Rane-Professional-Audio-Notes 电路图 维修手册.pdf

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1、Headphone Power-1 INTRODUCTION Much confusion abounds regarding headphone power requirements. This Rane Note is intended to disperse some of the mist surrounding headphone specifications and hopefully give you a clearer understanding of how much power is really needed for your application. Understan

2、ding Headphone Power Requirements Headphone Sensitivity Listing of Headphones HC 6 Power vs. Loudness HC 4 Power vs. Loudness Table of Common Sound Pressure Levels Dennis Bohn Rane Corporation RaneNote 100 1983 Rane Corporation RaneNote UNDERSTANDING HEADPHONE POWER REQUIREMENTS RadioFans.CN 收音机爱 好者

3、资料库 Headphone Power-2 HEADPHONE SENSITIVITY Headphone manufacturers specify a “sensitivity” rating for their products that is very similar to loudspeaker sensitiv- ity ratings. For loudspeakers, the standard is to apply 1 watt and then measure the sound pressure level (SPL) at a distance of 1 meter.

4、 For headphones, the standard is to apply 1 milliwatt (1 mW = 1/1000 of a watt) and then measure the sound pressure level at the earpiece (using a dummy head with built-in microphones). Sensitivity is then stated as the number of dB of actual sound level (SPL) produced by the headphones with 1 mW of

5、 input; headphone specifications commonly refer to this by the misleading term “dB/mW.” What they really mean is dB SPL for 1 mW input. Think about these sensitivity definitions a moment: headphone sensitivity is rated using 1/1000 of a watt; loud- speaker sensitivity is rated using 1 watt. So a qui

6、ck rule-of- thumb is that you are going to need about 1/1000 as much power to drive your headphones as to drive your loudspeakers since both of their sensitivity ratings are similar (around 90- 110 dB SPL). For example, if your hi-fi amp is rated at 65 watts, then you would need only 65 mW to drive

7、comparable headphones. (Actually you need less than 65 mW since most people dont listen to their loudspeakers at 1 meter.) And this is exactly what you find in hi-fi receiverstheir headphone jacks typically provide only 10-20 mW of output power. Take another moment and think about all those portable

8、 tape players. They sound great, and loud. Why, you can even hear them ten feet away as the teenage skateboarder that ran over your foot escapes. Power output? About 12 mW. THE LIST As an aid in finding out how much power is available from either the HC 6 or HC 4 Headphone Consoles, we have compiled

9、 a listing of popular headphones. Included is a column giving the maximum SPL obtainable using the HC 6 or HC 4 and any particular headphoneultimately, it all gets down to actual SPL. The power rating really doesnt matter at alleither its loud enough or it isnt (of course it has to be clean power, n

10、ot clipped and distorted). The SPL numbers shown are for maximum continuous SPL; for momentary peak SPL add 3 dB. Note that the maximum achievable SPL varies widely for different models and manufacturers, ranging from a low of 107 dB to a harmful 146 dB! The table also shows there is very little rel

11、ationship between headphone impedance and sensitivity, and that power output alone means nothing, since in one case 80 mW produces a maximum SPL of 107 dB, yet in another case the same 80 mW yields an SPL of 124 dB! Sensitivity (dB) is the measured sound pressure level with 1 mW of power. The Max Po

12、wer (mW) columns are typical continuous average (rms) power, 20 Hz-20 kHz, with THD less than 0.1%. If headphones are not yet owned, or replacements are desired, use this listing as a guide for selecting headphones with sufficient sensitivity for the maximum desired SPL. Note: headphones with an imp

13、edance of less than 32 ohms are not recommended for use with the HC 6 or the HC 4. RadioFans.CN 收音机爱 好者资料库 Headphone Power-3 rerutcafunaMl edoM ecnadepmI )smho( yt i v i t i sneS )Bd( xaM4CH )Wm(rewoP xaM4CH )Bd(LPS xaM6CH )Wm(rewoP xaM6CH )Bd(LPS GKAM141K006899871108711 FD042K,M042K006889870108701

