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#ubitx SSM2167 mic compressor speaker feedback issue - resolved #ubitx

John <passionfruit88@...>
 

I thought I would mention this as it could be helpful to someone.

In another thread there was the mention that inserting an SSM2167 mic compressor circuit between the microphone and the uBitx mic-preamp would create some feedback when the microphone was placed near the speaker while in Rx.

The solution I applied was to connect the shutdown pin of the SSM2167 (pin 3) to the Raduino T/R digital output (D7) through a 47KOhms resistor. This disables the chip while in RX and removed the mic feedback issue.

Thanks Simon, VK3ELH for pointing out that issue. 

73, John (VK2ETA)

Picture below of where I picked up the pin 3 on the SSM2167 on my module. The purple wire is connected to what is the right hand side of the R4 resistor on my picture. The 4.7KOhms resistor on the RHS is for the mic-bias and the 51KOhms on the top-left is for bringing the compression ratio towards 4.



Nigel G4ZAL
 

Great info - thanks.
My SSM2167 module has just landed from the slow boat...

Nigel.

KE0GYC
 

Thanks for the great post!  I ordered a couple of these myself and have been trying to figure out how they wire up with an electret mic.  This probably just saved me a ton of headache.  I had a couple questions on your setup.

Do you need a DC blocking cap?

Does the 4.7K resistor provides VCC for the chip from the mic bias, or do I need to provide VCC separately?

The 47K resistor you mentioned is between the D7 Raduino wire and the header pin connected to the purple wire, and is not pictured, correct?

John <passionfruit88@...>
 

I feed the Vcc of the board from the regulated 5V of the Raduino. I measured its consumption at 2mA which is a very small extra load on the Raduino regulator.

There is a DC blocking cap on the input and output on the board. So no external blocking capacitors needed, and also this is why I had to add the bias resistor.

Correct, the 47KOhms resistor is external, not shown on the picture.

Also not shown on the picture are an axial choke of 100uH between the in pin and the Mic, plus a 1nF capacitor between the in pin and ground to block RF feedback when Txing on the higher frequencies. For me the feedback was noticeable from 15m to 10m. You may not have that issue.

I also have a 10kOhms adjustable potentiometer between the out pin and the original Mic input to the uBitx. Mine is turned to about 80% of its range.

I mounted my board on header pins so I can remove it if I want to, and I extended the header pin on the out side (bottom LHS on picture) past the board to provide and extra connection for the shutdown wire.

I think that the compression and noise gate work quite well on this circuit. When I am silent the background noise does not trigger any movement of the power needle, but it goes up as soon as I speak in the Mic. Also despite showing quite an increase in average power I haven't had any negative comments on my audio. I was told that it was noticeable, but not unpleasant, "good for DX".

And this was with the resistor added for the 4/1 compression.

73, John (VK2ETA)

John <passionfruit88@...>
 

I noticed an error in my resistor value for the shutdown pin. I listed it as 47KOhms in my original post, and in fact I ended up with a 2.7KOhms.

It will work with higher values but it will not blank the mic input 100%.

Sorry for the mistake.

73, John (VK2ETA)

alans77@...
 

John: Where did you pickup D7 on the Raduino?
73,
Alan N4AYE

John (vk2eta)
 

Hello Alan, yes I have added a little 4 pin molex connector for D7 (T/R), the two I2C bus lines and +5V for my 2nd Arduino.

All the best,

73, John

KE0GYC
 

Is there an equivalent point to connect the shutdown pin to on the bitX40?  D7 doesn't appear to work on mine.

Peter LB0K
 

Where can one acquire these modules with an SSM2167 from ?

Ralph Mowery
 

On Sun, May 20, 2018 at 5:14 PM, Peter LB0K <lb0k@...> wrote:
Where can one acquire these modules with an SSM2167 from ?
_._,_._,_


MVS Sarma
 

Kevin Rea
 

Hi John,
could you perhaps put up a schematic drawing of everything you did to install this module ?

thanks,
kevin rea
k6rea
lancaster, calif.

John (vk2eta)
 

Hello Kevin,

I will.

73, John (VK2ETA)

Kevin Rea
 

HI John,
I just had a problem understanding where you put the 10k pot to adjust the output of the amp.
the write up on: https://ubitx.net/tag/vk2eta/
says this:
John also has a 10K adjustable potentiometer between the “out” connection on the module and the original Mic input to the uBitx.  

I just don't quite understand that.. I would think you would put the pot on the output, at the + output of the module and the purple wire going to the microphone element itself ?

kevin

Kevin Rea
 

here is the picture i found of your connections...

Kevin Rea
 

never mind.. i figured it all out..
works good.
thanks for the info you put up on this John.

Kevin 

John (vk2eta)
 

Hi Kevin, 

Glad you sorted it out. Enjoy.

73, John

John (vk2eta)
 

Schematic as per Kevin's request. Too late for him as he resolved the issue by himself but may be useful for others.



Picture of 4 pin molex connector added to the V3 Raduino for pickup of T/R (D7), +5V, I2C SDA, I2C SLD.

Please note that the Arduino was replaced and put on headers as I have a remote LCD display.





Source of SSM2167 module as per previous posts in this thread.

A friendly reminder that raising the mic drive was linked with a rise in spurs (plenty of threads of this).

73, John (VK2ETA)

Kevin Rea
 

hi John,
thanks from everyone for the schematic.
I made a larger copy for everyone just in case it helps.

Kevin Rea

Kevin Rea
 

oh, it doesn't show up as larger.. oh well.

kevin