Lima 704 Kit Instructions

The instructions for building the Lima 704 kit are broken down into steps, In this document, each step begins after a solid horizontal line. Before soldering, glance through the entire step and take note of the photos and various instructions. Some steps have special instructions to take note of.

schematic

TOOLS

You will need a soldering iron and solder, of course. In fact, we are assuming that you are familiar with basic electronics construction techniques, so you will no doubt know pretty much what is needed. There is nothing special, but you will need the following nut drivers or sockets or approximation thereof for doing the metal assembly:

3/16" for the standoffs
1/4" for the 4/40 nuts
3/8" for the rotary switch nuts

Also a #1 Phillips screwdriver will come in handy.

We have determined that some assembly steps are better performed before others to facilitate soldering.

Below are step-by-step instructions that correspond to the Assembly Guide document. Please refer to the Assembly Guide for specifics on part values, part numbers, and the order of installation.

The method we employ is to install the shortest parts first and work up to the tallest parts. This allows us to place a board on top of the parts just inserted, turn it all upside down, and solder while the parts rest against the board. Gravity does the work here. If you install the transformers first, for example, it is harder to deal with the little short parts. But use the method you like best.

STEP 1

RESISTORS: FRONT PCB

866Ω, 0.1%:
R17-26, R30-39

1.4kΩ, 0.1%:
R27


Fig. 1

Begin by installing the resistors in the front panel (Fig. 1). Note that there is one rogue resistor among these, which is R27 (1.4kΩ, 0.1%). All the remaining front panel resistors are 866Ω, 0.1%. These, plus a couple more on the main PCB, are the boost/cut resistors. The low tolerance insures accurate boost and cut steps between two 704 EQs.

NOTE: 704 pairs (consecutive odd/even serial numbers) built by Lima Audio will have hand-matched EQ capacitors. The capacitors included in this kit are 5% tolerance and will have been randomly selected unless you have specified a matched pair.
STEP 2

HEADERS: FRONT PCB

18-pin, 90 degrees:
H1-2


Fig. 2

Install the 18-pin 90 degree headers to the front PCB. Insert the straight legs into the back side of the front PCB, making sure the bent legs point toward the outside of the board (Fig. 2). Make certain that the header is exactly seated against the PCB. If it is at an angle, you may have difficulty fitting the front PCB to the main PCB and the two boards may not form a right angle when attached. Unlike the resistors, the headers will be soldered on the top side of the board. Clip the excess leads off when soldering is complete.

STEP 3

HEADERS: UB-EL PCB

5-pin, straight:
HS1-2


Fig. 3

Attach the two 5-pin straight headers to the UB-EL* PCB. The easiest way to do this is to position the long pins of the headers into the holes on the front PCB. DO NOT SOLDER THEM TO THE FRONT PCB AT THIS TIME - this is just a convenient way to hold them in place while soldering them to the UB-EL PCB (Fig. 3).


Fig. 4

Then place the UB-EL PCB onto the headers and solder in place. (Fig. 4). Remove the UB EL assembly from the front PCB.

*UB-EL stands for UB switch (the NKK series designation) elevator.

STEP 4

PUSHBUTTON SWITCH: UB-EL PCB

UB pushbutton switch:
S6


Fig. 5

Install the UB pushbutton switch to the UB-EL PCB. The switch has already been labeled, so make sure the switch label is positioned correctly with the silkscreen of the UB-EL PCB (Fig. 5).

NOTE: Although it is not shown in the photos, the right side of the UB switch will diplay the NKK logo. Double check this. The IN label can be taken out and reoriented, but the switch will not work properly if it is installed upside down.


Fig. 6

Solder the switch in place (Fig. 6).

If you plan to clean your PCBs (a good idea), do that now on the UB-EL PCB.

STEP 5

ROTARY SWITCHES: FRONT PCB

DP6T:
S1

SP12T:
S2-5


Fig. 7

Install the four SP12T rotary switches and the DP6T rotary switch (Fig. 7).


Fig. 8

The DP6T has two center pins, whereas the SP12T switches each have only one (Fig. 8).

