Neovibe transistor and other question.

[Steve Connochie]

Hello I've constructed the vero board version.  https://www.aronnelson.com/gallery/main.php/v/cathexis/Veroboard+Layouts/Neo-Vibe/Neo-Vibe.jpg.html

I'm currently debugging my build, i now have a working LFO but no sound coming out when I connect the guitar in either switch position. As far as  can tell all the components are in the correct position. I've checked  all resistor values and tested each transistor. I've measured the voltages at the points on the GEOFEX schematic and they are in good agreement I,m currently checking the transistor bias starting with the feedback preamp so here's my question. The notes say every transistor should have a min base voltage 0.5-0.7V  greater than the emitter and both less than the collector. Q2 and 3 check out OK however Q1 has the following C 2.15V B 0.85V E 1.00V as the guitar input feeds to the base does this elevate the voltage to the required level or is there something wrong here, should I reduce the size of R3 to 33K would this elevate the base voltage? Second question what is the function of R1 and 2 it appears to me you only need one or the other. Thanks in advance

[Kevin Mitchell]

The audio probe is your friend.

-KM

[Steve Connochie]

Thanks for the tip Kevin, what an awesome little tool! Got the neovibe up n running now. I must have gone over the board maybe 50 times and missed a single cut out. Sadly the phasing is a bit lacklustre probably down to the LDRs which I can't source the exact spec in Scotland I've a few different ones to swap out so I'll see which ones I like best. Thanks again. SteveT

[Joncaster]

Thanks for the tip Kevin, what an awesome little tool! Got the neovibe up n running now. I must have gone over the board maybe 50 times and missed a single cut out. Sadly the phasing is a bit lacklustre probably down to the LDRs which I can't source the exact spec in Scotland I've a few different ones to swap out so I'll see which ones I like best. Thanks again. SteveT

The "offset" mod is your friend for getting the bulb swing into the right range for your LDR's.
There are a few ways to implement it, depending on what you have on hand (250k pot, 50k trim, etc).
I used a lower value R50 for mine at the moment, but might try adding resistance to R47 and messing around with it some more.
The business really happens at R47, R49, R50 and the Bias trim.

I tried removing C16 as per JC's recommendation, but it seemed to get a bit more polite...which I'm not going for.
SteveB recommended between 4k7 and 47k for R49, I like 8k2 so far...it accentuates the wobble in mine.

Did the "speed mod", but in all honesty, will never really use it that fast. I'm more of a tremolo guy for faster speeds.
Tried the "mix resistor mod", but actually found I liked a slightly offset mix, in favour of the vibrato signal side. That gives the max depth in the 'chorus' setting a bit more out-of-hand wobble.
But the adjustments were so subtle, as most people say. So i've left mine with the stock 2 x 100k.

Upped R3 to past a Meg (1 or 2.2M, can't remember right now). That brings the level up and makes it brighter, but also drives the whole circuit harder, so you might get a bit of distortion on loud notes. I quite like that for mine (I never run a super clean signal anyway), but I'm still gonna try upping the overall voltage from the regulator and see what happens.

Good luck with finding your tone!

[Steve Connochie]

Thank you very much Joncaster, that gives me a pile of options to tweak. I've come across some 50K trimpots at work so I'll start at R47 tonight. Much appreciated I'll keep you posted👍

[Joncaster]

One can spend a lifetime tweaking this circuit.

I thought I had a good thing going until I changed my LDR's with some other ones I ordered.
Boom, the wobble came out completely (the dual-sided sweep), and I could adjust the offset and bias in a more meaningful way.
The LDR's range from about 50k - 20M.
I'm sure I could have gotten the previous ones working, but these work perfectly with close to stock R47/R50 values

I also put in a slightly larger bulb, but still a wire end, about 40mA. That helped spread the light more than the tiny one I had. A bit more...something.

I replaced the 7815 with a 7820, to up the preamp voltage, and I think I like the change. The guitar sounds a bit clearer, and a bit more headroom. Subtle, but it does feel more open.

Gone down to 4k7 for R49, cause it gives me more range with the Depth pot. Full intensity is crazy.

Still need to lower the bias a tad more to get into a bit of a more watery base line. That would mean lowering R47 a touch to keep the swing the same.

