Neovibe prebuild questions

[smallbearelec]

You couldn't find those lamps till now because they just came off the boat last week. I will offer a companion socket for the one with the screw base as soon as I get the samples I have ordered and make sure the base and socket match.

NB: Aharon Colman was good enough to test samples for me and assure me that they worked.

Regards
SD

[alderbody]

Damn nice build! Is that a BB with the 2' walls?
Just wondering.... did you use a printer for the UNI-VIBE logo decal? If so, could you PM me the image... I'm planning on using that logo but I just can't find one.

Sorry for the delayed reply. Somehow i was dis-joined from this thread.

first of all thanks for your kind words.

The box is the one that's mentioned in the project file (i guess...) can't really tell if it's 2" high,
but i surely remember that it's the "shorter" one.

This decal, as all my decals, is laser-printed on a adhesive transparency.

For the font, just used the one called "signature".
It's "dead-on", except for the dash between "uni" and "vibe", which has to be custom made.

[axg20202]

Well, as the OP, I thought I'd keep this thread alive :-)

I now have the last few components (thanks Steve at Smallbear! You're a star) to complete my neovibe build and will be doing so tonight. I might wait until tomorrow but I've got a burning desire to finish it as soon as possible. Unfortunately, I was forced to get a few parts from the gypsys at Maplin. Hopefully my next post will be to share my experience of a successful build and not a debug post LOL.

Being bold and jumping the gun, I'm already thinking about how my enclosure will be laid out and, in particular, how I can use LEDs on it. If the circuit works and I'm in electric ladyland, I've already decided to have two stomp switches - one for effect/bypass and another for Vibe/Chorus - with an LED for each. I've also considered using a foxy bi-colour LED for the vibe/chorus status. Anyway, I'm drifting off topic. I'll post back on how the circuit works out first, but if anyone has any more tips on this that would be cool.

Andy.

PS. Alderbody - would be good to know which 'signature' font you used - there has got to be thousands of fonts called that. Is it a standard font in some piece of software you have - which one?

[3/4 North]

The font is very common, usually called brush script.

Here is a pic of my board with mods on a daughter board.  The input buffer #1 and the stereo mixer.  I'm waiting for parts when it's finished I'll post some clips, but it sounds just like the clips in the stereo vibe thread.

[axg20202]

Cool. Got it, thanks.

[alderbody]

Alderbody - would be good to know which 'signature' font you used - there has got to be thousands of fonts called that. Is it a standard font in some piece of software you have - which one?

i only have one in my pc and it's the one needed...

since i'm not on that machine right now, i can't give more info.

later...

[marlin]

The "brush script" font nails it There are a zillion fonts called terminal. 

[axg20202]

Thanks. I might use it for my enclosure...I'm thinking about having a go at etching it. 

Meanwhile, I have completed the build of the neovibe and........it doesn't work....boohoo! I've started a new debug thread for it with readings etc...I would really appreciate some help with it. I took great care over the build (knowing the problems people have with neovibes) so it has to be something quite simple....(


Thanks,

Andy.

[albatross]

I see in the parts list 5% resistors, can i just use 1% metal film all round?

is the 5% for originality purposes, or there for a good reason?

I am just about to populate and im in doubt as to use metal film, which would most likely mean less noise too

So is it wise to use 1% all round?

[R.G.]

Metal film is fine, 1% is fine.

At one time, metal film resistors were 10 to 50 times as expensive as 10%, then 5% resistors. Today they are only marginally more expensive. This is one of the wonders of modern automated production of parts.

When there was that much cost difference, engineers were taught to use the lowest-precision part possible. There is a branch of circuit analysis called "sensitivity analysis" which looks at how circuit parameters vary with part value. The idea is to design circuits with the least sensitivity to part tolerance or part value drift that is possible.

Originality is not really why 5% is specified. It was a matter of economy, and the fact that 5% is good enough.

[albatross]

Thank you very much for the very informative reply

I just wondered as all my 5% resistors need sorting, when all my metal film are sorted in bags and somewhere someone stated 1% would be wise to use on the lfo part.

