Porkbarrel 2019 Not Chorusing? Update - Weakly Chorusing?

[csermonet47]

Hey everyone! New here and my first plea for help.

Just threw together my Porkbarrel 2019 build and I am trying to make sure everything is working properly before boxing it up because it is such a tight fit.

I am getting a clean signal through the amp with no chorus effect at all. When I adjust the blend knob however, I do get the vibrato effect. I went ahead double checked that all components are the correct values with the correct orientation and I did not see any issues there. All resistor and capacitor values were checks before soldering. I took the voltages below and have highlighted the areas that look a little unusual compared to what is listed on the build sheet. When I initially hooked up the power to the breadboard, I put the positive and negative power supply hookups on the same rail by accident, so I think something may have gotten fried. All ICs and transistors are from smallbear so they should be genuine. All other components are from Tayda.









Any ideas? Thank you in advance!

[zgrav]

the voltage readout for your TL062 is the opposite of what is set out in the other chart.    did you record the voltage correctly when you measured it?

[csermonet47]

I rechecked pins 5 and 6 on the TL062 and they are indeed positive!

[somnif]

The circuit has polarity protection so hooking it up backwards shouldn't damage it (hypothetically).

Do you have a spare 4558 to pop in? All the voltages on yours seem a bit high compared to the standard (though that is fiddled with by the trimmer), and it wouldn't be the first time Tayda has sent a bad chip in a batch.

[csermonet47]

I do not have a spare 4558 unfortunately. I did turn T1 down a bit though and got it to match the voltages listed in the build guide. The ICs were sourced through smallbear so I think they should be legit.

Thank you for the help so far guys!

[somnif]

Hmm, how about the zener, what are the voltages on either side of D4 (the chunky fellow tucked up under Q5 in the top corner)?

It looks like something's weird with the Vc rail, but I don't see any resistor values around it that are incorrect. Hrmph.

[csermonet47]

I am getting 9v on the banded side (cathode?) and 0v on the non-banded side (anode?).  Does this sound correct? I am really a rookie so I don't fully understand how everything works haha.

[somnif]

I am getting 9v on the banded side (cathode?) and 0v on the non-banded side (anode?).  Does this sound correct? I am really a rookie so I don't fully understand how everything works haha.

Yeah that's what it should be (the zener is used as a protection device, if the voltage goes over its limit of 12V the excess gets dumped to ground.)

[mickey.bellinello]

Probably an idiot reply but..did you set the trimpot halfway before testing it? It seems that is fully clockwise in the photos.

[csermonet47]

I did have the trim pot set to half when I tested voltages. All the way gave the best vibrato effect which is why it was set that way in the photos. I just don't really know what it could be at this point other than something with the ICs?

[somnif]

My next suggestion would be to cook up a simple audio probe and poke around. Super simple to make, just need a spare capacitor (I use 100n).



Power up the circuit as normal, squirt some sound into it (I use a little white noise generator, but anything that will put a signal into the input will work), then treat the probe as the output to the amp. Read the schematic, and follow the audio path from input on. Then, figure out where things get weird.

[csermonet47]

I made an audio probe for another project, but I haven't tried it on this one. What would I be looking for since it is passing audio fine, there is just no chorus effect?

[somnif]

Compare what you're hearing on pin 3 of the BBD to what you hear at pin 7/8. I'd recommend having rate and depth both about half way

Also, does your multimeter have a frequency counter setting? If so, poke it at pins 2 and 4 of the MN3101 (and/or pins 2 and 6 of the MN3007), see if you're getting a clock signal out (The rate knob should alter the count)

[csermonet47]

Pin 3 gets a nice clean signal. 7/8 gets a slightly distorted, louder clean signal with no modulation. When I adjust the trim pot, anything below half kills all signal coming from 7/8.

I measured hz at pins 2 and 4 of MN3101 and I am getting a fluctuating read of 70-90hz that increases and decreases with the rate knob. Does this all sound right?

[thomasha]

The lack of modulation could be due to a problem with the LFO, since it is parked at a fixed frequency defined by the rate knob.

Could you test it? Just add a LED and a 2k resistor between pin 7 of the LFO and ground and it should blink. If it's not blinking, dark or on all the time check the LFO path, there could be a short to ground or a bad connection somewhere.