MTU K-1002-2 User manual

l|ioro

Teehnology

IInHmlted

K-1

002-2

8

Blr

AUDIO

DIGITAL

TO ANALOG

CONVERTER

FOR COMMODORE

PET.2OO1

HARDWARE

MANUAL

JULY

1979

coHrRIGlrT

rrcnrcE

197.9

This

manual

is

crcpyrighted. Ttris includes

the verbal

description,

PC artworK,

diagnostic

programsi,

cgnraLional

prograns,

and

specification

sheets. The custqner

rnay

make machine readable

copies of

the software

routines for use only oT

corqr.rters cr'med

directly by him

or

his

scmpany.

lftrey

nay not be reproduced

for

use

with

systems sold

or rented.

Micro Techrnlogy

Unlimited

841

Galaxy

Way

PO Box

4595

llanchester,

NlI 03108

K.1002.2

UNPACKING AND INSTALLATION

The K-1002-2

8

Bit

Audio System

for the

PET

is

a carefu'l'ly

engineered,

manufactured,

and

tested

product

that should operate

perfectly

when handled

and

installed accord'ing to the

following instructions.

Since CMOS integrated

circuits

are used on the board, damage from

static

discharge

is

possjble.

When

handling

the

board,

always

pick

it

up

by

the

output

jack

which is connected to

ground.

Before

plugging

it

jnto

or

removing

it from the PET,

discharge

yourself

to

the PET

case

first.

Installation is

quite

simple,

merely

plug

the

unjt onto

the

user

port

and

second cassette

port

of

the PET.

If other accessories

or

a second

cassette

unit

are

to

be

used,

p'lug

these onto the

edge

fingers

of the K-1002-2.

Our unit

does

not load any

of the user

port

signals

signifjcantly because

of the

CMOS logic

ut

jl

ized.

Any 4,

8, or

16

ohm

speaker

may be

p'lugged

into

the RCA

phono

jack

at

the

rear

of the board. Alternat'ive1y

an

aud'io cable

may

be

p'lugged

in and an

external anplifjer used

for

more

volume such as at

a club

meetjng

or show.

If the K-1002-2 Musjc Software

package

has

been

purchased,

follow

the

instructions included wjth the

cassette

to

verify that

the board is

working.

0therwise

enter the following

BASIC

program

and RUN it:

A=0: B=255:

C=59459

POKE

C,A: POKE C,B: G0T0 20

The resulting

sound should

resemble that

of a

misfiring race car. The volure

control on the board should have a

range from

complete

s'ilence

to

slightly above

the

point

of distortion.

Note that

the

CB2 s'igna1

from the 6522

UIA

is

also connected

'into

the

audjo

anpl

if ier

circu'itry.

Theref

ore any

game

programs

or simple

music

programs

that

use

thjs

signal to

generate

sound will still

be usable with

the K-1002-2. One of

these

prograns

could

also

be

used to check out

the board.

This

completes checkout of the

I Bit Audjo System. If any

problsns

are

experienced,

see

the sectjon

on

troubleshootjng

before returning

the board

to the

factory.

10

20

SP

ECIF

ICATIONS

Phys'ica'l Sjze:

5 inches wide

by 4

inches deep overall by 1.13 inches

thick

Connections:

I 24

p'in

edge

connector, I

12

edge connector, 1

set of

24

edge

fingers, and one

set

of

12 edge

f ingers.

All

s'ignals are

fed through

frqn

the edge connectors to

the corresponding

edge

fingers.

DAC section:

B bits, offset

binary

encoded,

typ'ica1 1/4 LSB linearity,

guarenteed

monoton'ic, 5 vol

t

swi

ng, 6.25K output

impedance, 5

vol

t

supply

'is

filtered

and used as

the

reference voltage.

Fil ter section:

6

po1es,

0.5dB Chebyshev

response,

cutoff

f

requency

'is

3.5kHz.

