Neovibe prebuild questions

[axg20202]

Hi all,

I'm thinking about building the Neovibe (GEO layout on the GGG site) and have been doing a fair bit of reading around the subject before I start. Hopefully someone can help with the following queries I have before I get cracking:

1) How to hook up power to the board. Looks like there is no power ground for the board. The board connections J and K - what goes to these? Surely it's not +18v to both of these pads? I'm planning on using an external 18v DC power supply and a panel mount boss-type DC connector. There's also a pad 'O' that has no off-board connections marked in the layout. Purpose?

2) Can someone tell me exactly how to hook up the 200K balancing pot in place of R35 and R36. Also, if I installed a 200k trimmer here, surely I can set it and leave it rather than measuring each side and replacing with individual resistors. Seems strange that a trimmer wasn't factored into the layout here if these values need tweaking - can someone explain?

3) The lamp - is this socketed in some way? Most bulbs will have either an eddisson screw type fitting or have an end cap, rather than having bare leads. How is this part best fitted to allow easy replacement?

4) Other than the lamp driver transistor and the bulb, are there other components that are likely to fail, particularly when probing or debugging? I want to make sure I order enough spares of any potentially 'problem' parts to allow for debugging.

5) Heat-sinking: do both 7815 and the lamp driver transistor require heat sinks?

6) 3PDT + LED true bypass switching: this isn't mentioned in the text but is there any reason why this would be a bad idea instead just using the DPDT as shown in the layout? I guess I would have to use a high-power rated resistor for the LED. Can someone recommend what type and value resistor I would need to use in front of the status LED, assuming it is OK to use one in this circuit?

7) In and out jacks - can these be grounded to the chassis or do they need to be isolated?

Finally, is there anything else vital I should know before starting this build that isn't in the notes?

Sorry for the list of questions, but I want to get clear on these things to save grief later. Looks like quite an advanced build and my experience so far only extends to preamps and disto/overdrive boxes.

Thanks,

Andy.

[cheech]

I just built my vibe but am waiting on a trimmer pot myself (used wrong value).  I will try and answer some of them.

1) Ignore pad O you will not use it.  Pad K and J indeed have 14Vac to 20Vac or 18Vdc to 24Vdc going to the pads.  It doesnt matter ac or dc beucase its feeding into a diode bridge that will rectify to dc.  Just make sure that you dont ground and of these to the case.  Just the ring and tip of the plastic connector jack from your power supply to the board K and J.  Make sure none of the electricity touches the chassis.  Even through the plug.  Just stright to J and K.

2) havent gotten there yet myself

3) The bulbs I used are radio shack 1.5v 25ma lamps you can also use 6v 25ma or 12v 25ma from them.  They have wires running from the base of it.  I found out if I cut the wires about where they end that there is still enough lead from the bulb in the resin that they use.  I can just take a soldering iron and melt the remaining resin and am left with 2 leads.  I can take them and solder on cut ends of resistors and just mount like any other component on the circuit board.

4) not that I know of unless you wire things wrong.

5) 7815 has its own built in driver tansistor no

6) Dunno dont like on lights on my pedals

7) The jacks are automaticly grounded on the case through the ring

start with the resistors and work from small to big components.  I found out if using a film canister dont bother with the #66 drill bit.  I just used some 20 gauge buss wire I had.  The cut leads of the resistors will work fine.  After I mounted the film canister by eyeballing it.  I put the resistor leads in a pair of vice grips and stuck it in the holes I wanted.  I didnt force it and when it stopped against the foam and film canister I took my soldering iron and heated the lead up.  It melts like a knife through butter.  They make very clean holes if you let it sit there hot for a few seconds and let it cool there.

Just make sure you got the right parts before you get carried away.  I was tired when ordering and ordered a 500k trimmer pot when it only needed to be 500 ohm.  I blew my bulb and I just changed my driver transistor just beucase .  I think it was still good anyway.

William

[axg20202]

Great stuff. Thanks.

So, K is the +18v and J is the negative from the power supply?

Andy.

[axg20202]

...also, I'm having difficulty finding a lamp bulb supplier in the UK. Anyone know a UK source for this part or, failing that, a non-UK supplier that will ship to UK?

