Projects => Beginner Project => Topic started by: JasonG on July 04, 2007, 11:25:43 PM

Title: Ok how many db's does this thing boost. I have looked I cant find it. Sorry
Post by: JasonG on July 04, 2007, 11:25:43 PM
I thought I read a post a few days ago that mentioned how much this thing boosed the signal. I cant find it now. Does anyone know ?
Thank you !
Title: Re: Ok how many db's does this thing boost. I have looked I cant find it. Sorry
Post by: Gus on July 05, 2007, 06:59:20 PM
That is kind of a hard thing to answer. It is only running at 9V.  How clean a signal?  And to me it was not important it was more how it sounded or how the distortion happened with gain and input level

I wanted to build something a little different using a min amout of parts and running at 9V.  I wanted  no bias adjustment needed,  That left BJTs.  Then I wanted a somewhat variable input resistance that was high enought for a guitar when at min gain that is were the bootstrap part is from.  I only wanted to use one transistor and the parts could be found with out to much work (at the time this was made radio shack still had parts in the store and had most of the parts to build this)

At min gain (about X2) and hard to tell that the circuit is on sometimes,  now the problem is there is only 9V for the power supply when the gain is turned up the circuit runs out of "headroom" also you have the different output levels from the guitar.

Now the circuit is not clean at higher gains most of the time the gain pot at 1/2 is when I realy hear distortion so that is about 2.5K not bypassed by the cap.  A circuit like this one will have ABOUT 10k(the collector resistor) divided by the 2.5K for about a gain of X4 at that setting.

  I have posted in the past to my ears a gain of X3 is about the limit for clean gain with 9V battery and middle range output guitar

Now circuits like this are not "clean" at higher gain settings.  This was made to go from a somewhat clean boost to " hit" the first preamp tube a little harder to   harder and distortion from the boost adding to the amp.

Maybe not the answer you wanted.   To me db gain on a 9V guitar boost to distortion circuit seems a little silly

So maybe you want to figure the db for X4

page 79 to 87, 97 in "The Art of Electronics" might be fun to read.
Title: Re: Ok how many db's does this thing boost. I have looked I cant find it. Sorry
Post by: JasonG on July 05, 2007, 08:26:11 PM
I love the boost ! I just wanted to give a friend some more info on it.
 Everyone here seems to love that book. My library doesn't have it. So I guess I get my own copy. I have read ( and taken notes from) the ultimate tone and The TAB guide to understanding electronics and electricity. Both great books. So I understand the basics.
  My main problem now is applying the knowledge. Its frustrating. I have been switching out caps and diodes for a few years, tried ot build a few pedals but was unable to get them up and running. When I am reading about how a circuit works I get it. I have conversations with techs about how stuff works the history of pedals and company's and can hold my own till they get into the nitty gritty.  I guess all of my stupid questions stem from that imbalance. For years I lucked out when it came to fixing pedals and amps it was allways a dirty pot or loose wire. Those experiences kept my intrest in electronics but didn't lead to growth.
 Another hindrance was money. With school, a few trips to Brasil ( my home away from home) and every day expenses. I couldn't spend the money on what I needed to get moving. But over the last year I have invested in some good tools so that isn't a problem anymore.
 So thats a short bio.
  I love this forum. There are alot of very sharp and intresting people who hang out here.
 Thanks again for the help! I will see you on the other beginner project when I am done with the vero.