But basically, I've gone around in a massive circle and arrived at largely stock values.

[Steve Connochie]

Hi Joncaster sorry for the LONG delay responding. Business trip and life got in the way of.. well you know doing cool stuff. Finally going to get some time again to tinker with the vibe. My main issue at the moment seems to be with the ac power supply causing nasty buzzing its a cheap wall wart so its my prime suspect thinking about making a charge pump to run it of a standard 9v dc power supply. Best wishes.

[Joncaster]

There's a ton of posts regarding noise in this build, with all sorts of causes.
I think most of them tended to be open grounds, or solder bridges, mis-wired power inputs (like grounding the negative lead of the DC input to the chassis), a few bad adapters, dodgy transistor soldering, etc. The filtering in the Neovibe is pretty thorough, though, should be able to take a lot of noise and spit out clean power.
My buzz was simply not having it in an enclosure, which took me days to figure out

There's also a lot of info regarding charge pumps and the issues in implementing them with this particular build, but didn't delve that far.
I'm using a 24V/750mA DC supply, and opted for a pretty fancy one (it even has protection against reversing the polarity which, I discovered, saved me from a blown-up board ).

Haven't boxed mine up yet, it's just sitting there waiting for me to find some time.
J

[Steve Connochie]

Mmmh that's given me be a bit more to think about I'll read up those posts before I try anything. It's not a shielding issue as it's boxed time to dig out the audio probe again I'm thinking.ive got too many projects on the go I need to focus on getting the vibe perfect cos it does sound sweet.ill let you know what I find. Regards Steve.


Success - I've eliminated the annoying hum and finalised my build, I've also gone round the houses and pretty much arrived back at stock values with the exception of R47 which is sitting at 151K. Revised my earth connections to a star as I think I'd created a couple of ground loops when I added an led and earthed both jack's. Stupidly I'd used self adhesive felt pads on the underside of the board to prevent grounding with the enclosure and the adhesive must be slightly conducting. One pad was sitting under the bridge rectifier meaning a small leakage from the ac was making it into the ground connection on the DC side of the chip causing the hum. So all good now and sounds beautiful through a Cornish buffer and before the deep blue delay from guitarfx veroboard website. Thanks again for all your help and wisdom with my build. Steve

[Joncaster]

Awesome! Glad it's come right:)

Now you mention it, I haven't hooked up a delay with mine...gotta hear that!
I'm gonna try get round to drilling the box this weekend, and maybe commit to a finish...still don't know what it needs to look like;)

Post pics, I would love to see a vero build of this:)

[Steve Connochie]

Not the most professional looking build, I'll spare my embarrassment and not show my soldering on the other side 😁the light sheild is the top of a marker pen lid which fits my build perfectly. Just got the knobs today and quite like them now just have to get round to some suitable  graffics for the box.
Still l'm pretty pleased with my first ever build and the others five I've done since...totally addicted to this😂
Steve

[Joncaster]

Wow, that's so great!
First ever build, you chose a vero Neovibe...that's very impressive!
Lovely build.

Yeah, the bottom of my pcb is a war zone. But good experience fixing two lifted tracks, cleaning flux off, reflowing, etc.

[Steve Connochie]

Cheers, Sweet tunes by the way love the range of your sound. Really like your work on forget my words edgy tense and reminiscent of Johnny Greenwood stripped back Radiohead work right up my street👍👍👍

[Joncaster]

Thanks for listening man! I did that EP ages ago, by myself before I had a band. I record and mix all our stuff, with the help of our bassist (also a mix engineer by trade).

So,
I did a comparison of two different size light shields. I was using the size that's on the Neovibe document, it's pretty small (but maybe I printed it out smaller scale...)
And I made one that's apparently the same size as the original (1.25" sq x 0.75" tall)

The bigger light shield had more high frequencies in the whole signal, which was strange. It really made the whole thing brighter.
More open, maybe, but not as chewy as the smaller shield.
It was more watery and had a really nice clarity to it.

I prefer the smaller shield for now cause I was going for more of a chewy, dark syrup feeling, has a nicer pick attack.

The bigger shield was a bit less shiny.

I went back and forth between the two for ages, cause they both had some cool things going on, regardless of bias trim setting (slightly different sweet spots).