Problem with ModBoard Switchable Wah-Wah, Midrange Booster

[jean]

EDIT: moved to Effects Devices by sumgai, 2/22/17 - concerns an effects device problem, not a guitar wiring problem. PM sent to jean at the same time.

Hi all,

My new guitar is almost finished but meeting with one last problem #
A bit of general description, it is a customed master built guitar with lot of electronics:
- sustainer
- piezo Ghost
- ModBoard TB-1
- XY midi pad
- 3 batteries checked by LoBat systems
- Tronical autotune mechanics
- kill switch in volume pot

The chain is as follow pickup->Sustainer->Modboard->Piezo->9 pin jack (offering stereo options). The 9 pin jack switch on the sustainer and the Ghost preamp when a jack cable is inserted.
The sustainer has is own battery and powers a solid state relay to switch on the XY Midi pad (with its own battery)
The Ghost preamp has as well its own battery and I'm using the power out to switch and power the Modboard (which drains less than 1mA)

Every things is now running EXCEPT... part of the ModBoard.
Here is description of the pb:
I wanted to connect it as Buffered Out, but then the output signal was extremely low, almost none. As soon as I switch the board on, it seems to work. If I wire it as "true bypass mode" it seems to work. I don't wanna use this output mode as the pop sound when activating the effect is really noticable.

Here is how I wired it:
- MB Input ground: to general ground (bridge/volume pot)
- MB Input Hot:  from out signal from Volume pot (maybe for this specific point I should go first to board then to volume, what do you think?)
- MB Buffered Bypass Out: to mag input of Ghost preamp (similar when I use the "True Bypass" Out)
- MB Output ground: to ground by connected on the Ghost board ground
- MB Battery Black: to ground by connected on the Ghost board ground
- MB Battery Red: power aux from Ghost board

I'm using the tone push-push as switch to activate the board (connected to J3/J4) and a 100k push-pull poti for switching the wah/boost and controlling effect (connected to J1 and J2 respectively).

Any help will be welcome...

Many thanks 





 

[sumgai]

jean,

As you can see, I've moved your query to a better-suited sub-Forum.

But now I want to ask you, do you have a diagram of what you've wired up?  We're big on diagrams around here.   Wiring layout or schematic, either one is good for us.

Even more specifically, we'd like to see one or more links showing how the Modboard is supposed to be connected to the adjoining circuitry.   If you please.

sumgai

[jean]

Hi Sumgai (and others),

Here is a handmade wiring diagram

Hope that helps to understand...

Cheers

Jea

Attachments:

MadGuitar_Wiring.pdf (431.58 KB)

[jean]

Forgot  to mention the frame around the pickups are Seymour Duncan Triple shot

[jean]

And the Modboard installation guide

Attachments:

MODboards_lo.pdf (695.23 KB)

[jean]

And a pic of the TB1 Modboard

Attachments:

[newey]

jean-

This is certainly a complex scheme. I'm actually somewhat surprised that the Modboard bypass mode is the only problem!

Unfortunately, even when I zoom your diagram up to the max size on my laptop screen, I can't make out much detail.

But:

The Ghost preamp has as well its own battery and I'm using the power out to switch and power the Modboard (which drains less than 1mA)

Again, I can't tell much, but it appeared to me that this method of powering the Modboard results in the Battery negative lug of the board being unused, not wired anywhere? Just a guess here, but it struck me that the buffered mode may make use of that ground.

So, one suggestion might be to temporarily give the board its own power, see if that helps.

Another solution, sort of a work-around solution, might be to use the true bypass mode and add a capacitor to alleviate the "pop". How to wire that and the value to use will require the input of someone more knowledgeable than I am.

[jean]

Thanks Newey. I will start by powering the Modboard to check if that the problem!

About the diagram, I attached previously pdf file thus is should be easier to read than using the jpg. Tell me if it ain't enough. Surprisingly,  indeed all the other parts are working. Additionally, I had LoBat systems to my 3 batteries in order to monitor their charge.

It's been quite challenging

[newey]

About the diagram, I attached previously pdf file thus is should be easier to read than using the jpg.

