en fs published my sem APY senate tooo pres some ten years ago,! I never tou woul ty to mae abe ver Slot hs hard enough wo seal wh the vcesnry low aoe eel for MC {imoringcoll) pickup ising semicon ductor, but mina pure abe MC phono, ice praticaly impossible to Chie he Se pay ie pe. formance that extn the es se tas avin the Yves sesh the ECSG with an equivalent noise Serer them ifalwaye sound oy mated semicon “tis wen ott ue te glen days of tbe au, boca the pep sro ine moa MAT Cin me ni hdmi hie opts a he Cavrent Ms, So: when the Mes Spear, people fad te inp ras itimers, Some ofthese were of ih ually, ponding vey satiny pe tenance, bt they tended to be expen she ator everyone col ator hem Ti slain by of cau, combine oid and ne technology tf JPET to menage the apne pr fem, ane ues mane he age sie tals Then you wil et he bes ofboth torts: ow nose and high oven Capa And sounds pod, oo MC-Preamp Considerations Tao felieve much has happened a terms of ploy sevity Tie ls ‘Src yous Mout MCS fn hat Stine dim opt stegor, which means an output of approximately OS a Semis BO inter veloc This abow 2008 ower than the nor hl evap of on Natura ere Ie ower ouput pups dan 0 bor they need an adioval gan. The Minontput MCs ane wry cle to the nsdn ocx an Over Kt gan of upto sod can be nec Sry int afte MM np fo nal all MCs on the market." to advantage of tubes are that thay work with very high supply sale des un that sel senathandting Capability sguncay beet than th of worsen, hi ey to enone smo wage of 30-100 RNB fom fee sage, companc to te ots HOV of wansstor ampli o the Spper limi ofthe apliers yma MEE very eo wh tes Dut wht about the omer hich is normaly reacted by noe? Here, 32 GLASS AUDIO 2/97 AN MC/MM PREAMPLIFIER tubes, Suppose you want an 800B signal tonoise ratio in an MM system, Referred to Sm, the input noise of a phono stage _must be less than 0.5uV. This is just about the limit of shat is possible with simple tube circuitry. However, if you watt the sume sigtabtosivise rato ina MC system with 0.5mV output, the input noise must he less than S0nV, which ‘would be very difficult with tubes. In, fret, such noise levels are not easy even with semiconductors Clearly, a compromise 1s necessary, and the best one Ehave found is 0 use semiconductors to handle the low noise and tubes to work with the large BY ERNO BORBELY signals. This is done in a cascode cir ‘cuit, where the lower part of the cas. code 18 a lownoise, dual JFET, and the ‘upper part isa low-noise dual triode, ‘The MC/MM Phono Preamp ‘The FB-1195/221 MC/MM phono pre- amp is a high quality, two stage tube pre amplifier with approximately 6348 gain fon the MC input and 4B gain on the MM input. The circuit uses three tubes and one dual, low-noise JFET per chan. nel, and works without feedback (Fig. 1). ‘The MC input stage is a low-noise, hybrid circuit made up of dual (or two matched) JFETs and 2 6922 double tei PHOTO 1: Prototype of phono proam, with enly MC input tubo intalled. Note the two HV rogulstors ‘and duseflanet roger on te thal side, Tu LEMO connector are used Tor he AC cane ‘aetons from tha transformer.FIGURE 1: MO/NI phono preamp. ode. The two JFETs and the two halves Of the double triode are connected in parallel and then in cascode. The cas- ‘code circuit derives from high-frequen: cy amplification, where low noise. wide bandwidl, and overload capabil ty are the major requisements, ‘The current in the inpit stage, deter. ined by the JFET source resistor Rf, is set to about 10mA to optimize noise ‘The reference voltage for the triodes develops across a 20V zener diode. ‘The voltage drop across V1 