14、S072K5729932511083811 103K00149522811582911 105K,104K02149022711092911 ac i nhceT -o i duA809-HTA,2MOC-HTA,1MOC-HTA0409022311044611 019-HTA0429022511044811 5P-HTA04001022321044621 04M-HTA06001832321004621 04D-HTA66201532621592721 X3M-HTA,X2M-HTA54001032321534621 c imanydreyeB051TD05279061911571911 1

15、13TD,112TD0489022121044421 052TD0889042121063321 114TD052201061421571421 135TD05259061611571611 133TD,134TD0468022901044211 ORP099TD,ORP077TD006699851108511 115TD,118TD,108TD05249061611571611 119TD,109TD05289061021571021 xetsoF5- T4469522911534221 7- T0789042121583421 02- T0569332021524221 04- T0589

16、332221524421 odarG523RS0469022911044221 asoH107-SDH0419022411044711 ssoK08/DT,031/A,002/A,052/A0689832321023521 002/R0648832801004011 54/R,001/R0658832901004111 51/BS,2/DH,09/R06001832321004621 sorPa t r oP,02/R,S53/R,08/R06101832421004721 53/BS,05/BS,B55/R,B07/R06101832421004721 04/R060983241100461

17、1 S03/R06601832031004231 01/R06301832721004921 57/DT0659832911004121 56/DT09101532421043621 16/DT8339212611044911 t r auQBM508PQ0038954102108711 res i ehnneS074,534,334,004DH2349002711054121 52DH07021042441083641 544DH2579532121093321 PS52DH58001532321053521 565,545,535,525,562DH05149702711091711 57

18、4,554DH0649832811004021 564DH00149522811582911 075DH02159022011092021 006,085DH0037954181108611 ynoS2KM001V-RDM2389002121054521 58-RDM04201022521044821 77D-RDM,006V-RDM54601032921534231 01DC-RDM2369002911054321 057DC,055DC-RDM54001032321534621 6DC-RDM54011032331534631 059DC,058DC-RDM2320100252105492

19、1 0003DC,0001DC-RDM23401002721054131 4057-RDM,55D-RDM,33D-RDM54401032721534031 6057-RDM36601042921004231 2057-RDM54201032521534821 notnatS0001ORPJD,ORPTS23001002321054721 xe l eT6-HP0065019842108421 ahamaYAM5HR2389002121054521 1HR2309002311054611 2HR2359002811054221 3HR0659832911004121 M01HR04201022

20、521044821 M04HR23301002621054031 RadioFans.CN 收音机爱 好者资料库 Headphone Power-4 DOC 103086 PN 02212 Sound Pressure Level Equivalents Bd-LPSelpmaxEnommoCBd-LPSelpmaxEnommoC 041egamade l baraper r I06no i t a s r evnoc l a mroN 031 f f ogn i katt f arcr i ateJ05c i sumro t a v e l E 021rednuhT/n i apfod l

21、ohserhT04)pee l sasd i k (dnuorgkcabemoh l a mroN 011 t r ofmocs i dfod l ohserhT03dnuorgkcabo i dutS 001rete v i R/ek i bt r iD02reps i hwte i uQ/sevae l fogn i l t suR 09s l ev e l e f asnufo t r atS01poowsy l f re t t uB 08 y r otc a f egarevA0gn i raehfod l ohserhT 07ya l p t a s d i K Permissib

22、le Noise Exposures Extracted from the U.S. Department of Labor Noise Regulations ruoH, yaDrePno i t aruDgn i t hgieW-A , ) Bd(leveLdnuoS 809 629 459 379 2001 1201 1501 011 ss e l ro511 Rane Corporation 10802 47th Ave. W., Mukilteo WA 98275-5098 USA TEL (425)355-6000 FAX (425)347-7757 WEB 1982 Rane C

