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Speech Compressor for FT-817

Ondrej Kolonicny (OK1CDJ) on February 22, 2006
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Speech Compressor for FT-817

Ondřej Koloničný, OK1CDJ

FT-817 doesn't have any type of speech processing built-in.This audio speech compressor is designed with the Analog Devices SSM2165 device. The circuit is small enough that it can be built into the microphone.Gain of whole circuit is about 18dB, compression ratio is set by R1 and can be varied from 1:1 to 15:1. Output level can be set by R2, R3. Power consumption is around 7.5mA. Compressor is supplied directly from microphone, no external power supply is needed.

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Fig. 1 - schematic

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Compressor is completely build using SMT on small board (15x11mm).

Fig. 2 - PCB

Part list:

C1 22uF /10V size B

C2 10uF /10V size B

C3 10uF /10V size B

C4 100nF 0805

C5 100nF 0805

C6 1nF 0805

C7 100nF 0805

IC1 SSM2165 SO08

R1 180k 0805

R2 22k 0805

R3 620 0805

Installation procedure

Installation of compressor. To MH-31 microphone requires skill with a soldering iron and other tools! Sometimes people have problem with RF-Audio feedback when using indoor whip antennas, than you need place ferriete breads or RF choke on power supply wire and on wire from microphone element.

  1. Remove the three screws from the rear of microphone and take off Back Cover

  2. Unsolder the white wire that is connected to the PCB at the location indicated by red circle # 1.

  3. Remove (by solder wick) solder on the pads locted by red circle #2

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  1. Remove three black screws that attach the PC board to the front case.

  2. Remove the PCB from front case

  3. Remove the capacitor.

  4. Next remove the wire connecting lug C on the Tone switch to point F on PCB.

  5. Wire from poit B move and solder to point F

  6. Next you need 4 pcs of wire, lenght aprox. 3cm (1.5 inch)

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  1. White wire from mic element solder to pad marked I on compressor PCB

  2. From pad marked I on compressor PCB solder first pcs of wire to lug A on switch.

  3. From output (pad marked O on compressor PCB) solder next wire to lug C on switch.

  4. Put back microphone PCB and srew taht you removed in Step 4.

  5. Connect GND of compressor (see picture) to point indicated by red circle#1 and power (on commpressor PCB marked by +) to point #2

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  1. Put commpressor to the microphone (see picture) and fix it by double sided tape.

  2. Replace the microphone Back Cover onto microphone

  3. Compressor is controlled by tone switch on the Back Cover of MH-31 microphone. Position #1 is ON and position #2 is OFF.

If you have any questions send me mail to

You can order KIT (contains documentation, professional quality PCB and all parts need to build) or complete board ready to build in to MH-31 microphone from

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Member Comments:
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Speech Compressor for FT-817  
by K8MHZ on February 22, 2006 Mail this to a friend!

Great article, thanks for taking the time to share this with us.

It sure looks like this can be used in many radios that have no compression.

Would this be applicable with no changes for older high impedance mikes on tube type rigs?


Mark K8MHZ
RE: Speech Compressor for FT-817  
by KG4RUL on February 22, 2006 Mail this to a friend!
WOW! The next level will be including the whole radio in the mic case.

SMT technology is marvelous but, be prepared to invest in a really good magnifier and soldering station if you plan on constructing or servicing equipment made with these devices.

Dennis KG4RUL
RE: Speech Compressor for FT-817  
by WA1RNE on February 22, 2006 Mail this to a friend!
by K8MHZ on February 22, 2006

Would this be applicable with no changes for older high impedance mikes on tube type rigs?

> >The source impedance most crystal mics will work into and maintain enough drive and low end fidelity is approx. 0.5 to 5 megohms - preferably on the high side.

The SSM2165's input Z is 180k, so an FET follower with some gain - say enough to provide 100mv rms to the 2165's input would work well. The parts count for this preamp is low so it would not require much more in the way of pcb real estate.

The only drawback might be the fixed noise gate threshold of the 2165. The 2166/67 are adjustable and have a higher threshold, -40 dBV versus -66 dBV for the 2165.

73, Chris
RE: Speech Compressor for FT-817  
by KN7T on February 22, 2006 Mail this to a friend!
In addition, there was a really great article in last month's QST about an outboard speech processor project for the FT-817 that uses the 2166 chip if you're into building something a little more complex.
RE: Speech Compressor for FT-817  
by K0BG on February 22, 2006 Mail this to a friend!
This is a nice article, and well written and documented. However....

There are several problems with respect to speech processors, and none of the included documentation (including the URLs) have any information about adjusting them, or when to use or not to use them. Almost universally, they are used all of the time, and with too much compression dialed in.

In this case, the radio in question is primarily a portable one. Similar radios are designed primarily for mobile use. Both essentially use battery power to run them; a comparably unstable power source. Add an over amount of speech processing, you not only shorten battery life, the associated IMD products increase noticeably.

Since there seems to be another resurgence of speech processors, an article about their proper use (or lack of it as the case may be), is in order.

Alan, KBG
Speech Compressor for FT-817  
by W6VPS on February 22, 2006 Mail this to a friend!
Well done article. Very informative.

