开云体育

Hi all,

I was googling around a bit, thinking of changing the gain on the
lm386, and found a simple solution for the popping problem.

I found in some reading that pin 7 can be used for muting the
amplifier. Muting will occur if either 0V or Vcc is applied to pin 7.
So I simply installed a 1N4148 diode between the transmit supply line
and pin 7 of the lm386 so that it conducts Vcc to the pin upon closing
of the ptt switch. There is still a small pop occuring after this mod,
but it is reduced in magnitude by a great amount. I feel this is a
nice mod and in keeping with the KISS theme of the BITX line :-)

I will put some photos up of my pcb after the mod, but it pretty easy
to do on the backside as the 4-pin readymate connector header is just
next to pin 7 on the lm386 and a diode reaches very easily between the
two.

I also read that it is recommended, when using increased gain on the
lm386 (like we are), to have a 1-10uF capacitor installed between pin
7 and ground in order to reduce power supply noise problems (see the
second graph on the datasheet). This in itself helped a little bit
with the pop problem (I tried this mod first) in that the pop sound
changed from a "squeal" to a "crunch" which was a bit less unpleasant
hi hi.

This mod is also easy to do on the backside as a small radial lead
electrolytic or tantalum cap can be laid down along the pins of the IC
and leads soldered between pins 7 and 2 (which is grounded).

Cheers and have a great day everyone!

Mark - N7EKU

Hi all,

I was googling around a bit, thinking of changing the gain on the

lm386, and found a simple solution for the popping problem.

I found in some reading that pin 7 can be used for muting the

amplifier. Muting will occur if either 0V or Vcc is applied to pin 7.

So I simply installed a 1N4148 diode between the transmit supply line

and pin 7 of the lm386 so that it conducts Vcc to the pin upon closing

of the ptt switch. There is still a small pop occuring after this mod,

but it is reduced in magnitude by a great amount. I feel this is a

nice mod and in keeping with the KISS theme of the BITX line :-)

I will put some photos up of my pcb after the mod, but it pretty easy

to do on the backside as the 4-pin readymate connector header is just

next to pin 7 on the lm386 and a diode reaches very easily between the

two.

I also read that it is recommended, when using increased gain on the

lm386 (like we are), to have a 1-10uF capacitor installed between pin

7 and ground in order to reduce power supply noise problems (see the

second graph on the datasheet). This in itself helped a little bit

with the pop problem (I tried this mod first) in that the pop sound

changed from a "squeal" to a "crunch" which was a bit less unpleasant

hi hi.

This mod is also easy to do on the backside as a small radial lead

electrolytic or tantalum cap can be laid down along the pins of the IC

and leads soldered between pins 7 and 2 (which is grounded).

Cheers and have a great day everyone!

Mark - N7EKU

Any time Arv,

Let me know how it works for you...

73s,

Mark - N7EKU

--- On Tue, 9/13/11, Arv Evans <arvid.evans@...
<mailto:arvid.evans%40gmail.com>> wrote:

From: Arv Evans <arvid.evans@... <mailto:arvid.evans%40gmail.com>>
Subject: Re: [BITX20] A simple mod for the ptt pop squeal problem...
To: BITX20@... <mailto:BITX20%40yahoogroups.com>
Date: Tuesday, September 13, 2011, 7:48 PM



Mark N7EKU

Nice mod. I will try it on the BITX20A that is lying on my workbench.

Thanks for the information.

Arv K7HKL

_._

On 09/13/2011 09:44 AM, Mark wrote:

Hi all,

I was googling around a bit, thinking of changing the gain on the

lm386, and found a simple solution for the popping problem.

I found in some reading that pin 7 can be used for muting the

amplifier. Muting will occur if either 0V or Vcc is applied to pin 7.

So I simply installed a 1N4148 diode between the transmit supply line

and pin 7 of the lm386 so that it conducts Vcc to the pin upon closing

of the ptt switch. There is still a small pop occuring after this mod,

but it is reduced in magnitude by a great amount. I feel this is a

nice mod and in keeping with the KISS theme of the BITX line :-)

I will put some photos up of my pcb after the mod, but it pretty easy

to do on the backside as the 4-pin readymate connector header is just

next to pin 7 on the lm386 and a diode reaches very easily between the

two.

