PAiA 9754 Preamplifier Owner's Manual
The Paia 9754 is a second-generation processing element for modular sound synthesizers. It is designed to provide high-quality sound and excellent value. This preamplifier can be used to match low-level signals from microphones to the line-level signals anticipated by modern modular synthesizers, or to perform a general signal boost. The 9754 module features adjustable gain control, balanced/unbalanced input selection, and LED signal level indication. It is compatible with most modular synthesizer systems and includes an optional external voltage source for phantom-powered microphones.
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Preamplifier
Model 9754
Assembly and Using Manual
This second-generation 9700-series processing element for modular sound synthesizers is designed to provide great sound and excellent value.
The 9754 is used to match low-level signals such as those from microphones to the linelevel (plus) signals anticipated by modern modular synthesizers, or, just to perform a general signal boost.
Inputs to the module may be balanced or unbalanced (two or three circuits), via XLR plugs, 1/4" phone plugs, or 1/8" phone plugs
(tip-sleeve phone, aka 3.5mm mono). An on-board regulated +12V DC or an optional externally-supplied voltage can be selected as an output power source for phantompowered microphones. The module has an adjustable gain control (to x1000) and an unbalanced 1/8" phone connector output.
This high-performance module is designed to be compatible with most modular synthesizer systems with little or no modification. Most active components are already mounted, making assembly a snap.
© 2009 PAiA Corporation
ASSEMBLING THE 9754 Preamplifier
Before beginning assembly, go through the manual. Look at the drawings.
Feel the parts. You're naturally eager to plunge right in, but take a few deep breaths first. Check the parts supplied against the packing list at the back of this manual.
In some cases, notes packed with the parts will be used to call your attention to special situations. If parts are missing, please notify PAiA at
[email protected] or by phone at (405) 340-6300, fax (405) 340-6378.
A NOTES page is included at the end of this manual.
Notice that each step in the manual is marked with acheckoff box like this:
DESIGNATION
( ) R27
DESC.
100ohm
MARKING brn-blk-brn-gld
Checking off each step as you do it may seem silly and ritualistic, but it greatly decreases the chance of omitting a step and also provides some gratification and reward as each step is completed.
Numbered figures are printed in the Illustrations Supplement in the center of this manual. These pages may be removed for easy reference during assembly.
THE CIRCUIT BOARD
The 9754 Preamplifier is built on a double-sided circuit board. Note the “top” side of the board has the connector and control placement designators.
Surface-mounted components are on the “bottom” of the board. Install parts to the top of the board and solder them on the bottom.
TOOLS
You'll need a minimum of tools to assemble the kit – a small pair of diagonal wire cutters, pliers, screwdriver, soldering iron, and solder.
2
Modern electronic components are small (in case you hadn't noticed) and values marked on the part are often difficult to see. Another handy tool for your bench will be a good magnifying glass. Also use the magnifier to examine each solder joint as it is made to make sure that is doesn't have any of the problems in the SOLDERING section which follows.
SOLDERING
Select a soldering iron with a small tip and a power rating of not more than 35 watts. Soldering guns are completely unacceptable for assembling solid-state equipment because the large magnetic field they generate can damage components.
Use only a high quality electronic solder. Your kit is compatible with lead-free and/or tin-lead flux-core solders made especially for electronic assembly. Plumbing solder will destroy your kit with its acid core. Jewelry solder (silver solder) will destroy your kit with its high working heat.
Neither is for electronics work.
A proper solder joint has just enough solder to cover the soldering pad and about 1/16-inch of the lead passing through it.
There are two improper connections to be aware of: Using too little solder will sometimes result in a connection which appears to be soldered when actually there is a thin layer of flux insulating the component lead from the solder bead. This situation can be cured by reheating the joint and applying more solder.
Too much solder may produce a conducting bridge of excess solder between adjacent pads causing a short-circuit. Continued feeding of solder into a hot joint can result in accumulation on the underside of the board and may cause bridges or impede the action of mechanical components. If you see this, position the board above the iron tip and the excess will flow to the tip.
Use care when mounting all components. Never force a component into place.
RESISTORS
Install resistors by bending the legs as shown to the right and inserting them through holes on the top side of the board (shown next page).
Solder each leg on the bottom side of the board and clip the excess as the top of the joint. The 100ohm is a 5% type with only four bands.
DESIG.
DESC.
MARKING A-B-C-D
( ) R13
( ) R14
( ) R15
6.81K, 1%
6.81K, 1%
100ohm, 5% blue-grey-brown-brown-brown blue-grey-brown-brown-brown brown-black-brown-gold
Ending brown band
A B C D
Ending gold band
A B C
3
CONTROLS AND CONNECTORS, LED
Controls and connectors will be installed on the top side of the board with the placement designators as shown in the illustration to the right. The LED indicator will also be installed at this time.
