Electrovibe Mini (Shin-Ei Uni-Vibe)

[MichaelW]

Build Rating

5.00 star(s)

A couple months ago @fig smacked me upside the head with a gauntlet and said "I dare you to build this pedal...." (or something along those lines as I recall.....)

Of course challenge accepted!

Not sure why I was intimidated by this, it's actually a very straightforward build. As usual, @Robert laid it all out very nicely and the most challenging part of the build is making sure you have the right size components. After building both the Tourbus and the Byzantium I was in pretty good shape with low profile caps so I already had everything I needed.....or so I thought. Ended up missing the C100k Dual Gang pot, which delayed finishing the build a few days.

But the blue and white truck of happiness dropped off a package from StompBoxParts today so I got it all buttoned up.

The build went pretty smooth and the only thing I really had an issue with was not setting the bazillion 2N5088's down deep enough on the top board. So I had to bend them a bit for the back lid to fit on.

I started out setting the Gain and Bias trimmers at noon but noticed the bulb intensity was pretty dim. So I have the gain pretty much cranked and the bias backed off from noon quite a bit, maybe around 9 o'clock, I get the most lush effect with these settings.

The vibrato setting has some cool sounds but the chorus setting is where it's at for me. Really nails some of the early Trower sounds and Dark Side of the Moon sounds.

Compared to the EQD Depths pedal I built a while ago, this sounds more like a traditional Univibe and has more of a "swirl" as opposed to the "throb" of the Depths pedal. The Depth's pedal also has a lot faster speeds so it was kinda cool running the EVMini into the Depth set fast for a neat Leslie effect.

There's also not a lot of output with this pedal. I'm not sure if anyone else has had this issue. I have the level full CW to barely get to unity. I'm going to have to go back and read some of @Big Monk 's mod threads. I decided to build it stock because I didn't know what I didn't know, you know?

Anyway, fun build, great sounding pedal, highly recommended build!

 

[Coda]

I borked mine when I built mine (caps too tall), and I haven’t had the inspiration to carry on. Still don’t, but this is a good looking build regardless. I remember the volume issue being mentioned by others…I believe there is a resistor value you can tweak.

 

[Dan0h]

Nice. I too was wondering about low output. I did the normal size build and the vibe side is Unity at full volume but the chorus side even at max is several db lower than Unity. There’s a mod out there I’m sure. Just need to find it.

 

[steviejr92]

Wow the color of the enclosure with the color of the knobs is beautiful! That faceplate looks like it was made for that color combo! Awesome build!

 

[enrosenzweig]

Looks awesome with the cream knobs!

When I built mine, I did the original unity volume mod. Even with that resistor change it’s still not enough. Fortunately, @Big Monk just posted a further mod for more gain. I haven’t has the motivation to pull apart my build yet, but am planning to at some point.

For those who have done the unity gain mod and are still wishing for a bit more signal:

1.) The traditional Univibe transistor preamp is in fact a discrete opamp.

2.) It’s overall gain is governed by the classic 1+(Rf/Ri) opamp gain equation.

3.) For either the Big Electrovibe or the Mini, this equation would be as follows:

1+(R2/R5)

Stock gain is ~4.

Here are some values of R2 (3.3k nominal) and their corresponding gain values;

3.9k = 4.25
4.7k = 4.91
5.6k = 5.66
6.2k = 6.16
6.8k = 6.66
7.5k = 7.25

 

[Big Monk]

Unity gain is a known issue on the original.

The culprit is generally accepted to be the input voltage divider:



This divider attenuates the input signal around 32%:



The fist thing you want to do is bump 47k resistor up quite a bit to around 5M:



Doing so essentially eliminates all the input attenuation before you enter the preamp. However, as some people have pointed out, and as I have personally noticed in my "travels", this is STILL often not enough to get much past unity gain, especially considering the interplay in other circuits on your board. In short, the unity gain mod alone may suffice if you are plugging directly into the Vibe without other effects, etc. but I have noticed that even removing ALL the signal attenuation of the input divider, you still may be below unity in certain playing situations.