Yes, much easier- I missed the link to the .pdf. I'll take a look at it but it may be a day or two- I'm on the road at the moment, Louisville KY tomorrow, Columbus OH on Tues., home again Wedesday. So it may be a day or two- and anyone else who wants to weigh in will probably be more qualified to give you meaningful answers than I am.

[jean]

Definitively waiting forward to your comments then!!!

About the battery negative lug, it is internally -on the board- connected to the "switching jack" one. The latest one is supposed to be the ring of a stereo jack connector for power switching in  "standard configuration".

[jean]

Just to be sure the problem is clear, when the effect us engaged in the "buffered" output does work. When I switch off the effect, then the "normal" output signal from the guitar is almost none.
Thus the board gets power (at least when effect us engaged).

The "true bypass mode" let the output signal going thru without pb.

What I would think of, is that the Board doesn't get power -by some obscure reason- when the effect is off. But I can't figure why... 😖

[jean]

Some update:
I got a second unit for testing and eventually as replacement one. Before installing it in the guitar went to some testing phase using a signal generator and measuring output thru a multimeter (I don't own an oscilloscope, but can get mV AC range, good enough).

Unfortunately, I got exactly the same results:
- signal out on the "true bypass output" both when effect engaged of disengaged, ok
- signal out on the "buffered output" ok when effect engaged but none when disengaged

Letting me think it might be a design problem of the board... or I really missed a point

[newey]

Yeah, I didn't see any obvious problems with what you did, and if you've tried 2 of these boards, I suspect you're right. maybe an internal design problem.

I'm back to my original suggestion- solve the "pop" problem.

[jean]

Any suggestion for it?

[sumgai]

Mar 13, 2017 2:34:29 GMT -5 jean said:

- signal out on the "true bypass output" both when effect engaged of disengaged, ok
- signal out on the "buffered output" ok when effect engaged but none when disengaged

Letting me think it might be a design problem of the board... or I really missed a point

I'm not sure I'd go so far as to say that you've missed a point.... but.....

These results are exactly what I'd expect from this kind of circuit. If the power is off to an active circuit (one that requires power in the first place), then no signal will ever get through. If something, hell if anything does get through, that would be a case for Ripley's Believe It Or Else!*

To restate your summary above, in more specific terms:

Active circuit (buffering) disengaged via True Bypass = signal gets through

Active circuit (buffering) disengaged w/o True Bypass = signal gets lost

<rant>

To me, I'm seeing a case where the switching logic has failed the Design Goals test.  No one can force a signal through an active circuit (buffering) without power.  The designer should have seen that one coming, and provided the user a way to get around that... or at least a strongly worded warning that they should expect this kind of result.  Seriously?  Yes.  I see this is a case of switch logic (or signal path logic, to be more accurate).  First year EE students should've already been able to deal with this, before even getting into Engineering school.

</rant>

Can someone here provide a work-around?  Potentially.  I think I see at least two ways to handle it, but neither is easy, nor cheap.  Probably best to ponder this a bit, and let others chime in before I spout off inappropriately (again!).

sumgai

* Actually, something may be detectable, but that would happen only because the incoming signal is traversing one or more paths of feedback and load resistors, which explains the vastly reduced output.

[jean]

Hi Sumgai,

On the board there are two outputs: buffered and true bypass (one shall choose which one to wire). The on/off function is  controlled by a double switch J3 & J4 (where J3 controls the "buffered" output and J4 the "true bypass" one), which from obscure reasons have both to be plugged and switched from the same controller (a DPDT is used to duplicated the switch).

To my understanding, the board remains under power to allow the buffered output.

Again, I ain't an engineer... but if I understand you correctly, the problem might come from a logic gate (or the lack of it)? Would it help if I attach pics of the board? I cannot myself follow the signal path and understand the compounds of the board

[sumgai]

jean,

Pics are always good, but I'm not sure just yet how they'll help in this case.

In any event, I don't see how we can get past that word "buffer".  By definition, it means an active circuit, which really translates to power being required in order to accomplish a complete circuit. (And yes, in school we learned that there are passive buffers, but really, they aren't intended to do the same kinds of jobs).

