SynthCube FuzzBass TTSH User manual

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TTSH Version 4 Build Guide
Covering Synthcube’s TTSH V4 release
Version 1.10 April 2020
By

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CONTENTS
About This Guide.....................................................................................................................................3
Transistor Coupling and Matching ...........................................................................................................4
Part Substitution .....................................................................................................................................6
Standard Substitutions ............................................................................................................................7
New in TTSH V4.......................................................................................................................................7
Known issues in TTSH V4 .........................................................................................................................7
Quirks......................................................................................................................................................8
Main Board Power System.......................................................................................................................8
Planning for Modifications.......................................................................................................................9
Construction –Getting Started ................................................................................................................9
Construction –Main Board Phase 1.......................................................................................................16
Construction –Main Board Phase 2.......................................................................................................21
Construction –Main Board Finishing Up................................................................................................25
Check out and Calibration......................................................................................................................27
Common Build Issues and Tips...............................................................................................................29
Fuzzbass TTSH VCO/VCF Pitch Calibration Routine.................................................................................30
Putting It All Together ........................................................................................................................... 35
Modification: Add Power Taps for Future Mods.....................................................................................37
Modification: AC Coupling on the VCF Audio Mixer Inputs..................................................................... 37
Modification: Gate Booster Installation .................................................................................................37
Modification: External Control –Electronic Switch.................................................................................39
Modification: Adding a MIDImplant.......................................................................................................40
Modification: Improving Calibration Accuracy .......................................................................................46
Modification: Increase Adjustment Range: LEDs ....................................................................................46
Modification: Reverb Improvements ..................................................................................................... 46

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ABOUT THIS GUIDE
This document presents one approach to building the TTSH. There are other approaches that are perfectly
valid. This approach is designed to minimize the time for construction. These steps have been used to
successfully build a large number of TTSH units. Typical build time for the author, using this method, is
32 hours.
The TTSH is not a beginner’s project, and this guide assumes general knowledge of through hole
electronics construction on the part of the builder. It does not describe how to make solder joints, or how
to identify parts. It describes a certain order to install parts, and then test and calibrate the synth.
It cannot be overstated the importance of using a good quality, temperature-controlled soldering system
to build this project. There are 3175 solder connections to be made. Use of a craft grade iron will
exponentially increase the time to build, and result in countless connections of poor quality or non-
connections, and possible component damage. If your soldering skills are not well developed, you will
have gained proficiency by the end. If necessary, refer to videos on YouTube with explainers for through-
hole soldering technique, and the various fault scenarios to watch out for.
During the main board construction, the soldering is split into two phases. The first phase includes
immersible parts only. This is to facilitate a process using organic / water wash flux. This phase may also
be built with no clean flux.
This document lays out an approach to soldering that is considered best practice. When through hole
components are installed, the tailings for these parts are cut to length prior to soldering. The benefits of
this approach are two-fold. First, cutting after soldering can shock or damage solder joints. Second, waste
material removed and disposed of will not be contaminated with solder. This is of particular value if you
use solder containing lead.
Cutting and then soldering necessitates immobilizing components, or moving them into place as solder is
applied. Both methods are used here. The bulk of the solder joints will be formed using a backer board
to press components flush with the PCB. Various components are installed in groups, based on their
profile in relation to the PCB. For example, horizontally oriented resistors and diodes hug very close to
the board, and are installed in the first pass. This process will be described in detail further down.
Resistors and diodes that are vertically oriented, or located on the front side of the PCB (LED circuits) are
set aside at first, and installed later.
The board is silkscreened with component values, and not component numbers (ex: 1K, not R1). A
separate document has been produced showing the count of each component type and value (resistors,
diodes, capacitors and transistors) for each section of the synth. This will speed the builder up locating
footprints and installing the parts.
If you purchased the Synthcube kit, you received quantity 8 50mm M3 M-F nylon standoffs. These are
intended as stilts to raise the main board from your bench so through hole components can be stuffed.
These are used only during construction. If you purchased the BOM components yourself, it is
recommended you obtain these as well. Brass or aluminum standoffs work even better if you want to
spring for them.
Required non-kit items:
•Temperature controlled Soldering system.