Po,ver

anp

sect

j

on:

power

output: 150MW

jnto

1.6 ohms,

300MW

into 8

olms, 500fvlW

'into

4

ohms.

Amp'l

if

jer

response

is

flat wjthin 3dB frqn 30 to ZAkHz

wjth

an

8

ohm

load. Distortjon at full

power

output

into

B

ohms

at

lkHz

is less than &.

Porver requ'irements:

Single

+5

volt

supply.

Ripple and noise within the aud'io

range should be

less

than

2S4V.

Pover Consumption:

Quiescent

current

drain is less than 50MA. Worst

case

drain

at

f

ul

I

power,

4

ohr

I

oad,

an

d

square wave output i s 30ft1A .

Signal

loading: Less

than L0uA

and

10pF load'ing on

the 8 b'inary inputs.

CBz

input

is

loaded

by

240<

to

ground.

P IN

CONNEgTIONS

(

i ndustry standard numberi ng)

SIGNAL

CONNEffM

1

2

3

4

5

6

7

8

9

t0

11

I2

S IGNAL

F.T

.

F.T .

F.T

.

F.T

.

F.T

.

F.T.

F.T

.

F.T.

F.T

.

F.T .

GROI,FID

GROLT{D

S IS'IAL CONNETTOR S IS{AL

F.T.

F.T

.

DATA B IT O

DATA B IT 1

DATA B IT 2

DATA B IT 3

DATA B IT

4

DATA B

IT

5

DATA

B

IT 6

DATA B

IT

7

cB2

F.T.

GR, OUN

D

+5

VOLTS

F

.T.

F

.T.

F.T.

A

B

D

E

F

H

J

K

L

M

N

CONNE

ffOR

A

B

c

D

E

F

POWER

CONNECTOR

***

F.T.

***

N.C

.

S

IGNAL

POWER

N.C .

N.C

.

N.C

.

N.C

.

N.C

.

N.C

.

1

I

2

3

4

5

6

2

Feed Through to

correspondi

ng edge

f ingers,

no on-board connect'ion

No connection

to edge

fingers

or

anything else

PRINCIPLES

OF OPERATION

The

K-I002-Z

I Bit Aud'io

System

consists

of

three dist'inct

sections.

The

8

bjt digital-to-analog

converter

(DAC)

accepts an 8 b'it b'inary input from the

user

port

on

the

PET

and

produces

a

DC voltage

d'irectly

proportional

to the

unsigned

binary value of the

input. The

6-po1e lowpass filter blocks

all sanpling

di

stortion

frequencjes

above

approx'imate'ly

3.5kHz. Thi

s

f il ter

j

s necessary

f

or

clean sounding

music from the

DAC. The audio

power

anp'lifier

boosts

the filter

output signa'l

to the level required

for drjv'ing a speaker. The

CB2

on

the

PET

user

port

is also tied'into the

anplifier circuitry. A

volume

control determines

the

gain

of

the amplifjer

and

thus

the volume of

the

sound reproduced'in the

speaker. In order for the board to

operate solely from

a

s'ing1e 5 volt

power

supply,

several

jnnovative

circujt techn'iques

have

been incorporated.

Looking at

the

DAC

sectjon

first

(1eft portjon

of

the

schematic

draw'ing),

it

is seen

that

the

weighted

resjstor

method of conversion is used.

The

Clv1OS

buffers

in Ul

and

U2 make

very

good

analog

switches

which switch thejr outputs between

exactly

lfound

and

exactly

the

supp'ly voltage

(+5

volts)

jn

response to the input

s'igna1.

The

only error

in thjs

switching act'ion

is

a

f inite

output impedance of

approximatel

y

200 ohms. Ctvl0S buff

ers,

rather

than

i nverters, are used because

the

two stages of

"gain"

internally

assures complete switching of

the output

even

jf

the

input

swings less than 5

volts.

