Low output on mosfet booster. Base lower then emmiter.

[demonstar]

Hi, I've built my mosfet booster and It's kinda working but not properly. The signal when the switch is activated is lower than when it's bypassed. It's nabout a fifth of the bypassed signal. I've measured the pins of the transistor. They are...

collector=4.67
base=3.86
emmiter=4.25

Is that good or bad. I've got a feeling it's not meant to be like that.

I did use a 4.7uF cap at the beggining of the circuit as opposed to the 10uF cap on the scematic as the man in the shop gave me the wrong one. I didn't think it would matter. should it matter?

I'm using the tonepad schematic and this is only my second project and first with transistors so sorry for my lack of knowledge.

[Mark Hammer]

I guess we're still on the left hand side of the learning curve.  It is a MOSFet booster, not a bipolar booster, so that's a MOSFet transistor in there (jeez I hope so!) no a bipolar.  The MOSFet has a drain, gate and source, not an emitter, base and collector.  Naturally, that is going to make your measurements a little hard to interpret.

Perhaps of more concern is the possibility that the pins might not be going to the right places.  Have you verified the pinout with a datasheet for your transistor?  My datasheets indicate a drain -> gate -> source pinout (pins pointing down, looking at the flat side of the tranny) for a Motorola BS170, and the opposite (source -> gate -> drain) for a Philips BS170.  It is quite possible that everything else about your build is spot on except for the transistor pinout.  Happens a lot.

Welcome to the wide world of "How many freakin' FET pinouts ARE there?".  Best to score a datasheet for whatever semiconductors you plan on using before you start a build, just to verify that everything is exactly where you think it ought to be.  Op-amps are often less of a problem, but there are more pinouts and pin orientations under heaven and earth for transistors than you can imagine.

[demonstar]

Ahhh... hmm maybe that could be a problem. I did try swapping it around in a few different orientations lol. I'll check about the orientation and which pins which. It's a 2n7000 in a little black case with one flat side and it's got  n7000 69 FD written on it.

Where did you guys learn all this stuff. Is there somewhere with some good reading. I'm off to wiki now to try and check my pin out.

[petemoore]

  The Data sheet on the transistor used is best source for pinout information...first place to try checking at least.

[GibsonGM]

Search google for data sheets....try "BS170 data sheet" for example.  You'll get tons of links...one of them will lead you to a data sheet for free, usually an Adobe .PDF.  I save mine in a special folder for future use...

[Mark Hammer]

I generally just enter the part number and "pdf".  Don't know if its better or worse but it works for me.

The datasheet for a Fairchild 2N7000 shows the pins as source -> gate -> drain, left to right, pins pointing down, looking at the flat side.  you will note that it is opposite to the orientation/pinout of the BS170 made by the very same company.

[demonstar]

I can't guarantee my pinout of my transistor but I guess it's the right way round because I'm getting some sound through.

Could it be the cap I changed at the start thats causing me problems?

I find it odd that I'm getting a little bit of sound through but not all of it.

[Mark Hammer]

It is actually a very frequent occurrence that you get sound with misinstalled components and sometimes even dead components.  There's too many paths for the signal to follow.

As for a bit of sound coming through when the pinout is wrong, hands up everyone here who has had that happen to them!

[demonstar]

Ok I think I need to go and have a think. I think I've found a place where theres a 5v drop across a cap just before the output resulting in next to no output. So i'm gona' check conncetions around that area. The text that explains the schematic says that shouldn't happen. I'm taking shots in the dark at the moment. a nights sleep mite help the situation.

[GibsonGM]

Have you taken a look at the "what to do when it doesn't work" and debugging threads?
Lots of handy info in there that will get you going in no time. 

Just stick with it - patience is an invaluable aid in this hobby!  As for where everyone got the little bits of knowledge that we're passing on to you - just experience, my friend!  We've all been in the 'what do I do now?' position, and others pointed us in the right direction.   Some stubbornness helps, too!

May I suggest throwing together an audio probe? That will help you find areas where things went wrong and will focus your attention where it should be. 

That 5v drop COULD be DC, which will be blocked by the output (last) cap and look like a major voltage drop for no reason...try reading it on AC....or, you might have friend the MOSFET if you tried it in backwards.

I get (DC) 5.5V on gate, 5.42 on drain and 3.58 on source, with a BS170.
Keep trying )

[demonstar]

Thanks and I have read the texts you mentioned. I checked and It was a DC drop across that cap so I guess thats meant to happen.

