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 Post subject: FET PreAmp not working
PostPosted: Thu Jun 21, 2018 1:02 am 
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Hi there, I completed the FET PreAmp a couple of nights ago and have been unable to get it working. When I initially plugged it in the pedal worked in bypass and when the engaged it was making a high pitched oscillating sound and the pitch would change as I moved one of the controls around. No guitar signal was present. I did some research on this site last night and removed the pedal from the case to make sure the pots where in the right locations, checked ICs orientation and swapped them around, and, this morning, went over the board and redid all solder joints. The pedal is no longer oscillating, however, what signal I am now getting is very weak (I mean VERY weak as in a need to turn amp up significantly to hear the signal at all). In spite of the very weak signal, all controls except the treble control seem to be working as I would expect them too except the treble control. The treble control is adding treble up to a point and then once I go past that point the entire signal dies. I have gone over all the capacitors with a multimeter and check them against the instructions to make sure they are all in the right location. All seem to be ok with the exception of 15K which is only reading around 9.5 to 10K. I've attached photos of the build. Any suggestions or assistance would be greatly appreciated.

thanks


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PostPosted: Thu Jun 21, 2018 4:42 am 
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OK, now here's the photos . . . . .


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PostPosted: Thu Jun 21, 2018 7:31 am 
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For starters you need to improve the quality of your soldering. I see several dome shaped joints which is an indication of poor heat transfer which results in a cold joint. In several places I can still see the solder pad. In some cases I can still see the hole thru the PCB. A quality joint should be cone shaped and cover the entire solder pad. You should not still be able to see down into the hole after you’ve soldered a component into place.

Once you’ve done that give the pedal another try and see what happens. If you still have issues we can get into checking the ICs. I seem to remember this pedal having issues with shipping with a bad IC on occasion. One of the others will chime in on the procedure. IIRC with the chips in one way you’ll have drive but no tone controls. Flip flop the chips and you’ll have tone control but no drive.

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PostPosted: Thu Jun 21, 2018 9:15 am 
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Here is some further guidance: http://www.byocelectronics.com/board/viewtopic.php?f=9&t=52211

http://www.byocelectronics.com/board/viewtopic.php?f=9&t=52188

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PostPosted: Thu Jun 21, 2018 3:05 pm 
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Are your pots insulated?


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PostPosted: Fri Jun 22, 2018 8:55 pm 
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Hey, thanks to everyone that has posted a response.

OK, I have been over all the solder joints again numerous times. I went over them yesterday and then tried the pedal again this morning. This time got the bypass signal only and not led light. I just finished going over it again this morning and used some gootwick to remove excess solder and solder bubbles from component side. Fired it back up and the good news is that I have the led light back but still no signal whatsoever when pedal is engaged??? (no oscillating / no faint signal)

One of the problems I seem to be having is that when I apply my soldering iron to the component and solder pads I'm finding that the solder is forming the dome shapes and when I reapply the iron to try and improve the connection it ends up escaping through too the component side of the board. I guess I just need to work on my technique. Any specific suggestions for this (eg. iron too hot, practice etc.)

Also, wondering if it could be a problem with the switch. I was looking around the forum yesterday and came across an article that discussed sensitivity of foot switches to soldering iron heat. When I was trying to wire up terminal four on the switch I did melt some of the plastic casing around the front corner. Is there a way I can test a footswitch with a multimeter?

Re question about about insulated pots: if it is not part of the standard build instruction then no they would not be insulated.

Thanks

John


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PostPosted: Fri Jun 22, 2018 9:48 pm 
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PS. How do I test the ICs? And is there some way I can test the board to see where the signal is dying?

John


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PostPosted: Sat Jun 23, 2018 4:19 am 
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Please post new photos of your improved soldering.

Sounds like your technique needs to be refined a little. It should only take a second or so to make a good solder joint. Keep your iron’s tip clean and tin it before each solder joint. This will promote good heat transfer and the likelihood you’ll have a quality solder joint when you’re done. Since the eyelets on BYOC boards are thru-plated it is difficult to keep all the solder on the solder side of the PCB. Flow thru isn’t necessarily a bad thing as long as the solder that flows thru doesn’t form a short on the component side of the PCB.

See this thread regarding checking your stomp switch’s functionality.

viewtopic.php?f=10&t=31545

If you have a DMM you can use it to take DC measurements of all the ICs. Apply power to the pedal, insert a plug into the input and take your voltage readings.
Image

To trace the signal thru the circuit will require a signal probe. A probe is nothing but a glorified capacitor and some wire and a connection to an amp. BYOC offers one in kit form or you can make one from an old instrument cable you don’t need anymore.

https://buildyourownclone.com/collectio ... gnaltester

DIY option…
Image

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"It’s your soldering."

If Gene Roddenberry were alive today I would punch him in the face.


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PostPosted: Wed Jun 27, 2018 4:29 am 
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Thanks for you response Stephen. Photos of revised soldering attached.

Whereabouts do I take the DC voltage readings on the ICs - the solder joints or IC prongs?

And just confirming I need at least a .1uf 16V to 600V capacitor to make the probe?


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PostPosted: Thu Jun 28, 2018 3:22 pm 
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You have a lot of flux on your PCB. You need to get some isopropyl alcohol and clean it up.

You can take the readings at either place. If you can get to the pin or the socket, that's best. I usually find that I need to stab the point of the probe into the solder to actually get it to read if I measure from the solder joint.

No, you do not need a .1uF cap for the probe. You can use almost any value. But if you use a small value cap, just be aware that it's going to sound very thin.

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