Author Topic: Newbie Questions  (Read 325 times)

cabphoto

Newbie Questions
« on: March 17, 2018, 07:02:19 PM »
Sorry in advance beginner here.

I have some questions maybe someone can start me in the right direction finding a resource that may cover all this or just be helpful answering what they know.

Just building my first simple fuzz face germanium circuit.

1.  Any reason to stay away from germanium transistors found on ebay?

2.  Instead of a 9volt battery can I use a DC input wired to the same place on a basic fuzz face kit type circuit board

3.  I think it would be cool to use a jewel lamp like light used on amps but not the led ones.  I believe they are 6.7v or something like that.   
     Most basic circuits for fuzz face i've seen (though i have not seen much) come with a small led.  Can I just replace that with the 6.7v
     jewel lamp or need something special to
     accomodate the lamp?

Hopefully none of these questions are annoying for some reason unknown by me. 

Thanks for your help

astrovic

Re: Newbie Questions
« Reply #1 on: March 17, 2018, 08:14:10 PM »
Welcome to the world of doing it yourself  :D

To answer your questions:

1. No real reason.  Broadly speaking, you'll get what you pay for, and they don't look especially cheap.  If you want to remove doubt as a newbie, maybe go to Small Bear as they are a guitar pedal diy specialist and they sell pairs of germanium transistors - http://www.smallbear-electronics.mybigcommerce.com/fuzz-faces-and-similar/  Not the cheapest but will be the good stuff.

Now don't forget that the transistors used in Fuzz Faces come in PNP and NPN variants.  You can use either - generally speaking, most germanium transistors are PNP.  In a fuzz face circuit, a PNP transistor requires negative polarity (whereas most other pedals run on postive polarity).  That means you wire up your power supply backwards, so that the + terminal of your battery/power supply goes to ground instead of the -ve terminal.  Kinda like this example:



(Note that wiring diagram also shows your typical "true bypass" method of wiring a stomp switch, if that is what you're interested in).

There is a way to connect a positive polarity power supply to a negative polarity pedal like a PNP Fuzz Face - you need to use a voltage inverter, which is a simple little circuit - here's an example designed using veroboard:

http://tagboardeffects.blogspot.com.au/2012/05/negative-voltage-inverter.html

If you want to keep it simple, and just flex your diy muscles you might want to go a silicon NPN fuzz face first up.  The parts are cheaper (2N3904 and 2N5088 silicon transistors cost about 1 cent each) and the power supply is positive polarity, so there's a lot less to worry about and if it doesn't work or you ruin some parts it won't have cost you much.  If it's winner you can always move to a germanium PNP version (cos who doesn't need 2 fuzz faces, amirite?)

2. You definitely can - in fact the picture I posted above shows how you can wire up a battery and a switched dc socket at the same time.  Basically, the dc socket has a switch in it - when you don't have a dc jack inserted, 2 of the poles are linked.  So you can connect the battery to one pole and the other to the PCB.  The current flows through the battery to one pole, straight to the other pole and then t the PCB.  When you insert the dc jack, this breaks the link (effectively disconnecting the battery), but instead you get the current from the dc jack.

That picture also shows how you can use a stereo input socket to operate as a power on/off switch...but I'll let you figure that one out  8)

You can always simply not connect up a battery at all if you want.  In that case, you don't need to use a switched dc jack - a simply dc jack like this one will do nicely:



https://www.taydaelectronics.com/hardware/dc-power/dc-power-jack-2-1mm-round-type-panel-mount-1.html

3. Sure!  I think most people use little LED's because of their small size, making it easier to squeeze a pedal into the smallest case possible.  But things like this are completely up to you.  As a general rule I would recommend to newbies that they just build something straight "off the shelf", just to build knowledge and confidence before starting to get creative.  But hey why not?

So...Those jewel lamps are almost always 6.3 volts (why 6.3 volts?  Because that's what the heaters of many vacuum tubes run on, and in tube amplifiers, the lamps are usually powered from the same supply as the heaters).  Given your input power supply in a pedal will by 9volts DC, you need to drop that voltage down to the 6.3volts DC the lamp runs on.  You do this using a resistor.