So, we have to then look to the preamp for more gain.

1.) The traditional Univibe transistor preamp is in fact a discrete opamp.

2.) It’s overall gain is governed by the classic 1+(Rf/Ri) opamp gain equation.

3.) For either the Big Electrovibe or the Mini, this equation would be as follows:

1+(R2/R5)

Stock gain is ~4.

Here are some values of R2 (3.3k nominal) and their corresponding gain values;

3.9k = 4.25
4.7k = 4.91
5.6k = 5.66
6.2k = 6.16
6.8k = 6.66
7.5k = 7.25

I used R2 = 6.8k in my recent Mini build in addition to R4 = 4.7M:

 

[Big Monk]

I borked mine when I built mine (caps too tall), and I haven’t had the inspiration to carry on. Still don’t, but this is a good looking build regardless. I remember the volume issue being mentioned by others…I believe there is a resistor value you can tweak.

I did the same thing and I'm really happy I bought a new board and redid mine.

 

[Coda]

I did the same thing and I'm really happy I bought a new board and redid mine.

I knew about the height requirement, but, for some reason, completely disregarded the fact that ALL of the electrolytics needed to be smaller, not just the ones on the top. I think a new pcb would probably be the best idea…

 

[Big Monk]

I knew about the height requirement, but, for some reason, completely disregarded the fact that ALL of the electrolytics needed to be smaller, not just the ones on the top. I think a new pcb would probably be the best idea…

I did use Tants for everything and lay down caps for the others but must have stress cracked the interface headers pads trying to cram the top mounted footswitch in. It was just too tall.

 

[MichaelW]

I've never been able to find a source for low profile 1u e caps, so I've been using 1u Tantalums. I get them from Amazon.

Here's the brand I get from Ammy. I also get the 10u's. The 47u's are humongous, bigger than an e-cap so kinda useless.

Out of the 50 pack of 1u's I usually reject about 30% of them for being too far out of spec. I won't use any that are more than 10% off.
Interestingly, I reject more of the allegedly "better" JB Capacitor tantalums I get from Tayda in 1u. I guess 1u is a hard value to nail in tantalum.

 

[Big Monk]

I've never been able to find a source for low profile 1u e caps...

Mouser baby!

 

[MichaelW]

Wow the color of the enclosure with the color of the knobs is beautiful! That faceplate looks like it was made for that color combo! Awesome build!

This is the last 125B I have in the Tayda Hammered Copper finish, I have one 1590BB in this color left that's waiting for a home.
If you go back through my build reports, early on I fell in love with this color and did my whole series of Paragon variants in this color.
So much to the point that I got a little tired of looking at the color...hahaha. I wish they did some other hammered colors. A pewter variant would be cool, or a dark steel.

 

[Big Monk]

This is the last 125B I have in the Tayda Hammered Copper finish, I have one 1590BB in this color left that's waiting for a home.
If you go back through my build reports, early on I fell in love with this color and did my whole series of Paragon variants in this color.
So much to the point that I got a little tired of looking at the color...hahaha. I wish they did some other hammered colors. A pewter variant would be cool, or a dark steel.

I really wish they had a dark blue color.

 

[Dan0h]

Unity gain is a known issue on the original.

The culprit is generally accepted to be the input voltage divider:

View attachment 39577

This divider attenuates the input signal around 32%:

View attachment 39578

The fist thing you want to do is bump 47k resistor up quite a bit to around 5M:

View attachment 39579

Doing so essentially eliminates all the input attenuation before you enter the preamp. However, as some people have pointed out, and as I have personally noticed in my "travels", this is STILL often not enough to get much past unity gain, especially considering the interplay in other circuits on your board. In short, the unity gain mod alone may suffice if you are plugging directly into the Vibe without other effects, etc. but I have noticed that even removing ALL the signal attenuation of the input divider, you still may be below unity in certain playing situations.