Thanks,

Andy.

[marlin]

Banzai has lamps, i bought mine there, 12v 20mA and it works for me

[Fuzzy-Train]

I'm thinking about making this pedal as well, I was going to post another thread some time next week so I hope you don't mind if I ask the question here.

Could someone clear up the transformer pos neg question? "So, K is the +18v and J is the negative from the power supply?"

Can I just wire K & J to a regular all plastic power jack like the one smallbear offers, and have it go to an 18v power supply like a VS 1spot (but obviously one that's 18v not 9v)? I'm asking because I've seen some gut pics of the Fulltone Deja-vibe2 and it has a transformer mounted inside with a weird plug to power it, but than I saw the one Basicaudio made http://www.diystompboxes.com/smfforum/index.php?topic=54665.msg418360#msg418360 and there is no transformer mounted inside. Is Basic using the same method I mentioned previously?

Thanks in advance.

[rockgardenlove]

Yeah, you can just hook a power jack up to an 18v supply no problem.
The transformer method would only work with an AC input, so that won't help if you're trying to use one adapter for all your pedals.

[Fuzzy-Train]

Awesome. I guess I'll just need to find a 18v power supply.

Can't wait to try this one out myself, looks like a good challenge for a someone with my experience.

[marlin]

No. 2. I used a 220k trimpot instead of R35-36 and put the wiper on one end and the other two lugs on the other end.

[cheech]

In a sense both wires in AC are + and - so it doesnt matter where they go.  Ac is a fluctuating sine wave.  The diode bridge on the board rectifies the AC to DC.  The diodes just take the top part of the sine wave and use it.  Then the electricity is flowing in just 1 direction hence direct current.  That is a half wave rectifier.  Another type of rectifier which I beleive is in this circuit is a full wave.  It takes the bottom part of the wave the 180 to 359 degree cycle in the generator and flips it up to the top and makes it go the right direction. The whole board is DC this is why it doesnt matter if you suppy it DC.  On some amps you have a choke.  The choke even helps more by adding a filler in between the peaks and smoothing out the current flow even more.  The DC in a battery has no sine wave its stright.  Rectified DC has peaks and valleys that is why you need a choke to smooth it out.  This is called pulsating DC.  It still is running at 60hz or whatever your wall voltage is running at.  Well enough of my rabling.  I need to figure out this R35 thing.

http://en.wikipedia.org/wiki/Rectifier

Look at the example of the sine wave.

William

[axg20202]

Thanks Cheech. That makes sense. So these two pads are for "live" and "neutral" AC.

I wonder though, if I was to use an 18V DC wall wart instead, one of the pads would be connected to the +18v (tip) and the other the negative (sleeve). I take it the same applies when using DC i.e. it doesn't matter which way round the two power wires are connected to the board?

Thanks,

Andy.

[axg20202]

Ignore my last post - I should be more observant of people's replies. So, to answer my own question, you can connect either AC or DC to these pads and polarity of the connections makes no difference since the on-board recitifier sorts all this out.

Onto other question before my build. Can I just go with the part values on the latest layout? Seems there is lots of talk in various threads of specific mods for speed, depth etc etc, but nobody actually describes what the changes are! If someone can list out some suggested values and their effects based on the latest layout it would be a great help.

Also, what's with all the various lamp specs used? Layout says 12v, others say 1.5v etc etc.  What is the right one to go for? Does anyone know what voltage is on the board at the point of the lamp? Seems like 1v is too low a rating, but people have had success with this.

Socketing: has anyone successfully used a screw socket for the lamp? Seems that soldering in the lamp is not very serviceable should the lamp blow at some point.

I think I need to work out the physical aspects of the LDR/lamp area when I get to it, but some tips would be great on achieving the best results.

Andy.

[R.G.]

1) How to hook up power to the board. Looks like there is no power ground for the board. The board connections J and K - what goes to these? Surely it's not +18v to both of these pads? I'm planning on using an external 18v DC power supply and a panel mount boss-type DC connector. There's also a pad 'O' that has no off-board connections marked in the layout. Purpose?

I think these were answered for you.

2) Can someone tell me exactly how to hook up the 200K balancing pot in place of R35 and R36.