NOTE: The SP12T switches have stop pins pre-installed. Beneath the nut and washers on each switch is a thin sticker that holds these pins in place. The sticker should hold just fine without the nut and washers, but it is probably best to keep them on until the PCB assembly is attached to the panels. (The DP6T rotary switch has permanent stop pins and thus no sticker.)


Fig. 9

Pay special attention to the placement of the SP12T switches. The angle is not the same on all four. Each of the rotary switches is numbered 1 through 12 around the perimeter (Fig. 9). The switch silkscreen on the PCB has a number 1 that corresponds to the number 1 on the switch. Make sure these line up.


Fig. 10

If in doubt, before soldering the switches in place, put a knob on each one and twirl it around from one extreme to the other to determine if you have the switch lined up properly. For S3 and S4 - the boost/cut switches - the extremes should be the standard positions of 7 o'clock counter-clockwise and 5 o'clock clockwise with respect to the upright orientation of the front PCB. S1, S2, and S5 each orient with their most counterclockwise position at 9 o'clock (Fig. 10).

Make sure each rotary switch is firmly seated against the front PCB and that the shafts appear to be parallel one with another (Fig. 7). Then solder the switches in place.

STEP 6

PUSHBUTTON SWITCH ASSEMBLY: FRONT PCB

Pushbutton on UB-EL PCB:
S6


Fig. 11

Install the UB-EL PCB with pushbutton switch to the front PCB. Again, make sure the headers seat nicely against the front PCB so that the switch will not be crooked (Fig. 11).

STEP 7

RESISTORS: MAIN PCB

90.9Ω:
R42

324Ω:
R10

402Ω:
R9

523Ω:
R8

649Ω:
R15

768Ω:
R7, R46

806Ω:
R14

866Ω, 0.1%:
R29, R40

1.05kΩ:
R13

1.1kΩ:
R6

1.4kΩ, 0.1%:
R16, R28

1.54kΩ:
R12

2.15kΩ:
R11

6.81kΩ:
R3

12.4kΩ:
R1-2, R41, R43-44

16.5kΩ:
R4

33.2kΩ:
R5


Fig. 12

Install resistors in the main PCB (Fig. 12). If you use a bending jig, use the 0.4" position.

STEP 8

DIODES: MAIN PCB

1N4004:
CR1-4


Fig. 13

Install the four diodes on the main PCB (Fig. 13). If you use a bending jig, use the 0.5" position.

STEP 9

CERAMIC CAPACITORS: MAIN PCB

330pF:
C29

0.1µF:
C3-4, C7-8, C27-28, C31-32, C34-35


Fig. 14

Install the ceramic disc capacitors on the main PCB (Fig. 14).

STEP 10

FILM CAPACITORS: MAIN PCB

680pF:
C20

2200pF:
C23

2200pF:
C23

1000pF:
C22, C26

1500pF:
C24

1800pF:
C25

3300pF:
C18

3900pF:
C21

4700pF:
C17

5600pF:
C19

0.033µF:
C14

0.047µF:
C10, C12, C16

0.068µF:
C15

0.15µF:
C13

0.22µF:
C11

0.39µF:
C9


Fig. 15

Install the small film capacitors on the main PCB (Fig. 15). If you look at the schematic, you will notice that these, the EQ frequency capacitors, are all in parallel pairs. This was done to create very specific values out of fairly standard capacitance values.

STEP 11

RELAYS: MAIN PCB

Relay:
RL1-2


Fig. 16

Install the two relays on the main PCB. (Fig. 16).

STEP 12

FILM CAPACITORS: MAIN PCB

2.2µF:
C5-6, C30


Fig. 17

Install the large 2.2F film capacitors (Fig. 17).

STEP 13

TRIMMER: MAIN PCB

1kΩ:
T1


Fig. 18

Install the trimmer (Fig. 18).


Fig. 19

Make sure the shaft aligns with the circle on the PCB silkscreen so that clockwise turning will increase the gain (Fig. 19).

STEP 14

FILM CAPACITOR: MAIN PCB

5.6µF:
C33


Fig. 20

Install the large 5.6µF film capacitor (Fig. 20).

