NPN Boost Circuit Help (From Wampler Book)

[SpringbokUK]

Hi guys

I've been reading one of Brian Wamplers books on building pedals, the advanced one to be exact. Anyways there's a little circuit in there using a 2n5089. So I breadboard it and nothing. I have a resistor and cap going to ground from the emitter, 9v with a trim pot for biasing going to collector, output cap coming off the collector and and input cap for the base. I thought maybe the manufacturer had it so the pinout was different, so I swap it round and nothing. I then try a 2n5088 with the "correct" orientation and nothing, I flip it and I get sound.. so the collector is doing what the emitter should be doing. At this point I think i burst a blood vessel out of sheer confusion and I checked the data sheet from the supplier to confirm what I'm actually seeing here. I try the 2n5089 again and now it's just splattering no matter where the trim pot is.

I also googled other npn boost circuits and people seem to be connecting the base to 9v so I tried that too and still nothing.

Can someone clear this up? I know I'm probably just missing something ridiculously obvious.

Nice one
Liam

[PRR]

Where's the base resistor(s) ??

There's gotta be base resistor(s).

Show/link that plan you think you are building, or pick another plan we can all see.

[aron]

Is this one like the NPN boost in the beginner project?

[pinkjimiphoton]

Where's the base resistor(s) ??

There's gotta be base resistor(s).

Show/link that plan you think you are building, or pick another plan we can all see.

not so fast, Paul,
it was YOU who taught me that one of my stupid little circuits would work better shorting the e to ground...

you don't need a b resistor necessarily. technically, if ya just use an input cap, an output cap, a pot at c to + and a bypassed e resistor or direct connection, IF you can reach the proper bias point with the trimmer or pot, it SHOULD fire. ge is easier to deal with for this than si, cuzza the leakage.

early fuzzes often had no biasing or voltage dividers feeding b. thats why they usually sounded gated, crappy, and were completley unpredictable.

i'd be concerned about 9v going to base directly... may have popped the q's cloggs doing that.

can you post us a screen shot of the project?
if ya don't know how, on windblowz, its usually ctrl + prt sc
then open any pic file, click edit, paste and then save as whatev and post.

it will be easier to help you if we know what we're talking about. brian's books have been out of print for a while, other than thru FSB, so we need your help to help you.

do you have a multimeter yet? if so, get us voltages. put the black lead to the - on your battery/power supply and read us the voltages ya get at e, b a nd c. yes, sometimes pinouts can be weird.

if its not firing, i'm suspecting a bad transistor, or a too-small biasing pot for the gain range of the q's ya got.

welcome to the forum, btw!!

[SpringbokUK]

Hey there!

Yeah I did put in a 1m to ground at B but nothing happened still.

I'm not sure whether it is from the beginners book but I'll attach the schematic anyways

The voltage readings are 0 on C and B and 6.22 on E. That's with a 500k trim pot at full resistance. This is the same for the 2n5089 and 88. I'm using a 1k and a 22uf on the E. Going to ground as shown in the schematic.

From the image I plucked out the book it shows the Q schematic correct but the actual transistor picture to the left shows it in reverse... I think.

Thanks for your replies!! And the welcoming! I've actually been on here a good few years but just inactive haha. Shy I guess.

[SpringbokUK]

Also I hope I did the image thing correctly. Clicked on "Add image to post" It took me to a postimage website? uploaded it from there...

I hope Brian is OK with that to haha.

[mac]

Yeah I did put in a 1m to ground at B but nothing happened still.

You could call this "input cap biasing"

With high gain Si or darlington, the guitar signal charging the input cap can turn the base on a bit, but I doubt it will do some boosting or sound.
But with a high voltage distortion before this circuit, who knows

Put that 1M from Vcc to B, or from C to B.

If you have a germ transistor, this circuit will work.

mac

[antonis]

Yeah I did put in a 1m to ground at B but nothing happened still.

