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Hi all, this is John, AD0RW, new to the group. I have built my BITX40 board into a full-featured transceiver, adding CW (a must for me), AGC, XIT/RIT, built-in keyer and SWR monitor, among other things. One of the last issues I needed to nail down was the PTT thump, which was a real annoyance. I came up with a circuit that does the job nicely and is much simpler than the muting board that was offered for the 3B/3C. Here it is: 
The concept is simple: put a short across the LM386 input very quickly when PTT goes low, before the relays have time to close causing the audio noise. C1 and R2 hold the muting on for a short time after PTT goes high to cover the relays' opening. R2's value was arrived at by experiment, and a 470k should work just as well but may be easier to find. R3 and R4 are only needed if you have a CW sidetone that you need to inject during transmit. The adjustable sidetone level is valuable because with this arrangement the volume control has no effect on it. With this addition, the rig is now a real pleasure to operate. 73, John
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So does this go between the wiper and the wire currently hooked up..Brown wire.. Just need a lil more detail and I'll carve this up tonight.? Any pictures or anything else that could help.
On Sun, Apr 30, 2017 at 6:28 PM, John Pieper <j.pieper@...> wrote: Hi all, this is John, AD0RW, new to the group. I have built my BITX40 board into a full-featured transceiver, adding CW (a must for me), AGC, XIT/RIT, built-in keyer and SWR monitor, among other things. One of the last issues I needed to nail down was the PTT thump, which was a real annoyance. I came up with a circuit that does the job nicely and is much simpler than the muting board that was offered for the 3B/3C. Here it is: 
The concept is simple: put a short across the LM386 input very quickly when PTT goes low, before the relays have time to close causing the audio noise. C1 and R2 hold the muting on for a short time after PTT goes high to cover the relays' opening. R2's value was arrived at by experiment, and a 470k should work just as well but may be easier to find. R3 and R4 are only needed if you have a CW sidetone that you need to inject during transmit. The adjustable sidetone level is valuable because with this arrangement the volume control has no effect on it. With this addition, the rig is now a real pleasure to operate. 73, John
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Steve, That's right...inserted in the wire between the volume control wiper and the connector on the BITX board. I built mine on a bit of vectorboard that I had mounted off a bit to the side specifically for afterthoughts like this. It really shouldn't be critical though. Just tap onto 12V and the PTT at some convenient point and run wires over. Don't forget the ground connection--I have done that on occasion! John
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Yea I spent hours trouble shooting that oops missing ground.? Thanks I'l have this done in the morning.
On Sun, Apr 30, 2017 at 10:06 PM, John Pieper <j.pieper@...> wrote: Steve, That's right...inserted in the wire between the volume control wiper and the connector on the BITX board. I built mine on a bit of vectorboard that I had mounted off a bit to the side specifically for afterthoughts like this. It really shouldn't be critical though. Just tap onto 12V and the PTT at some convenient point and run wires over. Don't forget the ground connection--I have done that on occasion! John
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Dumb question but I should be able to use a 2n2907 in place of the 3906 right
On Sun, Apr 30, 2017 at 10:06 PM, John Pieper <j.pieper@...> wrote: Steve, That's right...inserted in the wire between the volume control wiper and the connector on the BITX board. I built mine on a bit of vectorboard that I had mounted off a bit to the side specifically for afterthoughts like this. It really shouldn't be critical though. Just tap onto 12V and the PTT at some convenient point and run wires over. Don't forget the ground connection--I have done that on occasion! John
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I think the 3906 is a PNP transistor.? I think the 2907 is a npn... It will not work.
Marco - KG5PRT?
On Apr 30, 2017 9:57 PM, "Steve Greer" < km4ous@...> wrote: Dumb question but I should be able to use a 2n2907 in place of the 3906 right
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Steve:
Probably, The 2N3906 and 2N2907 are more or less interchangeable.
It should work.
john
AD5YE
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I should have looked first.? It should work.? It seems to be a PNP transistor.? I was wrong.
Marco - KG5PRT?
On Apr 30, 2017 10:04 PM, "M Garza" < mgarza896@...> wrote: I think the 3906 is a PNP transistor.? I think the 2907 is a npn... It will not work.
Marco - KG5PRT?
