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Hello all, I'm planning to build the analog vibrato but I want to double up the circuits to make this a stereo effect. Obviously I could build two separate units into the same enclosure but I need the effect to be controlled by the same knobs and the effect to stay in sync (i.e. the sine waves are perfectly in sync). The second part of the modification I want to do is to remove the 'unlatch' mode and the 'rise', which aren't needed. I'm not averse to keeping the components there unused but if I can save some money and (more importantly) space on the PCB then awesome.

The effect is going to be a little desktop unit on the master of my mixer to apply a wow/flutter effect on some synths (which is why it needs to be stereo in and out).

With this in mind, I'm trying to understand what modifications I need to make to the circuit to implement these changes. My initial idea is to identify the circuitry responsible for producing the sine wave modulation, and include 1 set of this, controlling two parallel sets of the audio path/BBD circuits.

From looking at the schematic I can see that the lower portion is the LFO section, and the upper portion is the audio path and these are linked by markers A, B and C of the BBD chip. It seems clear that what I need at the high level is then 1x the LFO section and 2x the audio section. But can I just split the A, B and C points from the LFO circuit to go to both the BBD chips, or do I need to do something a bit more complicated?

On the subject of the ramp function, I can see SW2 activates this, which means that anything down stream from that (C25, R54, R55 ramp footswitch) I can safely get rid of, however there is plenty of stuff upstream from that that is clearly involved, such as the RISE pot of course. Where should I draw the line for what to chop?

Thanks!

Having never actually done this myself, I must accompany this with the disclaimer that this is only theoretical. If I was to attempt to make a stereo vibrato, this is how I would attempt to do it:

1. I'm not trying to upsell you, but I think it would definitely be easier to build 2 units. You can probably save a little $ by not ordering the enclosure for either because you will definitely need to house the whole thing in a larger enclosure. Use one as the master for the LFO and the other as the slave. You will also need to build a small bit of extra circuitry to split the LFO into a second wave that is 180 degrees out of phase. This will require 1 op amp and a couple resistors. You can easily build it on a bit of vero or perfboard.

2. Build 1 unit completely stock. Probably best to get that working first before anything else. I know you don't need the ramp feature, but I would just build the master with it to keep things simple. Just don't use it.

3. On the second slave unit, you can omit everything from the LFO section (the bottom half of the schematic) except for the Clock Driver. This is the 3102 chip and all its supporting components up to R43. The slave unit won't need its own LFO, but it will still need its own clockdrive to drive its BBD.

Make sense so far? Now you need to tap into the Master LFO and split it. For this, we are going to look at the Roland CE-300 schematic. You can also look at the Dimension C DC-2 schematic to see have a dual wave LFO is created, but the CE-300 is a little more straight forward. The DC-2 has those weird buttons for depth and speed rather than just pots. https://www.audioservicemanuals.com/b/boss/boss-ce/329656-boss-ce-300-schematics

4. You want to recreate on veroboard, the bit of circuit between R58 and IC9b

5. The input of this circuit will tap into the LFO output of the Master at pin 8 of the BA6110. You'll also need to tap into the +9v, 1/2v and ground as well to power the veroboard. There is a trimpot and a regular pot for depth and depth limit. You should probably just use two trimpots here, as you don't need a secondary depth pot and I'm not sure what the hardwired resistor value would be.

6. This new bit of circuit will have 2 outputs. The first at TP9 will be the out of phase "stereo" LFO. The second at TP8 will be in phase. You'll connect these to the throws of a SPDT switch. The pole of the switch connects to R43 of the Slave unit.

_________________
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Please do not PM me. email is prefered. keith@buildyourownclone.com

Thanks for the detailed info!

