JMP-1 translation from French - Google

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After studying the internal topology and operation of the Marshall JMP-1 preamp (see Guitarist No. 132 of February 2OO1), let's get serious with some more changes easy to implement and relatively inexpensive. Dr Boost

 This time, operate the beast with open heart. But beware, in addition to caring for one such operation, please have good tools to work, otherwise deface any preamp legend. You need a soldering iron of 15 watts (maximum) to sharply pointed tip (JBC style, for example), good tin / lead type Sn6QVPb4Q (money not required) mm of diameter or smaller (0.5 mm], a desoldering pump (especially not of the braid that could toast the printed circuit tracks), a small cutting pinc9 for electronics, a small needle nose pliers, a tiny screwdriver (size 0 or 00), two 9 volt batteries and a multi-meter [voltmeter in position on a continuous rating of 20 volts). Do not forget the small Phillips screwdriver (size 1) and a small Allen key 2 rnm which will be used to disassemble the box, If you do not have this tool, that fon can acquire for less than 300 francs, reassure your portfolio saying that such investment will always and will be amortized rather quickly.

Preliminaries

Start with completely disconnect themselves JMP-1. Then press the "Power" button and leave switched on for 1 minute, to discharge the capacitors in the circuit high voltage tubes. The dismantling of the enclosure shall be effected as follows: a few Phillips screws and a few BTR (Allen bolts) release the lid (do not forget the three screws on the rear panel), the front el connections. Careful, do not forget to unscrew the nuts jacks, both front and rear:

can make themselves at J3 hand, knowing that a 6-point key may deform the plastic nuts. Mo not forget the tiny screws on either side of the base area and taking tootsvuitcn. Then you have to gently remove tubea their supports (in silent sway gently pull the two légèremenE ECC83) and store them in a safe place. Same for hardware that does not drag on the pool table or lose a few copies of BTR and others. Due to the presence of digital circuits in the JMP-1, Jim Marshall has treated the grounding of the box: It will suffice to remove the few terminals to son ei yellow green that hold the motherboard to the enclosure, without ouDIier o: e unsolder one who reaches the outlet Disconnect the two ribbon cables gray side of the main circuit. Ser-vez-i/ous of small needle nose pliers to squeeze one by a small black plastic cffps that block the card at the bottom of the chassis. It should gradually lift and pull forward so that the jacks are leaving their openings on the rear panel.

Detail the magnetization series: IC5 IC6 and were replaced by êgubteirs DKE, recognize their ajustai blue for fine adjustment (average have a small risk} of the output voltage. Should the regiïateurs, Jes & ucroe BBUS are dee capacitors of 100 nF rm-derslein, tiny compared to ct / amic CONMe original C41 and DW {jaanesl small drops.

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Power Optimization

Potential source of transmission of parasites, the primary supply of Marshall has no special filtering. The most economical and most effective is to place a varistor 250 volts between phase and neutral themselves, directly to the back of the base area. This small component eliminates much of the noise from outside. The most rich added this layout to an external power Cabie filtered connectors: decision-mura: fe contains two inductors and a capacitor, while the IEC connector that plugs preamp side contains two capacitors tie kind diflérentG, Speaking precisely capacity, if still also possible to weld 4 capacitors of 47 nF (nanofarad) in the diode bridges BR1 and BR2, the first devoted exclusively to audio, the second for digital circuits (memories, displays, etc.). To best fulfill their role, these capacitors must be made of polypropylene, because of the speed d9 dielectric response of such a deal with parasites. Jl enough to weld diamond, one after the other, between the four contacts of the diode bridges and voila. If you can not find facifement of 47 nF polypropylene, you can fall back on in capas polysiyrène, gender Mrffeuil Thomson (small yellow models that are found everywhere). Éleclrochiniques dee power capacitors are original quality more than adequate, it will not be replaced: they are all polarized capacitors (equipped with a positive terminal and a terminal •). However, they are decoupled by small capacity of 100 nF. To improve the silent operation of power supplies, replacing these elements by models in polypro 'provides a more significant: these capabilities smooth the undulations of the signal with more rje quickly than would auîres of dielectrics.

Regulators of the audio

There are several kinds of voltage regulators. These elements receive on their input a DC voltage and any deliver an output voltage regulated ©. The example of the JMP-1, rather simple, meets four voltage regulators format called Tu 220: two 7805, one 7815 and 7915, the first two generate 5 volta, the third of 15 volts, and the last of-15vofts. The first two digits of the reference indicate a positive voltage (78) or a negative voltage (79), the last two determine the output voltage. • The voltages + 5 volts are dedicated to digital circuits, while 15 M5 dedicated to feeding audio circuits. The former are solicited will handle almost constant by digital technology. However, regulators of audio, forming a symmetrical alimentalion © (two voltages of opposite sides of the mass, is therefore of zero volts], undergo changes in level (where dynamic) signal fa guitar : the current drawn by the sound is not constant ei your regulators may have to provide a large inrush current snapshot. To obtain good results in this field, II would have the series resistance of regulators tends to zero, Quf, unfortunately, no, is not the case. Moreover, the measured voltages on the 7815 and 7915 show a CFE-rigging: +14.4 volls to you first, second uoltspourlG -15.2.

