Phaedrus Audio PHAB User manual

Ver. 1.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
User Manual for
PHAB - tube microphone preamp'
PHAME - tube instrument preamp'
&
PHI - tube DI box
This manual is also available as a pdf do nload, Go to: .phaedrus-audio.com

Ver. 1.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Preface – About Phædrus Audio
Phædrus Audio as formed to design, manufacture and sell high-quality products for the
professional and semi-professional audio market. Phædrus Audio's founders remain inspired by the
music and the recording practices of the fifties and sixties, and are motivated to re-establish the
values of the great audio-technology legends of the past ith their ideals of transparency, hand-
built quality, and serviceability. Using modern manufacturing techniques and the benefits of
modern component technology, Phædrus Audio's aim is to reproduce the quality and character of
classic equipment but in a modern, highly reliable, and cost-effective ay.
Chapter 1 - Background
The Phædrus Audio PHAB, PHAME and PHI products came about because t o, recording musicians
anted to o n a "classic" console from the nineteen-sixties. Ideally a famous EMI, REDD, all valve
(vacuum tube) mixer used to record The Beatles.
But those desks make a collection of
hen's teeth look positively prosaic -
as ell as cheap! So, e set about
researching ith the idea of
producing a replica console.
In order to do this, first it as
necessary to have a design for the
amplifier modules around hich the
mixers of this vintage are organised.
In the famous EMI REDD mixers,
these amplifiers ere either the
German manufactured V72(S)
amplifiers or the, very rare, EMI
built, REDD.47 amplifiers.

Ver. 1.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
V72 and REDD.47 modular amplifiers
Ironically, despite the fact that many more V72 amplifiers exist than do REDD.47s, the EF804
valves hich the German amplifiers use are no longer in current production and are becoming very
expensive: hereas the EF86 and ECC88 (E88CC) valves employed in the REDD amplifiers remain in
production and are idely available. So, a ne amplifier, designed from the common source of
Mullard's reference audio designs, and thereby sharing a common heritage ith the REDD
amplifiers, as developed. We called this amplifier the Phaedrus "PHILHARMONIC" (literally ,
music loving
). This PHILHARMONIC amplifier forms the heart of the Phædrus Audio LONDON
Mark II console. The PHILHARMONIC amplifier circuit is described in detail belo in section
Circuit descriptions .
Mullard published many reference designs which were used by EMI in developing the REDD
amplifiers. Phædrus Audio went back to these same references to develop the PHAB, PHAME
and PHI products.
The prototype London Console (Mark II)

Ver. 1.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
PHAB
The Phædrus Audio PHAB microphone preamplifier is essentially the front-end of a single-channel
of the LONDON console, in hich PHILHARMONIC modular-amplifier is combined ith a rotary
attenuator, s itchable pad, high-pass filter and gain-s itching circuitry similar to that employed in
the famous sixties consoles.
PHAB microphone preamp’ and PHAME instrument preamp’
PHAME
The Phædrus Audio PHAME is a development of the PHAB in hich the very high input impedance
of the input pentode valve is exploited to provide a very high quality instrumental preamplifier.
PHI
The Phædrus Audio PHI DI-Box is a product designed for a
ide range of applications; from live use to the recording
studio. Partnered ith the PHAB it provides a solution for
almost any instrumental or vocal preamp' application.
Construction - or star earths (grounds) and
curly tracks
Given their vintage, the V72 amplifiers and the REDD.47 amplifiers ere built on a metal chassis,
ith the components hard ired onto tag-strips. Although Phædrus Audio equipment uses printed
circuit boards to ensure consistent performance and reliability, the equipment follo s "classic"
practices such as star earths and "natural contour" tracking, just like hook-up ire.
Every Phædrus Audio PHAB, PHAME and PHI product is hand assembled and individually tested. A
test pro-forma is provided ith every unit. Phædrus Audio offer comprehensive service for
products both inside and outside of their arranty period.
PHI DI-Box

