Re: [BITX20] Audio pre-amplifier for microphone?

The microphone operating voltage can be isolated from the transistor input with a suitable
value capacitor (observe polarity if using an electrolytic cap).  The output of your transistor
amp can be isolated from the input to a following stage by also using an isolating capacitor.
That said, it might not be a good idea to add additional amplification to the microphone input
because that could over-drive the existing microphone amplifier and following modulator
circuit.  It really depends on your microphone, speech level, and room acoustics. 

Arv  K7HKL

On Thu, Aug 22, 2019 at 2:15 AM Ian Reeve <ian.radioworkshop@...> wrote:
The uBITX as it stands sends a positive voltage to the unit that sends the mic signal,how do you arrange a one transistor amplifier to work without a separate supply.I have tried and failed.Any help or a schematic would be great. Thx. Ian M0IDR

From: <> on behalf of Gordon Gibby <ggibby@...>
Sent: Wednesday, August 21, 2019 10:26:40 PM
To: <>
Subject: Re: [BITX20] Audio pre-amplifier for microphone?
A simple one transistor preamp makes a huge improvement, but don’t overdrive the amplifier!

On Aug 21, 2019, at 16:52, Neil Tolman via Groups.Io <k1nbt@...> wrote:

Has anyone used a mono pre-amp for the mic on the v5 uBITX?
Any thoughts or references would be helpful.
Thank you and 73,
Neil K1NBT

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