Phaedrus Philter User Manual

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User Manual for

PHILTER - passive EQ and tube amplifier

This manual is also available as a pdf download, Go to: www.phaedrus-audio.com

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Preface – About Phædrus Audio

Phædrus Audi o w as formed to design, manufacture and sell high-quality products for the professi onal and semi-professi onal audi o market. Phædrus Audi o's founders remain inspired by the music and the recordi ng practices of the fifties and si xties, and are motivated to re-establi sh the values of the great audio-technology l egends of the past with their i deals o f transparency, hand- built quality, and s ervi ceability. Using modern manufacturing techni ques and the benefi ts of modern component technology, Phædrus Audi o's aim is to reproduce the quality and character of classi c equipment but in a modern, highly reliable, and cost-effecti ve way.

Chapter 1 - Background

The Phædrus Audio products came about because two, recording musicians wanted to own a "classi c" console from the nineteen-sixties. Ideally a famous EMI, REDD, all valve (vacuum tube) mixer used to record T he Beatles.

But those desks make a collection of hen's teeth look posi tively prosaic - as well as cheap! So, w e set about researching with the idea of producing a replica console.

In or der to do thi s, first it was necessary to have a design for the amplifi er modules around which the mixers of this vi ntage are organised.

In the famous EMI REDD mi xers, these amplifi ers were ei ther the German manufactured V72(S) amplifi ers or the, very rare, EMI built, REDD.47 amplifiers.

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V72 and REDD.47 modular amplifiers

Ironi cally, despite the fact that many mor e V72 ampli fiers exi st than do REDD.47s, the EF804 valves which the German ampli fiers use are no longer in current production and are becomi ng very expensive: whereas the EF86 a nd ECC88 (E88CC) valves employed i n the REDD amplifiers remain in production and are w i dely available. So, a new amplifi er, desi gned from the common source of Mullard's reference audio designs, and thereby shari ng a common heri tage w i th the REDD amplifi ers, was developed. We called this amplifi er the Phaedrus "PHILHARMONIC" (li terally

music loving

). This PHILHARMONIC amplifier forms the heart of the Phædrus Audio LONDON

Mark II console. The PHILHARMONIC amplifier circuit is described i n detai l below in section

Circui t descriptions

Mullard published many reference designs which were used by EMI in developing the REDD amplifiers. At Phædrus Audio, we went back to these same references to develop our products.

The prototype London Console (Mark II)

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Construction - or star earths (grounds) and curly tracks

Given their vintage, the V72 amplifi ers and the REDD.47 amplifi ers were built on a metal chassis, with the components har dwired onto tag-strips. Although Phædrus Audi o equipment uses printed circuit boards to ensure consistent performance and reliabi lity, the equi pment follows "classic" practices such as star ear ths and "natural contour" tracking, just like hook-up wire.

Every Phædrus Audi o product is hand assembled and individually tested. A test pro-forma is provided w i th every unit. Phædrus Audi o offer comprehensive service for products both i nsi de and outsi de of thei r w arranty peri od.

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Chapter 2 - Warranty and Service

Please register your purchase w i th Phaedrus Audio at www.phaedrus-audi o/registration.htm . This will si mplify service & repair should you need this service. Your name will be placed on our mailing list (unless otherwi se requested) for future updates and new product announcements.

Service

If you experi ence a problem wi th a Phædrus Audio Ltd. product, contact:

suppor t@pha edrus-audi o.com TELEPHONE: +44 207 193 4609 Skype ID: phaedrusaudi o