23、orporation NN O T E 1 0 2 Professional Audio Products ANALOG I/O STANDARDS 3-PIN CONNECTOR WIRING BALANCED INPUTS it must be equal for the minimization of hum and RFI pick up. With equal common mode impedance, you get unequal differential impedance. For some designs (where all resistors are equal),

24、the mismatch can be as much as three to one, with the positive input impedance being three times the negative input impedance. This sounds like a big problem, when in fact, it is not. All it means is that the load impedance seen by the positive and negative line drivers are not equal, so the negativ

25、e driver has to deliver more current. But, as long as the impedance are within reason (at least 5k ohms or greater), you really do not have a problem. AUTOMATIC BALANCED-UNBALANCED OPERATION Figure 1 shows a balanced stage with a TRS phone jack input. There is a bit of cleverness going on here that

26、comes for free. Using a stereo phone plug into the stereo jack gives you the balanced line input. Not so obvious is that by using a mono phone plug the circuit automatically switches to unbalanced single line opera- tion. Nice, huh? What happens is that the ring of the jack gets shorted to ground by

27、 the mono plug and turns the difference amp into a non-inverting stage with a gain of two (assuming all resistors equal), but there is a 6dB pad (a loss of ) hung on its positive input, so the net result is a unity gain unbalanced input. The stage becomes universal now, being either balanced or unba

28、lanced, depending on whether the input plug is stereo or mono. TRANSFORMERLESS BALANCED OUTPUTS Balanced outputs have evolved in similar fashion to balanced inputs, starting out with everything using transformers and gradually moving toward transformerless solutions. The most commonly seen solid-sta

29、te circuit involves two op amps as shown in Figure 2 (or some variation of this configuration). There is one problem and one myth that must be overcome Figure 2. BALANCED OUTPUT STAGE Figure 1. TRANSFORMERLESS BALANCED INPUT STAGE FLOATING UNBALANCED OUTPUTS On many Rane products fitted with outputs

30、, a floating unbalanced drive circuit is used. What is re- quired is an output scheme compatible with balanced or unbalanced inputs that allows signal ground and shield (chassis) grounds to be isolated. are bolted together in the same rack. All of Ranes products may be intermixed with other brands w

31、ith minimal hum problems. Like the balanced input stage of Figure 1, the floating output stage of Figure 3 automatically switches to a conventional unbalanced output stage if a mono phone jack is used for interconnection. The ring of the jack gets shorted to the sleeve, thus grounding the sleeve as

32、you would in a normal unbalanced system. CHASSIS GROUND Signal ground is tied to chassis ground by a network consisting of a 10 ohm resistor and a .01 microfarad capacitor in parallel. (Update Note: the resistor has been replace by a Ground Lift switch on most products.) The small resistor allows th

33、e signal ground and the chassis ground to be at different potentials for all audio frequen- cies; while the capacitor shorts the two grounds together for high radio frequencies. The actual chassis is carefully tied to the chassis ground path at only one point. This is critical if proper chassis shie

34、lding is to be realized. SIGNAL POLARITY THROUGH RANE PRODUCTS While not wishing to engage in the controversy that rages on in the audio world regarding whether or not signal inversion is audible, it is Ranes policy to not invert signals through its products. Our position is very simpleoverall signa

35、l inversion is not necessary, so why do it? The best solution, as is so often true, is the simplest. It is no more complex than Figure 3. By taking a regular single-ended (unbalanced) line driver and floating its ground you create a compatible system for driving differential (balanced) inputs that i

36、s trouble free. Figure 4 shows the interface between the two systems. Note that while the chassis of each unit may be at the same poten- tial, their signal grounds are allowed to be at different potentials. This is very important in keeping hum common mode, and not differential. Any difference of po

