Rangemaster question

[carboncomp]

What is the function of the C3 capacitor coming of the emitter to ground, and what effect will changing its value have?

I assume the R3 it's in parallel is setting the level of gain?

[sajy_ho]

It's a bypass cap. Omitting will lower the gain and changing the value will affect the frequency response; higher values for more bass, I think.
:DI love this circuit, I Think it's the old one used in many of epic songs like "Free Bird".

[R.G.]

What is the function of the C3 capacitor coming of the emitter to ground, and what effect will changing its value have?

I assume the R3 it's in parallel is setting the level of gain?

C3's effect is to bypass R3 entirely above some frequency, getting all the gain possible from the transistor.

With the C3 and R3 values shown, all frequencies much above 0.87Hz will get nearly the full gain the transistor can produce - that is, all of the audio range.

Changing C3 will affect only the lowest frequency where the gain drops.

[carboncomp]

Changing C3 will affect only the lowest frequency where the gain drops.

Bigger the cap the lower the frequency drop off?

(see the JHS boost is really similar but has a 80uf cap. S0o would more of the lower frequency bypass the R3 resistor resulting in less treble?)

[thelonious]

(see the JHS boost is really similar but has a 80uf cap. S0o would more of the lower frequency bypass the R3 resistor resulting in less treble?)

Not less treble, but more bass.

Guitar frequencies start at 82Hz, so you'd have to make the cap much smaller to hear much difference. You might start to hear it at ~2.2uF, and I think you'd really hear the difference at ~0.47uF or smaller.

In this circuit, though, the 5nF input cap and 68K resistor make a high pass filter at 468 Hz anyway, so the size of the bypass cap makes somewhat less of an audible difference than it otherwise would.
________
Edit: this is completely technically wrong and not what is happening  , but think of the Rangemaster like an engine and the negative feedback from the emitter resistor (R3) like friction. The cap C3 is gets rid of the friction and makes the engine more efficient.

In the case of the Rangemaster, negative feedback from the emitter resistor R3 is like anti-signal that "pushes the brake pedal" on your transistor amplifier. C3 allows that negative feedback to (by)pass to ground. The value of R3 and the value of C3 together determine at which frequency the negative feedback starts getting dumped to ground. Keeping R3 value the same, an increasingly large C3 will dump increasingly lower frequencies of negative feedback to ground which = you hear more bass.

Low E string on a guitar is 82Hz.

At R3=3.9K, if you make C3:
80uF..... 0.5Hz
47uF..... 0.9Hz
2.2uF.... 18.2Hz
0.47uF... 86.9Hz

Those frequencies are the -3dB corner frequency, so you will probably start to hear the difference before 0.47uF. However, the difference between 80uF and 47uF is going to be negligible, IMO.

[njkmonty]

Sorry to hijack thread,
last night i was installing a little charge pump circuit into my pnp germanium rangemaster clone, and works great.. (using the -9v tap from circuit)
except when  10k Log (boost) pot is fully on , the sound "Gates" a little when strummed hard.
is this the nature of the beast?
anyone else had experiences like this?

[PRR]

> C3's effect is to bypass R3 entirely above some frequency, getting all the gain possible from the transistor.
> With the C3 and R3 values shown ....

With the values shown, the very low frequency gain is 10K/4K or 2.5.

At 3900+47uFd or 0.9Hz something changes. Gain goes up a wee bit.

To bypass R3 "entirely", to get "all the gain", C3 must be comparable to transistor Hie. Assuming a half a mA, this is like 60 Ohms. 47uFd against 60 Ohms is 59Hz.

This assumes transistor parasitics are small and drive impedance is small. Parasitics are just a few Ohms and vanish in uncertainty. Source impedance may be 5K or 100K, not small. Assuming hFE is 100, this reflects down to emitter as 50 Ohms to 1K.

Any of these errors puts the "getting all the gain possible" frequency below 59Hz. So it is "all the gain" (within 2dB) for all guitar frequencies.

> what effect will changing its value have?

We can poke at it and debate the "all the gain" frequency, but the interactions are *SO* complex that the wise designer reads theory books which advise making C3 as BIG as the budget will tolerate. In this case 47uFd is *probably* right on the mark (less might shave bass, bigger would cost more).

You can just try it. Figure an octave-change (2:1, 22uFd) for a small tweak, a decade-change (10;1, 5uFd) for a "big" tweak. A 1980s VCR should yield a wide selection of small electrolytics and large film-caps for trial.