Silicon Rangemaster?
olav b
transistor instead of the germanium. I mean not just replacing the Ge
with a Si, which will most likely mot work, but getting the same kind
of response and effect with a silicon based design.
?
/o
RichL
It's possible. It just won't sound the same. Si transistors clip
"harder" than Ge ones, and that's key to the difference between the
sounds of transistor-based pedals that are driven hard (like treble
boosters and fuzzes).
Dean
wrote:
I heard that you could turn down the volume control on your guitar
with a silicon transistor and get it to clip the same as germanium.
Does anybody know if this is true?
I'd like to learn more about this. Can anybody cite some reputible
source of information? There's so many opinions on the subject it's
hard to know what's true and what's not.
thanks.
- Dean
RichL
No, it won't clip the same.
I did some digging on the web to try to find something that would help
explain this. The only thing I could get quickly was a set of
current-voltage characteristics for silicon and germanium diodes that
were part of a sample lab report, but they're still accurate.
Keep in mind that a transistor can be viewed as a pair of back-to-back
interacting diodes, so the properties of a transistor are largely
determined by those of a diode made from the same material.
You've got to scroll down a bit to see the current-voltage
characteristics (look for the plot called "diode curves from curve
tracer"). As you can see, the silicon diode "turns on" at about twice
the voltage as the germanium diode does. Based on that, you might think
that the germanium diode is similar to the silicon one except that you
operate it at roughly half the voltage. But look again: the turn-on for
the silicon diode is much more abrupt than that for the germanium diode
(i.e., the "knee" is more pronounced). The curve for the germanium is
much smoother, and the "turn-on" is more gradual.
What this means is that, as you feed a signal to the diode, the silicon
diode more-or-less "hits a wall" as you try to increase the voltage,
whereas for germanium it's a really mushy wall. Meaning it clips more
softly and gradually.
This all translates into the same sort of behavior for transistors made
from the same materials.
Bottom line: in a superficial way, the clipping for the two transistors
are similar except that germanium clips at lower voltage. But really,
in terms of properties that affect the nature of the nonlinearities in
the two types of transistors (which translates into how they "sound"
when overdriven), they really are intrinsically different.
Dean
differences. I guess I didn't specify that the clipping I meant refers
to the top and bottom of the tone gets chopped off. I saw a
demonstration of this on a test instrument once. The more signal going
in, the more the top got chopped off. That's what I had in mind when I
posted the question. Nevertheless, thanks for the response.
- Dean
On Fri, 25 Dec 2009 19:00:07 -0500, "RichL" <rple...@yahoo.com>
wrote:
RichL
> Hi Rich. Interesting information. I knew about the diode voltage
> differences. I guess I didn't specify that the clipping I meant refers
> to the top and bottom of the tone gets chopped off. I saw a
> demonstration of this on a test instrument once. The more signal going
> in, the more the top got chopped off. That's what I had in mind when I
> posted the question. Nevertheless, thanks for the response.
>
> - Dean
You mean like in this picture?
<http://en.wikipedia.org/wiki/File:Clipping_1KHz_10V_DIV_clip_A_5ohms-1-
.jpg>
If so, this is precisely the sort of thing that follows from the nature
of the current-voltage characteristics that I posted in the previous
post.
Here's what happens. As you follow a sinusoidal cycle of current, the
voltage is determined at a particular instant of time by the voltage for
that current on the current-voltage graph. So as the current approaches
the "knee" of the current-voltage graph, the voltage begins to flatten
out. Because a transistor is basically comprised of back-to-back
diodes, the same thing happens when the current goes negative, too.
Hence, what you see is that the tops and bottoms of the sinusoid are
chopped off, just like in the picture I just posted.
For a germanium transistor, because the "knee" in the current-voltage
curve is more rounded, the tops aren't as flat as in the scope trace,
however. The edges of the clipped regions become rounded, more like
what happens in a vacuum tube, which is shown here:
http://www.diyguitarist.com/Images/McTubeWave4.JPG
See the difference?
What this means is that the germanium transistor will have
lower-amplitude high-order harmonics compared with the silicon
transistor, which translates into a smoother, less "harsh" sound.
Dean
stuff to me. That second picture looks like what I remember a TS9
looks like. Maybe.
I would like to set up an experiment to actually demonstrate this.
There's lots of programs, freeware, of audio scopes and harmonics
analyzers that can run on a laptop. All I need to add is a guitar or
something and some electronics parts to do it! Any suggestions would
be helpful.
- Dean
On Sat, 26 Dec 2009 17:20:38 -0500, "RichL" <rple...@yahoo.com>
wrote: