VFE Tractor Beam - Analog Phaser

[MAO]

Hate to say it, but goodbye Maxon PhaseTone and MXR Phase 45/90.

The VFE Tractor Beam (as seen at madbean) blows them away...IMO

Requires a bipolar power supply and matched DSG jfets (2n5952) 

I made the charge pump daughter board as small as possible to squeeze it in under the main board. The charge pump's filter caps and zener protection are on the main board.  I used SIP sockets so to route the wires under the IC and through the board. I also bent the 10uf cap over and placed the mini board under the main board, component side down, between the pots and switches.

I'll post some pictures on how I laid it out once I decide on the graphics, but it was an easy fit in a 125B.

Verified by me...and it sounds awesome! (Standard true bypass switching, noiseless suggested such as a relay type or optical bypass)

[Mulekicker]

Awesome! I'm gonna have to order those ic's and some matched jfets and build this one. Can never have too many phasers. I have some W20k pots but if anyone doesn't I remember reading (maybe on the madbean forum?) that linear taper 10 times smaller will get closest. So, B2k. VFE uses a lot of those W taper pots.

[MAO]

Yeah, It's excellent.

I'm building another layout using DGS jfets (2sk246). I really liked those jfets in the Maxon Phase Tone, it will be interesting to hear how they compare with the 2n5952s in this design.

As for the Feedback pot, you might be better off with a 20k linear if you don't have a 20k W-taper.

Using a 1-10 scale, the 2-8 range on a linear pot is compressed to about 3.5 - 6.5 on a W pot, essentially narrowing the center most range of the pot and conversely extending the outer most ranges.  So 0-2 and 8-10 on a linear are spread out to 0-3.5 and 6.5-10 on a W pot.

And 0-1 on a linear is about 0-2.5 on a W, giving 2 1/2 times the rotation for easier fine tuning the 0-1 range on a linear. Same thing applies to the 9-10 range on a linear.  
 
In this pedal, the Feedback pot looks like a mixer between the positive and negative feeds, so a W taper would somewhat accelerate the onset of either feedback from the center (noon) position, and allow easier fine tuning at the furthermost CW and CCW rotations.

Bottom line is, it will be easier to dial in the more extreme CW and CCW settings with a W than a Linear. And the feedback will be noticeable sooner from the center/noon position.

So try a 20k linear 1st if you already have one. If you find you usually set it between say 3 and 7 when you want to add some feedback, no need for the W taper.  If you are going below 3 or above 7, you'd be better off with the W.

Hope that makes sense.

[Hozy31]

Hey MAO, are stages sw 4 & 6 connected? Also you mention three cuts are for routing holes but i only see one. Could you point out the other ones for me. Does center 2,3 have one? Cheers.

[MAO]

Hey Hozy,

Yes, sorry for any confusion.

Stages SW 4 & 6 are connected, so you can run just one of those wires from the board to both switch lugs if you like.

The dual cuts/routing holes are Stages SW4, Center 2-3, and Speed 3.  I color coded those connections to help spot where the wires actually connect to the board.

Stages SW4 - purple wire connects to column 2, row 18. Wire routes through cut at column 2, row 17
Center 2,3 - blue wire connects to column 4, row 7. Wire routes through cut at column 3, row 7
Speed 3 - light blue wire connects to column 17, row 4, Wire routes through cut at column 17, row 7

Hope that makes sense.

Also, a couple suggestions:

Socket the "vibe" caps, Mode SW6 - 2n7 and Mode SW3 - 220n. Adjust to taste. Some standard 'vibe' values to try are 470p, 4n7, 15n, 100n, 150n. With the speed control at noon in the Vibe setting, I like 15n and 100n there, more of an auto-wah sound for leads.

Reduce the 12k if more positive feedback is desired with slower speeds in the 2 stage setting. I need to spend more time with the 2 stages mode to see if more feedback is really needed.  

The bias adjustment is pretty narrow on mine, I think reducing the trimmer from 200k to 150k or 100k and increasing the connecting 10k and 47k proportionally may give a better window for fine tuning. I would just keep the total resistance between the three at around 257k like the original values. (My rail voltages are +9.0 and -8.7V, this gap between the two and ground probably effects the range for the bias, maybe the closer the gap the more narrow the bias window...not sure). But I was able to dial it in with the 200k, took a few minutes and a couple trys to get it just right.

