PCB Guitar Mania Active EQ Problem

[duck_arse]

indeed yes you have attached the schem I was also looking at. those opamps are both duals, but the circuit diagram only shows three opamps. without knowing how the fouth opamp is connected, we can't say what correct voltages on that half of the IC should be.

the part marked IC1_B on your schem also looks to me to be wrong voltages, as it is being biased by the part marked IC2_B, which shows about half supply volts. we'd be expecting IC1B to be close to that same voltage.

but without a complete, accurate circuit, it's all guesswork.

[eh la bas ma]

And, there is sound if I turn up the Charakter trimmer

Sorry if this is redundant but just to be clear, there is no sound when the circuit is switched off, and there is when it's powered on, if you turn this trimmer ? That would suggest that the signal can go all the way through the signal path on the pcb.

Maybe some more experienced forum member could show you the signal path on schematics. Then you would be able to audio probe this path to see where the signal stops when the circuit is switched off.

About these voltage readings, did you try Iain's idea with the extra cap and resistor ? If so, maybe you should do the test again to see if something's changed.

Edit : i tried to find the signal path, correct me if i'm wrong :

[eh la bas ma]

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.

Is it what you're looking for ? Looks like it mentions IC1 and IC2 pin 4 and 8.




Edit : i guess i'm wrong. We need pin 1,2,3...

[ElectricDruid]

Edit : i tried to find the signal path, correct me if i'm wrong :

That looks like it to me! 

[idy]

One thing I am seeing (and maybe understanding after reading the blurb at the seller's site), is that the active EQ is not designed to be a stand-alone circuit...thus the absence of a DC blocking cap on the input. Adding one would maybe help keeping that first opamp biased when you plug in a guitar (or pedal that has a volume control leading to the output.)

The docs do reccommend boxing the EQ (and a group of other add-on eq tools) as separate pedals, but say things like

...you should be able to read schematics and spot which is the best part to place them and which parts of the original circuit you should remove...

So there is the provision of leaving the volume control out and patching your circuit in there.

Further info:

Active EQ: Based on the Freeman BE-OD and the Dirty Shirley EQ section. We consider this EQ the best fit for Preamp emulator projects and high gain pedals.
Certainly the most complex of the pack. Includes an internal Presence control, followed by Character trimpot that regulates how a set of LEDs compress the signal. Then we jump into a passive treble control, followed by an Active Bass section. Now's when you have to choose if you want to have a volume control of the overall circuit inserted here from your main PCB board (Tube screamer, Plexi, etc) or to place just an internal trimmer as an additional control. After this volume section it comes the active mids control.
One of the characteristic that makes this board the best solution for preamps and high output circuits it's the Power output option, this works the best for those high output preamps to go and feed directly into a power amp, and the regular output will be tamed into a more pedal friendly volume. If you are using this board with a pedal that's not famous for his big output (Klon centaur for example) you should use the power output.

[eh la bas ma]

Being a member of the pcb guitar mania group on facebook, I tried to ask about IC2A.

https://www.facebook.com/groups/1066092703545364/posts/2104453826375908/?comment_id=2104626933025264&notif_id=1641518406738909&notif_t=group_comment&ref=notif

If you can't or won't go on Fb, here the answer that an other member kindly gave me :

"Took a quick look, the input to that first op amp isn't biased properly on the schematic. possibly before the input, there needs to be a decoupling cap & a biasing resistor (in that order).

In the original circuit (BEOD), the input comes from an opamp's output, so it's already bias'd and has low output impedance when it gets to the presence control.
BTW, I always considered that 470k biasing resistor after the volume control to be unnecessary and was mistakenly left in."

I also asked for voltage readings from people who built the same EQ, to have some exemples, but no luck so far...

