GA30RVS 电路图.pdf

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1、RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 1 GIBSON GOLD TONE GA-30RVS CIRCUIT DISCRIPTION Please refer to circuit diagram for DC voltages and other information INPUT SECTION AND PREAMP SK1 and SK2 are the HI and LO sensitivity inputs respectively. When the LO socket is

2、used R51, R52 and R83 act as a potential divider to reduce the input level to the preamp. C45 has two purposes, firstly to block any DC from the input that may unintentionally be present, this would otherwise change the bias point of the first valve stage, secondly the value of the capacitor has bee

3、n chosen so that there is a slight roll off of lower frequencies, this prevents the sound from getting too muddy. V1a is the first gain stage and is configured as a cathode bias, common cathode, voltage amplifier with bypassed cathode resistor for increased gain. R50 and C27 give a slight presence l

4、ift and the frequency of the Bright effect is set by C3, which, when switched in, is across pins 2 and 3 of RV1 (Volume). Obviously connected like this the amount of brightness added will decrease as RV1 is turned up. RL1 switches the extra gain stage in or out of the signal path. The relay itself i

5、s switched on or off by the push/pull switch on RV1. With RV1 pulled out the relay can also be switched on or off by the tip connection of SK3, Footswitch 1. V1b is the extra gain stage configured similar to V1a but without the cathode bypass capacitor. C62 is added across the anode resistor R87 to

6、smooth out the top end, and R53, R88 and C28 set the amount of signal sent to the next stage as well as giving a slight presence lift. V2a is the next gain stage configured similar to V1a but with C64 across the anode resistor R91 again to smooth out the top end. The signal is then fed into V2b whic

7、h is configured as a cathode follower. This reduces the impedance to drive the tone network. The Tone network is passive and controlled by RV2. This is a dual ganged potentiometer, one part of which effectively controls the mids (RV2B) while the other part inversely controls the treble (RV2A). R10,

8、R11 and R12 act as a potential divider to lower the signal sent to the reverb and effects loop circuitry. The J175 FET, TR1, is used to effectively short out R12 when the extra gain stage is not in use. This sets the volume level difference between the two preamp configurations. 2 REVERB AND EFFECTS

9、 LOOP SECTIONS The signal from the preamp is fed into IC3A which is configured as a boot strapped voltage follower. Z1 and Z2 have been added to prevent any nasty spikes from damaging the opamp, this should in practise never happen. The output of IC3a is fed to the reverb and effects loop sections.

10、C12 and R22 roll off a lot of the lower frequencies before the signal gets sent to IC3B and IC1A. These opamps are configured for current gain, the actual gain being dependant on the impedance/frequency curve of the reverb tray. Because of this it is crucial to the correct operation of the reverb th

11、at the right reverb tray is used. This should be an Accutronics 8CA3B1B. The output of the reverb tray goes into IC1B. This is configured as a differential amplifier as a way of reducing any hum that may be picked up on the sensitive reverb return leads. RV3 controls the level of the reverb. Across

12、pins 1 and 2 is TR4, a J175 FET. When the ring connection on SK3 is shorted out, i.e. by a footswitch, TR4 is also effectively shorted which results in the reverb being turned off. The reverb signal is then split and sent to the two mixer stages in IC4, however one side goes through a unity gain inv

13、erting transistor stage, TR6, just before the mixer stage. This obviously puts one of the reverb returns out off phase which produces the surround sound reverb effect. The signal from the output of IC3a is split two other ways for the effects loop. One goes to the series/parallel switch, SW1A, the o

14、ther goes to the SEND socket. R34 and R1 are a potential divider to reduce the nominal send level to about -20dBu. SK6 and SK7 are the LEFT/MONO and RIGHT RETURN sockets respectively. Each of these are fed into the two sections of IC2 which are both configured as non-inverting gain stages. The outpu

15、ts of these then go into RL2. This relay basically turns the effects loop on or off. Without a jack is inserted into SK6, LEFT/MONO RETURN, the LOOP_MUTE line is held down at 0V, this keeps TR5 turned off, which turns on TR3 and effectively shorts R70 to 0V. This turns RL2 which means the effects lo

16、op is bypassed and cannot be switched on. When a jack is inserted into SK6 the reverse happens, TR5 is turned on, TR3 is turned off and the effects loop is activated. In this mode, shorting out SK4, Footswitch 2, will turn the relay on and again bypass the effects loop. TR5 and TR3 were needed to is