Ver. 1.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Chapter 2 - Warranty and Service
Please register your purchase ith Phaedrus Audio at .phaedrus-audio/registration.htm . This
ill simplify service & repair should you need this service. Your name ill be placed on our mailing
list (unless other ise requested) for future updates and ne product announcements.
Service
If you experience a problem ith a Phædrus Audio Ltd. product, contact:
[e-mail]
TELEPHONE: [phone]
Skype ID: phaedrusaudio
We ill diagnose the problem remotely and advise you of the arranty status. If a repair or
replacement is required, e ill issue a Return Merchandise Authorization (RMA) number and tell
you here to send the unit to be repaired. You MUST have an RMA number before you return the
equipment to Phædrus Audio Ltd.'s support service. Be sure to rite RMA number on outside of
shipping box and to include your name, address, phone number, a copy of original sales invoice and a
detailed description of the problem. Phædrus Audio Ltd. ill not accept responsibility for loss or
damage in shipping or for equipment returned ithout valid paper ork and/or a valid RMA number.
Remember, arranty is void if product serial numbers have been removed or altered, or if the
product has been damaged by abuse, accident or unauthorized modification and/or repair (see
Phædrus Audio Ltd. Limited Warranty for details). There are no user serviceable parts inside.
PLEASE RETAIN YOUR SALES RECEIPT. IT IS YOUR PROOF OF PURCHASE COVERING YOUR
LIMITED WARRANTY. LIMITED WARRANTY IS VOID WITHOUT SUCH PROOF OF
PURCHASE.
Phædrus Audio Ltd.'s Limited Warranty
This limited arranty is valid only if you purchased the product from Phædrus Audio Ltd. of from a Phædrus Audio
authorized dealer in the country of purchase: a list of authorized dealers can be found on Phædrus Audio ebsite
.phaedrus-audio.com, or by contacting [e-mail]. Phædrus Audio Ltd. arrants tha t the equipment it
manufactures shall be free from defects in material and orkmanship for a period of one (1) year from the original date of
purchase; unless a longer minimum arranty period is mandated by applicable local la s. If equipment fails due to such
defects ithin this period, Phædrus Audio ill, at its option, repair or provide a replacement for the defective part or
product. Valves (vacuum tubes) are excluded from the one-year arranty, but are arranted for 90 days from day of
purchase. This arranty does not extend to any Phædrus Audio Ltd. product that has been damaged or rendered defective
as a result of: accident, misuse, or abuse; or by the use of parts not manufactured or supplied by Phædrus Audio Ltd.; or by
unauthorized modification or attempted repair to the product; or by acts of God/Nature (accident, fire, flood, etc) or any
other condition that is beyond the control of Phædrus Audio Ltd. There are no user serviceable parts inside. This limited
arranty is invalid if the factory-applied serial number has been altered or removed from the product. This limited
arranty is extended exclusively to the original buyer (customer of Phædrus Audio Ltd., or authorized retail dealer) and is
not transferable to anyone ho may subsequently purchase the product. No other person (retail dealer, etc.) shall be
entitled to give any arranty promise on behalf of Phædrus Audio Ltd. Phædrus Audio Ltd. makes no other arranties,
expressed or implied, of merchantability, fitness for a particular purpose or other ise. Phædrus Audio Ltd. liability is
limited to repair or replacement by Phædrus Audio Ltd., at its sole discretion and, in no event, ill Phædrus Audio Ltd. be
liable for any direct, indirect, special, incremental or consequential damages resulting from any defect in the product,
including lost profits, damage to property and, to the extent permitted by la , damage for personal injury, even if Phædrus
Audio Ltd. has been advised of the possibilities of such damages.

Ver. 1.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Shipping Charges
For any hard are defects experienced by the customer hile the product is under arranty, Phædrus Audio Ltd. ill incur
the shipping cost to the customer and the customer is responsible for the shipping costs to Phædrus Audio Ltd's
designated after-sales service office. For defective products that are out of arranty the customer is responsible for all
shipping costs to and from Phædrus Audio Ltd’s designated after-sales service office.
Extended warranty and out-of-warranty services
Various services are available from Phædrus Audio Ltd. These include repair services for
equipment once the arranty period has expired, and the ability to extend the arranty period.
These are:
PHAB-REP - Repair of a defective PHAB preamp', charged at a flat-rate
PHAME-REP - Repair of a defective PHAME preamp', charged at a flat-rate
PHI-REP - Repair of a defective PHI DI box, charged at a flat-rate
PHAB-MISEAJOUR - Mise à jour for PHAB preamp'*
PHAME-MISEAJOUR - Mise à jour for PHAME preamp'*
PHI-MISEAJOUR - Mise à jour for PHI DI box*
PHAE-EXTWARR - Extends standard arranty (see above) by a further year**
* A mise à jour service includes a complete inspection, re-valve (re-tube) and the implementation
of any engineering updates as ell as a re-test to performance specification.
** If extended arranty is ordered after the initial arranty has expired then the intervening
period is charged ithout exception.
Please contact your dealer or Phædrus Audio Ltd. for current prices.
Warranty service conditions are subject to change ithout notice. For the latest arranty terms and conditions and
additional information regarding Phædrus Audio Ltd. limited arranty, please see complete details online at
.phaedrus-audio.com .
Chapter 3 - Safety
General
Before using any piece of equipment manufactured by Phædrus Audio Ltd., be sure carefully to
read the applicable items of these operating instructions and the safety suggestions. Keep them
for future reference. Follo the arnings indicated on the unit, as ell as in the operating
instructions.
Selection of PSU
Suitable PSUs for the Phædrus Audio Ltd. PHAB and PHAME preamplifiers and the PHI DI-Box
are available as line items from Phædrus Audio.
They are:
PHAE-PSU(110) - 110V mains plugtop PSU: plug is North American type.
PHAE-PSU(220Euro) - 220V mains plugtop PSU; plug is European type
PHAE-PSU(220UK) - 220V mains plugtop PSU; plug is 3 pin 13 AMP, British type