We will di agnose the problem remotely and a dvise you of the warranty status. If a repair or replacement i s required, w e wi ll issue a Return Merchandi se Authori zati on (RMA) number and tell you where to send the unit to be repaired. You MUST hav e an RMA number before you return the equi pment to Phædrus Audio Ltd.'s support service. Be sure to w ri te RMA number on outsi de of shipping box and to include your name, address, phone number, a copy of ori ginal sales invoice and a detai led descri ption of the problem. Phædrus Audi o Ltd. will not accept responsi bili ty for loss or damage in shipping or for equipment returned w i thout vali d paperw ork and/or a vali d RMA number. Remem ber, warranty i s void i f product seri al numbers have been removed or al tered, or if the product has been damaged by abuse, accident or unauthorized modificati on and/or repair (see Phædrus Audi o Ltd. Li mited Warranty for detai ls). 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 warranty is val id 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 website www.phaedrus-audio.com, or by contacti ng sales@phaedrus- audio.com. Phædrus Audio Ltd. warrants that the equipment it manufactures shall be fr ee fro m defects in material and workmanship for a period of one (1) year from the original date of purchase; unless a longer minimu m warranty period is mandated by applicable local laws. If equi pment fails due to such defects within this period, Phædrus Audio will, at its option, repair or provide a replacement for the defective part or product. Valves (vacuum tub es) are excluded from the one-year warranty, but are warranted for 90 days from day of purchase. This warranty does n ot extend to any Phædrus Audio Ltd. product that has been damaged or render ed 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 ins ide. This limited warranty is invalid if the factory-applied serial number has been altered or removed from the product. This limit ed warranty is extended excl usively to the or iginal buyer (customer of Phædrus Audio Ltd., or authorized retail dealer) a nd is not transferable to anyo ne who may subsequently purchase the product. No other person (retail deal er, etc.) shall be entitled to give any warranty promise on b ehalf of Phædrus Audio Ltd. Phædrus Audio Ltd. makes no other warranties, expressed or impli ed, of merchantability, fitness for a particular purpose or otherwise. Phædrus Audio Ltd. liability is limited to repair or replacement by Phædrus Audio Ltd., at its sole discretion and, in no event, will Phædrus Audio Ltd. be liable for any direct, i ndirect, special, incremental or consequential damages resulting from any defect in the product, including lost pro fits, damage to property and, to the extent permitted by law, damage for personal injury, even if Phædrus Audio Ltd. has been advised of the possibilities of such damages.

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Shipping Charges

For any hardware defects experienced by the customer while the pr oduct is u nder warranty, Phædrus Audio Ltd. will incur the shipping cost to the customer and the customer is r esponsible for the shipping costs to Phædrus Audio Ltd's designated after-sales s ervice office. For defective products that are out of warranty the customer is responsible for all shipping costs to and fr om Phædrus Audio Ltd’s designated after-sales service office.

Extended warranty and out-of-warranty services

Various services are avai lable from Phædrus Audio Ltd. These include repair services for equi pment once the warranty peri od has expi red, and the abili ty to extend the warranty peri od. These are:

PHILTER-REP - Repai r of a defective PHILTER equaliser, charged at a flat-rate

PHILTER-MISEAJOUR - Mise à jour for PHILTER* PHAE-EXTWARR - Ex tends s tandar d warranty (see above) by a further year**

* A mise à jour service includes a complete inspection, re-valve (re-tube) and the implementa tion of any engineering updates as well as a re-test to performance speci fication.

If extended w arranty is ordered after the initi al warranty has expi red then the intervening

peri od i s charged wi thout exception.

Please contact your dealer or Phædrus Audio Ltd. for current prices.

Warranty service conditi ons are subject to change without notice. For the lat est warranty terms and conditions and additional information r egarding Phædrus Audio Ltd. limit ed warranty, please see compl ete details online at

www.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 i nstructi ons and the safety suggesti ons. Keep them for futur e reference. Follow the warni ngs i ndicated on the unit, as well as in the operating instructions.

Selection of PSU

Suitable PSUs for the Phædrus Audi o Ltd. products are avai lable as li ne items from Phædrus Audio.