is 90Y, the maxi ‘mum permitted for the tube. The stage ‘must be supplied trom +210V, which ‘can be derived frum ue main 260V sup- ply through a 3.3k/4.5W resistor, or from a secondl regulated supply of 210V (ce below), Typical specifications for the MC input stage (all specs measured with 100k load: Gain 508 Frequency response | ~3dB at 80117 ™D 1v 0.08% BY 0.25% Tov 08% ‘ABOUTTHE AUTHOR ton Boraly tat been employes by National Ser Cencac Europe rhe ns 17 Yous Ho was anaes ‘rtecmeal tang ans wate as constant human reeoroe developmen He rceed an Wie dapean tecorc eres fom te nse of Tecmony UUniersy of Nanay 195 areca see yar the Noman Bradetng Corporation desing po tesa! ud equpmert. or 2 na ne ved fe US ard wa rel of erga fe Dyraco ard The Osis Hater Company. Pron 1973-1878 he workes or Noto Canara, Sie, a8 snares serge x eppleaons menage Heeb ak en ‘es rae tom Natal Semeanduioy, nas ec ior OE eutone rw he can sin nd ‘ta equ Ho Ena aloes BuleyAasu rinede Te distortion ie second harmonic, quivalent input noise: 1200 MM Input Stage The MM input stage is a cascode-con- niccted 6922. The reference voltage for the cascode tube is 80V, developed across twa zener diodes. The cirenit Works at around 9MA to get the Dest noise performance. Typical specifications for the MM input stage (measured with @ 100K load): Gain 30d8 Frequency response ~3dR at S0KH7 Distortion 03V 0.027% Vv 0.05% BV 015% lov 05% 20V 1% All distortion is second harmonic. Equivaleat input vise: 0.6:V Both MC and MM inputs have an impedance of 47k. If you need other terminating resistors for your pickups, you can solder the appropriate resistor either on the PCB or on the input con: ncctor, Capacitors Cl and C7 are sol dered on the PCB. Again, you might ‘want t0 leave these off the board and solder the appropriate ones on che input terminal or connector. You can also place hoth the terminating resistor and capacitor on a backpanel switch, Both input stages use the 6H23P- #156922 Russian military tube, which has the lowest noise I have ever mea: sured on any tube. Equally important, it has practically no microphony. You can use other equivalent tubes, but. although they might provide bewer sound, di ‘would probably degrade the circuit's noise performance Que kits are deliv TABLE PARTS LIST FOR PHONO PREAMPLIFIER ep-ies221 Resistors RIT a6 Re az PARI 10 1%, 20, ROE MIS Pe 1240 asst a 10m FS.RIS.F21, Fe" Mt 8,7, 0" tk Ps 3G 450, ROE Wee 9 [Fic 450, ROE Ws ig.nen Reo argo. Ru 100 ie ie air” az Ria ti nig eo ez Heer ean ay 120, ROE Ws rer 180 1 ROE Wi ma 100k 14, ROE re, reo 703,31 NOC WE ‘Aes are, Yo mean unless rasa rte, Capacitors chow pF, e063, PP ClcRon.cis ow eV oraan PP cacao (.2uF 400, WIAA M10 onc ‘Wu, 40, ROE EXO e {TAF 100, ROE EXO 8,018 tu, co, vA Nr -40 o Oar, 1800630, > co Snr, 1% 601, PHE 405 ors SSHF, Vor, PP 8 uF 250, MAA MP0 IFT, Tubes, Diodes a 234081 01 22K EL, malas vive IRRERE0C Rinien 3 ECCAMERIGC Tungsam mt EW seer 2 be 20Y, Wea P20 Miscellaneous 6 pn oa sockets with ga dl eras » ‘arm soder ps 2 emiagezi Poe * Leave cut 6 NL nol tans sxcbeton sep sa, 2100 rela. “A Tava ess up eae tase res, 21 GLASS AUDIO 2/9/ 33cercd with the Russian tubes, but we can The Second Stage network has an attenuation of 25dB also provide them with Siemens ESSCC The second stage, common to both MC and provides an RIAA accuracy of bet fr other equivalent tubes. Please see our and MM, contains the passive RIAA ter than +0.5d8 across the audlo band. price lst for upgrade. ‘equalization and a nmu stage. The RIAA 10 page 38 ie oe gs Te ae as FIGURE 2: Preao copper sido (100%), FIGURE 3: Preamp component sie (858. 