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Good spot to insert audio preamp on V6 #v6

 

Hi all,

I have noticed that my V6 uBITX receive audio is just a bit low especially on 20 meters. I pretty much run the volume all way the open on all bands and can hear okay. I was wanting to add a audio preamp,  https://www.sparkfun.com/products/9816 somewhere to pick things up a bit. Any ideas on where might be a good spot to do that on a V6 board? It would be easy on any of the prior versions as we had external volume control pots, but with the pot being onboard on the V6 it makes it a bit harder to interrupt the audio going to the wiper.

Joel
N6ALT

 

What antenna are you using Joel?

Raj


At 29-02-20, you wrote:
Hi all,

I have noticed that my V6 uBITX receive audio is just a bit low especially on 20 meters. I pretty much run the volume all way the open on all bands and can hear okay. I was wanting to add a audio preamp,  https://www.sparkfun.com/products/9816 somewhere to pick things up a bit. Any ideas on where might be a good spot to do that on a V6 board? It would be easy on any of the prior versions as we had external volume control pots, but with the pot being onboard on the V6 it makes it a bit harder to interrupt the audio going to the wiper.

Joel
N6ALT

Evan Hand
 

You might want to look into this as an alternative to a pre-amp:
https://www.amazon.com/XLX-TDA2030A-Amplifier-Speakers-Converter/dp/B07QNW61G5/ref=sr_1_1?keywords=XLX+5PCS+TDA2030A&qid=1582959342&sr=8-1

The tda2030a can deliver 8 watts into 8 ohms as opposed to the lm386 0.700 watts.  It would be connected between the output of the board and the speaker.  It would also add some gain to the audio.

Just a recommendation
73
Evan
AC9TU

Curt
 

Not too surprising signals will be less robust on 20m than 80m in these solar conditions, but if you want more audio - go for it.

On my v4 I added a NESCAF audio filter at the output of the ubitx main board, so it feeds headphone jack and speaker.  I like this filter on both CW and SSB, but not being sold just now (maybe an alternative SCAF is out there)

If you go with Evan's solution - and use headphones - be careful and that's a lot of power into the ear (or just put this amplifier in the speaker path). 

Plan B may be try different headphones if you have them, to see if they are more sensitive.  I do imagine the v6 has more audio than the v4.

73 curt

Bill Cromwell
 

Hi,

I have the NEScaf filter. I got it as an unbuilt kit from another ham who was cleaning out the desk drawers. The schematics and theory/explanation of operation are available. There is no reason we cannot buy the parts and build one dead-bug ugly style. I have come to prefer the sound card DSP for performance but that requires a @#*! computer! Not very convenient carrying all that up a mountain. It will force several trips to and from parking lot to county park picnic table, too. Computers are not nearly as lenient on batteries as 3 watt radios either.

73,

Bill KU8H

On 2/29/20 9:29 AM, Curt via Groups.Io wrote:
Not too surprising signals will be less robust on 20m than 80m in these solar conditions, but if you want more audio - go for it.
On my v4 I added a NESCAF audio filter at the output of the ubitx main board, so it feeds headphone jack and speaker.  I like this filter on both CW and SSB, but not being sold just now (maybe an alternative SCAF is out there)
If you go with Evan's solution - and use headphones - be careful and that's a lot of power into the ear (or just put this amplifier in the speaker path).
Plan B may be try different headphones if you have them, to see if they are more sensitive.  I do imagine the v6 has more audio than the v4.
73 curt
--
bark less - wag more

 

Hi Raj,

I use a dipole on 40 meters and a EFHW on 20 meters.

Joel
N6ALT

 

Hi Evan,

I used a 5 watt amp, ( the one included in Sunils case), hooked directly to the output of my V4 and it works great, plenty of audio. I have used a lot of LM386's in my day and they are totally usable if driven properly, the one in the V6 is just coasting along and needs more drive. I just need to find a easy place to insert a preamp without having to modify the board too heavily. I will keep studying the schematic, maybe I will have to open a trace on the bottom of the board.

Joel
N6ALT

Evan Hand
 

I would agree with what you are saying based on the v5 that I have.  I did not need to add the outboard amp as I had plenty of sound from the speaker.  However I still run the volume almost maxed out.

I did need the amp on the v4 boards that I have.  This is why Sunil included it in the kits.

Since I do not have a v6, you will need to work out the best place on your own, or hopefully someone else has done it already.

Before you cut into your rig, you might want to run the calibration again.  If the master crystal is off there may be an impact on the 45 MHz roofing filter.  Just a guess on my part and I have not done the math.  As stated above, my v5 with basically the same audio circuits does not have the volume issue as you have stated.

FWIW
73 and good hunting for the solution.
Evan
AC9TU

 

I decided that I would go another direction for my low audio problem, instead of trying to insert a preamp I just am using the uBitx's audio amp as the preamp to a TDA2030 module, it works so much better. See picture attached as to how I mounted it. I screwed the chip to the side of the cabinet to keep the chip cool.

Joel
N6ALT

 

If any desire to add a amp as I did you might want to remove C75, a 1mfd cap across pins 1 and 8 of the LM386 chip, this will lower the gain of that chip from 200 to 20 which makes the audio noise floor go down considerably.

Joel
N6ALT

Walter
 

Get a auto preamp and plug into the ext audio port. Problem solved.

ca4wqp@...
 

Gracias funciona perfecto

_Dave_ AD0B
 

Since extending our big loop antenna, have had to turn on attenuation  to prevent the Audio signals from over-driving the audio.  Even without the attenuation on there is hardly any noise except for signals. 

Just saying::: that perhaps instead of looking for more amplification maybe your antenna system may need to be worked on.
--
73
Dave
ADOB
Raduino bracket and Ham_Made_Keys

 

No problems with my antennas or my radio, works fine now. Thanks anyway.

Joel
N6ALT