Different Transistor for LPB-1 Booster

[doitle]

I was looking at building the LPB-1 Booster as my next pedal as it seems very simplistic and I thought it might be fun to really drive that valvecaster I built with a booster. Looking through my stock of parts though, I have a few NPN general purpose transistors but I don't have the 2N5088 that the schematic calls for. Has anyone here ever built it with a different transistor or maybe have some thoughts on the design as it pertains to the electrical characteristics of the transistor chosen? I notice that the 2n5088 has an absurd max hfe of 900 vs the theoretical max of 300 for a 2n2222. In short, any ideas or things I should be investigating to figure out what I could maybe replace it with?

Or maybe I should just bread board it and start throwing transistors in until it sounds good?

[THOMMO]

I'm using a 2N3904 in my BB of this circuit because I couldn't find any 5088's.

After about 9o'clock it starts to head into drive territory.

I also tried a S8050. It sounded very similar to 2N3904.

Jason.

[Renegadrian]

Mike, a suggestion I wrote time ago in the main Valvy topic...
I think it's good to drive it harder with a booster before it, but my personal choice wouldn't be the LPB.
The Valvy is not so brilliant, it's a little on the dark side, and the LPB is known for boing a little darkish too...
I tried them togheter and didn't like the result at all...
While I had a really good sound with the Tillman.

My

[doitle]

Hmm...

http://www.till.com/articles/GuitarPreamp/

Is that what you meant by the Tillman?

Maybe instead of switching transistors for the LPB or building this Tillman I should go back through the valvecaster thread and design my own booster with a submini tube... : ) Tubes are so cool I can't wait to do something else with them.

[petemoore]

  Once the circuit is correct, and medium gain or high gain or low gain transistor.
  2n5088, 2n3904, BCxxx's etc. any Si bipolar transistor'll fire it up, low gain of course..you know what that means, gain isn't everything though...
  LPB Is one fine booster !
  Jfet anything or whatever is one fine booster, they're all a touch or two different.
  Tubes are fun to play around with, but tend to be a bit more expensive and time consuming.
 

[Renegadrian]

Hmm...

http://www.till.com/articles/GuitarPreamp/

Is that what you meant by the Tillman?

Maybe instead of switching transistors for the LPB or building this Tillman I should go back through the valvecaster thread and design my own booster with a submini tube... : ) Tubes are so cool I can't wait to do something else with them.

Yes, that's the Tillman! (I used this layout HERE and it works so good, even better with a 2n5457)

I second the submini tube booster you want to try...I'd suggest you a submini pentode (they also are cheaper, for what I've seen...) or a single triode...If you go pentode, it shouldn't be difficult for you to find some circuits already verified as a starting point...Like I did...

[Gus]

The text book circuit design of the LPB limits the gain to about X23 so hfe does not matter as much.

[Ben N]

Gus's NPN boost has a flatter response than the LPB, so you could try that if you want to use a BJT. Any medium to high gain should work. I tried both a 2N3904 and a MPSA18 in my NPN boost and I really couldn't hear any difference, even though on paper the MPSA18 has a higher hfe.

[doitle]

I couldn't pass up tryign to breadboard the LPB-1 as it was just so dirt simple... So I thought... I've been troubleshooting this thing for about an hour and a half. No matter what I do, the guitar signal will pass through with no power. IE the 9V Adaptor is not plugged in, I can still hear guitar signal getting to my amp. It seems to be almost traveling through the ground or something... I have pulled everything connecting the input side to the output side save the ground and I still hear it. Add to this when I plug in the 9V Adaptor the amp loudly pops and goes AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA super loud. So I can't even get voltages because I am afraid something is majorly hooked up wrong and I'm afraid to leave it plugged in for a second. I've been over the schematic many times and cannot seem to figure out where the problem is. The only major changes I made were switching .1uF caps to .01uF because I didn't have .1s, using a 2n3904/2n2222/Others Transistors and instead of having a volume pot I just added a 100K Resistor to ground to simulate the pot cranked. Does anyone have any suggestions of things I could try to troubleshoot this thing?

Here's a picture of the Breadboard annotated:



I was following the schematic found here: http://www.beavisaudio.com/techpages/SchematicToReality/

[Solidhex]

Don't worry about it

  I'd say plug it all in and see if it works. If it doesn't, then you'll know if you've done something wrong. Its such a simple circuit troubleshooting won't be hard. Most of the time with a simple booster like that if its not working and I don't know why I just pull everything out and start over.

--Brad

[doitle]

I did plug it in and it makes that insanely loud noise from the amp even with the volume on 1. I'm worried about damaging the amp more than the circuit. I suppose I could just disconnect the output jack and plug it in and take some voltages... That might be helpful for troubleshooting eh? Maybe I'll do that tomorrow... it's 5AM and I'm still up :/

[jonfoote]

youve got no volume pot so you're getting full output straight to the amp! that 100k resistor isnt working like you think it is.
put another 100k in series with it, with the output lead in the middle so the volume is effectively at 50%, should help (like with the 1M and 100k)

[earthtonesaudio]

First, get some sleep.  Come back tomorrow, after breakfast and a cup of coffee, with fresh eyes and a clear head.

