PCB Guitar Mania Active EQ Problem

[joelo]

Happy new year!
I am not sure if this is the right place to ask for help with this but here it goes.

I have built the Active EQ from PCB Guitar Mania. I had it combined with their Soldado preamp. the Level pot on the Soldado and the Treble pot on the EQ were having issues. I have since separated the 2 and just by doing that the Soldado works fine (sounds good!). But the Active EQ has the same problem.

With the Bass, Middle & Treble pots, and the 3 trimmers at noon, there is no sound. Turning up the Charakter trimmer the Treble pot is acting like a volume control with a loud/rough part toward the end of the rotation. I currently have a 9v and 2 1/4' jack wired to the board so plugging it in it is "on."

I have been receiving help from great people on the PedalPCB forum for a while but it was suggested I come here. I can post a link to that thread.

Here is the Active EQ:
https://pcbguitarmania.com/product/active-eq/

[ElectricDruid]

Hi Joelo,

Can you post voltages around the op-amps please? That'd give a us a good clue.

Ta!

[eh la bas ma]

Hi, I think  this is the perfect place to ask questions about your builds.
If you are stuck with issues on circuits, it's always a good idea to post here, in my experience.

I am not sure i understand the issue : The EQ worked when it was coupled with the soldado, there was a signal both in bypass and with the circuit powered on. Bass and Mids were fine, there was only a problem with Treble. And now that the EQ board is separated from the soldado preamp board, there is no sound, both in bypass and active? Did i get it right ?


Did you check that both tl072 receive 9V on pin 8 ?

Soldering looks fine but, from what i can see on pics, there are some pads with (maybe) not enough solder.

The pcb is small, few components, so i would reflow every pads just to make sure it isn't a bad contact.

Edit : If you lost the signal after taking the board out of the first enclosure, it might be a wiring issue. Can you give the link to your pedalpcb forum post, please  ?

[joelo]

Hi Joelo,

Can you post voltages around the op-amps please? That'd give a us a good clue.

Ta!

I measured the Active EQ pins when the Soldado and EQ were world up together. I can give you those, or, I'm assuming I soul re-measure now that the EQ is a stand alone unit.

[joelo]

I am not sure i understand the issue : The EQ worked when it was coupled with the soldado, there was a signal both in bypass and with the circuit powered on. Bass and Mids were fine, there was only a problem with Treble. And now that the EQ board is separated from the soldado preamp board, there is no sound, both in bypass and active? Did i get it right ?

Yes, however when it was complied with the Soldado the EQ board did have the Charakter trimmer pampered and the LED diodes omittted, with a 1M resistor in D1. I was advised of this early on (let's not get into that). However since then the Active EQ board is with all the parts from the build documents.

And, there is sound if I turn up the Charakter trimmer. And, the Soldado's Level control had a problem when combines, but by itself, it's fine.

[joelo]

Did you check that both tl072 receive 9V on pin 8 ?

Edit : If you lost the signal after taking the board out of the first enclosure, it might be a wiring issue. Can you give the link to your pedalpcb forum post, please  ?

I will check.

Here is the thread from PedalPCB:
https://forum.pedalpcb.com/threads/soldado-active-eq-from-pcb-guitar-mania.9570/

[eh la bas ma]

Here is TL072 pin out. Just to make sure there will be no confusion with pin numbers when you will post your readings.

Edit : You got a full kit or did you get the pcb and the components separatly ? Are you sure about the Character trimmer value ?

On the pedalpcb thread, I think there is something suspicious around reply #25, about led1 and 2. You suddenly lost the signal by adding them on the board. They might not be in opposite direction on your build as they are supposed to be. You made a signal probe, following the schematics you can check if the signal passes before and after these leds ?

The signal goes first in a Presence trim. I would probe the tip of the In jack, to check the normal volume (coming from your instrument or a looper, etc), and then on R1, after the Presence trim, to make sure the trim is set to let the signal pass at approximatly the same volume as on the IN jack.