I also read that it is recommended, when using increased gain on the

lm386 (like we are), to have a 1-10uF capacitor installed between pin

7 and ground in order to reduce power supply noise problems (see the

second graph on the datasheet). This in itself helped a little bit

with the pop problem (I tried this mod first) in that the pop sound

changed from a "squeal" to a "crunch" which was a bit less unpleasant

hi hi.

This mod is also easy to do on the backside as a small radial lead

electrolytic or tantalum cap can be laid down along the pins of the IC

and leads soldered between pins 7 and 2 (which is grounded).

Cheers and have a great day everyone!

Mark - N7EKU

[Non-text portions of this message have been removed]

Any time Arv,

Let me know how it works for you...

73s,

Mark - N7EKU

--- On Tue, 9/13/11, Arv Evans <arvid.evans@...

<mailto:arvid.evans%40gmail.com>> wrote:

From: Arv Evans <arvid.evans@... <mailto:arvid.evans%40gmail.com>>

Subject: Re: [BITX20] A simple mod for the ptt pop squeal problem...

To: BITX20@... <mailto:BITX20%40yahoogroups.com>

Date: Tuesday, September 13, 2011, 7:48 PM

Mark N7EKU

Nice mod. I will try it on the BITX20A that is lying on my workbench.

Thanks for the information.

Arv K7HKL

_._

On 09/13/2011 09:44 AM, Mark wrote:

Hi all,

I was googling around a bit, thinking of changing the gain on the

lm386, and found a simple solution for the popping problem.

I found in some reading that pin 7 can be used for muting the

amplifier. Muting will occur if either 0V or Vcc is applied to pin 7.

So I simply installed a 1N4148 diode between the transmit supply line

and pin 7 of the lm386 so that it conducts Vcc to the pin upon closing

of the ptt switch. There is still a small pop occuring after this mod,

but it is reduced in magnitude by a great amount. I feel this is a

nice mod and in keeping with the KISS theme of the BITX line :-)

I will put some photos up of my pcb after the mod, but it pretty easy

to do on the backside as the 4-pin readymate connector header is just

next to pin 7 on the lm386 and a diode reaches very easily between the

two.

I also read that it is recommended, when using increased gain on the

lm386 (like we are), to have a 1-10uF capacitor installed between pin

7 and ground in order to reduce power supply noise problems (see the

second graph on the datasheet). This in itself helped a little bit

with the pop problem (I tried this mod first) in that the pop sound

changed from a "squeal" to a "crunch" which was a bit less unpleasant

hi hi.

This mod is also easy to do on the backside as a small radial lead

electrolytic or tantalum cap can be laid down along the pins of the IC

and leads soldered between pins 7 and 2 (which is grounded).

Cheers and have a great day everyone!

Mark - N7EKU

[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

Hi all,

I was googling around a bit, thinking of changing the gain on the
lm386, and found a simple solution for the popping problem.

I found in some reading that pin 7 can be used for muting the
amplifier. Muting will occur if either 0V or Vcc is applied to pin 7.
So I simply installed a 1N4148 diode between the transmit supply line
and pin 7 of the lm386 so that it conducts Vcc to the pin upon closing
of the ptt switch. There is still a small pop occuring after this mod,
but it is reduced in magnitude by a great amount. I feel this is a
nice mod and in keeping with the KISS theme of the BITX line :-)

I will put some photos up of my pcb after the mod, but it pretty easy
to do on the backside as the 4-pin readymate connector header is just
next to pin 7 on the lm386 and a diode reaches very easily between the
two.

I also read that it is recommended, when using increased gain on the
lm386 (like we are), to have a 1-10uF capacitor installed between pin
7 and ground in order to reduce power supply noise problems (see the
second graph on the datasheet). This in itself helped a little bit
with the pop problem (I tried this mod first) in that the pop sound
changed from a "squeal" to a "crunch" which was a bit less unpleasant
hi hi.

This mod is also easy to do on the backside as a small radial lead
electrolytic or tantalum cap can be laid down along the pins of the IC
and leads soldered between pins 7 and 2 (which is grounded).

Cheers and have a great day everyone!

Mark - N7EKU

Hi all,

I was googling around a bit, thinking of changing the gain on the

lm386, and found a simple solution for the popping problem.

