[sdiy] Sound Lab Mini Questions

[Ray Wilson]

Hi Gabbe

Here are some answers to your questions. I hope all goes well with your
project. Be sure to read the entire Sound Lab web page before starting to
build there is a lot of info there.

Cheers

Ray


I used all linear pots in mine. But Logs might be nice for the attack and
decay pots so you get finer adjustment for the fast attack and decays and
perhaps for the low frequency pot again so you get a better range. With the
linear pot the LFO range is pretty crowded towards the extreme clockwise
side of the adjustment. I mean it works quite well wth linears but if you
can find them and you have the luxury to experiment with the logs then let
me know how it turns out.

Capacitor Substitution
You should know that where ceramic capacitors are specified below you could
substitute: Mylar, Polyester, Polystyrene, Polypropylene, or Mica. The value
should be within 10% of what is specified below. In other words you can
substitute a .022uF for a .02uF or a 2.2uF for a 2.0 uF. The circuit is
forgiving enough to handle that variation with no problem. Do not substitute
electrolytic caps with non-electrolytic caps.
Resistor Substitution
Where resistor values are greater than or equal to 47K a 1/8-Watt resistor
will work as well as 1/4-Watt. Use of 1/2-Watt resistors will probably
require vertical mounting if they fit at all. Also as long as values are
within 5% of the values specified below you can substitute resistors. And
don't forget that you can put resistors in parallel or series to get a
resistance value you don't have on hand.


This text is from the MPF102 spec available here:
http://pubpages.unh.edu/~aperkins/pdf/MPF-devices/MPF102.pdf

Any N-FET that comes close to this will do.

MPF102
TO-92 G S D
N-Channel RF Amplifier
This device is designed for electronic switching
Applications such as low ON resistance analog switching.
Sourced from Process 50.
Absolute Maximum Ratings * TA=25 degree C unless otherwise noted
Symbol Parameter Value Units
VDG Drain-Gate Voltage 25 V
VGS Gate-Source Voltage -25 V
IGF Forward Gate Current 10 mA
TJ,Tstg Operating and Storage Junction Temperature Range -55 to + 155 degree
C
* This ratings are limiting values above which the serviceability of any
semiconductor device may be impaired.
NOTES :
1) These rating are based on a maximum junction temperature of 150 degrees
C.
2) These are steady state limits. The factory should be consulted on
applications involving pulsed or low duty cycle operations.
Thermal Characteristics TA = 25 degrees C unless otherwise noted.
Symbol Characteristic Units Max
PD Total Device Dissipation
Derate above 25 degrees C
350
2.8
mW
mW/degrees C
RqJC Thermal Resistance, Junction to Case 125 degrees C/W
RqJA Thermal Resistance, Junction to Ambient 357 degrees C/W
* Device mounted on FR-4 PCB 1.5" X 1.6" X 0.06"
ã1999 Fairchild Semiconductor Corporation
N-Channel RF Amplifier
( Continued)
Electrical Characteristics TA= 25 degrees C unless otherwise noted
Symbol Parameter Test Conditions Min Typ Max Units
OFF CHARACTERISTICS
V(BR)GSS Gate-Source Breakdown Voltage IG=-1.0mA, VDS=0 -25 V
IGSS Gate Reverse Current VGS=-15V,VDS=0 -2.0 nA
VGS(off) Gate-Source Cutoff Voltage VDS=15V, ID=2nA -8.0 V
VGS Gate-Source Voltage VDS=15V, ID=200mA -0.5 -7.5 V
ON CHARACTERISTICS
IDSS Zero-Gate Voltage
Drain Current
VDS=15V,VGS=0 2.0 20 mA
gfs Forward Transconductance VGS= 0V,VDS=15V,f=1kHz. 2000 7500 mS
Capacitance
Ciss Common-Source Input
Capacitance
VGS=15V,VDS=0V
f=1 MHz.
7.0 pf
Crss Common-Source reverse
Transfer Capacitance
VGS=15V,VDS=0V
f=1 MHz.
3.0 pf



----- Original Message ----- 
From: "Gabriel Lindeborg" <gali at tiscali.se>
To: "diy" <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, June 17, 2004 1:26 PM
Subject: [sdiy] Sound Lab Mini Questions


> I finaly has taken the time to start bulding the Ray's Sound Lab Mini
> (http://www.musicfromouterspace.com) and have some initial questions:
> Should all the pot's be linear?
> Is it okey to use standard values on resistors and caps (ie 2,2uF
> instead of 2uF)?
> Can the mpf102 be exchanged w. bf245(B or C)?
> Any ideas on this are welcome...and if some of you who has finished your
> SLMs has anything other to point out, please do so.
>
> //Gabbe of Sweden