So, we have to then look to the preamp for more gain.

1.) The traditional Univibe transistor preamp is in fact a discrete opamp.

2.) It’s overall gain is governed by the classic 1+(Rf/Ri) opamp gain equation.

3.) For either the Big Electrovibe or the Mini, this equation would be as follows:

1+(R2/R5)

Stock gain is ~4.

Here are some values of R2 (3.3k nominal) and their corresponding gain values;

3.9k = 4.25
4.7k = 4.91
5.6k = 5.66
6.2k = 6.16
6.8k = 6.66
7.5k = 7.25

I used R2 = 6.8k in my recent Mini build in addition to R4 = 4.7M:

View attachment 39580

Awesome. On the big board R1 and R4 are next to each other and away in their own little space on the board COOL. My question is by letting more into the pedal is there a risk of the distorting? Looking forward to swapping these resistors out.

 

[Big Monk]

My question is by letting more into the pedal is there a risk of the distorting?

You're talking 2-4 dB so while I'm not 100% certain, I'd doubt it.

 

[Mentaltossflycoon]

A pewter variant would be cool, or a dark steel.

Hard agree.

 

[MichaelW]

Unity gain is a known issue on the original.

The culprit is generally accepted to be the input voltage divider:

View attachment 39577

This divider attenuates the input signal around 32%:

View attachment 39578

The fist thing you want to do is bump 47k resistor up quite a bit to around 5M:

View attachment 39579

Doing so essentially eliminates all the input attenuation before you enter the preamp. However, as some people have pointed out, and as I have personally noticed in my "travels", this is STILL often not enough to get much past unity gain, especially considering the interplay in other circuits on your board. In short, the unity gain mod alone may suffice if you are plugging directly into the Vibe without other effects, etc. but I have noticed that even removing ALL the signal attenuation of the input divider, you still may be below unity in certain playing situations.

So, we have to then look to the preamp for more gain.

1.) The traditional Univibe transistor preamp is in fact a discrete opamp.

2.) It’s overall gain is governed by the classic 1+(Rf/Ri) opamp gain equation.

3.) For either the Big Electrovibe or the Mini, this equation would be as follows:

1+(R2/R5)

Stock gain is ~4.

Here are some values of R2 (3.3k nominal) and their corresponding gain values;

3.9k = 4.25
4.7k = 4.91
5.6k = 5.66
6.2k = 6.16
6.8k = 6.66
7.5k = 7.25

I used R2 = 6.8k in my recent Mini build in addition to R4 = 4.7M:

View attachment 39580

AWESOME! It was an easy enough mod with minimally invasive surgery. I just lifted R2 and R4 from the top and replaced with with 6k8 and 5M respectively and top soldered them. Now unity is around 11:30 on the dial, PERFECT!

At full CW there is a slight bit of distortion.

Thanks @Big Monk!

@Dan0h definitely worth doing, easy mod and easily reversible.

 

[Dan0h]

AWESOME! It was an easy enough mod with minimally invasive surgery. I just lifted R2 and R4 from the top and replaced with with 6k8 and 5M respectively and top soldered them. Now unity is around 11:30 on the dial, PERFECT!

At full CW there is a slight bit of distortion.

Thanks @Big Monk!

@Dan0h definitely worth doing, easy mod and easily reversible.

Best thing I’ve heard all day. Lol.

 

[Dan0h]

AWESOME! It was an easy enough mod with minimally invasive surgery. I just lifted R2 and R4 from the top and replaced with with 6k8 and 5M respectively and top soldered them. Now unity is around 11:30 on the dial, PERFECT!

At full CW there is a slight bit of distortion.

Thanks @Big Monk!

@Dan0h definitely worth doing, easy mod and easily reversible.

Finally got around to doing this mod and wow what a huge difference it makes even on the effect itself. Thanks @Big Monk