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•Flux Core Solder wire (lead free or leaded). Expect to consume about 75 feet of .031 solder
wire.
•Nylon cable ties - small
•Isopropyl Alcohol and cotton swabs
•¼ inch Heat shrink tubing (can be subbed with cable ties)
•Cutters
•#2 Phillips driver
•Nut drivers 5/16 and 1/2 inch. (Synthcube kit includes hex nuts for the 3.5mm jacks)
•2.5M hex key
•Fine tip needle nosed pliers
•Voltmeter or Multimeter, with frequency counter capability
•Oscilloscope
oA very basic kit scope such as the DSO138 is sufficient.
•ARP 2600 Service Manual
https://drive.google.com/open?id=1TUjsTKBTVcuaf_m3qcXhh3aoX6WBkeX2
•Corrugated cardboard –continuous and unbent or creased, at least as big is the main PCB.
Useful non-kit items to have on hand:
•Liquid flux or flux pen
•Desoldering braid
•Dust-off (compressed air).
•Magnifiers
•Lead forming tool for ¼ watt resistors (Mouser part 5166-801). You will be sorry if you embark
without one of these.
TRANSISTOR COUPLING AND MATCHING
Footprints showing transistors face-to-face indicate locations for thermally coupled transistor pairs.
When such transistors are of the same type, matching them is highly recommended.
To thermally couple two transistors, place them, and add a small amount of thermal paste between them.
Place a small (3/16) length of ¼ inch heat shrink tubing over them and apply heat. Do this before soldering.
Alternatively, you can couple them using small nylon cable ties. When you are matching transistors, you
can couple them off-board. But for locations with NPN-PNP pairs that are coupled, do this on-board, to
avoid getting them reversed later during assembly.
Some builders have reported good results without hand matching the transistors. Doing so increases the
risk of poor performance (especially in the filter) or tracking. At a minimum, buy name brand (ex:
Fairchild/On) transistors from a reputable source, and use units from the same batch. Buying them on
feed tape for automated assembly machines ensures the units come from the same batch. Matching will
also go faster with tape feed transistors.
While some may forego matching, every location showing transistors face-to-face requires thermal
coupling.

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There are many ways to match transistors, and all of them require a moderately precise voltmeter (4.5
digits), and a process to minimize your body heat from affecting the results. The author uses the Ian Fritz
transistor matching method with a home-built rig constructed on protoboard, and employing a Ziff Socket.
https://dragonflyalley.com/synth/images/TransistorMatching/ianFritz-transmat0011_144.pdf
The Synthcube kit contains the exact number of transistors needed to complete the build. It may or may
not yield the required number of matched pairs. The Synthcube kit used in preparation of this document
did yield all the required matches.
Recommended matched pairs:
•2N5087 –four pairs, 4072x4
•2N3904 –eight pairs, RMx2, VCAx1, 4012x5
•2N3906 –six pairs, RMx2, VCAx2, 4012x1, 4072x1
There are six locations that indicate a complementary pair (NPN + PNP): the 4027-1 sub boards, 4012,
4072 and VCA. Tolerances for match with these pairs is not as stringent, and often times builders get
good results without any special selection.
However, the NPN/PNP pair on each 4027-1 (and 4012/4072 cores) is sensitive to differences in gain
between the two transistors, and wide mismatch can cause problems with calibration. These two are
2N3904 and 2N3906 transistors, the most common type available, and the most widely made by different
makers. You will find wide differences in gain between variously sourced units. On Semiconductor is
producing units on the old Fairchild fabs, and can be considered the reference example. The spec sheets
for these list gain (hFE) of minimum 100 and maximum 300. There is a wide variance in there, and you
will find examples all over the map. Every batch they make is different. The point being is that you can’t
ask your supplier to send you transistors more accurately spec’ed than this. You have to order them and
see what you get.
Measurement can be performed with better handheld DMMs that have hFE function, or the Peak Atlas
DCA75. Just remember that these measurements are taken at voltages lower than is typical in the TTSH.
So, these will get you in the ballpark, but cannot eliminate all errors.
The complementary pair in the 4027-1 core functions in a temperature compensated, negative gain
amplifier for the bias voltage that fixes the operating point - the base point from which voltage sources
modulate - for the VCOs. The bias voltage going in comes from the 100k Frequency Adj trimmer. If there
is a significant gain mismatch between the two transistors, the following can happen:
•If the NPN has >20% higher gain than the PNP, the range of the Frequency Adj trimmer will
be very wide, and difficult to set precisely.
•If the PNP has gain >20% higher than the NPN, the overall construct won’t have enough gain
to bring the operating point for the VCO into its base operating frequency for calibration.
For example, defining the base operating mode for a VCO during calibration:
All modulation sources minimized
VCO in KBD mode
0V or nothing connected to the KBD CV bus
Coarse Frequency control minimized