Thanks, hopefully wont be back here on the debug thread later or tommorow;)

[axg20202]

Here's how it turned out, if anyone's interested. Sorry for the poor photo.

http://picasaweb.google.com/ipitythecrazyfool/UntitledAlbum/photo#5047090078423473778

[3/4 North]

Too late for me to edit my previous post, but the 24vdc transformer I listed from Mouser doesn't work - it'll work for a while but the 7815 regulator eventually goes up in smoke.

I'm going to order the Peavey.

[albatross]

hi,

I think you have the regulator the wrong way round, thats what happened to me until i found the correct way.. I burnt 3 out untill I swapped one round, it would work for a whilethen get to hot, then smoke.

I bought mine from bardwells, and they are non standard to look at.
measure with aDMM after, you will see.

[3/4 North]

Could be it.  I thought I followed the instructions but the readings from the DMM were always high.

btw - you can see it in the photo I posted above - is that backwards?

[axg20202]

If the black square body of the 7815 is facing us in the photo, I think it could well be in the wrong way round.....

[3/4 North]

DOH!! That explains alot - guess I better order a new one

[momo]

First of all, a great thank you to Mr R.G, I did get the torrodial transfo from digi key # 62921 and that fits great!, now the only thing is im geting 26 volts Ac from the serial secondaries. So how do I bring it down to 20 Vac max, as requiered for the neovibe?
Sorry everyone for the newbie question...im pretty close to trying my build, im waiting for the double ganged pot and figuring this survoltage issue. thanks !

[R.G.]

First of all, a great thank you to Mr R.G, I did get the torrodial transfo from digi key # 62921 and that fits great!, now the only thing is im geting 26 volts Ac from the serial secondaries. So how do I bring it down to 20 Vac max, as requiered for the neovibe?
Sorry everyone for the newbie question...im pretty close to trying my build, im waiting for the double ganged pot and figuring this survoltage issue. thanks !

You load it.

First, I think you mean the TE62021, not the 62921, a typing error. I couldn't find a 62921. I checked the datasheet on the 62021 and it says that the open circuit voltage is 12.4V. You'd see over 24V open circuit.

However, it drops to 18V under 278ma of loading. What I'm about to do is not strictly correct, but it's an approximation that is a useful way to think of things. We can compute an equivalent "resistance" of the transformer. It's 24.8Vac with no load and 18V with 278ma, then it acts like there is a resistance of (24.8-18)/0.278 = 24.4 ohms inside the transformer. This crude approximation will let us do some estimating.

What you're going to do is to full wave rectify this voltage and filter it, then power the unit. The process of full wave rectification makes the DC that comes out of the filter cap look like an RMS current from the transformer of about 1.8 times the DC current. So the 278ma from the transformer looks like 278/1.8 = 154ma. This tells us that the transformer will sag to about an 18Vac output at 154ma of DC from its secondaries.

At no load, the rectified DC is 24.8*1.414 = 35+ volts. But we lose 1.4V in the diodes, giving a peak voltage of about 34Vdc.
At full load of 278ma RMS AC or 154ma rectified DC, the DC voltage becomes (18*1.414) - 1.4 = 25.052Vdc. We know the rectified DC will be no less than 25Vdc and no more than about 35Vdc. That's a little high but not disastrously so.

I would say that you can do one of four things.
1. Ignore it. Put in 50V filter caps and use 35 or more volt caps in the LFO and it will probably work fine, mostly.
2. Load it down. Put a load resistor of about 470 ohms/2W on the secondaries of the transformer. This will pull the voltage down.
3. X it out with an amplified Zener. Use an NPN transistor plus a resistor and 1/2W zener between the rectifiers and the first filter cap. If you want to do this, I'll generate a schematic for you.
4. Only use half the transformer secondaries. If you open one secondary and only use a single one, not two in series, you'll see about 12Vac, which rectifies to 16.98Vdc, and this is so close that the 15V regulator will probably be fine. 

My apologies - I even know that small transformers have horrible regulation, but I was a bit surprised to see that this one has a 45% drop in voltage from no load to full load. That's amazing. But it can be made to work fine.

[momo]

R.G, you are awsome, there should be laws for people like you!, you should be paid a fee everytime you generously fork out years of experience to us newbies! That being said, I have no Idea what the he%% your talking about , almost!
Ill print that out and use it as a mantra!! LoL But seriously thanks alot, Ill digest that before I move on.I think i will load down because I used 16 volt 10uf caps instead of 25 volts which I did not have.
Cheers!