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O2 headamp output booster PCB
O2 headamp output booster PCB
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Old 12th March 2014, 04:37 PM   #121
agdr is offline agdr  United States
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O2 headamp output booster PCB
Default Fliege notch filter series resistor works after all..

Turns out I was wrong in my post above about adding a small series resistance to the center 0.047uF cap affecting the filter's Q and notch depth. I just handn't turned the frequency adjust pot far enough yet to fully null it. Took about 5 turns from the center on the 20 turn pot, which was centered when I installed it. Also turned out that only 4.99 ohms is needed to isolate that 0.047uF cap from the op amp output, not 20 ohms. So the other isolation method above, the BUF634 chip added to the inner op amp, really isn't needed since this simple resistor trick does the job.

The LT Spice simulation comes within the ballpark of matching the real-word results, if the 27R resistors are changed to 2R to shift the frequency to match the pot turn. The simulation gives around 2.4mV out with 200mV in at the notch frequency, or 20log(2.4/200) = -38dB. The real world results shown on the DMMs below are 0.97mV out with 37mV in, or -31.6dB. The pre-amp (not yet populated) on the Fliege notch filter board is set for +33dB. So the net result would be to restore the fundamental to its original level, but boost all the device harmonics by 33dB, useful for looking at the harmonics on a scope's FFT.

* The first two photos show the test setup. I'm using DMMs instead of the scope to get more accurate absolute values.
* The next photo shows the series resistor modification in the red circle. Just a 4.99R 1206 resistor put in series with the 0.047uF 1206 capacitor. The resistor isolates the capacitive load from the output of the LME49990 and restores the waveshape. The other LME49990 doesn't have that problem in the circuit. The board now has the proper filter caps on the power supply and BNCs after another bunch of parts from Mouser.
* The next two photos show in the input signal from the generator, 37mV, and the output from the Fliege notch filter, 0.97mV = -31.6dB. The pot is adjusted for maximum null, about 5 turns from center with the 2 27R frequency set resistors in place. The second photos shows the frequency out of the generator, 999.96Hz.
* The next two photos are a test of notch wall width and symmetry. These are +/-1Hz from the 1kHz (1001 Hz and 999Hz).
* The final two photos are the same thing, a notch width and symmetry test, but I'm shooting for -10dB here, up from the notch bottom's -31.6dB. This happened at +/-17Hz from the 1kHz Fc, as the meters show. 11.5mV on one side of the notch wall and 12.0mV on the other, reasonably symmetrical.
* The schematic has the 4.99 isolation resistor now in series with the circuit's middle 0.047uF cap.
Attached Images
File Type: jpg IMG_2376.JPG (75.8 KB, 201 views)
File Type: jpg IMG_2377.JPG (84.0 KB, 200 views)
File Type: jpg IMG_2379_1.jpg (99.7 KB, 196 views)
File Type: jpg IMG_2380.JPG (46.4 KB, 193 views)
File Type: jpg IMG_2381.JPG (32.4 KB, 183 views)
File Type: jpg IMG_2382.JPG (48.6 KB, 10 views)
File Type: jpg IMG_2383.JPG (53.6 KB, 9 views)
File Type: jpg IMG_2385.JPG (47.9 KB, 11 views)
File Type: jpg IMG_2386.JPG (48.1 KB, 10 views)
File Type: png Fliege notch filter circuit 1.png (26.3 KB, 16 views)

Last edited by agdr; 12th March 2014 at 04:53 PM.
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Old 24th March 2014, 03:55 AM   #122
mcandmar is offline mcandmar
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Hi Agdr, can you please confirm a couple of things for the V3 board,

-Is the positive end of C16 closest to the edge of board?

-When running the power management circuit in the stock config with R13 and no R14 does it need the jumper cable, or is that only for the modified version with no R13 and a diode across R14?

If anybody in the UK has a stash of 2N7002LT1G fets i would really appreciate a couple. I somehow forgot to put them into my last Mouser order
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Old 24th March 2014, 07:10 AM   #123
agdr is offline agdr  United States
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Quote:
Originally Posted by mcandmar View Post
Hi Agdr, can you please confirm a couple of things for the V3 board,

-Is the positive end of C16 closest to the edge of board?
That is correct, the banded end goes closest to the board edge. Any other type of capacitor would have the band on the negative end, but on those SMD tantalums the banded end is positive. I just noticed in looking at the layout that I didn't put the additional text about the banded end on that capacitor, just the band on the symbol. I'll add that on the next board run in a few weeks.