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Fine Frequency control centered
•If the NPN has too much gain with respect to the PNP, sweep of the Freq Adjust trimmer will
show a range of 0hz to >90hz
•On the other hand, if the PNP has too much gain with respect the NPN, sweep of the Freq
Adjust trimmer will show a range of 0hz to 30hz or less, which won’t get you to (required for
Fuzzbass Calibration) 32.7hz. A borderline situation will have the trimmer maxed to get this
frequency, and should be avoided.
On top of this, if the transistors are both very high gain, smaller differences in the gain between them will
be exaggerated in the result.
Ideally you want examples of both NPN and PNP that are in the range of 180 –220 hFE, to yield a sweep
range on the trimmer of (ideally) 0hz –40hz, with 0hz –90hz acceptable. Shifting the window for match
downward (ex: 150 –190) is probably fine, but moving upward from this point, the delta has to reduce,
as the effect of mismatch increases. Just remember that you need to get, with the trimmer maxed, to at
least 40hz, and the wider this range gets, the less granularity there will be setting the base frequency
during calibration.
Worth noting here: the ARP 2600 Service Manual VCO calibration is a bit more forgiving of mismatch in
this location.
PART SUBSTITUTION
If you are fulfilling the BOM yourself, here are some notes regarding part adjustments.
All resistors are ¼ watt through hole types and for the sake of consistency are stated as metal foil 1%.
Synthcube may pack a few in the kits that are 5%, or 1/8 watt, and this is fine. It is assumed that most of
the resistors used in the ARP 2600 were 5% carbon composition types, with probably a small number
either higher precision, or hand selected. Generally you can get away with using carbon comp resistors,
but there are no guarantees, and most carbon comp type resistors have a way of soaking up moisture and
degrading slowly over time. The only resistors dissipating an appreciable amount of wattage are the four
10R units in the Amp section, and the 100R unit preceding the output to the reverb pan. Any others
around the synth should be swappable with 1/8 watt types if you have those on hand.
All Electrolytic capacitors are polarized, and must have 5mm or less diameter and 2mm lead spacing. For
longer life, they should be rated for 105c operation, although only the capacitors on the DC-DC converter
sub-board will be exposed to any significant heat. The 47u units should be rated for 25V operation, and
the rest may be 25V or 50V. You will find the best selection of caps with the correct dimensions will be
rated 50V. The best choice of the 10u caps have 5x7mm dimensions, 105c and 50V rating, and 2mm lead
spacing. If you get caps here that are max 7mm tall, they will fit better on the sub boards. If you have
some caps that meet all these, except are 11mm tall, you can install them on the back sides of the VCO
and VCF cores.
With one exception, all non-polarized caps have 5mm footprint, so try to get units with legs formed to
that. The exception is the two .022u box film capacitors in the Noise and S&H sections, which have 7.5mm
lead spacing. For the sake of consistency and cost, most of the non-polarized capacitors are listed as
MLCC-COG types. There are a few .1u MLCCs that are X7R rated, including the 0805 SMD capacitors on
the VCO cores. Excepting the SMD caps, any of the MLCCs can be replaced with box film types if you have

