Cumbria designs Minifilter User manual

CONTENTS

1 INTRODUCTION 2

2 PREPARATION 2

3 CIRCUIT DESCRIPTION 3

4 ASSEMBLY 4

5 TESTING 6

6 SET UP AND OPERATION 7

APPENDICES Schemat c A

Overlay B

Parts L st C

Troubleshoot ng D

Spec f cat ons E

Template F

M n f lter

DSP Aud o Processor

User Manual

M n f lter v1.0 Doc vers on 1.4 Page 2 of 14

1 Introduction

Thank you for purchas ng the Cumbr a Des gns “M n f lter” k t. Th s manual descr bes

the assembly and operat on of the M n f lter k t, even f you are a seasoned

constructor, please read th s manual and fam l ar se yourself w th the nstruct ons and

k t contents before commenc ng solder ng. If assembled carefully, th s un t w ll

prov de many years of rel able serv ce. We hope that you enjoy construct ng and

us ng your new M n f lter.

________________________________________________________________

2 Preparation

2.1 Tools

We recommend that the follow ng tools

are used dur ng assembly and test ng;

25W f ne t pped solder ng

60/40 Ros n cored solder

5” or smaller d agonal s de cutters

Small po nted nosed pl ers

Solder sucker (just n case!)

Mult meter

2.2 Conventions

The follow ng symbols are used w th n

the assembly nstruct ons to draw

attent on to cr t cal steps such as

component or entat on and ant -stat c

precaut ons. The assoc ated narrat ve

descr bes the act on requ red.

Cr t cal Step

Stat c Sens t ve

2.3 Assembly

The product on of a successful

f n shed work ng k t s dependent upon

careful component handl ng, careful

placement and good solder ng!

Don’t be tempted to rush the

construct on, even though th s s a

relat vely s mple k t, a wrongly placed

component can prov de hours of

frustrat ng fault f nd ng. Also, as th s k t

uses a double s ded Pr nted C rcu t

Board (PCB) w th through plat ng,

removal of a wrongly soldered part

can be d ff cult. Follow the assembly

nstruct ons carefully to avo d

m stakes.

2.4 Component Identification

All parts carry a coded dent ty to

descr be the r values. It s mportant to

be able to recogn se these dur ng

assembly. Capac tors have the r value

pr nted numer cally, e.g. 104 = 100nF,

103 = 10nF etc. Res stors have the r

values represented by coloured bands

– th s s a frequent source of

confus on!

To s mpl fy component dent f cat on,

the assembly notes carry the dent t es

of each component as t appears on

the dev ce. For res stors the colour

cod ng s g ven. Th s should be

referred to dur ng assembly to ensure

the r ght parts are placed n the r

respect ve pos t ons on the PCB.

2.5 Component Leads

Many of the pass ve components w ll

requ re the r leads to be formed to

al gn w th the holes on the PCB. Th s

ma nly appl es to the ax al parts such

as res stors and d odes. Form ng

component leads s eas ly done w th a

pa r of po nted nose pl ers and us ng

the hole spac ng on the PCB as a

measure. Alternat vely, small formers

made from scrap off cuts of Vero

board etc., make deal templates that

produce cons stent results. Some

parts, such as var able res stors, have

preformed leads des gned for mach ne

assembly. These w ll requ re

stra ghten ng to al gn w th the board

layout. Aga n, a pa r of po nted nose

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pl ers should be used to carefully

flatten the factory perform ng to

produce stra ght leads.

2.6 Soldering

Before apply ng solder check carefully

that the co ponent you have

placed is in the right position! Th s

s a through plated double s ded

board. Wh lst some of the pads are

very small, the area presented by the

through plat ng s more than adequate

to allow good solder flow to form

mechan cally strong good electr cal

jo nts. However, these can be d ff cult

to undo, so please double check

placement!

