Rupert Neve Designs Portico 5024 User manual

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By:
Serial #:
Operations Manual
Portico 5024
Quad Microphone Amplifier

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Portico 5024: Quad Microphone Amplifier
Thank you for your purchase of the 5024 Quad Mic Amp. Everyone at Rupert Neve Designs hope you
enjoy using this tool as much as we have enjoyed designing and building it. Please take note of the fol-
lowing list of safety concerns and power requirements before the use of this or any Portico
Series product.
Safety
It’s usual to provide a list of “do’s and don’ts” under this heading but mostly these amount to common
sense issues. However here are some reminders:
The Portico 5024 dissipates about 15 watts, which means that it will get warm in use. The heat generated
is radiated through the case work. To avoid overheating Portico™ modules should not be stacked imme-
diately above or adjacent to other equipment that gets hot. Also bear in mind that other equipment may
radiate strong hum elds which could spoil the performance of your Portico module.
Don’t operate your Portico™ module in or around water! Electronic equipment and liquids are not good
friends. If any liquid is spilled such as soda, coffee, alcoholic or other drink, the sugars and acids will
have a very detrimental effect. Sugar crystals act like little rectiers and can produce noise (crackles,
etc.). SWITCH OFF IMMEDIATELY because once current starts to ow, the mixture hardens, can get very
hot (burnt toffee!) and cause permanent and costly damage. Please contact support as soon as possible
at [email protected] for resolution.
Don’t be tempted to operate a Portico module with the cover removed. The cover provides magnetic
screening from hum and R.F. stray elds.
Power Requirements
Each 5024 unit has a high quality, low noise switching power supply that is further ltered and shunt
regulated for an exceptionally quiet and reliable power source for the audio circuits. The power sup-
ply is considered “universal” in the sense that it will accept 100V through 240V AC and complies with
standard mains voltages around the world. Be absolutely sure to disconnect mains power (remove
the power cable from the IEC power connector at the back panel) before checking the fuse. The fuse is
located in the IEC power input connector and is accessed by opening the small panel labeled “FUSE”.
The fuse should always be replaced with the correct value and type. The 5024’s power supply requires a
5x20 mm 2.5 amp fast acting ceramic body fuse Bussman type GDA 2.5A or equivalent.

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Portico 5024: Block Diagram

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MICROPHONE PREAMPLIFIER DESIGN NOTES
In former years, before the introduction of solid state ampliers, transformers were necessary to
step up to the very high input impedance of tubes, and to provide a balanced input for the
microphone line. An input impedance of 1,000 or 1,200 ohms became established for microphones
having a source impedance of 150 or 200 ohms, with connection being made on a twisted twin
screened cable (This type of cable, while excellent for low impedance work, has high capacitance
between its conductors and between each conductor and screen. Resultant high frequency losses
are excessive with piezo pickups and may cause resonances with magnetic pickups.) Thus
microphones were not heavily loaded. Condenser microphones worked off high voltage supplies
(300V!) on the studio oor which polarized the diaphragms and powered a built-in pre-amplier.
More and more microphones were needed as “Pop” music gained ground and this led to the popular
and efcient method of 48-volt “Phantom” powering that was built into the multi-channel recording
Console – in place of numerous bulky supplies littering the studio, a miniature pre-amplier now
being tted inside the microphone casing.
The 48-volt supply was fed to the microphone through balancing resistors so it was impossible for
this voltage to actually reach the microphone, resulting in low polarizing volts and virtual starvation of
the little pre-amp inside the microphone. Nevertheless amazingly good microphones were designed
and made, becoming the familiar product we use today. If a low value resistive load is connected to
the output of an amplier, that amplier has to produce power in order to maintain a voltage across
that load. Obviously if we want more voltage (output from the microphone) we need to provide a
larger supply for the amplier or settle for a lighter load. A microphone is a voltage generator, not a
power amplier. Most microphones give their most accurate performance when they are not loaded
by the input impedance of a traditional preamplier. If the microphone uses an electronic circuit
(transformerless) output, a low value of load impedance can possibly stress the little microphone pre-
amplier, causing slew rate and compression at high levels.
On the other hand, a high value of load impedance allows the microphone to “breathe” and give of
its best, this being particularly advantageous with very high level percussive sounds. If the microphone
has an inductive source (such as would be the case if it has a transformer output) a low value of load
impedance causes the high frequencies to roll off due to leakage inductance in the transformer in
addition to the above amplier distortion (This can be an advantage with some microphones!).
For this reason we have provided a high value of input impedance that will load microphones to the
smallest possible extent and makes the best possible use of that limited “Phantom” 48-volts supply.
DYNAMIC RANGE
Traditionally, high quality microphones such as ribbons, had very low source impedances – as low as 30
ohms at the output of a ribbon matching transformer. Moving coil microphones were higher but had not
been standardized as they are today. Condenser microphones, before the days of semiconductors, used
tube head ampliers that were coupled to the outgoing line with a transformer. Microphone ampliers,
such as in a mixing console, also used tubes and these typically have a high input impedance.
Microphones are Voltage generators, not Power generators. It is always desirable to deliver the
maximum possible signal voltage into the amplier. It was traditional to provide an amplier input
impedance of about 1,000 or 1,200 ohms; about 5 or 6 times the source impedance of the microphone.
This provided relatively low loading on the microphone – whatever its type – and went a long way to
avoid voltage loss.