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those on hand. Any type listed as film should not be subbed with a ceramic cap of any rating. Generally,
any capacitor can be subbed with a nearby standard value. For instance, 4.7p caps are fine for 5p
locations.
Generally (and where available values overlap):
•A C0G MLCC is an improvement over X7R, X5R or disc capacitor;
•A box film capacitor is an improvement over a C0G MLCC;
•A polystyrene film capacitor is an improvement over a box film type.
If you are a confident builder, you may elect to omit the IC sockets. If you do, buy a couple of extra op
amp chips, in case you mangle one removing it. If you are socketing, don’t buy low cost sockets with leaf
type contacts. Just DON’T. Use only machined contact sockets.
STANDARD SUBSTITUTIONS
Some capacitor locations on the TTSH are silkscreened to indicate a value that is not common and may be
difficult to purchase retail. Substitutions have been made in the BOM/kit to the nearest common value,
and in all cases the substitute value is acceptable.
PC Board Marking
BOM Equivalent Part
20p
Capacitor, MLCC, C0G, 22p
30p
Capacitor, MLCC, C0G, 33p
50p
Capacitor, MLCC, C0G, 47p
2n
Capacitor, MLCC, C0G, 2n2
20n
Capacitor, Film, 7.5mm LS, 22n
u1
Capacitor, Film, 5mm LS, 100n
Table 1 - Marked Capacitors and Their Equivalents
In the Voltage Processor, Lag Processor section, the LM301 op amp location is marked for an alternate
TL071 op amp. This change is standard and is typically performed on ARP 2600s when they come in for
service. The tracking accuracy of the TL071 is advantageous in this location, and the BOM/Kit reflect this
substitution.
NEW IN TTSH V4
•All but one of the many bugs in the V3 boards have been resolved (see next section).
•The unused PDIP8 pad in LED section has been removed.
•A field change of one 220R resistor to 680R is formalized (clock rate indicator).
•Mounting points for the Fuzzbass Gate Booster PCB have been added to the EG section.
KNOWN ISSUES IN TTSH V4
•TTSH V3 was revision 8 of the main board. This designation should have been updated for V4,
but was overlooked. V4 main boards can be identified by the lack of a DIP8 footprint in the
main LED section (front of the board, near the Ring Modulator inputs) and the word “REV8”
silkscreened on the back of the main PCB, top right corner.

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•The 2N3954 dual JFET footprint in the VCO2 section (still) has reversed pins 5 and 6.
Instructions are included below to correct for this during construction.
•On the power sub-board, there are a couple of test pads marked +15.00 and -15.00,
respectively. These points are, in fact, common with the V+ and V- (main system) rails, and
not the +15.00 / -15.00 (LED) rails.
•Signal traces transiting under some jacks can become shorted to the jack’s ground connection
via the jack enclosure. This problem affects 19 of the jacks. A further explanation, the
locations of these jacks, and suggested fixes are below in the section covering the jack
installation.
QUIRKS
Questions may arise due to some of the silkscreened information on the boards.
•As stated above, the main board is marked “REV8” whereas the 4V TTSH is a subsequent
revision.
•In the speaker amp section, there are two capacitor footprints marked “u1”. These are .1u
(100n) film capacitors.
•There are some resistors marked with an alternate value in parentheses. Ignore the alternate
value.
•There is an oddly marked resistor location next to the pad for the reverb return RCA jack. It
says “TOBU3 1K”. This is just a 1K resistor location.
•Some capacitor values are marked with non-standard values, and these are traditionally
substituted with standard values. See the preceding section “Standard Substitutions”.
•Power connection points marked on the board +15.00 and -15.00 will typically read on the
DMM ~ +15.8v and -15.8v.
MAIN BOARD POWER SYSTEM
The power rails are distributed to all sections in a middle layer of the main board. This is hidden from
view, and cannot be modified. This means you cannot drill holes in the main board without risk of
permanent damage to the system. It also means you cannot selectively power individual sections.
There are two power distribution systems. Power rails are tapped on the DC-DC converter both pre and
post the LDO regulators. On the 5 pin headers that connect the DC-DC converter to the main board, the
pre-regulator rails are identified as +15.00V and -15.00V. When you measure them, you will find them to
be more like +/-15.8V. This is intentional, and provides for the ~.5V drop incurred by the LDO regulators.
The regulated outputs are V+ and V-. All of these are referenced to the “0” pin. Misleadingly, there are
two test points on the DC-DC converter marked +15.00 and -15.00, when in reality they are V+ and V-,
respectively. These test points are used to initially set the regulated output voltages for V+ and V-, via the
500R trimmers. +15.00 and -15.00 power the LED sections. V+ and V- power everything else.
Although the power and ground planes are internally routed in the board, the old power connector pads
from TTSH V1 (where power was wired up with jumpers) are still in the design, and now function as vias
from the internal power layer. These consist of twelve sets of pads for .1 pitch 2x3 pin headers. There is
one in each of the major sections on the main board. Nothing needs to be installed in these locations, but