34 GLASS AUDIO 2/97from page 34 “The mu stage nses an EFCOR3 and oper ates at approximately ImA. The typical specifications atc Gain 38dR Frequency response ~3dB at 75kH2 TD Vv oo1ze BV 0.028% Tov 0.095 20V 02% ‘The mu stage reaches 1% distortion at ahont 30V and saturates at over 40V This stage determines the overall distor don of the phono preamp because it works with the highest signal levels. Although the output impedance is rex sonably low (Several k2), you can't load the stage very much without loss of amplitude and distortion. The recom. ‘mended minum Toad fs 100%, but it ccan drive 50k without significant losses A Sle or 100k volume control in the fol owing lineamp works very Well Note that all coupling capacitors consist of two capacitors in parallel Although all the coupling caps are polypropylene, [use a suas one in pat allel with a larger. This appears to improve the tnidrange and the hgh end of the audio range. The layout accommo. dates the use of two caps, Fel fice to experi ment with different capacitors to get the best sound from yous amplifier. In case you wish 10 experiment with difer: ent types of tubes, the second-stage layout al allows the use of both, CO83 and 6922 pinout TABLE? PARTS LIGT FON TWO-OUTPUT MOSFET REGULATOR FR2aeniea Resictors fu 45H RARE LW RO,RO,R® 27k Law ALR? iq 31 Capacitors CLC UR.S0V aaa, Siemens Calc Fae vaio (06,08,67, 08 10UF&S0Y. Rada ROE EXO, Pabyeon ‘Semiconductors or SAT ov, 08, NEC V2 for MND. This limits the filament cu rent 10 about 6O0mA per channel. If you have two pickups, one MC and one MM, you can operate hoth input stages and sswiteh between them. The filament cur rent will then be 900mA. The kit comes ‘with all three tubes for each channel Due to the high gain and the RIAA bass boust, the circuit iy very sensitive FIGURE d: Tucsoutpt MOSFET egultor G203 “BURR GOV, 3A Sarre },02,08,08 BYTT-000 O00, Aleta 3 BOSt 81,050 er 03 Deve SIV. 1W. 20m 7,08 Zero 0, W, zat oaio —Zevi8 jay, 2m Miscellaneous 1 Exog218A POS 10 tm elorpne 2 iTS x G2, 03 i From ners ord 1 Fuse dese Wenn 1646, ‘wsroge encore 1 scl, hm, mediums ice to hum pickup. Hum can come from power supplies or transformers. I rec ommend using regulated power sup: plies for both the high voltage and the filament, It is also good procedure to place the mains wansfosmer and Une rey tulators in a separate box for maximum ‘hum protection. For additional protecuion, you should tubes in this position, All that's necessary is 10 reconfigure te fila ments: the 6922 needs 6.3V between pins 4 and 5; for the ECCS3, connect pins 4 and $ and make the 6 3V con nection between pins 4/5 and 9. In case you use 2 6922 here, you should connect pin 9 to ground. ‘Combining Stages ‘Only one of the input stages is operational at any one time, and only the appropriate tube is ag FE az Ss 3 8 i ag ma FIGURE 6: MOSCT regulator copper side (100%) installed (V1 for MC, or 38 GLAss AUDIOuse shielded tube sockets for VI and ‘V2. Although shielded! PCR sockets are ‘not readlly avallable (and are not sup: plied with the kit, you can make them from shielded chassisype sockets by cutting off half of the pins with a pair of very sharp pliers, and then ground- ing the socket and the shield to a ‘ground track on the PCB, The filaments are biased wo approst mately +100V, which keeps the maxi mim voltage hetween cathode and fl lament within the limits given in the data shect. This also helps reduce the tubes’ hum susceptibility, which is very important in low-noise circusts like a phono preamp. Phono-Preamp Setup Procedure Trecommend that you test the ampli cet modules