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In the early 1960’s when the “Pop” music scene was exploding and sound levels in the Studio became
very high, there was concern that the head ampliers in Condenser microphones would overload if the
Console input impedance was too low. In the early days of Consoles I was asked to provide higher input
impedance than the normal 1,000 ohms. This of course, resulted in less “step-up” in the Console input
transformer and there were then fears that we would lose out at the other end of the scale; Noise. The
fact that microphones were less heavily loaded allowed an increased microphone signal. The reduced
loading also resulted in less deviation of frequency response due to variation of microphone impedance
and consequently less distortion at high levels.
The Portico 5024 microphone amplier provides an input impedance of 10,000 ohms which means that
variations in microphone source impedance with frequency, have only a very small effect on the sonic
quality. This high input impedance has minimal effect on microphone output and loading with the result
that microphone distortion is very low adding up to a noticeable improvement in “transparency”.
A NOTE ON DISTORTION
The human hearing system is a remarkably complex mechanism and we seem to be learning more
details about its workings all the time. For example, Oohashi demonstrated that arbitrarily ltering out
ultrasonic information that is generally considered above our hearing range had a measurable effect on
listener’s electroencephalo-grams. Kunchur describes several demonstrations that have shown that our
hearing is capable of approximately twice the timing resolution than a limit of 20 kHz might imply
(F=1/T or T=1/F). His peer reviewed papers demonstrated that we can hear timing resolution at
approximately with 5 microsecond resolution (20 kHz implies a 9 microsecond temporal resolution,
while a CD at 44.1k sample rate has a best-case temporal resolution of 23 microseconds).
It is also well understood that we can perceive steady tones even when buried under 20 to 30 dB of
noise. And we know that most gain stages exhibit rising distortion at higher frequencies, including
more IM distortion. One common IM test is to mix 19 kHz and 20 kHz sine waves, send them through
a device and then measure how much 1 kHz is generated (20-19=1). All this hints at the importance
of maintaining a sufcient bandwidth with minimal phase shift, while at the same time minimizing
high frequency artifacts and distortions. All of the above and our experience listening and designing
suggest that there are many subtle aspects to hearing that are beyond the realm of simple traditional
measurement characterizations.
The way in which an analog amplier handles very small signals is as important as the way it behaves
at high levels. For low distortion, an analog amplier must have a linear transfer characteristic, in other
words, the output signal must be an exact replica of the input signal, differing only in magnitude. The
magnitude can be controlled by a gain control or fader (consisting of a high quality variable resistor
that, by denition, has a linear transfer characteristic.) A dynamics controller - i.e. a compressor,
limiter or expander - is a gain control that can adjust gain of the amplier very rapidly in response to
the uctuating audio signal, ideally without introducing signicant distortion, i.e. it must have a linear
transfer characteristic. But, by denition, rapidly changing gain means that a signal “starting out” to be
linear and, therefore without distortion, gets changed on the way to produce a different amplitude.
Inevitably our data bank of “natural” sound is built up on the basis of our personal experience and
this must surely emphasize the importance of listening to “natural” sound, and high quality musical
instruments within acoustic environments that is subjectively pleasing so as to develop keen awareness
that will contribute to a reliable data bank. Humans who have not experienced enough “natural”

