RUPERT NEVE DESIGNS 500 Series Mic Pre with Silk User Manual

Portico 511
500 Series Mic Pre with Silk By:

Operations Manual

PORTICO 511 MIC PRE WITH SILK
Thank you for your purchase of the 511: 500 Series Mic Pre with Silk. Everyone at Rupert Neve Designs hopes you enjoy using this tool as much as we have enjoyed designing and building it. Please take note of the following 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: 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, alcohol, or other drink, the sugars and acids will have a very detrimental effect. Sugar crystals act like little rectifiers and can produce noise (crackles, etc.). SWITCH OFF IMMEDIATELY because once current starts to flow, 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.

1. Read these instructions.
2. Keep these instructions.
3. Heed all warnings.
4. Follow all instructions.
5. Do not use this apparatus near water.
6. Clean only with a dry cloth.
7. Do not block any ventilation openings. Install in accordance with the manufacturer’s instructions.
8. Do not install near any heat source such as radiators, heat registers, stoves, or other apparatus (including amplifiers) that produce heat.
9. Refer all servicing to qualified service personnel. Servicing is required when the apparatus has been damaged in any way, such as when the power-supply cord or plug is damaged, liquid has been spilled or objects have fallen into the apparatus, the apparatus has been exposed to rain or moisture, does not operate normally, or has been dropped.
10. Do not expose this apparatus to rain or moisture.

511 DESCRIPTION

With a truly legendary microphone preamplifier and the flexibility of variable Silk/ Texture, Rupert Neve designed the 511 to provide classic sonic performance with 500-series value. Incorporating the pristine preamp circuitry from the 517, the universally useful sweepable high pass filter from the 5012, and the thickening power of a variable silk circuit derived from our flagship Portico II Channel, the 511 is a Rupert Neve-designed workhorse for all your most important tracks.

PORTICO 511: FRONT PANEL

PORTICO 511: BLOCK DIAGRAM

DESIGN NOTES FROM MR. RUPERT NEVE

From Rupert Neve: In former years, before the introduction of solid-state amplifiers, transformers were necessary to step down from 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 the connection being made on a twisted twin screened cable (This type of cable, while excellent for low impedance work, has a high capacitance between its conductors and between each conductor and screen. Resultant high-frequency losses are excessive with high impedance sources like piezo pickups and may cause resonances with magnetic pickups.). Condenser microphones worked off high voltage supplies (250V!) on the studio floor which polarized the diaphragms and powered a built-in pre- amplifier.
More and more microphones were needed as “Pop” music gained ground and this led to the popular and efficient 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-amplifier now being fitted inside the microphone casing.
The 48-volt supply was fed to the microphone through balancing resistors so it was impossible for all of this voltage to actually reach the microphone, resulting in low polarizing volts to the microphone capsule 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 amplifier, that amplifier 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 amplifier or design amplifiers with a higher input impedance, and therefore a lighter load. A microphone is a voltage generator, not a power amplifier. Most microphones give their most accurate performance when they are not loaded by the input impedance of a traditional preamplifier. If the microphone uses an electronic circuit (transformerless) output, a low value of load impedance can possibly stress the little microphone pre-amplifier, causing decreased slew rate and compression at high levels.
On the other hand, a high value of load impedance allows the microphone to “breathe” and give 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 amplifier distortion (This can be an advantage with some condenser 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 impedance, but had not been standardized as they are today. Condenser microphones, before the days of semiconductors, used tube pre-amplifiers that were coupled to the outgoing line with an impedance matching transformer. Microphone amplifiers, such as in a mixing console, also used tubes, which typically have a high input impedance.
Microphones are voltage generators, not power generators. At the low operating level of a microphone, it is always desirable to deliver the maximum possible signal voltage into the amplifier. It was traditional to provide an amplifier 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 avoiding voltage loss.

In the early 1960s when the “Pop” music scene was exploding and sound levels in the Studio became very high, there was concern that the capsule amplifiers 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. Because the microphone preamplifiers in the early recording consoles used transformer gain in the input stage, this 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 511 microphone amplifier 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 which results in mic distortion which 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 filtering out ultrasonic information that is generally considered above our hearing range had a measurable effect on the listener’s electroencephalograms. 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 5-microsecond resolution (20 kHz implies a 9-microsecond temporal resolution, while a CD at a 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 sufficient 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 amplifier handles very small signals is as important as the way it behaves at high levels. For low distortion, an analog amplifier 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 definition, has a linear transfer characteristic.) A dynamics controller – i.e. a compressor, limiter, or expander – is a gain control that can adjust the gain of the amplifier very rapidly in response to the fluctuating audio signal, ideally without introducing significant distortion, i.e. it must have a linear transfer characteristic. But, by definition, 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 upon 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” sound may well have a flawed 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 the recording because some flavors 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 fidelity 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 omparing 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 can not 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)