I found in some reading that pin 7 can be used for muting the

amplifier. Muting will occur if either 0V or Vcc is applied to pin 7.

So I simply installed a 1N4148 diode between the transmit supply line

and pin 7 of the lm386 so that it conducts Vcc to the pin upon closing

of the ptt switch. There is still a small pop occuring after this mod,

but it is reduced in magnitude by a great amount. I feel this is a

nice mod and in keeping with the KISS theme of the BITX line :-)

I will put some photos up of my pcb after the mod, but it pretty easy

to do on the backside as the 4-pin readymate connector header is just

next to pin 7 on the lm386 and a diode reaches very easily between the

two.

I also read that it is recommended, when using increased gain on the

lm386 (like we are), to have a 1-10uF capacitor installed between pin

7 and ground in order to reduce power supply noise problems (see the

second graph on the datasheet). This in itself helped a little bit

with the pop problem (I tried this mod first) in that the pop sound

changed from a "squeal" to a "crunch" which was a bit less unpleasant

hi hi.

This mod is also easy to do on the backside as a small radial lead

electrolytic or tantalum cap can be laid down along the pins of the IC

and leads soldered between pins 7 and 2 (which is grounded).

Cheers and have a great day everyone!

Mark - N7EKU

Mark, Arv,

Would reversing the diode and picking up the PTT ground
work? That way the audio amp would be muted before the
transmitter was turn on. This might eliminate the pop
all together.

Frank - W4NHJ

On 9/13/11 6:29 PM, Mark wrote:

Any time Arv,

Let me know how it works for you...

73s,

Mark - N7EKU

--- On Tue, 9/13/11, Arv Evans <arvid.evans@...

<mailto:arvid.evans%40gmail.com>

<mailto:arvid.evans%40gmail.com>> wrote:

From: Arv Evans <arvid.evans@...

<mailto:arvid.evans%40gmail.com> <mailto:arvid.evans%40gmail.com>>

Subject: Re: [BITX20] A simple mod for the ptt pop squeal problem...
To: BITX20@... <mailto:BITX20%40yahoogroups.com>

<mailto:BITX20%40yahoogroups.com>

Date: Tuesday, September 13, 2011, 7:48 PM



Mark N7EKU

Nice mod. I will try it on the BITX20A that is lying on my workbench.

Thanks for the information.

Arv K7HKL

_._

On 09/13/2011 09:44 AM, Mark wrote:

Hi all,

I was googling around a bit, thinking of changing the gain on the

lm386, and found a simple solution for the popping problem.

I found in some reading that pin 7 can be used for muting the

amplifier. Muting will occur if either 0V or Vcc is applied to pin 7.

So I simply installed a 1N4148 diode between the transmit supply line

and pin 7 of the lm386 so that it conducts Vcc to the pin upon closing

of the ptt switch. There is still a small pop occuring after this mod,

but it is reduced in magnitude by a great amount. I feel this is a

nice mod and in keeping with the KISS theme of the BITX line :-)

I will put some photos up of my pcb after the mod, but it pretty easy

to do on the backside as the 4-pin readymate connector header is just

next to pin 7 on the lm386 and a diode reaches very easily between the

two.

I also read that it is recommended, when using increased gain on the

lm386 (like we are), to have a 1-10uF capacitor installed between pin

7 and ground in order to reduce power supply noise problems (see the

second graph on the datasheet). This in itself helped a little bit

with the pop problem (I tried this mod first) in that the pop sound

changed from a "squeal" to a "crunch" which was a bit less unpleasant

hi hi.

This mod is also easy to do on the backside as a small radial lead

electrolytic or tantalum cap can be laid down along the pins of the IC

and leads soldered between pins 7 and 2 (which is grounded).

Cheers and have a great day everyone!

Mark - N7EKU

[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

Hi Kishore,

You're very welcome! I hope especially the cap added from pin 7 to

ground should help with the hum -- that's what the datasheet shows it

is for.

NOTICE!!! I tried moving the muting diode to the ptt position

(cathode to ptt and anode to pin 7) so it should conduct ground to pin

7 when the ptt is pushed however it was not very effective in this

position. I think it has something to do with large inductive energy

in the relay coil. I do have a protection diode in there, but I'm

afraid I may have partially fried my lm386. So, I wouldn't recommend

using the muting circuit in this position!