[duck_arse]

Being a member of the pcb guitar mania group on facebook, I tried to ask about IC2A.

https://www.facebook.com/groups/1066092703545364/posts/2104453826375908/?comment_id=2104626933025264&notif_id=1641518406738909&notif_t=group_comment&ref=notif

If you can't or won't go on Fb, here the answer that an other member kindly gave me :

"Took a quick look, the input to that first op amp isn't biased properly on the schematic. possibly before the input, there needs to be a decoupling cap & a biasing resistor (in that order).

In the original circuit (BEOD), the input comes from an opamp's output, so it's already bias'd and has low output impedance when it gets to the presence control.
BTW, I always considered that 470k biasing resistor after the volume control to be unnecessary and was mistakenly left in."

I also asked for voltage readings from people who built the same EQ, to have some exemples, but no luck so far...

mmmmmm, yes, nice work eh la bas ma, but really, the build docs? isn't that the place to put all the information a builder will need? here's our new pre monster tone amp drive over board, we're not going to tell you how to build it tho, you need to search out a geezer on fakebook, he knows a guy has seen a pencil copy of the circuit diagram, might point you to someone who can guess at the board designators  .......

[joelo]

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.

I've been too busy to do anything with this for a few days but I see the latest posts, so thanks for all the continued interest!

I pulled the ICs and here's what I'm getting:

IC1
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 9.14

IC2
1 0
2 0
3 0
4 0
5 4.73
6 0
7 0
8 9.14

[joelo]

Sorry if this is redundant but just to be clear, there is no sound when the circuit is switched off, and there is when it's powered on, if you turn this trimmer ? That would suggest that the signal can go all the way through the signal path on the pcb.

No problem, I currently have it wired directly to the jacks, no footswitch, so when I plug it in it's on. There is no sound with all pots and trimmers at noon. Turning up the Charakter trimmer lets sound through.

[joelo]

One thing I am seeing (and maybe understanding after reading the blurb at the seller's site), is that the active EQ is not designed to be a stand-alone circuit...thus the absence of a DC blocking cap on the input. Adding one would maybe help keeping that first opamp biased when you plug in a guitar (or pedal that has a volume control leading to the output.)

The docs do reccommend boxing the EQ (and a group of other add-on eq tools) as separate pedals, but say things like

...you should be able to read schematics and spot which is the best part to place them and which parts of the original circuit you should remove...

So there is the provision of leaving the volume control out and patching your circuit in there.

Further info:

Active EQ: Based on the Freeman BE-OD and the Dirty Shirley EQ section. We consider this EQ the best fit for Preamp emulator projects and high gain pedals.
Certainly the most complex of the pack. Includes an internal Presence control, followed by Character trimpot that regulates how a set of LEDs compress the signal. Then we jump into a passive treble control, followed by an Active Bass section. Now's when you have to choose if you want to have a volume control of the overall circuit inserted here from your main PCB board (Tube screamer, Plexi, etc) or to place just an internal trimmer as an additional control. After this volume section it comes the active mids control.
One of the characteristic that makes this board the best solution for preamps and high output circuits it's the Power output option, this works the best for those high output preamps to go and feed directly into a power amp, and the regular output will be tamed into a more pedal friendly volume. If you are using this board with a pedal that's not famous for his big output (Klon centaur for example) you should use the power output.

That seems confusing then. Would it be better to pair this back up with the Soldado then? Since we know that works on it's own?

[eh la bas ma]

I don't think so. Friedmann BE-OD and your Soldado don't have the same design. It'll be easier to make it work first.

Edit : Besides, you already tried both together and it didn't work it only prevented the Soldado from working correctly.

In your position, I would fully wire the circuit (3pdt switch), untill it works, even if i have to take it off later.

I did a similar project (OD + EQ) and both circuit have their own footswitch, with an order switch (spdt). I can engage both or just one circuit, and decide in wich position they are, OD before or after EQ. I found the wiring method on this forum ( looking for "order switch"), I can find it again if you need it.

I strongly suggest that you try Iain's idea with the extra cap and resistor, and if it still doesn't work, to take some fresh voltage  measurements of both TL072 with this modification, and post them.

