Distortion / Clipping in an LPB1

[chromesphere]

Hi all,
I built an smd version of the lpb1 for some smd practice.  it works as it should but ive noticed it clips the more i increase the input signal. Bridge pick up, slightly,  neck pick up more so.

I used the smd substitute for the transistor: an BC849C as recommended in another thread.  Would the transistor be too high gain or not compatible with the circuit, or is it normal to have some very slight clipping?

As a bonus question, these came from tayda, looking at the chip it actually has 2Cp50 on top of it.  Another SMD transistor i bought from them also has a totally different code on top of it.  Is this usually how smd works?

Thanks for you help!
Paul

[radio]

Depends on your pickups too, normally bridge PUs are hotter so

nothing unusual so far, but are you using activ pickups??

[chromesphere]

Yeah, like i said, increase the input into the effect -> more clipping.  Hotter pickups -> more clipping as well.   They arent active pickups though. 

So its NORMAL for this effect to have some clipping / distortion?

Paul

[radio]

Mine is not clean at max volume,however I used an 2N5088 and no SMD.

[amz-fx]

The LPB is running at full gain all of the time, and the volume control is on the output, padding down the always-boosted-signal.

When the input is sufficiently large, the transistor is not able to produce a clean output because of the limitations of the power supply voltage.

Let's say the input is 1v pk-pk when you pluck the guitar string...  if the gain of the LPB is 20x, then the output before the volume pot should be 20v, but that is not possible when powered by a 9v battery, and the output is clipped when the transistor swings to its limits.

Two possible solutions; turn down the guitar's volume control, or power the booster with 18v so there will be more undistorted headroom.

regards, Jack

[radio]

Nothing to add to Jack Ormans comment than the schematic for reference:

http://www.beavisaudio.com/techpages/HIW/HIW.png

[alparent]

Is it  possible to change te gain factor or limite the input?

[chromesphere]

Awesome!  Thanks for the explaination jack makes perfect sense!

Alparent, i have some lower gain transistors that i might try and see how that affects the output.  I assume lower gain will equal less distortion...?  Worth a go anyway.  Also, a resistor on the input might pull back the input signal to help reduce clipping but of course the output boost will be lower....might experiment with that as well.

Cheers
Paul

[Resynthesis]

No expert here, but couldn't you also tinker with the emitter resistor to modify the gain?

[RandomGlitch]

No expert here, but couldn't you also tinker with the emitter resistor to modify the gain?

Yes that works, its what I've done when I've used the LPB-1 as a make-up gain stage in pedals I've built and needed to tame the boost a bit.

In my application I used 1.5 or 2k with good results.

[chromesphere]

No expert here, but couldn't you also tinker with the emitter resistor to modify the gain?

Yes that works, its what I've done when I've used the LPB-1 as a make-up gain stage in pedals I've built and needed to tame the boost a bit.

In my application I used 1.5 or 2k with good results.

Thanks guys i will give it a try!!
Paul

[Perrow]

Are you using my layout? This one?

[chromesphere]

Hey Perrow,

Nah, i'm using my own layout.  I've checked it over a few times, it should be working.  I did borrow your suggestion on the transistor though

Paul

[Perrow]

As long as the pinout is correct the layout I posted should be good to go. It's almost possible to "see" the schematic in that layout.

[chromesphere]

The thing works as it should, its just got a bit of a clip when using a hotter pick up.  Ill probably try a different value emitter resistor or the other transistors I have that are lower gain.

Paul