Neovibe build help - LDRs and light shield

[Governor]

Ok so I've finally got to the stage where I'm looking to power up my neovibe project.  I've made the light shield out of an aluminium soft drink can and just want to check if this will be reflective enough? Or do I still need to line it with aluminium foil?

Also, just wanted to check if the heights of the LDRs and Lani look correct?  From the circuit board to the top of the LDRs is 7mm, and to the top of the lamp is 12mm.  The top of the light shield is 15mm.  Will this work ok?  Thanks.

[Kevin Mitchell]

Your arrangement isn't considered traditional in any sense. So it's a matter of what works best for your situation.

There is a guide for the light shield ya know.
Neovibe Build Guide

[Marcos - Munky]

Why don't just point the ldrs to the light bulb? It works with a led, so it should work with a light bulb.

This is how I soldered my univibe clone ldrs. No light shield, the enclosure itself act as a shield. Well, you'll need a shield to test the board outside the enclosure - or just turn down the lights of the look, like I did .

[R.G.]

If you insist on pointing the LDRs up as in the picture, you will need something shiny as a light shield. You can actually use anything you want for the shield if it fits mechanically, and simply glue kitchen aluminum foil inside it, shiny side out. With the LDRs pointing up, the shiny light shield both keeps ambient light out, and mixes the internal light to be more even, as well as reflecting it down on the LDR faces.

I'm not sure how effective a shiny-inside light shield is as a light mixer.

You can use anything, shiny or not, that fits mechanically as a light shield to keep ambient light out, but you would need to bend the LDR leads and point their faces at the light bulb.

Either way works. I've done them both.

[thermionix]

Either way works. I've done them both.

Do you have a preference?

[Governor]

Either way works. I've done them both.

Do you have a preference?

I'd like to know this as well, I've read various forums that mention with ldrs pointed up sounds preferable and more comparable to the original than with pointed at the lamp, I'm not sure if this is the case?

Thanks for the relpies, so would the inside of a soda can be reflective enough?  Or should I line it with foil?  Does it matter how high the reflective top of the light shield sits above the LDRs and lamp? in my case there is 3mm between the top of the lamp and shield, and 8mm between LDR and shield.  Or do I need to make another shield that is a little higher?  Cheers for the help.

[Joncaster]

I made a bigger shield to test in my build, and I noticed that there was more high frequency content in the whole effect.
Moved the sweep frequency center up as well (and compensating for that in the bias didn't get it darker in tone).

Liked it at first cause it sounded more airy or something, but wanted the deeper chew of the smaller shield. Smaller shield had more musicality for me.
Went back and forth for ages, and I might build the next one with some of these differences.
I think my bulb is actually almost touching the top of the shield.

I preferred LDR's facing up, and polished aluminum instead of shinier foil inside...fwiw...

[R.G.]

Either way works. I've done them both.

Do you have a preference?

Not really. Digging through layers of what changes what for what advantage, you ultimately get to the micro details of which LDR you're using, its own response in terms of resistance per light intensity, its spectral response, how evenly or not the light hits all four LDRs, and whether evenness is good (as in, all LDRs are identical in response) or bad (in that varying LDRs get "compensated" by the un-evenness of light on them making up for or making worse their differences.

The micro details of which LDR in which position and what the light shield is doing in mixing or not makes the question of which is better, even allowing for what "better" might mean.

The complexity of the interacting factors makes me despair of coming up with a one-size-fits all solution on this question. Add to that variability in each person's building details, and I rapidly get to "try it; if you like it fine, if you don't, try another style". I don't think there is a definitive answer.

[Governor]

Great info, thanks RG.

I just powered this up (it's only taken me 4 months to finish!), and works first go, and sounds awesome- warm and chewy, pretty happy with that!

I've followed the geofex instructions to the tee and temporarily put in 200k pots for  R35 and 36.  I think it sounds best with r35 and 36 at around 60-80 ohms.  It sounds pretty good, how do know if I need to replace the r50 on the base of q50 to increase from 47k?  I can get the lamp to glow very dimly with depth knob all the way down using the emmitter trimpot.  I'm just not sure where to go from here, thanks.

[Governor]

One thing I also noticed was that lamp brightness changes along with the speed knob.  With the speed knob dialed all the way back the lamp looses some brightness, as the speed increases do does the brightness of the lamp (the speed works as expected).  Is this normal?

[Joncaster]

One thing I also noticed was that lamp brightness changes along with the speed knob.  With the speed knob dialed all the way back the lamp looses some brightness, as the speed increases do does the brightness of the lamp (the speed works as expected).  Is this normal?

Very normal for that particular LFO.

[Governor]

One thing I also noticed was that lamp brightness changes along with the speed knob.  With the speed knob dialed all the way back the lamp looses some brightness, as the speed increases do does the brightness of the lamp (the speed works as expected).  Is this normal?

Very normal for that particular LFO.

Ok, thanks.

I'm still not sure what I'm looking for to fine tune this thing and dial in a proper bias?  Any help is appreciated, thanks.

[Joncaster]

Well if it's "awesome, warm and chewy", that sounds like a pretty good bias. Compare it to SteveB's clips (search on here), and listen to how it sweeps and the frequencies, etc.
Then it's all personal preference and messing around with things to see what changes what... But if it sounds good, then it's good.

[Jay]

Agreed - if it sounds good, box it up you're done.  Don't overthink the bias, other than maybe making sure the lamp doesn't go completely out.

And FWIW I built mine after repairing two originals.  They both had the LDR's flat to the board facing up under a not dramatically shiny tin box much like yours.  Built mine the same.  I did the wet/dry tuning for max. notch, trimmed the bias for no blackout. 

The two originals sounded great, one a little better than the other.  Mine sounds just like the better one.  The bat eared Hendrix genius player owner of them, who is very sensitive to how his kit sounds, couldn't tell the difference between mine and his.

Enjoy it!

[Governor]

Thanks, yes I'll mess around a little more with the R35 and R36 and then leave it as is I think.  Good to know its normal for the lamp brightness to drop off as the speed is reduced - with the both and speed knob at 12 o'clock the effect isn't very pronounced.

Also, has anyone had any luck with an LED to pulse with the effect?  I've done search and found some info on how to do it - does it affect the sound?  I was thinking about making the status (on/off) LED flash with the speed of the effect, but with both the rate set low I'm guessing the LED brightness will be hard to see which wouldn't be ideal as would be hard to see if the unit was on or off.

[PRR]

> LED to pulse with the effect?

Try this. Not verified.

[Joncaster]

...with the both and speed knob at 12 o'clock the effect isn't very pronounced.

Lowering the value of R49 (from 47k to, say, 10k or 4k7) increases the amplitude of the LFO sine wave (but changes the bias too, so has to be adjusted for),
So at max settings its a bit more choppy, and half way settings the effect is a bit more present.
Will put more strain on the bulb driver, though (2N3904 more suitable than 5088). Some guys do a whole darlington thing there.

Doing this might make your max settings a bit too crazy and thumpy (I think one can change out C11 for something smaller than 1uF, but never tried it)
Or removing C16 entirely (cleans the vibe output up a bit, IIRC)
I'm using 4k7, as I like being able to get really seasick thumpy if I want to, and my 1 o'clock depth is perfect. down to 9 o'clock on faster speeds.

The R35/R36 mix thing is a bit more subtle than the bias changes one can do.