aion IVP Preamp User manual

IVP PREAMP 1
PROJECT NAME
IVP PREAMP
BASED ON
EFFECT TYPE
PROJECT SUMMARY
DOCUMENT VERSION
Intersound™ IVP
A pedal conversion of the Intersound Instrument Voicing Preamplifier, a rack unit from the late 1970s
notably used by Steve Albini (Shellac) and Bob Weir (Grateful Dead).
Preamp & tube overdrive simulator 1.0.0 (2021-07-30)
BUILD DIFFICULTY
Expert
Actual size is 7.15” x 2.30” (main board) and 6.61” x 0.67” (bypass board).
This is a complex circuit and it takes experience and attention to detail in order to build it
successfully. If you’ve never built a guitar pedal before, this shouldn’t be your first. Please read all of
the build documentation to familiarize yourself with the project before you begin. Aion FX cannot
provide direct technical support.
IMPORTANT NOTE

IVP PREAMP 2
TABLE OF CONTENTS
1Project Overview 16-17 Schematic
2Introduction 18-19 Drill Template
3-4 Circuit Design Notes 20 Enclosure Layout
5-6 Usage 21-22 Wiring Diagram
7-12 Parts List 23 Licensing
13-15 Build Notes 23 Document Revisions
INTRODUCTION
The IVP Preamp is based on the Intersound™ Instrument Voicing Preamp (IVP), a rackmounted preamp
that was first released in 1978. The IVP has a six EQ bands (four semi-parametric and two Baxandall)
and two channels, clean and drive.
The drive channel, called “Tube Voice”, is of particular interest and is the main reason for its enduring
reputation. It uses a combination of op-amp gain, a transistor amplifier and a transformer to get its
overdrive tone—no clipping diodes in sight. All of the EQ comes before the overdrive, so it can be used as
a tool to get a wide variety of drive tones and clipping characteristics.
The “Tube Voice” channel doesn’t quite nail the tube tone as it claims, but it’s such a unique sound that
the IVP has built up a reputation in the four decades since its release. Steve Albini is perhaps the most
well-known advocate of the IVP, using it as part of his own live rig as well as in the studio. It was also
used by Bob Weir of the Grateful Dead.
The Aion FX IVP Preamp is a direct clone of the rackmounted unit in pedal format. It runs on the same
voltage as the original, using a DC-DC converter to get +/-15V from a standard 9VDC input. The Clean
and Tube Voice channels are footswitchable, and the other footswitch allows the whole unit to be
bypassed. It does not include the two effects loops (pre-drive and post-drive) by default, although these
can be added with a few trace cuts, described in the build notes.
The Isotope Amp Overdrive is another project based on the IVP, an adaptation of just the Tube Voice
channel and 2-band Baxandall EQ. It’s much simpler to build, but without the parametric EQ and clean
channel, it’s a very different piece of gear than the full IVP.

