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I7SWX PTT Pop Mute

KC8WBK
 

It is the schematic labeled: "BITX-40 TRIAL 4 PTT CLICKS FIX 3"

https://groups.io/g/BITX20/attachment/30784/0/BITX_40%20PTT%20CLICKS%20V3.png

It should be linked above, and it is also attached to one of Gian's posts below.

Dexter N Muir
 

My installation of this, as per diagram, reduced the 'pop' but didn't eliminate it. A fresh look at the diagram, with eyes accustomed to audio amps with differential inputs just like this, led me to the conclusion, borne out in practice, that Pin 3 is the best mute point. I don't know what currents flow, but with both pins 2 and 3 'earthed' what can go wrong? Pin 7 to earth gave just as much 'pop', if not more! Earlier trial by shorting the volume control wiper to 'earthy' side produced all sorts of squeals - track and lead capacitances playing tricks? Anyhow, my version, on veroboard floating loose on a couple of inches of ribbon cable wire, is quite stable.
The Vero module is dual-purpose: along with the anti-pop there is a 'super-cap', 100uF with an emitter follower to feed Q16 by 'tombstoning' R113. Complete elimination of tuning-click hash. All this on 0.6" x 0.6". All components sourced from a scrapped PC PSU (which also provided a toroid for a balun :) ). Photo(s) to follow if anyone's interested ...
Earlier reference to audio helped with this construction too. Years back (70's?) I created a stereo amp with Sanken 20W module power amps and preamp built around 4 discrete-component op-amps (essentially 741's), and I squeezed each of these into not much more 'real estate' than this latest effort. Memory dims, but if they were more than 1" square it wasn't by much. Circumstance forced disposal: some lucky audiophile got the ultimate quality there! :)

Art Olson
 

Dexter

Glad all worked out for you. Looking forward to pictures 

Art
 N2AJO

Sent from my iPhone

On Aug 11, 2017, at 4:02 PM, KC8WBK via Groups.Io <cruisenewsnet@...> wrote:

It is the schematic labeled: "BITX-40 TRIAL 4 PTT CLICKS FIX 3"

https://groups.io/g/BITX20/attachment/30784/0/BITX_40%20PTT%20CLICKS%20V3.png

It should be linked above, and it is also attached to one of Gian's posts below.

Mvs Sarma <mvs_sarma@...>
 

Dexter,
 Nothing to fear while earthing both pin2 and 3.
regards
 sarma
 vu3zmv


On Sunday, 13 August 2017 4:35 PM, Dexter N Muir <dexy@...> wrote:


My installation of this, as per diagram, reduced the 'pop' but didn't eliminate it. A fresh look at the diagram, with eyes accustomed to audio amps with differential inputs just like this, led me to the conclusion, borne out in practice, that Pin 3 is the best mute point. I don't know what currents flow, but with both pins 2 and 3 'earthed' what can go wrong? Pin 7 to earth gave just as much 'pop', if not more! Earlier trial by shorting the volume control wiper to 'earthy' side produced all sorts of squeals - track and lead capacitances playing tricks? Anyhow, my version, on veroboard floating loose on a couple of inches of ribbon cable wire, is quite stable.
The Vero module is dual-purpose: along with the anti-pop there is a 'super-cap', 100uF with an emitter follower to feed Q16 by 'tombstoning' R113. Complete elimination of tuning-click hash. All this on 0.6" x 0.6". All components sourced from a scrapped PC PSU (which also provided a toroid for a balun :) ). Photo(s) to follow if anyone's interested ...
Earlier reference to audio helped with this construction too. Years back (70's?) I created a stereo amp with Sanken 20W module power amps and preamp built around 4 discrete-component op-amps (essentially 741's), and I squeezed each of these into not much more 'real estate' than this latest effort. Memory dims, but if they were more than 1" square it wasn't by much. Circumstance forced disposal: some lucky audiophile got the ultimate quality there! :)


KC8WBK
 

Regarding version 3:

If I wanted the mute to hold a few milliseconds after releasing the PTT, would a capacitor parallel with the 10k resistor at the base of the npn be the solution?

Dexter N Muir
 

As a friend of mine was fond of quipping: "Good t'inkin' O'Rourke, you're foired!" :) Well, the first part anyway ... There's still room for that, so I'll be trying it - there's still a fragment of 'pop' on release. T=RC, so 10k  gives about 10 milliseconds per uF. I doubt more than 1uF would be needed for the most persistent 'pop'. I suspect any remaining 'pop' would be the dis/reappearance of signal, and would most likely vary with the level of QRM/QRN prevalent.
Further rationale: earthing Pin 1 has to discharge a DC component (and allow it to recharge on release); not so pin 3.

Dexter N Muir
 

News and pictures will be delayed a week or so: I'm going to 'respite' at a retirement home (founded by my wife's brother). i'll still be in contact; I take along my Raspberry Pi.

KC8WBK
 

I am experiencing an intermittent 0.1kHz frequency shift on key down with version 3. 

KN4AAG Kevin Estep
 

Another data point on the V3 fix (using LM386 pin 1). This reduced the "pop" to a mere click that is much more acceptable.

Thanks Gian (and others) for the fix!

 

This is one of the issues with LM386. In my first board, whenever the volume was turned down the chip
produced a buzzing noise.

I feel that the wiper lead should have anything from 1K to 10K in series. This does not affect the volume.
With a resistor there is no instability.