separately hefore building, them into the chassis (Figs 2 and 3). AS a minimum, you will need a digital voltmeter (DVM) to sct up the circuit Use utmost caution in testing the cit. cuit, for you are dealing with high volt ages, If you have no expeticuce with tube circuits, you should ask an experi PHOTO 2: Tho twocutput HV MOSFET regula vor (EB-2962188), Firs, short all three inputs to ground, Insert one tube ata time, starting with V5. Apply 260V and 6.8V regulated volt ages (0 he buard. Connect the DYM across R24 and check the voltage drop, ‘which should he ahont 0 75V, indicating. 4 current of 0.9mA. Switch off the sup: enced friend or an electronics techni- ‘clan co test your circult for you. plies and wait until the capacitors on the board have discharged Now remove V3 and install V2. Check the voltage across D1-D2 which is the reference volkage for the cascode tube. It should be 82-84V, Connect the DVM across R14. The volt age drop is 135mV, indicating a current of 9mA in V2. Also check the anode voltage om pint 6 of V2; it should be lose to 170¥. Repeat the procedure of switching, off the supplies and discharging the NHC BRENNER'S CORP. er: by Fax of latter: ‘Al pie is export» shipping fee + pacha, Nici. 100U3B ‘Guanuty scout avai. We shall send proterma invoice i necessary, Shipping SEA MAIL. AIR MAIL, EMS, UPS, TNT EXPRESS, Wavilgatinsnel aseniy: [CEG|USA, DOEB)GXUTGECIUE, SC8RGEC, 7SB6/RCA: BOSGLUSA: TTSAUSA; ETBECOISIEMENS: E2S8CCISIEMENS; EASCCISIEMENS; 4822)GXU2/GEC; ESZCC|SIEMENS; A89/300GAPHILPS: ‘O82/250/PHILIPS; QEL2/250/PHILIPS; CEOE/20UPHIUPS: QOEDA/AOPHI IPSIRFT; BIEBCIBLOSIGECIUSA: GISECIGECUSA, ‘ic BRENNEN'S conP wisKOLG Perez! or u2 9526 HUNGARY | MISKOLC avenk by Cre Car, Perczel Mor u.2. EuroCerd Mestercard, VISA, Bankers H.3520 HUNGARY Daf, Trasfer or Postal money order Cano i ‘iba a aes ail manned OCA! .TUNGSRAM —sp.lsMeach EZ 4 TUNGSRAM. 5S-USDInch PLEDQHOKOS. TINGSRAM wu 70-UO)nch E6002. TONGGRAM.. 82-USDlent) EZ Gf “cTUNGSRAM._. G2 USD PLSIANONGRA TUNGSRAM "9 USDeaL Ecce “tuNesmall 65 UsDeah Ecce Sern SE USbean — Ravsosoiotewinsccet” iesUsblach fou." TUNesma Te VeDeen ——ECERE Bet Goveneen suc en nue > 33 uabroen feces Tunas eo-usuean ——Eccae Gt “lebustfen —se50"” | aussuy > 33-usofeen ance TUNasRuM 143 USblewn FL ae me Rp.usneess 87 Aussi Go UsDlnch Eroce Gprnasraal-—ies-usmeen —EooHe =. TEA gauamean BGA Btw oa (sna eeushiom —Eremis TESA o1goUsDeasn © SW68 srvana “> 80-Usbpe Sree “runeanal ee-uognen Daan Enoor te UD ESF TUNGSHAM .) 96-USDIeech WOR GIN 4p. USDjech EIDE TESLA soa 2 “cmMesmat Go-UsQean — epimucaaqaienmuom — 4z-usocen EEE “= PURE iach kz 2 “cTNGsRAM1NG-uSOIma rari. ns — 2S-Usomee, SSRN A elec AZ A TUNGGRAML” "ES USDess ——ecrgoce “mts — 93 Usofech SR, YEA m= 80. Uae 2 “4 \tuNsral.. 72-USDe0 poiwiee “AES — 50-Usbjemn Elem mmeaeaa ” S Uaeet fe at = tovsral 5 USD ‘eowte, ASML —H80-Usbewh Ego” UMESMAt —. secusofcch Piaoedi TonGeRau 66 UeDeen —iGtauon —“netn— 28-UBDeast hoe msg Se-bgpins FveouieTUNGSAAM ve-USieem —Sactelee «ASM = aa-USDea «ESSN a see tance Fra Tuwoseau'ss-Usbeah —Skeruetes “no "Se Usbeeet oor See 20: veolach Ez TuNOSraM agus twartst” anno ciea-usiena sir oes 85: usoe | aber ipes ERC ECG ECCS oce0ss, ecu, 18060, Er8106, E18200, FL3, E18, ELfspae, 618, BOB, ete ert TAK TERA TEEN, EAE MLS, The next EiYugo tubes avaible: ECC, Eos, E134, 6047, 6LBGC, KT9D, EL519 big cuanty ava GLASS AUDIO 2/97 39FIGURE 6: MOSFET egultr stufig guide (100% capacitors on the board. Remove V2 and install V1, Then switeh on the sup- plics and check the vollage actoss D2, which should be 20V, Connect the DVM across R4, where the