They are:

PHAE-PSU(110) - 110V mains plugtop PSU: plug is North American type. PHAE-PSU(220Euro) - 220V mains pl ugtop PSU; plug is European type PHAE-PSU(220UK) - 220V mains plugto p PSU; plug is 3 pin 13 AMP, British type

A 12V AC supply is required for the Phædrus Audio PHILTER. A direct current (DC) supply i s NOT suitable and will damage the unit. If a supply is sourced elsewhere than from Phædrus Audio, it must have the following specifi cations:

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• 12V AC, 12 Watt supply or greater (> or = 1000mA supply current)

• Must be sui table for connection to the appropriate mains voltage

• Must be Class-II, double-i nsulated

• Must have 30% r egulation or better

• Must contai n one-s hot thermal fuses, resettable fuses, or Polyswi tches for over-current

protection.

UK and Euro units should comply wi th EN 60950-1 and CE requi rements and only PSUs with UL and CSA approvals s hould be provi ded on North Ameri can units. Units supplied to other countri es shoul d be veri fied to comply wi th the relevant standar ds whi ch obtain in those territori es.

User Access & Servicing

Phædrus Audi o equipment employs thermi onic valve (vacuum-tube) technology and employs hazardous voltages for the hi gh-tensi on supplies. THE USER SHOULD NOT ATTEMPT TO SERVICE THE UNIT. ALL SERVICING SHOULD BE REFERRED TO QUALIFIED SERVICE PERSONNEL OR FACTORY ONLY.

Phædrus Audi o products should NEVER be connected to the external power supply or in any other w ay ener gi sed w hen the case is opened and/or the circuit board is accessi ble.

Ground (earth) issues

Phædrus Audi o Ltd.'s products are all powered by external (12V AC) power supplies w hich shoul d be double insulated, class-II types (see above). It should therefore be appreciated that,

A CONNECTION TO EITHER THE PHAB, the PHAME, PHILTER of the PHI product CAN NEVER BE RELIED UPON PROVIDE A PROTECTIVE OR SAFETY EARTH (GROUND). Thi s advice obtains IRRESPECTIVE OF THE SETTINGS OF ANY "EARTH

OR GROUND LIFT" SWITCHES

General Safety Instructions

• Do not operate Phædrus Audi o equipment near any source of w ater or i n excessively moist environments.

• Keep your P hædrus Audio equipment aw ay from babies, children and pets.

• Do not let objects do not fall, or li quids be spi lled, i nto the enclosure.

• Situate the Phædrus Audio equipment aw ay from heat sources or other equi pment that

produce heat.

• Ensure Phædrus Audi o equipment has adequate ventilati on. Improper ventilati on will cause overheating, and can damage the equipment.

• When cleaning Phædrus Audio equipment, remove all connecti ons to the uni t; including power and gently wipe wi th a clean li nt-free cloth; if necessary, gently moi stened w i th lukew arm or di stilled water. Use a dry lint-free cloth to remove any remaining moisture. NEVER use aerosol sprays, solvents, or a brasives on Phædrus Audi o equipment.

• Phædrus Audi o equipment should be servi ced by quali fied servi ce personnel or returned to Phædrus Audi o Ltd. when: an object (or objects) have fallen into the enclosur e; or li qui d has fallen into, or been spi lled into the unit; or the unit has been exposed to rain or hi gh

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humi dity; or the unit does not operate normally or exhibi ts a marked change in per formance; 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 preamplifi ers and the PHILTER equali ser employ an EF86 pentode i nput valve (tube) and an ECC88, or E88CC, valve (tube) as the output device. Positi ons for the valves are very clearly marked on the PCB si lkscreen as i ndi cated i n the illustration. The valves (tubes) that are i nstalled i n Phædrus Audi o’ s products during assembly are selec ted to give the best possible performance. We offer v ersi ons of all products with NOS (rather than current production) valves. But these must be chosen carefully, and be pr e-screened. Replacing the supplied valves (tubes) wi th di fferent, collectible, or “high-end” valves (tubes) types may not affec t any i mprovement and mi ght cause deterioration of per formance.

