DEMO Vibrobot

[DGWVI]

Build Rating

5.00 star(s)

Just a quick one to demonstrate the Amazon 8038 (featured in vid). I built 2 at once to compare 8038s, and they function identically.

This is an awesome, simple Trem. Im really quite enamored with the Square Wave mode, but the Tri and Sine are also pretty pleasing. Almost gets up into ring mod or fm territory, but not quite. It does bring the stutters and wobbles, though.
The trim pot is pretty touchy, and needs to be set just right for minimal distortion in the Sine and Tri modes.

Otherwise, super quick builds, made possible by @Robert's awesome layout.

No mods to these ones, but if you want a variety of speed ranges, you could put the 220n just below the 8038 on a switch- lower values = faster speeds, higher values = slower.
There are some other things that could be done to effect the symmetry of the waveshapes, but I haven't experimenters with those yet

Being a Fran circuit, I have to recommend this one, especially if you're a fan of tremolo effects. I'll be using one of these in my envelope trigger chain, and possibly another in my HOG signal chain


Note that regardless of 8038 source, you will need to lift pin 6 out of the socket. The chip will not function properly at 9v with this pin connected.

 

[Robert]

Note that regardless of 8038 source, you will need to lift pin 6 out of the socket. The chip will not function properly at 9v with this pin connected.

I keep reading this scattered around the net but pin 6 was connected to VCC in the original and my prototype worked perfectly fine without lifting it.

 

[DGWVI]

I keep reading this scattered around the net but pin 6 was connected to VCC in the original and my prototype worked perfectly fine without lifting it.


View attachment 67823

It will work / modulate with it connected, but it won't match the depth and speed I've seen in demos of the original. Lifting it corrects this issue

 

[KR Sound]

No mods to these ones, but if you want a variety of speed ranges, you could put the 220n just below the 8038 on a switch- lower values = faster speeds, higher values = slower.

This might be worth doing. I’m going to be building it this week, and to me, the first half of the speed- the fastest- seemed a bit too fast.

It will work / modulate with it connected, but it won't match the depth and speed I've seen in demos of the original. Lifting it corrects this issue

Wonder why that is

 

[DGWVI]

This might be worth doing. I’m going to be building it this week, and to me, the first half of the speed- the fastest- seemed a bit too fast.

I like it's range as-is, but I could definitely see wanting something a bit slower, especially for the sine and triangle modes

 

[Robert]

It will work / modulate with it connected, but it won't match the depth and speed I've seen in demos of the original. Lifting it corrects this issue

Ahhh, interesting, and puzzling.... I'll have to dig the prototype out and compare.

Here's a pic of a newer version, and while I can't say with certainty where it's going, pin 6 is still connected to something. (assuming the square pad is pin 1)

 

[DGWVI]

Ahhh, interesting, and puzzling.... I'll have to dig the prototype out and compare.

Here's a pic of a newer version, and while I can't say with certainty where it's going, pin 6 is still connected to something. (assuming the square pad is pin 1)

View attachment 67825

What comes to mind for me is that perhaps Fran had a strange batch of 8038s that didn't draw as much power or something. Or, the chips underwent some undocumented change at some point. But, I've tried three different sources for them (Intersil, Harris, Amazon unbranded), and they all have to have pin 6 lifted to get the full range

 

[Mentaltossflycoon]

Can confirm with my build, it was fine but didn't go nearly fast enough to be useful until I pulled pin 6. Now it's a tasty tasty tremolo that does everything I wanted it to do. Thanks again for the help, @DGWVI

 

[KR Sound]

Would a linear pot be more suitable for the speed, wonder why it’s not?

 

[DGWVI]

Would a linear pot be more suitable for the speed, wonder why it’s not?

I find the sweep with the log pot to be fairly smooth . It's also wired parallel with a 220k resistor

 

[KR Sound]

I find the sweep with the log pot to be fairly smooth . It's also wired parallel with a 220k resistor

That would do it! Just noticed that.

 

[Mentaltossflycoon]

This might be worth doing. I’m going to be building it this week, and to me, the first half of the speed- the fastest- seemed a bit too fast.

I may mess with this later tonight if I have the right caps. It would be nice if slowest setting could be a bit slower too.

 

[electricb]

Ahhh, interesting, and puzzling.... I'll have to dig the prototype out and compare.