The DAC network

produces

an output vo'ltage

d'irectly wi

th

a source

impedance

of approximately

6.25K. tl'ith

al

I

zeroes

input,

the output is zero

volts; with all ones

input, the

output

is 5

volts.

Loading

the

output

has no

effect on

ljnearity but it

will

reduce the

s'igna'l swing.

In order to

insure

accurate, monotonic

performance

of

the DAC, the most

si

gn'if

jcant

bit

js

actually

f

our ClvlOS

gates

and

four 51K res'istors in

parallel

whjle

the next most sign'ificant b'it is two in

paralle'I.

The remain'ing

b'its

are

single

gates

sjnce

the

ratio of the wejghting resjstors to the

gate

output

'impedance

is

large

enough

to ignore.

By

using

para'l'lel

and series combinations

of

51K

resistors for the most

sjgnificant

5

bits,

jt'is

possible

to

use

relatively

jnaccurate

res'istors

in the DAC

and still achieve

1/4 LSB linearity wh'ich

js

about

.4.

This'is due to statistjcal averag'ing

among

the resistors,

particularly

the

critical most

significant

b'it. Even

so,

factory assembled units have

had the 51K

resjstors

matched to w'ithin 1%. Although the

more common

R-ZR

res'istor

ladder

network could have

been

used, more resjstors would have been

required to

get

the

sane

degnee

of statist'ical match'ing.

An integrated

circuit

DAC

was

not

practical

sjnce

all that are currently ava'ilable require a

negative

supply voltage

for

either

the

DAC

itself

or

for

a current-to-voltage

converter

operational

anplifier.

Note

that the 5 volt

power

supp'ly

is fjltered and used as a

reference

for

the

DAC.

Wh'ile small anounts

of

noise

are

fi'ltered

out, 60Hz ripp'le on

the 5

volt

supply

is

I

jkely

to

result

in

hum

from the

speaker.

The filter

c'ircu'it is where things start

getting

unconventional.

The f ilter

actually

consists of

three.two-po1e

stages connected

'in

cascade.

Each section

js

a

resonant lowpass filter,

'i.e.,

the response

curve

may

peak

somewhat

just

before

cutoff .

t^lith

proper

sel ection of section cutoff

frequenci es and

Q

f

actors

(peaking),

a very nearly

flat

passband

and sharp

cutoff

is

obtained.

Passband

ri

pple

'is

less

than .5dB and

the

cutoff slope

is such

that

30dB attenuat

jon 'is

obta'ined

at

just

1.35 tjmes the

cutoff

frequency of 3.5kHz.

Note

that the

5

volt

sw'ing of the

DAC

'is

reduced

to

about

2,5 volts through

the

filter by virtue of

the

22W,'input

resistor to

the f irst

fjlter

stage.

Each filter

sectjon'is

implsnented as a

biquadratic

fjlter which

consjsts

of

an

invertjng

surnming amplif

jern

d

leaky

inteE"fEEb7i-ffi? an

ideal

integrator all

connected'in a

1oop. Although three operational anplifiers

are

required

for

the

ci

rcu'it,

'its

advantages are

many. In

parti

cul ar,

hi

gh

Q

f

actors are

possi

bl

e

wi

th

modest

anpf

ifier

gain.

In addjtion, sensjtivity of the response curve

to

component tolerance'is

very

1ol. These

characteristics allol

the use of

linearly

bjased

Cl{S

gates

as

jnverting

operational anpf

if iers.

Perf

ormance

of the

f ilter

using

the

CtflS

gates

'is

indist'inguishable from the

performance

using

true

op-anps

such

as

the

741.

See

the

National Semiconductor

CISS

data

book for

more

jnformation

on

linear

CIOS applicat'ions.

3

. Ihg

audio

power

arpliflef is-a

spegia]

high

efficiency desigrr

that

allo,'ls

a

significant

power

output

with

only a single

5 vo'lt

power

supply-and

no output

transf

ormer. Three

para'l1e'l

connected

CiOS

gates provide

most

of the

voltage

anplification

in the

circujt as

well

as

presenting

a high input

impedance

and

having a moderately 1or

output

impedance.

