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Amplimo A5 - Audio Preamplifier module
RATINGS
| Description | The AMPLIMO A5 amplifies and equalizes signals from 2mV to provide a 1 V output. This two stage preamplifier also provides truly professional performance in a small, robust package.
The first stage of the preamplifier contains the amplification and equalization circuits for phono and microphone inputs, the second stage amplifies the larger signals and contains the volume and active tone control circuits. The only additional components required for the A5 are potentiometers for volume and tone controls. No output capacitor or supply capacitors are needed as the module contains its own voltage stabilization circuits. |
| Features |
* High performance op-amps containing both JFET and bipolar transistors allow a dynamic microphone to be amplified without the need for a microphone transformer.
* Lots of headroom with gain control and inputs for phono, CD, tape, tuner, and auxiliary.
* Symmetrical microphone input for maximum hum suppression.
* The possible use of a phantom supply.
* Immunity to high frequency interference.
* Phono input with RIAA equalization accurate to 0.2dB, very low noise and with the possibility of a rumble filter.
* Active volume control making the A5 almost impossible to overdrive while keeping the noise level very low. Even a +6dB CD input will not overdrive the A5.
* Sophisticated active tone controls with optimum characteristics and large control ranges. Because of their low impedance, the tone controls are immune to hum and oscillations and therefore do not require the use of screened cables.
* Wide frequency range that is slightly limited in the first stage to ensure stability.
* Short-circuit proof output (pin 17).
* Suitable for use with all AMPLIMO power supplies and power amplifiers. Supply voltages are ± 20V (symmetrical voltages). The supply current is 15mA maximum. |
| Packaging | The entire surface-mount hybrid circuit is fully protected against mechanical shocks, dust and moisture by a protective coating of lacquer.
Uses a seventh of the material of similar potted modules, so more environmentally friendly. |
| Mixer Application | The A5 provides professional performance and versatility for audio mixer applications. Check out the application note. |
| Accessories | Mounting Support
The A5 can be quickly and securely mounted using the adhesive mounting support Z5, eliminating the requirement for a printed circuit board or even a drilled hole. The gold plated terminal pins are easily accessible, and leads can be directly soldered to them.
Part number Z5.
Connector
A 20 pin, 0.1" pitch connector for fast replacement of the A5 module, or as a transitional PCB mount connector.
Part Number K5. |
| Power supply requirements | The A5 can be connected to the power supply of the power amplifier, as the supply voltages are internally stabilized in the A5 module.
Use the following resistors to drop the voltage to the correct level:
| Value | Power | Amp Supply Voltage |
| Wire Link | ¼ W | ±20 to ±23 V |
| 390 ohm | ¼ W | ±23 to ±29 V |
| 1 k ohm | ½ W | ±29 to ±37 V |
| 1.8 k ohm | ½ W | ±37 to ±49 V |
| 3.3 k ohm | 1 W | ±49 to ±70 V |
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| Stereo | Two A5 modules are required for stereo use, along with double gang potentiometers and double pole switches. The balance control consists of wiring each output (pin 17) to the input of the relevant power amplifier via a 150 ohm resistor. A 1 k ohm linear pot is wired between the two power amplifier inputs with the slider connected to ground. |
| Mounting | The module can be mounted to a flat surface by using the adhesive mounting support Z5. The A5 is first slid horizontally into the support with its pins up. The support cannot be repositioned once it is in place. The mounting surface must be clean, dry and free from grease. The A5 can also be mounted directly to a PCB by soldering, or by using the K5 connector. |
| Layout | The plugs for microphne, phono and the first stage of the A5 handle extremely low voltages and are susceptable to hum and oscilations. All leads should be as short as possible. Keep the A5 module, input sockets and potentiometers close to each other. The preamplifer circuitry should be screened from other circuitry by a piece of tin-plated sheet metal connected to ground. |
| Wiring | Leads to and from the A5 should not run near to other leads or pass close to transformers.