[ElectricDruid]

Hi Joelo,

Can you post voltages around the op-amps please? That'd give a us a good clue.

Ta!

I measured the Active EQ pins when the Soldado and EQ were world up together. I can give you those, or, I'm assuming I soul re-measure now that the EQ is a stand alone unit.

Re-measure please. Just take the voltage from ground to each pin on the TL072 in order CCW round the chip.

Thanks.

[iainpunk]

the circuit i found on the website of PCBmania is really really sketchy.

i mean, there is DC continuity to the input, from the Vb... basically making one diode always conduct. next to that, the Vb point must first overcome a diode before it charges the capacitors and makes the part of the circuit biased the way it should be.



try a 100n capacitor between the input jack and the board, and a 1M resistor parallel to the 2 clipping diodes.

cheers

[joelo]

Hi Joelo,

Can you post voltages around the op-amps please? That'd give a us a good clue.

Ta!

Here's what I'm getting:

IC1
1 4.38
2 4.38
3 4.31
4 0
5 2.79
6 3.79
7 3.78
8 9.14

IC2
1 1.43
2 1.23
3 1.19
4 0
5 4.73
6 4.79
7 4.79
8 9.14

[joelo]

Did you check that both tl072 receive 9V on pin 8 ?

Those are reading 9.14 on both #8 pins, so that looks good, no?

[joelo]

Here is TL072 pin out. Just to make sure there will be no confusion with pin numbers when you will post your readings.

Edit : You got a full kit or did you get the pcb and the components separatly ? Are you sure about the Character trimmer value ?

On the pedalpcb thread, I think there is something suspicious around reply #25, about led1 and 2. You suddenly lost the signal by adding them on the board. They might not be in opposite direction on your build as they are supposed to be. You made a signal probe, following the schematics you can check if the signal passes before and after these leds ?

The signal goes first in a Presence trim. I would probe the tip of the In jack, to check the normal volume (coming from your instrument or a looper, etc), and then on R1, after the Presence trim, to make sure the trim is set to let the signal pass at approximatly the same volume as on the IN jack.

The photo you posted doesn't show up for me but I think I got it correct. #1 is the upper left, then counting going down, across the bottom to #5, then up the right side to #8.

It was not a kit and I think the trimmer is the correct value. If it is wrong, then one off the others are wrong. Is there a way to check once they are soldered to the pcbs? I do know that I have the short lead in the square pad for both LEDs.

Turning the Presence trimmer all the way up seems about the same volume, all the way down is slightly quieter. Signal is hitting the Treble pot lugs which is after the LEDs if I am reading the schematic correctly.

However I don't get any signal from any of the LED leads. And when it is plugged in to power, LED 2 visibly lights up, but not LED 1. Not sure of those things mean anything.

[joelo]

the circuit i found on the website of PCBmania is really really sketchy.

i mean, there is DC continuity to the input, from the Vb... basically making one diode always conduct. next to that, the Vb point must first overcome a diode before it charges the capacitors and makes the part of the circuit biased the way it should be.



try a 100n capacitor between the input jack and the board, and a 1M resistor parallel to the 2 clipping diodes.

cheers

Haha, if you say so! This is the first schematic I've studied and I am just starting to see how it works.

Just for my knowledge, what would the cap and resistor do? My goal is to combine this with their Soldado (link below) so if I was to try what you are suggesting, would that work when combined?

https://pcbguitarmania.com/product/soldado/

Schematic:

[eh la bas ma]

#1 is the upper left, then counting going down, across the bottom to #5, then up the right side to #8

That's right.

Is there a way to check once they are soldered to the pcbs?

Probably not with a multimeter, because the components around are connected to it. They will prevent you from reading the resistance accurately. Values are usually written on the side of the trimmer, hard to read : you might need a good light to look at it (I always wear an headlamp for this kind of things). Hopefully, you can manage to read at least two of them.