You hit the nail on the head with the comment about "gate".  You understand the following, but let me explain in 500 words or less, for the rest of the crowd:

The shortest way to describe a buffer, or any active circuit, is to say that there are actually two circuits, called Input and Output.  Between these two, and connecting them together, is the active component, usually either a vacuum tube or a transistor*.  I'm sure I don't need to articulate the need for some kind of electrical power in order for these two devices to work, yes?  OK.  That active component/part/device is properly known as a gate - it acts to control what passes over from the Input to the Output.  (As a side detour, the term "gate" is usually used in a digital reference - either fully on or fully off.  But it's a useful term to ease the learning curve in our analog world too.) 

Once that concept is understood, we can step up our game.  In total reality, no electrons pass through the controlling device from one circuit to the other.  In fact, the current flow through the Input circuit uses the active device to modulate the current flow going through the Output circuit.

So why is this important?  Simple - because it's not a common notion that power applied to the circuit(s) is actually flowing through everything, not just the active device.  So the analogy becomes, a small amount of power (electricity) is flowing through the Input circuit, and I mean every component therein; and a comparatively large amount of power is flowing through the Output circuit - every component included.  And where it all comes together is:  the Input circuit (small current) is controlliing the transistor or tube, and in turn that controls the Output circuit (large current).  Fortuitously, this explains how an amplifier works, but the analogy is clear - the idea works everywhere - small controls large.

(And yet another detour.... We can do other things besides just modulate/control power.  Specifically in the case of a buffer, we want to change impedance so that two components will "play nice" with each other.  But let's leave that area of interest for another thread, eh?)

Anyway, the point has been made, hopefully clearly - if there's no power, then the gate won't transfer anything from one side to the other.  Good, let's return to the thread's original intent.  (All of the foregoing was to get to this point, where we can speak to the concept of a 'gate'.)

I can't be certain about how and where power is applied to this Mod board at any given time.  I'd like to think that if power is always on, then there should always be an output.  But the kink in that particular rope is "what if the user doesn't want the output just now?"  Cue the William Tell Overture, it's switching logic to the rescue!

It would not be a failure like I spoke of in my last message, if the switch disconnected the signal instead of the power.  jean, your description of everything needing to be connected together, and then controlled by yet another external switch, I'm afraid I didn't understand that.  No fault of yours, but perhaps I do need to look at the documentation more closely.  Let me hem and haw over this for awhile, eh?  In the meantime, I'll bet that John has something to say, he's been pretty quiet down there in 'Straya.

sumgai

* In the world of electricity, well before we had tubes and transistors, we controlled large amounts of power with either relays or transformers.  A relay still needs power, that was obvious, but a transformer doesn't need power, per se, it only controls it.  Circuits still need their own power in order to accomplish work (as in the scholarly definition of work), but the transformer is acting only as a coupler - it doesn't transfer elctrons directly, it only uses magnetism to modulate the power flowing through the Output circuit.  And hopefully, that bit about magnetism will clear up any lingering questions about how one circuit modulates the other.

[jean]

If that can help, here is the provided documentation of the Modboard (generic) and the specific one.

Attachments:

TB1_lo.pdf (692.47 KB)

MODboards_lo.pdf (695.23 KB)

[sumgai]

Thanks, jean, I'll investigate more thoroughly tonight.

[jean]

And some pics of the board (ok, not extreme good quality)...

Attachments:

IMAG3348.pdf (814.92 KB)

IMAG3345.pdf (899.91 KB)

[jean]

Hi all,

I couldn't solve the "klang" problem and despite hours of wiring/rewiring/testing I couldn't make the buffered bypass working on both units I got. I then decided to go to plan B: instead of the Modboard I did install a Mr Fuzzzy from Lee Jackson and a microbooster (clean FET boost) from BECOS.

The chain is then now: pickups (both with triple shot system)--> Sustainer-->Mr Fuzzzy--> Microbooster -->Piezo-->stereo output
additional features are: the kill-switch (shadow on volume pot), the XY Midi pad, the Tronical system and I'm using two "regular" Humbuckers, the sustainer pickup being used only as driver.

The whole monster is working on three batteries (checked with LoBat systems), two of them being operated from the 9 pin switching jack, the third one switched on/off from a solid state relay.

My little baby is now fully working and sounding terrific....I'm definitively an happy man