Here's a pic of a newer version, and while I can't say with certainty where it's going, pin 6 is still connected to something. (assuming the square pad is pin 1)

View attachment 67825

Has anyone tried lifting pin 8 instead of pin 6 to see what happens? In the version that was traced, they are connected, which seems strange. As per the datasheet for the ICL8038, pin 6 is where the V+ rail should connected. Pin 8 is for the FM Sweep input.

I noticed that in the revision (above) pins 6 and 8 do not appear to be connected (unless there is a trace on top of course), which makes more sense to me.

 

[KR Sound]

Ya, lifting the V+ seems weird to me, but what do I know.

 

[DGWVI]

Has anyone tried lifting pin 8 instead of pin 6 to see what happens? In the version that was traced, they are connected, which seems strange. As per the datasheet for the ICL8038, pin 6 is where the V+ rail should connected. Pin 8 is for the FM Sweep input.

I noticed that in the revision (above) pins 6 and 8 do not appear to be connected (unless there is a trace on top of course), which makes more sense to me.

I've tried pin 8 lifted / pin 6 plugged, and it ceases to function at all

I did find this application note which doesn't explain the pin 6 thing, but does expound a bit on pin 8, with Question 2 & 3 seemingly the most relevant

The datasheet does have one application that omits the V+ to pin 6, but then every other app and schematic I've seen using the 8038 has that as the positive power pin, but they're also using bipolar supplies

 

[Kroars]

Just a quick one to demonstrate the Amazon 8038 (featured in vid). I built 2 at once to compare 8038s, and they function identically.

This is an awesome, simple Trem. Im really quite enamored with the Square Wave mode, but the Tri and Sine are also pretty pleasing. Almost gets up into ring mod or fm territory, but not quite. It does bring the stutters and wobbles, though.
The trim pot is pretty touchy, and needs to be set just right for minimal distortion in the Sine and Tri modes.

Otherwise, super quick builds, made possible by @Robert's awesome layout.

No mods to these ones, but if you want a variety of speed ranges, you could put the 220n just below the 8038 on a switch- lower values = faster speeds, higher values = slower.
There are some other things that could be done to effect the symmetry of the waveshapes, but I haven't experimenters with those yet

View attachment 67821

View attachment 67820

Being a Fran circuit, I have to recommend this one, especially if you're a fan of tremolo effects. I'll be using one of these in my envelope trigger chain, and possibly another in my HOG signal chain


Note that regardless of 8038 source, you will need to lift pin 6 out of the socket. The chip will not function properly at 9v with this pin connected.

Beautiful build and demo! Thank you very much for the info on lifting pin 6 on the 8038 to get it to work. I thought I got a couple fakes on eBay, until I read your post and gave it a shot. Clipped pin 6 and it now works perfectly! Now off to eBay to compose an apology….

I’ll make a quick post about that for quick reference, I’m sure others will have the same issue.

 

[DGWVI]

Beautiful build and demo! Thank you very much for the info on lifting pin 6 on the 8038 to get it to work. I thought I got a couple fakes on eBay, until I read your post and gave it a shot. Clipped pin 6 and it now works perfectly! Now off to eBay to compose an apology….

I’ll make a quick post about that for quick reference, I’m sure others will have the same issue.

Let's see a build report too

 

[DGWVI]

So I just finished mine and my max speed is significantly slower than yours. Everything built as spec’ed on the board.

I also snipped pin 6 and it sounds great.

Ensure that the capacitor tied to pin 10 is 220n (the one immediately below the 8038), and the resistors tied to pins 4 & 5 are 390r

Otherwise, post some pics / sound samples in the troubleshooting section

 

[KR Sound]

Ensure that the capacitor tied to pin 10 is 220n (the one immediately below the 8038), and the resistors tied to pins 4 & 5 are 390r

Otherwise, post some pics / sound samples in the troubleshooting section

Nevermind- I deleted it and was going to rewrite it.

It’s the same as yours. I fuckin mislabeled the knobs on the enclosure smh.

So I had the speed all the way ‘up’ CW which was actually down/slowest and when I turned it all the way CCW I thought it was off since it was so fast.

I’m an idiot. Looks like I’m going to be doing some creative wiring.

 

[DGWVI]

Nevermind- I deleted it and was going to rewrite it.
It’s the same as yours. I fuckin mislabeled the knobs in the enclosure smh.

So I had the speed all the way ‘up’ CW which was actually down/slowest and when I turned it all the way CCW I thought it was off since it was so fast.

I’m an idiot. Looks like I’m going to be doing some creative wiring.

We've all done similar, I'm sure. At least it just two pots

Glad you got it sorted, though