If you remember paying attention to the trimmers values when you built the circuit, you should be ok.

I do know that I have the short lead in the square pad for both LEDs.

Ok, that's right. Led orientation's case closed...

My goal is to combine this with their Soldado (link below) so if I was to try what you are suggesting, would that work when combined?

Yes, it will. We are trying first to get the EQ fully working . Once this is done, there won't be any trouble to put it back with the preamp circuit (good idea by the way, I was curious about this soldado preamp, seen it on musikding...but I am cautious with pcbguitarmania, I built 2 effects and they're not my best, by far ). Be that as it may, I guess IainPunk ' s suggestion is your best shot so far...

Did you try to reflow the pads ? Integrated Circuits like TL072 are sensitive to heat, so you might want to take them off the board before re-heating pads around them.

Looks can be deceiving... On my last build my soldering seems as good as yours, but one cap's leg wasn't allright (I knew it thanks to the signal probe). I reflowed it and the connection was restored, to my greatest surprise.

[iainpunk]

i suggest this simple mod. it just solidifies the biasing of the opamp. more reliable


cheers

[joelo]

Did you try to reflow the pads ? Integrated Circuits like TL072 are sensitive to heat, so you might want to take them off the board before re-heating pads around them.

Looks can be deceiving... On my last build my soldering seems as good as yours, but one cap's leg wasn't allright (I knew it thanks to the signal probe). I reflowed it and the connection was restored, to my greatest surprise.

Got it, I didn't reflow yet.

[joelo]

i suggest this simple mod. it just solidifies the biasing of the opamp. more reliable


cheers

Are you suggesting this in addition to what you suggested earlier ("try a 100n capacitor between the input jack and the board, and a 1M resistor parallel to the 2 clipping diodes")?

EDIT: I now see by your diagram that the answer is "yes."

Also, how would I add a 1M resistor parallel to the 2 clipping diodes, and a 10uf where you say? Sorry for what may be to most of you a basic question, but I'm not far past noob

[eh la bas ma]

how would I add a 1M resistor parallel to the 2 clipping diodes, and a 10uf where you say?

1M resistor : one leg goes to Treble pot's pin 3, other leg to LED2 negative side (the pad wich isn't connected to the Character trimmer). You might need to use your multimeter on continuity test and have a look on the schematics to find the right locations .

10 uF cap : It's polarized, so the positive side goes to the Character trimmer's middle pin. Negative side goes to C1's pad, the one  that is connected to R1.


For your curiosity, here is a pic to illustrate the difference between "in series" and "in parallel" :





i hope you can see it...

"VB", in case you were wondering and as far as i understand, is an internal network, each point marked VB should be connected together. Could also mean something like "Voltage Biasing"...

[duck_arse]

the circuit i found on the website of PCBmania is really really sketchy.

cheers

can anyone see an explicit mention on the schematic of IC2A for the build in question? it's possible/probable those voltage measures are wrong, but without some idea of how it is wired, we can't tell.

possibly, if you pull the IC's from their sockets, repower the circuit and then measure the voltages on the empty socket pins, we might see something. possibly.

your C7 - why mount underside, space reasons? wrong or bad connection there will cut all signal flow to the following stages.

[joelo]

the circuit i found on the website of PCBmania is really really sketchy.

cheers

can anyone see an explicit mention on the schematic of IC2A for the build in question? it's possible/probable those voltage measures are wrong, but without some idea of how it is wired, we can't tell.

possibly, if you pull the IC's from their sockets, repower the circuit and then measure the voltages on the empty socket pins, we might see something. possibly.

your C7 - why mount underside, space reasons? wrong or bad connection there will cut all signal flow to the following stages.

Yeah the underside mount was because of not planning ahead, I got to C7 and it didn't fit.

The IC2 measurements look weird?

I've attached the entire schematic.