17、olate the LOOP_MUTE line from the relay circuit to reduce switching noise. MIXER SECTIONS The two halves of IC4 are used as standard virtual earth mixer sections. Here the dry, effects loop and reverb signals are mixed together depending on the settings of the series/parallel switch and RL2. The out

18、puts from each half of IC4 then provide the left and right signals sent to the two power stages. 3 POWER STAGES The two phase splitters (V3 and V4) are differential input splitters which each produce the anti phase signals necessary to drive the push pull output stages. The outputs from V3 drive the

19、 EL84 power valves V5 and V6 for the left side power stage. V4 drives V7 and V8 for the right side power stage. The two pairs of EL84 output valves are configured as push pull, cathode biased, class A power amplifiers. The quiescent current of each power stage is set by R71 and R73, which are bypass

20、ed by C41 and C43 for extra gain. D3, D4, D5 and D6 have been added to give protection to the output transformers should a fault arise. OUTPUT TRANSFORMERS AND SPEAKER CONNECTIONS The output transformers have secondary taps for 16 and 8. The four LINK positions are provided on the PCB so that differ

21、ent impedance internal speakers can be used in production. Depending on whether the internal speaker is 16 or 8 the correct LINK should be fitted. This has been done purely so that different impedance speakers can be used if there are any problems with supply. SW3 selects the output impedance of the

22、 External Speaker Outputs, SK8 and SK9. These can be set to either 16 or 8. When a jack plug is inserted into either of these sockets the corresponding internal speaker is disconnected. POWER SUPPLIES All three supplies, HT, ac heater, and DC supplies have secondary fusing on the PCB. This is for ap

23、provals and to protect the mains transformer. The HT supply is a simple bridge rectifier diode network, with 4n7 1KV capacitors across each diode for EMC reasons, which is then smoothed by C82, to supply the centre taps of the output transformers. R126, C81, R127 and C80 have been added to isolate t

24、he two centre taps at high frequencies. The main supply is then further smoothed to supply the screen grids, phase splitters and preamp. R128 is added to discharge the high voltage capacitors when then unit is turned off. The ac heater supply is simply connected via two twisted pair connecting leads

25、 to V5, V6, V7 and V8, after first going through the secondary fuses. The 25.2V DC supply is a highly regulated supply using a BD647 (TR8) as the main regulating device. (Please ensure that the heat sink is attached to TR8 and heat sink compound has been used) 4 TR7 and TR10 provide a constant curre

26、nt source for Z3 the 15 volt zener. The output voltage is set by the ratio of R119 and R120 which provide the feedback to TR8 via TR11 and TR12 to stabilise the whole circuit. TR9 with R121, R122 and R123 form a current limiter. This allows the supply voltage to ramp up at switch on when the heater

27、filaments of the preamp valves draw considerably more current while cold. R117 and R118 halve the supply voltage to provide the opamp bias voltage, and as shown on the circuit diagram the DC supply is routed through the filaments of two of the valves in series. This will result in each filament havi

28、ng the nominal 6.3 volts across them. Paul Stevens 30 June 1999 1 VELOCETTE TWIN VALVE GUITAR AMPLIFIER Introduction Congratulations on your purchase of a Velocette Twin. The Velocette Twin is part of the Trace Elliot Velocette range. This is basically a range of no nonsense, compact, valve guitar a

29、mplifiers with the minimum controls necessary to produce a good range of sounds. However, with the addition of such features as a switchable gain boost, stereo effects loop, pseudo-stereo reverb, and a stereo power stage, the Twin model takes the range as far as it could possibly go while still just

30、ifying a Velocette badge. The circuit topology has been based on traditional guitar amplifier designs, with new ideas incorporated where beneficial. The main preamp and both power stage sections are 100% valve. The valves used are four ECC83/12AX7s and four EL84/6BQ5s run in Class A in stereo (two E

31、L84s per side). REAR PANEL CONTROLS INPUTS - HI & LO/LINK Two jack sockets are provided for connection to your instrument. The HI input is a high impedance, high sensitivity input. This can be used with both passive and active guitars and, depending on the level of output from the guitar and the VOL

32、UME setting, allows the amplifier to be driven hard into overdrive, if desired. The LO/LINK socket can be used in two ways. Firstly as a lower impedance, low sensitivity input, for use with high output guitars when the user wishes to keep the overdrive under control. Alternatively this socket can be

33、 used as a LINK to chain together two or more Velocettes, simply plug your guitar into the HI socket, take an output from the LO/LINK socket and plug this into the input of the next amplifier in the chain. BRIGHT The BRIGHT switch adds more high frequencies when selected. It works in the traditional