You'll see from the diagram above how there is a 3.3K resistor attached to one leg of the LED?  That resistor is dropping down the 9volts DC to the LED's voltage.  The size of the resistor depends on the specs of the lamp we're using - LED's tend to run on lower voltages than 6.3V lamps, so they need a greater voltage drop (and therefore a bigger resistor).

What size resistor do you need?  Well you can figure it out 2 ways.  One is to use maths, the other the "suck it and see" approach.

Using maths, you need to know Ohm's Law.  Very simple.  V = I x R.  Voltage = current x resistance.  Or to flip it around, R = V / I.  Resistance = voltage divided by current.

Here, we want to find out the resistance need to drop the voltage by 2.7 volts (9v minus 6.3v).  We need to know the current.  That will depend on the lamp you use, but the first google result I found was for a jewel lamp with a current of 0.15 amps.  That'll do for now.

So...R = (9-2.7) / 0.15, or R = 2.7 / 0.15 = 18 ohms.  So an 18 ohm resistor.  You don't need to be exact here - the nearest value (like 15 or 20) will do.

The other way is to suck it and see.  This is my preferred approach, because I can figure out exactly how bright I want my LED to be.

I grab a 9V battery and a battery clip, 3 alligator clips, a 5K or 10K potentiometer and my lamp.  I then put the potentiometer in about the middle of its travel, and connect all that up as follows:

+ve terminal of battery ... alligator clip...potentiometer lug 3 ... then potentiometer lug 2 ... alligator clip ... positive leg of lamp...then negative leg of lamp ...alligator clip ... -ve terminal of battery.

If you have it right, the led should light up to some degree of brightness.  You can then turn the pot until you get the brightness that works for you.  My favorite are the bright blue led's, which when you turn them up too far go a piercing white colour  :D

(Basically the, potentiometer is a variable resistor.  As you turn the pot, you change the amount of resistance which in turn changes the voltage drop.  The greater the voltage drop, the less bright your led gets and vice versa).

To translate that to a fixed resistor - ensuring not to disturb the position of the pot, you remove the alligator clips and then use a multimeter set to measure  the resistance between lugs 2 and 3 of your pot.  That number is the size of the resistor you need (or the nearest available value).

You'll note from the application of ohm's law above that you don't need much resistance to provide a 2.7v drop to a 6.3v/0.15A lamp.  Only 18 ohms.  So trying to use a 5K or 10k pot like I described won't work very well - that approach works best for standard led's where the voltage drop need is higher so a resistor in the thousands of ohms is required.  However it is a fun approach to play around with.

In fact, when mucking around in my workshop while writing this up, I found that using a 15 ohm resistor on a 6.3v lamp that I had made it a little dull.  I actually found that giving the lamp the straight 9 volts from the battery looked the right amount of brightness.  That's fine, if that works.  Of course, the brighter the lamp the quicker it will die, but we're talking about lamps that are designed for thousands of hours of use.

I hope that helps, and I didn't bore you too much!

ElectricDruid

Re: Newbie Questions
« Reply #2 on: March 17, 2018, 08:30:03 PM »
1.  Any reason to stay away from germanium transistors found on ebay?

Only the cost and potential for sub-standard parts. There are good and bad germanium transistors, and you don't always know which you're buying.

Quote
2.  Instead of a 9volt battery can I use a DC input wired to the same place on a basic fuzz face kit type circuit board

Yes, absolutely. No problem with that.

Quote
3.  I think it would be cool to use a jewel lamp like light used on amps but not the led ones.  I believe they are 6.7v or something like that.   
     Most basic circuits for fuzz face i've seen (though i have not seen much) come with a small led.  Can I just replace that with the 6.7v
     jewel lamp or need something special to
     accomodate the lamp?

Why not just accommodate the LED in the correct jewel housing and ignore the awkward original bulb? I mean, who uses incandescent bulbs these days?! So "last century", right? Just put a LED in the jewel housing and no-one will ever know!