The major ty of problems are l kely to

be caused by solder ng faults. These

can somet mes be d ff cult to f nd. Here

are some bas c golden rules that w ll

help you to avo d poor solder jo nts;

• Clean Iron

Make sure your solder ng ron t p s n

good cond t on and t nned. A small

mo stened pad for clean ng t ps,

regularly used to w pe off excess

solder and flux, w ll ensure that your

ron performs well. Remember to t n

the ron mmed ately after each w pe.

• Clean Leads and Pads

All of the component leads and PCB

pads n th s k t are pre-t nned and

should not need clean ng before

solder ng. Please ensure that parts are

handled so as to avo d contam nat on

w th grease or f ngerpr nts.

• Soldering

Th s s the b t that can tr p up even

exper enced constructors. For the

solder to fuse w th the surfaces to be

jo ned t s necessary for them to be

hot – but not so hot as to damage the

parts! It’s as s mple as 1-2-3;

1. Place the tip of the iron against

the joint, hold it there briefly to

bring the metal surfaces up to

temperature.

2. Apply the solder allowing it to

flow smoothly onto the

surfaces.

3. Remove the iron and inspect

the new joint.

The f n shed jo nt should have a

smooth sh ny coat ng of solder. If the

jo nt s dull grey or has formed a

spher cal “blob”, apply the ron to the

jo nt, remove the old solder w th a

solder sucker and re-solder.

3 Circuit Description

3.1 General

The M n f lter c rcu t compr ses of three

sect ons; an nput ampl f er (MCP618),

a m croprocessor (dsPIC33FJ) and an

output ampl f er (LM380). The nput

ampl f er n conjunct on w th the nput

level pot VR1 enables the M n f lter to

operate w th a w de range of nput

s gnal voltages. Th s offer flex b l ty n

us ng the M n f lter, allow ng t to be

used w th low level aud o sources such

as AF pre-amp outputs w th just a few

tens of m ll volts up to h gher level

sources such as headphone outputs

wh ch may produce a volt or more of

output. The m croprocessor performs

the analogue to d g tal s gnal

convers on, the f lter ng, aud o

process ng and convers on back to

analogue to dr ve the AF power

ampl f er. The var ous funct ons of the

M n f lter are selected by ground ng the

control nputs. Ground po nts are

prov ded on the control header for use

w th external sw tch controls. To

prevent damage to the m croprocessor

t s mportant that no voltages greater

than 3.3V are appl ed to the control

nputs.

3.2 Theory of peration

At the heart of the M n f lter s a 16b t

m croprocessor w th Analogue to

D g tal Converter (ADC) and an aud o

D g tal to Analogue Converter (DAC).

The m croprocessor samples the aud o

from the nput ampl f er 11,000 t mes a

second convert ng each aud o sample

M n f lter v1.0 Doc vers on 1.4 Page 4 of 14

nto numer cal values represent ng

ampl tude. These values or "samples"

are passed to a F n te Impulse

Response (FIR) f lter that appl es

l near phase 501 tap band pass

f lter ng. The f lter algor thm s based

upon a delay l ne along wh ch samples

traverse and at each "tap" are

mult pl ed a set of data constants

called a "kernel". The results of all of

the mult pl cat ons are summed to

produce the f lter output. The f ltered

aud o samples are then steered

through the deno ser and auto-notch

processes f selected. These two

programs are almost dent cal to each

other and are short adapt ve FIR f lters

that constantly adjust the r frequency

response to track any repet t ve

(coherent) components w th n the

aud o samples. The deno ser output s

the output of the track ng f lter, wh ch

because of ts narrow bandw dth

reduces random no se. The auto-notch

output s the aud o less the output of

the track ng f lter caus ng t to remove

any constant coherent s gnals.

Processed aud o samples are then

passed to the DAC for convers on

back to an analogue voltage to dr ve

the AF power ampl f er.

4 Asse bly

The follow ng assembly sequence s recommended. Th s allows most of the smaller

parts to be held n place w th the board turned over wh lst solder ng the unders de.

