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A minor bug in the ubitx circuit

Ashhar Farhan
 


Replace the R253 (a resistor) with a 0.1uf capacitor to get the sidetone going properly. 

The long story:
I was fooling around with an upgrade to Raduino, (more over the weekend) . I noticed that the sidetone was not proper. After a day's frustration, I put a scope probe on the sidetone line and saw that as the sidetone made a square wave of 0 to +5v and back, the average voltage rose to 2.5 v. This was directly coupled (well, me!) to the LM386 audio amp's volume control. Replacing the final resistor(R253) in the low pass filter with a 0.1uf capacitor fixes the problem. 
The problem was that the sidetone would 'vanish' after a start blip. That's because the LM386 was being pushed to the rail by the 2.5v DC on the input!
I am enclosing a picture of the mod. 

73, f


Ashhar Farhan
 

The volume with the 0.1uf cap in place of the R253 was too old. I placed a replaced a 10 K resistor in place of 1K at R250 and the volume is not reasonable.
You can solder the regular through hole resistors in place of the SMDs if your junk box is low on SMD components.

- f

On Wed, Dec 4, 2019 at 3:03 PM Ashhar Farhan <farhanbox@...> wrote:

Replace the R253 (a resistor) with a 0.1uf capacitor to get the sidetone going properly. 

The long story:
I was fooling around with an upgrade to Raduino, (more over the weekend) . I noticed that the sidetone was not proper. After a day's frustration, I put a scope probe on the sidetone line and saw that as the sidetone made a square wave of 0 to +5v and back, the average voltage rose to 2.5 v. This was directly coupled (well, me!) to the LM386 audio amp's volume control. Replacing the final resistor(R253) in the low pass filter with a 0.1uf capacitor fixes the problem. 
The problem was that the sidetone would 'vanish' after a start blip. That's because the LM386 was being pushed to the rail by the 2.5v DC on the input!
I am enclosing a picture of the mod. 

73, f


Jerry Gaffke
 


This is kind of cryptic:
>  The volume with the 0.1uf cap in place of the R253 was too old. I placed a replaced a 10 K resistor in place of 1K at R250 and the volume is not reasonable.

Auto-correct is the devil's tool.
And typing with thumbs is an abomination.

Perhaps  old==low,  and  not==now  ??? 

Jerry
 
 

On Wed, Dec 4, 2019 at 01:57 AM, Ashhar Farhan wrote:
The volume with the 0.1uf cap in place of the R253 was too old. I placed a replaced a 10 K resistor in place of 1K at R250 and the volume is not reasonable.
You can solder the regular through hole resistors in place of the SMDs if your junk box is low on SMD components.
 
- f
Hide quoted text

 

On Wed, Dec 4, 2019 at 3:03 PM Ashhar Farhan <farhanbox@...> wrote:
 
Replace the R253 (a resistor) with a 0.1uf capacitor to get the sidetone going properly. 
 
The long story:
I was fooling around with an upgrade to Raduino, (more over the weekend) . I noticed that the sidetone was not proper. After a day's frustration, I put a scope probe on the sidetone line and saw that as the sidetone made a square wave of 0 to +5v and back, the average voltage rose to 2.5 v. This was directly coupled (well, me!) to the LM386 audio amp's volume control. Replacing the final resistor(R253) in the low pass filter with a 0.1uf capacitor fixes the problem. 
The problem was that the sidetone would 'vanish' after a start blip. That's because the LM386 was being pushed to the rail by the 2.5v DC on the input!
I am enclosing a picture of the mod. 
 
73, f
 

Ashhar Farhan
 

Precise! I should also wear my glasses while typing!


On Wed 4 Dec, 2019, 10:20 PM Jerry Gaffke via Groups.Io, <jgaffke=yahoo.com@groups.io> wrote:

This is kind of cryptic:
>  The volume with the 0.1uf cap in place of the R253 was too old. I placed a replaced a 10 K resistor in place of 1K at R250 and the volume is not reasonable.

Auto-correct is the devil's tool.
And typing with thumbs is an abomination.

Perhaps  old==low,  and  not==now  ??? 

Jerry
 
 
On Wed, Dec 4, 2019 at 01:57 AM, Ashhar Farhan wrote:
The volume with the 0.1uf cap in place of the R253 was too old. I placed a replaced a 10 K resistor in place of 1K at R250 and the volume is not reasonable.
You can solder the regular through hole resistors in place of the SMDs if your junk box is low on SMD components.
 
