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Table of Contents
Summary of Contents for Slightly Nasty 1221
- Page 1 M O D E L 1 2 2 1 D I S C R E T E L OW PA S S A M P. L PA M O D E L 1 2 2 1 D i s c r e t e L o w p a s s A m p l i f i e r Co nstru ctio n L PA &...
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Page 2: M O D E L
D i s c r e t e L o w p a s s A m p l i f i e r M O D E L 1 2 2 1 S P E C I F I C A T I O N S PHYSICAL FORM FACTOR: Loudest Warning / 4U... -
Page 3: Table Of Contents
Differential Amplifier CHOOSING COMPONENTS Bill Of Materials (BOM) Choosing Components CONSTRUCTION Construction Overview Physical Assembly CALIBRATION Calibrating the 1221 CONTROLS Controls REFERENCE PCB Guide This document is best viewed in dual-page mode. C i rcui t Ove rv i ew... -
Page 4: Introduction
1 2 2 1 I N T R O D U C T I O N The Slightly Nasty Model 1221 Discrete Lowpass Amplifier is a dual discrete- M O D E L 1 2 2 1 D I S C R E T E L OW PA S S A M P. -
Page 5: Circuit Overview
For full schematics, please download the separate schematics PDF. Excerpts shown in this manual may be outdated and are provided for reference only. The Model 1221's circuitry can be broken up into three main subsections: CV processor / Attenuverter - This is the circuit that applies attenuverter scaling to the CV input jack, mixes it with the Bias knob setting, and feeds the result into the linear/exponential control circuit. - Page 6 C i rcui t Overv i ew S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A...
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Page 7: Cv Processor / Attenuverter
1 2 2 1 P R O C E S S O R The CV processor in the 1221 serves a few different purposes - it provides attenuverter functionality for the LEVEL CV input, combines it with the voltages from the BIAS knob and the trimmer potentiometer, and then creates the linear and exponential response voltages that the RESPONSE control sweeps between. - Page 8 V C A C O R E The VCA core in the 1221 is based around a classic discrete transistor differential pair circuit - comprised of input transistors Q306 and Q310, and the current source transistor Q307, which controls the current that is pulled through the VCA core, and consequently the gain of the output.
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Page 9: Vca / Lpa Core
D i s c r e t e L o w p a s s A m p l i f i e r A s y m m e t r i c S l e w L i m i t e r M O D E L M O D E L 2 2 3 1... - Page 10 F I L T E R L A D D E R The filter stage of the Model 1221 consists of a 2-pole transistor ladder grafted to the top of the VCA transistor pair. The working principle of the ladder filter can be analysed in a few different ways, but one of the simplest is to think of each...
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Page 11: Bill Of Materials (Bom)
B I L L M A T E R I A L S Bi l l Of Mate ri a l s S L I G H T L Y N A S T Y E L E C T R O N I C S A D E L A I D E , A U S T R A L I A... -
Page 12: Choosing Components
C H O O S I N G C O M P O N E N T S Like all Slightly Nasty modules, the Model 1221 is designed to use common "jellybean" components wherever possible, so getting hold of parts is relatively straightforward. -
Page 13: Construction
I personally like to clean up any remaining protrusions with a few passes of a needle file as well. The DPDT mode switch in the 1221 is probably the component that requires the most attention during construction . As mentioned in the "Component Selection"... -
Page 14: Physical Assembly
D i s c r e t e L o w p a s s A m p l i f i e r M O D E L 1 2 2 1 P H Y S I C A L A S S E M B L Y Assembling the finished PCBs and front panel is very simple. -
Page 15: Calibration
D i s c r e t e L o w p a s s A m p l i f i e r M O D E L 1 2 2 1 C A L I B R A T I O N Calibration of the 1011 consists of adjusting the three calibration trimpots on the back of the module to set the following values (in order): 1. -
Page 16: O U T P U T O F F S E T
D i s c r e t e L o w p a s s A m p l i f i e r M O D E L 1 2 2 1 C E N T R E A D J . To set the CV centre adjustment, disconnect the squarewave signal used in the previous step from the "LEVEL"... -
Page 17: Controls
Allows the amount of CV sent to the amplifier to be adjusted between -100% and +100%, with 0% at centre. L PA S L I G H T LY N A S T Y SLIGHTLY NASTY JACK COLOURS Bipolar signal output BLUE Bipolar signal input YELLOW... -
Page 18: Pcb Guide
D i s c r e t e L o w p a s s A m p l i f i e r M O D E L 1 2 2 1 P C B G U I D E LOWER BOARD - TOP UPPER BOARD - TOP P C B Gui de... - Page 19 D i s c r e t e L o w p a s s A m p l i f i e r M O D E L 1 2 2 1 P C B G U I D E LOWER BOARD - TOP UPPER BOARD - BOTTOM P C B Gui de...
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