Tried building this circuit, no sound ):

[PointOfGravity]

Hiya, I tried building this twice (the first time I just decided to recycle bits off it) and both times I haven't got any sound off them. Wondering if you could give me any pointers? Here are pictures, ask me if you need more:

[aron]

The first thing is to use a multimeter and just check that your voltage are close to what you see here:
http://www.diystompboxes.com/smfforum/index.php?topic=80734.0

[PointOfGravity]

The first thing is to use a multimeter and just check that your voltage are close to what you see here:
http://www.diystompboxes.com/smfforum/index.php?topic=80734.0

Thanks. My DMM is at the office and I only have an old analog one here, which is a bit hard to see. It's a public holiday tomorrow (Hong Kong) so I won't be able to get it...I'll post back the voltages I'm reading.
 
Seeing as I don't have my DMM though, can you visibly see anything wrong with the circuit?

[aron]

It's hard to see visually. It looks like you didn't use the same layout as shown in the tutorial.

[PointOfGravity]

This is the circuit I'm using. It should pass signal, right? However, I noticed I was getting some weird voltages when I was measuring, and the resistance values didn't quite match the color bands when I measured them. I'll see if changing the resistors work.

[duck_arse]

test the resistance of the 100k connecting to the 47k. if it is actually 1k, it would give very close to the voltage you have marked in pencil.

when you meter across resistors, they will often read lower than they are marked, because they are connected in parallel/series networks with other parts. if the resistor reads (steady) higher than it is marked, you would have cause to worry, but if it reads "some" lower, it is not necessarily bad. a 100k reading 1k tho, is a different matter.

I also think the 100k connected to the output cap and ground should go on the outerside of that cap as drawn.

[PointOfGravity]

I also think the 100k connected to the output cap and ground should go on the outerside of that cap as drawn.

Ah, Interesting, I seem to have wired that up wrong from the schematic provided. Oops.So the 100k should go from the output cap's negative leg to ground, right?

[PointOfGravity]

Alright, I've half sorted it out. It passes signal. Kind of.

Corrections were:

• some cold joints
• resistor to ground from the output cap on the wrong side

So I'm happy that I can hear stuff, but the signal coming from it is tiny. When I probe the input, the signal is huge compared to the output. Also, the ground hum is ridiculously huge.  Is this all just a matter of tweaking components now? it's more like an attenuator rather than a booster, but I am getting some distortion effect which is nice.

Edit: Also, I managed to get a better signal coming through connecting the lugs on the output jack that were exposed (there are two each for tip and sleeve, when I tied the two tip and two sleeve ones I could hear the music.

At the moment, the issues I am having is:

• Really loud ground hum
• Signal getting 'grainy' when I turn the pot
• Signal being attenuated rather than boosted, both at transmitter's emitter and at output cap

[duck_arse]

go round your drawing, and measure all those voltages again, write them on so we can see. this with something plugged into the in jack, but no signal.

[PointOfGravity]

I left the other schematic at the office and between that I added a barrel jack, so I'm getting lots of practise drawing schematics. This time I broke out the ruler.

go round your drawing, and measure all those voltages again, write them on so we can see. this with something plugged into the in jack, but no signal.

I didn't quite understand what you meant by that, but I plugged a 3.5mm to 1/4 Jack adapter into the input without anything plugged in. When I was measuring with a battery attached, I noticed the voltages were dropping slowly, does this eat battery up that much? Anyway, I measured both plugged into the wall and using a battery. With battery is in pencil, wall power (what's the proper name for that?) is in pen.



Edit: oh, and the drawing I did with the pot - is that the right way to wire it up? The wiper being the negative leg of the cap
Double Edit: Oops, forgot to measure the cross junction with wall power. that one's 3.504v. My wall plug is set to 9V DC, it's just showing up as closer to 12V (When I set it to 6V it shows closer to 8V...)

[PointOfGravity]

Right, so I've just found something pretty annoying. Both of the supposedly "10K" resistors were reading 180 Ohms. I think I was reading them the other way round and mistook violet for red (brown black black red brown instead of brown violet black black brown). I do remember the label on the tub saying 10k at the store, though.

I'll update tomorrow, it's half one in the morning here.

[PointOfGravity]

I did it! I switched the 180 Ohm Resistors for 10k resistors and now I can hear my guitar. Here's a video:


Next steps:

• Minimize mains hum using this circuit at the power stage.
• Try different transistors
• Try polyester capacitors for the output capacitor
• Add a 3PDT switch for true bypass

Questions: how does the value of the output capacitor change the signal? I'll think of some more later.

[bluebunny]

I think I was reading them the other way round and mistook violet for red (brown black black red brown instead of brown violet black black brown).