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I think you are confusing the 2N3906 (PNP) and the 2N3904 (NPN).
It is easy to do. They are complementary.
john
AD5YE
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Something else I should mention: I have been puzzled by the circuit around the K1 coil, and suspect that it might not optimally protect any semiconductors connected to the PTT line. So before doing this mod, I installed another diode across the K1 coil in the conventional manner (see K2). Just a little cheap insurance. John AD0RW
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John Wondering if the added diode alone did anything? ?Did you try this by itself?
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Are you referring to the 2 diodes for strong signal rejection?? So you added to same pins as K2?
On Mon, May 1, 2017 at 1:07 AM, John Pieper <j.pieper@...> wrote: Something else I should mention: I have been puzzled by the circuit around the K1 coil, and suspect that it might not optimally protect any semiconductors connected to the PTT line. So before doing this mod, I installed another diode across the K1 coil in the conventional manner (see K2). Just a little cheap insurance. John AD0RW
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NM I just read it a 3rd time you said the coil not the tx/rx switching. So just between the coil power cathode to +
On Mon, May 1, 2017 at 7:02 AM, Steve Greer <km4ous@...> wrote: Are you referring to the 2 diodes for strong signal rejection?? So you added to same pins as K2?
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Tried this tonight and it works!
Only small issue is that when the volume is on full there is an audio oscillation. Its right at the end of the pot though so not a problem because i never turn it up full volume. There is also some digital noise from the raduino leaking through the power supply i think that comes through the audio whilst the cap on the receiver power supply still has some charge. Hoping the click power supply mod will get rid of it.
A massive improvement overall and i can now use my BITX40 witb headphones as i found the ptt pop literally painful without this mod. Also tried the diode across k1 by itself first. There was no change to the ptt pop.
Thanks and 73 John.
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I built this up today and it made a world of difference. I used a 470K and installed R4 in case I want to add the side tone later. Thanks! Jeff N9ARZ
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I was unable to make this work not sure what I did wrong only thing different was the PNP transistor.? Maybe if someone has some pictures of what they did that would help me see what I did wrong.? I only get a reduced audio level and by having my lm386's gain cap removed it's too low.? So I will look over this circuit again, it's working for others so it must be something I did.
On Mon, May 1, 2017 at 11:49 PM, Jeff <jeff@...> wrote: I built this up today and it made a world of difference. I used a 470K and installed R4 in case I want to add the side tone later. Thanks! Jeff N9ARZ
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I must add I do have farhan's AGC inline as well and may be causing undesired affects
On Tue, May 2, 2017 at 6:16 AM, Steve Greer <km4ous@...> wrote: I was unable to make this work not sure what I did wrong only thing different was the PNP transistor.? Maybe if someone has some pictures of what they did that would help me see what I did wrong.? I only get a reduced audio level and by having my lm386's gain cap removed it's too low.? So I will look over this circuit again, it's working for others so it must be something I did.
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Steve, Is your audio reduced all the time? If so, a couple of things I can think of: (1) If you have a sidetone, it does need to have a fairly hefty input level so that the pot R3 doesn't have to be turned way to the low-resistance end to hear it (that could load down the LM386 input), or (2) either your 2N7000 might be defective (leaky), or Q1 might be leaky and partially turning it on in receive. If it's OK in receive but just doesn't mute completely, it's possible that your Q1 needs to be driven harder than the 2N3906 does. Maybe try reducing R1 to 1k and see if that makes a difference. John
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Well I have removed the Cap on pins 1-8 on the lm386 which reduces the audio level and sounds cleaner.? Do you think i need to run the PNP transistor in darlington to function correctly?? No sidetone.
On Tue, May 2, 2017 at 4:23 PM, John Pieper <j.pieper@...> wrote: Steve, Is your audio reduced all the time? If so, a couple of things I can think of: (1) If you have a sidetone, it does need to have a fairly hefty input level so that the pot R3 doesn't have to be turned way to the low-resistance end to hear it (that could load down the LM386 input), or (2) either your 2N7000 might be defective (leaky), or Q1 might be leaky and partially turning it on in receive. If it's OK in receive but just doesn't mute completely, it's possible that your Q1 needs to be driven harder than the 2N3906 does. Maybe try reducing R1 to 1k and see if that makes a difference. John
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Jeff