Edit 2 quick recap : It has been established that one op amp can't work correctly, the board on its own doesn't work properly, it  needs the Friedmann amplifier to do so (replies #24 and 25). The build doc gives a warning about being a complex project that needs you, the builder, to know how to make it work (!). The seller never did the necessary arrangements neither to adapt this circuit for stand-alone use, nor even for average hobbyists, wich is rather uncommon. Fortunatly, a solution has been suggested to overcome this issue (reply #14).

[duck_arse]

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.

I've been too busy to do anything with this for a few days but I see the latest posts, so thanks for all the continued interest!

I pulled the ICs and here's what I'm getting:

IC1
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 9.14

IC2
1 0
2 0
3 0
4 0
5 4.73
6 0
7 0
8 9.14

much as i hate to say it, those voltages look right, according to the schematic. the 4V73 at IC2B is buffered and fed to IC1 a and b as bias but as the opamp is not fitted, the buffering and feeding isn't being done, so everything is nought.

[joelo]

In your position, I would fully wire the circuit (3pdt switch), untill it works, even if i have to take it off later.

I did a similar project (OD + EQ) and both circuit have their own footswitch, with an order switch (spdt). I can engage both or just one circuit, and decide in wich position they are, OD before or after EQ. I found the wiring method on this forum ( looking for "order switch"), I can find it again if you need it.

I strongly suggest that you try Iain's idea with the extra cap and resistor, and if it still doesn't work, to take some fresh voltage  measurements of both TL072 with this modification, and post them.

Edit 2 quick recap : It has been established that one op amp can't work correctly, the board on its own doesn't work properly, it  needs the Friedmann amplifier to do so (replies #24 and 25). The build doc gives a warning about being a complex project that needs you, the builder, to know how to make it work (!). The seller never did the necessary arrangements neither to adapt this circuit for stand-alone use, nor even for average hobbyists, wich is rather uncommon. Fortunatly, a solution has been suggested to overcome this issue (reply #14).

OK, recap (mostly for me) on what I am going to do next:
I am going to wire it to a footswitch
Add a 100n capacitor between the input jack and the board (reply #8)
Add a 1M resistor parallel to the 2 clipping diodes (reply #8)
Add a 10 uF capacitor between Charakter trimmer & C1 (reply #14)

I have added a diagrams of what I think is the correct wiring. Look ok?

As far as the order switch, I like that idea but I already have an enclosure drilled for the combination of these 2.

[eh la bas ma]

I am not sure you still need the 100n cap. I have a feeling that it was a first idea, and that Iain would have add it on the diagram, reply #14, if it was still necessary.

Your wiring looks ok to me, I would have used the ground pad on the pcb, to connect to the switch ground, but I don't think it makes any difference.

If all this still doesn't work, you can also try to connect the switch "fx out" to the "power out" pad, instead of "out", just in case... Power out should be louder, with more volume.

You said you have a signal when the character trimmer is in a certain position, does the EQ works too ? Bass, Mids, Treble ?

[joelo]

I have added the 1M resister and the 10 uf cap. Still the same situation.  Bypass works. When on, with Charakter trim all the way CCW (this works backwards I'm assuming), Volume trimmer all the way up, Charakter at noon, and all 3 pots at noon, there is no sound. Turning up the Treble pot CW there starts to be scratch sound at about 2 o'clock, clean strong signal at about 3 o'clock and scratchy signal past that. Bass & Middle pots seem to do what they are supposed to when there is a signal. Turning the Charakter trimmer CW the signal disappears pretty quickly. Turning the Presence trimmer CCW the signal gets quieter and scratchy (to the point of no sound) and turning it CW it gets louder and scratchy. I have included a photo of the added components.

Shouldn't the Charakter and Presence trimmers not have a volume effect, just EQ?