4.1 Fixed Resistors (Broad tolerance band shown in capitals)

2R7 R6, R10 Red, Mauve, Black, S lver (BROWN)

100R R2 Brown, Black, Black, Black, (BROWN)

470R R3 Yellow, Mauve, Black, Black (BROWN)

1K R8 Brown, Black, Black, Brown, (BROWN)

10K R1, R4, R5, R7 Brown, Black, Black, Red, (BROWN)

47K R9 Yellow, Mauve, Black, Red, (BROWN)

4.2 Diode

F t the 1N4004 supply protect on d ode D1 not ng or entat on marked on s lk screen.

4.3 Inductor

F t the 15uH ax al nductor (resembles a large brown res stor) n pos t on L1 next to

D1. Form leads at 90 degrees close to nductor body so as to al gn w th PCB holes.

L1 15uH Brown, Green, Black, S lver

4.4 IC Sockets

Ensure correct or entat on! Match ndex cut out on socket to board pr nt ng. T p;

solder one p n only then check pos t on ng before cont nu ng. Heat the solder and

repos t on f necessary. Two 14 p n sockets are prov ded to make the 28 p n socket

requ red for IC3.

a) F t the 2x14 p n sockets n 28 p n socket pos t on for IC3.

b) F t 8 p n sockets for IC4 and IC5.

4.5 SIL Resistor RN1

The or entat on of the 10K SIL res stor s cr t cal. Install w th the text s de of the SIL

package fac ng IC3 sockets. The spot mark ng p n 1 w ll be adjacent to C8.

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M n f lter v1.0 Doc vers on 1.4 Page 5 of 14

4.6 Dipped Ceramic Capacitors

Small yellow body, 0.1” p tch. Used for general s gnal coupl ng and supply

decoupl ng. Use a magn f er to conf rm values, these are s m lar n appearance to the

10nF ceram cs!

100nF C2, C4, C5, C6, C7, C8, C9, C19 104

4.7 Dipped Ceramic Capacitors

Small yellow body, 0.1" p tch. Used for decoupl ng +12V supply nput, aud o nput

and AF ampl f er nput. Use a magn f er to conf rm values, these are s m lar n

appearance to the 100nF ceram cs!

10nF

C1, C11, C14

103

4.8 Variable Cermet Resistor

The pre-formed leads w ll requ re to be stra ghtened to f t. Remove the corrugat ons

by gently compress ng each lead w th a pa r of small pl ers.

10K Aud o Input Cermet VR1 103

4.9 +3V3 Regulator

Polar ty consc ous component, ensure that or entat on s correct. Carefully form leads

so as to be able to nsert the TO92 style regulator nto IC2 pos t on tak ng care to

al gn the body and leads w th the outl ne marked on the s lk screen.

3v3 regulator IC2 MCP1700

4.10 Polystyrene Capacitors

Rectangular body, no polar ty.

0.47uF C12, C16, C17 u47

4.11 Electrolytic Capacitors

Polar sed capac tors, observe the polar ty shown by the s lk screen. The negat ve

lead s marked by a str pe on the capac tor body.

10uF

C3, C10

100uF C13, C15

4.12 Tantalum Capacitor

Polar sed capac tor, observe the polar ty shown by the s lk screen. The pos t ve lead

s marked bold a bold l ne and a small "+" symbol.

10uF C18

4.13 Connectors

Recommended P n Header Connector or entat on s w th rear lock ng tab fac ng nto

the centre of the board. The AF Ga n header s mount w th rear tab adjacent to IC5.

a) F t the two, two p n headers +12V, AF, LS

b) F t the three way AF Ga n header AF_GAIN

c) F t the twelve way Controls header

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M n f lter v1.0 Doc vers on 1.4 Page 6 of 14

4.14 +5V Regulator

Polar ty consc ous component, ensure that or entat on s correct. The regulator s

mounted vert cally w th the metal face towards the outs de edge of the PCB. Heats nk

not requ red.

+5V regulator IC1 MC7805CT

4.15 Integrated Circuits

Stat c sens t ve parts. D scharge yourself to ground before handl ng. Avo d wear ng

stat c generat ng cloth ng (e.g. wool, man made f bres etc) dur ng assembly.