IVP PREAMP 3
CIRCUIT DESIGN NOTES
Parametric EQ scaling
The original IVP uses 2MC (reverse audio or reverse log) potentiometers for the parametric EQ section.
This value is almost impossible to find today. There are two available options to get around this:
Option 1: Use 1MC potentiometers instead of 2MC with no other changes
This reduces the frequency range of each control, raising the lower frequency by around 30% in each
band, with the upper-end frequency staying the same. The lower frequencies are affected as follows:
• Low: 30 Hz →40 Hz
• Low-Mid: 100 Hz →130 Hz
• High-Mid: 450 Hz →620 Hz
• High: 1.2kHz →1.6kHz
Since the four bands overlap, and are rarely used at the lower extreme of rotation, this has almost no
practical impact on the usability of the EQ. However, we can do even better than this.
Option 2: Use 1MC potentiometers and scale all resistors and capacitors in the EQ section
The gyrators can easily be recalibrated to have the same frequency range by way of something called
scaling. Since the potentiometer (which acts as a resistor) is cut in half, all of the other resistors in the EQ
section should also be reduced by half, and the capacitors should be doubled in value.
The only caveat with scaling is that it results in some non-standard resistor and capacitor values—and
in the case of the capacitors, some values that don’t exist. Since precision is important, we’ve taken the
straightforward route of adding a second capacitor of the same value in parallel with each of them so
that the scaled value is exact.
Option 2 is electronically identical to the way it’s done in the IVP, so it’s the default in this
implementation. If you build it according to the parts list, each band will have the full frequency range of
the original unit. But if you compare it against the original IVP schematics and want to know why there
are more capacitors and different resistors in the EQ section, this is why.
Power supply design
Like most solid-state preamplifiers of the 1970s and 80s, the IVP operated on a bipolar +/-15V supply.
This voltage can’t be supplied by an external adapter, and the current draw of the circuit is too high to
use a charge pump.
When developing the Lab Series L5 Preamp, which uses the same supply voltage, we adapted a supply
scheme from Alesis rack units in the early 1990s that involved a 9VAC adapter and an AC voltage tripler.
This was then rectified to bipolar +/-19V DC and regulated down to 15V on each rail.
This solution used cheap and readily-available parts, and it has worked very well for several years since
the L5 Preamp was first developed. But the power adapter requirement has always been the major flaw.
A 9VAC adapter will destroy most other pedals if it’s plugged in, and if you own one, there’s an infinitely
higher chance that it’ll be mistaken for a 9VDC adapter and plugged into the wrong pedal at some point.

IVP PREAMP 4
CIRCUIT DESIGN NOTES, CONT.
Because of this, when developing the IVP project we set out to find a reliable way to supply +/-15V from
a standard DC adapter. Fortunately, there are a few more options available today than there were in
2015 when the L5 Preamp was originally developed, and a high-quality DC-DC converter module will
give us exactly what we need. They’re not cheap (USD$9-13 each), but once you account for the fact
that you no longer need a specialized power adapter, the total cost is about the same.
See the build notes on page 13 for more information on the specific DC-DC converters that are
recommended for use in this project.
Channel levels
The original IVP suffers from a very noticeable volume imbalance between the Clean and Tube Voice
channels. If the Tube Voice channel is run at high drive levels (which affects its amount of distortion, not
just its volume), the clean channel doesn’t have enough volume to match it, meaning there’s no way to
switch seamlessly between Clean and Tube Voice without adjusting the master volume.
This is impractical for live use. Because of this, the volume level of the clean channel has been boosted
so the range is closer to the Tube Voice channel and they can be better matched in level when switching
channels. The tone is unchanged.
Input channels
The original IVP has two isolated inputs, each an exact copy of the other. These are labeled as “channels”
on the front panel of the original unit, but there is no switching between the two and they are mixed
together before the EQ after their respective Pregain controls, so they are not channels in the
conventional sense. They serve the same purpose as a an amplifier with two input jacks, though it’s a
little more sophisticated since each input has its own op-amp stage.
Because of this, the pedal conversion removes one of these inputs and simplifies it down to one op-amp
input stage.
Output section
The original IVP has three separate outputs: line level, unbalanced -10dB, and XLR balanced -10dB. For
this project, we’ve converted this to a toggle switch that selects between line level and -10dB. The XLR
output has been eliminated.
If you need XLR, it’s recommended to use an external direct box from the -10dB output. The original
IVP’s XLR output is essentially just a simple direct box, with a single transformer that splits the -10dB
attenuated signal into the inverted copy needed for a balanced connection. An external direct box will
have the exact same result.
Effects loops
The IVP has two effects loops, one that comes after the EQ and one that comes after the clean & drive
channels. While these loops have been omitted from the pedal conversion, they can be added back
without too much trouble. See build notes for more information.