EF86

The EF86 is a low noise pentode, originally manufactured by many di fferent factories and branded by Philips, Mullard, Telefunken, Valvo, and GEC, TESLA and Siemens/RFT. Many NOS valves are still available. Equi valents include the CV2901 (the UK service desi gnation for the EF86) and the CV4085; a special quality versi on for mi litary use. The EF86 tube is still being produced in Russia and in the Slovak Republi c under JJ Electronics brand name (formerly Tesla). Chinese close equivalents are also sti ll being manufactured.

ECC88

The ECC88 is a frame-grid, sharp cut-off, twin (dual) tri ode wi th an internal, separating screen. The valve w as ori gi nally designed for s ervi ce in the front ends of VHF radi o recei vers. The ECC88 (E88CC) tube type is equivalent to the North American 6DJ8 tubes and the (rare) mi litary branded CV2492. The transposition of the fi gures from ECC88 to E88CC was Mullard's way of denoti ng a speci al quali ty build and is equivalent to the US 6922. Russian 6N1P tubes and the Chi nese 6N1 tube are NOT equi valent. NEVER install a 6N1(P) in the Phædrus Audio PHAB, PHILTER or PHAME product. The ECC88 valve is sill bei ng manufactured in China and in the Slova k Republic under JJ Electronics brand name (formerly Tesla).

12AU7 or ECC82

The 12AU7 is a popular, mini ature 9-pin medium-gain dual tri ode valve (tube) and is used i n many instrument and hi-fi amplifi ers. Both triodes are used, i n cascade, in the Phædrus Audi o PHI product. The 12AU7 i s also known in Europe under i ts Mullard-Phi lips tube designation ECC82. Thi s tube i s wi dely available both new and NOS and a number of speci al quali ty equivalents are available. Current production of 12AU7 takes place i n Russia, Slovaki a, and

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Chi na. Phædrus Audi o selects and recommends the long anode (plate) version of the ECC82 (ECC802S) or 12AU7 valve for appli cation i n the PHI DI-Box.

Valve (tube) lifetime

You shoul d replac e the valves in the tubes i n the Phædrus Audio products only when you start to notice changes in the sound quali ty. If the gai n of the preamplifi er decreases noti ceably, then this is certai nly evi dence of the onset of valve (vacuum tube) fai lure. Before this, the tone may become "dull" and transients may be become "blunted".

That said, the lifeti me of a valve (tu be) i s largely determined by the li feti me of its cathode emissi on and the small-si gnal valves (tubes) used in the PHAB, PHAME, PHILTER and PH I use oxi de cathodes, w hich can provide adequate cathode emissi on 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 few years service.

Phædrus Audi o Ltd. can provi de sui table valves (tubes) as spar es w hich, after a burn-i n period, are screened for best performance in your Phædrus Audio product. These are avai lable 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 Audi o’ s products employ valves (vacuum tubes) as the ONLY ACTIVE DEVICES i n the audio path. Valves (vacuum tubes) and their associated ci rcuitry need time to reach an electronic equi libri um befor e they will operate at opti mal speci fications. Please therefor e allow these products to w arm up for, at least, 5 to 10 mi nutes before usi ng them in your si gnal chain. To prolong the life of your valves (tubes), it is recommended that you turn off these units when not in use.

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Typical connection set-up for the PHILTER

PHILTER

Application and connections

The PHILTER equali ser is a self-contained, line-level device. The loss due to the passive equali ser circuitry is made-up in the included, internal line-ampli fi er. The figure below i s a block-diagram, of the unit. The unit i s connected by balanced, earth-free, tra nsformer-coupled connections on professi onal XLR connectors. Operating levels are covered below.

One word of w arning: remember the li ne-amplifier makes up for the loss i n the passive Q circuits when the controls are central (and no boost is applied). In a passive equali ser, boost is actually provided by r eversing the loss of the equaliser over a range of frequencies. In other words, w hen boost i s appli ed, bass frequencies are “un-cut”. Thi s means that, when large degrees of boost ar e applied, it may be necessary to reduce the signal level sent to the PHILTER to stop it overloading.