The

output

stage is

fully

comp'lenentary

and

incorporates

considerable local

feedback

of its

orn.

The

voltage

gain

of

the

outptt stage is

approximately

18.

0verall

feedback

from the

output back to

the

vo'ltage anplifier input comp'letes

the loop

and

gives

a closed

loop

gain

of

about

3.5

with

maximum

volume.

The 92P1,01

(NPN)

and 92PU51.

(Pl'lP)

output

transistors

actually contain a one-anp capability

transjstor

chip

in

a

modified

T0-92

plast'ic

case.

Thjs is

ttp sane chip as used in

the

Motorola

MPSttrL and

MPStlSl

plast'ic

power

transistors. Wjth an 8

ohn

'load,

the

anp'l

if ier

outprt can

swing

to

within

.3 volts of the

5

volt supply or

gnound

before

saturating.

The

2.7

otm

resistor

and

.luF capacitor

(R46

and C9) accross

the outpt

prevent poss'ible

osci'llation

w'ith'induct'ive'loads.

R39, R40, 01,

and

D2 form

a

bjas

network

wh'ich allols

a

couple

of mjlliamps

to

flol in

the

output trans'istors at

all

times

to minimize

class-B

crossover distortion. R45

mixes the CB2

s'igna1

from the

connector

in

with

the

filtered DAC

output

to

allor continued

use of

this

s'igrra1 with

existing

game

and simple

music

prograns.

TROUB

LESHOOT

ING

D'iagnosing

problems

with the K-1002-2 board

is

fairly

simp'le because

of

the

un'id'irectional

s'igna1

flor

and

minimal

interaction anong circujt

components.

If

the

board is

completely'inoperative, first do a thorough

visual inspect'ion

of the

board. Look on the sol

der

si de of the board for

component

I

eads that may be

bent

and

shorting out to adjacent

pads

or

PC

runs. Check for loose

components

and the

possj

bi 1 ity

of a col

d

sol

der

joi

nt.

If careful inspection fails to turn

up anything,

enter and

run

the

prognam

given

earl

ir. Then

using a scope or

anpl

if ien/speaker

if a

scope

is

unavajl

ab]e,

find out where

the

sigal is being lost.

The first

point

to

check

is

the node

where all of

the DAC resistors

are

tied together.

The signral should be

a square

wave

modulated at a 60Hz rate

(ca'used

by

timr

interrupts in

the PET)

with

ground

and

+5

voltage

levels.

the

output of the first filter

section which'is

U3-8.

The

waveform should

be

sorneylhat rounded wjth

voltage

levels

of

about

L.25

and

3.75 volts.

The

next stage output

(U3{)

should

be

ssns{hat less rounded

w'ith

a hint of

ringing

on

the

square wave

edges.

Again the

signa'l

levels

(1ess

ringing) should

be 1.25

snd 3.75 volts. The

'last

stage output

(U4-6)

has

cons'iderable

ringing

at a

little

over 3kHz but

still

the sane

voltage levels. If

the sigrtal

js

lost

anylhere

jn

the fjlter

or

the

voltage

levels

are

cons'iderably

offset

(greater

than

.5 volt

deviat'ion)

from thejr

proper

valrcs first

wiggle

all

associ ated components

to see

'if

anythi

ng

changes. If

thi

s

f

a'i1s, the associ

ated

CD4069

(the

74C04

is

an equivalent) should

be

replaced.

Be

sure to

use a CD4069

or

a

7464;

other varieties oF inverters may

not

be

suitable

f

or

I

inear operation

or

may have too h'igh

an

internal

impedance.

If

the

problsn

is in the

power

amp'l

'if

ier, first measure the

output

trans'istor

collector

voltage

(tfte

little tabs

sticking out the top of the transistors

are the

collectors)w'ith

no sigrra'|. This voltage

should

be

within a

quarter

volt

of

2.5

volts.