[eh la bas ma]

I think Presence should interact with the signal volume, because it adds some resistance to the signal. Character should add some compression to the signal with leds, so it could interact with the volume too.

Can you please confirm that :

_ Every pads have been reflown.

_ All parts values and orientations are double checked, trimmers and leds first (you can download something like "Atlence resistor viewer " to check the resistors values without taking them out of the board). I know I insist a lot on these leds, but if there is something wrong with the character trimmer, it's the first place to look...

If everything seems allright, you can try to find where the scratches come from, or where the signal behaves suspiciously, with an audio probe, following the signal path, with the circuit powered on, (see path reply #21) until you notice something. Then you can focus on that part of the circuit.

Here is an audio probe tutorial in case you never had to use one before :

https://diy-fever.com/misc/audio-probe/?fbclid=IwAR1hzfEJN-ErFMBhlLGe9pyGj1KKzid53vWKblD6U4e-glaxIuFiJuPVork

Always connect the ground first, and at a safe location, like IN or OUT 's ground lug.

Edit : ...and you don't have to waste a good cable to build a probe, an input jack will do the trick. You can connect a cable from your amp to the probe's input.

[joelo]

I think Presence should interact with the signal volume, because it adds some resistance to the signal. Character should add some compression to the signal with leds, so it could interact with the volume too.

Can you please confirm that :

_ Every pads have been reflown.

_ All parts values and orientations are double checked, trimmers and leds first (you can download something like "Atlence resistor viewer " to check the resistors values without taking them out of the board). I know I insist a lot on these leds, but if there is something wrong with the character trimmer, it's the first place to look...

If everything seems allright, you can try to find where the scratches come from, or where the signal behaves suspiciously, with an audio probe, following the signal path, with the circuit powered on, (see path reply #21) until you notice something. Then you can focus on that part of the circuit.

Here is an audio probe tutorial in case you never had to use one before :

https://diy-fever.com/misc/audio-probe/?fbclid=IwAR1hzfEJN-ErFMBhlLGe9pyGj1KKzid53vWKblD6U4e-glaxIuFiJuPVork

Always connect the ground first, and at a safe location, like IN or OUT 's ground lug.

Edit : ...and you don't have to waste a good cable to build a probe, an input jack will do the trick. You can connect a cable from your amp to the probe's input.

Will do!

I did search the PCB Guitar Mania Facebook group and found this thread, don't know if it means anything helpful to where we are here:

https://www.facebook.com/groups/1066092703545364/posts/1861889947298965

[Vivek]

Ah, that old thread at PCB GUITAR MANIA !

I had done some work in guiding Stephan Kah to get his EQs working in different configurations.

[eh la bas ma]

Ah, that old thread at PCB GUITAR MANIA !

I had done some work in guiding Stephan Kah to get his EQs working in different configurations.

So you are the same Vivek !

I always had some doubts...

[eh la bas ma]

I did search the PCB Guitar Mania Facebook group and found this thread, don't know if it means anything helpful to where we are here:

https://www.facebook.com/groups/1066092703545364/posts/1861889947298965

Looks like there is everything you need here.

S. Kah managed to make this EQ work with a Soldado and every steps are described.

On the other hand, it is a lot of work : you have to use IC2 pin 1, 2, 3 ... you need 2 extra resistors and 2 silicon diodes instead of leds (like 1N4148), in order to modify the first part of the circuit :


...Or an easier way you can try is  mentionned here : " I build the Soldado yesterday, connected the Active EQ at R23 (before volume and the last cap). There I have about 4-5V DC bias and it now does an awesome job!"


If it still doesn't work, in your situation, I would forget about this one and build an other EQ. I know this EQ from guitarpcb is more seriously designed and will work with every circuits without any overcomplicated mods :

https://www.musikding.de/Tone-TWEQ-active-EQ-kit

At any rate, you can forget about making this circuit work on its own as it is, unfortunatly. I was trying to help you do that and I wasted your time, I am sorry !