December 24, 2018 at 1:07 pm #3500
i’ve built the Emexar micro amp version. The led works, i’ve got signal. But in effectmode there is no boost and the volume works counterclockwise.
what did i do wrong?December 24, 2018 at 1:56 pm #3501
The volume pot is wired backwards. Reverse the wires to lug 1 and 3. Do this at the pot, not on the board.
Now that you have the board removed to fix the pot, send us a better photo of the front and one of the back. If you have no boost, you may have a resistor value wrong. Check all of them. Let us know the results.December 25, 2018 at 2:19 am #3503December 25, 2018 at 2:20 am #3504December 26, 2018 at 1:43 pm #3518December 26, 2018 at 4:49 pm #3522
“Tack solder” a jumper (short wire or leftover resistor lead) connecting both the anode and cathode sides of R10 (currently a diode) together and see what happens.December 27, 2018 at 3:00 am #3544
Now I read following voltages on the ic from pin 1 to pin 8:
Still no volume boost….December 27, 2018 at 8:55 am #3548
Your pin 3 voltage is low. It should be 4v.
I cannot clearly see the entire board. Update with a clear new board photo.
Because I cannot see everything please check that you followed these instructions from the build document for the MA build:
● The MicroAmp only has a single Level control. If you wish to keep your build true to the original, we suggest using a hand wired potentiometer connected to the “Gain” pads so you can center the single knob on your enclosure. If you do this, you will need to solder a fixed 10k resistor between “Volume” pads 1 and 2, and a jumper between pads 2 and 3.December 27, 2018 at 11:39 am #3549
I measured all the resistors. They are the right value and in the right place. I reflowed the solder. Pin 3 Still measurs 2,5 volt.
Capacitors should also be correct.
I use the volume slots, not the gain. Kit is from Musikding and the hole in the predrilled enclosure is offset. That’s why.December 27, 2018 at 12:02 pm #3550
The pot needs to be in the Gain pads. Also you need to have a 10K resistor and a jumper in the volume (level) pads per the directions.
Whether you hand wired the pot or not it does not matter you still need to do what the final directions say above. The pot must be in the gain pads and you need to solder a fixed 10k resistor between “Volume” pads 1 and 2, and a jumper between pads 2 and 3.
This is why I was asking for an updated picture because I cannot see what is happening.December 27, 2018 at 12:07 pm #3551December 27, 2018 at 12:09 pm #3552
I Still have to change the pot to the gain sideDecember 27, 2018 at 12:10 pm #3554
- The potis must be used in the Gain pads and you must:
- solder a fixed 10k resistor between “Volume” pads 1 and 2,
- and you must place a small jumper between “Volume” pads 2 and 3.
Then you will still need to make the connection from VB to IC3 in Purple above.
This can be done on the back side of the board best IMHO.
If it helps I think we are very close now.December 28, 2018 at 3:45 am #3568
Thanks for all the help. I got it working now. Apparently, the resistors and jumper in the volume slots are a “have to”, not a “want to”. Volume boost starts on the last 2 millimeters of the pot. Is that normal? If so, would a lineair pot help solve this?December 28, 2018 at 1:02 pm #3571
“Want to” in my tongue means you must in a nice manner or we would say it is optional.
In other words if you take that pill you will want to eat first.
I completely understand so that is why I was extra clear with you. My daughter speaks German which was my next move.
That said congrats and you are welcome to try a different taper pot. We simply chose what the manufacturer did but we always encourage experimentation.
Also note that the Micro Amp is more of a Mod based on the more popular circuit varieties since it was so close schematically the Mod was too easy to pass up. That said all of our other builds are much more “straight forward”.
I am glad I have helped and you have a working circuit.
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