PAiA Electronics 9305 User's Manual

TubeHead

Model 9305

Assembly and Using Manual

If you love vacuum tubes, here’s a device that’s

got your name on it. The TubeHead is a low-cost,

two-channel vacuum tube pre-amplifier with a

twist. The twist is that this circuit is designed

to be adjustable from crisp solid-state

transparency to an exaggerated caricature of tube

amp warmth. In between these extremes, you’ll

find tonal coloring options than you’ve never had

before and sounds that mimic every tube amp you

ever heard. This circuit is so versatile that you

may use it in place of compressors, limiters and

sustainers even though, technically, it is none of

these.

(c) 1993 PAiA Electronics, Inc.

Portions of this document are excerpted from

an article in the December 1993 issue of

Electronic Musician magazine, copyright 1993,

and are reprinted by permission of the Publisher.

TubeHead 1

ASSEMBLING THE TubeHead

Before beginning assembly, go through the manual.
Look at the drawings. Feel the parts. You’re
naturally eager to plunge right in, but take a few
deep breaths first.

Notice that each step in the manual is marked with
a checkoff box like this:

DESIGNATION VALUE COLOR CODE
( ) R27 100 ohm brown-black-brown

Checking off each step as you do it may seem
silly and ritualistic, but it greatly decreases the
chance of omitting a step and also provides
some gratification and reward as each step is
completed.

Numbered figures are printed in the Illustrations
Supplement in the center of this manual. These pages
may be removed for easy reference during assembly.

THE CIRCUIT BOARD

The TubeHead is built on a single-sided circuit
board. Before beginning assembly, clean oxidation
from the copper side of the circuit board using
scouring cleanser and water. The copper should be
bright and shiny before beginning assembly.

Once you begin putting parts on the circuit board,
it’s a good idea to continue until all the parts
are mounted. Stopping overnight may allow the
copper to oxidize and make soldering more difficult.

TOOLS

You’ll need a minimum of tools to assemble the kit

- a small pair of diagonal wire cutters and pliers,
screwdriver, sharp knife, ruler, soldering iron and
solder.

Modern electronic components are small (in case you
hadn’t noticed) and values marked on the part are
often difficult to see. Another handy tool for
your bench will be a good magnifying glass. Also

2 TubeHead

use the magnifier to examine each solder joint as
it is made to make sure that it doesn’t have any of
the problems described in the SOLDERING section
which follows.

SOLDERING

Select a soldering iron with a small tip and a
power rating not more than 35 watts. Soldering
guns are completely unacceptable for assembling
solid state equipment because the large magnetic
field they generate can damage components.

Use only rosin core solder (acid core solder is for
plumbing, not electronics work). A proper solder
joint has just enough solder to cover the soldering
pad and about 1/16-inch of lead passing through it.
There are two improper connections to beware of:
Using too little solder will sometimes result in a
connection which appears to be soldered when
actually there is a layer of flux insulating the
component lead from the solder bead. This
situation can be cured by reheating the joint and
applying more solder. If too much solder is used
on a joint there is the danger that a conducting
bridge of excess solder will flow between adjacent
circuit board conductors forming a short circuit.
Accidental bridges can be cleaned off by holding
the board upside down and flowing the excess solder
off onto a clean, hot soldering iron.

Use care when mounting all components. Never force
a component into place.

TubeHead 3

WIRE JUMPERS

Assembly begins by forming and installing the
eleven wire jumpers indicated by bold lines on the
circuit board parts placement designators and the
illustration to the right. For each jumper,
cut a length of the bare wire supplied by
measuring it against the distance between the
circuit board holes and adding about 1/2". Bend
1/4" of each end down and push through the circuit
board holes. Press the jumper fully against the
board and solder both ends. Trim off excess wire
flush with the solder joint.

Notice that three of the jumpers will be covered
with the insulating sleeving provided. Cut a
piece of sleeving slightly shorter than the
distance between the holes and slip it over the
jumper before bending the wire ends down and
placing.

( ) As outlined above, form and install the

eleven wire jumpers used on the circuit
board.

RESISTORS

Solder each resistor in place following the
parts placement designators printed on the circuit
board and the assembly drawing Fig 1. Note that
resistors are nonpolarized and may be mounted with
either lead in either of the corresponding holes.
Before mounting each resistor, bend its leads so
that they are at a right angle to the body of the
part. Put the leads through the holes and then
push the resistor firmly into place. Cinch the
resistor in place by bending the leads on the
solder side of the board out to an angle of about
45 degrees. Solder both ends of each resistor in
place as you install it. Clip each lead flush
with the solder joint as the joint is made.

4 TubeHead

DESIGNATION VALUE COLOR CODE A-B-C

( ) R1 100 ohm brown-black-brown
( ) R3 100 ohm brown-black-brown
( ) R4 33K orange-orange-orange
( ) R5 33K orange-orange-orange
( ) R12 22K red-red-orange
( ) R22 330 ohm orange-orange-brown
( ) R27 150K brown-green-yellow
( ) R28 8200 grey-red-red
( ) R29 1K brown-black-red
( ) R40 22K red-red-orange
( ) R50 330 orange-orange-brown
( ) R55 150K brown-green-yellow
( ) R56 8200 grey-red-red

listed below: 10K brown-black-orange

( ) R6 ( ) R30 ( ) R33
( ) R34 ( ) R61

listed below: 100K brown-black-yellow

( ) R9 ( ) R37 ( ) R62
( ) R63

listed below: 270K red-violet-yellow

( ) R10 ( ) R11 ( ) R38
( ) R39

listed below: 82K grey-red-orange

( ) R13 ( ) R14 ( ) R41
( ) R42

listed below: 470K yellow-violet-yellow

( ) R17 ( ) R25 ( ) R45
( ) R53

listed below: 47K yellow-violet-orange

( ) R19 ( ) R21 ( ) R26
( ) R47 ( ) R49 ( ) R54

TubeHead 5

DESIGNATION VALUE COLOR CODE A-B-C

listed below: 2700 red-violet-red

( ) R31 ( ) R32 ( ) R59
( ) R60

The following resistors are installed vertically
on the circuit board.