You hook up the outside lugs where the two resistors don't meet, and the wiper where they do.

Also, if I installed a 200k trimmer here, surely I can set it and leave it rather than measuring each side and replacing with individual resistors.

Yes, you can. Frankly, it's probably better to use a 50K trimmer and make R35 and 36 75K in series with the outer lugs, for reasons you'll find next.

Seems strange that a trimmer wasn't factored into the layout here if these values need tweaking - can someone explain?

Nope. I know why I didn't put one in there - it wasn't in the original Univibe, which this is the exact circuit of. I think one should have been. The reason a trimmer is needed is tolerances. To get good phasing notches, the audio signals at R35 and R36 need to cancel exactly. R35 and 36 are 5% parts, so chances are they won't. Even using 1% parts wouldn't help, because 5% parts are used in the phase splitter at Q3 and in the phasing stages along the signal path. And we don't even need to discuss the variations in caps and transistors, do we? When I did the original Neovibe board back in 1995?96? I got chewed on quite a bit because although the signal path was completely original, I subbed in a 7815 regulator instead of the resistor/cap filters on the original, like that made a sound difference other than better. So I never put one in.

I don't know why the original didn't have them. I do know the originals varied a lot in sound quality, which I ascribe partly to this reason.

3) The lamp - is this socketed in some way? Most bulbs will have either an eddisson screw type fitting or have an end cap, rather than having bare leads.

No, it's not.

How is this part best fitted to allow easy replacement?

Solder it in. Original Univibes run for decades on the same bulb. I've only ever heard of three originals with blown bulbs. Once you get past the "...oops, I killed it while I was tinkering with the circuit.." stage, it'll last a long time.

4) Other than the lamp driver transistor and the bulb, are there other components that are likely to fail, particularly when probing or debugging? I want to make sure I order enough spares of any potentially 'problem' parts to allow for debugging.

That just about covers it.

5) Heat-sinking: do both 7815 and the lamp driver transistor require heat sinks?

Most people don't heat sink either one. If you use a TO-220 device for them, I'd say you don't need to, especially if you use an 18V power supply as you mentioned.

6) 3PDT + LED true bypass switching: this isn't mentioned in the text but is there any reason why this would be a bad idea instead just using the DPDT as shown in the layout?

It's not a bad idea. 3PDT switches cost $25 back when I did the text.

Then there's "originality". The original Univibe did not do true bypass. It didn't do bypass at all, it just cut off the LFO.

I guess I would have to use a high-power rated resistor for the LED. Can someone recommend what type and value resistor I would need to use in front of the status LED, assuming it is OK to use one in this circuit?

15V-2.0V = 13V
For Iled = 5ma, Rled = 13V/5ma = 2600 ohms
using Rled = 2.7k, Pr = 13*13/2700 = 0.06259 = 63mW
Therfore, a 1/4W (240mW) resistor will work fine at 5ma.

7) In and out jacks - can these be grounded to the chassis or do they need to be isolated?

They can be grounded to the chassis.

Can I just go with the part values on the latest layout? Seems there is lots of talk in various threads of specific mods for speed, depth etc etc, but nobody actually describes what the changes are! If someone can list out some suggested values and their effects based on the latest layout it would be a great help.

Just build it with the values on the latest layout. This is a lot like getting married - find out if you like it the way it is before you go changing it.

Also, what's with all the various lamp specs used? Layout says 12v, others say 1.5v etc etc.  What is the right one to go for? Does anyone know what voltage is on the board at the point of the lamp? Seems like 1v is too low a rating, but people have had success with this.

That's because the lamp is driven by a current source, not a voltage source. The driver transistor feeds the lamp only the amount of current it wants to, not a voltage where the lamp can pull all the current it wants. The current rating on the lamp is what matters, but lamps are sold by voltage. Actually, that's an oversimplification. The POWER rating on the lamp is what matters, but DC lamps are sold by voltage, not power like household light bulbs.

Socketing: has anyone successfully used a screw socket for the lamp? Seems that soldering in the lamp is not very serviceable should the lamp blow at some point.

See above. It's not very serviceable. But then they seem to never blow if you ever get them installed right.