The DXE

While I worked in technical service of the NRJ Group, I ar is making negative regulators in bootmaker TO 220, which did not exist in the range of French society DXE, which offered for sale as positive regulators in this format. Interest (I these little gems of electronics is manifold: they have a pinout compatible with the 78XX and 79xx. Can finely adjust the output voltage through a multi-turn potentiometer (20 to 22 laps) and series resistance borders on infinitesimal only 1.5 milli Ohm, With these adjustable regulators, it can jam the voft exactly zero between real and 15-15 volts while the zero volt offset (the offset voltage) is found throughout the audio below and may, as appropriate, degrading the overall definition of the audio (this is seen, heard, compare, & c). In addition, the DXE enable a rapid response when calling current circuits downstream regulators. Dalix Hubert, the founder of DXE achieved a master stroke with VR 300 (positive regulators in TO 220) and RV 337 (e negatives same box). In his address, he must first worry about three little son on two 9 volt batteries connected in series to obtain 18 volts: just connect the - of a battery - on the other. It • are left with a + and a - fiber, Regarding adjustment of VR 300 for 15 volts, connect the + iJ be the first pin of the regulator and - to his second. We read the output voltage with a multimeter , the black wire on pin 2 of VR 300 and the red wire on the 3.

For VR 337R proceed the same way, but beware: the pinout is different from the positive regulator. Facing the housing of a positive regulator, the three pins are as follows: entry, mass exit. However, a negative regulator, we reverse the first two pins: mass.

The floor of the JMP-û'ertrêe the revised and corrected, with the exception of the circuit iirtégrê fflfc subtelii 5201A of excellent quality. Note the pdypropyfëne capacitors of 100 nF and 22 if the signal conditioning ggitare there at the entrance. On the left, the TLQ72 (IC331aètêremplacé by Burr Browi OPA 2604, which sounds a ampltop • tubes.

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input, output. -15 Volts to drive "it is necessary to connect the f-stack" 18 volts "on the first pin-VR337 and the second. Then, at the cost of adjustment (using the small screwdriver) we must read -15 volts on the multimeter's red wire should connect to pin 3 and 2 on the black. Why settle before soldering? For good reason: as we do not know what their blood output when Tachât, you can not install them without the risk of creating an imbalance in the tension theoretically symmetrical, Imagine, in the worst case which is generated from 15 vofts positive side and nothing (0 volts) of On the negative side: it is irreparably damaged the operational amplifiers. We will discuss these elements further, because we will change them almost entirely ...

Signal Path

The signal path (literally] takes many detours, such as buffers, filter circuits, corrections actrves stamp (low, mid, presence aigur), the gain circuits and so on. In order to block the DC component in the audio circuitry, the signal passes through a large number of capacitors, ceramic overwhelmingly. This dielectric has never been an attractive solution for audio, if not for filtering high-frequency generally above the audible spectrum. Designing a high-pass filter (passing the signal above 0 volts and blocking this side] for audio lie better than these tiny ceramic capacitors. Again once, polypropylene metallized polyester 9l "sound" better, and there is no need to possess supernatural gifts for the difference to you jump instantly to the ears. History not to ruin, II have to select the capacitors being really on the signal path and possibly some other change contained in the feedback circuits against (reblouclage back on the output of an operational amplifier to stabilize the assembly, the gain value set, in association with resistors, and filter unwanted frequencies. As discussed above, the capacitors éfectrochimiques (large capacity polarized) light by all their good quality. We checked in power supplies, and we can only see well in the audio circuits : an impressive 030 series Philips are prominent, especially on the outputs. We will leave these powerful elements in place. Concerning the replacement of non-polarized capacitors located on areas of strategic importance, their values s' range from 1 nF to 220 nF (1 nF = 0.001 uF = 10 -9 Farad). Nothing to ruin, despite their rather large number. Depending on what you find in the specialized pharmacies, a voltage of 63 or 100 volts will do. The away-rnent of contacts on the circuit is around 12 mm. As this is rather rarely no, it will take a little off the legs of the capacitors, most often, in these formats, feature a step of 5, 10 or 15 mm. The simplest solution F is to cut the legs of the capacitors directly home to resolder the new models over the polypropylene; it goes faster, it is less risky and equally strong , if one goes well the solder at the right temperature. A number of these small capacities decouple 4-15/-15 volt power supplies, they SONL present on the table against. The reference capacitor is easily legible with silkscreen of the PCB. Take your time and pay attention to your every move,