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Portico 5024: Front Panel
Portico 5024: Back Panel
ACIN
MicInput
100-240VACinput
50/60Hz
.5Amp
LineOut
Transformercoupled
fullybalancedandfloating
1=GND2=Hot3=Cold
GroundLift
Liftstheground
connectionon
theDIInputs
3
MIC IN MIC INLINE OUTMIC INLINE OUTLINE OUT
MIC IN
LINE OUT
12
4
GND
LIFT
100-240 VAC
50/60Hz
POWER
Rupert Neve Designs, LLC
Model 5024
.5 Amp
TLA&Transformer
Balanced,10KOhm
1=GND2=Hot3=Cold
M/S
Polarity
DI
HPSFrequency
Mute
HPF
EngagestheHPF
circuitry
Selectsbetween30Hz
and90HzfortheHPF
TransformerIsolated
Hi-Z,DIInput
ChangesCH3&4from
independenttoMid(CH3)
andSide(CH4)
Mutestheoutput
signal
Reversesthe
polarityofthe
Silk
Addsnostalgicwarmth
andpresencetosignals
whenengaged
GroundLift
Liftstheground
connection
ontheDIInput
Thru
ParallelThruoutput
forusewithan
externalamplifier
Gain
+66dBin6dBincrements
with+/-6dBTrim
Trim
+/-6dBlevel
control
LEDMeters
8PointLED
PeakMeters
sourcematerial
Rupert Neve Designs
36
30
24
18
12
60dB 66
60
54
48
42 36
30
24
18
12
60dB 66
60
54
48
42
36
30
24
18
12
60dB 66
60
54
48
42
36
30
24
18
12
60dB 66
60
54
48
42

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ACIN
MicInput
100-240VACinput
50/60Hz
.5Amp
LineOut
Transformercoupled
fullybalancedandfloating
1=GND2=Hot3=Cold
GroundLift
Liftstheground
connectionon
theDIInputs
3
MIC IN MIC INLINE OUTMIC INLINE OUTLINE OUT
MIC INLINE OUT
12
4
GND
LIFT
100-240 VAC
50/60Hz
POWER
Rupert Neve Designs, LLC
Model 5024
.5 Amp
TLA&Transformer
Balanced,10KOhm
1=GND2=Hot3=Cold
M/S
Polarity
DI
HPSFrequency
Mute
HPF
EngagestheHPF
circuitry
Selectsbetween30Hz
and90HzfortheHPF
TransformerIsolated
Hi-Z,DIInput
ChangesCH3&4from
independenttoMid(CH3)
andSide(CH4)
Mutestheoutput
signal
Reversesthe
polarityofthe
Silk
Addsnostalgicwarmth
andpresencetosignals
whenengaged
GroundLift
Liftstheground
connection
ontheDIInput
Thru
ParallelThruoutput
forusewithan
externalamplifier
Gain
+66dBin6dBincrements
with+/-6dBTrim
Trim
+/-6dBlevel
control
LEDMeters
8PointLED
PeakMeters
sourcematerial
Rupert Neve Designs
36
30
24
18
12
60dB 66
60
54
48
42 36
30
24
18
12
60dB 66
60
54
48
42
36
30
24
18
12
60dB 66
60
54
48
42
36
30
24
18
12
60dB 66
60
54
48
42

