¿ªÔÆÌåÓý

ctrl + shift + ? for shortcuts
© 2025 Groups.io
  1. QRPLabs
  2. Topics

QCX 40m - Audio

 

Ladies and gents,

I wrote a few notes on my experience with the QCX's audio. It would be interesting to hear other's experiences in this regard. My only concern with the QCX.

See?

73 de Eddie ZS6BNE
 

Hi Eddie

I read your blog entry with interest. I believe there must be a fault somewhere in your radio. The QCX receiver was designed with PLENTY of gain. I spent a lot of time studying other similar receiver architectures during the design process. One important consideration was, what total gain to provide. I always like to provide a little extra gain, because you never know what different people are using for antennas, and there is a huge range of sensitivity between different earphones, etc. So I configured the QCX design with 5-10dB more gain than other similar designs. I also felt justified in doing this because the very low noise HiFi op-amp LM4562 is used throughout - so providing additional gain which is later attenuated by the gain control does not damage overall sensitivity.?

These design considerations have also been confirmed by all feedback received so far (until yours, hi hi). I have received several comments from people who are operating the radio with the audio gain control barely off its minimum. Others have measured and confirmed the high sensitivity.?

So, according to the design and the results people are having - it seems to me that your experience is atypical and therefore suggests a fault somewhere. You should NOT need to add an LM386 to get sufficient gain <shudder /> the provided gain should be more than enough. Adding an LM386 masks the fault but does not address the underlying fault causing the low audio.?

I think that it would be worth re-checking T1, have you got all the windings correctly phased and is there DC continuity everywhere with good joints? Since you have an RF signal generator it would also be a good idea to trace the signal through the LPF and through the RxTx switch to make sure that there is not a fault there in Q5. I'm not sure what else to suggest but this should be a start. If you sent it to me I'd be happy to take a look at it, but postal times are likely rather slow.?

73 Hans G0UPL

On Fri, Oct 27, 2017 at 9:14 AM, Eddie Leighton <edleighton@...> wrote:
Ladies and gents,

I wrote a few notes on my experience with the QCX's audio. It would be interesting to hear other's experiences in this regard. My only concern with the QCX.

See?

73 de Eddie ZS6BNE
 

Eddie, my experience has been the opposite of yours - I find the audio quite loud on my 40m QCX. In fact, I tried using a pair of computer headphones with an inline volume control and had to reduce that control by 50% for comfortable listening. Now, after getting a proper adapter, I'm using my usual CW headphones, Astrocom high impedance military surplus phones, and it sounds even better.

?

Based on my experience, it sounds like what is happening to you is not normal. I hope you can get it sorted out.

?

Steve, N4IAG
 

Thanks Hans and Steve. Monday night back on the bench with my QCX. Thanks for the feedback.

73 de Eddie ZS6BNE?

On 27 Oct 2017 3:58 PM, "Steve via Groups.Io" <senglish222=[email protected]> wrote:

Eddie, my experience has been the opposite of yours - I find the audio quite loud on my 40m QCX. In fact, I tried using a pair of computer headphones with an inline volume control and had to reduce that control by 50% for comfortable listening. Now, after getting a proper adapter, I'm using my usual CW headphones, Astrocom high impedance military surplus phones, and it sounds even better.

?

Based on my experience, it sounds like what is happening to you is not normal. I hope you can get it sorted out.

?

Steve, N4IAG
 

Hi Steve and Hans,

tonight I wired my 49er amp section to the QCX's volume control just before the audio amp section and Steve I now have the same experience as you, a lively receiver!!!

It would seem there is a fault around IC10 which should be simple enough to trace. Visually all looks OK.

Thanks for the feedback once again. Once I get a chance I'll probe around there!

73 de Eddie ZS6BNE




On Fri, Oct 27, 2017 at 8:48 PM Eddie Leighton <edleighton@...> wrote:
Thanks Hans and Steve. Monday night back on the bench with my QCX. Thanks for the feedback.

73 de Eddie ZS6BNE?
On 27 Oct 2017 3:58 PM, "Steve via Groups.Io" <senglish222=[email protected]> wrote:

Eddie, my experience has been the opposite of yours - I find the audio quite loud on my 40m QCX. In fact, I tried using a pair of computer headphones with an inline volume control and had to reduce that control by 50% for comfortable listening. Now, after getting a proper adapter, I'm using my usual CW headphones, Astrocom high impedance military surplus phones, and it sounds even better.

?

Based on my experience, it sounds like what is happening to you is not normal. I hope you can get it sorted out.

?

