Neovibe Transistor selection

steelerkid · November 05, 2011, 06:37:12 AM

I put together a Neovibe using all 2N3904's thinking it would fire up but am getting absolutely no response that I can detect from the effect. When bypassed it works, when engaged no sound at all. The bulb doesnt even light up and Im thinking it may be due to me using all 2N3904's?? I read it should work with these so I'm not sure that is the problem. I've rechecked all of my wiring and part placement and think that is fine. I'll take measurements and post them soon but just am curious if the transistors all being the same could be the problem. I've built compressors, OD's, distortions, etc with no problems ever.... This Neovibe is throwing me for a loop though... thought I'd be able to do it based on previous success with simpler builds but Sheesh!! I bought the PCB from GGG and it says to reverse C16 due to a polarity error on the website... so I did. All other polarities are placed as stated on the board. Thanks in advance.

R.G. · November 05, 2011, 10:42:12 AM

Quote from: steelerkid on November 05, 2011, 06:37:12 AM
I put together a Neovibe using all 2N3904's thinking it would fire up but am getting absolutely no response that I can detect from the effect. When bypassed it works, when engaged no sound at all. The bulb doesnt even light up and Im thinking it may be due to me using all 2N3904's??

2N3904s are not the problem, given only that they're all in the correct places and orientation. I've built the Neovibe from all 3904s as well as other transistors. It's modestly immune to transistor type, with only a few exceptions.

What you describe is more like a problem with wiring (wires in wrong places), power supply (no juice = no sound), or soldering (bad joint = no conduction). The bulb not lighting up argues for power supply. If the bulb were the only problem, you'd get sound but no effect.

There's not a lot more that's guessable from the description. Go read and follow "what to do when it doesn't work".

steelerkid · November 05, 2011, 12:18:04 PM

Ok, thanks. I'll do a search for that. I oriented the transistors based on the shape marked on the board.... Im pretty sure they are correct but I will check again. I wired everything according to the layout as well but will recheck everything there also.... again. I've havent had any problems in the past so this one is confusing me.

Thanks.

Jaicen_solo · November 05, 2011, 04:22:43 PM

Mine is made entirely from 2N3904's, and it works perfectly.

steelerkid · November 05, 2011, 06:39:11 PM

Good to know. I'll focus on the power... although not sure what to look for.

steelerkid · November 05, 2011, 07:15:17 PM

I am trying to use an AC/AC adaptor with an input of 120VAC and output of 18VAC 500mA. I bought this from SmallBear as suggested on their site. Do I need to modify anything from the layout and plans to get this power source to work?

R.G. · November 05, 2011, 07:29:44 PM

Quote from: steelerkid on November 05, 2011, 07:15:17 PM
I am trying to use an AC/AC adaptor with an input of 120VAC and output of 18VAC 500mA. I bought this from SmallBear as suggested on their site. Do I need to modify anything from the layout and plans to get this power source to work?

No. It will work fine if properly connected.

But be sure you do not use a power plug/jack that connects one side of the 18Vac to the chassis or to signal ground. Many people have discovered the intolerable hum that this causes. The power supply on the PCB is intended for an isolated (from ground) AC supply, just like the original.

steelerkid · November 05, 2011, 10:53:29 PM

I appreciate the replies. On my power jack I switched the positive lug that was wired and used the other one instead. It fired right up... I thought I could use either lug... guess not? Thanks for sending me in the right direction

R.G. · November 05, 2011, 11:07:23 PM

Quote from: steelerkid on November 05, 2011, 10:53:29 PM
I appreciate the replies. On my power jack I switched the positive lug that was wired and used the other one instead. It fired right up... I thought I could use either lug... guess not? Thanks for sending me in the right direction

Good! It works!

However, do take my advice on the power jack. The AC input wires do not have a positive lug or negative lug. You must make sure that NEITHER side of the incoming AC is connected to the metal box or to signal ground connections. It would be very good if you used a plastic bodied power jack.

If you did, I'm guessing that you had a wire connected to the normally closed battery contact. This wire is opened by a switch inside the jack when a power plug is inserted.

steelerkid · November 06, 2011, 06:45:40 AM

Yes, it works!! I'm thrilled about it too... sounds great! About my jack, it is all plastic but there are 3 "lugs" ... 2 are parallel to one another (I thought they were +) and 1 is perpendicular to the others ( I thought that was -)... not sure why I thought that though...

It's a standard jack 2.1mm DC jack that I have used on all of my other builds... I've seen pictures online where others have used the same jack (at least it appears that way in the pics) so thats what I rolled with. Any issues there? Seems to work fine so far...

R.G. · November 06, 2011, 10:53:30 AM

That solves the mystery. An all plastic jack with 2.1 inner plug and three leads out has two of the three leads connected internally when there is no jack in it. The two that are parallel to each other are the ones that are disconnected from each other when a plug goes in. The idea is that you connect a battery lead to ground and to the third lead. The power coming in connects to the other two. Only two leads go to the circuit to be powered. When you pull the plug out, the battery is connected to one of the circuit leads, and powers the circuit. When you push in the plug, the external power runs through the two leads to the board and the battery is disconnected. With no battery, you just picked the wrong two of three pins on the jack to take to the board, and were getting no power at all.

So, power connected and now it works. Good work.

You need to be aware of a little trap you have laid for yourself. As your mom may have said, don't run with a knife or scissors in your hand.

It works fine, and will continue to do so for that pedal. However, you have introduced to your pedalboard a wall wart with an 18Vac output that has the same plug as your 9Vdc plugs. If (when!) you ever get mixed up and plug your 18Vac plug into a jack that expects 9VDC, it is likely that the 18Vac will kill any pedals that get it, regardless of whether they have polarity protection or not. AC wall warts plugged into 9Vdc jacks with the standard polarity protections will first fry the protection diode, then kill the rest of the pedal when the diode dies. Plug the 18Vac into a daisy chain of 9V pedals, and the weakest one dies first; then the next weakest, then the next, until they're all gone.

You need to set up some way to make as sure as you can that you never plug the wrong plug into the wrong jack. Changing out jacks and plugs to something not fitting the other DC jacks is one way. So is using bright yellow tool handle dipping plastic from a hardware store to coat the 18Vac plug and cord with bright yellow or red so you at least get a visual hint.

steelerkid · November 08, 2011, 05:47:55 AM

Sorry for the late reply... I got hit by a bug Sunday evening and have been laid out since. I think I'll look into getting an adapter and jack that are unique to this pedal only to prevent me from frying my others. I can definately see me in a hurry or distracted and making a mistake. I appreciate the tip and all of your responses. It's a great pedal!! I absolutely love it!!

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Neovibe Transistor selection