Also I think the product is identical in purpose (though perhaps more modern in design) to the
"One Big Punch" speech processor for MH-31 microphones available from W4RT Electronics
RE: Speech Compressor for FT-817  
by VA3TR on February 23, 2006 Mail this to a friend!
For those of us that are challenged when it comes to finding parts and building, does anyone know if there is a kit version of this device?
RE: Speech Compressor for FT-817  
by N1GNV on February 23, 2006 Mail this to a friend!
Unlikely.... unless you're willing to go through all the work of reading the original article and clicking on the link provided.

>>For those of us that are challenged when it comes to finding parts and building, does anyone know if there is a kit version of this device?
RE: Speech Compressor for FT-817  
by N0NV on February 24, 2006 Mail this to a friend!

Here is the direct link to the similar "One Big Punch"
sold by W4RT Electronics:

You can also see the manual at:

Jack - N0NV
Speech Compressor for FT-817  
by KC2MMI on February 25, 2006 Mail this to a friend!
Unless I'm misreading it, the chip maker is indicating that this chip is already being discontinued:

SSM2165-1P Obs...

All the versions appear as obsoleted or "last time buy" which seems to mean they'll be gone as soon as existing stock is depleted.
RE: Speech Compressor for FT-817  
by WA1RNE on February 28, 2006 Mail this to a friend!
The current status from Analog for the SSM-2165-1P is obsolete. This is a 8 pin PDIP version, or Plastic Dual Inline Package.

However, the SSM2165-2SZ is statused as Last Time Buy, which is the 14 pin SOIC version. Allthough not a match for the 8 pin DIP board layout, it could be adapted to it.

DigiKey currently shows 119 of the -2SZ's in stock for $3.87 each for qty = 1.

Chris, WA1RNE
RE: Speech Compressor for FT-817  
by N0NOB on March 2, 2006 Mail this to a friend!
Kit version available and info provided near the bottom of the article.
Speech Compressor for FT-817  
by DG2IAQ on March 4, 2006 Mail this to a friend!

A few additions to that great article:

This is nearly a copy of the "central" circuit of the german "FUNKAMATEUR Kompressor for the Yaesu FT-817" (, or for international orders via, ..-> see "DYC-817").

--> schematic + description:

As I own two of those accessories (one MH-31 internal, one external) I had my own experiences with that which I like to share here.


The OK1CDJ compressor is mainly designed for usage with electret capsules. The DYC-817 ( has an additional 1-stage adjustable transistor pre-amplifier. That would NOT mean, that the OK1CDJ compressor wouldn't work on dynamic capsules ! But it depends on the used dynamic capsule if it works with the permanent and not-to-turn-off noisegate, or if the input level would be too low to work properly. I tested several dynamic mikes and those with lower audio levels didn't open the noisegate safely, even not if I talked very close to the mic capsule.

On the other hand an electret capsule can cause a too high audio input level, so that the noisegate always would be open or "flickers" on each breathe-in of the operator. So the audio line of an electret capsule might to be reduced by a resistor in series to the INPUT (C6). Or you can use a resistor-divider, consisting of a series of 2k2 and a 1k to ground just before C6.

As the OK1CDJ simple compressor has no adjustments you have to play with the mic capsule or mic input level to work in the proper range.

I like to point out once more: This MIGHT happen, it MUST NOT happen ! I don't want to criticize this great, simple and really tiny circuit but I had my own bad experiences and for you it might save the time for the self-detection, ...hihi.


On some mic capsules you might hear a "PLOPP" sound on opening/closing of the noisegate. This can drive your QSO partner mad, ...hihi.

To prevent this ALWAYS use non-polarized capacitors for C6 (INPUT) and C4 (OUTPUT), e.g. ceramic types.

Another (and the better) trick is to put a 47k resistor in parallel to the Attack-/Release-Capacitor C1(22F = AVG CAP) ! This "smoothes" the attack-/release curve and eliminates the "PLOPP" sound in 99% of the cases.

And the noisegates acts much quicker with that resistor as it reduces the attack-/release time constant. On looking into the datasheet of the SSM2165 a 22F would be ok for MUSIC purposes. But in the QSO's you always hear a SIGNIFICANT raise of the audio level after you stopped talking and 1 - 2 additional seconds just before the noisegate would close. This drives your QSO partner mad as well, ..hihi.
On using the 22F with the 47k in parallel the noisegate would close immediately after you stopped talking or after you would make a short break (e.g. for breathe in). I call this "..the noisegate is "glued" to your speech..", ..hihi.

That's all.

One or maybe both two little "adjustments" and the compressor would "improve your life" as well, ...hihi.

RE: Speech Compressor for FT-817  
by WA2JJH on March 8, 2006 Mail this to a friend!
Speech procs can help, they can also cause splatter.

I have seen a few designs where the proc was of the of the RF type.

The mic capsules audio is upconverted to 500khz. The
corresponding LF-RF signal is compressed and clipped.
At 500khz, the RF signal is then easy to filter with a 2 pole xtal filter. The RF is then downconverted back to audio.

One still has to be carefull not to over drive the rigs mic input. One could induce the exact same audio distortion as the simpler audio procs.

Even when I use the RF speech proc in my Kenwood TS-950SDX, I disable the proc. if I can maintain the DX contact without it.

Thanks for the very detailed artical. Even the simpler audio proc. can do wonders. However check your rigs ALC response when setting the amount of audio compression.

It is nice to make that extra contact. However as another poster mentioned, it can be all to easy to splatter.
Speech Compressor for FT-817  
by OK1CDJ on March 26, 2006 Mail this to a friend!
Hello, you can buy kit or complete board here:

73 Ondra OK1CDJ
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