( ) R2 330 ohm orange-orange-brown
( ) R57 100 ohm brown-black-brown
( ) R58 100 ohm brown-black-brown

CERAMIC DISK CAPACITORS

Some of the capacitors used in the TubeHead are
non-polarized ceramic disks, either lead can go in
either of the holes on the circuit board. Leads
are already parallel to one another but still may
need to be bent slightly to match the spacing of
the circuit board holes. Like the resistors, push
the leads through the holes in the board and push
the part against the circuit board as far as it
wants to go. Don’t force it, it’s OK if it sits a
little off the board.

Capacitors are often marked with obscure codes
that indicate their values. The 1, 2 or 3 digit
number that specifies value may be preceded or
followed by letters indicating such things as
tolerance. If you get confused about which
capacitors are which, it may help to group them by
same type and check them against quantities on the
packing list at the end of this manual.

DESIGNATION VALUE MARKING

( ) C7 220 pF 221
( ) C11 .01 uF 103
( ) C14 20 pF 20
( ) C16 5 pF 5
( ) C20 .05 uF 503
( ) C21 .01 uF 103
( ) C24 20 pF 20
( ) C26 5 pF 5

6 TubeHead

TRIMMER POTENTIOMETERS

Mount the two trimmer potentiometers by inserting
their three pins into the holes provided. Press
them down until the “shoulders” of the solder pins
are resting on the surface of the circuit board.
Solder all three pins on each part

DESIGNATION VALUE

( ) R23 100K
( ) R51 100K

DIODES

Two types of diodes are used in the TubeHead, five
1N4148 silicon signal diodes in small transparent
glass cases and two 1N400x power diodes in larger
opaque cases.

Unlike the previous components, diodes are
polarized and must be installed so that the lead
on the banded end of the part corresponds to the
banded end of the designator on the circuit board.
Bend the leads so they are at right angles to the
body of the part and insert them through the holes
provided in the circuit board.

Diodes are also somewhat heat sensitive so the
soldering operation should be done as quickly as
possible.

DESIGNATION VALUE

( ) D1 1N4001, 1N4002 or 1N4003
( ) D2 “ “ “

listed below: 1N4148 or 1N914

( ) D4 ( ) D5 ( ) D6
( ) D7 ( ) D8

ELECTROLYTIC CAPACITORS

TubeHead 7

The remaining capacitors are electrolytic types.
Like the diodes, electrolytic capacitors are
polarized and the leads are not interchangeable.
Leads are marked “+” and/or “-” and the “+” lead
must go through the “+” hole in the circuit board.
Frequently the positive lead of the capacitor is
significantly longer than the negative lead.

Usually the Negative lead of the capacitor is
marked rather than the positive. It naturally goes
through the hole not marked “+”.

Capacitors supplied with specific kits may have a
higher Voltage (V) rating than the minimum
specified below.

DESIGNATION VALUE

( ) C1 100 uF /25v.
( ) C2 1000 uF /16v.
( ) C3 100 uF /25v.
( ) C4 1000 uF /16v.
( ) C17 2.2 uF /25v.
( ) C27 2.2 uF /25v.

listed below: 33 uF /25v.

( ) C5 ( ) C6 ( ) C8
( ) C9 ( ) C10 ( ) C19
( ) C29

listed below: 1 uF /50v.

( ) C12 ( ) C13 ( ) C15
( ) C18 ( ) C22 ( ) C23
( ) C25 ( ) C28

INTEGRATED CIRCUITS

Of all the parts, the ICs are the most easily
damaged and should be treated with some respect.
In particular, they may be destroyed by discharges
of static electricity. Modern ICs are not nearly
as sensitive to this kind of damage as were

8 TubeHead

earlier versions, but it is still good practice to
handle these parts as little as possible. Also
good practice: don’t wear nylon during assembly.
Don’t shuffle around on the carpet immediately
before assembly (or if you do, touch a lamp or
something to make sure you’re discharged). Don’t
be intimidated. It’s rare for parts to be damaged
this way.

ICs are polarized in one or both of two ways; A
dot formed into the case of the IC corresponding
to pin 1 or a semicircular notch that indicates
the end of the package with pin 1. Take care that
this polarizing indicator corresponds to the
similar indicator on the circuit board graphics.

The pins of the ICs may be splayed somewhat and
not match the holes in the circuit board exactly.
Carefully re-form the leads if necessary
so that they are at right angles to the part.
Solder each IC in place as it is installed by
initially soldering two pins in diagonal corners
of the pattern. Make sure that the part is seated
firmly against the pc board by pressing it down
while remelting the solder joint at first one
corner, then the other. Finally, solder the
remaining connections.

DESIGNATION PART NO. DESCRIPTION

( ) IC1 4049 Hex inverting buffer
( ) IC2 5532 Dual low noise op amp
( ) IC3 5532 “
( ) IC4 5532 “

LEDs

When the TubeHead is installed in its case, the
three LEDs will engage the holes in the front
panel and be supported by their leads. Using six
2" lengths of the bare wire, extend the leads of
the LEDs as shown.

TubeHead 9