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ElectroMix 842 (Part 2) | |
Article from Electronics & Music Maker, November 1982 |
The second and final part of our superb professional quality studio mixer project
This month we continue our superb mixer project with construction and setting up details.
Although construction should be fairly straightforward, there are a few points worth noting. Before assembling any of the boards, slots for the buss wires have to cut in the edge using a hacksaw and/or small file. The buss wire should be 16swg, stretched to form straight lengths. IC sockets should be used although none were used in our prototype. A socket for IC1 of the Channel Module can be made by carefully cutting a 16 pin socket in half.
Insert and solder the required links on each board as shown in Figures 1, 2, and 3, with reference to the photographs of the completed boards. Next insert the veropins; on the component overlays these are shown with crosses when they protrude from the track side and with dots when they protrude from the component side. The resistors and capacitors can now be inserted and soldered, taking care with electrolytic capacitor polarities. If you are using IC sockets these can now be positioned and soldered. The switches and pots come next, not forgetting the pre-set on the monitor board. After this stage the IC's can be pushed into their sockets or soldered into place.
As PCB mounting jack sockets seem almost unobtainable except to equipment manufacturers, normal types with solder tags are used which are fixed to the boards with short lengths of tinned copper wire, (soldered first and then inserted into the PCB's). The sockets and the switches must be seated squarely on the board to avoid problems when mating the PCB's to the front panel. There is a link to be added on the routing switches of each channel board and one on the monitor board which are soldered directly to the switch tags (see overlay diagrams). There is also an earthing link from each PCB to the back of one of its potentiometers. The LED's are bent and soldered to Veropins after the PCB's have been mounted to the face plate. The bulk of the wiring is to the Aux, Group and Monitor sockets which is made with screened wire. The returns of the Group faders should be screened although this is not necessary for the Channel faders (see wiring details). As the power supply is remote, miniature 3-core mains cable was used to feed the Channel supply busses. These should be linked to the Group and Monitor busses (see Figure 4).
After checking wiring, IC, diode and LED orientation, power up and test supply voltages. If all is well, connect a suitable amplifier and speaker set-up to the Monitor outputs. Turn the Monitor level to maximum, little or no background noise should be heard. Plug a signal source (tape deck, radio etc.) into Channel 1 line input and select line input. Bring the Channel and Group faders to 0VU and the Panpot to central position. Press Group 1 and 2 switches on the Monitor module and adjust Monitor level. Run through all the functions on the Channel i.e. Input select (check Mic input is more sensitive), EQ, Routing, Pan, Aux sends, etc. This is repeated for the other Channels selecting the appropriate outputs on the Monitor select switches each time. If all inputs and outputs appear to operate correctly, disconnect the signal source and turn Monitor level to maximum. Run through all controls and switches which should operate quietly. Any thumps or clicks produced by switches indicates a DC level, which should be checked out with an oscilloscope or voltmeter. If any controls produce a small amount of noise this should be compared to normal listening levels to see if any further investigation is necessary.
Peak to peak voltages | Signal level |
---|---|
880mV | -10dBV |
2.8V | 0dBV |
2.2V | 0dBm |
3.5V | +4dBm |
13.8V | +16dBm* |
22V | +20dBm |
*Recommended level for Clipping indicator.
The only preset which has to be set on the mixer is the Reference for the clip LED's. Set all faders to 0VU and insert a signal. If using as a level indicator for recording adjust the LED's to come on at a 0VU reading on your Tape recorder. In a P.A. situation the LED's could indicate a signal level for full output power of the amplifiers used. Alternatively as a clipping indicator, reduce the level of signal with the fader and increase the gain until definite distortion is heard. Reduce the gain so the distortion is no longer audible and adjust the LED's to just light. If you have access to an oscilloscope Table 1 gives peak to peak values for various signal levels.
The mixer requires a ±15V regulated supply at approx. 200mA. A supply designed specifically for the ElectroMix is shown in Figure 5. This circuit uses standard voltage regulators IC1 and 2 fitted with on board heatsinks. This supply will also power the meter bridge.
Construction is straightforward with components inserted in the usual order; veropins, diodes, capacitors and IC's. (— correct polarities are very important!). See Figure 6.
Double check all connections before connecting to the mains supply.
Please note; LF351 and LF353 IC's were specified on the circuit diagrams last month. Certain samples of LF353 seemed to burst into high frequency oscillation, so alternative types TL071 and TL072 were tested and proved to be more suitable, with the added bonus of being a lot cheaper.
The Retro-fit input channel with an electronically balanced Mic input and the Meter Bridge will be described in a forthcoming issue.