I've done this with "Amber" LEDs with extremely good results. Probably doesn't work so well with some crazy "ultraviolet" or "deep blue" that never existed in the days of jewel lamps...you choose, I guess.:)

HTH,
Tom

smallbearelec

Re: Newbie Questions
« Reply #3 on: March 17, 2018, 11:04:15 PM »
Sorry in advance beginner here.

No apologies necessary!
1.  Any reason to stay away from germanium transistors found on ebay?

If you buy unsorted devices from anywhere (including my store), you have to be prepared to test them for gain and leakage. There are methods for doing this at GEOFEX and in my DIY files:

http://www.geofex.com/Article_Folders/ffselect.htm
http://diy.smallbearelec.com/HowTos/FuzzFaceFAQ/FFFAQ.htm

A matched pair will be much more expensive, but then you have a guarantee that someone hs audited the parts and tweaked the bias.

2.  Instead of a 9volt battery can I use a DC input wired to the same place on a basic fuzz face kit type circuit board

Nothing to stop you from powering with a wall wart. However, be aware that cheap, consumer wall warts are neither regulated nor well-filtered. Power with one of those and you will wonder why you get an awful hum. There are models that are designed for powering high-gain audio gear, but they cost more:

http://www.smallbear-electronics.mybigcommerce.com/morley-wall-transformer-9v-dc-300-ma-regulated/

It's possible to add filtering and regulation to a consumer wall-wart, and might be the way to go if you want to use that incandesant lamp in the amplifier jewel, but that's a mod that's beyond the scope of this response. See further.

3.  I think it would be cool to use a jewel lamp like light used on amps but not the led ones.

If you do use an incandesant, it would not be possible to power the pedal with a battery because of the current draw of the lamp. Get the effect circuit working before you think about adding this. I like the Druid's suggestion of replacing the lamp with a high-brightness LED; then all you need is a small series resistor and you can choose to power from a battery if you wish.

My first recommendation to all first-time builders of the FF: Build using silicon, and on a breadboard! You 'll learn to set up and tweak performance. Once you have learned to use the tool, germanium devices can be swapped in with relatively few changes. The parts can be re-used when you commit to solder. This kit of mine:

http://www.smallbear-electronics.mybigcommerce.com/breadboarding-the-fuzz-face/

is pretty popular.

Welcome to the Forum, and to my Cave.
« Last Edit: March 17, 2018, 11:12:51 PM by smallbearelec »

cabphoto

Re: Newbie Questions
« Reply #4 on: March 18, 2018, 01:55:46 AM »
This was all awesome info from everyone.  Thank you so much.  I'm sure I will be checking back in with you guys.  Thank you for all the time you put in replying and helping the new guy.

I think I can hear the difference between silicon and Germanium and that Germanium is the sound that gets me going. If it's a bit more challenging that's ok I wired up a guitar for my first guitar so I was thinking a pedal would be the next step.  I love to solder anyhow

I also like the old school lamp Idea.  I come from the world of photography and LED lights are destroying famous city scape's around the world.  I'm a light nerd sort of.

I bought a cheapish on sale wall wart at guitar center ,it was justt lose in a bin, to power a nice reverb pedal recently and the pedal hums like crazy. It's def not the single coils .  One of you mentioned that in your reply so now I'm thinking its the wall wart not the pedal. 
 

thermionix

Re: Newbie Questions
« Reply #5 on: March 18, 2018, 04:23:19 AM »
The 6.3v lamps in (Fender) tube amps are known as #47 bulbs.  They draw considerably more current than an LED, not necessarily a problem if your power supply is up to it, but many people like batteries in Fuzz Faces and an incandescent bulb would be impractical with a battery, something to think about.  Also the fixtures are quite large, some take up more space than a battery.  One thing you can do is get a pilot jewel like an amp has but run an LED inside, without the bulky fixture.  Once the light is diffused by the jewel you probably can't tell the difference.
FDH