Biasing NPN transistors

[R.G.]

OK, but what I don't understand is why should I do so? 60K is too low an impedance for connection to a guitar (and arguably lots of pedals too, although it matters a lot less),

True. I didn't know that was the intended use. If the JFET+NPN is for a guitar input, there are better circuits of several kinds. Notably, a bootstrapped darlington would be fine for most uses.

Also, I see tutorials (that say a lot and say nothing at all) talking about much higher base currents than what I seem to achieve (like up to 40uA), and my collector current is kinda lowish for a BJT? I see much higher currents quoted around for general purpose BJTs, even if used as amplifiers and not switches. So am I sort of misusing the device? I don't have a necessity to save on current, it would be a mains powered pedal (well, through a power supply).

The OnSemi datasheet for the 2N2222 lists a minimum beta of 50 at 1ma, and no maximum. What the device really is depends on your luck at getting a 2N2222. That could account for the higher base currents you see. Maybe. The operating collector current and gain of a BJT have a lot of side effects on the transistor's effective current gain and bandwidth. I don't know that you're really misusing the device, but if you want it for a guitar input, I'd go for a bootstrapped darlington, JFET/PNP pair, something like that.

Bipolar design seems to be sliding into a little bit of a lost art, much like tubes did in the 1970s.

[PRR]

....much higher base currents than what I seem to achieve (like up to 40uA), and my collector current is kinda lowish for a BJT? ...

Base current is not a goal but an unavoidable flaw.

Collector current on modern Silicon can be VERY low. In the 1970s we designed phono preamps for 20uA which was off the chart. Old parts might mis-bias but after 1977 "any" very small Si bipolar was stable at 20uA. And processes have got better since then.

IMHO, your proposed plan is probably 10X more current than you need. Maybe make 2.4k to 22k? BUT it depends entirely on the LOAD.

2N5088 is your friend below 10mA (i.e. almost all audio needs). While the datasheet curve still shows fall-off below 20uA, today it is much better than specified.

Compounds (such as Darlington) so you get hFE^2 are very valuable.

PLAGIARISM is a good teacher.

Did someone cite Douglas Self Small Audio? At least the older editions went into discrete design. Later he realized that you get equal/better performance cheap enough with chips (hint).

[Clint Eastwood]

Using one NPN and one PNP transistor, you could build a circuit like the one below.

- Zin= several megaohms

- Zout= a few hundred ohms

- gain= (R5+R7)+1 edit: (R5+R7)/R7

[fryingpan]

....much higher base currents than what I seem to achieve (like up to 40uA), and my collector current is kinda lowish for a BJT? ...

Base current is not a goal but an unavoidable flaw.

Collector current on modern Silicon can be VERY low. In the 1970s we designed phono preamps for 20uA which was off the chart. Old parts might mis-bias but after 1977 "any" very small Si bipolar was stable at 20uA. And processes have got better since then.

IMHO, your proposed plan is probably 10X more current than you need. Maybe make 2.4k to 22k? BUT it depends entirely on the LOAD.

2N5088 is your friend below 10mA (i.e. almost all audio needs). While the datasheet curve still shows fall-off below 20uA, today it is much better than specified.

Compounds (such as Darlington) so you get hFE^2 are very valuable.

PLAGIARISM is a good teacher.

Did someone cite Douglas Self Small Audio? At least the older editions went into discrete design. Later he realized that you get equal/better performance cheap enough with chips (hint).

I'm not against chips. In fact, this design employs four opamps. That said, the range of readily available through-hole opamps is sort of lacking, and good opamps for audio capable of working well at 9V, single-supply, isn't that great. Also, if a discrete transistor (or two) can do a good enough job, why not?

I understand that base current is a relative drawback, but I guess that what I was trying to say is that I don't know how well a transistor works at low currents. Maybe noise increases. Maybe distortion increases. Due to the Early effect, I would expect distortion to be less but at the same time have less of a dynamic range.

I guess I should really get hold of one of Self's books.

[Steben]

Vref is a fixed voltage in the supply circuitry; usually 1/2 Vsupply.
Forget the diode and you wille see the circuit layout as shown here.

[antonis]

Bipolar design seems to be sliding into a little bit of a lost art, much like tubes did in the 1970s.

How very true and correct..!! 

[antonis]

Vref is a fixed voltage in the supply circuitry; usually 1/2 Vsupply.
Forget the diode and you wille see the circuit layout as shown here.

I don't think OP likes to involve in CFP with gain and all that nasty V_BE count in conjunction with Collector(s) bias level..

[antonis]

Using one NPN and one PNP transistor, you could build a circuit like the one below.
- Zin= several megaohms

I should point that the higher the gain the lower the bootstrapping effect on R9..
(in the mean of in case of R5 equals to zero Ohms, we have almost 100% NFB resulting into almost unity voltage gain - hence almost infinite R9 apparent resistance..)

[Steben]

Using one NPN and one PNP transistor, you could build a circuit like the one below.
- Zin= several megaohms

I should point that the higher the gain the lower the bootstrapping effect on R9..
(in the mean of in case of R5 equals to zero Ohms, we have almost 100% NFB resulting into almost unity voltage gain - hence almost infinite R9 apparent resistance..)

True, but many Mohms is not important on guitars. High input impedance is great for a neutral clean basic tone, yet those megas we see now and then are abundant.

[Steben]

Bipolar design seems to be sliding into a little bit of a lost art, much like tubes did in the 1970s.

How very true and correct..!! 

While the harmonic spectrum of slightly feedbacked BJTs is very agreeable and that of jfets overrated.
Jfets are simple to bias but very finicky in their characteristics and sound. I never found a jfet circuit I actually liked... so those natural 2nd harmonics are not the one thing to settle everything.

A fuzz face on the other hand is magic.

[antonis]

Another way to do this is to leave R8 at 47K, make R41 18k, and insert a 120K resistor between the junction of R8 and R41 and the base. This reproduces a very similar Vbase and a similar base current and other bias points, and allows you to use a capacitor to bypass the junction of R8 and R41 to ground, lowering the bias part of the noise.

I think OP is confused a bit now 'cause you didn't mention the input signal connection point..
(although the cap placement on divider resistors junction should warn him to move the existing input connection..)