Oh Daft...Clean Boost LPB ?

[petemoore]

hOW did start another thread. this was to have been a response to the 'anybody know a clean boost'.
 I just whipped up an LPB.
 I raised the input impedance a tad [100k to 120k and 830k to about 940k, the emitter resistor is a little bigger too], used a 2n5088 and some boxed metal film caps.
 Fairly Pristine, sounds just great.
 My Jfet jobby I was putting in a console, kind of, well it died, and I couln't figure out what it was, did some buggin, decided it was easy enough to build another and dug till a schem popped up for the LPB.
 Took about 20 minutes to wire it up.

[zpyder]

I put together an LPB based on the tonepad schematic, and unfortunately I'm getting distortion.  Don't know why.  The circuit is so simple I've checked it and double checked it, everything seems to be correct.  I didn't have a 43K or a 430K resistor, so I used a series of 2 or three to accomplish proximity values.  Is it possible that these are fing up my bias and giving me distortion??  Other than that everything is per the tonepad schematic.

I'm wanting a clean boost so that I can raise the volume of a microphone signal to use with a guitar-based effect.  shouldn't take much boost, but I want it to be clean.  I'll try out the AMZ Mosfet boost which I've heard is great, but I don't have any Zener diodes that I know of.

Any idea why My LPB is distorting??

thanks!
zpyder

[amz-fx]

I'll try out the AMZ Mosfet boost which I've heard is great, but I don't have any Zener diodes that I know of.

Leave out the zener and try the pedal.  The worst that can happen is that you blow the mosfet...  add the zener later.  Plugging and unplugging is where you might generate a spike that causes problems - minimize the number of pluggings you do until you get the zener in.

regards, Jack

[MartyMart]

I think you could use a "standard" 3mm LED to protect the mosfet also 

MM.

[coffyrock]

my lpb2 is clean to about 1/4 of the way up on the pot, then ceases boosting and begins distorting the amp, which I suspect is by design to some extent. I'm also looking to build the most pristine clean boost I can, but I've heard different things about different circuits... how clean is the AMZ mosfet? Any idea how much db you can boost with it?

[fixr1984]

how clean is the AMZ mosfet? Any idea how much db you can boost with it?

The one I made is very transparent. Even turned way up the sound is affected very little. Louder of course.
How much boost? With the gain all the way down mine boosts...think of turning your amp from 2 to 2.5.
Turn the gain up and it sounds like your amp in on 10 even tho you are still on 2.

[John Lyons]

The amount of distortion is going to depend on the amp. A fender twin reverb or Roland JC120 isn't going to distort at all with with a "clean boost" but a marshall or very slightly distorted amp will go into distortion very easily with even a clean boost.
John

[Meanderthal]

 One clean boost I never see mentioned is Tim Escobedo's CMOS Boost. I built it, and it has an enormous amount of gain, but is incredibly clean. It's also very, very simple. Something worth trying if you have a spare CMOS chip (or even a single CMOS gain stage).

[KerryF]

I built the LPB 2 times on veroboard and neither ever worked.  I built it on breadboard and it worked perfectly.  Seems that this pedal causes a lot of confusion 

Kerry

[Gus]

The NPN is a standard book circuit like the LPB but with input bootstrapping setup for min gain of about X2, 10K/5K.  It also has the operating points "designed in" for Ic so most npn transistors can drop in even Ges.

I am not a fan of the LPB because of the input Z


Now a few have noted the 10K at the input and questioned it.  I believe it was RG that posted 100K should be better.  I left it at 10 K because it seemed to have lower noise and still sounded OK. 

The NPN goes from clean to mild dist.  It does this in a different way than some other boosters that go from clean to dist. 

It is a taste thing.

[Ronsonic]

my lpb2 is clean to about 1/4 of the way up on the pot, then ceases boosting and begins distorting the amp, which I suspect is by design to some extent. I'm also looking to build the most pristine clean boost I can, but I've heard different things about different circuits... how clean is the AMZ mosfet? Any idea how much db you can boost with it?

I haven't tried the AMZ boost, but it looks as if it should be truly clean.

All these simple one transistor circuits really have not chance of being truly clean. At the very least their low Zin loads the guitar making it murky and then when you drive it the thing starts trying to draw base current and the pickup turns to mud.

To me the simplest thing would be a 5532 use the noninverting input of the first stage and get your gain there, then use the other half strapped as a buffer. Wanna get fancy you can use a quad version then add a bypassable inverting buffer stage to restore absolute phase.

This will give all the clean headroom and gain you can get from the power supply.

Ron

[newbie builder]

I used a 1K instead of 390ohm resistor and that made my LPB much cleaner.

[coffyrock]

I used a 1K instead of 390ohm resistor and that made my LPB much cleaner.

I'll do some resistor tinkering, methinks!