- f
Hide quoted text

 

On Wed, Dec 4, 2019 at 3:03 PM Ashhar Farhan <farhanbox@...> wrote:
 
Replace the R253 (a resistor) with a 0.1uf capacitor to get the sidetone going properly. 
 
The long story:
I was fooling around with an upgrade to Raduino, (more over the weekend) . I noticed that the sidetone was not proper. After a day's frustration, I put a scope probe on the sidetone line and saw that as the sidetone made a square wave of 0 to +5v and back, the average voltage rose to 2.5 v. This was directly coupled (well, me!) to the LM386 audio amp's volume control. Replacing the final resistor(R253) in the low pass filter with a 0.1uf capacitor fixes the problem. 
The problem was that the sidetone would 'vanish' after a start blip. That's because the LM386 was being pushed to the rail by the 2.5v DC on the input!
I am enclosing a picture of the mod. 
 
73, f
 

paul_hvidston
 

Thanks for the helpful tip, Ashhar. I can see how this slipped through the evolution of the AF amp. I'm focusing on CW for this rig and have been busy up to this point working on the firmware. Had not even gotten to the point of transmitting CW with my brand new V5.

72 de N6MGN

KG5MG
 

Ashhar,


Does this pertain to all boards of all versions?  I have a v5 I just finished.  All I need to do is make a power cord and a mic cable.  I haven't even applied power to the board, yet.
Do I need to make these alterations?

I have been inactive in amateur radio for over 10 years and just getting back into the hobby.  I don't have a spare parts box, unfortunately. I will need to order the replacement cap and resistor. Can you give specs on the SMD cap and resistor? I've never worked with them.

Do you anticipate any other alterations?  If so I will wait before ordering parts.

Hamp Yearwood
KG5MG 

Evan Hand
 

short answer is it applies only to the v5, as the others do not have an LM386 in the audio chain. 


if you do not use CW, or you have a keyer with it’s own side tone, it would not be an issue and you could wait for other changes. If you want CW now, Oder the part. Note that it is surface mount device.  


I would look into other mods that are of interest like the age mods or digital operation, and add the needed components or wire and hardware for those if you are trying to save on shipping. Otherwise just order a selection of values pack, as caps always seem to come up as a required device in adding features to a radio. 


73
Evan
AC9TU

Ashhar Farhan
 

The trouble is that even the earlier version of 2822 audio amplifier will have the same problem. It is best to make the mod for all versions. However, don't fix it if it ain't broke. Only if you are having a trouble with CW should this mod be tried.

- f

On Thu, Dec 5, 2019 at 7:35 AM Evan Hand <elhandjr@...> wrote:

short answer is it applies only to the v5, as the others do not have an LM386 in the audio chain. 


if you do not use CW, or you have a keyer with it’s own side tone, it would not be an issue and you could wait for other changes. If you want CW now, Oder the part. Note that it is surface mount device.  


I would look into other mods that are of interest like the age mods or digital operation, and add the needed components or wire and hardware for those if you are trying to save on shipping. Otherwise just order a selection of values pack, as caps always seem to come up as a required device in adding features to a radio. 


73
Evan
AC9TU

paul_hvidston
 

After further review, I would recommend a series combination of R253 and a 0.1 uF cap, otherwise you are changing the side tone level and shunting the received audio by 0.05 uF (series string of added cap and C252). This may also improve possible "thumping" in the mute circuit due to the DC bias from the side tone.

72 de N6MGN

Russ KR0EHM
 

How does this problem manifest itself? Just no CW tone at all or something else? My CW is working on relatively new v5 board so wanted to make sure. I’ve noticed it is a bit lower than I expect it to be (100-200 Hz) but that could be my BFO off, correct?

Ashhar Farhan
 

Russ,
The dashes dont seem long enough on the sidetone though they are transmitted properly. The dashes sound like blips. What is happening is that as a number of square waves pass through the filters caps, they charge up to an average of 2.5v (average of 0 and 5v). The 2.5v DC at the input of the LM386 DC saturates the chip and the audio input stops being amplified. The caps diacharge as soon as the sidetone ceases. The cycle repeats in the next dash. The dots are small enough to be finished before the DC rises enough to saturate the LM386.
- f

On Fri 6 Dec, 2019, 6:17 AM Russ KR0EHM, <russ@...> wrote:
How does this problem manifest itself? Just no CW tone at all or something else? My CW is working on relatively new v5 board so wanted to make sure. I’ve noticed it is a bit lower than I expect it to be (100-200 Hz) but that could be my BFO off, correct?