voltage drop should be 12omV, Indicating a ‘current of 10mA, If the current is more than that, increase the value of Ré: if it is less, decrease the value of R4, After ‘adjusting the current to Loma, check the anode voltage on pins 1-6 of V1 which should be L10V. If yon have andio instrumentation, T recommend you test eich stage separate ly. Connect the audio oscillator to the MC input and measure its performance atthe output ofthat stage. Similarly, con: ect the oscillator to the MM input and check the performance there. Finally connect the oscillator to the second stage (V3) and check it through. Ifyou wish wo check the whole circu, you may need to connect a 40-50dB attennatar at the input of the amplifier The “RintaktA” Class A Single Ended streo amplifier 2 13 watts Frequency response 220He-20KH 0.308, (<20Hz-S0KH2 34B) Regulated high voltage supply, rezulated DC hater supply. Soft start circuitry. Tum off mute cicuit, standy switch 9 sclct bias level. Tuhe compliment FCLR6 predriver. KTRRIGSSOA. ont. Optional with 300R's (era charge), [Excellent sound quality and low distortion makes this an ideal amplifier for use with high sensitivity and hom loudspeaker systoms. Flawless nickel plated finish males tis unit Work of art. Experience the diference! Cassie Series High tind Tube Amplifiers from 13W to 180\¥, Fully assembled or Kit ‘Output and power ‘transformers, chokes. ‘and moving coi transformers. © Tw east kits aloo avaiabl experience Hlectromis, Classic Series, for over ten years these high quality tube amplifiers have been manufactured in Germany by Gerhard Haas, designer and builder of Sennheiser's Orphous tube headphone amp. All units feature a high= ly polished Nickel Plaved aluminum chassis, Rooderstsin 1% resistors, Wim Capaitors. WBF connectors, custom de signed power and output transformers and soft-start circuitry. 3 Year pats and labor warranty on factory assembled ‘units Mail order only Vis/Master MO. International Audio Group, Inc. ‘5014 Bending Trail Killeen, TX 76542 Tel (817) 699-8702 Fax (817) 699-8792 40 GLASS AUDIO 2/97PHOTO 9: The siglecuput IV MOSFET regulator (EB-296028), Gry a 10k, 1000, resistor for a 40dB, attenuator); otherwise, ground loops and hum ‘will make the measurements ficult, To check the RIAA accuracy use an inverse RIAA circuit, such as the fone described by Lipshitz and Jung ‘The RIAA accuracy should be within 20.50B, ‘The phono preamp kit comes with Roederstein MK-? metal film resistors and WIMA MKP.10 palypeapy! capacitors, You are free to experiment ‘with other components like tantalum, resistors, other eapacitors, and so an. 1 recommend using tantalum resistors in selected locations. These are available as an upgrade kit; please see our price lis. High-Voltage Regulator In order to preserve the low noi capability of the phono preamp, it is IMPROVE YOUR HEARING, _Wsre a open mits ud pes nu THe sen es ee lsatary a meee a io th yee wl seu. Grune system races Sets tes at hve sou eterna charts, moth He the cles youd pars na mcophoes, Gre Vb Ro omy Sou eer aa tng, ut en 0 he (ur los mode hasan of ysl mains gig on Ste ver Ge as ard wel css eang mgs suchas ee Kae and Roy ‘rors Gee Our aad pone tut a red 10 10nd room abe 8 or poe. We als tue waa cas vauum tube can mics, ie Preamps, un rlence amps, ube gar an ibe compresses. {td aor GT ps aed olor You Hain Trews open a8 mace indy Pe ey eed So ape opin ‘is wea hive rep 3] frst rs te ||castom Crafted Oitpat Transformers Sterling Audio Made in the USA Pre-Amp & Power Tubes Dy Tala Sek, Seta, Gt, & Others Now In Stock 9,5Kot Push-Pull 150W OT 4808 Ohm Seoundary Tape, Ms