Transistors?

[Handcrafted Tone]

Hey guys,

Anyone have a source for learning about transistors? Like specific uses for different transistors, and why?

I'm thinking of putting together a big muff type distortion circuit http://www.generalguitargadgets.com/diagrams/bmpsc.gif . It's not going into a stomp box, I'm adding it to another project that is already running on +/- 16V.

Can I feed that circuit 16V instead of 9V? Can I use both +16V and -16V power rails to somehow improve sound quality / dynamic range?

Thanks in advance :grin:

 

[clintrubber]

[quote author="Handcrafted Tone"]Hey guys,

Anyone have a source for learning about transistors? Like specific uses for different transistors, and why?

Can I feed that circuit 16V instead of 9V? Can I use both +16V and -16V power rails to somehow improve sound quality / dynamic range?

Thanks in advance :grin:[/quote]

There's diode clipping in that circuit, which is supply independent. But in general overdrive/fuzz/distortion circuits can have signals hitting the floor & ceiling as well here & there (dep. on settings), so when you increase the supply rails the behaviour of the circuit is changed. Not better or worse, just different.
I'm not sure if this holds for the given circuit though. The diodes obviously keep the signals at the various nodes more away from the supply rails compared with this circuit without diode-clamping.

FX-circuits often have a suited sensitivity for what they're designed for (hey ! :wink: ) but if you increase the supply of a distortion stage that doesn't use diode clipping you might not get any distortion at all. Or at least less for given input-signals.
Could suit you or not.

Discussions on improving the sound quality of a circuit that's intended to distort can be tricky :wink: but I see what you mean about dynamic range. I wouldn't bother.

For various other circuits a higher supply lets you work with higher signal levels so you can obtain noise benefits (as long as the incoming signal isn't already the noise-bottleneck) but I'm not sure it'd all be worth while.

I mean, some people do all their FX-ing between preamp & power stage, often by using hi-quality studio grade rackmount gear using 'pro-signal levels'. Can sound good and is more healthy from a technical side of things.
But if just slamming a few good stompboxes in front of an amp did sound way worse then people wouldn't be still doing that.

For your situation I'd say just try it if you like to fiddle around with the influence of various supplies (keep voltage ratings of caps in mind & in general check those transistors as well to be sure), but if you're in a just get the job done mood then I'd just throw a 9V regulator at the EH-circuit.
You could still hadd a few diodes beneath the centre leg of the regulator to toy around with voltages slightly higher than 9V.

BTW, you'll have heard that the fun for dist.-circuits is often on the other side of 9V: lower voltages and/or increased supply impedance. A topic of its own...

Regards,

Peter

 

[recnsci]

You can theoretically use +16V if you don't exceed maximum voltage or
current ratings on any component. However, transistors will bias
differently, so "tone" will change. This is fuzz, so apropriate "tone" is
highly subjective matter. What are you planning to use this
thing for, guitars or general purpose mangler? Depending on this,
you can drop first and last transistor stages, and replace them with
something "transparent" (or whatever). Improving dynamic range of
fuzzbox seem like oximoron to me. And improving "sound" of fuzzbox
is way beyond subjective. Generaly, you can't drive single suply circuit
with bipolar suply, without changing circuit.

Just quick transistor tutorial: your first concern here is how will transistors
bias when you change suply. So you are examining conditions after suply
is turned on and everithing is settled, but there is no signal in sight.
First thing to do is to asume capacitors are ideal and you replace them
with open circuit. Now first three stages look the same.

So you will check just first stage.
You are left with suply (Vcc), ground, Q1 ,R2, R3, R4 and R5. Erase
everything else.
Now you asume few things: Q1 is in forward active mode (you need this
for amplification)so colector and base are sucking curent, and that
current flows out of emiter, hfe (or beta, whatever you call it) is large
enough so that you asume Ic=Ie and Vbe is number you choose freely
between 0.6 and 0.7 volts. This asumptions will ease your life and
parameter tolerance will **** you up much more than these asumptions.

Emiter voltage is:
Ve=Ic*R4

Base voltage is:
Vb=Ve+Vbe=Ic*R4+Vbe

Now asume that base current is much (more than ten times) smaller
than currents through R2 and R3, so you can neglect it.
In that case colector voltage is:
Vc=R3*Vb/R2+Vb=(R2+R3)*(Ic*R4+Vbe)/R2

Finaly, R5 current is equal R3 current plus colector current, so you
write this:
(Vcc-Vc)/R5=Ic+(Vc-Vb)/R3=Ic+Vb/R2

You replace Vc and Vb with equations derivated above. You get
big ugly equation, where only unknown thing is Ic. You fiddle
with that equation till you get Ic on one side and everything else on other.
So you will have equation how Ic (thus bias point) depends on
components and suply voltage.
When you find Ic for some particular values, just check
if your asumption that base current is much smaller than current trough R3
is still valid. If not, back to square one.

Hope spelling errors and bad english didnt made this completly unreadable

cheerz
urosh

 

[Handcrafted Tone]

Thanks Peter, there's some good info in there.

Yeah I pretty much figured "Just go try it out" would be the answer, but I thought I'd get an opinion before I start buying parts.

I'm not a raging metal head anymore :grin: and I wouldn't mind less distortion if it meant I could lower the noise floor. I like a warm saturated crunch, I try to stay away from that high freq white noise like distortion .

I usually lower the volume on my guitar about 10% so I have room to change the dynamics and gain during the song.

 

[Handcrafted Tone]

Wow, thanks Urosh, thats the kind of stuff I'm looking for. I'll have to sit down with those equations and build a few circuits.

I'm all about the tone, so looks like I'll have to do a lot of experimenting.

thanks guys!