Correct or entat on s essent al. IC p ns w ll need to be gently formed for correct

al gnment before nsert on nto sockets. IC p ns can be pushed nwards by plac ng the

dev ce on ts’ s de on a f rm surface, and gently press ng the body down aga nst the

p ns. When nsert ng parts, take care to check p n al gnment to prevent damage.

a) Insert IC3 dsPIC33F128GP802 Processor (28 p n DIL)

b) Insert IC4 MCP618 Operat onal Ampl f er

c) Insert IC5 LM380N-8 AF Power Ampl f er

4.16 Connector Assemblies

Connector shells and p ns are suppl ed to allow connect on of power and s gnal l nes

to the M crocode DSP. The use of good qual ty, colour coded, heat res stant, mult

stranded w re s recommended. To avo d acc dents, a colour code convent on should

be chosen to represent funct on, e.g. Red +ve supply, Black ground, str ped colours

controls etc.

The connector assembl es compr se of two components; the shell and the p ns. To

term nate a conductor f rst str p back about 2mm of nsulat on and t n the exposed

w re. Place the t nned end of the w re nto a p n such that the t nned w re s ts ns de

the nner pa r of tabs and the nsulat on s ts w th n the outer tabs. W th small po nted

nose pl ers carefully compress the outer tabs onto the nsulat on to hold the w re.

Repeat th s w th the nner tabs to gr p the exposed conductor. Very carefully solder

the exposed conductor n place tak ng care not to allow solder to flow onto the

lock ng tab.

F nally, nsert the p n nto the shell w th the small lock ng tab or entated to the face of

the shell w th the small cut outs. Push home unt l the lock ng tab snaps nto the cut

out. Should you need to remove a p n, gently press the lock ng tab n w th a small

screwdr ver or the end of a pa r of po nted nose pl ers. The p n w ll be released and

can be pulled out of the shell.

Asse bly co plete, well done! Now carefully check the co ponent

place ent and soldering work before oving on to testing.

5 TESTING

Before connect ng your M n f lter to your power supply for the f rst t me, carry out

these s mple checks to conf rm that the supply ra ls are clear of shorts to ground.

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5.1 Electrical Tests

5.1.1 +12 Volt Input

W th a mult meter set to res stance, place the Red meter lead onto +12v and the

Black to Ground and check for a h gh res stance. Prov d ng there s not a short c rcu t

then all s well.

5.1.2 +5 Volt Rail

Carry out the res stance test on the output s de of the regulator (IC1) to check the

+5v ra l ensur ng that t s clear of shorts to ground.

5.1.3 +3.3 Volt Rail

Carry out the res stance test on the output s de of the regulator (IC2) to check the

+3.3v ra l ensur ng that t s clear of shorts to ground.

5.1.4 Powering Up

Connect a loudspeaker and AF ga n potent ometer (10K log) as shown n F g.1

6 SET UP AND OPERATION

6.1 Power and Audio Connections

6.1.1 Loud Speaker

The aud o output should be connected to a 4 to 8 Ohm mpedance loudspeaker.

6.1.2 AF Gain Potentio eter

The AF Ga n potent ometer s connected as shown above. Th s w ll produce

ncreas ng aud o output w th clockw se rotat on.

6.1.3 AF Input

A screened aud o cable should be used to connect the s gnal source to the AF Input

connector.

AF Source

S gnal

Screen

Speaker

Volume

Control

(front)

Ground

+12V

Controls

Fig. 1 Power and Aud o Connect ons

M n f lter v1.0 Doc vers on 1.4 Page 8 of 14

6.1.4 Power

Connect +12V to the power header observ ng the polar ty shown above. Advanc ng

the AF Ga n control should produce a not ceable h ss from the loudspeaker. If

noth ng s heard d sconnect and check the supply, loudspeaker and AF Ga n control

w r ng. Check the or entat on and placement of all ICs and electrolyt c capac tors.

