Topics

Audio pre-amplifier for microphone?

Neil Tolman
 

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

Gordon Gibby <ggibby@...>
 

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

Ian Reeve
 

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

Tom, wb6b
 

On Thu, Aug 22, 2019 at 01:15 AM, Ian Reeve wrote:
how do you arrange a one transistor amplifier to work
Here is a possibility that was posted some time ago.
http://ubitx.net/2018/12/05/dynamic-mic-preamp-runs-off-phantom-power-from-ubitx/

Tom, wb6b

Ian Reeve
 

Hi Tom,

 

Thankyou very much for pointing me towards this neat little circuit.

 

I have a dynamic mic insert so I will give it a go later today

 

Thx and 73

 

Ian M0IDR

 

Sent from Mail for Windows 10

 


From: BITX20@groups.io <BITX20@groups.io> on behalf of Tom, wb6b <wb6b@...>
Sent: Thursday, August 22, 2019 10:54:28 AM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] Audio pre-amplifier for microphone?
 
On Thu, Aug 22, 2019 at 01:15 AM, Ian Reeve wrote:
how do you arrange a one transistor amplifier to work
Here is a possibility that was posted some time ago.
http://ubitx.net/2018/12/05/dynamic-mic-preamp-runs-off-phantom-power-from-ubitx/

Tom, wb6b

SV9CVJ Nikos
 

Ian Reeve
 

Thx Nikos, I will take a look at the specifications of this, I tried one similar a while ago and found the gain far too much.Anything is worth a try,the modulation level on Ssb is far too low only producing around ,2 watts output on speech peaks.  Cheers. Ian M0IDR


From: BITX20@groups.io <BITX20@groups.io> on behalf of SV9CVJ Nikos <sv9cvj@...>
Sent: Thursday, August 22, 2019 12:28:08 PM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] Audio pre-amplifier for microphone?
 

Gordon Gibby <ggibby@...>
 

This is actually easier than it looks. Awful lot of microphones work exactly this way.    

 Life is easier for you if you simply bring out a dc positive voltage from the Radio as a separate work, but if you don’t want to do that, you can use a diode to rectify the microphone line, then run it into a big capacitor and bingo you have DC.   Used at DC to provide power for the electric through a resistor, about 2000 ohms.  Use a capacitor, about 10 µF, to take the output from the electric, to the base of a transistor.   The two N3904 would work fine.  Connect the emitter to ground.  Use simple biasing with a 470,000 ohm resistor from the base to the collector of the transistor.   Connect the collector directly to that DC biased microphone wire from the radio.   

Done.   

I’m in a car, so I can’t draw it for you.




On Aug 22, 2019, at 04:15, 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

Gordon Gibby <ggibby@...>
 

If the gain is too high for your taste, simply stick a 1000 to 10,000 a resistor in the emitter wire of the transistor

Instant negative feedback

On Aug 22, 2019, at 08:50, Ian Reeve <ian.radioworkshop@...> wrote:

Thx Nikos, I will take a look at the specifications of this, I tried one similar a while ago and found the gain far too much.Anything is worth a try,the modulation level on Ssb is far too low only producing around ,2 watts output on speech peaks.  Cheers. Ian M0IDR


From: BITX20@groups.io <BITX20@groups.io> on behalf of SV9CVJ Nikos <sv9cvj@...>
Sent: Thursday, August 22, 2019 12:28:08 PM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] Audio pre-amplifier for microphone?
 

Ian Reeve
 

Gordon,

 

Thx so much for the advice. I would rather use the existing”phantom” supply as I have fitted a miniature 3 pin mic socket. I will try both methods, I already have a switched dec supply on tx from the relay.

I have now three solutions and would thank you all for helping me out on this low audio problem on SSB.

 

I will use my oscilloscope to monitor the output direct from the mic and compare it to the level at the input to the uBITX to get a gain comparison between the different suggestions

 

Having fun with uBITX!

 

73

 

Ian M0IDR

 

Sent from Mail for Windows 10

 


From: BITX20@groups.io <BITX20@groups.io> on behalf of Gordon Gibby <ggibby@...>
Sent: Thursday, August 22, 2019 3:02:22 PM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] Audio pre-amplifier for microphone?
 
This is actually easier than it looks. Awful lot of microphones work exactly this way.    

 Life is easier for you if you simply bring out a dc positive voltage from the Radio as a separate work, but if you don’t want to do that, you can use a diode to rectify the microphone line, then run it into a big capacitor and bingo you have DC.   Used at DC to provide power for the electric through a resistor, about 2000 ohms.  Use a capacitor, about 10 µF, to take the output from the electric, to the base of a transistor.   The two N3904 would work fine.  Connect the emitter to ground.  Use simple biasing with a 470,000 ohm resistor from the base to the collector of the transistor.   Connect the collector directly to that DC biased microphone wire from the radio.   

Done.   

I’m in a car, so I can’t draw it for you.




On Aug 22, 2019, at 04:15, 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

Arv Evans
 

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

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

VK3HN
 

I bought one of these to experiment with, thinking there may be an op amp gain stage between the electret and the A pin (audio out). Unfortunately, there isn't. So unless you want a VOX, this module doesn't improve over an electret mic insert and a series resistor to the phantom DC supply. Note also that A has DC on it, there is no series capacitor. 

There is apparently a similar Arduino/breakout module, about the same size, with an on-board electret insert, that does have an op-amp gain stage, leading to an audio output.  This could replace the mic amp on a homebrew exciter.  I am not thinking of the SSM2167 modules which are another thing altogether.   If anyone knows where these are, please post a URL.

73 from Paul VK3HN.  

Paul KL7FLR
 

Paul,
Might this be what your looking for?  https://www.adafruit.com/product/1713

Paul
KL7FLR

Dennis Zabawa
 

I have one sitting on my bench that I have not had the chance to wire up.  From the specs, it looks ideal for the task.

Gordon Gibby <ggibby@...>
 

It looks like an excellent solution.  


On Aug 23, 2019, at 16:01, Dennis Zabawa <kg4rul@...> wrote:

I have one sitting on my bench that I have not had the chance to wire up.  From the specs, it looks ideal for the task.

Don, ND6T
 

Here is what I use: A dynamic mic element feeding a 3-component common-base amplifier. Fits right inside the microphone case. Matches the 600 ohm element to the pre-amp and great frequency response.
Doesn't get much simpler. 73, Don

Tom, wb6b
 

On Fri, Aug 23, 2019 at 04:50 PM, Don, ND6T wrote:
common-base amplifier
It is great to be reminded that there are other configurations than the knee-jerk choice of common emitter.

Because the impedance of the microphone is low and you are basically trying to raise the voltage, not so much the current, this works just like the ever popular common grid arrangement of vacuum tube days of the (not completely) past.

Tom, wb6b

Donald <donwestpwl@...>
 

Once again, very good art work from ND6T. --KB5PWL, Donald

Voitto Vataja
 

How to connect this to uBITX?
Vote oh3jve