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

 

Ian M0IDR

 

Sent from Mail for Windows 10

 


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

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: BITX20@groups.io <BITX20@groups.io> on behalf of Gordon Gibby <ggibby@...>
Sent: Wednesday, August 21, 2019 10:26:40 PM
To: BITX20@groups.io <BITX20@groups.io>
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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