Pin 20 is used for mid-tone control. |
| Shielding | Only one end of the shield of shielded cable should be terminated to prevent ground loops. The entire preamplifier circuit should be sheilded in a metal case. Each panel of the case must have good ohmic contact to the others. Therefore, surface coatings (paint, anodization, etc.) must be removed at contact points to ensure good continuity. Use an ohm meter to to check continuity between all case parts and the ground connections of input and output sockets, especially chassis-mounted versions. Leads to the volume potentiometer should be twisted, but there is no need to shield these. |
| Earth Grounding | Pin 1 of the A5 module should be connected directly to the ground connections of the input sockets. These, plus the zero volt point of the power supply, should then be connected to the chassis. |
| Inputs | If an input signal contains a DC component, then a 47uF capacitor must be connected in-series to the A5 module. Series resisors should be used to attenuate higher signal inputs. If the first stage of the A5 is not used, pins 1, 2 and 3 should be connected to ground. |
| Recording | An output voltage for recording is available on pin 7 of the A5 (this is before the tone and volume controls), via a series 10k ohm resistor. |
| Inspection | It is important that all connections are checked before switching on for the first time as dangerous oscillations could occur. |
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Tone Control Stage
 See Schematic
| Input impedance | 47 k ohm (pin 7) |
| Input voltage | 0.1 V nominal, 7 V maximum. |
| Gain factor | 10 = 20 dB |
| Output impedance | 47 ohm |
| Output voltage | 1 V nominal
6 V maximum at 10 k ohm load
5 V maximum at 1 k ohm load
30 ohm headphone can be connected. |
| Frequency range | 4 Hz- 60 kHz at gain of 10.
3 Hz- 117,000 Hz at gain of 1 |
| Treble control | ±15 dB at 20 kHz, active, constant centre frequency |
| Bass control | ±20 dB at 20 Hz, active, constant slope. |
| Noise at output (pin 17) | -97 dBV (Arms) with all pots centred. |
| THD | 0.009% |
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Asymmetrical Preamplifier
See Schematic
| Input impedance | 47 k ohm |
| Input voltage | 2.2mV nominal, 160mV maximum |
| Gain | 46 for e.g. microphone = 100mV nominal on pin 6
24 w/ 1k ohm resistor in-series w/ pin 3
10 w/ 3k9 ohm resistor in-series w/ pin 3
5 w/ 10k ohm resistor in-series w/ pin 3
1 w/ 2.2M ohm resistor in-series w/ pin 3
For use with a guitar, 100k ohm linear potentiometer in-series w/ pin 3 |
| Output impedance | 47 ohm |
| Frequency range | 3 Hz - 35,000 Hz
20 Hz - 35,000 Hz w/ 4.7 uF capacitor in-series w/ pin 2 and 3
100 Hz - 35,000 Hz w/ 1 uF capacitor in-series w/ pin 2 and 3 |
| Noise at input | -119 dBV (Arms) |
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Symmetrical Microphone Preamplifier
See Schematic
| Input impedance | 2 x 1000 ohm |
| Input voltage | 2.2mV nominal, 160mV maximum |
| Gain | 46 = 33dB |
| Frequency range | 3 Hz - 35,000 Hz
20 Hz - 35,000 Hz w/ 4.7 uF capacitor in-series w/ pin 2 and 3
100 Hz - 35,000 Hz w/ 1 uF capacitor in-series w/ pin 2 and 3 |
| Noise at input | -119 dBV (Arms) |
| CMRR | 60dB |
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Phono Preamplifier with RIAA Equalization
See Schematic
| Input impedance | 47 k ohm |
| Input voltage | 2.5 mV nominal, 177 mV maximum |
| Gain | 40 = 32 dB at 1 kHz |
| RIAA accuracy | +0.2 dB between 20 Hz and 20,000 Hz |
| Rumble filter | with double-pole switch S open |
| Noise at input | -124 dBV (Arms) |
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A30 | A60 | A120 | A180 | A5 | DE | LRZ
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| Copyright © Plitron Manufacturing, 2007 | |
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