Alternative FETs in Oz

A

Andrew Howard

Guest
I'm planning out the construction of a guitar effects pedal, with the
circuit from www.generalguitargadgets.com .

It is the "Blue Magic" distortion pedal. which requires two components that
I can't seem to get hold of here. These are:
Q1 - BS170 (MOSFET)
Q2 - J201 (JFET)

Does anyone know where in Sydney, Australia I could hold of these, or
equivalents? The main stores I am limited to are:
www.jaycar.com.au
www.dse.com.au
www.altronics.com.au

Additionally, could someone please tell me how I go about finding
equivalents for components? (Do I just browse through as many datasheets as
possible, then select the one with the closest specs? Seems a bit clumsy to
me, that's all...)

Thanks
Andrew Howard
 
Hi,

It is the "Blue Magic" distortion pedal. which requires two components that
I can't seem to get hold of here. These are:
Q1 - BS170 (MOSFET)
Q2 - J201 (JFET)

Does anyone know where in Sydney, Australia I could hold of these, or
equivalents? The main stores I am limited to are:
Click to expand...

The BS170 could probably be replaced with the common 2N7000.

And the J201 with most any N-channel JFET (BF245, 2N3819).


Cheers - Joe
 
The BS170 could probably be replaced with the common 2N7000.

And the J201 with most any N-channel JFET (BF245, 2N3819).
Click to expand...
Thanks for the info. I can get the 2N7000 easily enough, but the only JFET I
can find at my local store is the 2N5484.

I have one last question though, will the substitution of these parts affect
the sound at all? Will it impair the pedal's ability to do what it's
supposed to do?

Thanks again.
Andrew Howard
 
Andrew,

I'm sorry, I know absolutely nothing about the type of
gear you are working with. I was simply saying that the BS
170 is very similar to the 2N7000. In fact if you do a
search with PDF and BS170 or 2N7000 as the keywords, you
can see that they are much the same and the ones I found
were both produced by Fairchild Semi. I put together a
counter just recently that used BS170s as mode switches and
would have used '7000s if I'd run out of '170s.

As for the JFET, without knowing anything about the
circuit, I cannot comment except to say I'd try any N-
channel JFET if you can't get the one you want as
presumably it is a piece of audio gear and not concerned
with such things as operation at VHF/UHF.

In any event, they only cost a few pence (cents) so why
not try what you can get your hands on.


Cheers - Joe
 
Thanks, I will buy a couple of types and see what sounds best.

Andrew Howard
 
Andrew Howard wrote:

It is the "Blue Magic" distortion pedal. which requires two components that
I can't seem to get hold of here. These are:
Q1 - BS170 (MOSFET)
Q2 - J201 (JFET)

Does anyone know where in Sydney, Australia I could hold of these, or
equivalents? The main stores I am limited to are:
www.jaycar.com.au
www.dse.com.au
www.altronics.com.au

Additionally, could someone please tell me how I go about finding
equivalents for components?
Click to expand...
There are thousands of transistor types, with small variations in specs.
So the approach most people take is to buy only a few types with very
good specs, which can be used in place of many others with inferior
specs. For example a transistor with 50 V max. supply voltage works in
applications that require only 20 V.

There are "Replacement Lists" on the market, which for each transistor
on the market lists one of only a dozen or so replacement types.

The 20 V transistor in the above example will be a little cheaper than
the 50 V type, but only if you buy large quantities (ouple of 10,000 or
so). For the hobbyist or small repair shop, the price difference is
negigeable.
 
The 20 V transistor in the above example will be a little cheaper than
the 50 V type, but only if you buy large quantities (ouple of 10,000 or
so). For the hobbyist or small repair shop, the price difference is
negigeable.
Click to expand...
I don't mind about cost as such, just about the sound.
The circuit uses a MOSFET to drive a JFET into distortion. The circuit is
here:
http://www.generalguitargadgets.com/v2/diagrams/bmagic.pdf

I'm just concerned about the effect on sound that the different FETs will
produce. If you could tell me what differences to expect, that would be
great.

Thanks
Andrew Howard
 
Andrew Howard wrote:


I'm just concerned about the effect on sound that the different FETs will
produce. If you could tell me what differences to expect, that would be
great.
Click to expand...
That probably would depend more on the amplification of the individual
transistor than on transistor type.
 
Dr Engelbert Buxbaum wrote...
Andrew Howard wrote:


I'm just concerned about the effect on sound that the different FETs
will produce. If you could tell me what differences to expect, that
would be great.

That probably would depend more on the amplification of the individual
transistor than on transistor type.
Click to expand...
In my opinion, neither transistor types (BJT FET IGBT) nor specific
parts "creates sound," rather poor amplifier circuit designs create
extraneous sound, distortion, etc. That said, with respect to power
MOSFETs, the so-called "lateral" FETs (i.e. not DMOS V-MOS FETs) made
by Hitachi (now Renesas) are superior to the conventional DMOS power
MOSFETs in that their low Vgs gate-voltage and near-zero temperature
coefficient helps solve several difficult amplifier-design problems.
Hence, FET amplifier designs using them are likely to be better. In
several ways these lateral FETs are similar to BJT power transistors.

Thanks,
- Win

whill_at_picovolt-dot-com
 
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