6.2 Controls Header

GND

AN GND

DEN

GND

GRP

GND

FL5

FL4

FL3

FL2

FL1

GND Ground supply p n for external sw tch

DEN Deno ser, h gh = deno ser off , low = deno ser on

GND Ground supply p n for external sw tch

GRP F lter Group, h gh = w de, low = narrow

FL1..FL4 F lter select b ts

6.2.1 Filter Selection Controls

1=Open c rcu t or +3.3V log c h gh

0=Ground or log c low

GRP

FL5

FL4

FL3

FL2 FL1

FILTER

W de F lter Group

1 1 1 1 1 1 300 - 2700Hz

1 1 1 1 1 0 300 - 2400Hz

1 1 1 1 0 1 300 - 2200Hz

1 1 1 0 1 1 400 - 2200Hz

1 1 0 1 1 1 400 - 2100Hz

1 0 1 1 1 1 450 - 2000Hz

Narrow F lter Group

0 1 1 1 1 1 400 - 900Hz

0 1 1 1 1 0 450 - 850Hz

0 1 1 1 0 1 500 - 800Hz

0 1 1 0 1 1 600 - 800Hz

0 1 0 1 1 1 500 - 700Hz

0 0 1 1 1 1 400 - 600Hz

6.2.2 Denoiser and Auto-notch Controls

1=Open c rcu t or +3.3V log c h gh

0=Ground or log c low

AN DEN Aud o Process ng

1 1 No aud o process ng

1 0 Deno ser

0 1 Auto-notch

0 0 Deno ser and Auto-notch

6.3 Control ptions

I portant! All M n f lter control nputs must be treated as "voltage free" nputs. In

other words they should only be operated by sw tches or dev ces such as open

collector trans stors so as not to apply an external voltage to the control port. W th no

M n f lter v1.0 Doc vers on 1.4 Page 9 of 14

control cond t ons appl ed all p ns are held h gh at 3.3V by the 10K SIL pull up

res stor. The ground p ns prov ded on the control port should be used as the sw tched

0V reference to pull any p n nto a log c low state.

The flex b l ty of the s mple control nterface allows many control scheme opt ons.

Several examples are g ven below.

6.3.1 Switched Control Sche es

Fig.2 Bas c Controls

A s ngle pole 6 way rotary sw tch and three toggle sw tches are used to access all of

the control states.

Fig.3 Us ng a rotary sw tch for Aud o Process ng controls

A 2 pole 4 way rotary sw tch replaces two toggle sw tches for Deno ser and Auto-

notch control.

M n f lter v1.0 Doc vers on 1.4 Page 10 of 14

Fig.4 Set of f lters from both groups selected by rotary sw tch

A two pole rotary sw tch prov des select on of f lters from both w de and narrow f lter

groups.

6.3.2 Microprocessor Control

The f lter and aud o process ng b ts may be controlled by an 8 b t w de port of an

external m croprocessor. Care must be taken to ensure that the log c h gh voltage of

+3.3V used by the M n f lter s not exceeded. If the external m croprocessor uses

3.3V log c then d rect connect on s poss ble. Ensure that the m croprocessor and

the M n f lter share a common ground.

If the external m croprocessor log c voltage s +5V then prov s on must be made to

protect the +3.3V control port of the M n f lter. Th s s conven ently done w th general

purpose d odes (1N4148, BAV21 etc) placed between the external m croprocessor

port and the M n f lter control port. The d odes are or ented w th the r cathodes (band)

towards the h gher voltage external m croprocessor port to block any current from

flow ng nto the M n f lter port dur ng a log c h gh state. The SIL pull up res stor on the

M n f lter control port w ll hold the control nputs at +3.3V.

6.4 Input Level

The nput level s set by adjust ng VR1, start w th VR1 set fully ant clockw se. If

connect ng to a po nt where the level s var able, e.g. a headphone socket on a

rece ver whose output s set by the rece ver AF ga n control, adjust the rece ver

output to normal l sten ng level. Next, connect the M n f lter and adjust VR1 slowly

clockw se (ensur ng the M n f lter AF Ga n s turned up so as to produce an output)

unt l aud o s heard. Cont nue unt l the aud o d storts sl ghtly (cl pp ng). Back off VR1

below the cl pp ng level.