All parts except panel and PCB's are available at most electronic component retailers. Details of complete kit suppliers will be published next month.
The fully finished panel and a set of PCB's are available from Electronics and Music Maker, (Contact Details). The prices are £24.95 for the drilled, sprayed and screen printed panel and £24.95 for a full set of PCB's inc. p&p and VAT. Order as ElectroMix 842 Panel and ElectroMix 842 PCB set. Please allow 28 days for delivery.
Channel Module — Quantities For One Board — 8 Required | ||
Resistors — 0.25W, 5%, Carbon except where marked. | ||
R1,6,27 | 47k | 3 off |
R2 | 2k7 | |
R4,5 | 100k Metal Film | 2 off |
R3 | 220R Metal Film | |
R7 | 82R | |
R8 | 22k | |
R9,10,16,19,20-24 | 100k | 9 off |
R11,14 | 1k5 | 2 off |
R12,15 | Ik0 | 2 off |
R13,17,18 | 10k | 3 off |
R25,26 | 4k7 | 2 off |
Capacitors | ||
C1,12 | 220nF Siemens multilayer | 2 off |
C2,5 | 47pF Ceramic | 2 off |
C3 | 100pF Ceramic | |
C4 | 22pF Ceramic | |
C6 | 220uF 16V PCB electrolytic | |
C7,11 | 100uF 10v PCB Electrolytic | 2 off |
C8 | 47nF Siemens multilayer | |
C9 | 4n7 Siemens multilayer | |
C10 | 10pF Ceramic | |
C13,15 | 47uF 25v PCB Electrolytic | 2 off |
C14,16 | 10nF Ceramic | 2 off |
Potentiometers | ||
RV1 | 10k Reverse Log | |
RV2,3 | 22k Lin | 2 off |
RV4 | 4k7 Log Slider | |
RV5 | 10k Lin | |
RV6,7 | 100k Log | 2 off |
Semiconductors | ||
IC1 | HA12017 | |
IC2 | TL071 | |
IC3 | 741 | |
D1 | OA90 | |
Miscellaneous | ||
JK1,2 | Mono switched jack socket | 2 off |
S1-4 | 2 Pole latchswitch | 4 off |
3mm Red Led | 1 off | |
Grub screw knob | 5 off | |
Knob cap | 5 off | |
Slider knob | 1 off | |
Switch cap | 4 off | |
Group Module — Quantities For One Board — 2 Required | ||
Resistors — 0.25W, 5%, Carbon. | ||
R1,8 | 220k | 2 off |
R2,6,9,13,16 | 47R | 5 off |
R3,7,10,14,17-22 | 100k | 10 off |
R4,11 | 4k7 | 2 off |
R5,12 | 10k | 2 off |
R15 | 330k | |
Capacitors | ||
C1,6 | 10pF Ceramic | 2 off |
C2,5,7,10,12 | 100uF 10V PCB Electrolytic | 5 off |
C3,8 | 2u2 16v PCB Electrolytic | 2 off |
C4,9 | 150pF Ceramic | 2 off |
C11 | 4p7 Ceramic | |
C13,15 | 47uF 25v PCB Electrolytic | 2 off |
C14,16 | 10nF Ceramic | 2 off |
Potentiometers | ||
RV1,2 | 4k7 Log Slider | 2 off |
RV3 | 10k Log | |
RV4 | 100k Log | |
RV5 | 100k Lin | |
Semiconductors | ||
IC1,3 | TL072 | 2 off |
IC2 | TL071 | |
Miscellaneous | ||
Mono unswitched jack socket | 4 off | |
Grub screw knob | 3 off | |
Knob cap | 3 off | |
S1 | 2 Pole latchswitch | |
Switch cap | 1 off | |
Slider knob | 1 Off | |
Monitor Module — Quantities For One Board — 1 Required | ||
Resistors — 0.25W, 5%, Carbon | ||
R1-8 | 100k | 8 off |
R9,11 | 220k | 2 off |
R10,12,1417 | 47R | |
R13,16,21 | 10k | 3 off |
R15,18,20,22 | 1k0 | 4 off |
R19 | 100R | |
Capacitors | ||
C1,3 | 10pF Ceramic | 2 off |
C2,4 | 100uF lOv PCB Electrolytic | 2 off |
C5 | Not used | |
C6,7 | 2u2 16v PCB Electrolytic | 2 off |
C8,11 | 150pF Ceramic | 2 off |
C9,12 | 100nF Siemens multilayer | 2 off |
C10,13 | 220uF 16v PCB Electrolytic | 2 off |
C14,16 | 47uF25v PCB Electrolytic | 2 off |
C15,17 | 10nF Ceramic | 2 off |