A very disapointing behavior for a n-chanel JFET..
(but very healthy behavior of a n-p-n BJT..) )

Your transistor needs an about 650mV voltage difference between Base & Emitter (V_BE where V_B>V_E)
(the opposite stands for p-n-p BJTs..)

Your transistor (in a working conditon) has its Emitter "some" volts above ground..
(there is a voltage drop across Emitter resistor due to Emitter current flowing through it..)

Connecting a resistor from Base to ground does nothing to "elevate" Base voltage above 0V.. !
(due to absence of current flowing through it - actually, there IS some current through it comming from signal source but it's AC - meaning you MIGHT have "some" bias but ONLY for positive halfwave cycle AND ONLY for signal voltage greater than V_E +V_BE AND^2 ONLY for signal source with low enough impedance - capable to feed the current for Base-GND resistor to elevate Base voltage up to desired level and simultaneously feed Base with current for desired amplification.. )
The above might be an excellent super-heavy fuzz but only in case of signal with high enough Voltage & Current and for a less than halfwave period..

IMHO, your circuit might work but only for bi-polar supply (+/- 4.5V say..) with C3 grounded (as it is..)

P.S.
I'd propose to connect a BIG resistor between Collector & Base, set TRIM pot somewhere around middle setting and see what happens then..
(for a clean boost that feedback resistor should be in 10M range..)

edit: Marcelo is faster..
(I'll agree for 1M feedback resistor only in case of very low h_FE transistor..)

[antonis]

Didn't see the following: 

The voltage readings are 0 on C and B and 6.22 on E.

Are you sure you didn't mismatch pin-out on voltage readings..??

[SpringbokUK]

Ah okay

I'll be completely honest my theory is terrible with this stuff. I've struggled with theory for years haha. But from what I can gather from what you're saying, the base voltage needs to be higher than the emitter voltage for it to work? Or just 650mv measured between B and E?

Would r1 be the feedback resistor or would that be the resistor from C to B?

And would I be right in thinking there are things missing from this schematic? Like the resistor between C and B?

Didn't see the following: 

The voltage readings are 0 on C and B and 6.22 on E.

Are you sure you didn't mismatch pin-out on voltage readings..??

Sorry yeah I meant to say B and E are 0 and C is 6.22..

[antonis]

the base voltage needs to be higher than the emitter voltage for it to work? Or just 650mv measured between B and E?

Let's incorporate them in a single phrase:
>the base voltage needs to be 650mv higher than the emitter voltage for it to work<

Would r1 be the feedback resistor or would that be the resistor from C to B?
And would I be right in thinking there are things missing from this schematic? Like the resistor between C and B?

Resistor from C to B IS the feedback resistor..(not R1)
And yes, it's missing..

[pinkjimiphoton]

ok, looking at the circuit, it should fire just the way its drawn.
i've built about 100 of these things, its a simple fairly clean booster.
works better with ge.

but the 6.22 volts to e tells us instantly the power supply hookup is backwards.

you should have 4.5- 6 volts to C, not e.

a small bypassed r at e to ground is fine. keep it under about 1k, and the paralleled cap under 47u

i think you hosed your transistor. it may be fine, but if its not passing signal, thats most likely your problem, there
simply isn't anything else in the circuit to fail, really..

try any freekin transistor you got. make the bias pot about 50k. it should quack immediately.

flip that q 180 degrees, it may fire then as a slightly less than unity buffer when ya get the bias EXACTLy right.

the bigger the pot, the more range, but the higher to dial in. i'd put a 3.3k-4.7k ish resistor between the bias pot and c, and use no more than a 50k pot. 10k would likely be fine. you may be overshooting the bias point as well.

but my money is on the transistor's cloggs being popped.

simple way to see if its the transistor or the rest, just run a jumper from b to c. if it suddenly passes some signal, the transistor is hosed.

if it doesn't,  the next bet would be you switched + and - connections.

literally, all ya should need is a directly grounded e, an input cap to b, a bias to + voltage and an output cap hangin off c to get it to work. won't DO much, like that, but it should pass signal.

check your wiring. i'm betting its reversed to your power supply, AND the transistor is dead.

