Beginner Project Voltages

[aron]

Thanks to Mike Parker (GibsonGM)

[micwatson]

hey aaron!

first of all, thanks for everything! this is really great!

i am new to electronics. how do i measure the voltages above? black end of the multimeter to ground, red end to the according solder point?

thanks a lot!

-michael

[Fortunado]

Voltage is a property of two points and thus can only be measured across two points. Depending on which component or where you want to measure the voltage, you will have to place the two ends of the multimeter accordingly. The red probe is the positive probe and so will be connected to the "source" of current and the black probe is the negative so it'll be connected to wherever the current flows to. Atleast, this is what I've surmised from various readings and knowledge of physics. I'm a novice myself, so I'm not sure if this helps, but good luck!

[phector2004]

black one to ground (if you've boxed this, an easy way to do it is to just stick the probe into a jack, assuming you've done the wiring right  )

red one touches the lead you wanna test

you'll wanna set your multimeter relatively low (20V should be fine) otherwise you'll be getting inaccurate readings

[roundman3gz]

I'm a super noob so forgive me if this sounds stupid.  I measured the voltages like the instruction manual for my meter said but they are all coming out negative.  Have I reversed something in the wiring that would cause this?  Thanks in advance for the help.

[.Mike]

You might have the red and black leads swapped on your meter.

Grab a 9-volt battery. Put the red lead on the + and put the black lead on the -.

If you get a negative value, the leads are in the wrong holes in your multimeter.

Switch. Try again.

Mike

[roundman3gz]

I don't have hole's for the leads for the type of multimeter I have.  The leads are soldered into the back of the meter.  They voltage is correct when I put the leads (red = +  |  black = -) on a 9v battery. Maybe I have the battery snap connections backwards?

[roundman3gz]

I fixed it!    Had the battery snap connections backwards.  Thanks for the help.

[borman09]

Nice circuit.But i don't understand when the input capacitor works.

[JebemMajke]

One noobish question, what if i put a transistor which has 1 as a hfe value?

[mistahead]

Nice circuit.But i don't understand when the input capacitor works.

Now I'm sure someone will correct me if I'm wrong... still learning a lot myself but this was one of the earlier things I think I understood.

The input cap works as a high-pass filter - that is it basically blocks signals at the lower end of the frequency range from crossing into the circuit. If my dodgy memory is serving correctly the larger the value the more mid/low/sublow is allowed through - the lower the value the more is blocked. To that end (assuming memory again) if you take a trebble booster with a 0.05 input cap and double that up to 0.10 input cap you can also boost some mids... a common trick with the Rangemaster circuit is to put a switch that allows just that.

[blackcorvo]

One noobish question, what if i put a transistor which has 1 as a hfe value?

I think you measured the HFE with the wrong pinout.
a low-gain transistor (like... let's say, a power transistor) usually shows a minimun HFE of 25. If it shows anything below that, your transistor is either damaged or you've put the leads in the worng position when you were measuring it.

usually, you get small HFE values when Collector and Emitter are swapped.
There's even an arcticle on AMZ about using a transistor connected backwards (collector in place of emitter and vice-versa) to make a booster/buffer, or a distortion stage (maybe being pushed by an op-amp... could be interesting!).

What transistor is it? If it's a BC546 - BC549, the pinout might be different from the standard. I once got one of these that had the collector and the base swapped! Check it in all positions you can, till you get a correct reading.

[gnort_2]

Do I need to have the switch and input jacks wired to test voltage?

Can I test voltage on just the circuitboard with the battery wired up?

[bluebunny]

Can I test voltage on just the circuitboard with the battery wired up?

Yep.

[mountianjustice]

Ok so i've got around 12vdc coming in from a 9vdc wall wart   and after the first 100k resistor I have 8.9vdc should i just add another 100k resistor in series with the first ? Seems right to me the first one would take my 12vdc down to 8.9vdc and the second would give me my 6.8vdc right ? Or do i even need to worry the trans is rated to 20v and it sounds great should i just leave it alone ?

[blackcorvo]

Here's a little tip for people who like to play with cap values:
If you change the input cap (.1uF) for a 4.7nF, you get a very Brian May-ish Treble Booster!
If you think it sounds too harsh, you may also want to add a 100pF-250pF cap between Base and Collector on the transistor. Higher value = less harsh.
Personally, I like it without.