buffer to a booster circuit

[Gus]

Here is something on my list to build
A buffer then a boost circuit
note the gain control part R8, R7 and C1
and grounded emitter
guitar and cable sim left of R11. Circuit starts at input and to the right

[kingswayguitar]

it's my own lack of knowledge but are q1 q3 some type of totem pole

[Gus]

http://www.diystompboxes.com/smfforum/index.php?topic=98244.0
Sziklai pair post 11

R.G. also has an article at GEOFEX with a circuit using a Sziklai pair

Sziklai input buffer with an input resistance I like with distortion effects and a .01uf cap for the high pass frequency I like with distortion.  the 1k is for stability.

Next stage is a grounded emitter with collector to base feedback bias.  Note the 4.7meg sets the DC bias and part of the closed loop gain
The transistor was selected to bias at a voltage range with a "large" enough bias feedback resistor (4.7meg)so adding a parallel gain network could be done with a 1meg control
AC part of the gain control of the stage is  set with C1, R8 and R7 in parallel with R6.  Note min gain (R8 at 0 ohms) is mostly set by R7/R5

R4 and Q1 emitter Q3 collector voltage were selected for good drive for the following gainstage

[kingswayguitar]

thank you
i kinda get it now
i will try it out in an effort to understand q2 as well
like i said... always learning (again)

[pinkjimiphoton]

dang it gus, every time i think i'm done building one of your fine sounding circuits, ya poot forth yet another!!

i really wanna build this... i think i can make it really tiny, and be able to add it to my pedalboard.

looks like it will be nice headroom.. the szikli pair is a way to get higher gain silicons to sound like germanium, right?
i remember looking at something on i think small bear.

downloading the schematic. are parts gonna be critical? got a usual 20% tolerance, or does it have to be tighter?
while i still got my stuff out, i'll see if i can cobble this together today.

thanks gus!!

[teemuk]

the szikli pair is a way to get higher gain silicons to sound like germanium, right?

Wrong.

A compound pair (a.k.a. Sziklai pair) actually boosts the gain even further because total current gain of the pair is the gain of both devices multiplied. If the first transistor (driver) has gain of 10 and the second (output) has gain of 5 the total gain is 10 x 5.

Sziklai and Darlington pairs are like A B C 's of transistor theory. In same category as understanding what is an emitter follower, common emitter or a common base circuit. Obviously some folks need to do a bit of mandatory reading.

[kingswayguitar]

ok
and r12 is the bypass resistor

[teemuk]

By the way, what's up with the pickup/guitar simulator?

I mean, I know what it does, but useful purpose of such circuit is simulating how the input stage interacts with anything downstream the input jack. When you use a waveform input to circuit the basic assumption is that the waveform input is already processed by response introduced by that interaction. You don't want to superimpose that response again to the source signal.

You can practically ignore what's downstream the input jack once you have verified that the interaction with the input stage is what you seek after. Now having the simulation of guitar's electronics there is sort of giving you false results.

[mac]

The input stage looks like a 9v Heathkit TA-28 

mac

[Gus]

By the way, what's up with the pickup/guitar simulator?

I mean, I know what it does, but useful purpose of such circuit is simulating how the input stage interacts with anything downstream the input jack. When you use a waveform input to circuit the basic assumption is that the waveform input is already processed by response introduced by that interaction. You don't want to superimpose that response again to the source signal.

You can practically ignore what's downstream the input jack once you have verified that the interaction with the input stage is what you seek after. Now having the simulation of guitar's electronics there is sort of giving you false results.

I did write in the first post the circuit starts at input and to the right.

I left the sim as an example of a guitar and cable sim.  I don't build a circuit with the guitar and cable sim.  I leave it so people know what I used in the simulation.  I hope they know to remove the guitar/bass, and cable sim part in the build.

I have not posted any frequency response graphs yet I find the guitar and cable sim useful for the added EQ it shows with the interaction with the following circuit.  
The overall guitar or bass, cables  effects, cable and amp does not sound like the frequency response graph.  
They sound like the guitar or bass electromechanical system (electromagnetic pickups AND the body, neck, etc. vibrations, that add and subtract to the pickup signal(s)) That signal is then "EQed" by the interaction of the effect or amp and the following signal processing done in the circuits

green input blue output, R8 min(0 ohms)and max(1meg) gain settings

[pinkjimiphoton]

By the way, what's up with the pickup/guitar simulator?

I mean, I know what it does, but useful purpose of such circuit is simulating how the input stage interacts with anything downstream the input jack. When you use a waveform input to circuit the basic assumption is that the waveform input is already processed by response introduced by that interaction. You don't want to superimpose that response again to the source signal.

You can practically ignore what's downstream the input jack once you have verified that the interaction with the input stage is what you seek after. Now having the simulation of guitar's electronics there is sort of giving you false results.

it's nice to know you know so much.

but when gus runs his circuit sims, it's kinda helpful to be able to see the interaction of the guitar and the effect. just remove it.

he makes it pretty clear why it's there, and to remove it when building the circuit.

you seem antsy. wanna snickers? maybe a donut?

[teemuk]

Yeah, I'm sometimes a bit grumpy.

But I seldomly mean anything bad, offensive or personal. Sorry if you ever felt that way. I guess I just have a habit of saying things straight and that comes off rude sometimes.

[pinkjimiphoton]

no worries brother. it's all good!!!

rock on! i learn something every day here, so thanks for hipping me.. remember glancing at it somewhere, something to do with a fuzzface or something, lol..

[pinkjimiphoton]

hey gus,
i worked up a vero for ya for this. hoping some other intrepid and brave soul will take the plunge.
tho i am a total fuzzaholic, i have more boosts than i will EVER use or need, and i hope you don't take offense, i just don't
wanna use resources right now on things i won't ever use.
there's so many things i want.... and most are far from boosts. i've gotta sho i built years ago that lives on my pedalboard.
i don't really need another.
if this is anything like the last one, the jfet boost, it's sure to sound ace tho!!




this isn't verified, but i believe it to be correct, i've checked the nodes a few times while revising this, so it should be good.

thanks bro

edit: all that said, in for a dollar, in for a dime. i'm in, will try and cobble this together over the next couple days if i can.

[Gus]

Jimi

Looked at the vero
move  the top  lead of C4 down one row
The gain control is wired like a rheostat so there is no ground connection
The output control should be a audio taper

[pinkjimiphoton]

good catch gus. thanks bro.

i'll be getting on this soon, it's in the list of stuff that's imminent.

should be soon.

so just input and wiper on the gain control.... got it. didn't see audio taper spec'd, so went linear. i don't know if i have them in stock other than linear. i'll look.

[Gus]

C4 should be .01uf

[pinkjimiphoton]

cool, thanks gus!