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they can be used to tap power and route it to optional boards. This is how the Gate Booster and VCO sync
modifications are powered.
The location/footprint on the main board for the .156 five pin locking (Amphenol) header for power
connection to the DC-DC converter board is silkscreened backwards. If the header is installed in the
indicated orientation, the wires coming of the connector may create a problem with case fitting. Install
this header backwards to avoid problems.
PLANNING FOR MODIFICATIONS.
A selection of common TTSH mods are presented at the back of this guide. Glance through this and decide
if any of them interest you. Almost every builder adds the Gate Booster. Some mods are more esoteric
or involved. The Electronic Switch mod is easy, has zero cost, requires no trace cuts, sacrifices no
functionality, and gets you a sub-oscillator! This one is highly recommended, and it remains a mystery
why ARP didn’t implement the Electronic Switch this way to begin with.
For mods requiring trace cuts, these cuts should be made before building commences.
Mods included in the guide:
•Extra power taps
•AC Coupling –VCF Audio Input Mixer
•Gate Booster
•Midi Implant
•Improved Calibration Accuracy
•External Clock capability –Electronic Switch
•Noise Improvements for Reverb
•Adjustment Range - LEDs
See these sections for installation steps and BOM info.
CONSTRUCTION –GETTING STARTED
1. Whether you purchased a full kit, or assembled the BOM components yourself, refer to the
Master BOM document and verify you have all the required parts on hand. There is generally no
need to test the components. Nonetheless it is a good idea to count them and verify at least one
of the components in each bag is marked with the correct value. If you have not memorized the
resistor color codes, this will help you to do so. Alternatively, use your meter. You can embark
on the build if there are some parts yet to be received, but doing so will increase the risk of an
error or omission during the build. If you purchased the Synthcube kit, you will want to report
any missing parts as soon as possible.
2. Visually inspect all PCBs and look for physical damage, scratches that cut through traces, illegible
screen printing, cracks, etc.
3. Visually inspect the panel for damage, paint or silkscreen problems. There is a step where the
panel is lowered down and fit over all the jacks and sliders, and then secured using screws. To
avoid frustration at this step, make sure all the panel opening swill accept the parts that poke
through and that the slider tangs do not rub or bind across their entire range of motion. It is
possible that some of the paint has gone into the drilling and needs to be filed or removed. Using

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a 3.5mm Jack, the 6.3mm TRS jack, one of the sliders, and an M3 screw, check each hole and slider
groove to make sure there is clearance for the parts. Check the 17 M3 screw hole punches to
make sure there is adequate clearance for the screws. Where issues are found, file out the
openings to resolve this. The evaluation panel sent to the author for review had a few paint
problems with jack and slider openings near the left and right edges of the panel. You want to
make sure you are not dealing with obstructed openings when you get to fitting the panel to the
main board.
4. If you are planning to build with hand-matched transistor pairs, match them now. Recommended
matched pairs:
a. 2N5087 –four pairs, 4072x4
b. 2N3904 –eight pairs, RMx2, VCAx1, 4012x5
c. 2N3906 –six pairs, RMx2, VCAx2, 4012x1, 4072x1
5. Cut apart the 4027-1 boards and the VCF/PSU boards (which are scored). Carefully bend and
break apart the boards. Use sandpaper or a Dremel tool to smooth the edges. There are six little
riser boards intended for the slide switches, on the main PCB, next to one of the speaker cutouts.
You can cut these away with nippers or the Dremel. Discard them –they won’t be used in this
build process. Lightly clean each PCB with isopropyl (not rubbing) alcohol and wipe dry.
6. If you plan to install the optional Gate Booster, or add AC coupling to the inputs of the audio mixer
in the VCF, there are some trace cuts to be made for these mods. A Dremel tool with a small
cutoff wheel is a good way to make these trace cuts. Be careful to make these cuts very shallow,
to ensure no damage to the center layer of the main board.
a. The standard install for the Gate Booster requires that the trace running from the tip in
of the Gate jack to pin 1 of the Gate Select switch be cut. The booster will be inserted in-
line here. See the picture below for reference.