The original location I had going from pin 7 to the transmit power

line works pretty well so I recommend putting there if you want to try it.

Cheers and 73s,

Mark - N7EKU

--- On Wed, 9/14/11, kishore vagisetty <kishorev001@...

<mailto:kishorev001%40yahoo.co.in>> wrote:

From: kishore vagisetty <kishorev001@...

<mailto:kishorev001%40yahoo.co.in>>

Subject: Re: [BITX20] A simple mod for the ptt pop squeal problem...

To: BITX20@... <mailto:BITX20%40yahoogroups.com>

Date: Wednesday, September 14, 2011, 3:39 AM

Dear Mark N7EKU,

thanks for info !! my BITX20 ver3 troubles me with 50hz hum. i think

ur discovery should make some difference.

73

v kishore

vu2-002swl

--- On Wed, 14/9/11, Arv Evans <arvid.evans@...

<mailto:arvid.evans%40gmail.com>> wrote:

From: Arv Evans <arvid.evans@... <mailto:arvid.evans%40gmail.com>>

Subject: Re: [BITX20] A simple mod for the ptt pop squeal problem...

To: BITX20@... <mailto:BITX20%40yahoogroups.com>

Date: Wednesday, 14 September, 2011, 1:18 AM

Mark N7EKU

Nice mod. I will try it on the BITX20A that is lying on my workbench.

Thanks for the information.

Arv K7HKL

_._

On 09/13/2011 09:44 AM, Mark wrote:

Hi all,

I was googling around a bit, thinking of changing the gain on the

lm386, and found a simple solution for the popping problem.

I found in some reading that pin 7 can be used for muting the

amplifier. Muting will occur if either 0V or Vcc is applied to pin 7.

So I simply installed a 1N4148 diode between the transmit supply line

and pin 7 of the lm386 so that it conducts Vcc to the pin upon closing

of the ptt switch. There is still a small pop occuring after this mod,

but it is reduced in magnitude by a great amount. I feel this is a

nice mod and in keeping with the KISS theme of the BITX line :-)

I will put some photos up of my pcb after the mod, but it pretty easy

to do on the backside as the 4-pin readymate connector header is just

next to pin 7 on the lm386 and a diode reaches very easily between the

two.

I also read that it is recommended, when using increased gain on the

lm386 (like we are), to have a 1-10uF capacitor installed between pin

7 and ground in order to reduce power supply noise problems (see the

second graph on the datasheet). This in itself helped a little bit

with the pop problem (I tried this mod first) in that the pop sound

changed from a "squeal" to a "crunch" which was a bit less unpleasant

hi hi.

This mod is also easy to do on the backside as a small radial lead

electrolytic or tantalum cap can be laid down along the pins of the IC

and leads soldered between pins 7 and 2 (which is grounded).

Cheers and have a great day everyone!

Mark - N7EKU

[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

Excellent advice Arv :-)

Turns out my amp chip was OK. For some reason now however (after
trying the other diode position) I have a little leakage or noise from
the mic circuit coming over the speaker at the beginning of transmit.
That wasn't happening before so I'm not sure what's up. I had the
chip in a socket already and switched it out but no change. Not a big
deal just wierd. Maybe my mic wiring is running with different
routing now since I had the set apart.

Yeah the mute mod didn't completely eliminate the pop for me either,
but now it's pretty tolerable and is just a bit louder than the relay
clicks on my set.

Cheers and lots of interesting ideas you have now Arv!

Mark - N7EKU

--- On Wed, 9/14/11, Arv Evans <arvid.evans@...
<mailto:arvid.evans%40gmail.com>> wrote:

From: Arv Evans <arvid.evans@... <mailto:arvid.evans%40gmail.com>>
Subject: Re: [BITX20] A simple mod for the ptt pop squeal problem...
To: BITX20@... <mailto:BITX20%40yahoogroups.com>
Date: Wednesday, September 14, 2011, 5:08 AM



Mark, & others...