IVP PREAMP 5
USAGE
The IVP has the following controls.
Potentiometers
• Pregain allows the input signal level to be reduced after the input stage. It comes after the Hi/Lo
gain toggle.
• Bass and Treble form a 2-band Baxandall EQ that come before the parametric EQ section. In the
12:00 position, the frequencies are flat. From there, they cut frequencies to the left and boost
frequencies to the right.
• Low Frequency sets the frequency for the lowest parametric band, from 30 Hz to 240 Hz.
• Low-Mid Frequency sets the frequency for the second parametric band, from 100 Hz to 800 Hz.
• Hi-Mid Frequency sets the frequency for the third parametric band, from 460 Hz to 3.6kHz.
• Hi Frequency sets the frequency for the highest parametric band, from 1.2kHz to 9.6kHz.
• Low, Low-Mid, Hi-Mid, and Hi boosts or cuts the frequency selected by the respective frequency
control. In the 12:00 position, the frequency band is flat and essentially out of the circuit. From
there, they cut the frequency to the left and boost the frequency to the right.
• Clean Drive sets the volume level of the clean channel. The tone is unchanged throughout the
rotation and it has no clipping, so its main use is for level-matching with the Tube Drive channel.
• Tube Drive sets both the gain (overdrive) and volume of the Tube Voice channel.
• Master is the master volume of the unit.
Switches
• Input reduces or boosts the gain of the input stage to allow it to be used with a variety of signals.
○High gain mode boosts the signal level with a gain of 4.3 (+12.7dB), suitable for input levels as
low as 50mV RMS. This is the mode that will typically be used for guitar or bass.
○Low gain mode reduces the signal level with an attenuation factor of -33dB. This mode is
suitable for high-output instruments with levels as high as 8V RMS.
• Output selects between two types of output. This comes after the master volume in the circuit.
○Line Out is suitable for going directly to a power amp or crossover.
○-10dB is used if it will be followed by other effects or will be sent to a guitar amp’s input.
○Note that this switch is just a simple attenuator, equivalent to turning the master volume down
slightly, and the master volume setting has a much larger impact on the output signal level.
• Channel (footswitch) changes between Clean and Tube Voice channels.
• Bypass (footswitch) bypasses the effect entirely.

IVP PREAMP 6
USAGE, CONT.
Peak indicator LED
The IVP has a peak indicator LED that senses the signal level and lights up if it gets close to the range
where unwanted clipping will occur. It’s important to understand how this LED works, how to read its
behavior, and how to use it to adjust your levels for the best sound.
First of all, peaking doesn’t necessarily mean clipping. If the levels are set properly, it will occasionally
blink in normal use. The goal is to adjust it so that it comes on sometimes, but not too much. If it never
comes on even with heavy strumming, the internal gain is too low. Conversely, if it’s on even with very
low-level signals, the internal gain is too high.
The IVP has four different areas where the gain can be adjusted:
• Pregain: the signal level coming out of the first op-amp stage (full-range)
• EQ: six frequency bands that can have a cumulative impact on the overall signal level
• Clean / Drive: the gain of the two individual channels, with the drive channel being intentionally
clipped after the gain boost
• Master: the master volume at the tail end of the circuit
The peak detector is located between the EQ and clean/drive sections. If it’s on constantly, it indicates
that some of the earlier stages may have clipped already and that the subsequent stages may clip as well
(prior to any intentional clipping from the drive channel).
With all this in mind, here is the setup procedure.
1. Set the input toggle switch based on the type of signal source. (Normally you’ll use the “high” input
mode. The “low” input mode is only needed if the signal level is so high that the pregain control is
hard to adjust.)
2. Set the bass, treble, and four EQ knobs to the 12:00 position (flat).
3. While strumming chords heavily, adjust the pregain control. Turn it up until the peak LED starts to
blink occasionally at the highest signal levels. If it illuminates for longer than a flicker, back off the
pregain control slightly.
4. Adjust the channel gain (clean or tube) to the desired level, then adjust the EQ until you have the
tone you want. Depending on the EQ adjustment, this may increase the overall gain and cause the
peak indicator LED to illuminate more frequently. If so, turn down the Pregain control again until it’s
back to normal.
5. Adjust the master volume to the desired output level.
If the pregain and EQ have been adjusted, the clean and drive channels and master volume can be at
any gain or volume setting without issue. All of the potential for unwanted clipping comes before those
stages, so the signal levels afterward are unimportant.
Note that if using the pre-voice effects loop, the peak detector comes before the loop, not after, so it
does not detect the level of the returning signal.