34、 way, therefore it has more effect at lower VOLUME settings. 2 VOLUME PULL GAIN This is a push/pull potentiometer. Pushed in the control acts like a normal volume control on a typical non-master volume amplifier, therefore it sets the overall volume level of the amplifier and has a huge effect on th

35、e tone and the amount of overdrive. From low to about halfway, depending on the output level of the guitar and which input socket is used, the sound should remain reasonably clean. Increasing the control further will progressively increase the level of power amp overdrive in the sound, obviously bei

36、ng a valve amp it will respond to the players dynamics and use of the instruments volume. Pulling the control out activates the additional valve preamp stage therefore effectively turning the control from a VOLUME into a GAIN control. This extra gain stage makes it possible to produce a fuller overd

37、rive sound especially when turned up as this blends preamp distortion with power amp distortion. With the control pulled out the extra gain stage is also footswitchable. This enables the user to footswitch between clean and dirty sounds. Setting the VOLUME at about 12 oclock gives lovely warm clean

38、sounds which can then be switched to a nice, not too saturated overdriven tone. For total and instant control over a range of clean and overdriven tones we recommend turning the VOLUME control all the way up. Without the extra gain stage switched in the player can then back off the volume on their g

39、uitar for clean sounds, turn up fully for some crunchy, responsive power amp overdrive, and then kick in the extra gain stage for thick lead tones with lots of sustain. TONE Unlike other single tone controls on other amplifiers, which act merely as a treble roll off, this control works in a differen

40、t way. It is a dual gang potentiometer which controls two functions simultaneously. In the fully anti-clockwise position the midrange is dominant in the sound, turning the control clockwise decreases the mids while at the same time increasing the higher frequencies. Start with it in the 12 oclock po

41、sition and try different settings with or without the BRIGHT switch to find the settings that you like. Bear in mind that as the VOLUME is turned up the BRIGHT switch has less effect. REVERB This single control is for adjusting the amount of reverb effect in the sound. The effect is produced by a th

42、ree spring reverb tray inside the cabinet. However due to a simple but extremely effective modification to the signal between the reverb tray and the stereo power stages, what you actually hear is a huge pseudo-stereo reverb that seems to fill the whole room. It is even more noticeable when using ex

43、tension cabinets. FOOTSWITCH SOCKETS 3 These sockets are for connecting to latching footswitches. The first one is dual function and operates the extra gain stage (with VOLUME pulled out) and reverb. The second turns the effects loop on or off if used. EFFECTS LOOP This has sockets for SEND, LEFT/MO

44、NO RETURN and RIGHT RETURN as well as a switch for SERIES or PARALLEL configuration. The SEND is for connection to the input of effects units and can drive floor type battery powered effects pedals or 19” rack type studio effects units. The RETURN sockets are for connection to the outputs of effects

45、 units. If a mono effect unit is used then use the LEFT/MONO RETURN. The SERIES/PARALLEL switch alters the configuration of the effects loop. In SERIES mode the whole signal comes out of the amp, into the effects unit and then back into the amp, whereas in PARALLEL mode the effected signal is mixed

46、in with the original dry signal, thus retaining tonal purity of the dry signal. The choice of which mode to use will depend on what kind of effects unit is used and what overall effect is desired. But generally if time delay effects are used, such as delay (echo), chorus, flanging, phasing, etc., th

47、en the PARALLEL setting is usually preferred. If volume or EQ related effects are used, such as overdrive/distortion, compression, graphic equalisation, wah-wah or volume pedals, or if a multi-effects unit is used with a combination of time delay and volume related effects, then it is usually best t

48、o set the switch to SERIES. There are no rules, it is best to experiment and see what you prefer. If PARALLEL configuration is used then if possible it is recommended that the dry/direct signal from the effects unit is turned off. The effects loop is not activated unless a jack plug is inserted into

49、 the LEFT/MONO RETURN socket. The loop is then footswitchable if a suitable latching footswitch is connected to the appropriate footswitch socket. It is also possible to use the Velocette Twin purely as a stand alone mono/stereo power amp. To do this set the loop to SERIES configuration, this will effectively eliminate the preamp and plug signal source(s) into the RETURN socket(s). EXTERNAL SPEAKER OUTPUTS 4 These have been provided throughout the Velocette range so that the user can connect them to external 16 speaker cabinets, such as 4x12s, for different sounds. This is useful for