You could probably use a small transistor to switch Pin-7 and avoid

possibility of

damaging the LM-386 during the experimentation process. I routinely use a

socket for the LM-386, mostly because I like to tinker with things and

have fried a

few AF amp IC's. If you do have to replace a soldered-in-place LM386,

the easy

way is to cut all the legs off and then remove them from the PCB one at

a time.

Arv

_._

On 09/13/2011 10:29 PM, Mark wrote:

Hi Kishore,

You're very welcome! I hope especially the cap added from pin 7 to

ground should help with the hum -- that's what the datasheet shows it

is for.

NOTICE!!! I tried moving the muting diode to the ptt position

(cathode to ptt and anode to pin 7) so it should conduct ground to pin

7 when the ptt is pushed however it was not very effective in this

position. I think it has something to do with large inductive energy

in the relay coil. I do have a protection diode in there, but I'm

afraid I may have partially fried my lm386. So, I wouldn't recommend

using the muting circuit in this position!

The original location I had going from pin 7 to the transmit power

line works pretty well so I recommend putting there if you want to

try it.

Cheers and 73s,

Mark - N7EKU

--- On Wed, 9/14/11, kishore vagisetty <kishorev001@...

<mailto:kishorev001%40yahoo.co.in>

<mailto:kishorev001%40yahoo.co.in>> wrote:

From: kishore vagisetty <kishorev001@...

<mailto:kishorev001%40yahoo.co.in>

<mailto:kishorev001%40yahoo.co.in>>

Subject: Re: [BITX20] A simple mod for the ptt pop squeal problem...

To: BITX20@... <mailto:BITX20%40yahoogroups.com>

<mailto:BITX20%40yahoogroups.com>

Date: Wednesday, September 14, 2011, 3:39 AM

Dear Mark N7EKU,

thanks for info !! my BITX20 ver3 troubles me with 50hz hum. i think

ur discovery should make some difference.

73

v kishore

vu2-002swl

--- On Wed, 14/9/11, Arv Evans <arvid.evans@...

<mailto:arvid.evans%40gmail.com>

<mailto:arvid.evans%40gmail.com>> wrote:

From: Arv Evans <arvid.evans@...

<mailto:arvid.evans%40gmail.com> <mailto:arvid.evans%40gmail.com>>

Subject: Re: [BITX20] A simple mod for the ptt pop squeal problem...

To: BITX20@... <mailto:BITX20%40yahoogroups.com>

<mailto:BITX20%40yahoogroups.com>

Date: Wednesday, 14 September, 2011, 1:18 AM

Mark N7EKU

Nice mod. I will try it on the BITX20A that is lying on my workbench.

Thanks for the information.

Arv K7HKL

_._

On 09/13/2011 09:44 AM, Mark wrote:

Hi all,

I was googling around a bit, thinking of changing the gain on the

lm386, and found a simple solution for the popping problem.

I found in some reading that pin 7 can be used for muting the

amplifier. Muting will occur if either 0V or Vcc is applied to pin 7.

So I simply installed a 1N4148 diode between the transmit supply line

and pin 7 of the lm386 so that it conducts Vcc to the pin upon closing

of the ptt switch. There is still a small pop occuring after this mod,

but it is reduced in magnitude by a great amount. I feel this is a

nice mod and in keeping with the KISS theme of the BITX line :-)

I will put some photos up of my pcb after the mod, but it pretty easy

to do on the backside as the 4-pin readymate connector header is just

next to pin 7 on the lm386 and a diode reaches very easily between the

two.

I also read that it is recommended, when using increased gain on the

lm386 (like we are), to have a 1-10uF capacitor installed between pin

7 and ground in order to reduce power supply noise problems (see the

second graph on the datasheet). This in itself helped a little bit

with the pop problem (I tried this mod first) in that the pop sound

changed from a "squeal" to a "crunch" which was a bit less unpleasant

hi hi.

This mod is also easy to do on the backside as a small radial lead

electrolytic or tantalum cap can be laid down along the pins of the IC

and leads soldered between pins 7 and 2 (which is grounded).

Cheers and have a great day everyone!

Mark - N7EKU

[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

Excellent advice Arv :-)

Turns out my amp chip was OK. For some reason now however (after

trying the other diode position) I have a little leakage or noise from

the mic circuit coming over the speaker at the beginning of transmit.