STEP 15

ELECTROLYTIC CAPACITORS: MAIN PCB

47µF:
C1-2


Fig. 21

Install the two electrolytic capacitors (Fig. 21). Make sure to get the polarity correct. The PCB is marked with + signs...the capacitors are marked with - signs. The negative side (in the white stripe) goes toward the top of the PCB.

STEP 16

OP AMPS: MAIN PCB

OP42FJ:
U1-5


Fig. 22

Install the five op amps. These solder directly in place without sockets (Fig. 22). We prefer to leave them sticking up in the air a ways like water towers, but you can place them at any height you wish. Take special note of the tab on the side and the matching tab in the silkscreen on the PCB. Be sure and get those lined up.

STEP 17

TRANSFORMERS: MAIN PCB

LL1540:
TF1

LL2811:
TF2


Fig. 23

Install the two transformers (Fig. 23).

STEP 18


Fig. 24

Attach the front PCB to the main PCB (Fig. 24). Be sure the headers fit down snugly against the main PCB and that the front PCB is square with the main PCB when viewed from the side.


Fig. 25

The front panel makes a handy square with which to check this (Fig. 25).

If you plan to clean the main PCB, now is the time, Kato.

STEP 19 (A Multi-part Step)

PANELS

Front panel

Side panel

Hardware:
621 brackets (2)
Thumbscrews (2)
Standoffs (4)
Machine screws, 1/2" 4-40 (4)
Machine screws, 1/4" 4-40 (2)
Steel washer (1)
Fiber washer (3)
Nuts (4)


Fig. 26

Assemble the metalwork. Start by attaching the front panel to the rotary switches. Remove the nuts from the switches. Remove the star washers (we aren't using them) and place the front panel over the switches with rubber washers between the switches and the front panel (Fig. 26). Tighten the nuts down moderately using a 3/8" nut driver.


Fig. 27

Attach the 621 brackets to the side panel using the 1/4" 4-40 machine screws. These go in the front two holes that are very close to the edges. Don't tighten them down just yet. Note that the bracket is longer in one direction than the other by about 1/16" or so. Position the bracket so that the short portion of it attaches to the side panel (Fig. 27).


Fig. 28

Position the bracket so that the short portion of it attaches to the side panel (Fig. 28).


Fig. 29

Install the 1/2" 4-40 machine screws and standoffs in the remaining four holes in the side panel. (Fig. 29). Tighten these with either a 3/16" nut driver or #1 phillips screwdriver (you shouldn't need both).


Fig. 30

Place the PCB/front panel assembly in place over the side panel. Insert the thumbscrews through the holes in the front panel and thread them into the 621 brackets (Fig. 30). Tighten by hand.


Fig. 31

Use the steel washer over the upper righthand machine screw where the PCB has a solder ring (Fig. 31). This forms the chassis ground for the PCB.


Fig. 32

Place the fiber washers over the remaining three screws, and install nuts on all four (Fig. 32). Tighten moderately with 5/16" nut driver.

Finish by tightening the two 1/4" 4-40 screws that attach the brackets to the side panel.

STEP 20


Fig. 33

Apply the serial number sticker to the side panel (Fig. 33). (You can put it wherever you like.)


Fig. 34

Using a fine Sharpie, write your serial number on the PCB (Fig. 34).

STEP 21

If you have a function generator and a VU meter, you can perform a frequency response test. The overall frequency response should be in the neighborhood of -3dB at 8Hz and 75kHz.


Fig. 35

It is nice to be able to set the trimmer (T1) to provide unity gain with the controls set flat. A tone and an AC voltmeter or VU meter will work fine for this. The difficulty is in accessing the trimmer while the 704 is plugged in and working. We have a handy device called the XQP 2045 Tester that we use for this (Fig. 35).


Fig. 36

If you are devoid of such an appliance, we recommend plugging your 704 into the left-most slot of your Lunchbox and removing enough modules to the right of it that you can reach in and turn the trimmer with a little tweaker screwdriver (a Greenie, we call it) (Fig. 36). Note that the trimmer is a 20-turn model, and it advances painfully slowly during this exercise, but you shouldn't have to adjust it more than a few dB (typically).

Even without a test tone and/or a meter of any kind, you should be able, with the controls set flat, to poke the IN switch back and forth and adjust the trimmer until you do not hear a gain change between in and bypassed.

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