I used 1k5 for the 1k43 resistors, next build I'm going to try 1k and 430R in series to see if there is a audible difference. I doubt it, but easy enough to check it out.  

Let me know how it goes.

 

 

[MAO]

Here is how it looks with the wire routing and mini road rage tucked underneath.  (waiting on 20k W pot)




Top view (temporary 250k bias trimmer, put some additional MLCC caps in parallel for the 1u and 10u due to poor tolerances. Optical " no noise" bypass with adjustable LED at the bottom)



Layout (dc jack, battery snap and led bezel not yet installed)

[Hozy31]

Thanks for the info MAO, still need to get that chip before i start.

[Hozy31]

Hey MAO, What type is the on/on/on DPDT as i have two types 1 & 2?

[Hozy31]

Oh, and should it be LM358 rather than LF358?

[MAO]

Yes, sorry LM358

The Phase/Vibe switch wiring was confusing me as I usually number switch pins facing you, but I believe in the Tractor Beam schematic he has the pins numbered with them facing away from you, top left being pin #1, top right pin #4.    

I made an assumption that the center position should select a 47n and a 2n7 and had originally used a 1=2 and 5=6 on/on/on (pins facing away, top left is 1, top right is 4). The choice for the middle selection is either 47n & 2n7 or 267n & 47n depending on switch type.  

So with pins facing away, and numbered 1 top left and 4 top right, each on/on/on switch type gives the following cap selections:

Type A - middle position 1=2 and 5=6
 
Phase Mode - 47n & 47n
Phase/Vibe Mode - 47n & 2n7
Vibe Mode - 267n (47n+220n) & 2n7

Type B - middle position 2=3 and 4=5
 
Phase Mode - 47n & 47n
Phase/Vibe Mode - 267n (47n+220n) & 47n
Vibe Mode - 267n (47n+220n) & 2n7

So, of course only the middle Phase/Vibe position is affected by the switch type. You might want to hook those wires up manually 1st to see which you prefer. Type A - 47n & 2n7 or Type B - 267n and 47n


I ended up changing the 2n7 to a 15n and the 220n to a 100n on mine, edit - mainly for the 2 outer selections, and used a Type A switch. So now I get

Phase Mode - 47n & 47n
Phase/Vibe Mode - 15n & 47n 
Vibe Mode - 147n (47n+100n) & 15n

Maybe my assumption was wrong about the 47n & 2n7 selection I'll have to try it again with the 267n & 47n.

Anyway, when I get a chance I'll see if anyone on the madbean forums has discussed the switch type. If not, I'll ask. And will update the layout once I know for sure.

 

[MAO]

I just looked at the build doc again and Brian has this switch linked in the BOM.

So it appears the middle position should select the 47n and 2n7 and you would need a Type A as noted above.

Note: On/On/On Switch Type's "A" and "B" are not an official naming convention that I'm aware of, just my way of distinguishing between the two types for this discussion. If there is an official naming convention, please let me know which is which.

[Hozy31]

Thanks for the info. Will try and finish it during the week if possible.

[GrooveChampion]

Welp, I am ordering some LF358's and some matched Jfets, should I get some from Smallbear? I usually buy everything from them.

I understand the LF358 is required but I'd like to know why to widen my knowledge. Also, on the same note, is the 2134 also required? Cos It IS an expensive high end dual OP Amp, or will any dual OP amp do?

Also, schematics for the opto bypass? Is it true bypass but with a soft switch?

[MAO]

Sure, but you should get a LM358, not a LF.

I had a typo is the original post, be sure you have thr most recent dated today.

Also, if you have the other type of on/on/on switch as discussed above, just flip flop the connections. 1&2 would be 4&5, 3 would be 6 and vica versa, 4 would be 1 and 5 would be 2.

[GrooveChampion]

Oh, well I guess  thats why Smallbear doesnt have LF358s

[GrooveChampion]

Goddammit, didnnt get 4.7 zeners or 200Kohm trimmers...

Nevermind, ordered them with some 12V Zeners and 20K trimmers.

Is the 2074 also important to this build or can it be replaced with a TL074? Is it a quad OP amp? Cos I remember a phaser using a resistor array....

[Sphere80]

I used both 2074 & TL074 on my build (on the pcb, not this layout) and they worked the same.  I also used the 2134, and a less expensive op amp.   Sounded the same to me, maybe one setup  is  cleaner, but feel free to build this with sockets.

[GrooveChampion]

Thanks for the info man, you saved me a lot of headache.