Amplifier

[patzik]

Moved the ‘question” to the correct item.
The 1.3.1 version doesn’t have the jumper for the vcc/gnd swap, I wasn’t referring to this.
The solder jumper on the back and the jumper on the front, as in the picture (enable/bypass d9 and amplifier on/off), how do I configure them? And why could the right led (act) and the amp not work?
If I reverse the led it is continuously on, so the current flows the wrong way...

[arananet]

Now I see what your mean.

So back jumper is to tell arduino's that there is an amp on the board. The front on-of is to shutdown the amplifier because some systems does not require so many amplifications levels, so it will work without it. Take the front slider switch as a high-low volume regulator. It will ok if we put a pot on there but there is not too much room left.

ACT led works when the sd is accesed. So if it does not work, you have a problem between the 4050d and the led. What's the value of the resistor that you used? 330ohm is proved that works ok. Higher values maybe will provide too much resistance and does not will power on the led.

Regards,
Edu.

[patzik]

So with the lm386 is solder the jumper to enable d9, and without the lm386 to bypass d9?
You talk about a front slider switch, but I have no idea what you mean :-) do you mean the 1k pot?
The jumper amplifier on/off is still not working,i see the left pin is totally not connected, is this correct?
I replace the 4050d, but no change in behaviour. When the sd is accesed the led lights up for a fraction of a second. Thereafter there is -5v on the led (wrong polarity) so the led is off.
The resistor I usd is 470ohm but with the current in the wrong direction this is irrelevant.

Did you (or someone else) ever have the 1.3.1 or 1.3.2 board made/tested?
There seems to be a problem in the design...

[arananet]

Maybe this photo will help to clarify this.

Solder jumper is for select between direct output from D9 to the jack (without amplifier) or D9 To amplifier and finally jack output.

Yes there are at list 20 tzxduino working already with the 1.31 and the final release.

Act led is working via CLK signal, when this is acceded, the led will poweron. The same system I use on my tapuino, so no failure.

Regards,
Edu.

[patzik]

Before I continue, I like to say thanks for sharing your design and your help. Good to hear the 1.31 is working, means I must be able to fix it. I will be abroad for a few days, so it's on pause for a few day.
I understand the schematic, the 'jumper' in it is the solder jumper. What I don't see is the jumper that is on the front of the board 'Amplifier ON/OFF' where does this connect to?
Come to think of it, that was one of my questions, why is the left pin of this jumper not connected to anything?

Still if baffles me why the current on the act led is reversed on my board, maybe a short or something. Or could it be software?

[patzik]

Took another look at the schematic, I see that the jumper connects the 5v either to the amp or to, well nothing so amp is off. With the amp unpowered, would there still be sound?

[patzik]

I looked at the tapuino I build from your design and I see that the act led on this also is not very active, just a few blinks here and there with minimal brightness, I see just about the same on the tzxduino so I guess it's ok. Still wonder why there is about 5v on the negative side of the led...
The tzxduino is working fine without the amp (solder jumper). With the amp (solder jumper) I get no sound with the jumper to amplifier off, and with the jumper to on I do get sound, but it's less loud I think than without the amp. The signal on a scope looks weird, and the spectrum doesn't accept it as a valid signal (no loading lines). Also the variable resistor doesn't seem to do much, the sound changes a bit but not really that much and I can't get the spectrum to load anything.

[arananet]

The leds acts when the buffer has data to read/write. The original version does not include the buffer, but I added to stabilice the 3v3 signals and make those signals amplified, just like any data buffer works.

The variable resistors that we use are 10k.

This design can be improved of course, I can accept any suggestions that you may have or want. I do this design because a friend ask me if I would to it.

Regards,
Edu.

[patzik]

Before I can do any suggestions I first need to know your thought behind some of the design choices regarding the amp circuit. In theory it should work, so I still have to do some troubleshooting on my board.
The thing I still don't understand is the 2 jumpers. The solder jumper I understand, I can choose between letting the signal go through the amp, or bypass the amp and have it go straight to the socket. The 'regular' jumper I still don't understand, why did you add this option? If I remove the 5v from the amp, there is no sound so the tzxduino is basically useless. Can you explain your thoughts behind this?

[arananet]

I always makes improvements on the design. Some are from the old design some of the new design. I want to change the amp to a more simple one and cheaper. But as is, the last version works great.

Regards,
Edu.

[patzik]

I am still,unable to get the op amp working properly on the 1.3.1. boards I have.
Now I read “23/04/2018: Fix some issues with the op amp, adding two resistors (jgilcas)”.
Could this be related? What was the fix by these 2 resistors,and can I adapt the boards to add these resistor?

[arananet]

Sorry, design changes each time a beta tester user detects a problem. I can't offer solutions to old design and maintain the new ones.

The current design of the OP amp is this, maybe can help you to fix yours:

[https://imgur.com/a/mMKjoIE]