Raj

At 13/08/2017, you wrote:

Earlier trial by shorting the volume control wiper to 'earthy' side produced all sorts of squeals - track and lead capacitances playing tricks?

Giancarlo
 

Hi,

 

I have not yet assembled my BITX-40 so sorry as I cannot help much with the trial, I do only “poetry” … hi.

 

1)      It is strange experiencing an intermittent 0.1kHz frequency shift on key down with version 3. This problem it is expected to be associated with LO1 or may be LO2. The current absorbed by the LM386 when muted at pin1 it is small and short duration, we may have a switching pulse generated by the driver and push-pull in addition too. Unless there is a pulse travelling on the TX +12V or ground modulating the oscillator, I do not see what can generate such change of frequency.

2)      Maybe we could try to keep the LM386 always powered in RX and TX and the pin 1 V3 muting circuit. This means to power the PA from +12V and removing the connection from R111. I am attaching a new schematic. This will avoid the PA driver and/or push-pull stage will not commutated. I suggest to add a 1K resistor from base to ground on the NPN transistor to be sure it keeps in the OFF state while in RX.

3)      Regarding the note that taking pin 3 to ground (input audio to gnd) silence the LM386 it may be possible but we have a higher current through the associated darlington transistors (1.2V at emitter) , in the IC, while with pin 1 to gnd we have a “real short” by the NPN muting transistor (probably 0.2V). The JRC NJM386 datasheet, reports that muting the IC with pin 1 to ground is a valid solution.

Thanks for spending the time with the trial.

Best 73

Gian

I7SWX

Jonathan Straub, N0JMS <jonmstraub@...>
 

Buonasera Gian,

I did not have any luck with this mod. While I tried the previous versions as well, the clicks remain throughout testing.

I did get the LM386 to mute properly by using a modified version of your Rev 5 schematic. I ran a 1n4148 from +12 to pin 6 of the amp, and used the collector of the 2n3906 through a 1n4148 to bring pin 8 of the amp high on PTT. The amp did not return from mute after PTT was released, however.

It should be noted my radio is up do date with Allard's code and hardware mods at Raduino v1.20.1.

Hopefully this will give some insight for the next steps.

Grazie,

Jonathan, N0JMS

Dexter N Muir
 

Hi Jonathan

Read later entries here - search on Gian's call or "PTT". My contribution: Gian's circuit except wire to pin 7 goes to pin 3. Try it, you'll like it.
73 de ZL2DEX ...

Jonathan Straub, N0JMS <jonmstraub@...>
 

Hi Dexter, 

Which version of Gian's schematic were you changing? My add-in board with his mod is currently at "Trial 5."

Whatever you suggest, I will try tomorrow after work. I want to remove this click as I am a headphone user when we go portable due to people talking.

Thanks,

Jonathan, N0JMS 

Giancarlo
 

Hi Jonathan,

thanks for your follow-up. I am sorry you are still having roblems with the pop.
I have just discovered I marked the wrong pin on my circuit diagram, I reported pin8 as the power input in place of pin 6. I am attaching the updated schematic.

Pin 1 should go to ground and not pin 8 to +12V via the 2N3904 collector. I hope the LM386 is still OK as I do not understand why it should not return from mute.

Please let me know. Thanks and 73

Gian
I7SWX

Jonathan Straub, N0JMS <jonmstraub@...>
 

Ciao Gian,

No worries about the LM386. It still works well. I have spares in the junk box if needed.

I was experimenting trying to discover other methods, and thought I would give what I described a try.

Will keep you posted.

Grazie,

Jonathan, N0JMS

Kevin
 

Can someone try grounding pin 1 of K2? That will take the input of the LM386 to ground when the PTT is pressed. Now pin 1 of K2 appears to be floating in the schematic I have. I've been working on a PCB to 'clean up' the Raduino some..
 

Dexter N Muir
 

Sorry, M1 and M2 are the other way around. Grounding K2.1 shorts the output of the pre-amp Q16 to earth on transmit, leaving the feed to the volume control and U1 open-circuit (and probably picking up hash). If you want to kill that 'pop' in and out of Tx, research back a few messages - I7SWX's circuit is a good start, Ted Doell and I have improved on that, and an earlier (much earlier) solution allows for CW sidetone (possibly also with better stability). Good luck - your 'logic' could use it ...
73

Kevin
 

I noticed that later last night (2am) on the M1/M2.. While looking at the drive required for the PTT relay I noticed the RX signal (+12 volt supply to the LM386) is switched by the PTT; Has anyone tried adding a 3.3k resistor to pin 6 of the LM386 and ground?
At any rate I came across K3NG Nano Keyer, I'm changing my layout to use his code. https://goo.gl/gfZqQY -- My 'Logic' normally stops around 10PM, that post was past my bedtime! Still waiting on my board.... My layout includes a TCXO for stability, +3 regulator instead of the nano 50ma source and voltage level shift for the Si5351, it does add a couple of dollars.    

Jonathan Straub, N0JMS <jonmstraub@...>
 

Everyone,

I have come up with a modification to Gian's circuit that makes the pop/click completely tolerable with headphones at full volume. Please see the attached modified schematic and report back with your results. The pop is still there, but does not tend to hurt the ears. I may get some crap for the layout/design, but I don't care. I am always open to friendly suggestions to make it better.



73

Jonathan, NØJMS