37、tential existing between the two grounds is seen as a common mode signal and is rejected. This problem is particularly acute where units of various manufacturers Figure 4. INTERCONNECTION Figure 3. FLOATING UNBALANCED 1/4 TRS OUTPUT Figure 5. PASSIVE BYPASS WIRING PASSIVE BYPASS It is Ranes philosop

38、hy that Bypass switches should not require power to operate. For this reason all bypass circuitry is totally passive as shown in Figure 5. (Update Note: Some digitally controlled products violate this rule, while others use relays to accomplish the same function. Technically not passive, but they wo

39、rk in a fail- safe mode so that bypassing is automatic with power failure.) With the Bypass switch engaged, all signal connections are rerouted directly to the output (including ground) thus turning the unit into a rather expensive 3- wire patch cord. (Note that the floating output ground reverts to

40、 a straight through balanced ground connection in bypass condition.) If at any time, power is lost to a Rane product, simply pressing the Bypass switch com- pletely restores the signal path. Some Rane products use relays to automatically restore signal path upon power loss. Check data sheets. RFI fo

41、r example, the ubiquitous 9V transistor battery. LINE DRIVING CAPABILITY Since the output impedance of the RA 27 mic is fairly high at 1800 ohms, exercise some precaution before attempting to drive long lines. The best way to define a “long line” is by total capacitance rather than total length. Sin

42、ce lines will exhibit so many picofarads per foot, they are really one and the same thing, but it is the total capacitance that is the problemnot the length. With an output impedance of 1800 ohms, the RA 27 mic exhibits a 3 dB loss of 16 kHz when driving 5500 pf. So something around 5000 pF becomes

43、a good rule-of-thumb. Anything greater starts showing up as a loss of high frequencies. Therefore, if your cable has 50 pF per foot of capacitance (a common figure), then you can safely drive 100 feet with the RA 27 microphone. Figure 1. RA 27 Mic Battery Power SupplyFigure 2. RA 27 Dynamic Mic Adap

44、tor USING OTHER MICROPHONES WITH THE RA 27 Since the TRS mic INPUT jack on the RA 27 has DC voltage (+2.2 V) internally wired to the tip contact, you must use mucho discretion before plugging any other manufacturers microphone directly into the RA 27. Most microphones take a great deal of offense of

45、 having DC voltage applied to their delicate little bodies; this being true, then what to do? Block the DC, thats what! This can be done in a couple of easy ways. The first is to simply use one of several line matching transformer adapters available for adapting 3-pin mic connectors to TS jacks. The

46、se are the “in-line” type built into the connector assembly. Examples would be the Shure A95FP, Radio Shack 274-16, or Cal Switch PS-42. The transformer blocks the DC voltage from the micro- phone and makes for a very convenient adapter. Since the voltage applied to the transformer secondary is very

47、 small and the DC current is limited to about 1mA by the internal 2200 ohm JFET load resistor, the transformer still operates just fine. A second method for do-it-yourselfers who would like to save the cost of the transformer adapter is to wire up a blocking capacitor as shown in Figure 2. You will

48、need a 3- pin female connector, a TS jack, a 10k ohm or larger resistor, and a capacitor rated 4.7 microfarads at 3 V or larger. Wire them together as shown, observing the proper capacitor polarity. If available, you can use a Switchcraft 3-pin to TRS adapter model number 386A and put the capacitor

49、and resistor inside. Wire the red and black wires as shown in Figure 2. Otherwise wire the circuit into a small plastic or metal enclosure. Happy soldering. Rane Corporation 10802 47th Ave. W., Mukilteo WA 98275-5098 TEL (425)355-6000 FAX (425)347-7757 WEB 1983 Rane Corporation Professional Audio Products NN O T E 1 0 6 Dennis Bohn V.P. Research some are even good; but none seem to offer just the right mix of features, technology and cost. Until now. An attempt will be made within this Note to present the essence of a Linkwitz-Riley design, and to introduce Ran