C18 | 470uF 16v PCB Electrolytic | |
Semiconductors | ||
IC1 | TL072 | |
IC2,3 | LM380 | 2 off |
Potentiometers | ||
RV1 | 10k + 10k Log Dual | |
RV2 | 100k + 100k Log Dual | |
RV3 | 22k Min. Vertical Preset | |
Miscellaneous | ||
S1-6 | 2 Pole latchswitch | 6 off |
JK1 | Stereo switched jack socket | 1 off |
JK2,3 | Mono unswitched lack socket | 2 off |
3mm Red Led | 1 off | |
Grubscrew knob | 1 off | |
Knob cap | 1 off | |
Switch cap | 6 off | |
Power Supply | ||
Capacitors | ||
C1,4 | 2200uF 25v Electrolytic | 2 off |
C2,5 | 100nF Siemens multilayer | 2 off |
C3,6 | 47uF 25V PCB Electrolytic | 2 off |
Semiconductors | ||
D1,4 | 1N4001 | 4 off |
IC1 | 7815 | |
IC2 | 7915 | |
Miscellaneous | ||
T1 | 15-015v, 30VA Transformer | |
S1 | Mains rated switch | |
FS1 | 500mA 20mm Fuse | |
20mm Fuse holder | ||
Case, to suit transformer used. |
FROM PIN | TO | REMARKS | |
---|---|---|---|
Channel Board | |||
1 | RV4/2 | - | |
2 | RV4/2 | - | |
3 | RV4/3 | - | |
Group Board | |||
1 | RV1/3 | - | |
2 | RV1/1- | Screen | |
3 | RV1/2- | *Conductor | |
4 | RV2/3 | - | |
5 | RV2/1- | Screen | |
6 | RV2/2- | *Conductor | |
7 | JK1/2 | Screen | |
8 | JK1/1 | *Conductor | |
9 | JK2/2 | Screen | |
10 | JK2/1 | *Conductor | |
11 | JK7/1 | *Conductor | |
12 | JK7/2, JK5/2 | Screen | |
13 | JK5/1 | *Conductor | |
Links:- 14 to 15, 17 to 19, 20 to 22 | |||
Group Board 2 | |||
1 | RV1/3 | - | |
2 | RV1/1- | Screen | |
3 | RV1/2 | *Conductor | |
4 | RV2/3 | - | |
5 | RV2/1- | Screen | |
6 | RV2/2- | *Conductor | |
7 | JK3/2 | Screen | |
8 | JK3/1 | *Conductor | |
9 | JK4/2 | Screen | |
10 | JK4/1 | *Conductor | |
11 | JK8/1 | *Conductor | |
12 | JK8/2, JK6/2 | Screen | |
13 | JK6/1 | *Conductor | |
Links:- 14 to 16, 17 to 18, 20 to 21. | |||
Monitor Board | |||
1 | Screen | ||
2 | Group Bd. 1/13 | *Conductor | |
3 | Screen | ||
4 | Group Bd. 2/13 | *Conductor | |
5 | Screen | ||
6 | Group Bd. 1/8 | *Conductor | |
7 | Screen | ||
8 | Group Bd. 1/10 | *Conductor | |
9 | Screen | ||
10 | Group Bd. 2/8 | *Conductor | |
11 | Screen | ||
12 | Group Bd. 2/10 | *Conductor | |
13 | JK2/1 | *Conductor | |
14 | JK2/2, JK3/2 | Screen | |
15 | JK3/1 | *Conductor |
This is the last part in this series. The first article in this series is:
ElectroMix 842
(EMM Oct 82)
All parts in this series:
Part 1 | Part 2 (Viewing)
Workbench - Lighting Effects on Stage — Update |
Lab Notes: Computer Music Without the Computer - or: What to do 'til your processor arrives. |
Workbench - Impedance. What is it?! |
A Digitally Addressed Transposer - for Your Analog Keyboard or Sequencer |
The Layman's Guide to Digital Logic Gates - (in one easy lesson) |
Analogue Equipment Design - for Rock 'n' Roll (Part 1) |
Adding an Independent Tracking Output to the 4780 Sequencer |
Speaker Drive Units - Control Room (Part 1) |
Workbench - CHECKA |
Workbench |
Interfacing External Signals with the Gnome Micro-Synthesizer - Guitar/Gnome Interface |
Experimenting With Analog Delay |
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Feature by Paul Bird
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