That wasn't happening before so I'm not sure what's up. I had the

chip in a socket already and switched it out but no change. Not a big

deal just wierd. Maybe my mic wiring is running with different

routing now since I had the set apart.

Yeah the mute mod didn't completely eliminate the pop for me either,

but now it's pretty tolerable and is just a bit louder than the relay

clicks on my set.

Cheers and lots of interesting ideas you have now Arv!

Mark - N7EKU

--- On Wed, 9/14/11, Arv Evans <arvid.evans@...

<mailto:arvid.evans%40gmail.com>> wrote:

From: Arv Evans <arvid.evans@... <mailto:arvid.evans%40gmail.com>>

Subject: Re: [BITX20] A simple mod for the ptt pop squeal problem...

To: BITX20@... <mailto:BITX20%40yahoogroups.com>

Date: Wednesday, September 14, 2011, 5:08 AM

Mark, & others...

You could probably use a small transistor to switch Pin-7 and avoid

possibility of

damaging the LM-386 during the experimentation process. I routinely use a

socket for the LM-386, mostly because I like to tinker with things and

have fried a

few AF amp IC's. If you do have to replace a soldered-in-place LM386,

the easy

way is to cut all the legs off and then remove them from the PCB one at

a time.

Arv

_._

On 09/13/2011 10:29 PM, Mark wrote:

Hi Kishore,

You're very welcome! I hope especially the cap added from pin 7 to

ground should help with the hum -- that's what the datasheet shows it

is for.

NOTICE!!! I tried moving the muting diode to the ptt position

(cathode to ptt and anode to pin 7) so it should conduct ground to pin

7 when the ptt is pushed however it was not very effective in this

position. I think it has something to do with large inductive energy

in the relay coil. I do have a protection diode in there, but I'm

afraid I may have partially fried my lm386. So, I wouldn't recommend

using the muting circuit in this position!

The original location I had going from pin 7 to the transmit power

line works pretty well so I recommend putting there if you want to

try it.

Cheers and 73s,

Mark - N7EKU

--- On Wed, 9/14/11, kishore vagisetty <kishorev001@...

<mailto:kishorev001%40yahoo.co.in>

<mailto:kishorev001%40yahoo.co.in>> wrote:

From: kishore vagisetty <kishorev001@...

<mailto:kishorev001%40yahoo.co.in>

<mailto:kishorev001%40yahoo.co.in>>

Subject: Re: [BITX20] A simple mod for the ptt pop squeal problem...

To: BITX20@... <mailto:BITX20%40yahoogroups.com>

<mailto:BITX20%40yahoogroups.com>

Date: Wednesday, September 14, 2011, 3:39 AM

Dear Mark N7EKU,

thanks for info !! my BITX20 ver3 troubles me with 50hz hum. i think

ur discovery should make some difference.

73

v kishore

vu2-002swl

--- On Wed, 14/9/11, Arv Evans <arvid.evans@...

<mailto:arvid.evans%40gmail.com>

<mailto:arvid.evans%40gmail.com>> wrote:

From: Arv Evans <arvid.evans@...

<mailto:arvid.evans%40gmail.com> <mailto:arvid.evans%40gmail.com>>

Subject: Re: [BITX20] A simple mod for the ptt pop squeal problem...

To: BITX20@... <mailto:BITX20%40yahoogroups.com>

<mailto:BITX20%40yahoogroups.com>

Date: Wednesday, 14 September, 2011, 1:18 AM

Mark N7EKU

Nice mod. I will try it on the BITX20A that is lying on my workbench.

Thanks for the information.

Arv K7HKL

_._

On 09/13/2011 09:44 AM, Mark wrote:

Hi all,

I was googling around a bit, thinking of changing the gain on the

lm386, and found a simple solution for the popping problem.

I found in some reading that pin 7 can be used for muting the

amplifier. Muting will occur if either 0V or Vcc is applied to pin 7.

So I simply installed a 1N4148 diode between the transmit supply line

and pin 7 of the lm386 so that it conducts Vcc to the pin upon closing

of the ptt switch. There is still a small pop occuring after this mod,

but it is reduced in magnitude by a great amount. I feel this is a

nice mod and in keeping with the KISS theme of the BITX line :-)

I will put some photos up of my pcb after the mod, but it pretty easy

to do on the backside as the 4-pin readymate connector header is just

next to pin 7 on the lm386 and a diode reaches very easily between the

two.