Lainatons Endl Vatical Tope Moving. (ore ws 21,345, & Otkers) Price $220.00ea. W luterested, Call Us for Details SA-70 (MA230 Replacement) ‘SAK Prana 48,16 Ohmi ec. M6 Lams. 7OW Stax (idan; eedack Wind lees Tack, South Lady, MA 01075 Phone/24Hir FAX (413) 588-7841 ~ Fat Soe Fis Comrd Peer aa eens rome 4 pecan ea eae See 28 GLASS AUDIO 2/97 41High Resolution Vacuum Tube Audio Modules Design Package w/ PC Boards & Full Instructions Blank or Assembled Boards & Finished Units Premium Quality Audiophile Grade components Active Regulation of All Stages & Channels VACUUM TUBE DIGITAL PROCESSOR Disorote TUBE Design from DAC to Output Propristary PLL for Ultra Low Jitter A Separate Regulated Digital, Analog, & HV Power Supplies PREAMPLIERS & CROSSOVERS Q Daniel Il Reference Preamp & Crossover DYNA PAS Phono, Line, & Power Supply / Regulator Modules POWER AMPLIERS (DYNA ST-70 & MK-3 Driver & Reg Power Supply Modules ‘Unique Cascade Diff Amp / Current Source Driver Design Ultra Hi Stability Direct Coupled Driver w/ On Board Regulation POST OFFICE BOX 24605 CURCIO SAN JOSE, CA 95154 AUDIO PHONE (408) 269-4273 ENGINEERING Visit us & view our catalogue & designs at nttpi/www.enter.nev-cae vwellemeankit ere fae i am vole jane The warm. ie, detain Mullard Tube Circuits For Audio Amplifiers = SSlanisarstcasee t Bee cas cr Cia ween ‘#GA-500-096 .. #GA-320-250.. Pants Express Now stocks HamMonp, =m Stereo Vacuum Tube Amplitior Volerean changes the ssc "ube sound” emaw alt reach ot Peiee ehaats? fateh meched EL-38 Hecommended for experineéa pulger. it wo. 421 ‘SUubut powet2 8b wats wus Case AB, 2 1 walle FMS Class Sousbut moscancd- 4 o 8 chma oF reaue ‘SHarmone gtorion 0.0et art walt Cea M95 uals Signa to ne ‘S102 de wsiohtec) «Channel sepnatinn ay aetna a Snes nk’nhms ein ses 977arn RMS amg acne 30 Sarre ‘essential to feed it from a power supply having litte ripple and noise. Older de signs used capacitors and choke filters to reduce the ripple to an acceptable level, I have found that 1n addition to reducing the ripple, its also an advan- tage to regulate the supply voltage, especially in low-level stages, because ic tends 10 improve the imaging, This applies to both semiconductor and tube cirenits The degree of regulation can vary from circuit to circuit, and in tube ci cuits you might get away with less reg. ulation than with semiconductors. The important thing 3s, of course, that the regulator removes the ripple and adds very little wideband noise to the DC. ‘The EB-296/218A power supply Photo 2: Figs. 4-6) combines a full wave rectifier with fast-recovery diodes, high-quality capacitors, and two MOSFET source-follower regula REFERENCES 1, Eno Beta, A Maing Tae, 167 2. Srey Lipehty as Wit Jng, A High Acar Inve PIAA Neto TAA 180, Prnan” Pat ard 2 Taare oF ponte! 4-100 Kis €9 8 $999%.,. ECE (RU eae ee tee el roe IHANMOND MANUFACTURING LW Audio Output Traneformere formers a featre 3 ipo blend mounts 2 Bik mate nah Al LCR Dual Section Capacitors toston dockonie pact fart x ‘Ste, ight blue ny cur, rd Bae ete ‘ae oder tape, Fro sy eapoac a8 S080 els 42 GLASS AUDIO 2/97 SOVTEK @ Vacuum Tubes {ss town Sore, Sretana, ea a Ete Ne ne aed 1-800-338-0531 Rass Sarintors, Using 450V capacitors, the maxi: mum AC input should be limited to approximately 280V, With 400V caps, the AC input should be less than 250V. RI and C2 provide additional filter ing after C1. You can also use RI t0 ‘drop the incoming DC voltage in case the required regulated voltage is signif cantly lower than the unregulated. The regulated output voltage is defined by the zener string a the gate of the MOSFETS. This