After reading all the posts about what I think are not so good beginner designer circuits, C to B bias/feedback resistor with no B to ground resistor let look at this take on that type of circuit without the B to Ground. How much interaction with gain setting and the source can we get?
(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=49535&g2_serialNumber=1)
and it frequency response
(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=49538&g2_serialNumber=1)
note the interactions
The high value C to B bias resistor for high hfe transistors gain interaction with the input series resistance can be controlled with an added resistor in parallel AC connected with a cap
Ohms law and feedback math helps to understand what that added resistor does
I don't understand why people keep building circuits NO B to ground like a BMP circuit fragment
Discuss
When the older stuff was built (BMP etc. etc.), many 'designers' didn't have much in the way of theory background. So they copied snippets of circuits they came across, but didn't know how to improve upon them. They didn't have the internet! We see this all the time, especially in tube amps which were snagged from old sources that had different applications than for guitar.
My guess is that even tho you get interactions, many of them are serendipitously 'happy' effects, so no further tweaking was attempted. Interesting, huh?
High enthusiasm, low knowledge?
Speaking for myself, not that I'd call myself a designer or anything, but often my enthusiasm overtakes my knowledge and then I wonder why it doesn't work, or doesn't work as well as I thought it should or don't realise I'm not taking full advantage of a circuit for whatever purposes it's designed for. Happens in other spheres, like that guitarist who tries hard to sound like x guitarist, buys all the same gear but still falls short because they have very little, or none at all, clue how said gear is used, modded, recorded, etc.
I've been taken down a notch in the past. Now I just try to keep calm and learn how things actually work and why. Don't always succeed, but I try.
I thought I would bump this for the current HP like circuit threads and other threads that have this type circuit.
With different transistor hfes you can adjust the gain lower than the collector to base bias/gain resistor.
If you build one of the simple circuit with a grounded emitter or emitter resistor and C to B bias/gain with a series input resistor and no base to ground the first post is to show the adjustment points
If you are using just R3 it sets bias and max gain by what is before the base (series resistor, cap, guitar cable, guitar/bass/effect...)
If you want lower max gain add C6 and R12 they are AC coupled so they don't change the DC bias but lower the max gain. Why you might want to lower max gain is for more control from the guitar volume control. You can adjust the cap value for a simple EQ I showed this in another thread.
You can add R2 and bypass it with a cap
You can have a brighten up effect by adding C7
The gain in the graph is the top curves the lower curves are phase
I have not built this it was posted to show three places that this type circuit can be adjusted. I like to select a collector resistor value and therefore a known collector current at a bias setting I like and then adjust the rest of the circuit with gain stages like this