IVP PREAMP 7
PARTS LIST
This parts list is also available in a spreadsheet format which can be imported directly into Mouser for
easy parts ordering. Mouser doesn’t carry all the parts (most notably potentiometers) so the second tab
lists all the non-Mouser parts as well as sources for each.
View parts list spreadsheet →
PART VALUE TYPE NOTES
R1 10k Metal film resistor, 1/4W
R2 2M Metal film resistor, 1/4W
R3 2M Metal film resistor, 1/4W
R4 51R Metal film resistor, 1/4W
R5 51R Metal film resistor, 1/4W
R6 43k Metal film resistor, 1/4W
R7 2M Metal film resistor, 1/4W
R8 10k Metal film resistor, 1/4W
R9 20k Metal film resistor, 1/4W
R10 43k Metal film resistor, 1/4W
R11 5k6 Metal film resistor, 1/4W
R12 5k6 Metal film resistor, 1/4W
R13 220k Metal film resistor, 1/4W
R14 3k3 Metal film resistor, 1/4W
R15 3k3 Metal film resistor, 1/4W
R16 20k Metal film resistor, 1/4W
R17 820R Metal film resistor, 1/4W
R18 13k7 Metal film resistor, 1/4W Can also use 14k, or two 27k resistors in parallel.
R19 820R Metal film resistor, 1/4W
R20 13k7 Metal film resistor, 1/4W Can also use 14k, or two 27k resistors in parallel.
R21 820R Metal film resistor, 1/4W
R22 13k7 Metal film resistor, 1/4W Can also use 14k, or two 27k resistors in parallel.
R23 820R Metal film resistor, 1/4W
R24 13k7 Metal film resistor, 1/4W Can also use 14k, or two 27k resistors in parallel.
R25 20k Metal film resistor, 1/4W
R26 13k Metal film resistor, 1/4W
R27 13k Metal film resistor, 1/4W
R28 10R Metal film resistor, 1/4W
R29 10R Metal film resistor, 1/4W
R30 51R Metal film resistor, 1/4W

IVP PREAMP 8
PARTS LIST, CONT.
PART VALUE TYPE NOTES
R31 100k Metal film resistor, 1/4W
R32 JUMPER Metal film resistor, 1/4W Used for effect loop modification. See build notes.
R33 100k Metal film resistor, 1/4W
R34 20k Metal film resistor, 1/4W
R35 10k Metal film resistor, 1/4W
R36 4k7 Metal film resistor, 1/4W
R37 10k Metal film resistor, 1/4W
R38 1k1 Metal film resistor, 1/4W
R39 1k1 Metal film resistor, 1/4W
R40 430R Metal film resistor, 1/4W
R41 36k Metal film resistor, 1/4W
R42 430k Metal film resistor, 1/4W
R43 47k Metal film resistor, 1/4W
R44 4k7 Metal film resistor, 1/4W Original value is 13k. See build notes.
R45 18k Metal film resistor, 1/4W Original value is 36k. See build notes.
R46 10k Metal film resistor, 1/4W
R47 10k Metal film resistor, 1/4W
R48 20k Metal film resistor, 1/4W
R49 13k Metal film resistor, 1/4W
R50 13k Metal film resistor, 1/4W
R51 10R Metal film resistor, 1/4W
R52 10R Metal film resistor, 1/4W
R53 100k Metal film resistor, 1/4W
R54 20k Metal film resistor, 1/4W
R55 4k7 Metal film resistor, 1/4W
R56 20k Metal film resistor, 1/4W
R57 13k Metal film resistor, 1/4W
R58 13k Metal film resistor, 1/4W
R59 10R Metal film resistor, 1/4W
R60 10R Metal film resistor, 1/4W
R61 51R Metal film resistor, 1/4W
R62 100k Metal film resistor, 1/4W
R63 1k1 Metal film resistor, 1/4W
R64 510R Metal film resistor, 1/4W
R65 47k Metal film resistor, 1/4W