Steve, N4IAG
 

Hans you did just great with the audio gain, I'm hard of hearing, and having enough volume is really great.
Eddie I'd definitely double check T1 too.
73
 

Regarding poor gain, I fixed a friends QCX and the problem was two resistors swapped, a 1K and a 10K that made the gain very poor. I think -90dBm was the weakest I could hear with the fault, and around -125dBm with the resistors in the correct locations. IIRC it was R34 and either R25 or R26. You should be able to measure the signal at each stage and see that it has the proper amplification as well, if you have a scope at hand.
So my tip is to double check the resistor values in the sections after the quadrature detector.
 

I thought there is much talk about T1 let me remove and rewind. That basically reduced my QCX to a Beacon unit. The tracks are so fine that damage was inevitable. Not all is lost. The transmitter is very good so my QCX will be put into service as a CW or WSPR Beacon and the HB1A put back into service for CW comms. My T1, although probably not perfect, worked.....?

On 31 Oct 2017 5:07 PM, "Daniel Ekman (kng)" <knegge@...> wrote:
Regarding poor gain, I fixed a friends QCX and the problem was two resistors swapped, a 1K and a 10K that made the gain very poor. I think -90dBm was the weakest I could hear with the fault, and around -125dBm with the resistors in the correct locations. IIRC it was R34 and either R25 or R26. You should be able to measure the signal at each stage and see that it has the proper amplification as well, if you have a scope at hand.
So my tip is to double check the resistor values in the sections after the quadrature detector.
 

Eddie

Pause and lets not concede yet. I envision you making those 8 connections somehow, with separate wires. Install the toroid on a piece of perf board, anything to hold it. How the wires run matters little as long as they don't come thru the toroid. The toroid doesn't need to rest on the board. With some thought you can pull this off. The key thought is making all those wire connections in spite of the damaged board, and then wiring them to the assembled coil.

Curt
 

Hi Curt,

That is an option. I think the damage occurred while using the solder sucker, I was careful not to overheat with the soldering iron. Those tracks are so thin (A few tenths of a millimeter) but yes with a little ingenuity it may be possible. I will need to find the patience though I think I have expended it all :)

My little audio board certainly worked and my gut feel told me there must be something wrong in the audio section of the QCX but still I never really got a sharp peak while calibrating the band pass filter (BPF) and thought well let's get that a little better first - fault! Once T1 is in it should be correct for you go past the point of no return you can never come back .....

Pity, it happened this way but such things happen. Resoldering and removing anything from a PCB even once is normally a recipe for disaster!

An opportunity to discover the WSPR facility .... I have a serial GPS (Garmin Legend) I usually use with my TH-D7A(g). Just last week I digipeated my coordinates via the International Space Station as it crossed the open sky :)

73 de Eddie ZS6BNE

On Wed, Nov 1, 2017 at 2:00 AM wb8yyy via Groups.Io <wb8yyy=[email protected]> wrote:
Eddie

Pause and lets not concede yet. I envision you making those 8 connections somehow, with separate wires. Install the toroid on a piece of perf board, anything to hold it. How the wires run matters little as long as they don't come thru the toroid. The toroid doesn't need to rest on the board. With some thought you can pull this off. The key thought is making all those wire connections in spite of the damaged board, and then wiring them to the assembled coil.

Curt

 

Ladies and gents,

The latest pic is now my QCX 40m transciever with a tiny addition :)

The audio amp is probably the easiest to debug but what puzzled me is that the audio GRADUALLY got worse until there was nothing. In the meantime I used my work around 49er add on amp but the reason was still bugging me and gave me a sleepless night or two. So I used a scope and traced the audio to the final capacitor, C51 to be exact ..... audio on one side, nothing on the negative side.



It wasn't the capacitor! It was the headphone socket shorting to ground!!! The strange thing is, it happened over time probably due to movement / heat. The tracks are very fine and the ground plane closeby too! Un-repairable, I remember the fit was tightish but the docs said, IT WILL FIT!!! :) It did, yes.

So, I moved the cap and a new socket to the 49er board and now I have TWO audio outputs. One HiFi and the other, well, err a LM386's quality. The HiFi output (Original QCX) works well with a MP3 recorder to record CW QSO's!!!

I have given mine it's name, "TUD!!!" - The Ugly Duckling ..... but it works ........... WELL!

73 de Eddie ZS6BNE
 

Oh, BTW, Peaking the BFF with the makeshift T1.

Much the same as the original situation - not a very sharp peak, even though I must have removed about 8 turns eventually (Note: T80-2). Now with C1 centralised there is a slight peak to maximum. Good enough, T1 and the BPF isn't that much of an issue. Mine peaks at around 09 / 10 on the scale and the receiver is sensitive enough (Going by ear).

73 de Eddie ZS6BNE

1 - 12 of 12