I also read that it is recommended, when using increased gain on the

lm386 (like we are), to have a 1-10uF capacitor installed between pin

7 and ground in order to reduce power supply noise problems (see the

second graph on the datasheet). This in itself helped a little bit

with the pop problem (I tried this mod first) in that the pop sound

changed from a "squeal" to a "crunch" which was a bit less unpleasant

hi hi.

This mod is also easy to do on the backside as a small radial lead

electrolytic or tantalum cap can be laid down along the pins of the IC

and leads soldered between pins 7 and 2 (which is grounded).

Cheers and have a great day everyone!

Mark - N7EKU

[Non-text portions of this message have been removed]

From: Dean Blake <dsblake1@...>
Subject: RE: [BITX20] A simple mod for the ptt pop squeal problem...
To: bitx20@...
Date: Friday, September 16, 2011, 11:45 AM

I used a reed relay in series with the LM386 output driven
by the TX voltage bus...

Reeds are known for their low power and fast switching
time...also very low ohmic resistance

I do hear a tiny, almost a light click when switching to
transmit...NOTHING like the POP I heard before.
Arv and I had a discussion on an early thread on the same
subject...
A transistor would work but much more complex

K4DSB
Dean




To: BITX20@...
From: pe1lnx@...
Date: Thu, 15 Sep 2011 13:04:41 -0700
Subject: Re: [BITX20] A simple mod for the ptt pop squeal
problem...


?



Hello, maybe another idea:

I've also played around with transistors and FET's at the
input of the LM386 of my BITX v3 to get rit of the pop.
It gave me no satisfaction, because the pop remained
somehow.
My solution is a small SMD relais at the output of the
LM386. It switches the output between the speaker and an 8
Ohm resistor. The relais gets his power from the TX signal
via a diode and a C, in parallel to the relais.
When keyed, it is activated immediately, but when de-keyed,
it remains active for 0,5s.
Now the pop has gone completely.

cheers and 73

Marcel - PE1LNX

________________________________
From: Arv Evans <arvid.evans@...>
To: BITX20@...
Sent: Wednesday, September 14, 2011 6:37 PM
Subject: Re: [BITX20] A simple mod for the ptt pop squeal
problem...

?
Mark

Adding 1/4 inch spacers under the PCB for the last BITX20A
I worked on
raised the
board high enough for all wiring to be run under the board
instead of
across the top.
This made it much easier to do measurements and to
troubleshoot. And,
it looks
better with most of the wiring hidden under the board.

It might be interesting to try a large capacitor from pin-7
to ground on
the LM386?
Thinking is that this might slow down how fast this
amplifier recovers
from power-
down during transmit and thus mask part of the changeover
feedback
period. Idea
is that this could possibly act as a timed mute function.
We could add
enough
components to do an actual time delay before allowing the
LM386 to
activate but
that seems contrary to the minimalist concept of BITX
design.

Arv
_._

On 09/14/2011 01:06 AM, Mark wrote:

Excellent advice Arv :-)

Turns out my amp chip was OK. For some reason now

however (after

trying the other diode position) I have a little

leakage or noise from

the mic circuit coming over the speaker at the

beginning of transmit.

That wasn't happening before so I'm not sure what's

up. I had the

chip in a socket already and switched it out but no

change. Not a big

deal just wierd. Maybe my mic wiring is running with

different

routing now since I had the set apart.

Yeah the mute mod didn't completely eliminate the pop

for me either,

but now it's pretty tolerable and is just a bit louder

than the relay

clicks on my set.

Cheers and lots of interesting ideas you have now

Arv!

Mark - N7EKU

--- On Wed, 9/14/11, Arv Evans <arvid.evans@...

<mailto:arvid.evans%40gmail.com>> wrote:

From: Arv Evans <arvid.evans@...

<mailto:arvid.evans%40gmail.com>>

Subject: Re: [BITX20] A simple mod for the ptt pop

squeal problem...

To: BITX20@...

<mailto:BITX20%40yahoogroups.com>

Date: Wednesday, September 14, 2011, 5:08 AM



Mark, & others...

