Let's Build A Uni-Vibe: Introducing The Pадио Москва (Radio Moscow) Atmospheric Modulator - Sound Sample Added 2/1/2022

[FuzzMonkey]

With the recent arrival of the enclosure for the prototype, it's now time to box up our proof of concept build.

The enclosure below is a 1590XX, larger than intended (the final version will use a 1590BB2 which is the same as the 1590BB but 5mm taller) due to the extra switches and LEDs and pre-drilled from me by the lovely people at Tayda Electronics (https://www.taydaelectronics.com). Because I can't seem to be able to drill holes in a straight line to save myself!

Since the prototype is just a proof of concept build, I didn't worry about the aesthetics as the control layout, especially the switching, aren't true to what I have in mind for the final version.

Below: The drilled enclosure ready to go.


With that said, I'd thought I'd take this opportunity to provide a bit of an update on how things have evolved/progressed since I started this whole prototype process begun and explain a few things in more detail.

Below: A mock-up of the controls. Nothing inside yet however.


But first, let me explain the controls on the prototype:

Potentiometer Controls (from left to right):
Speed One
The default speed control used to adjust the speed of the oscillation.

Speed Two
The auxiliary speed control used to adjust the speed of the oscillation. Switching between the two speed controls is done via the footswitch on the left.

Intensity
Controls the intensity of the oscillation.

Volume
Control of overall output of the effect.

Toggle Switches (from left to right):
Mode Toggle Switch
Toggles between the Chorus mode that the Uni-Vibe is famous for and lesser used Vibrato mode.

Input Mode Toggle Switch
Toggles between the Vintage and Modern input modes. The Vintage mode provides a warmer, slightly darker tone with a little less output and is the stock circuitry as found in the original. The Modern mode provides a bright tone with more output and clarity.

Status LEDs (from left to right):
Effect Mode LED
Indicates which mode the pedal is in; either Chorus or Vibrato using a bicolour LED. Which colours exactly, I've yet to decide.

LFO LED
Provides visual indication of the speed and intensity of the modulation. Turns off completely when in Cancel mode.

Input Mode/Status LED
Indicates whether the pedal is in bypass mode or the effect is engaged i.e. the LED on or off. Also doubles as an indicator of the Input mode using a bicolour LED. Blue indicates Vintage mode and Red, Modern mode.

Footswitches (from left to right):
Speed Selection
Toggles between the Speed One and Speed Two.

Cancel Mode
Turns the LFO off just like the original so you can still use the pre-amp. Note: The volume control remains active still.

Bypass
Your typical true bypass.

How will these controls differ from the final version you ask? The potentiometer controls will remain exactly the same. The toggle switches will disappear totally as will one of the LEDs and one of the footswitches. All of the switchings will be done via two soft-touch footswitches each with multiple functions assigned to them via a microcontroller. A quick-tap does one thing, a double-tap does something else, and a press-and-hold does yet something else. One footswitch will control the bypass and the Cancel function and the other controls the toggling between the two speed controls, the two effect modes, and the two input modes.

The Input Mode/Status LED will remain the same in terms of functionality but the separate Effect Mode LED will also disappear and instead, its functionality will be incorporated in the LFO LED i.e. still with two separate colours each representing either the Chorus or Vibrato mode while still flashing to represent the speed and intensity of the modulation. But once in Cancel mode, the LED will stop flashing and instead, turn a solid red to indicate the LFO is turned off. The magic of the RGB LED.

So what has changed circuit wise? Remembering this was a straight to PCB design so I hadn't played around with it on a breadboard etc. But in short, a few things.

First of all, the power supply wasn't up to par. While functional, the first issue it caused was the sagging under load. Using the high-side switching to cancel the modulation by killing to power altered its behaviour since the circuit wasn't being loaded down by the current hungry lightbulb; it would operate as intended when the blub was on but not when off.

Secondly, I had yet to include the over-voltage protection that I was intending to use to protect the charge pump (rated to up to 15-volts) so things were getting rather complicated so I made the call to simplify a few things. The power supply now uses an XL6009 DC-DC converter that can handle an input of up to 36-volts. Thus, making the need for any over-voltage protection pretty much redundant. It is also simpler to implement than the LT1054 that I originally intended to use and can pump out higher voltages to boot and much more current. All while using a standard, Boss-style 9-volt DC power supply.

The power filter also needed to be beefed up as it was a bit squelchy otherwise. These changes actually made it closer to the original unit in terms of voltages i.e. 18-volts to the audio section using the exact same power filtering as the original and a hair under 23-volts to the LFO section. A win here I feel; both in terms of simplifying trying while staying true to the source material. One of my aims when setting out on this journey.

