Help with muffer circuit

[lukeferg]

Hi guys,

I really didn't want my first post to be asking for help but I am completely stuck. I've decided that after modding a few pedals (a DS-1 (keeley mod), crybaby wah and creating a monster out of my big muff) I thought I'd try to build my own pedal from scratch.
This was harder than I first thought...

I've followed the muffer schematic from here http://www.muzique.com/schem/muff.gif
My battery is measuring just under 9 volts.
I've used all recommended component values and have measured all my resistors about 10 times each.
I've checked my transistor pinout more times than I can count. I'm using a 2N3904 and I've tested and the middle lead is the base. I've also tried turning the transistor around to see if I've got it in backwards but to no avail. I've also tried different transistors of the same type and a couple of different ones with no change.
I've made the circuit about 6 separate times on my breadboard and I can't get this thing to work.
The circuit just makes the sound slightly muffled and a bit quieter. No distortion that I can hear.
I've made an audio probe and have poked around the circuit and it sounds normal until I get past that 470k resistor. Then the volume drops and It never recovers. The audio probe shows that the base pin of the transistor is normal volume (which it should be because it only has to pass through the 1uf cap). The emitter pin is also pretty loud but then this doesn't change when I flip the transistor around but I can't see where this could be compromised because the only other lead connecting to that pin is going through a resistor to ground.
I've also tried getting rid of the 2 diodes and the capacitor as they also suggest on the site to have a clean boost (the idea was to create a pedal with an extra switch on it so I can choose whether I want it dirty or clean.) but this doesn't change anything since I'm not getting any distortion to speak of whether they're in or not.
I'm more than happy to measure voltages for you but I have no idea what I'm looking for or where and how to measure these so if that's going to help then please let me know what to do.

Please help because I am so confused and I don't know where to go next. I'm guessing I'm making some stupid basic mistake but I've checked everything so many times that I'm doing my head in trying to figure out what I haven't checked

Thanks,
Ferg

[lukeferg]

I should probably also mention that none of my caps are polarised. I've tried both those little ones and the bigger plastic ones and it doesn't make a difference.
The thing that's confusing me the most is that no matter which way the transistor is facing the lead that's attached to the 150 resistor is coming out at the original (slightly muffled and slightly quieter) volume. Should this be happening or is my circuit compromised some way? Or does the transistor suck? Like I said, I've tried a few other transistors and they all have the same results.
I should further mention that my volume pot is turned all the way up.

Ferg

[Ronan]

If you could measure and post the voltages across R1, R2, R3 and R4, that would be a good start to give help. Just across each resistor, measure from one end to the other.

[Pyr0]

What exact type of capacitors did you use, they are both supposed to be polarised electrolytic one.
Like these


Maybe if you could post a picture it would help.

[lukeferg]

If you could measure and post the voltages across R1, R2, R3 and R4, that would be a good start to give help. Just across each resistor, measure from one end to the other.

Thanks for the suggestion. I'll do that when I get home today and let you know. Is there a particular voltage drop I should be looking for?

I've just checked what my caps are called and I've tried monolythic and boxed capacitors (I think they're called polyester film). I was under the impression that using non polarised caps wouldn't be a problem. Maybe I'm completely wrong. I'll try to dig up some 1uf electrolytic ones when I get home and give them a go. I'm not sure I've got any though.

They look like this




I should've mentioned that the cap that I'm using as part of the diode loop is polarised. I haven't seen any 10uf non polarised caps anywhere near me.

Thanks for your help,
Ferg

[PRR]

> 150 resistor is coming out at the original (slightly muffled and slightly quieter) volume. Should this be happening

Yes. (80% original level.)

> Is there a particular voltage drop I should be looking for?

That's cheating: asking for right-answers before you start. Measure voltages... there aren't that many. B E and C would be a great start.

Also check that "150". If you are not reading color-codes, 150 and 150K look a lot alike on some meters.

[lukeferg]

> 150 resistor is coming out at the original (slightly muffled and slightly quieter) volume. Should this be happening

Yes. (80% original level.)

> Is there a particular voltage drop I should be looking for?

That's cheating: asking for right-answers before you start. Measure voltages... there aren't that many. B E and C would be a great start.

Also check that "150". If you are not reading color-codes, 150 and 150K look a lot alike on some meters.

I reckon that might be part of it. I'm pretty sure I've put 150k resistors in there. I didn't even notice the lack of a "k" on the schematic.

[lukeferg]

Ok, so I feel like a dick

The 150k resistor instead of 150 was the problem. I didn't have a 150 so I put a 330 in there and it works awesomely. I'll get some 150s and chuck it in coz I reckon I'd like the tiny bit of extra gain that would give me.

Thanks everyone who suggested things, I will hopefully not need to bother you with such stupid questions in the future.

Ferg

[Ronan]

Don't worry, been there done that, will probably do it again too...
10 out of 10 for being honest and straightforward, welcome to the forum!
Just glad to hear (1) you got it going, and (2) you like the sound.

[lukeferg]

Funnily enough I wasn't completely happy with it once I plugged it in to my amp. The muffer side of the circuit was really fuzzy and the clean side was really bassy. So I swapped my diodes for LEDs and I lowered the front capacitor and a couple of resistors to brighten it up a bit. Now it sounds great!

[PRR]

> 150k resistor instead of 150

It is a VERY popular accidental mod. While I said that it is hard to see the "K" on some meters, before convenient meters we liked to confuse the colors: orange and red look the same under fluorescent lights.

And once you got it wrong, it can be VERY hard to see your own mistake.

It is wise to have some "ignorant" person double-check your values and placements. A sharp child. Or a synth-player. My old chum John was no theorist but dogged at finding my screw-ups.

The 150/150K mistake would have been seen in DC checks. The transistor, 10K, and 150 split the battery voltage. What the transistor does not take is split in a 10,000:150 ratio. Normal would be about 4V end-to-end on the 10K, 0.06V across the 150. But with 150_K_ we have a 10,000:150,000 split, almost nothing across the 10K, several volts (instead of a small fraction of a volt) across the 150K.

Another clue for deep pondering: "The emitter pin is also pretty loud..." With the right value, I'd expect a small but noticable drop of volume. The observation suggests the emitter resistor may be larger than specified.

> this doesn't change when I flip the transistor around

Not unexpected. The difference between E and C is small, especially in 9V systems. Often you can swap C and E with little or no change in action.

[LucifersTrip]

a couple quick notes:

1) if you took transistor voltages at the beginning, we would've pinpointed the problem right off. just for your own education, check the transistor voltages (e,b,c) with the 150 and the 150K

2) two 330's in parallel with give you 165, which is easily close enough

[lukeferg]

a couple quick notes:

1) if you took transistor voltages at the beginning, we would've pinpointed the problem right off. just for your own education, check the transistor voltages (e,b,c) with the 150 and the 150K

2) two 330's in parallel with give you 165, which is easily close enough

I will do that thanks, it'll be good to see the difference myself.
I've already put the two 330s in together and it's a small difference but it's what I was after.