This Week on the Breadboard: a BBD Reverb

[Chuck D. Bones]

After being whelmed, but not overly, by the Belton Brick, I thought I'd give a BBD-based reverb pedal a try. I ran across a vintage MN3011 (U3) in my stash and this is what I ginned-up. It's mostly based on an example circuit in the datasheet, with a few extra features thrown in. The MN3011 has a total of 3,328 stages, with 5 taps along the way and an output at the very end. The taps are staggered to mimic the multiple reflections in a room. OUT6 is at the end of the line. All 6 outputs are combined, filtered and mixed with the dry signal. The signal at OUT6 is also fed back to the input of the BBD via the DECAY control. There is some filtering up front and a Gain Trim to compensate for the chip-to-chip insertion loss variation. U4 generates the clock using its internal oscillator. The DELAY control sets the clock rate. Based on our discussions of the Belton Brick's LFO dither, I went with Betty Wont's idea and used the guitar envelope to modulate the clock freq a little bit. It works quite well. The clock freq is always moving, but it's gradual and somewhat random, nudged along by the guitar's envelope. U5A is a slow peak detector that sort of follows the guitar's envelope. It pushes the clock freq up and down a few percent. This was the hardest part of the circuit to get right. I tried doing it a few different ways with fewer parts, but nothing work anywhere near as well as this version. I might make a few component value tweaks, but the basic topology is solid. I'll snap a pic of the breadboard tomorrow AM after the sun comes out.

 

[Chuck D. Bones]

Controls (L-R): REVERB MIX - DECAY - DELAY

The MN3011 is top center, 3101 clock chip top right. Top left is the output filter. Bottom right is the input filter. Bottom center is the output buffer & peak detector. Bias Trim is on the left. Gain Trim is on the right. Turns out the Bias Trim was unnecessary. Setting the Vref = 1/2 Vcc works just fine.

 

[fig]

How do you like it?

 

[Chuck D. Bones]

Better than The Brick. I'm only using the top 1/2 of the DELAY knob's rotation. The "room" gets way too tiny below noon. Gonna try increasing C17 for longer delays.

MN3011's seem to be pretty damned scarce. At the end of the day, the FV-1 may well be the best option for a purely electronic reverb.

 

[teal]

I very like the idea building a pure analogue Reverb Pedal.
The Last Gasp Arts Transroom uses two MN3011's for example. I don't know if that would do the trick.
Unfortunately the chip is very hard to get and expensive to try

 

[Nic]

Noob question here, I see 3 transistors on the breadboard, but can't seem to find them in the schematics. What are those and what are they used for here?

Edit: I think there is a post where you explain when to use which type of caps, like I see no ceramic, but box, film and tantalum... I picked some in my last order but not sure where would be best to use them.

 

[fig]

Noob question here, I see 3 transistors on the breadboard, but can't seem to find them in the schematics. What are those and what are they used for here?

Edit: I think there is a post where you explain when to use which type of caps, like I see no ceramic, but box, film and tantalum... I picked some in my last order but not sure where would be best to use them.

It’s Chuck’s board but it doesn’t look like those transistors are used.

 

[Cybercow]

Nice! The MN3011 is a very rare BBD. I've been using a few of those MN3011 BBDs in our X100 Rehouse project and they (the MN3011 BBDs) are actually a 6-tap delay line. We've examined that chip in the X100 (rev 10) up, down, inside and out and it does have some decent flexibility. Tom (Scholz) locked it in at a specific and tight setting for the X100.

When we ran out of resources for acquiring the MN3011 at a decent price, (they're up to around $45 each when they can be found), we started looking seriously at the FV-1 as a replacement. Turns out, the SpinCAD Designer app (by Digital Larry) has a dedicated MN3011 building block for developing FV-1 patches. We're pretty darn close to nailing the original X100 settings for an FV-1 replacement patch. The real challenge has been to get a true stereo version of the patch to fit into the 128 line-code limit of the FV-1. The plan is to get the minimum control settings of the MN3011 SpinCAD block to match the X100 settings, while allowing clockwise trace of the FV-1 internal control pots to increase the delay time and feedback. We know it can be done in true stereo with a pair of FV-1s, but we're still pushing to get the code to work well with a single FV-1 in stereo.

Looking forward to hearing a demo of your build.

 

[Chuck D. Bones]

Noob question here, I see 3 transistors on the breadboard, but can't seem to find them in the schematics. What are those and what are they used for here?

Those are all abandoned, from previous design iterations. I should have pulled them out before taking the pic.

 

[Chuck D. Bones]

Nice! The MN3011 is a very rare BBD. I've been using a few of those MN3011 BBDs in our X100 Rehouse project and they (the MN3011 BBDs) are actually a 6-tap delay line. We've examined that chip in the X100 (rev 10) up, down, inside and out and it does have some decent flexibility. Tom (Scholz) locked it in at a specific and tight setting for the X100.

I'm gonna have to take another look at the X100 schematic and consider modding my design to take advantage of Tom Scholz's work.

 

[fig]

Those are all abandoned, from previous design iterations. I should have pulled them out before taking the pic.

What? They’ve been there through a few designs…I named the two in the corner Horace and Doris.

 

[Chuck D. Bones]

…I named the two in the corner Horace and Doris.

You would.

 

[Nic]

I had the feeling the two left ones where not used, but was really puzzled by the third one! Thanks

 

[Chuck D. Bones]

I'm gonna have to take another look at the X100 schematic and consider modding my design to take advantage of Tom Scholz's work.

OK, I see what they did there, using the odd numbered taps (and OUT6 delayed an additional 1024 stages) to make the right channel echo and the even numbered taps to make the left channel echo.

Given that the MN3011 is so scarce, one could do something similar with 4 or 5 V3207s. It's important to do like Scholz did and run them all on a common clock to avoid aliasing the clock feedthru down into the audio band.

 

[fig]

...or maybe a couple of MN3005s? They are 4096 stage up to 204ms

 

[music6000]

So 4 or 5 rare chips to replace 1 very rare chip, that will be the way to go!

 

[fig]

So 4 or 5 rare chips to replace 1 very rare chip, that will be the way to go!

It's not logic, it's Rock N Roll!
Of course the 3207s and the 3005 are much easier to manage than a 3011.....unless I'm doing something wrong.

 

[music6000]

It's not logic, it's Rock N Roll!
Of course the 3207s and the 3005 are much easier to manage than a 3011.....unless I'm doing something wrong.

I wonder why Xvive hasn't revived the MN3011?

 

[Chuck D. Bones]

So 4 or 5 rare chips to replace 1 very rare chip, that will be the way to go!

CoolAudio makes a V3005. Not rare, and not expensive (if you buy 100 at a time).

 

[Bricksnbeatles]

I wonder why Xvive hasn't revived the MN3011?

Because we didn’t petition for them to do it yet?

Let’s fix that:

Sign the Petition

Have Xvive revive the MN3011 BBD chip

chng.it