Another issue with the LFO LED circuitry itself. There was some minor interaction with biasing that section of the circuit and biasing the bulb for the LDRs. Again, in the name of simplicity, I decided to drop it altogether i.e. the op-amp buffer in the LFOs path and opt for an alternate, much simpler version that does the same thing but without unnecessary complexity or the bothersome interaction. Another win for simplification and staying true to the source material.

The final major change following that same theme (simplification and staying true to the source material), was to the Cancel function. It originally used a high-side mosfet switch that I designed to trickle a small amount of power to the bulb in order to reduce the turn-on time of the bulb and hence the delay time until the modulation kicking it due to the bulb's warm-up time. However, with the simpler LFO LED arrangement now in place, this small amount of power resulted in issues with the functionality of LFO LED again. Whack-A-Mole anyone? So, I reconfigured it to use a low-side mosfet switch instead and to be once again more in line with the functionality of the original unit i.e. shorting the signal from the LFO to ground rather than killing to power to the bulb. This means there is a slight delay if using that option (a quirk shared by the original) but the increase in power to the LFO section helped and it is dependant on the speed and intensity settings that control the amount of current flowing through the bulb.

I also made a change to expand the speed range available to the LFO by tweaking and experimenting a little with three resistor values thanks again to another mod suggested by J.C. Maillet (http://www.lynx.net/~jc/pedalsUnivibe.html). The last minor change was to the use of multi-turn trimpots instead of their single-turn cousins. Since the biasing of the bulb is SO vitally important to getting the Uni-Vibe to sound right, these allow for much finer adjustment to really dial in that sweet spot.

Don't worry; it still sounds fantastic!

Below: The current stage of play.


For the audio section of the circuit, nothing changed. Oh; I did get the correct SMD 68k resistor that I had previously forgotten to order.

Below: Before.


Below: After.


Any questions and comments, as always, are most welcome.

~ Blake.

[AiRdAd]

This has been a great thread to follow, the unit looks awesome

I always like to have a fiddle with the internal trim pot on the univibes I've had, to dial it up the way I like it - is it possible with this circuit? Or would an inexperienced user like me get themselves into trouble?

[FuzzMonkey]

This has been a great thread to follow, the unit looks awesome

I always like to have a fiddle with the internal trim pot on the univibes I've had, to dial it up the way I like it - is it possible with this circuit? Or would an inexperienced user like me get themselves into trouble?

Thank you for taking the time to share those kind words. It means a lot to me that others are getting some enjoyment and maybe learning a few things as I share this journey with you all.

Yes. It is possible to fiddle with the internal trimpots on this design without getting into any trouble.

The bias of the bulb is controlled by two separate trimpots, each with a specific function. The first trimpot controls the Gain of the blub; its brightness basically. It does this by varying the amount of resistor between the emitter of the bulb driving transistor and ground. The more resistance there is, the duller the bulb glows and vice versa if there is minimal resistance.

The second trimpot replaces one of the fixed resistors used to bias the bulb driving transistor in order to adjust the Offset. Offset being the amount of time the blub stays off for during each cycle of the oscillation. It sets the off. High amounts of offset result in the bulb turning fully off at the bottom of the sweep. While a moderate or low offset means the lamp will pulse but never go fully dark.

Obviously, the two are very interactive in terms of dialling in the Uni-Vibe for sound right. A high offset with a bright blub means more depth than a low offset and a dimmer bulb. The diagram below from J.C. Maillet's website might help to explain the relationship better.


(Image courtesy of the J.C. Maillet's viva Analog Univibe+ website http://www.lynx.net/~jc/pedalsUnivibe.html).

I believe that the latest version of the Vibe Machine by Dry Bell has two trimpots called Symmetry and Range that read like they do the same functions as the Gain and Offset trimpots. Range being the Offset and Symmetry being the Gain. These can be accessed from the outside with a small screwdriver.

I hope this help explain things in regards to the trimpots.

~ Blake.

[FuzzMonkey]

The prototype build is coming along nicely after a few busy days at work. The wiring looks pretty messy only because I've left plenty of length in case it is needed. Better too much than not enough.

Below: Controls in place.


Below: Everything ready for the PCB to be installed. Note the EVH tribute wiring.


Another thing to add to the list of PCB revisions is the bi-colour LED daughterboard. I discovered that I mixed up the Collector and the Emitter so I had to bend the pins on the through-hole PNP transistor around to achieve the correct orientation instead of using the intended SMD transistor to get to work correctly. Oh well; that's why we do prototypes.

~ Blake.

[MiniForklift]

Wow, only read through this last page and what an interesting read it was. Kudos to you. Look forward to reading through the rest of it from the start and ultimately seeing the finished product. Sounds like it will be a very cool vibe, nice work Blake

[FuzzMonkey]

Wow, only read through this last page and what an interesting read it was. Kudos to you. Look forward to reading through the rest of it from the start and ultimately seeing the finished product. Sounds like it will be a very cool vibe, nice work Blake

Thanks. I'm planning on get the prototype completely boxed up today. Then take some time to reflect on what worked and what didn't before doing the required revisions for the PCB.