IVP PREAMP 9
PARTS LIST, CONT.
PART VALUE TYPE NOTES
R66 47k Metal film resistor, 1/4W
R67 4M7 Metal film resistor, 1/4W
R68 4k7 Metal film resistor, 1/4W
R69 160k Metal film resistor, 1/4W
R70 220k Metal film resistor, 1/4W
LEDC 4k7 Metal film resistor, 1/4W
LEDR 10k Metal film resistor, 1/4W
LEDT 10k Metal film resistor, 1/4W
C1 47uF Electrolytic capacitor, 5mm
C2 47pF MLCC capacitor, NP0/C0G
C3 100uF Electrolytic capacitor, 6.3mm
C4 47uF Electrolytic capacitor, 5mm
C5 47uF Electrolytic capacitor, 5mm
C6 100n MLCC capacitor, X7R
C7 100n MLCC capacitor, X7R
C8 10uF Electrolytic capacitor, 5mm
C9 47pF MLCC capacitor, NP0/C0G
C10 10uF Electrolytic capacitor, 5mm
C11 47n Film capacitor, 7.2 x 2.5mm
C12 470pF MLCC capacitor, NP0/C0G
C13 100n MLCC capacitor, X7R
C14 100n MLCC capacitor, X7R
C15 470n Film capacitor, 7.2 x 3mm
C16 68n Film capacitor, 7.2 x 2.5mm
C17 68n Film capacitor, 7.2 x 2.5mm
C18 120n Film capacitor, 7.2 x 2.5mm
C19 120n Film capacitor, 7.2 x 2.5mm
C20 6n8 Film capacitor, 7.2 x 2.5mm
C21 6n8 Film capacitor, 7.2 x 2.5mm
C22 100n MLCC capacitor, X7R
C23 100n MLCC capacitor, X7R
C24 68n Film capacitor, 7.2 x 2.5mm
C25 1n2 Film capacitor, 7.2 x 2.5mm
C26 1n2 Film capacitor, 7.2 x 2.5mm
C27 6n8 Film capacitor, 7.2 x 2.5mm

IVP PREAMP 10
PARTS LIST, CONT.
PART VALUE TYPE NOTES
C28 6n8 Film capacitor, 7.2 x 2.5mm
C29 820pF MLCC capacitor, NP0/C0G
C30 820pF MLCC capacitor, NP0/C0G
C31 100n MLCC capacitor, X7R
C32 100n MLCC capacitor, X7R
C33 22pF MLCC capacitor, NP0/C0G Original uses 20pF here. 22pF is the closest common value.
C34 10uF Electrolytic capacitor, 5mm
C35 10uF Electrolytic capacitor, 5mm
C36 100n MLCC capacitor, X7R
C37 100n MLCC capacitor, X7R
C38 10uF Electrolytic capacitor, 5mm
C39 22pF MLCC capacitor, NP0/C0G Original uses 20pF here. 22pF is the closest common value.
C40 10uF Electrolytic capacitor, 5mm
C41 22pF MLCC capacitor, NP0/C0G Original uses 20pF here. 22pF is the closest common value.
C42 100n MLCC capacitor, X7R
C43 100n MLCC capacitor, X7R
C44 47pF MLCC capacitor, NP0/C0G
C45 10uF Electrolytic capacitor, 5mm
C46 10uF Electrolytic capacitor, 5mm
C47 100n MLCC capacitor, X7R
C48 100n MLCC capacitor, X7R
C49 100uF Electrolytic capacitor, 6.3mm
C50 10n Film capacitor, 7.2 x 2.5mm
C51 100uF Electrolytic capacitor, 6.3mm
C52 100uF Electrolytic capacitor, 6.3mm
C53 100uF Electrolytic capacitor, 6.3mm
C54 47uF Electrolytic capacitor, 5mm
C55 10uF Electrolytic capacitor, 5mm
C56 10uF Electrolytic capacitor, 5mm
Z1 1N4743A Zener diode, 13V, DO-41
D1 1N914 Fast-switching diode, DO-35
D2 1N914 Fast-switching diode, DO-35
D3 1N914 Fast-switching diode, DO-35
D4 1N914 Fast-switching diode, DO-35
D5 1N914 Fast-switching diode, DO-35