511 FEATURES

MICROPHONE INPUT
The microphone input is balanced but not floating, being a variant of an instrumentation amplifier. Our well-proven “Transformer-Like-Amplifier” (T.L.A.) configuration 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 511 microphone pre-amplifier 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 a 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. The maximum output level is more than +20 dBu, which provides a large margin over and above the likely maximum requirement of any destination equipment to which the 511 is connected.

MIC GAIN
A 12-way precision rotary switch controls gain from 0 to 66 dB in 6 dB steps.
TRIM
Continuously variable +/-6 dB level control.
+48V
Engages phantom power on the microphone input, as supplied by the 500 series rack.
POLARITY
The Push-button inverts the polarity of the signal path and illuminates when engaged. The symbol “Ø” is often used to denote opposite polarity.
HIGH PASS FILTER
The high pass filter is continuously variable from 20-250Hz and engaged by the HPF switch, which illuminates when engaged. It is a valuable aid in any signal chain, but particularly so in a microphone preamplifier. Signals below the selected frequency are attenuated at a rate of 12db / octave, getting rid of proximity effect, building rumble, air handling, motor hum, etc.
SILK / TEXTURE
Pushing the Silk button engages the red Silk circuit, which reduces the negative feedback on the output transformer, adding harmonic content as the texture is increased. Red Silk accentuates the saturation in the mid and high frequencies, similar to that of the red silk mode on the Portico II Channel. By manipulating the Texture control, the amount of Silk can be changed from essentially absent, to roughly 10 times the amount of coloration/distortion found in Silk from the original Portico Series. With Silk / Texture engaged, the distortion characteristic and harmonic content of the unit are very reminiscent of many of Rupert’s class-A vintage designs. The Silk button illuminates red when engaged.
LEVEL METER
An Eight-segment LED bar-graph meter displays output level (pre-Silk). The color range proceeds from green for lower level signals, yellow for intermediate signals, and red for high levels. When the 511 is clipped, the highest red LED will hold longer depending on how far above the clip threshold the signal was.

SPECIFICATIONS

NOISE:
Measured at Main Output, un-weighted, 22Hz-22kHz, source impedance 150 Ohms balanced. Noise performance can vary depending on the 500 series and/or interference from stray magnetic fields.

Unity Gain Better than -103dBV
With Gain @ +66dB Better than -60dBV
Equivalent Input Noise -125dB

FREQUENCY RESPONSE
Main output, no load
Main Output
+/- 0.1dBu from 10Hz to 31.5kHz
-2.6dB @ 120kHz
MAXIMUM OUTPUT LEVEL +23dBu
TOTAL HARMONIC DISTORTION AND NOISE
@ 1kHz, +20dBu output level, no load. Better than 0.0025%
@ 20Hz, +20dBu output level, no load. 0.025% Typical (2nd and 3rd harmonic)

TOTAL HARMONIC DISTORTION AND NOISE WITH SILK ENGAGED

TEXTURE @ min
@ 100Hz, +20dBu input level, no load 0.015%, mostly 3rd harmonic (typical)
TEXTURE @ max
@ 100Hz, +20dBu input level, no load 2%, mostly 2rd harmonic (typical)
GAIN
Unity up to +66dB in 6dB steps.
Trim continuously adjustable from -6dB to +6dB.
PHANTOM POWER
Supplied by the 500 series rack power supply. Switch selectable on the faceplate.

HIGH PASS FILTER
Continuously variable swept frequency from 20Hz to 250Hz.
Slope: 12dB/Octave
POWER REQUIREMENTS
@ +/-16VDC 100mA

PRODUCT WARRANTY

Rupert Neve Designs warrants this product to be free from defects in materials and workmanship for a period of three(3) years from the date of purchase and agrees to remedy any defect identified within such three 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 modified 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 EXTENT 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 contact our support staff ([email protected]) for troubleshooting. If it is determined that the device is malfunctioning, we will issue a Return Material Authorization and provide instructions for shipping the device to our service department.

Rupert Neve Designs
PO Box 1969
Wimberley TX 78676
www.rupertneve.com
tel: +1 512-847-3013
fax: +1 512-847-8869
775-00017 Rev B

References

• Rupert Neve Designs – The Most Trusted Name in Sound.

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