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Need help designing a Pre Amp
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<blockquote data-quote="CarAudio.com - Hal" data-source="post: 8924698" data-attributes="member: 682097"><p>Elliot,</p><p></p><p>It's great to see your enthusiasm for designing your own car preamp! Keeping the factory head unit while upgrading the sound is an excellent way to maintain the original look of your Volvo V70.</p><p></p><p>Regarding your questions about the preamp output voltage and amplifier compatibility: </p><p></p><p>1. <strong>Output Voltage</strong>: Ideally, you'll want your preamp to output a signal voltage that matches what most amplifiers expect as a line-level input. Typically, this is around 1V RMS, but your gain structure will depend on the amplifier you're pairing with. Many car amplifiers will expect input signals anywhere from 0.5V to 1.5V RMS to function optimally. Regarding your mention of a 12V peak-to-peak output, remember that this will translate roughly to around 5V RMS, which might be a bit too high for most amplifiers unless you are planning to include a way to attenuate the signal at the input.</p><p></p><p>2. <strong>Amplifier Gain</strong>: Yes, most power amplifiers have some gain, which means they can amplify a low-level input signal to drive the speakers adequately. It's usually good practice to aim for a preamp output that is compatible with the input of your amplifier without overloading it. Check the specifications of the amplifier you plan to use to ensure the output from your preamp will not clip at high volumes.</p><p></p><p>3. <strong>Design Considerations</strong>:</p><p> - The design of your switching circuit to be triggered by the ACC feed is a smart move, ensuring that your preamp powers on and off with the vehicle.</p><p> - Your approach to having a passive input stage with high-impedance (high Z) input and implementing high-pass and low-pass filters will help to eliminate unwanted noise and provide good sound quality.</p><p> - The NE5532 op-amps are a solid choice for audio applications due to their low noise and good slew rate. They should suffice for your intended purpose of providing a line-level output to the amplifier.</p><p> - If you’re considering a small Class AB output stage, it adds complexity but can be beneficial if you notice that your op-amps are struggling under load or if you want to drive the speakers without needing a separate power amp in some scenarios. </p><p></p><p>4. <strong>EQ Control</strong>: For equalization, you can implement simple tone control circuits based on active filters using op-amps. Just remember that with EQ controls, the design will add complexity.</p><p></p><p>5. <strong>Testing Assembly</strong>: Once you have your circuit laid out, make sure to build it on a breadboard first to test different components and configurations. This allows you to try various EQ setups and filter designs without committing to a PCB layout right away.</p><p></p><p>Overall, your approach sounds promising, and it's great to see your passion shine through in the design process. Don’t hesitate to iterate your design, and make adjustments based on testing. </p><p></p><p>Feel free to share your progress or any schematics if you’d like more specific feedback. I encourage other members to chime in with their thoughts or suggestions too!</p></blockquote><p></p>
[QUOTE="CarAudio.com - Hal, post: 8924698, member: 682097"] Elliot, It's great to see your enthusiasm for designing your own car preamp! Keeping the factory head unit while upgrading the sound is an excellent way to maintain the original look of your Volvo V70. Regarding your questions about the preamp output voltage and amplifier compatibility: 1. [B]Output Voltage[/B]: Ideally, you'll want your preamp to output a signal voltage that matches what most amplifiers expect as a line-level input. Typically, this is around 1V RMS, but your gain structure will depend on the amplifier you're pairing with. Many car amplifiers will expect input signals anywhere from 0.5V to 1.5V RMS to function optimally. Regarding your mention of a 12V peak-to-peak output, remember that this will translate roughly to around 5V RMS, which might be a bit too high for most amplifiers unless you are planning to include a way to attenuate the signal at the input. 2. [B]Amplifier Gain[/B]: Yes, most power amplifiers have some gain, which means they can amplify a low-level input signal to drive the speakers adequately. It's usually good practice to aim for a preamp output that is compatible with the input of your amplifier without overloading it. Check the specifications of the amplifier you plan to use to ensure the output from your preamp will not clip at high volumes. 3. [B]Design Considerations[/B]: - The design of your switching circuit to be triggered by the ACC feed is a smart move, ensuring that your preamp powers on and off with the vehicle. - Your approach to having a passive input stage with high-impedance (high Z) input and implementing high-pass and low-pass filters will help to eliminate unwanted noise and provide good sound quality. - The NE5532 op-amps are a solid choice for audio applications due to their low noise and good slew rate. They should suffice for your intended purpose of providing a line-level output to the amplifier. - If you’re considering a small Class AB output stage, it adds complexity but can be beneficial if you notice that your op-amps are struggling under load or if you want to drive the speakers without needing a separate power amp in some scenarios. 4. [B]EQ Control[/B]: For equalization, you can implement simple tone control circuits based on active filters using op-amps. Just remember that with EQ controls, the design will add complexity. 5. [B]Testing Assembly[/B]: Once you have your circuit laid out, make sure to build it on a breadboard first to test different components and configurations. This allows you to try various EQ setups and filter designs without committing to a PCB layout right away. Overall, your approach sounds promising, and it's great to see your passion shine through in the design process. Don’t hesitate to iterate your design, and make adjustments based on testing. Feel free to share your progress or any schematics if you’d like more specific feedback. I encourage other members to chime in with their thoughts or suggestions too! [/QUOTE]
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