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sound may well have a awed data bank! Quality recording equipment should be capable of retaining
“natural” sound and this is indeed the traditional measuring stick. And “creative” musical equipment
should provide the tools to manipulate the sound to enhance the emotional appeal of the music without
destroying it. Memory and knowledge of real acoustic and musical events may be the biggest tool and
advantage any recording engineer may possess.
One needs to be very careful when one hears traces of distortion prior to recording because some avors
of distortion that might seem acceptable (or even stylish) initially, may later prove to cause irreparable
damage to parts of the sound (for example, “warm lows” but “harsh sibilance”) or in louder or quieter
sections of the recording. Experience shows that mic preamps and basic console routing paths should
offer supreme delity otherwise the engineer has little control or choice of recorded “color” and little
recourse to undo after the fact. Devices or circuits that can easily be bypassed are usually better choices
when “color” is a consideration and this particularly is an area where one might consider comparing
several such devices. Beware that usually deviations from linearity carry at least as much long-term
penalty as initial appeal, and that one should always be listening critically when recording and generally
“playing it safe” when introducing effects that cannot be removed.
1. Tsutomu Oohashi, Emi Nishina, Norie Kawai, Yoshitaka Fuwamoto, and Hishi Imai. National
Institute of Multimedia Education, Tokyo. “High Frequency Sound Above the Audible Range,Affects Brain Electric Activity and
Sound Perception” Paper read at 91st. Convention of the A.E.S.October 1991. Section 7. (1), Conclusion.
2. Miland Kunchur,Depart of Physics and Astronomy, University of South Carolina. “Temporal resolution of hearing probed
by bandwidth restriction”, M. N. Kunchur, Acta Acustica united with Acustica 94, 594–603 (2008) (http://www.physics.
sc.edu/kunchur/Acoustics-papers.htm)
3. Miland Kunchur,Depart of Physics and Astronomy, University of South Carolina.Probing the temporal resolution and
bandwidth of human hearing , M. N. Kunchur, Proc. of Meetings on Acoustics (POMA) 2, 050006 (2008)
5024 FEATURES
MICROPHONE INPUT
The microphone input is balanced but not oating, being a variant of an instrumentation amplier.
Our well-proven “Transformer-Like-Amplier” (T.L.A.) conguration is used, which includes an
accurate toroidal Common Mode Low Pass Filter that rejects Common Mode signals and excludes
frequencies above 150 kHz. (There are high powered broadcast transmitters at and above this
frequency in several Continents and, even if you can’t hear them, any vestigial intermodulation
products must be excluded!)
When the Mic Gain switch is set to Unity (0 dB), the Portico 5024 microphone pre-amplier can handle
a balanced input signal of more than +20 dBu without an input attenuator pad! This is a unique feature
that enables this input to double as an additional line input.
THE LINE OUTPUTS
The main output signal comes from the output transformer secondary which is balanced and ground
free. A ground free connection guarantees freedom from hum and radio frequency interference when
connected to a balanced destination such as the input to another Portico module or a high quality ADC.
However the transformer may be used with one leg grounded without any change in performance. It
is not necessary to “ground” one leg at the Portico output. It would normally get a ground connection
when fed to equipment that is not balanced. Maximum output level is + 26 dBu, which provides a large
margin over and above the likely maximum requirement of any destination equipment to which the