Ver. 1.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
A 12V AC supply is required for the Phædrus Audio PHAB, PHAME and PHI units. A direct current
(DC) supply is NOT suitable and ill damage the unit. If a supply is sourced else here than from
Phædrus Audio, it must have the follo ing specifications:
•12V AC, 12 Watt supply or greater (> or = 1000mA supply current)
•Must be suitable for connection to the appropriate mains voltage
•Must be Class-II, double-insulated
•Must have 30% regulation or better
•Must contain one-shot thermal fuses, resettable fuses, or Polys itches for over-current
protection.
UK and Euro units should comply ith EN 60950-1 and CE requirements and o ly PSUs with UL
a d CSA approvals should be provided on North American units. Units supplied to other countries
should be verified to comply ith the relevant standards hich obtain in those territories.
User Access & Servicing
Phædrus Audio equipment employs thermionic valve (vacuum-
tube) technology and employs hazardous voltages for the high-
tension supplies. THE USER SHOULD NOT ATTEMPT TO
SERVICE THE UNIT. ALL SERVICING SHOULD BE REFERRED
TO QUALIFIED SERVICE PERSONNEL OR FACTORY ONLY.
The PHAB and PHAME preamplifiers and the PHI DI-Box should
NEVER be connected to the external po er supply or in any
other ay energised hen the case is opened and/or the circuit board is accessible.
PHI – Exposed valve (vacuum tube) safety
The Phædrus Audio PHI DI-Box has an exposed 12AU7 (ECC82) valve (tube). In order to ensure
safety, in all circumstances - even if the glass envelope of the valve (tube) ere smashed, the
exposed voltages ensure touch-current is limited to a safe value. Nevertheless keep this product
a ay from babies, children and pets. DISCONNECT THE EXTERNAL PSU AND ALL OTHER
CONNECTED EQUIPMENT WHEN REPLACING THE VALVE (TUBE).
Ground (earth) issues
Phædrus Audio Ltd.'s PHAB, PHAME and PHI products are all po ered by external (12V AC) po er
supplies hich should be double insulated, class-II types (see above). It should therefore be
appreciated that,
A CONNECTION TO EITHER THE PHAB, the PHAME of the PHI product CAN NEVER
BE RELIED UPON PROVIDE A PROTECTIVE OR SAFETY EARTH (GROUND). This
advice obtains IRRESPECTIVE OF THE SETTINGS OF ANY "EARTH OR GROUND
LIFT" SWITCHES .
General Safety Instructions
•Do not operate Phædrus Audio equipment near any source of ater or in excessively moist
environments.
•Keep your Phædrus Audio equipment a ay from babies, children and pets.
•Do not let objects do not fall, or liquids be spilled, into the enclosure.

Ver. 1.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
•Situate the Phædrus Audio equipment a ay from heat sources or other equipment that
produce heat.
•Ensure Phædrus Audio equipment has adequate ventilation. Improper ventilation ill cause
overheating, and can damage the equipment.
•When cleaning Phædrus Audio equipment, remove all connections to the unit; including
po er and gently ipe ith a clean lint-free cloth; if necessary, gently moistened ith
luke arm or distilled ater. Use a dry lint-free cloth to remove any remaining moisture.
NEVER use aerosol sprays, solvents, or abrasives on Phædrus Audio equipment.
•Phædrus Audio equipment should be serviced by qualified service personnel or returned to
Phædrus Audio Ltd. hen: an object (or objects) have fallen into the enclosure; or liquid
has fallen into, or been spilled into the unit; or the unit has been exposed to rain or high
humidity; or the unit does not operate normally or exhibits a marked change in
performance; or the unit has been dropped, or the enclosure has been damaged.
Chapter 4 - About Valves (Vacuum Tubes)
Valve (tube) types
The Phædrus Audio PHAB and PHAME preamplifiers
employ an EF86 pentode input valve (tube) and an ECC88,
or E88CC, valve (tube) as the output device. Positions for
the valves are very clearly marked on the PCB silkscreen
as indicated in the illustration. The valves (tubes) that
are installed in Phædrus Audio’s products during
assembly are selected to give the best possible
performance. We offer versions of all products ith NOS (rather than current production) valves.
But these must be chosen carefully, and be pre-screened. Replacing the supplied valves (tubes)
ith different, collectible, or “high-end” valves (tubes) types may not affect any improvement and
might cause deterioration of performance.
EF86
The EF86 is a lo noise pentode, originally manufactured by many different factories and
branded by Philips, Mullard, Telefunken, Valvo, and GEC, TESLA and Siemens/RFT. Many
NOS valves are still available. Equivalents include the CV2901 (the UK service designation
for the EF86) and the CV4085; a special quality version for military use. The EF86 tube is
still being produced in Russia and in the Slovak Republic under JJ Electronics brand name
(formerly Tesla). Chinese close equivalents are also still being manufactured.
ECC88
The ECC88 is a frame-grid, sharp cut-off, t in (dual) triode ith an internal,
separating screen. The valve as originally designed for service in the front ends of
VHF radio receivers. The ECC88 (E88CC) tube type is equivalent to the North
American 6DJ8 tubes and the (rare) military branded CV2492. The transposition of
the figures from ECC88 to E88CC as Mullard's ay of denoting a special quality
build and is equivalent to the US 6922. Russian 6N1P tubes and the Chinese 6N1
tube are NOT equivalent. NEVER i stall a 6N1(P) i the Phædrus Audio PHAB or
PHAME product. The ECC88 valve is sill being manufactured in China and in the