I think I need to work out the physical aspects of the LDR/lamp area when I get to it, but some tips would be great on achieving the best results.

Actually, the suggested methods with either the 35mm film can or the soldered-up metal box took about a week of my thought. You're welcome to try to improve on that, but many, many people liked those and have units that have worked for a long, long time that way.

My suggestion - calm down. Build it, get it working. Then make it perfect. The odds are it's not going to be perfect the first shot no matter what you do. Get it running. Learn what it's like. Then make it perfect.

[3/4 North]

I've got my Neo working, but not boxed yet. It's taken a while to put it together during which I've gone through every Neo-Uni post here.

The mods talked about are:

1) unity gain for true bypass - and those resistor changes are 3.9k for R9, 910 ohm for R8 and are listed in the pdf

2) For speed it was suggested changing R49 from 4.7k to 47k (someone also suggested 10k) and R48 to 120 ohm.  There's no reason to change R48 since trimmer 1 controls it.  I put a 50k trimmer in for R49 but switched it out for a 47k resistor.

3) The 200k trimmer in place of R35 & R36. This is easy to do, I put a jumper between the two holes where they connect to N and soldered the middle lug of the trimmer to the center of it.


When I get mine finished I'll post some pictures, but I'm pushing forward with the input buffer and stereo mods, so it may be awhile.

R.G.  The original seems to have had a status lamp (not a LED) any info on that and how it was wired?
I've tried a 6.3 v .15a (the type on Fender amps) but the resistors fry with 24vdc.

Is 24vdc too much? It's listed on the instructions and mine works fine with it (except for the status lamp).
But when I measure the voltage of the effect (from the positive at Q8 to ground) I get 21v not 15.

[axg20202]

Wow! Excellent advice as ever. Thanks!

I'll be etching and populating the board this week, but it'll probably be a while until completion.

Thanks again.

Andy.

[cheech]

Hey RG

I just finished mine and I have stock values in the R35 and R36 area.  Mine vibes great after I adjusted the bias from a faint red to a bright glowing red.  It vibes great except it seems to vibe a little non uniform across the frequency spectrum.  The lows vibe great the highs dont vibe as much.  Will adjusting the R35 and R36 help this?  Is this what you mean by depth?

Thanks
William

[Fuzzy-Train]

It's not a bad idea. 3PDT switches cost $25 back when I did the text.

Then there's "originality". The original Univibe did not do true bypass. It didn't do bypass at all, it just cut off the LFO.

Holy crap!! That's pretty damn expensive.

15V-2.0V = 13V
For Iled = 5ma, Rled = 13V/5ma = 2600 ohms
using Rled = 2.7k, Pr = 13*13/2700 = 0.06259 = 63mW
Therfore, a 1/4W (240mW) resistor will work fine at 5ma.

Pardon my lack of knowledge but.. whaaa LOL

I was planning on using this LED from PPP and this power supply from jameco:
http://pedalpartsplus.com/mm5/merchant.mvc?Screen=PROD&Store_Code=PPP&Product_Code=5001&Category_Code=LO5
https://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&langId=-1&catalogId=10001&productId=100108

What value resistor would I need for the LED? (keep in mind I don't like really bright LED's)

I just want to confirm something: can I just wire the LED from the stomp to the + lug of the DC jack like I would normally do? Also which lugs do J & K go to on this DC jack? http://www.smallbearelec.com/Detail.bok?no=93 I'm just a little confused because of the "DO NOT GROUND EITHER WIRE!!! DO NOT LET POWER JACK TOUCH CHASIS!!!" warnings from the PDF file.

[momo]

This thread will be my bible for my Neovibe build! Thanks to everyone, especially on the mods done after the pdf was done....
Awsome

[Fuzzy-Train]

+1 We have some damn kind, and helpful users on this site... truly a privilege.

I did some searching for the bulb on this site, I think RS stopped selling them and the only good place so far that I've been able to find is banzai. Anyone know of a US or canadian site that sells the proper bulbs?

[KB]

Anyone know of a US or Canadian site that sells the proper bulbs?

Email Steve at Small Bear....

I remember him saying that he has a small stock of bulbs, but they are not listed on the regular stock list.

Kevin.