frequencycentral Hermida Zendrive PCB Layout

[frequencycentral]

Verified! Enjoy!

[tasos]

is there a soundsample please??

[kurtlives]

is there a soundsample please??

http://www.youtube.com/watch?v=VHXmGBhfSno&feature=related

[tasos]

great!but what is the voice pot doing exactly?

[Brymus]

Thanks Rick!
My first effect was Burchtone's version of the Zen drive.
It used 1N5711 diodes instead of the FETs.
But otherwise the same basic circuit.
Great for driving a tube amp.

[kurtlives]

great!but what is the voice pot doing exactly?

It's like a tone control and gain control all in one. It's altering the low end response and gain simultaneously. It's actually a useful control.

[Mark Hammer]

great!but what is the voice pot doing exactly?

We need a running start for this.

In a non-inverting op amp configuration, the gain is determined by two resistances: the one in the feedback loop, and the one between the inverting pin and ground.  The gain is increased as the feedback resistance gets bigger, the resistance to ground gets smaller, or both.

In the standard TS, the ground resistance is held constant at 4k7 but the feedback resistance is varied between 51k and 551k.  In the Zendrive, BOTH resistances are variable.  The ground resistance is labelled VOICE and the feedback resistance is labelled GAIN.

Right now, you are probably saying "But then why aren't they both called gain?".  Excellent question.  You learn fast.

The bandwidth of the signal, or rather how much gain is applied to what portions of the signal, depends on the product of the feedback resistance and any feedback capacitance, and the ground resistance and any capacitance to ground.  Holding each of those two capacitances constant, as the feedback resistance is increased, the treble rolloff moves downward (i.e., less treble is passed/amplified), and as the ground resistance is increased so does the bass rolloff (i.e., more bass is passed/amplified).

But wait!!  Since those two resistances work in opposite fashion when it comes to gain, there is a curious relationship between adjustment of gain, and resulting tone.  When the gain is increased by making the feedback resistance larger, the cap value will result in less treble being passed as the gain is increased.  But when the gain is increased by making the ground resistance smaller, there will be more bass cut as the bass rolloff moves upward.

Given that the overall circuit is intended to produce more harmonic content, and that the harmonic content will increase as the drive goes up, rolling off more treble as you increase the drive via the feedback resistance makes perfect sense.  Think of it like changing to a less efficient gear as you start down a steep grade - you're counteracting something that could easily run away with you.

In the case of adjusting gain via the ground resistance, something extra comes into play.  Remember that most of the signal lives in the bass end.  If you make the bass rolloff juuuust right, increases to gain are offset by an evening out of the amplitude across the spectrum/fretboard, such that lower notes don't hit the clipping element/s any harder than upper notes.  That particular aspect is what makes the Tube Screamer such a keeper, but also what leads to complaints about the nasal midrange; it's a result of attenuating the bottom.

The VOICE control is essentially a means of adjusting how much bass is included in the signal that hits the clipping element.  The bass rolloff on the Zendrive goes from 145hz, when the VOICE is set to lowest gain, to 1560hz when set to highest gain.  Of course, because the pedal also has a feedback resistance GAIN control, you can offset where you needed to put the VOICE control, and get different tonalities or pre-clip tone shaping at the same gain.  Since altering of the bass content will have more impact on the distortion sound than trimming of the treble in the feedback resistance path, Alfonso (Hermida) called it a "Voice" control, since it changes the voicing of the pedal.

A number of other commercial and boutique pedals will come with a switch to select between standard TS-style tone-shaping and something with more bass in it and less midrange honk.  That's an extremely useful feature.  The Zendrive makes that feature continuously variable.

Make sense now?

[kurtlives]

Great explanation Mark, thanks.

[9mm]

What's the best replacement for BAT41? 

[Paul Marossy]

Hey, wasn't Hermida a member of this forum in one of its iterations? I could swear I remember seeing some posts from him sometime in the last 10 years...

[Ben N]

Yup--although I'm not sure if it was within the past ten years or not.

[Huub2O]

Hi,

I want to build the zendrive 2, the tube version, but i can't find a layout. Is it the same but with the tube replacing the diodes? Or is it a whole different layout? Has anyone built it?

Thanks in advance!
Huub

[pappasmurfsharem]

I'm attempting to print this out but even when setting to 100% scale its coming out to large.

Any thoughts?

[CodeMonk]

I'm attempting to print this out but even when setting to 100% scale its coming out to large.

Any thoughts?

Trying setting image to 300DPI

[pappasmurfsharem]

I'm attempting to print this out but even when setting to 100% scale its coming out to large.

Any thoughts?

Trying setting image to 300DPI

Well doesn't seem quite right, in images settings I can set pixel/in however it way too small now.

I guess I need to know the exact dimensions.