Pork Barrel - Low Output [FIXED]

[BuzzKing]

I just finished populating a Pork Barrel PCB. This is the latest version built from a purchased PCB.

I have not boxed it yet. The test is done with a test rig.

Everything seems to work fine except the output with the effect engaged is roughly 50% quieter than when the effect is bypassed at the test rig. Both pots seem to do what they are supposed to and the effect actually sounds quite good, just much quieter compared to when bypassed. I am testing other boards at the same time so I know its not the test rig.

I built this board with the following modifications:
1) Added Monte Allums mods: C1 = 0.1 uF film cap; C8, C13, C17 = 0.047 uF boxed film caps; C2, C7, C12 = 1 uF tantalum caps; IC1 = OPA2134PA
2) I have socketed R9, R39, C18, C17, and R27 so that I can eventually test tonepad mods and the LFO indicator / depth mod. Currently the stock values are in place. No mods have been tried at this point.
3) I have omitted D4 as I am using the M3101/M3007 chips. Does this need a jumper? Or just omitted?
4) I have omitted R1 and will only add it if needed after boxed. Once again does this need a jumper? Or just omitted?

I have checked and do not visually see any solder bridges or cold solders. I have checked and double checked the values of the components. I have tested voltages (see pic below). I have tried 2 different sets of ICs with similar results and voltages.





I don't know what to expect for the voltages. There are some wonky readings on TL063 3,5,7. The voltage on  pin 8 of the M3101 seems low but again I don't actually know what is correct for this build. It is also interesting that at ground points there is a small voltage ~1.1 - 1.3 mV. Does this indicate an issue?

Any help is greatly appreciated.

Thanks,
Rick "BuzzKing" Kienle

[Clayford]

R1 D4 - omit is correct no jumper needed.

I can't see them - but I'll assume you've double checked your tant cap polarities.
I assume you have your shunts for the chip selection going Left-Right not North-South
I'll double check my build here in a few re this:
You have + voltage at IC2-4... That's a negative pin. Can you double check that?
Looks like you copied my excel sheet for voltages - FYI those are vias not testpoints, I didn't know any better at the time.

[Clayford]

I'm looking at your pictures and seeing these color codes - They seem to be incorrect.
R6 R9 and R8 are HIGHLY suspect - Yellow Violet Red Gold is 4k7 not 47k Yellow Violet Orange Gold
R12 is HIGHLY suspect - Yellow Violet Yellow Red  is 470K not 470R  which should be Yellow Violet Brown Red
R27 is also Highly suspect - Yellow Violet Red Gold is 4k7 not 47k which is Yellow Violet Orange Gold


I suggest you might go through and double check all of your resistors especially your 47 value resistors - they seem to be the problem spot. It's a VERY easy mistake looks like a bag or drawer got mixed up. Some of us are how to say it delicately... "retentive" and measure each resistor as we place them to verify. 

After doing all that - can you repost pics?
can you replace the OP2134 with a JRC4558 ? I know the OP is supposed to be the superior device - I'm asking to swap it out with a completely different device to eliminate the possibility of both of your chips being "bad"

Question - are you putting + lead on +9v and - lead on pin
or + lead on chip and - lead at ground?
IE Red at +9v and black at IC1-4 you get 9.37v
or Red at IC1-4 and black at GND you get 9.37v

[Clayford]

If you want a quick check - look at this picture and verify your board against it.
You'll need to IGNORE the 0R resistor at R1 - that was my mistake when I made mine.
The pork barrel prehaps much like a Dr.Boogie seems to have become a right of passage build for many.

If you click it you'll go to Imgur click it again at imgur you'll get a very nice re sizable one.

[BuzzKing]

Thank you so much for all the info. Also, the pictures of the finished board will be a good resource. I did copy your spreadsheet. I kept a blank one to use for othe projects. By the way, what is are vias?

I hope its as easy as the wrong "47" resistors. I only measure resistors that come out of unlabeled bags. It may be that I ordered wrong or they were bagged wrong. Or maybe I placed them in the wrong slot in my parts bin.

So later tonight, or over the next few evenings, I will take a much closer look and measure all the resistors and caps on the board. I will replace any that are wrong and then repeat the voltage measurements.

I will post a new pic after appropriate repairs. If that doesn't work I acually have a 4558 chip I can try.

Thanks much,
Rick "BuzzKing" Kienle

[BuzzKing]

BTW, all my tests were done with black lead of meter on ground and red lead probing the chips. Is that correct?

[Clayford]

Oh and because I'm a complete moron and didn't mention these things before (I was fixated on getting you sorted) -
In no particular order:

WELCOME TO THE FORUM!
Congrats on getting together a rather complicated build with what appears to be a *very* easily made mistake
Thank you, for using the search function!
Welcome to the madness that is pedal building!
Thank you, for using the search function!

That said, Blk to ground and Red as a "probe" is the correct method - but I couldn't duplicate your voltage on pin4 unless I did Red on +9v and Blk as the probe. I did quick check when I found the initial resistor was wrong and didn't see anything others, except the ones I mentioned. That doesn't mean I've caught them all either - My silly butt shunted the entire signal to ground on my build via R1. My suggestion to check all of your 47 value resistors was a good precautionary step given the apparent swap, and me checking it over on a 14" laptop screen. Your cap values looked good aside from what I assume are the Monte Allum mods. I'm not familiar with Him or his mods, but that means nothing.

http://www.digikey.com/us/en/mkt/calculators/4-band-resistors.html
A great tool for checking by color code, while there are many who can remember all this stuff by heart (and I applaud them) I can not and rely on tools and tricks. This is also a great piece of freeware - and I did donate.
http://www.electronics2000.co.uk/download.php?source=ea_calc_ad#assistant

[BuzzKing]

Thanks for the welcome to the forum.

I have built several relay based bypass strips / pedals using boards from AMZ. I also built an AMZ Q&D compressor that passes a signal but I am not sure it works correctly. Then I built a test rig because I could tell I was gonna get real into this DIY pedal thing.

I have also modded several Boss and Ibanez pedals using Monte Allums mods. In case your interested you can check out his site. Great guy and great mods to get your feet wet with DIY pedal work. http://www.monteallums.com/

The Pork Barrel is my first attempt at a more difficult build.

I checked the resistors you mentioned both with the codes and with an ohm meter and you are correct. I was off by a decimal point. At this point I am going to go through the BOM and test every component on the board and will replace the incorrect ones.

I will report back on my progress in a few days cause I will only have a little time in the evenings to do the work.

Thanks a ton for all your help.

Rick "BuzzKing" Kienle

[BuzzKing]

So I tested all the components on the board. The ones Clayford pointed out were indeed wrong as well and R10. So it looks like when I was populating the 47k resistors I picked up the wrong bag. Lesson learned. I will check codes and meter all parts before placing on any board. Good insurance.

After replacing those resistors, the board works perfect. Unity volume and nice sounding chorus.

I did a quick run of voltages across the ICs:
Listed as 1 2 3 4 5 6 7 8
IC1 6.77 6.77 6.77 1.5mV 6.77 6.77 6.77 9.43
IC2 *** 4.70 *** 1.3mV 4.7 4.7 *** 9.43 (*** = highly variable)
IC3 9.32 4.76 1.4mV 4.8 0.42 3.22 0.625
IC4 9.32 4.80 5.99 0.625 1.4mV 4.76 6.14 6.14

Is it odd that there is ~1.3-1.4 mV at ground throughout the board?

BuzzKing