Quote:
Originally Posted by mcandmar View Post
-When running the power management circuit in the stock config with R13 and no R14 does it need the jumper cable, or is that only for the modified version with no R13 and a diode across R14?
That is right, no cable needed in that case. You will still get a small amount of turn-off thump though, although I measured it in one of the posts above to be greatly reduced. Removing R13, adding the zener for R14 and adding the cable will give you zero turn off thumps.

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Originally Posted by mcandmar View Post
If anybody in the UK has a stash of 2N7002LT1G fets i would really appreciate a couple. I somehow forgot to put them into my last Mouser order
I'll drop a couple in an envelope, no charge. They are so small they would fit in a regular letter envelope. I need to send two transistors out to another builder anyway who bought a parts kit, since I screwed up and sent him a strip of 3 with 2 already missing from the strip. In fact, I'll drop a zener for "R14" in too and you can give that zero thump mod a try if you want. I'll get those in the mail tomorrow.

Last edited by agdr; 24th March 2014 at 07:19 AM.
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Old 24th March 2014, 04:42 PM   #124
agdr is offline agdr  United States
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mcandmar - I just remembered something. C16 is a capacitor you probably won't want to install. That capacitor is just in parallel with C7 to create an (optional) much longer turn-on delay for the relay if someone wanted. The 10uF C7 is providing about 5 seconds worth of delay, which is probably fine for most folks. Adding C16 would bump that up to around 45 seconds. For a longer delay replacing C7 with a 22uF Mouser #810-C3216X5R1V226M would roughly double the turn-on delay to 10 seconds.

I should probably leave the pads for C16 off entirely on the next board spin. I originally put C16 on the board to provide some flexibility in testing different turn-on delay times.

Last edited by agdr; 24th March 2014 at 04:46 PM.
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Old 24th March 2014, 05:25 PM   #125
mcandmar is offline mcandmar
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45 seconds does sound a bit much so i'll pull that capacitor off again, i just ordered everything in the BOM (or so i thought).

One bit of constructive criticism, the orientation of the diodes, LED's and tants isn't that clear so i had to refer to your pictures to verify i had them the right way around. Rather than the little dots can you make them a vertical line under each component so its more obvious. Would also be worth noting the position of the relay on the bottom of the board, only reason i knew that was from seeing a picture you had posted previously, most people would assume it goes topside. Or does it matter?

Thanks for the parts offer Agdr, you are a true gentleman
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Old 25th March 2014, 03:48 AM   #126
agdr is offline agdr  United States
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Hey thanks for the suggestions! I'll add those. I've just put "relay mounts under PC board" on the top on the new design. In the process I also noticed I had the "K1" part label on the wrong side of the board. Fixed.
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Old 5th April 2014, 09:13 PM   #127
esiuda is offline esiuda  United States
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Ok, I put mine together over the last 2 days.
Left channel gives a "pop" when turned on, (when the relay clicks on?) no input present
volume of music after that is very low.

Right channel seems to be good. No pop when turned on, music starts playing at what seems to be normal level.

Both LED's light up at the same time.
did not modify the O2 board as of yet. It did work fine before the addition of the O2 Booster Board.

This is using the battery only.

Reverted back, and everything works normaly.

I am going to be going over the solder points, and reflowing them, Any idea on which ones to concentrate on, since it is the left channel?..
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Old 5th April 2014, 10:09 PM   #128
Tony72 is offline Tony72  United States
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Hi, I started to put my board together and have a question. D2 is not marked for a direction on the board. Which way does it go?
Thanks
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Old 5th April 2014, 10:16 PM   #129
esiuda is offline esiuda  United States
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Found a solder bridge on IC3. Now everything is working great! Next weekend I will convert the O2 board to 15V!

Tony72, I put the D2 in right side up. IE the print reads the same as the board. That worked for me. On mine that put the band on the left, towards K1
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Old 5th April 2014, 10:26 PM   #130
mcandmar is offline mcandmar
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Quote:
Originally Posted by esiuda View Post
I am going to be going over the solder points, and reflowing them, Any idea on which ones to concentrate on, since it is the left channel?..
Double check the orientation of the two opamps, or post a pic in case we can spot something..

Quote:
Originally Posted by Tony72 View Post
Hi, I started to put my board together and have a question. D2 is not marked for a direction on the board. Which way does it go?
Thanks
Same as D1.

@agdr: Recived the transistors and diodes on friday, thanks again for those, i'm going to try and finish it off over the weekend
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