Which Class A/B amp/driver configuration should I use?

Discussion in 'Analog & Mixed-Signal Design' started by AMandler, Oct 27, 2018.

  1. AMandler

    Thread Starter New Member

    Oct 27, 2018
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    I am in the process of building a set of 2way active loudspeakers. I am however at this point better at construction than electronics, and therefore will be grateful for any help and directions concerning the following questions-

    A: How do I wire a 2way active loudspeaker setup (two separate wireless loudspeakers), where each loudspeaker (about 30watts RMS), consist of a woofer, tweeter, a Class D amplifier board and rechargeable batteries with an expected playtime of 8 hours?

    B: Is there a particular wiring/amp setup that is best suited for this configuration?

    OR

    C: Can I just use a two channel D-Amp and connect the tweeter to the left channel, and the woofer to the right channel, and repeat the same amp/wiring setup in the other speaker, and expect them to play with synchronized timing in stereo?

    D: Is there a particular class amp that you would suggest, considering that I would like to integrate Bluetooth and/or airplay/Wi-Fi in the mix?

    P.S. My goal is to build a set of speakers that are able to function both as a stereo pair, and individually. And last but not least, must be above average quality.
     
  2. Audioguru

    Expert

    Dec 20, 2007
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    A speaker with two 30W amplifiers does not blast 60W continuously. The average power when playing music or speech loudly will be only 6W to 12W. For 30W RMS into 4 ohms you need a battery voltage of about 42V to about 45V. If each channel on the amplifier is bridged then you need a battery voltage of about 13V.

    A bridged class-AB amplifier sounds good and an example is the TDA7386. It produces 25W per channel into 4 ohms with a 16V supply.
    A bridged Class-D example is the TDA7492 that produces 30W per channel into 4 ohms with a 20V supply but its many pins are tiny and close together.

    The class-AB amplifier gets hot that uses about 50% more battery power. Then the 16V battery must supply an average of about 15W which at 16V is a current of 15W/16V= 0.94A. The battery must be rated at 0.94 x 8 hours= 7.5Ah. Pretty big battery.

    The class-D amplifier is more efficient so it needs a battery that is about 20V at 4.4Ah.

    The transmitter for the woofers must have lowpass filters and the transmitter for the tweeters must have highpass filters that make crossovers.

    China has Bluetooth amplifiers sold on ebay, AliExpress, Banggood and Amazon but their output power is less than you want.
     
  3. AMandler

    Thread Starter New Member

    Oct 27, 2018
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    Hi Audioguru

    Thank you for your prompt reply.

    With reference to my earlier inquiry, I would appreciate any advice regarding how many watts-RMS would you suggest would be appropriate for a 0.85 liter (0.03 cubic foot) sealed cabinet?
     
  4. ArakelTheDragon

    Active Member

    Nov 18, 2016
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    Your PC (desktop computer) is "2.5W", "6W" is more than enough.
     
  5. AMandler

    Thread Starter New Member

    Oct 27, 2018
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    Thank you for your reply.

    I do however not follow what you mean, by referring to my pc. Please elaborate?
     
  6. ArakelTheDragon

    Active Member

    Nov 18, 2016
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    The speaker on your desktop computer is "2.5W", if your speaker is "6W" that is more than enough for a small office. You can estimate by turning your dekstop computer's volume to the maximum and compare to "6W".
     
  7. AMandler

    Thread Starter New Member

    Oct 27, 2018
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    Thank you.

    I understand your reference. I am assuming you have read my previous inquiry. I would like to ask the following-

    1. Even though the wattage will now be reduced from a 30watt to a 15watt D-Class amp, per your instructions, I assume a high-pass/low-pass filter amp is still appropriate as each cabinet will feature both a woofer and tweeter?


    2. Are all the below features in balance as per wattage and battery power? If not, please advise of any modifications I may make?


    Per Sealed Cabinet-

    Amplifier - 1 X 15 watt DSP controlled stereo class D amplifier

    Connectivity - 1 X AirPlay, Play-Fi, Bluetooth.

    Tweeter - 1 X Peerless by Tymphany OC25SC65-04 1" (25Watts/4 ohms)

    Woofer - 1 X Dayton Audio TCP115-8 4" (40watts/8 ohms)

    Power - 1 X Switching power supply = 24V, 2500mA

    Battery - 1 X Rechargeable Lithium Ion 16.8 V 2600 MaH 24V, 2500mA

    Cabinet - 1 X Internal volume: approximately 0,8 liters/
     
  8. Audioguru

    Expert

    Dec 20, 2007
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    I knew it. Your speaker enclosures are tiny so your woofers are little 4" diameter that produce no deep bass sounds. Your woofer is 8 ohms and your tweeter is 4 ohms but with the same amplifier type their sensitivities match fairly well since the tweeter is more sensitive.

    The 16.8V lithium battery is 4 cells but produces 14.8V at half-charge and produces only 12.8V when almost dead so the amplifier bridged power will be much less than you want.
    There is no 24V lithium battery available. 6 cells produce 25.2V at max charge, 22.2V at half charge and 19.2V when almost dead.
    You need a balanced battery charger made for charging a lithium battery.