To ensure the best alignment with these parts and the panel accessory, begin by soldering only one of the multiple terminals associated with each of the following parts as it is installed.
Then, if a part is tilted or crooked, it is only a matter of reheating the joint as the part is aligned.
The potentiometers have tabs extending from their body for stability. They have a snap-fit to the board. Align the tabs and pins with their holes and press them into place. There is no need to bend the tabs or terminals.
If you will be attaching the board to the panel in a later step, check the fit before proceeding with the soldering of the remainder of the terminals for these parts.
Take care the solder doesn't run through to the opposite side of the board when soldering the mounting tabs. With practice, it is possible to flow solder to cover the opening; otherwise, just flow a bit to secure the tab to the pad ring.
Match the tab of the polarized power connector with the corresponding board marking.
DESIG.
DESC.
MARKING
( ) J2
( ) J3
( ) LED1
( ) SW1
( ) P1
TRS socket
TRS socket
Housed LED
Slide Switch
2K ohm potentiometer, audio
Header
A2K
( ) PWR1
We will delay the installation of the last connector until the capacitors have been installed.
4
Top of circuit board
TRS Connector
“stereo phone jack”
Housed LED
Slide Switch
Potentiometer
Header
CAPACITORS
There are both Polarized and Non-Polarized electrolytic capacitors used in the Preamplifier. The polarized type has a stripe marking the polarity, likely the minus pole. Match the plus leg with the plus hole and the minus leg with the minus hole. Solder each leg on the bottom of the board and clip the excess at the top of the joint.
( ) C4 47uF/63V Electrolytic Capacitors
Install the non-polarized electrolytic capacitor. Note that even though one leg is longer than the other and the board shows a difference for the two holes, either lead can go in either hole.
( ) C5
( ) C10
10uF/35v Non-Polar. Electrolytic Capacitor
10uF/35v Non-Polar. Electrolytic Capacitor
( ) C6
( ) C7
10uF/63V Non-Polar. Electrolytic Capacitor
10uF/63V Non-Polar. Electrolytic Capacitor
CONNECTORS (cont.)
Now, the final, tallest connector may be installed.
Steady this combination TRS/XLR flat against the board. Solder one of the legs, then the others after confirming it has not tilted.
( ) J1 TRS/XLR connector
Polarized electrolytic capacitor
Non-polarized electrolytic capacitor
Combo TRS/XLR connector
5
COMPLETION
The front panel is used for mounting the module in a rack system or cabinet. Complete the module assembly by mounting the 9754 PCB sub-assembly to the front panel as follows:
Referring to Fig. 1A of the illustration supplement, use the knurled phone jack nuts to secure the sub-assembly to the front panel. Check for clearance of the potentiometer shafts to ensure they rotate freely. Finger-tighten the phone jack nuts and then use the tips of the diagonal cutters to give them another quarter of a turn or so.
Complete the soldering of all multi-terminal parts. Take care the solder doesn't run through to the opposite side of the board when soldering the mounting tabs. With practice, it is possible to flow solder to cover the opening; otherwise, just flow a bit to secure the tab to the pad ring.
Cut a 3/8" (10mm) long shim sleeve for each pot from the length of polyethylene sleeve provided. Set the shafts fully counter-clockwise, slip the shims over the pot control shafts, put the knob in place with the pointer aligned to about a 7:00 setting, and use a small screwdriver to tighten the set-screw just enough that it grips.
6
POWERING AND TESTING
Power to the circuit is via a four-circuit, dual-polarity DC power supply. A power connector cable matches the header for connection with one of the PAiA 977x supplies at 15v or more.
Connect the circuit labeled (+) to the positive DC source (V+), the circuit labeled (-) to the negative DC source (V-), the circuit labeled (G) to the power ground (G), and the circuit labeled
(SG) to the signal ground (SG). For other supplies without separate signal and power grounds, use two wires to join the two grounds (G and SG) to the one ground (aka GND, 0VDC or common) at the supply.
Before applying power, check again, to be sure the wiring for the two DC polarities and that the polarized 4ckt connectors are as intended (see Fig.1B).
Use balanced XLR or TRS, and/or unbalanced two-circuit, Tip-Sleeve (TS or mono), cords for patching in or out of the Preamplifier when connecting with external devices. Within a 9700series system, either single conductor (Tip-only), or TS cords may be used. If this seems confusing, remember that a regular mono cable will always work for most home studios. PAiA equipment allows tip-only connections for professional applications where star grounding is required.
