Diezel VH4 Pedal  [schematic]

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plush
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Post by plush »

jhergonz wrote:I'am no expert, but maybe this is the reason why we must use shielded wire when not mounting the I/O jacks and pots when building high gain distortions, and maybe your fingers act like a ground(I'm not really sure, so please correct me if I'm wrong.)
Hi,

I'm no expert too, but here's my 5 cents:

Yep, human body can act as a filter, effectively attenuating certain frequencies.

But more commonly it introduces additional noise to the signal line, than filters it.
You can touchy-touch a tip of 6.3 plug of a cord plugged into working amplifier or a pedal and experience added noise.
There is also a bunch of stuff, like multipath fading, that can be related to one's body position relative to the device and bunch of other stuff that I don't want to go into .

The whole thing with whine and ocillations in this pedal is very strange.
High freq. whine can be intruduced by build-in power booster.

Oscillations are more common to occur due to capacitive coupling between signal lines.

As for shielding, it's more to mitigate electric interference (more commonly 50hz hum from AC heaters in tube amplifiers, tremolos with high swing and poorly designed old circuitry).
But, there is really nothing in this pedal, that can generate electric field that can possibly be a source of a feedback and cause oscillations due to non-shielded wires.

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Post by jhergonz »

That was very informative! Thanks a lot. :wink:

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Post by DoomchildXXL »

Well, mine is still wailing, and I used (makeshift) shielded wire. (twisted gound wire around the input wire) But I'm gonna try proper shielded wire as a last resort and see where that gets me. It's also the UK-version btw. Since it's an absolute killer pedal, I'm gonna keep trying to get this sorted. :hmmm:
Unbenannt.JPG

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Post by deltafred »

plush wrote:But, there is really nothing in this pedal, that can generate electric field that can possibly be a source of a feedback and cause oscillations due to non-shielded wires.
Incorrect, as this design would appear to demonstrate.

The oscillation in this circuit is no doubt caused by one or more of the following.

Badly laid out circuit. When designing a layout for a PCB or point to point it is good practice to keep inputs away from outputs (and anything carrying heavy current) as much as possible.

Inadequate power supply decoupling. One section of a circuit can influence another if there is inadequate power supply decoupling which can cause or assist oscillation/noise/instability.

Unscreened input lead/s. In high gain circuits it is often necessary to use screened input leads (connecting the screen only at one end is good practice so there can be no current flowing through it).

Unscreened output lead/s. Not always necessary in pedals but worth a try if all else fails.


All the above are taken very seriously when designing measuring instruments, look up "guard ring" if you want to see the what lengths you need to go to prevent inputs picking up unwanted signals from adjacent PCB tracks.
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Post by jimroot »

hi, i got mine done. (still no finish, i'll get it a white one later...)

But there is something not right in sound/function with the Presence and Deep pots. So the pots are working. and everything else too but i can't imagine that the original pedal sounds like that.
The presence and deep dont really do what you normaly expect from them frequency wise. Both lower the volume a lot when you turn them down and they dont really increase only there specific frequencies when you turn them all the way up.
there is almost only a volume boost and just slightly lower mids (around 400Hz) coming in with the deep knob and some 1kHz with the presence knob. but there is no "resonance" frequency boost/cut or presence boost/cut with these knobs.

i got mine from UK-electronic. in the documentations from uwe and pcb maniac and the schematics earlier in this thread are several inconsistencies regarding values of some resistors (R26, 28, 34....). (all the ones around the negative feedback circuit/area)
I tried almost all values and combinations but there is no usual behavior of the presence and deep pots. i also checked for any solder bridges, changed ICs, checked every value of all parts again. everything fine. its not the first pedal i built (TS, Friedman BE-OD...) and i cant find the problem. ^^ :hmmm: :?

btw: i made only one out jack with a switch to select between the levels. advantage is i got bypass now in both output levels. ;) i'm slightly curious why Baja doesn't make a true bypass cause the buffer in bypass slightly changes the overall sound for some other distortion pedals. (like wampler or bogner ones)
*i did that at final step, so the problem isn't related to this routing.


any suggestions/help?? (i tend to order the original pedal to compare the sound and board) Does anyone here actually compared this/his built/clone with the original vh4 pedal?
My used values for the neg. feedback parts are now R26=1k; R28=100R; R34=1k (as printed on the board, i tried also R26=100R and R28=1k, almost same result. checked the C17/18 caps for funkction too)

ebbf3820-cdbd-4ce1-80ac-5f1ab63e7e31.jpg

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Post by jimroot »

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Post by plush »

deltafred wrote:
plush wrote:But, there is really nothing in this pedal, that can generate electric field that can possibly be a source of a feedback and cause oscillations due to non-shielded wires.
Incorrect, as this design would appear to demonstrate.

The oscillation in this circuit is no doubt caused by one or more of the following.
deltafred wrote: Badly laid out circuit. When designing a layout for a PCB or point to point it is good practice to keep inputs away from outputs (and anything carrying heavy current) as much as possible.
Mostly hhis
deltafred wrote: Inadequate power supply decoupling. One section of a circuit can influence another if there is inadequate power supply decoupling which can cause or assist oscillation/noise/instability.
And this
deltafred wrote: Unscreened input lead/s. In high gain circuits it is often necessary to use screened input leads (connecting the screen only at one end is good practice so there can be no current flowing through it).