I think either I've completely misunderstood the need for the extra circuitry from the boss ce300 unit or I haven't explained what I want very well. You say the LFO should be split and one put out of phase with the other, but what I want is for the two LFOs to be in phase with each other perfectly. Does this negate the need for the veroboard circuit you described? The idea of the effect is not to have a vibrato that changes across the stereo field, but to have the same vibrato applied to two separate L and R signals in the exact same way. The effect will be to simulate the subtle pitch variations you find on tape recordings. FYI I'm also interested in changing the values of C19 and C20 as outlined in another post here to get a slower rate, and possibly have different values for each to get a skewed LFO for a more tape-warble effect (will be selectable buy a switch)

The explanation of the output of the LFO makes sense, can you explain though why the BBD chips need their own 3102 rather than just being driven by one shared? Is it a case of the 3102 not having the power to drive both 3207s?

I'll be designing the PCB from scratch which is why I'm keen to not include the ramp portion of the circuit (hopefully it's not too cheeky to ask for help here when I'm not actually buying the kit from your site ). Just need to figure out where to chop it off, pin 4 of the BA6110 makes sense to me, but could I actually just get rid of the BA6110 itself, and tie R39 directly to R43 for example?
Thanks for the help!

Ah. Okay. Generally, when people ask for stereo chorus, vibrato, phaser, flanger, etc. mods they want the left out bending pitch up while the right out bends pitch down rather than the signal simply being out of phase. What you're looking for is something to create more of a "double tracking" effect? Or do you just want a sort of global post mix that effects the left and right exactly the same?

In that case, then no. You do not need that extra bit of circuitry to split the LFO. And no, you do not need two 3102 clock drivers. One clock driver is powerful enough to drive at least 4x 3207, possibly more.

If you don't want the ramp effect, you can just amputate the BA6110 portion of the circuit entirely. It's an envelope trigger VCA. It has nothing to do with the actual generation of the LFO. It's really more of a secondary depth knob. To bypass it, you'd simply connect R39 330k to Q6/C21 junction. You may want to reduce the value of R39 if you find the depth lacking. Typically, you see a 220k resistor in this position in most BOSS effects. But this twin-T oscillator also isn't the typical LFO in most BOSS effects, so who knows.

Just my 2 cents....I would still opt for two separate 3102 clock drivers. This will allow you to apply slightly different delay times to each of the BBDs via the TRIM2 500k delay trim pot. This will create two signals that aren't quite exactly in synch and aren't quite exactly hitting the same pitch at the exact same time....where talking a couple milliseconds and the tiniest fraction of a semitone, which is what multi-tracking is really about....if that's what you're going for. But if you really do only want two signals that are 100% exactly the same, you can certainly run both BBDs off one 3102. In fact, you should only use one clock driver because you'll likely never get the two to match up perfectly.

Two more cents....if you're going to go to the trouble of designing a new PCB for it, and you do decide to use two separate clock drivers, you might as well just throw in that little bit of extra circuitry for the true stereo effect.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

That's a great question to be honest. What I'm looking for is to recreate the pitch variation found on old vinyl records, and tape like cassettes and VHS, which comes from the sought variations in motor speed, or the slight unevenness of the record, typically called wow and flutter. My understanding is that this is best recreated by applying the effect exactly the same to the left and right. The motor speed varying the pitch would affect both the left and right channels on a tape exactly the same, and the unevenness of a record would be present on both the left and right grooves in a record, so I think that makes sense and is what I need to do. You're right that the effect is going to be a general master effect so the only reason it needs to be a stereo unit is to preserve the stereo signal path from my mixer.

It's good to hear that I can use a single 3102 as I think I've figured out that this is the only way this could work, for the reason you stated that two parallel ones will never stay perfectly in sync.

Now I've had some food for thought, I'm wondering if it's possible to have two parallel LFO circuits, one for a wow effect (slow) and one for a flutter effect (fast) so I can have both affecting the audio at the same time. I'm imagining two LFO circuits, mixed together with a simple mixer circuit, which feeds into one 3102, which controls the left and right circuits. In this case my mixer would be mixing the outputs of two R39s and feeding into Q6/C21 junction I think, does that sound feasible? Essentially just combining two LFOs to create a more complex LFO which then modulates the BBD. Having one 3102 is still key here as I don't want the wow to be on the left channel and the flutter to be on the right, I want them both applied to both left and right in the exact same amounts, hence the combination of LFOs.

Thanks for your help.