I'm almost definite now that I've got the pinout right on the 2n7000 T092 style case transistor I've got.

The DC voltages at the pins are....

S=4.67
G=3.86
D=4.25

I measured the input of the guitar jack and when it's bypassed the full signall off the guitar input flows through. Put when I engage the effect the input at the input jack drops by about one fifth. I don't see why this should happen. Despite this the full one fifth of the signal is getting through the board. So whats going in is whats comming out but when engaged the full signal isn't going in.

Whats going on there. Is something in the circuit dragging the input voltage down when it's engaged?

I'm very suspicious of that cap thats meant to be 10uF electrolytic and I used 4.7uF electrolytic.

I know I'm a pain but thatnks for all the help.

HOPEFULLY ONE DAY I'LL BE ABLE TO HELP OTHERS LIKE YOUR HELPPING ME!

[GibsonGM]

Umm, demonstar, it sounds like a possible problem in the switching - if you have signal going to the fet when it's bypassed, and none when it's engaged, that's the clue!   The actual voltage you can measure may vary due to impedance changes, however...the best way to know is to build an audio probe - have a friend strum your guitar or use a CD player, and listen in at the gate, and output.  You should have NO signal at gate but signal at the input jack when disengaged, and hear it at the jack and gate when engaged.

Check your switch wiring if that seems buggy....and, 99.9999999% of the time, 10uF and 4.7uF will be interchangeable (at c3?) as long as the polarity is correct. You're not filtering audio with them, so the exact value isn't critical. 
You're using the 9V zener, right? Is it oriented correctly?
Gotta check, check, and double check...then it will become second nature!  )

[demonstar]

What I said before was a little confused. it was my fault it was the way I worded it.

The DC voltages are the same at the pins whether the effect is engaged or bypassed. Should I be measuring these in AC?

Yes, I am using a 9v1 zener and the cathode is at the gate.

i will double check the wiring.

I do have one cap that isn't too ground. It's just going to nothing but thats the optional 47pF cap to eliminate radio interferance so I'm not worrying about that.

I shall go and check the switching. But I think there is no signal going to the board when bypassed but when the effect is on it is going in but a very low level signal. Lower than when bypassed. That whole low signal is getting through the circuit.

Is that any clearer? Sorry.

I'm just going round and making notes of all resistances and voltages both AC and DC when effect is on and off to try and find fault.

[dmk]

strangely enough, the 2n7000's i get from maplins have the same pinout as bs170's, NOT reversed.
its a funny old world

[demonstar]

thats the 2n7000 i've got. The maplin one. what did you say the pinout is please?

[demonstar]

OMG if what dmk says is true which i assume it is my trasnsistor was in the wrong way round. If i now put it in the right way if I short out the gate and the drain with a wire it works. The pot has no effect but I get sound. I guess that means the signal is getting to the fet but i don't get it why it only does it when i short it out or turn it up mega loud.

What could be the main reasons for a low signal getting to the gate?

I'm going to get another cap to increase the capacitance in the input buffer stage so that it's the 10uF the schematic says. I believe this thats why it's not working after reading this about caps in potential dividers...

"http://www.answers.com/topic/voltage-divider-rule"

So by altering the 10uF to 4.7uF i could have altered the refference voltage meaning theres a low signal which is not great enough for the gate. Am I getting carried away here or could that be right?

I'm gona' try it anyway! 

[GibsonGM]

The 10uF cap is not an input buffer...it's a power supply filter.  It helps 'smooth' out the power, giving it 'clean' power during spikes (like when you slam the guitar hard, or use a less than perfect adapter).  Don't worry about the filter factor for that cap...you are dealing with DC there, freq=zero!  ;o)  Let's keep it simple.

#1.  Make SURE the pinout is correct for your MOSFET.  If you had it in backwards, you might have killed it, so try a new one if you have it!  If the pinout is not right, nothing else will ever make this work. I suspect that if you have ANY signal going to output at all.  That means things are connected enough to pass a signal, lol.   When you solder a new one in or play with the old one, hold it with really small pliers or a heatsink when soldering, and work quickly.  They are static and heat sensitive!  Hold above the PC board and work below. This channels the heat into the pliers and not the FET.

