Author Topic: Please let me know if you have built this project  (Read 241636 times)

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acorrales

Re: Please let me know if you have built this project
« Reply #420 on: June 04, 2015, 06:47:37 AM »
Hello all,  This is my first post here, but my second booster. It is intended to be used to return unity gain to a passive mixer (2 ch. pot 250k R100k). 

I built a LPB1 that does not work as expected, cause is not boosting the mixer if I use it in the output (mix), and it is killing my strat highs (SSL-5 pup)  if I use it in front in one channel.

I decide to check the V2 of this one and I have it in a breadboard using a 2N2222A that I thing is working OK: it boosts, but  now I'm losing some bottom end when used strat > Mixer Ch1 dry / Mixer ch2 delay 100% wet > booster V2 > amp (the setup is more complex than that, but that's the idea).   Also, I have the bottom end loss if I set up Strat > boost > mixer ch1: Boosted dry signal / ch2: Delay 100% wet > amp. I don't really know if the cut is because the breadboard, as I also have a lot of noise that I still need to track, or if it can be solved by changing the value of some component.

Of course, no amp equalization can fix this, so, Does anybody can recommend a change in the booster, to recover that low frequencies?

duck_arse

Re: Please let me know if you have built this project
« Reply #421 on: June 05, 2015, 06:14:45 AM »
hello and welcome, acorrales. we need voltages! if you go here and follow the rules, then post results, and maybe some photos of what you have built, we'll get you fixxing it.

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0
"It starts with toilets and ends up costing us our Australian way of life" - she who will not be named
>>south-hemi handmaders<<

acorrales

Re: Please let me know if you have built this project
« Reply #422 on: June 06, 2015, 12:46:47 PM »
yups... Sorry!  I found the schematic directly on Google, and haven't saw the rules.  I'm going to read them and report back.

midwayfair

Re: Please let me know if you have built this project
« Reply #423 on: September 15, 2015, 04:33:38 PM »
If you like the NPN boost you might want to try ver2


R5 and R10 are one 5K gain control, 22uf to wiper,  It is drawn this way to sim the 5K control.  The sim steps though the param list and does the math "moving" the wiper, gset as .1 then .25 etc

Input is R8 and R11 node omit C4 and to the left that is a simple guitar sim

Gus (or anyone else who knows) can you explain what C1 is doing?
My band, Midway Fair: www.midwayfair.org. Myself's music and things I make: www.jonpattonmusic.com. DIY pedal demos: www.youtube.com/jonspatton. PCBs of my Bearhug Compressor and Cardinal Harmonic Tremolo are available from http://www.1776Effects.com!

Groovenut

Re: Please let me know if you have built this project
« Reply #424 on: September 22, 2015, 08:59:35 AM »
I could be all wet here (probably) but it looks like C1 is providing positive feedback of higher frequencies, possibly to offset the low input impedance loading on the guitar pickups. The Cornish buffer uses something similar to do the same thing but his has a slightly different config.

My 2cents
You've got to love obsolete technology.....
LPD Custom Effect Pedals*iTunes Music*

midwayfair

Re: Please let me know if you have built this project
« Reply #425 on: September 22, 2015, 09:08:31 AM »
I could be all wet here (probably) but it looks like C1 is providing positive feedback of higher frequencies, possibly to offset the low input impedance loading on the guitar pickups. The Cornish buffer uses something similar to do the same thing but his has a slightly different config.

My 2cents

Ah, makes sense. Is there a benefit to that instead of just, say, having higher input impedance?
My band, Midway Fair: www.midwayfair.org. Myself's music and things I make: www.jonpattonmusic.com. DIY pedal demos: www.youtube.com/jonspatton. PCBs of my Bearhug Compressor and Cardinal Harmonic Tremolo are available from http://www.1776Effects.com!

Groovenut

Re: Please let me know if you have built this project
« Reply #426 on: September 22, 2015, 11:08:47 AM »
The issue with using BJTs as input amplifiers fed by guitars, is they have a low input impedance determined by the Emitter resistor. Even bootstrapping that cap only brings it up to around 300k-500k at best. The bias resistors will always be in parallel with the Emitter resistor as far as input impedance is concerned.

Again I could be wrong here, but that's how I understand it.
You've got to love obsolete technology.....
LPD Custom Effect Pedals*iTunes Music*

midwayfair

Re: Please let me know if you have built this project
« Reply #427 on: September 22, 2015, 02:39:59 PM »
The issue with using BJTs as input amplifiers fed by guitars, is they have a low input impedance determined by the Emitter resistor. Even bootstrapping that cap only brings it up to around 300k-500k at best. The bias resistors will always be in parallel with the Emitter resistor as far as input impedance is concerned.

Again I could be wrong here, but that's how I understand it.

No no, you're definitely right. I just couldn't figure out that it was intentional positive feedback for the purpose of punching up the highs. Clever.
My band, Midway Fair: www.midwayfair.org. Myself's music and things I make: www.jonpattonmusic.com. DIY pedal demos: www.youtube.com/jonspatton. PCBs of my Bearhug Compressor and Cardinal Harmonic Tremolo are available from http://www.1776Effects.com!

Gus

Re: Please let me know if you have built this project
« Reply #428 on: September 23, 2015, 01:43:41 PM »
Bootstrapping is in "The Art of Electronics"
The Vbe drop is fairly constant
The emitter "follows" the base one Vbe drop lower in voltage
So if you have a large cap from base to emitter the emitter drives the three resistors node in phase one Vbe drop apart
The resistor from the node to base has a close to constant voltage across it

for more information
Pages 96 and 97 in the 2nd edition
C1 adjusts the "bottom bump"
the 1st ver had a greater value cap from emitter to the node

Also think about what happens as the wiper moves closer to the emitter
« Last Edit: September 23, 2015, 01:46:39 PM by Gus »