    A Texas Instruments TAS5751M class-D bridged stereo amplifier produces about 17W per channel at low distortion when powered from 22V.
    It has digital inputs. It has 48 tiny very close together pins and will be a nightmare to solder.
    Since you will use wireless signals probably have analog outputs then a bridged class-D amplifier with analog inputs is more suitable. A TPA3128D2 stereo amp IC produces about 25 per channel at low distortion into 8 ohms when powered by 22V. It has 32 tiny very close together pins and will also be a nightmare to solder.
     
  9. AMandler

    Thread Starter New Member

    Oct 27, 2018
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    Thank you all for your valuable contributions.

    After re-evaluating your latest suggestions, I researched the matter, and have come up with the following configuration. Please advise if this revision is a better fit for my goal (https://forum.allaboutcircuits.com/...amp-wiring-configuration-should-i-use.153469/) and /or can be moded / improved upon?
    P.S. Some of the manufacturers are willing to customize their units, as they are within the OEM realm of their product portfolio.

    Per Sealed Cabinet-
    Amplifier - 2 x 30 Watt Class D Audio Amp with Audio DSP - JAB3-230 / PBTL Configurable
    Or
    2 x 50 Watt Class D Audio Amp with Audio DSP - JAB3-230 / PBTL Configurable

    Connectivity - 1 X AirPlay, Play-Fi, BT 4.0 APT-X

    Tweeter- 1 X Peerless by Tymphany OC25SC65-04 1" (25Watts/4 ohms)

    Woofer - 1 X Dayton Audio TCP115-8 4" (40watts/8 ohms)

    Power - 1 X Switching power supply = 24V, 2500mA

    Battery - 3 pieces Rechargeable Lithium Ion battery pack
    Plus: 3S 18650 Lithium Battery Charger and Balance Protection Board - BCPB2

    Cabinet - 1 X Internal volume: approximately 0,8 liters (0.03 cubic feet)
     
    Last edited: Oct 29, 2018
  10. Audioguru

    Expert

    Dec 20, 2007
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    Three 18650 battery cells produce 12.6V when fully charged which drops quickly to 11.1V at half charge.
    The Sure 2 x 30W amplifier has a spec of maximum current of 0.5A at 12V. That is only 6W, not 60W.
    PBTL is connecting the two bridged amplifiers in parallel so that they can drive 2 ohm speakers with higher current to produce double the power of a single amplifier driving a 4 ohm speaker. But your woofers are 8 ohms which halves the power down to 7.5W or 3W?
    The spec's for the Sure amplifier are meaningless.
     
  11. AMandler

    Thread Starter New Member

    Oct 27, 2018
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    Thank you for your evaluation of the configuration.

    If I may ask, is there a number of batteries, amp board and driver/tweeter configuration you would suggest that will get the job done?

    I would be grateful for any suggestions.
     
  12. Audioguru

    Expert

    Dec 20, 2007
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    I hope you did not buy the little 8 ohm woofers because an amplifier to drive 8 ohms at 20W to 25W needs a lithium battery with 8 cells. The same woofer is available at 4 ohms then a 4 cell battery can power a class-AB bridged TDA7396 single channel amplifier IC. This IC has normal through holes pins that can be soldered easily. The battery is 16.8V when fully charged then the low distortion output will be 26W into the 4 ohms. When the battery has discharged halfway its voltage will be 14.8V and the power will be 21W.

    I was wrong before when I said the 4 ohm tweeter matches the output level of the 8 ohm woofer. A 4 ohm tweeter is too sensitive with an 8 ohm woofer and is also too sensitive with a 4 ohm woofer. Select a less expensive 8 ohm tweeter that will match the output level of the little 4 ohm woofer.
     
  13. AMandler

    Thread Starter New Member

    Oct 27, 2018
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    As always, thank you for your prompt expert reply and insight.

    I have however not been able to find an OEM class – AB bridged amp board with the suggested IC chip. This is causing me great concern, and I am at a loss at this point. Please advise if you are aware of any manufacturer that produces such an amp. If not, keeping in mind that I am a novice at electronics, I will appreciate any specifics on how best to achieve this goal?

    With respects to the chosen 8ohm woofer; the choice was made based on the fact that the manufacturer suggested a 0.03 cubic ft. sealed volume, while the 4ohm woofer suggest a 0.06 cubic ft. sealed volume.

    And as my sealed cabinet volume was in step with the 8ohm woofer, I felt it to be the appropriate choice. If you however believe the 4ohm variant will function just as well, then of course, that altercation will be made, or otherwise, I will find an alternative to meet the new specs.
     
  14. Audioguru

    Expert

    Dec 20, 2007
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    I design and make amplifiers, I do not know any amplifier boards that are already made. You might find a cheap Chinese amplifier board that works. Beware that amplifier manufacturers exaggerate the power and distortion.

    Since the 4" woofers have the same part number I looked at their identical frequency response curves which are faked since the woofer spec's are different. If the spec's are believable then the 4 ohm speaker is more sensitive and goes down to a lower frequency.

    The 8 ohm woofer is not available and Dayton says they do not know when it will be available. The newer 4 ohm woofer will be available on November 24.
     