You could probably use a small transistor to switch

Pin-7 and avoid

possibility of

damaging the LM-386 during the experimentation

process. I routinely use a

socket for the LM-386, mostly because I like to tinker

with things and

have fried a

few AF amp IC's. If you do have to replace a

soldered-in-place LM386,

the easy

way is to cut all the legs off and then remove them

from the PCB one at

a time.

Arv

_._

On 09/13/2011 10:29 PM, Mark wrote:

Hi Kishore,

You're very welcome! I hope especially the cap

added from pin 7 to

ground should help with the hum -- that's what

the datasheet shows it

is for.

NOTICE!!! I tried moving the muting diode to the

ptt position

(cathode to ptt and anode to pin 7) so it should

conduct ground to pin

7 when the ptt is pushed however it was not very

effective in this

position. I think it has something to do with

large inductive energy

in the relay coil. I do have a protection diode

in there, but I'm

afraid I may have partially fried my lm386. So, I

wouldn't recommend

using the muting circuit in this position!

The original location I had going from pin 7 to

the transmit power

line works pretty well so I recommend putting

there if you want to

try it.

Cheers and 73s,

Mark - N7EKU

--- On Wed, 9/14/11, kishore vagisetty <kishorev001@...

<mailto:kishorev001%40yahoo.co.in>

<mailto:kishorev001%40yahoo.co.in>>

wrote:

From: kishore vagisetty <kishorev001@...

<mailto:kishorev001%40yahoo.co.in>

<mailto:kishorev001%40yahoo.co.in>>

Subject: Re: [BITX20] A simple mod for the ptt

pop squeal problem...

To: BITX20@...

<mailto:BITX20%40yahoogroups.com>

<mailto:BITX20%40yahoogroups.com>

Date: Wednesday, September 14, 2011, 3:39 AM

Dear Mark N7EKU,

thanks for info !! my BITX20 ver3 troubles me

with 50hz hum. i think

ur discovery should make some difference.

73

v kishore

vu2-002swl

--- On Wed, 14/9/11, Arv Evans <arvid.evans@...

<mailto:arvid.evans%40gmail.com>

<mailto:arvid.evans%40gmail.com>>

wrote:

From: Arv Evans <arvid.evans@...

<mailto:arvid.evans%40gmail.com>

<mailto:arvid.evans%40gmail.com>>

Subject: Re: [BITX20] A simple mod for the ptt

pop squeal problem...

To: BITX20@...

<mailto:BITX20%40yahoogroups.com>

<mailto:BITX20%40yahoogroups.com>

Date: Wednesday, 14 September, 2011, 1:18 AM

Mark N7EKU

Nice mod. I will try it on the BITX20A that is

lying on my workbench.

Thanks for the information.

Arv K7HKL

_._

On 09/13/2011 09:44 AM, Mark wrote:

Hi all,

I was googling around a bit, thinking of

changing the gain on the

lm386, and found a simple solution for the

popping problem.

I found in some reading that pin 7 can be

used for muting the

amplifier. Muting will occur if either 0V or

Vcc is applied to pin 7.

So I simply installed a 1N4148 diode between

the transmit supply line

and pin 7 of the lm386 so that it conducts

Vcc to the pin upon closing

of the ptt switch. There is still a small

pop occuring after this mod,

but it is reduced in magnitude by a great

amount. I feel this is a

nice mod and in keeping with the KISS theme

of the BITX line :-)

I will put some photos up of my pcb after

the mod, but it pretty easy

to do on the backside as the 4-pin readymate

connector header is just

next to pin 7 on the lm386 and a diode

reaches very easily between the

two.

I also read that it is recommended, when

using increased gain on the

lm386 (like we are), to have a 1-10uF

capacitor installed between pin

7 and ground in order to reduce power supply

noise problems (see the

second graph on the datasheet). This in

itself helped a little bit

with the pop problem (I tried this mod

first) in that the pop sound

changed from a "squeal" to a "crunch" which

was a bit less unpleasant

hi hi.

This mod is also easy to do on the backside

as a small radial lead

electrolytic or tantalum cap can be laid

down along the pins of the IC

and leads soldered between pins 7 and 2

(which is grounded).

Cheers and have a great day everyone!

Mark - N7EKU

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