If it is off

consjderably, one of the

4

transistors in the output

stage

may be shorted or open or the CttOS voltage

anpl

if ier may be bad. Temporarily

cut

the

l

jne

running

from

U4€, 10,

and

12 to the

junction

of

Dl

and

D2

and measure

the

col

I

ector

vol tage agai n. If it i

s

now

centered, the CI'OS is

bad;

otherw'ise

one

or

more transistors

are

bad

or one of the

biming resistors

(R38-R43)

'is

open.

The

anplifier

is only

partially protected

fnom outout shorts so exercise care

in

connecting

the speaker

and

don't run the

unit with

the volune

full

up

when there

'is

an obvious

probl

sn such as a speaker l'ine short.

If

the

custoner

is

unable to f ind the

prob'lan,

return

the

un'it to the factory

f

or

servicing

a'long w'ith a description of the malfunct'ion.

This is

a

rel

at'ive1y

simple

board and

factory

repair

can usually

be

accomplished

in

a couple of days.

4

qJAN.

1

2

1

2

t3

I

3

1

4

L2

1

2

L

1

2

6

2

1

2

1

2

I

1

t

1

PART

2.7

ff'tti

10 c}tM

100 fir{

1K

10K

51K

(MATfiED

T0

390K

820(

22W.

24U,

1Ofr

180K

13(X

680K

I.M

POT

220t.F D 6V ELEgt

47OPF

PO.Y

CAP

.lUFD

L?U ZsU

1000r,F

10v ELEcr

11,14148 DIOIES

Ptu222

Pr{2S7

92

Pml

92

PU51

cD4050

cD4069

PHONO PLUG

PC

BOARD

CONN PC SINGLE

6

CONN

PC

DUAL

1.2

K-1002.2

PET

PARTS

LIST

DES

IGI{ATION

R46

R44

R41, R43

R42

R39,

R40

11) Rl

-

R13

Rt4

R15

-

R17

R29

R21,

R34, R36, R45

R18,

R19, R23

-

R26,

R28, R30

-

R33, R37

R35

R20, R22

R27

R47

c1o, c1l

cl-c6

c7; ce

c8

01, D2

q2

Q1

Q3

Q4

ul, u2

u3, u4

.156SP

5

nffiffiffi

[*'-]

f-=-l

ffiffi

f-:"1

[Hffi

3ffiffi,ffi

i*,.,?Rr1b

Hoffi%

6

Rr9

tooK

t@K

R3+

z40K

R20

rhx

I

lhri

'3rDsr>Or2

lr/z

r

5lK

R3

5lK

I

h\

.,V

f--.F>

I

t'/'

l--,1h.>

cw,t- L

I

Lt'

-----t-,,h>

W

+

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,ror*,

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f,

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,|ib,

L"'

oco'Nt-r ,.S

coNNt-lt

D'.-

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coNNt-F |u}\

o-'V'

COMN

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o-ll

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S9!!l-tF"

t-.-

co&^ll-C luz\

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W

I

,-L

couil/

-n

ct

47OPF

R4

5tK

Rlt

5rK

Rra Rl3

stK

slK

Rrl

Rt6

azoK azo(

DATA

8

/f

7

pATt

B/T

4

D/rt

8/T

5

2^T/l

8/7 |

2/T/4 B

/T

3

DATA I

/T

2

rloK

'F

f/tfFR

ouT

+

| r ,lUO/o

R46

2.7

JL

l2v.

RAW

DAC OUT

R44

lo4

DA.A

a/7

95

c82

S/6MAt

crl

2?Orf

Rtz

R5

Rrg

RZ1

R23

loo^

t2

caNN/- //.

/2

coNtu2-

A

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K-ICA2.Z

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DAC

rOR

PfT

MTU K-1002-2 User manual

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