  15. AMandler

    Thread Starter New Member

    Oct 27, 2018
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    Thanks again for your dedication to resolving my plight.

    May I suggest the following interim email (mrspeaker@mail.com) to allow us a private forum to negotiate the possibility of you designing a schematic, and potentially a prototype of such a board. If not, then kindly suggest another forum or solution to your liking.
     
  16. AMandler

    Thread Starter New Member

    Oct 27, 2018
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    By the way, is it possible to build a comparable Class-D amp to the A/B Bridged amp you have suggested?
    My reasons for asking, are primarily based on my concerns regarding generated heat and the potential size of components in general, and the heat-sink required to deal with the issue.

    But as a matter of fact, two factors play a significant role in the build of the board, which are; size and quality; both in regards to hardware and acoustics.

    If you believe, the A/B bridged amp you envision can fulfill all the specs, please do let me know. And last but not least, can you possibly give a quote on what the cost will be for a schematic, and/or prototype board?

    At any rate, I thank you kindly for your engagement, and look forward to any advice you might further offer on the matter.
     
  17. Audioguru

    Expert

    Dec 20, 2007
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    The class-D amplifier ICs with the power you want are available only in tiny packages with tiny very close together pins. They are made to be soldered by a robot machine, not by hand. The TDA7396 class-AB amplifier IC I recommended is easy to solder by hand. I looked again and found the TDA7377 IC that has two channels similar to the single channel TDA7396. It is also class-AB and is easy to solder by hand.
    All western amplifier ICs have a datasheet with detailed spec's and schematics of circuits that use them.

    I looked on ebay for ready-to-play audio amplifier boards and there are many very cheap class-D even with a Bluetooth receiver and remote control but I do not recommend them. You can try them if you want.
    Here is a video of a guy who ordered a 100W per channel class-D Bluetooth board from ebay and it arrived 3 months later. He shows that it actually works but says that its 100W is a lie, it is more like 20W per channel and its terminals fall apart.
     
  18. AMandler

    Thread Starter New Member

    Oct 27, 2018
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    I appreciate your guidance.

    Question 1.
    I am curious as to why both DIY amps, and many of the Chinese D-Class amps are prone to all kinds of volatilities, distortions and pops (when turned on/off), compared to commercial amps?

    Question 2.
    At any rate, I believe per your advice, that the Class A/B amplifier (PBTL configurable) is the way to go. And with that in mind, I kindly ask once again, that If you believe, the A/B bridged amp you envision can fulfill all the specs, plus keep to a minimum size and commercial grade quality (hardware, acoustics and stability), then kindly propose a quote on what the cost will be for a schematic, and the expected size of the board
    (H x W X B)?
    P.S. For each active loudspeaker, the board should, other than the amplifier, integrate circuitry for connectivity of the above mentioned wireless systems (AirPlay 2, Play-Fi, Bluetooth), (wireless headphone pairing), battery charger and balance protection (can be a separate pcb), with power supply input.

    Question 3.
    And last but not least, other than the 4ohm woofer, that is supposed to be available on November 24, all that is needed to complete the system is a 4ohm tweeter that will complement the woofer?

    If there is anything I have missed/misunderstood, then please advise.

    Thank you.
     
    Last edited: Nov 1, 2018
  19. Audioguru

    Expert

    Dec 20, 2007
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    The datasheet of every amplifier IC has a datasheet listing detailed spec's. It also has a recommended schematic showing most parts that are needed. The datasheet shows that the TDA7377 class-AB bridged class-AB stereo amplifier produces 20W per channel at 10% distortion into 4 ohm speakers when its supply is a 14.4V charging car battery. I calculated that it produces about 16W per channel at low distortion into 4 ohm speakers with a 16.8V supply. You need to add volume controls and Bluetooth and other wireless inputs yourself.
    Two TDA7396 mono amplifier ICs produce more power with this battery.

    The 16.8V battery can be four series lithium-ion cells. Its voltage is 16.8V when fully charged, 14.8V at half-charge when the power per channel will be reduced to about 11.9W per channel. You must add a lithium balanced battery charger and battery cutoff circuit which disconnects the battery when it drops to 12.4V.

    The tweeter you selected is too sensitive and too expensive. An 8 ohm tweeter will match the woofer sensitivity and will probably be less expensive. Of course you need proper crossover networks to feed low frequencies to the woofers and feed high frequencies to the tweeters. The tweeters will be destroyed without proper crossover networks and the woofers will sound awful.

    Some amplifiers that use a single supply voltage cause a POP when turned on and turned off because the supply voltage charges capacitors suddenly. The TDA7377 and TDA7396 amplifiers have an RC that slowly charges and discharges and the datasheet says, "Every ON/OFF operation is virtually pop free."

    Isn't the 8 ohm woofer not in stock and they do not know when (and if) it will be available but the newer 4 ohm speaker comes on Nov 24?
     
  20. Audioguru

    Expert

    Dec 20, 2007
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    The TDA7377 is not available but the TDA7375 is available but at a high cost. Its output power is a little higher than the TDA7377 and uses the same schematic and pcb.
     
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