If the M n f lter s to be used as a replacement aud o sect on n a rece ver t should be

connected to the output of the AF pre-amp stage before the rece ver's AF ga n

control. The rece ver's AF ga n control may be used as the M n f lter AF ga n control

by w r ng t as shown n F g.1.

M n f lter v1.0 Doc vers on 1.4 Page 11 of 14

6.5 perating Notes

The follow ng po nts w ll help you to get the best performance from your M n f lter;

• Set the M n f lter nput level just below that wh ch causes cl pp ng - ev dent as

a "crackl ng" on aud o peaks. Ma nta n ng a h gh nput level mproves the

performance of the deno ser and auto-notch.

• The deno ser operates on random no se only, any no se source w th a cycl cal

content w ll not be suppressed.

• Use the steep edges of the aud o f lters to remove adjacent s gnals that are

encroach ng nto the passband. For example, f an adjacent s gnal s caus ng

h gh frequency aud o nterference w th n the passband sw tch to the next

narrower f lter to lower the cut off frequency.

M n f lter v1.0 Doc vers on 1.4 Page 12 of 14

Appendix A Sche atic

Appendix B Co ponent Overlay

M n f lter v1.0 Doc vers on 1.4 Page 13 of 14

Appendix C Minifilter Version 1.0 Parts List

Res stors

2 2R7 R6, R10

1 100R R2

1 470R R3

1 1K R8

4 10K R1, R4, R5, R7

1 47K R9

1 10K CERMET TRIMMER VR1

1 10kx8 SIL RESISTOR RN1

Capac tors

3 10nF CERAMIC C1, C11, C14

8 100nF CERAMIC C2, C4, C5, C6, C7, C8, C9, C19

3 0.47uF POLYSTYRENE C12, C16, C17

1 10uF TANTALUM C18

2 10uF ELECTROLYTIC C3, C10

2 100uF ELECTROLYTIC C13, C15

Inductor

1 15uH CHOKE L1

Sem conductors

1 7805 +5V REGULATOR IC1

1 MCP1700 +3V3 REGULATOR IC2

1 DSPIC33FJ128GP802 PROCESSOR IC3

1 MCP618P OP AMP IC4

1 LM380N-8 AF POWER AMP IC5

1 1N4004 DIODE D1

Connectors

3 2 WAY HEADER +12V, AF, LS

1 3 WAY HEADER AF_GAIN

1 12 WAY HEADER CONTROLS

3 2 WAY SHELLS

1 3 WAY SHELL

1 12 WAY SHELL

21 CRIMP PINS

IC Sockets

2 8 PIN DIL IC4, IC5

2 14 PIN DIL IC3

M sc

PCB M n f lter v1.0

APPENDIX D Specifications

D mens ons W66mm, H47mm, D22mm (Overall w th connectors f tted)

Supply Voltage Nom nal +10V to +20V

Supply Current 54mA

Operat ng Temperature -20ºC to +70ºC

M n f lter v1.0 Doc vers on 1.4 Page 14 of 14

Appendix E Troubleshooting

Sy pto Action

No audio output • Confir supply on pin 7 and ground on

pin 4 of IC5

• Check IC5 place ent, soldering and

orientation, check soldering and

orientation of electrolytics

• Check soldering of AF Gain header and

wiring to AF gain pot

• Confir continuity and soldering of C16

and R9 and pin 23 of IC3

Controls not functioning

correctly

• Check soldering on controls header and

associated IC3 pins

• Re ove controls and confir input pins

at 3.3V

• Check orientation of RN1

• Check ground condition is being

applied as per tables in Section 6.2

Audio distorted • Reduce input level by turning VR1

anticlockwise

• Check orientation of C18

Appendix F Mark through te plate for preparing enclosure. Use centres as

guides, check and edit positions before drilling and cutting.

END

Cumbria Designs Minifilter User manual

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