Architecture of the PHILTER equaliser

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Controls

Bass, Treble and Frequency-select controls

The equalisati on controls on the PHILTER are simple and intuiti ve to operate. Remem ber, these circuits were invented well before the complex, analogue equalisers of the nineteen-seventies. When the middle fr equency-control is turned to the two most anti -clockwise posi tions, the bass and treble controls (marked w i th the appropriate musi c clefs) act as they do on a hi-fi; as a boost and cut control: clockwi se to boost (in 2dB steps); anit-clockwise to cut (in 2dB steps). The central control may be used to modify the character of the treble-frequency boost. Depending on the frequency setting: 2.5kHz; 3.5kHz; 5kH z; 8kHz; 10kH z; 12kH z, when the treble control is rotated clockwise beyond the central posi tion, boost i s applied wi th a bro ad peak in the response at the indi cated frequency. Note that thi s control i s NOT active when treble-frequency cut i s appli ed; this alw ays remai ns as a shelving response. The graph below illustrates the 121 separate response curves whi ch result form the 121 com binations of treble and bass control when the central switch selects the 5kHz, peaking-response. Note that the cut curves do not exhi bit a complementary notch to the boos t peak.

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Operating levels

Because of the vintage of the PHILTER desi gn, and its origin in German manufactured broadcast

televisi on and radi o equipment, the envisaged operating level for this equi pment i s slightly lower than modern recor ding industry standar ds. When feedi ng

downstream equi pment, the output level should be set to a nominal 0dBu (0.775V RMS). This means that if monitori ng the output on a standard VU instrument, the input attenuator should be set so that the output level reads around -4VU, wi th occasi onal peaks to 0VU on programme. On a digital meter, this is equivalent to si gnal peaks reading +6dB above recording i ndustry standar d +4dBu alignment level. This i s equivalent to +10dBu (or -8dBFS on equipment aligned to EBU R64-1992 standar d and

-14dBFS on equi pment aligned to SMPTE RP155 as i llustrated). On a broadcas t sta ndard PPM, peaks shoul d be s et to read 6 on the BBC scale, or +8 on the European EBU scale. Output level is sufficient easily to modulate semi-pro' equipment (mi xers, DAT, soli d-state recorders and many sound cards) to 0dBFS.

That said, the headroom o n the PHILTER is considerabl e, and no noticeable distortion i s evident when operating the equipment at standard recording industry levels of +4dBu=0VU, or even hi gher. Ther e is thus

considerable scope for experi menta tion with over drivi ng this vi ntage circuitry to explore i ts character i n gradual overload. For example, peaks may be allowed to reach +18dB above alignment level without cli pping. The Phædrus Audi o PHAB and the PHAME preamplifiers and the PHILTER equali ser may thus be used di rectly to feed modern A to D conversi on equi pment aligned to EBU or SMPTE standar ds following the recommenda tions illustrated (ri ght).

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Chapter 6 - Circuit descriptions

PHILTER

The Phædrus Audio PHAB and the PHAME preampli fiers and the PHILTER equaliser all share roughly the same preamplifier circuit.

The ampli fier block is a two-stage design incorporating an EF86 low-noise pentode in the first stage and a paralleled ECC88 hi gh mutual-conductance double- triode as the output stage. All the landmark ampli fier desi gns fr om Mullard's applicati on labora tories specifi ed the EF86. In fact, Mullard described the EF86 as

a low noise pentode i ntended for use as a RC coupled AF vol tage amplifi ers; particularly in the early stages of high gain audio amplifiers, microphone preampli fi ers and magnetic tape recorders

The output stage compri ses a dual triode valve in whi ch the tw o devi ces are wired in parallel. This paralleling of the two triodes has the benefi ci al effects of doubling the mutual conductance and halving the anode resistance. The latter characteristi c is parti cularly valuable in ensuring a low impedance drive to the output transformer.