#2.  Audio Probe!  Read the thread "Debugging"...and use a cap with it, or you will send DC to your amp.  Any cap, .1 to 10 uF should be fine.  You should have the same guitar signal at the input jack as at the gate with the effect engaged.   That clears you up to the gate of the fet.  When you switch it off, you should have signal at the input and output jack but NOT at the input cap or FET. If you do, the switch is wired wrong.  You'll need an audio probe down the road, so chuck the meter for a minute and make one, very simple )

#3.  If it still is crappy, review your work on the power supply resistors (or do that first, before playing with the FET; I would).  Check grounds. You should have [roughly]  half the battery voltage at the drain.   If you do, that end is OK.   Make sure all resistors are the right values! Re-read the color bands.  If they are out, you will get a weird/weak signal. 

#4.  Check out your pot connections and bypass cap.  Be sure it is wired correctly.  Make sure you have the 2.7 in para with the cap/pot.

#5. At this point, your audio probe should give you output at the drain, both before AND after the .1 output cap, C4.   That cap is filtering and blocking DC from your output is all.

If this process doesn't work, I don't know what will!!  ;o) 
I'll be around this evening and see what you come up with - keep at it, you'll get it!

[demonstar]

Thankyou

I'VE GOT IT WORKING!!!!!

I've been silly again. When I went round recording all the voltages at every point in the circuit I noticed that the input cap had a resistance of 0.01 ohms. I figured that wasn't right it also had no DC drop across it. when I looked it was shorted out underneath. I hadn't broke the track on the stripboard as it was an alteration to the design I'd made on-the-fly.

I figured the 10uF wouldn't make a difference when I sat and looked at some maths. I realised because it was a DC voltage going in theres no frequency so it's as if it isn't there. The only reason I could think it's there for is to get rid of any AC that sneaks through the DC input from the AC to DC jack.

I calculated things like what Vout should be from the potential divider and realised It was correct to two decimal places so I figured that was all O.K. That was when I found the cap error.

Anyway now I'm sorted and it's all working. I've just got to case it etc. and put the optional 47pF cap to ground to stop radio interference.

The millennium bypass LED isn't working at the moment so I'm going to check for short circuits around there, check the switching again and check the transistor pinout etc. I believe I can probably sort this problem myself. I may have just fried the transistor when I kept altering it's orientation.

Well, THANKYOU SO MUCH to everyone thats helped me! I've just got to finish this one off next then decide on the next project. I think I may go for something like the green ringer or maybe something less electronics based and maybe a little more woodwork like the Ruby. I really don't know yet. I just want to learn some more. Maybe a little reading on transistors may be a good idea 

Stuff I've learnt....

1.CHECK PINOUTS
2.BE SURE TO DOUBLE CHECK THE LAYOUT BEFORE STARTING
3.DOUBLE CHECK EVERYTHING INFACT.
4.MEASURE AC AND DC VOLTAGES NOT JUST DC
5.CHECK PARTS BEFORE YOU INSTALL THEM. EG. RESISTORS MEASURE WHAT THEY SHOULD
6.ALL THINGS GO TO GROUND THAT SHOULD
7.CALCULATE VALUES THEN CHECK THEY ACTUALLY ARE AT THAT VALUE EG. Vout
8.A GOOD NIGHTS SLEEP BRINGS A MORE WIDE VIEW AND YOU SPOT THINGS YOU DIDN'T BEFORE
9.A MOSFET ISN'T THE SAME AS YOUR STANDARD TRANSISTOR. EG NOT A COLLECTOR, BASE, EMITTER, IT HAS A GATE SOURE AND DRAIN
10.IMPEADANCES ALTER WITH FREQUENCY

Theres more but thats the main stuff i think.

And while I'm on... OTHER USEFUL THINGS I'VE LEARNT LATELY...

GERANIUMS COME FROM GARDEN CENTRES NOT ELECTRONICS STORES
GERMANIUM TRANSISTORS COME FROM ELECTRONIC STORES.

[GibsonGM]

Hey, good work, Demonstar. You did it, not us.  Add another to your list:
11.  BUILD AN AUDIO PROBE    )

Voltages are useful for like 5 minutes on a debug...they 'are' or 'aren't'.  There's no substitute for hearing the thing in action.  Continuity testing, too.

Enjoy the booster, and happy next build!  Now you'll be addicted!

~Mike

[demonstar]

Thanks this is my second build and I was addicted after the first.