Begin testing with the Gain control at the lowest setting. Connect a TRS, XLR, or miniPhone terminated low-level signal source such as a microphone or guitar and patch the output for listening through a mixer and/or amplifier with speakers or headphones connected. When listening through speakers, be aware that too much volume combined with too much Gain or boost of a microphone will can result in feedback. Turning down volume or the Gain will stop this. The Balanced/Unbalanced control functions as a selector of the two input choices for the gain stage. The LED indicator will begin to glow as the signal peaks exceed about 2-3 volts.
This is a range compatible with modular synthesizer modules. So for most patches, you'll want to see the LED on for most of the audio signal activity. Some microphones need a phantom power supply to enable output from them. The usual 48V phantom voltage is not available from the XLR; however, a wiring point exists so an external voltage can be input to the board, or, a link may be made to the 12V supply which is likely suitable.
Balanced XLR or TRS Microphone
Guitar or other low-level, unbalanced signal source
Boosted signal level indicator LED
Input Selector Switch (Bal/Unbal.)
Gain adjust control (to x1000)
Line-level (to 26dBV), unbalanced output
7
Notes
A +12VDC wiring point is situated alongside a PPIN (phantom power-supply input) wiring point and a link may be made here, or an external, 48V source connected (with circuitcommon/ground too, if not common to the system).
Resistor R10 may be installed to parallel or replace on-board resistor R11 to match the current flow for a substitute LED (subtract the LED voltage from 10v and divide this result by the current (ie 0.01) for the resistance value).
Mounting holes are provided on the board for custom applications.
8
Builder's Notes
9
DESIGN ANALYSIS
The preamplifier is based around a common instrumentation amplifier configuration. This approach provides a very high input impedance to prevent any loading on input signals and can be used to accept signals either differentially or single-ended. If the switch SW1 is lowered, the inverting input of the instrumentation amplifier is grounded and signals are input through J2 into U1C. If SW1 is in the high position, the XLR/TRS combination jack will input differential signals through the non-inverting and inverting inputs of the instrumentation amplifier. Potentiometer P1 varies the gain of the amplifier from 0 dB to 60 dB. The output of the instrumentation amplifier feeds an LED driver circuit that provides useful signal level information. Provisions for phantom power are provided with R15, C4, R13 and R14 and allow for use of either 12V phantom power (through a wire jumper) or 48V phantom power from the an external source.
9754 Test Point Data
TP1
TP2
TP3
TP4
+12 VDC
-12 VDC
0 VDC
LED Drive Tap
9754 Power Requirements
Voltage
+15 VDC
-15 VDC
Current
10.3 mA
12.1 mA
10
9754 Parts List
Please check the parts against this list. As you locate a part type and verify the quantity (and mounting hardware -- if required) check it off in the space provided.
Because we have introduced surface-mount parts with these kits, we are providing the printed circuit card as a sub-assembly with the surface-mount parts already in place.
Also, we want to make you aware that we are using both linear- and audio-taper potentiometers in some of the modules. They are marked differently so we are asking that you check carefully.
If anything is missing please notify PAiA at
or by phone at (405) 340-
6300, fax (405) 340-6378.
Quan Description
( ) 1 9754 PCB Sub-assembly, Preamplifier
( ) 1 9754 Front Panel, Preamplifier
( ) 1 2K ohm Potentiometer, 9 mm Snap-In, Audio
( ) 2 Phone Jack, Stereo, 3.5mm
( ) 1 XLR Connector, Female, Combo, Panel-Mount, 3 pole
( ) 1 Switch, Slide, DPDT, RA, PCB Mount
( ) 1 Knob, Set Screw
( ) 1 Shim, Knob, Polyethylene Sleeve
( ) 1 47uF, 63V Capacitor, Electrolytic, Radial
( ) 2 10uF, 35V Capacitor, Electrolytic, Non-Polarized, Radial
( ) 2 10uF, 63V Capacitor, Electrolytic, Non-Polarized, Radial
( ) 2 6.81K ohm Resistor, Metal Film, 1%, 1/4W, Axial
( ) 1 100 ohm Resistor, Carbon Film, 5%, 1/4W, Axial
( ) 1 LED, Yellow Diffused, RA, PCB Mount
( ) 1 Header, Vertical, 1row, 4pin
( ) 1 Cable Assembly, Power, 4-wire
( ) 4 Screw, Self tap, #4 x 3/8, Pan Head Phillips, Black Oxide
Ref Des Marking
P1
J2, J3
J1
SW1
C4
C5, C10
C6, C7
R13, R14
R15
LED1
PWR1
A2K
11
9754 Preamplifier www.paia.com

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Key features
- Adjustable gain control
- Balanced/unbalanced input selection
- LED signal level indication
- Phantom power option
- Modular synthesizer compatibility
- Compact design