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5024 is connected.
MIC GAIN
A 12-way precision rotary switch covering from Line (0) and Mic from 0 to 66 dB in 6 dB steps.
TRIM
A continuously variable pot provides +/- 6dB level adjustment on each channel
IN and THRU 1/4” JACKS
These 2 jacks on both CH1 & CH2 are used for DIRECT INJECTION (DI) or INSTRUMENT inputs, and
are simply paralleled and wired together. Inserting a plug into either jack breaks the normal MIC input
and the user has the full range of MIC GAIN and TRIM. These jacks have a 3 mega ohm input impedance
that will provide less loading (better highs) than most DI boxes. The sheer amount of clean gain that is
available makes these inputs extremely versatile.
M-S
For M-S, recording engineers typically use a cardioid pattern for the Mid channel and a Figure 8 pattern
aimed side to side for the Side channel. Generally the most predictable results happen when the two
mics are placed in very close proximity and are of similar design so usually mics that have switchable
patterns or swappable capsules are employed. You can either record the M & S signals directly and
later decode to Left and Right, in which case no not press the MS button, or you can decode to Left and
Right while recording by pressing the MS button. There may be some benet of recording the M & S
signals directly and then decoding and tweaking the width in the mix, and the 5024 can be used for that
decoding, because it will accept line level signals into the mic XLR inputs if the GAIN switch is in the
zero position and phantom is turned off.
SILK
Much could be written about this feature, sufce to say, that it gives a subtle option to enhance sound
quality in the direction of vintage modules. The silk button reduces negative feedback and adjusts the
frequency spectrum to provide a very sweet and musical performance. We suggest you try it and make
your own judgment.
+48V
Front panel switch makes phantom power available on each microphone input.
POLARITY
Push button inverts the polarity of the signal path. The symbol “Ø” is often used to denote opposite
polarity.
HPF
The high pass lter is a valuable aid in any signal chain but particularly so in a microphone preamplier.
Signals below the selected frequency (30Hz or 90Hz) can be attenuated at a rate of 12db / octave,
getting rid of building rumble, air handling motor hum etc.
Level Meters
8 Segment peak LED meters on the 5024 provide monitoring for signal level on each channel.

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SPECIFICATIONS
Frequency Response:
Main Output, no load,
–0.2 dB @ 10 Hz
–3 dB @ 160 kHz
Noise:
Measured at Main Output, unweighted, 22Hz-22kHz,
Terminated 150 Ohms.
With gain at unity better than –100 dBu
With gain at 66 dB better than –62 dBu
Equivalent Input Noise better than –128 dBu
Noise Factor 1.5dB
High Pass Filter:
Frequency: 30Hz or 90Hz
Slope: 12 dB/Octave Bessel
Maximum Output Level:
Maximum output from 20 Hz to 40 kHz is +26 dBu.
Total Harmonic Distortion and Noise:
@ 1kHz, +20 dBu output: Main Output: Better than 0.001%
@ 20Hz, +20 dBu output: Main Output: Better than 0.002%
Silk Engaged: Better than 0.2% Second harmonic
Crosstalk:
Measured channel to channel: Better than –90 dB @ 15kHz.
Phantom Power:
+48 Volts DC +/- 1%
Power requirements:
3-Pin EIC Input
100-240VAC
50/60Hz
.5 Amp
Part # 775-00004 Rev C

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Rupert Neve Designs
PO Box 1969
Wimberley TX 78676
www.rupertneve.com
tel: [phone]
fax: [phone]
PRODUCT WARRANTY
Rupert Neve Designs warrants this product to be free from defects in materials and
workmanship for a period of one (1) year from date of purchase, and agrees to remedy
any defect identied within such one year period by, at our option, repairing or replacing
the product.
LIMITATIONS AND EXCLUSIONS
This warranty, and any other express or implied warranty, does not apply to any product
which has been improperly installed, subjected to usage for which the product was not
designed, misused or abused, damaged during shipping, damaged by any dry cell battery,
or which has been altered or modied in any way. This warranty is extended to the
original end user purchaser only. A purchase receipt or other satisfactory proof of date of
original purchase is required before any warranty service will be performed. THIS
EXPRESS, LIMITED WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES,
EXPRESS OR IMPLIED, TO THE EXTEND ALLOWED UNDER APPLICABLE
STATE LAW. IN NO EVENT SHALL RUPERT NEVE DESIGNS BE LIABLE FOR
ANY SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES RESULTING
FROM THE USE OF THIS PRODUCT. Some states do not allow the exclusion or
limitation of consequential damages or limitations on how long an implied warranty lasts,
so this exclusion may not apply to you.
WARRANTY SERVICE
If you suspect a defect in this product, please call us at 512-847-3013 or email us at
[email protected] to discuss the suggested defect (it is possible that a suspected
defect could be due to improper usage) and to obtain a return authorization number. It
shall be your responsibility to pay for shipping the product to us, and, if the product is
determined to be defective, our responsibility to pay for shipping the product back to you.