Evan Hand
 

Russ,

The side tone is generated by the Raduino Nano and fed to the audio.  The CW signal to the power amp is from the Raduino Si5351 VFO direct.  The BFO is disabled during CW transition. 

Sp a low side tone is just that the setting is lower in the Nano. 


73
Evan
AC9TU

 

Hi Ashhar,

Has this mod already done on the new V6 transceiver boards?

Joel
N6ALT

Ashhar Farhan
 

Yes, updated in v6


On Wed 18 Dec, 2019, 9:47 PM Joel Caulkins/N6ALT, <caulktel@...> wrote:
Hi Ashhar,

Has this mod already done on the new V6 transceiver boards?

Joel
N6ALT

 

Great, thanks.

Joel
N6ALT

Anthony Gomes
 

Farhan ji, Will it be true for V3 R253 also or will it be just true for V5 R253 with LM386 ?  I am asking this question because with my scratch build I have taken the V5 schematic but audio system I kept TA2822 circuit. However, I am not able to try CW because I had to make the audio section offline during transmit to avoid the audio feedback problem during transmit, it is getting into the audio section via Q6 emitter (as mentioned on my previous post). Which I am still trying to resolve any suggestion will be very helpful.

73
Anthony
VU3JVX

Jerry Gaffke
 

In post   https://groups.io/g/BITX20/message/73383
Farhan states that this can also be a problem with the v3 TDA2822.

Paul suggests replacing R253 with the series combination of a 0.1uF cap and the original R253.
Sounds like a good idea to me.    https://groups.io/g/BITX20/message/73405

Jerry, KE7ER


On Wed, Dec 18, 2019 at 09:50 AM, Anthony Gomes wrote:
Farhan ji, Will it be true for V3 R253 also or will it be just true for V5 R253 with LM386 ?  I am asking this question because with my scratch build I have taken the V5 schematic but audio system I kept TA2822 circuit. However, I am not able to try CW because I had to make the audio section offline during transmit to avoid the audio feedback problem during transmit, it is getting into the audio section via Q6 emitter (as mentioned on my previous post). Which I am still trying to resolve any suggestion will be very helpful.

73
Anthony
VU3JVX

Anthony Gomes
 

Thanks Jerry for referring to the correct post. I thought we are discussing this for the first time. Any recommended solution about the audio feedback leak. I know these are not related and I have searched the forum and did try all the recommended solution provided. e.g changing the value of R63, R64 but it has not helped. Hence I have connected the Audio system 12V supply with RX power rail. I have also tried all the 3 audio circuit (TA2822, transistor only build & LM386) same result. So I feel it has to be fixed at the mic input section. Let me know if I have missed out something.

73
Anthony
VU3JVX

Anthony Gomes
 

Hmm... Interestingly I am not able to see the complete discussion chain in my mail inbox. However, I am able to see all the discussion post if I login to the forum and check. Not sure if it's just my mailbox or other;s have notice this. Looks like trying to ask question via mail inbox is not a good idea.

73
Anthony
VU3JVX

Arv Evans
 

Anthony

This group, and gmail, does not automatically show the whole topic chain for every
response.  If you click on "View Reply on-line" at the bottom of messages you will
be able to then click on "see the entire discussion chain" for that topic or thread. 
This minimizes the amount of network bandwidth that is used for each response. 

Some of the discussion topics go on for weeks or months and involve hundreds of
responses.  Minimizing what is sent to just individual responses also decreases
confusion that might occur if the whole chain were exposed for responses to really
old posts.

Arv  K7HKL
_._


On Wed, Dec 18, 2019 at 12:30 PM Anthony Gomes <vu3jvx@...> wrote:
Hmm... Interestingly I am not able to see the complete discussion chain in my mail inbox. However, I am able to see all the discussion post if I login to the forum and check. Not sure if it's just my mailbox or other;s have notice this. Looks like trying to ask question via mail inbox is not a good idea.

73
Anthony
VU3JVX