After that, begin debugging.  Verify all the parts are what you think they are (check datasheet to verify transistor pinout, make sure you're reading the color codes on the resistors correctly, etc), if all checks out good, then apply power.  Check with a meter to be sure that Ground is at 0V, and the positive power line is at +9V.

Next, check to be sure the guitar shield is at and signal wires go to the right places.  Same goes for the amp shield/signal wires.

Now hook up the amp.  Still bad?  Turn the amp off, check voltages, and report back.

[doitle]

I just plugged it in without it outputting to the amp. Rails at 9.01V, Base is at .6V and the Collector is at 7.12V. Emitter is at .073. That's pretty much perfect in regards to my simulation which has them at 9, .603, 7.32, and .068 respectively...

EDIT: Bit of an update, decided to disconnect the 9V adapter and use a 9V battery. Now the AAAAAAAAAAAAAAAAAAAA sound is gone and it seems to be partially working but instead of a nice clean boost I'm getting the fart pedal from hell: http://doitle.markdelano.com/stuff/earrape.mp3

Maybe the transistor is dead from all the messing about before? I will try to hunt down another 2N3904 from my box...

Oh also EDIT EDIT: () I checked the battery and it is showing a voltage of 9.01 Volts so it's not just a dead battery causing this, it's something more sinister...

[newfish]

My meagre experience of this sort of thing would be to check your biasing.

Do you have a schematic you're working from?

Hopefully, I'll get time to build something very similar to this on my BB tonight - and will let you know what I get, if that helps...

[newfish]

OK, so...

Breadboarded this quickly using components as close as I could get to yours (12K and 330R on the Transistor).

I used 1uF input and output caps as I need to order more small caps.

Either way, mine worked first time - so I tried to break it to get mine to sound like your MP3 sample (very helpful by the way).

Swapped the Transistor round, for starters - with the obvious lack of sound, so it's not that.
Swapped the 1M and 100K bias network over (100K from +ve, 1M to ground), and this gave a crappy tone - but not like yours!

I put the Bias network back the way it should be (1M *then* 100K) and took each resistor out in turn.

With the 1M missing, there was no sound.

1M went back in place, and I removed the 100K.

Bingo!  Mine sounded exactly like your MP3.

I repeated the 100K in / out test with a different Transistor and got exactly the same results - same crappy tone.

Transistors I used were a 2N2222A and a BC107.

*either* there's a break somewhere inside your BB, or you've missed a hole (easy to do - happens all the time) when putting your 100K in place.  Or it's simply not a 100K resistor.  Check you've got the correct value in there, then check your jumper wires to ground.

Really hope this helps you - I've just discovered what a handy little boost this is.

Cheers,

Ian.

[earthtonesaudio]

Awesome, Ian.

[doitle]

Ian if you've still got it breadboarded any chance you could take some voltages? Maybe just the three pins of the transistor. I have millionuple checked that resistor. It is most certainly 100K and is connected properly and I've moved it all over the bread board. I was really excited to see your post but sadly it doesn't seem to have correlated to my build. One of the most peculiar effects I am noticing with this thing is the volume swings wildly to the point where I can really hit the strings hard and no sound comes out and other times I barely tap the string and it blasts a note out. Hopefully comparing voltages will tell more about what to try next...

[doitle]

Got it fixed... -_- the battery was dead. I measured it again just now... 4.4V... I decided to plug back in the 9V Adapter I was using before and sure enough AAAAAAAAAAAAAAAAAAAAAAAAAA... Then I thought I should just filter it and put a 330uF cap between the rails. There's a little hum but it works. At least It hink. I don't really know what a boost like this is supposed to sound like through a terrible SS amp but it is certainly much louder. Thanks for helping me try to troubleshoot it everybody. Now I wonder if I could put this thing on protoboard or if I'd flub that up... I'd like to make this a permanent effect if I can tweak the sound a bit more or get a better amp to boost .

http://doitle.markdelano.com/stuff/lpbworking.mp3

Wowzers this thing sounds awesome with 4.7uF input and output caps. Soooo meaty. My room mate came over and played his bass through it and it sounded cool too.

http://doitle.markdelano.com/stuff/lpbbass.mp3

Note the bass was tuned to C-Standard so it's pretty durn low. This is the same amp that the previous clip was through.

Also strangely enough, playing an electric acoustic through this same exact setup makes it very trebly. This is a clip of my room mate's acoustic electric guitar through the same exact setup as that bass clip.

http://doitle.markdelano.com/stuff/lpbacoustic.mp3

[newfish]

Fantastic news!

Glad you got it working. 

My voltages are very similar to yours (c is 4.68v) - I measured them this morning when I got up.

For reference, they are...

(2N2222A - Battery at 9.29 volts.  C = 4.68v, B = 0.67v, E = 0.10v).

Larger input / output caps will give you much more 'booty' to your tone, as will a couple of other tricks.

I'd recommend trying a FET-based booster next if you have any - they sound great.