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Re: Audio pre-amplifier for microphone?


Ian Reeve
 

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Hi Arv,

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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.

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

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Best 73

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Ian M0IDR

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Sent from for Windows 10

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From: [email protected] <[email protected]> on behalf of Arv Evans <arvid.evans@...>
Sent: Thursday, August 22, 2019 4:47:35 PM
To: [email protected] <[email protected]>
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
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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

Get


From: [email protected] <[email protected]> on behalf of Gordon Gibby <ggibby@...>
Sent: Wednesday, August 21, 2019 10:26:40 PM
To: [email protected] <[email protected]>
Subject: Re: [BITX20] Audio pre-amplifier for microphone?
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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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