[SpringbokUK]

but the 6.22 volts to e tells us instantly the power supply hookup is backwards.

Yeah that was my mistake. I just typed it out wrong as I meant to say I had 6.22 at C not E.
I put a 560k resistor between B and C and now I have a boosted signal.
Could it still be goosed?

[pinkjimiphoton]

not if you have signal, but 560k between e and ground is gonna seriously limit the gain and boost of the circuit. try 470r, 1k, 100r even.. anything between about 16 r and 5 k will do to get it running. try a 1k resistor and a 10-47uf cap in parallel, from e to ground. that should get ya where you wanna be.

[SpringbokUK]

I have the 560k between B and C. Without that it doesn't work. I tried a j201 without the 560k and it was fine but 2n5089 doesn't work without it.

I have 1k and 22uf to ground from E

[pinkjimiphoton]

sounds like ya got it sorted! good for you man!

try a diode instead of that 560k resistor. anything. led, 400x, 914, 4148, batxx whatever ya got. try it both directions.
you may find it works better with the b-c resistor, or ya may not need it.

glad you got it workin.

keep doing it. before ya know it, you'll be designing fuzzes that sound slightly different from the other fuzzes you create.

[SpringbokUK]

Thanks man

I got it at a fuzz/od at the minute. Sounds great!

Just gotta see where I can take it now.
This book is helping but there's a few things that confuse me like how he keeps the signal clean at low gain by adding a cap to the gain pot. To me it looks like it would do the opposite because as you bring the gain down you're taking the cap to ground and that's a LPF, right? And the way he has HPFs is a resistor and cap in parallel as opposed to a cap in series and resistor to ground. I'm sure it works the same way but this is all for a whole new thread entirely haha!

I'm sure y'all will soon recognise me as the guy that questions EVERYTHING.

Take it easy.
Liam

[pinkjimiphoton]

liam,
think of bass = distortion. the more bass ya let in, the more it will overdrive and distort.
so a bass cut.. basically, a cap in parallel with a variable resistance, will let you control not only the amount of distortion, but its contour and what frequency it will be centered at.

a hi cut is a variable resistance into a cap to ground, and will change the signal by shunting high frequencies to ground.

if you add a cap to a pot, you can make it so that as you turn it up or down it will "bleed" the signal thru. smaller caps bleed treble, bigger caps bleed mids, but too big and it turns to shite.

so if ya have a volume control before the overdrive, by adding a low pass filter from wiper to ground, it will seem to get muddier, where as if its between wiper and input, as you turn down, it will get brighter, up to whatever point you set with the cap value.

so you can kinda compensate for variations in volume. way back in the day, a lot of times pots would have taps so you could build bass boost circuits... basically low pass filters, that increased the bass as you turned the volume down to keep it full.

the wampler books are cool, but don't stop there. some of the stuff isn't really well laid out and can be confusing.
brian is re-writing them last i heard a couple years ago, and updating them. he's a gem of a guy, if ya ever need to contact him.

the more ya @#$% around, the more you'll learn. rock on, bro

[SpringbokUK]

That makes a lot more sense.

There was a distortion circuit in his book and it had a cap between lug 1 and 2 of gain and lug 1 was going to ground but he said that it would give a cleaner tone as you bring the gain down. Surely that wouldn't though? But yeah maybe I should get in touch with him. I imagine he's super busy though.

[pinkjimiphoton]

well, i am sure he's busy, but he has a LOT of peeps building for him.
but no, you are right.

remember, a parallel variable resistance with a cap makes a hi pass filter. so by doing that as you described, as you turn it, you cut the lows, which makes for a cleaner signal with less distortion.

its exactly as easy as it sounds and looks