Ver. 1.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Slovak Republic under JJ Electronics brand name (formerly Tesla).
12AU7 or ECC82
The 12AU7 is a popular, miniature 9-pin medium-gain dual triode valve
(tube) and is used in many instrument and hi-fi amplifiers. Both
triodes are used, in cascade, in the Phædrus Audio PHI product. The
12AU7 is also kno n in Europe under its Mullard-Philips tube
designation ECC82. This tube is idely available both ne and NOS
and a number of special quality equivalents are available. Current
production of 12AU7 takes place in Russia, Slovakia, and China.
Phædrus Audio selects and recommends the long anode (plate) version
of the ECC82 (ECC802S) or 12AU7 valve for application in the PHI
DI-Box.
Valve (tube) lifetime
You should replace the valves in the tubes in the Phædrus Audio products only hen you start to
notice changes in the sound quality. If the gain of the preamplifier decreases noticeably, then this
is certainly evidence of the onset of valve (vacuum tube) failure. Before this, the tone may become
"dull" and transients may be become "blunted".
That said, the lifetime of a valve (tube) is largely determined by the lifetime of its cathode
emission and the small-signal valves (tubes) used in the PHAB, PHAME and PHI use oxide cathodes,
hich can provide adequate cathode emission for 100,000 hours or more. That's over eleven year’s
continuous use. So do not replace valves (tubes) just because they have seen a fe years service.
Phædrus Audio Ltd. can provide suitable valves (tubes) as spares hich, after a burn-in period, are
screened for best performance in your Phædrus Audio product. These are available as line items:
PHAE-12AU7 – Selected 12AU7/ECC82 type valve
PHAE-ECC88 - Selected ECC88 type valve
PHAE-EF86 - Selected EF86 type valve
Please contact your dealer or Phædrus Audio Ltd. for current prices.
Chapter 5 - Instructions for use
Phædrus Audio’s PHAB, PHAME and PHI products employ valves (vacuum tubes) as the ONLY
ACTIVE DEVICES in the audio path. Valves (vacuum tubes) and their associated circuitry need
time to reach an electronic equilibrium before they ill operate at optimal specifications. Please
therefore allo these products to arm up for, at least, 5 to 10 minutes before using them in your
signal chain. To prolong the life of your valves (tubes), it is recommended that you turn off these
units hen not in use.

Ver. 1.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Typical connection set-up for the PHAB
PHAB
Application and connections
Mixer and computer interface manufacturers operate in a very competitive environment. Even a
small mixer must (by definition) contain 8, 16 or perhaps 32 microphone amplifiers. Similarly, a
computer interface designer has to "shoe-horn" a microphone amplifier into a box ith a host of
other features and a noisy, semi-digital environment. Unsurprisingly, these amplifiers are designed
on a careful budget and contain some compromises. Hence, the use of a fe dedicated, stand-alone
microphone preamplifiers, solely designed ith sound-quality in mind, can transform the quality of
your recorded signals. That is the aim of the Phædrus Audio PHAB tube microphone preamplifier:
to offer just such a no compromise microphone amplifier in a product hich incorporates the
standards and qualities adopted in classic recording gear. A block diagram of the PHAB is given
belo . The unit is connected as sho n in the accompanying diagrams.
Architecture of the PHAB preamp'
Controls
Input rotary attenuator, Pad and Gain switch
The PHAB microphone preamplifier operates ith a constant-gain amplifier and attenuates the
signal reaching the amplifier for level control. This is NOT common ith modern equipment; in
hich the gain is adjusted by modifications to the feedback net ork. Yet this approach as
completely standard in the 1950s and 1960s.