If you were wondering about that matter I PM'd you about. It was purely for research purposes.

~ Blake.

[MiniForklift]

Apologies in advance as I haven’t read through the thread yet, is your one using photocells? Seems like this is an important part of all of the legendary and revered vibe pedals, I remember making sure the Deja Vibe used them before I purchased it. However I’ll admit I don’t really understand their role and/or how they work

Guessing I may have more knowledge once I have read through your posts Blake. Look forward to hearing how the final boxing goes

[FuzzMonkey]

Apologies in advance as I haven’t read through the thread yet, is your one using photocells? Seems like this is an important part of all of the legendary and revered vibe pedals, I remember making sure the Deja Vibe used them before I purchased it. However I’ll admit I don’t really understand their role and/or how they work

Guessing I may have more knowledge once I have read through your posts Blake. Look forward to hearing how the final boxing goes

It does indeed. Here's a rather shakey GIF of the lightbulb and the surrounding photocells or LDRs.



From my research, most do use the traditional arrangement of the lightbulb and the LDRs. Some do differ in the technology used in the audio path of the circuit. A discrete transistor circuit is traditional and is what the original unit used by something like the Voodoo Lab Micro Vibe while keeping to the original in terms of the LFO and lightbulb/LDR arrangement, the audio path is made of op-amps.



For those Audiophiles, the Effectrode Tube-Vibe uses 12AX7s in the audio path.



The newer Dunlop/MXR versions; the Jimi Hendrix and the Uni-Vibe versions differ entirely and use Jfets much like the MXR Phase 90 instead of the LDR/bulb arrangement.





There is a great article covering the history of the Uni-Vibe on Brad Burt's Classic Amplification website that covers all the versions of the Uni-Vibe over the years, including these ones.

https://www.classicamplification.net/info/uvh.html

~ Blake.

[sty]

This is great marketing. Unless they’re stupidly expensive I’m going to be buying one of these when they launch, I’ve always loved the univibe sound but following the dev story adds even more to the GAS.

Hope you do a special launch edition for us lot

[FuzzMonkey]

This is great marketing. Unless they’re stupidly expensive I’m going to be buying one of these when they launch, I’ve always loved the univibe sound but following the dev story adds even more to the GAS.

Hope you do a special launch edition for us lot

I have yet to do anything regarding the possible price point at this stage. Still a bit early in the process as there are still too many things to finalise. But I'd be interested to hear what ballpark figure you'd equivalate to stupidly expensive.

I know there are some expensive Uni-Vibe-style pedals out there; not taking into account any original vintage units. Or what sort of price point you or anybody else who has been following this thread would consider paying for one given the information provided etc.

I'm sure I can work something out in terms of a special edition for you lot come launch time.

~ Blake.

[MiniForklift]

Depending on when you launch I’d probably be keen for one too

[FuzzMonkey]

Depending on when you launch I’d probably be keen for one too

My goal is within the first quarter of this year.

[FuzzMonkey]

Just a quick update to share a few photos of the prototype going into its enclosure.

The new make-shift power supply utilises an XL6009 DC-DC Converter module and the same power filtering as the original Uni-Vibe. It still has the non-sacrificial Mosfet-based reverse polarity protection and doesn't need the over-voltage protection as the XL6009 can withstand up to 36-volts. The voltage is trimmed so the audio section sees exactly 18-volts which means the LFO section sees a hair under 23-volts; 22.99-volts to be exact.

Below: The revamped power supply utilising a XL6009 DC-DC Converter and beefed up filtering.


I might try running the audio section at 24-volts as an experiment in the next day or so. Just because...

Below: The PCBs all wired up.


I really like how the light shield retainer turned out. There's a dob of hot glue to secure it to the underside and four pieces of brass rod soldered to it and the PCB that holds everything in place.

Below: The light shield capped off and held in place.


I left things messy as I'll no doubt continue tinkering with it as I can't help myself. Fear not; this won't roll over into the final version.

Below: Still a bit messy for tinkering purposes.


It works perfectly and sounds great! Even if I do say so myself.

Thanks for following and for all the kind words.

~ Blake.

[Miza]

Cool watching this genius-level project come together.

Bit more to it than your average fuzz face clone huh?!

[FuzzMonkey]

Cool watching this genius-level project come together.

Bit more to it than your average fuzz face clone huh?!

There's nothing wrong with a good Fuzz Face clone. A bit more involved; yes. But still nothing wrong with it.

In fact, the second pedal I ever built was just that.

~ Blake.