Some of the paints on resistors can be a bit indistinct.  Red/brown/orange/violet often look similar to my eyes.  And orange/yelllow; sometimes blue/green; white/grey.  So if in doubt, measure.

BTW, just to appease my brain (which is hurting right now...), could you draw your schematics with input at the left and output at the right, 9V at the top and ground at the bottom?  The office is not the place to stand on one's head...   

[PointOfGravity]

BTW, just to appease my brain (which is hurting right now...), could you draw your schematics with input at the left and output at the right, 9V at the top and ground at the bottom?  The office is not the place to stand on one's head...   

Here you go!


And yes, it doesn't help that you can't tell if the red paint has faded to violet or not...at least on blue resistors anyway.

[Cozybuilder]

Go back to the schematic in the beginner project, and study how the 5K pot, 47uF cap, and 22uF cap are connected to the emitter.

[PointOfGravity]

Go back to the schematic in the beginner project, and study how the 5K pot, 47uF cap, and 22uF cap are connected to the emitter.

Ah crap, I forgot to draw that line. It goes in between the 5k pot and the 22uF cap.  I know that the 47uF is to make the pot logarithmic, and the pot controls the gain of the transistor by controlling the current at the collector, but what is the use of the 22uF cap?

[duck_arse]

when I said plug something in, you have a switched jack at your input, controlling the circuit power supply. if no jack is plugged, now power flows, Jack is a dull boy. so plug in and power on - BUT - we only really want static DC voltages around the transistor (so we can guess at which resistors are the wrong values), so we don't put any signal input when DC measuring.

the cap across the pot to wiper does not change/affect the taper or value of the pot. the pot actually controls the cap, it varies how much of the emitter resistor (in this case the pot itself [from memory]) is bypassed to ground for AC signal by that cap. this means that the AC gain of the circuit changes, but the DC voltages stay as you've set them.

and if your LED CLR resistor really is 220R, it might explain why your battery is fading so much. bump it up, use 4k7 or more, the higher value saves more battery for longer rocking out.

[PointOfGravity]

when I said plug something in, you have a switched jack at your input, controlling the circuit power supply. if no jack is plugged, now power flows, Jack is a dull boy. so plug in and power on - BUT - we only really want static DC voltages around the transistor (so we can guess at which resistors are the wrong values), so we don't put any signal input when DC measuring.

the cap across the pot to wiper does not change/affect the taper or value of the pot. the pot actually controls the cap, it varies how much of the emitter resistor (in this case the pot itself [from memory]) is bypassed to ground for AC signal by that cap. this means that the AC gain of the circuit changes, but the DC voltages stay as you've set them.

and if your LED CLR resistor really is 220R, it might explain why your battery is fading so much. bump it up, use 4k7 or more, the higher value saves more battery for longer rocking out.

oh right, yea I basically connected the ring to ground then. Anyway, on to your next paragraph -

it varies how much of the emitter resistor (in this case the pot itself [from memory])

Could your memory be validated if we say on the schematic, the emitter's closes resistor is the pot, so that makes it the emitter resistor? I get what you mean by the pot controlling the capacitor, though - signal will go through one leg, the remainder goes through the middle leg into the cap, and out the last leg.

thanks for the tip about the LED, though, I'll stick a bigger resistor on it.

[duck_arse]

ok, I have the original schem here now. all the emitter current (DC) flows through the pot, so yes, it is the emitter resistor (but with a wiper fitted). and the 22uF is the bootstrapping cap, only affecting the AC conditions.

I thought it sounded pretty good, too.



if you want to add DC filtering for supply noise, all you need is a 1k in series with the +9V, fitted between the dirty supply and the "9V" point on the dia, and an electro cap, anywhere from 33uF to 220uF, from where it say "9V" and ground. feed the led and its clr from the dirty side of the resistor, not the clean/audio side.

[PointOfGravity]

ok, I have the original schem here now. all the emitter current (DC) flows through the pot, so yes, it is the emitter resistor (but with a wiper fitted). and the 22uF is the bootstrapping cap, only affecting the AC conditions.

I thought it sounded pretty good, too.



if you want to add DC filtering for supply noise, all you need is a 1k in series with the +9V, fitted between the dirty supply and the "9V" point on the dia, and an electro cap, anywhere from 33uF to 220uF, from where it say "9V" and ground. feed the led and its clr from the dirty side of the resistor, not the clean/audio side.

Okay, I gotcha on the 22uF cap. Only allows AC gain to be changed, right? (Is gain another way of saying current? What I meant by that was does AC Gain in this case mean the difference between two voltages, as in dBV?)



Is this okay?

Also, I went ahead and changed the transistor for one of these. Is that dangerous? Also, my coworker told me to chang ethe output cap for a non polarised polyester cap, is that gonna break the circuit?