The output stage directly feeds the output step-down transformer. The output is balanced and earth free. A modest degree of negative feedback is taken from the anode of the output valve(s) to the cathode ci rcui t of the input stage to stabi li se gain, extend frequency-res ponse and low er di storti on. Thi s feedback resi stor is selected to give different gains dependi ng on the par ticular product.

Performance

At recording industry line-up (0VV=+4dBu) the magnitude of all di stortion components on a 1kHz sine wave input are less then -55dB below fundam ental. This, and the A-weighted noise response relati ve to maximum output, is i llustrated below.

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Equaliser performance

Equaliser performance is best defi ned graphically and that is how it is presented below .

Control extremes

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Peaking responses

Mi d-position response <1dB vari ation

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Specifications

Electrical connections

Input:

Unbalanced: 3 pin XLR Co nnector Balanced: 3 pi n XLR Connector Pin 1 – Gro und Pin 1 – Ground Pin 2 – (+) Signal Pin 2 – (+) Signal Pin 3 – Connect to Pin 1 Pin 3 – (-) Signal

Output:

Unbalanced: 3 pin XLR Co nnector Balanced: 3 pi n XLR Connector Pin 1 – Gro und Pin 1 – Ground Pin 2 – (+) Signal Pin 2 – (+) Signal Pin 3 – Connect to Pin 1 Pin 3 – (-) Signal

PHILTER Specification

Circuit configuration: 3 valv e (vacuum tube) design Output: Balanced, transformer coupled Maximum output lev el: +18dBu @ 1kHz Input: Balanc ed, transformer coupled Maximum input level: +18dBu @ 1kHz Gain: No minall y 0dB, maximum boost is +10dB Frequency respons e: 40Hz to 15kHz , ±1dB: 15Hz to 30kHz ±3dB, control flat. Distortion: <0.2%, 1kHz @ -4VU (0dBu), gain 40dB : <1%, 40Hz @ -4VU (0dBu), gain 40dB Noise: <-120dB referred to input Power supply: 12V AC Power consumption: 8 Watts

Phaedrus Audio Ltd. res erves the right to alter these specifications without notice.

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Declaration of Conformity

The Manufacturer of the Products covered by this Declaration is

Phædrus Audio Ltd. head office address

The directives covered by this declaration are:

89/336/EEC Electromagnetic Compatibility directive 73/23/EEC Low Voltage Equipment directive

The products covered by this declaration are:

Phædrus Audio PHAB – microphone preamplifier; Phædrus Audio PHAME – instrument preamplifier; Phædrus Audio PHILTER – passive equalizer & tube recovery amplifier and Phædrus Audio PH I – DI-Box.

The basis on which conformity is being declared:

The manufacturer hereby declares that the products identi fi ed above comply wi th the protection requirements o f the EMC directive and with the principal elements of the safety objectives of the Low Voltage Equi pment directi ve, and that the following standards have been applied:

IEC INTERNATIONAL STANDARD 60065 - Audio, video and similar electronic apparatus – Safety requirements

The techni cal documentati on requi red to demons trate that the products meet the requirements of the Low Voltage Equi pment directive has been compiled and is available for i nspection by the relevant enforcement authoriti es. The CE mark was first applied in 2011.

Signed:

Richard Brice, Technical Director

Date:

January 2011

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Appendix - TEST PRO-FORMA

Product: PH ILTER Seri al Number: ________________

Tested by: ________________ Tube complement: _____________________________

V1 volts: ___________

Volts TP1: ___________ Volts TP2: ___________

Gain set: ______dB (40dB or LOW GAIN position)

High ain test Pass / Fail

Distortion test: Pass / Fail

PAD test: Pass / Fail

Frequency response tes t: HF (-3dB) extension: Pass / Fail

Frequency response tes t: LF (-3dB) extension: Pass / Fail

Phantom (+48) supply tes t: Pass / Fail / N/A

Listening test: Pass / Fail