string is fed from a constant-current source to make sure that ripple is not transmitted to the zen: cers, The constant-current source, QU, is again using a zener (9.1) as a reterence. ‘The 3.1V zen is fed Uavigl 270k resistor, and both it and the string of, high-voltage zeners are fed with a cur. rent of 1-2mA. The output of the zener string is further filtered with a 10kQ resistor and a 10,F capacitor. The 1k0 resistors in series with the gate, a5 well as the 18V zener between the gate and the source, provide protection for the [MOSHFET in case of overioad, ~ | —fexcorenpRwr AvbIO E-X-P-A-N-D-I-N-G OUR SERVICES “for those who appreciate fine sound for a sound price” QUALITY HANDWOUND S.£. OUTPUT TRANSFORMERS * Primaries from 1.8K to 10K + Exclusive wideband design +16, 8, 4, or2 ohm secondary * Gold ating CUSTOM-BUILT POWER TRANSFORMERS/CHOKES, * Wound to your requirements + Heavy-duty dasign for Class A use DC tlament supply winaings “HV chokes to 15H, 300ma + Low voltage, high current flamont chokes S.E.TRIODE AMPLIFIERS BUILTTO ORDER + Stereo oF monoblocks + Our exclusive Harmonic Canceling circuit + Your choice of power triodels 2. to DU watts, pure Class A + Chirome-plated chassis or hardwood base PREAMPLIFIER AND LINE AMPS * Choice of circuitry and components available * Conventional chassis layout + Choice of input/output arrangements ‘Component pricing and specifications catalog available. Call, write or fax for preliminary design and quotes on custom-built amplification. ELECTRA-PRINT AUDIO 4117 Roxanne Drive Las Vegas, NV 89108 702-396-4909 | FAX 702 396 4910 4 GLASS AUDIO 2/97 ‘Output +Vs1 is fed diceetly from the top of the three zener diodes; the second output, +Vs2, can be selected between te wp and the second zener. You can therefore have two equal voltages, or one Ihigher and one lower In the ease of the phono preamp, the higher voltage is 260, and the lower onc, which feeds the MC input stage, is 210V. By using dif. erent zeners, you can adjust the two Vort ages to your needs Naturally, you can use the two-output regulator in many other applications, sucl as lineups, crossovers, and driver stages for power amplifiers, as well as, for stahiliving the voltage for grid 2 of ‘ourput pentodes, ‘You should heatsink Ql, Q2, and Q3. The heatsinks for Q2 and Q3 are ‘mounted on the PCR, and that for Q1 is, freestanding. All heatsinks should be mounted with mica or silicon rubber {or insulation, ulator Selup Procedure “To test the regnlator, connect 27k, 45W fesistors to Doth outputs. Connect 250 AC to the AC input. Insert a 100mA medi tum fuse in FI. If you have a Variac, imerease the mains slowly and monitor de output vollages with a DC voluneter. ‘The DC should stabilize close to the zener reference voltage(S) after 2 couple of min- tues. If you have a scope or an AC mV meter, check the ripple at the output, It should be less than SmV peaketo-peate Borbely Audio also offers @ simpli fied version of the high-voltage cegula tor with only one output (type number EB-296/218) (Photo 4). All BA kits include eposy PC boards, all resistors, capacitors and mechanical components that go on the hoard. Main transform. ers for 115/230Y, 50/60Hz are also available on request. + Rorhely Andia reserves the right to. | improve or otherwise alter any specification supplied in this docu: ‘ment or any documentation sup. plied hereafter, ‘The £B-1195/221 Phono Pream- plifler and the EB-296/218A Two- ‘Output MOSFET Regulator design is the property of Erno Borbely/ Rorhely Andio, Commercial use is hot permitted without a license fiom Erno Borbely/Borbely Audio,