SSM2167 board – improving compression control

Brad N8YG has been reading over posts concerning the ssm2167 compression pre-amplifier with quite a bit of interest. So he finally integrated the board into his ubitx v5.

He put a trimmer on the output of the board, and potentiometers on the compression, and noise gates. The problem that he ran into was that on the air, rotating the 100K compression potentiometer had little to no effect.  However he was getting compression that was clearly audible on the air.

He re-read the data sheet for the ssm2167 more thoroughly and found that the input voltage need to be quite low at -20 to -30 dBV.  A quick check on the electret microphone output using the oscilloscope, showed a much higher output from his microphone.

This led to him adding another pot to trim the input voltage.  He still needed the 5V to get to the electret so he wanted the trimmer after the 0.1 uF surface mount capacitor on the board.

Brad modded the board by removingthe 0.1 uf capacitor, and he made connections for the trimmer after the 0.1 uF capacitor.

The net result is a board with three additional potentiometers and one trimmer.  The trimmer adjusts the output voltage, and potentiometers control the input voltage to the board, compression and noise gate.

On the air.. with the compression potentiometer turned down the rig sounds like it has no compression… while turning up the potentiometer makes a profound difference in on the air sound.  The rig now has a LOT of punch and the power meter goes way up.   

Brad believes that what was happening was that the input level was too high forcing the chip into the limiting portion of the transfer curve.  Now that the chip is operating back in the linear portion, all is well!  

Reference

Mini-microphone for your uBITx

David N8DAH suggests you can use your µBITx stock switch and microphone element with this nifty mini-microphone case from Kit Projects.  They cost US$10 plus shipping.  These are 3d printed  with all hardware included (Mic’s use the stock element and tac button that came with your bitx40 or ubitx).

Kit Projects has red and black microphones right now and grey is coming soon!

The also have 3D printed mini paddles available to purchase, that may be of interest to µBITx constructors.

Reference

SSM2167 install details

John VK2ETA some time ago provided information about his experiments with the SSM2167 module available on eBay.com and Aliexpress.com for a few dollars.   The following shows the wire up diagram:

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

Note that the Arduino was replaced and put on headers as John uses a remote LCD display.

Reference

A microphone pre-amp with no additional power requirement

Karsten DB7JB provides this simple circuit to boost mic gain (perhaps if you are quietly spoken) that does not require any modification of the μBitx board. It is powered off the existing microphone line (which already provides bias for the electret microphone).   It could be built right into your microphone housing, given it has only seven parts and the electrolytic capacitors are very low voltage components.

With the supplied electret microphone in the kit you will get additional gain for fully modulating your SSB signal. However, you will need to be careful not to overdrive the mixer, which as Allison has indicated in her post, is easily over-driven, which can result in spurious emissions from unintended mixer products.  

 

 

Some great mods from PH2LB

 

Lex PH2LB  wrote to uBITx.net to tell us about a page on his website where he describes his uBitx (V3) mods.   This is a very nice build, and he has some good ideas.   Check his page out here

http://www.ph2lb.nl/blog/index.php?page=ubitx-mods

In particular Lex has developed some custom firmware that firmware geeks may be quite interested in …

“Second mod : custom firmware”

Originally based on the v2 software but merged to v4.3 and updated to code to have a lower RAM footprint (usage of F(…) macro and strcpy_P) with about 50%.

Source files can be found here : https://github.com/ph2lb/ubitx4

Over the last few months there have been a range of ideas to boost mic drive output or to add compression.  Here’s a mod designed to work with a dynamic microphone …

“Fourth mod : dynamic microphone amplifier.”

Because I like to work with dynamic microphones, I added a dynamic microphone amplifier based on the microphone preamp designed by Javier Solans Badia, EA3GCY for his ILER transceivers.

There are a whole bunch of ways to add buttons. KD8CEC does this through paralleling up buttons with different series resistor values on the encoder analogue port).   Lex has taken a different approach that will be of interest to some constructors.   He uses a PCF8574 I2C encoder (like the backpacks for a 16×2 or 20×4 LCD display) and uses the existing I2C bus…

“Fifth mod : again adding extra buttons.”

Using a PCF8574AP I2C IO Extender and hooked it up to the all-ready existing I2C bus on the Raduino for more direct menu buttons. Needs the custom firmware to direct switch between bands with a PA bandplan limitation (also has FULL option) and Step size up and down.

 

Something that a number of constructors have done is to remove the 7805  and supply 5v to the Raduio using a separate 5v supply.  Most are using buck or buck boost modules, but Lex has used a P-MOSFET.   There’s a good description of his approach on his website …

“Sixth mod : removing 7805 from Raduino and reverse power protection.”

Relocating the 7805 is a good idea, but adding a reversed voltage polarity to a uBitx is a must. I used a P-MOSFETs for that (also link to good video about using P-MOSFETS for reverse power protection).

Finally, you may be interested in Lex’s use of the Manhattan style technique for PCB layout.  It can look very professional as per this example:

Microphone idea

Dave KD0UYH has made a microphone from an old desk lamp purchased from a “resell it” shop.  He says, “Not much to look at, but it serves my purpose. Used some vacuum tubing to attach the mic element and hot glued a handful of nuts into the base to give it some weight.”