Unscreened output lead/s. Not always necessary in pedals but worth a try if all else fails.


All the above are taken very seriously when designing measuring instruments, look up "guard ring" if you want to see the what lengths you need to go to prevent inputs picking up unwanted signals from adjacent PCB tracks.
I don't see any way 3cm of shilded input of output fixing pcb coupling. That's all I'm saying.

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Post by plush »

plush wrote: I don't see any way of 3cm of shielded input/output fixing pcb's internal coupling. That's all I'm saying.
Sorry, I've tripped

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Post by bmxguitarsbmx »

Coupling to ground rarely causes the problems that coupling between circuitry causes. Try taping down some of that wiring with copper tape. It'll be messy, but may give you an idea of what wires are talking to each other.

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Post by deltafred »

plush wrote:I don't see any way 3cm of shielded input of output fixing pcb coupling. That's all I'm saying.
I appreciate what you are saying but ask anyone who works on valve amps about the need for careful cable routing and the need to sometimes screen input leads.
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Post by plush »

deltafred wrote:
plush wrote:I don't see any way 3cm of shielded input of output fixing pcb coupling. That's all I'm saying.
I appreciate what you are saying but ask anyone who works on valve amps about the need for careful cable routing and the need to sometimes screen input leads.
Thanks, I've actually did this multiple times.

This is why i want to debate on this. And learn something which I yet don't know or can't even imagine.

Yet still I don't get why should we compare tube amps and their voltage swings and their internal field emissions/interference to solid state stompbox circuitry.
I see that the principle is the same, but the tehcnology and scale are not.
Cable management and cable shielding in tube amps is a huge deal, I completely understand this, since I do understand (mostly) the possible sources of interference.

But, speaking about stompboxes, Imo, if we already have a coupled signal lines on the pcb, shielding the wire that is coming to the pcb's pad won't fix a thing, it won't remove the coupling.
If we have, lets say, an opamp, that oscillates because of whatever, and induces the noise back to the wire coming to the pad and later to said opamp's input, shielding couple centimeters of said wire will only drop the noice a couple of dbs, since we still have unshielded traces on the pcb, that still can experience coupling, interference and whatever. Yet this still can be applied to tube amps, but said shielding again won't fix the problem.

I'd appreciate your thoughts on this.

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Post by DoomchildXXL »

Just purely as an empirical addition, I'm super happy to say, proper shielded wire just fixed my pedal yesterday. Very happy camper here. :D Because as I said above already, this pedal is an absolute beast! :horsey:

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Post by plush »

DoomchildXXL wrote:Just purely as an empirical addition, I'm super happy to say, proper shielded wire just fixed my pedal yesterday. Very happy camper here. :D Because as I said above already, this pedal is an absolute beast! :horsey:

Nice to hear it worked for you.

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Post by icziko »

DoomchildXXL wrote:Just purely as an empirical addition, I'm super happy to say, proper shielded wire just fixed my pedal yesterday. Very happy camper here. :D Because as I said above already, this pedal is an absolute beast! :horsey:
DoomChildXXL, did You shielded all wires going to board or only output wire? Can You show some photo so I can have better understanding how to do that?
Thx in advance

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Post by DoomchildXXL »

icziko wrote: DoomChildXXL, did You shielded all wires going to board or only output wire? Can You show some photo so I can have better understanding how to do that?
Thx in advance
It's similar to what jimroot posted a few posts up. But I only shielded the input, which should suffice in theory, because you are trying to keep anything from re-entering the circuit that way.
Be sure to attach only one side of the shield to ground to avoid creating a ground loop. The other side is shrink tubing to not have anything dangling around.

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Post by DoomchildXXL »

I attached a pic that got lost somehow...
IMAG3080.jpg

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Post by icziko »

Thanks DoomchildXXL, this helped a lot.
Finally I was able to get rid of oscillation. However in my case I needed to shield not only INPUT cable but also GAIN wiring since I am using Veroboard version from Tagboard.
It is magnificent pedal.

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Post by icziko »

Thanks DoomchildXXL, this helped a lot.
Finally I was able to get rid of oscillation. However in my case I needed to shield not only INPUT cable but also GAIN wiring since I am using Veroboard version from Tagboard.
It is magnificent pedal.

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Post by DoomchildXXL »

Cool, congrats! :horsey:

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Post by DimebuGG »

Here's mine.
I designed my own pcb and sent it to JLCPCB. Used 7815 for the regulator since I have a 33V x 4 unregulated PS. Opamps were labeled OPAs but I think they're just a relabeled 072's(got them from Aliexpress cheap shit) and LT1054 for the charge pump.

This thing sounds really good. It oscillates like crazy when I didn't use the shielded cable at the input at first, yeah that's the pcb track right there from the input jack to the footswitch. After shielding, still, it oscillates past 3 o'clock but I'm not a fan of crank up gain anyway in a distortion pedal. TBH, gain at 12 o'clock is more than enough. For sure the charge pump is the cause of the oscillation/feedback. I also tried 7660CPAZ also but a high frequency whine is there even at bypass. Lastly, named it after my daughter's nickname. :)
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