Active circuits

Again, Marshall chose good people of ordinary quality, divided into three categories: we will leave in place the operational amplifiers doubles Mitsubishi A52Û1Ah because of their very good quality and their high output current. We use this kind of circuit to power the high-fidelity headphones outputs. In contrast, two other models of operational am-plilicateurs deserve a replacement without regret: the JMP-1 contains TL072 (am-ply double-op ') and their big brothers TL074 (quad op-am-ply'). Medium quality, these elements produce a sound very banal. There are ways to do better by replacing the 4 double and quadruple in five models much more sophisticated and more accurate sound reproduction. Instead of trying to desolder
TL072 and TL074, we must cut off their legs with

Above the ECC83 tube. if pmt LED ER3 aisocie another diode, a capacitor hidden Philips 220 nF. It is here that the JMP-1 generates its saturation, Note toue las capacitors changed (-BUdes-blue, black, brown, jaunw) chosen for their role in the circuit.

Demiers floors trr.tr wind JMP-1. placed online on the printed circuit. The polypropylene capacitors are almost everywhere. The second half of i-r anshficatei quad operational LT1058 is used to feed the headphone output: polypnw 'of 4.7 nF 1 nF and 100 nF required).

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wire cutters and then unsolder one to one by cleaning the via hole through the pump part. Then, instead of asking the new amplifiers directly on the motherboard, it will suffice to weld brackets integrated circuits, called "tulip media" for the shape of their gold-plated contacts. This improvement of the JMP-1 therefore requires 4 brackets 8 and 5 media contacts 14 contacts. Well mark the direction of connecting the opera-tional amplifiers, the asymmetric shape of the supports used to distinguish the front from the back, which can not be wrong when inserting the circuit in order to improve contact tulip-the definition of the Marshall sound without betraying its specificities, I chose the Burr Brown OPA 2604 for the replacement of double and Linear Technology LT 1058 for quadruple. There are many other combinations to identify which of the hundreds of references suggested by Jes manufacturers. However, the solution presented here is the best quality / price / performance. If these amps-op1 are more accurate than those of origin, they share certain common, as a similar rise time, for example, respect of such a parameter to ensure an excellent result, the JMP-1 does not become soft (TM too slow) or abrupt (TM too quickly). In addition, OPA 2604, to FET technology, have an absolutely "tubes" very interesting. The FET is only too rarely farms in the lower register, the association of bipolar LT 1058 to design reinforces the seat in the lower spectrum

Référence     Valeur en nF

C121	100	C22	100	
C119	22	C23	100	
C11G	68	C24	100	
C117	100	C3	4,7	
C110	100	C6	4,7	
C9Q	220	C12	100	
C91	220	CI 3	100	
C50	100	C102	100	
C70	10	C103	220	
C72	220	C104	220	
C60	220	C106	4,7	
C63	220	C107	4,7	
C45	10	C109	220	
C46	47	C95	10	
C47	47	C96	47	
C48	47	C97	4,7	
C49	47	C98	10	
C50	10	C99	4,7	
C29	2,2	C84	47	
C30	1,5	C86	220	
C31	1,5	C64	220	
C32	2,2	C53	22	
C19	100	C54	22	
C20	1	C37	100	
C21	1	C40	100	

These tests, which can seem strange from long experience in the closed world of hi-fi high-end, in which yours truly continues to rage, to be regularly consulted by often known trademarks and / or prestigious.,. \

Circuits (retro) active

N exists in the world more brands of tube amplifiers that brand of transistor amplifiers. Tube technology has enjoyed a revival in the first half of the 70s, but we must recognize that the tube has never disappeared from the audio and pi of us alone I ampiification of our beloved guitars, No wonder rje find a pair of ECC83 tubes in the JMP-1. These double-triodes wear out over time and should consider replacing the batteries. You have two solutions: either you buy the bulbs original stamped logo Marshall, or you visit a specialty pharmacy to choose other tubes of different origins. I bought a pair of ECC83 Chinese at Valve House Music in Paris and the sound is to die for, a real massacre, at a cost of more than Marshall, but the fun is at this price.

Boost your JMP-1!

Because of my long practice of electronic circuits, I knew few details about what to expect in operating in the JMP-1. The result far exceeded my expectations: the sound is closer to its "tube" full, it is denser in the clear, he crunche more harmoniously, and, combie paradox, since the leaves rather spend polypropylène harmonics that most other dielectrics, we get sounds saturated with beauty, endowed with perfect intelligibility scores in the agreements, that the JMP-1 core was not able to return to this point before custornisation. Outwardly nothing distinguishes a JMP-1 "Dr. Boosted" a model home. But as soon as the branch, improvements to the ears pop. At your soldering irons and soon! •

At the condc'jvit bet '. -. poJyprop ^ ene in a variety of sources and the "power of i me: retra-wt L: • - operational amplifiers Burr Brown OPA 2604 (bottom dwte) ies and Technology LJneaf LTlÛSSfen top left s] greatly improve the sound dU JMPd , replacing TL072 and TL074 respectively your home.