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Bluetooth and Amplifiers

Bluetooth AmplifierAll of my audio projects involve bluetooth and amplification. This can be two separate boards, or a single integrated one. The amplifers are all compact and energy efficient class D (3-15w). The amplifiers can produce a surprising amount (time and db) of good sounding music from a single 18650 battery (stepped up to 5 or 9v). The speakers I have been using are all pretty small, 45 - 55mm (~1-3/4 - 2-1/4"), with relatively low power ratings (3-7w). It's fun to see how far I can crank it up with the larger amps, but I'm happy with three watts and the pictured 2 x 3 watt bluetooth amplifier board makes it easy.

Sanwu 3W Bluetooth

Sanwu SW-HF43B v2.0The 2 x 3 watt SW-HF43B v2.0 Sanwu board can be identified by the two inline IC's, the relatively large aluminum capacitor and the easy to read model number. The earlier SW-HF43 v1.1 board has offset IC's and a hard to read model number. There are similar looking boards from unknown manufacturers, e.g. the HW-332-C8 (perpendicular IC's).

I had trouble with the Sanwu v1.1 board. It may have been flawed from the get-go, but my pushing it ended up partially killing it - bluetooth connects, but no audio. I'm pretty sure that this is the board with Chinese accented voice prompts. One advantage of the v1.1 board is thickness, the tallest component is the speaker wire socket and that can be removed. If ease is more important, XH2.54 4-Pin plugs with ~8" wires are cheap on eBay.

While I have been able to overload (causing it to reboot) the Sanwu V2.0 board at max volume, I have yet to kill it. I'm no audiophile, but this sounds as good as any other PAM8403 3 watt amplifier and the gain is just enough higher to make a difference. It pairs quickly with appropriate level audio tones (I've got another board with overly loud/distorted audio prompts) and has good reception. At less then four bucks on eBay, this is a hard to beat low power bluetooth amplifier... Which had me happy enough to forget the white noise that was noticeably gone when I switched to the KRC-86B (below). It's not much, but you can hear it in the background at minimum volume.

I got over 36hrs of runtime using a 2.5ah 18560 running through a 5v step-up. It is interesting that this is only 2hrs more than I got with the TPA3110/KRC-86B combination using the same battery running through a 9v step-up. It is also worth noting that the charger battery protection circuit was the cuttoff point (~2.5-2.6v). The TPA/KRC setup cutout at 3.25v (bluetooth minimum, not on step-up) which could mean that the TPA/KRC combo is actually more efficient. All my tests are done with the same speakers and at pretty much the same volume (relatively low).

The following includes comparisons that are likely inaccurate because I used a preexisting 8403/KRC setup that has different speakers.

...At center volume, the PAM8403/KRC-86B combination is twice as efficient (30ma) as this board (60ma). There's less relative difference at the highest volume. This board is louder, using up to 120ma, than the 8403/KRC using up to 70ma (spikes a bit higher). While the extra volume of this board is nice, the overloading/rebooting is starting to bug me (not an issue w/ the 8403/KRC).

...With a slightly different setup, running this board at 4v (directly off the battery) the draw is only 30-40ma and I can max the volume. The board will start beeping when the battery starts getting low. The trigger point depends on the volume level/load and battery voltage level. I got it to start beeping at 3/4 volume with the battery at 3.2v. The max volume is ~5db higher (79 VS 74 @ 1M from one speaker) than with the 8403/KRC. For equivalent decibel output, the 8403/KRC volume level needs to be set two (of 15) steps higher than with this board.

...After over 48hrs of running this board directly from a 2.5ah 18650 battery, beeping starts at almost maximun volume (3.25v). It looks like, at medium volume, the board consumes ~36ma (only 6ma more than the 8403/KRC). A 500mah (real capacity) battery should provide over 9hrs of runtime... The real capacity of my "500mah" Li-Po is ~332mah and it lasted 6-1/4hrs (...7:44... 7:46).

Another plus of this board is that it can be used as an alarm clock. This is possible because the amplifier shuts down when there is no audio signal... It looks like this standby mode uses ~14ma (16hrs with that 332mah battery). At ~.05w that's significantly less than most wall chargers use on standby (nothing plugged into them).
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KRC-86B V4.0 Bluetooth

KRC-86B V4.0 BluetoothI've tried a lot of bluetooth receivers and the KRC-86B has better reception than most and provides the cleanest audio (no white noise). I use it with any amplifier that doesn't provide bluetooth. It has options for adding control buttons and an aux-in socket. The potential drawbacks are that it is relatively large (30x30mm), expensive (~$8), has no pairing/paired prompts, and can be a bit slow to pair. The provided capacitor and LED can be replaced with smaller surface mount versions.
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PAM8403 3W Amplifier

PAM8403 3W AmplifierThere are numerous inexpensive amplifier boards that use the PAM8403 IC. These 2 x 3w amplifiers are surprisingly adequate, even when run off 3.7v. After I damaged my v1.1 Sanwu board, I put together the pictured PAM8403/KRC86-B combo. I run this daily (5v) in my shop and have not found it lacking in any respect. While running it off an 18650 battery (3.7v) sounded fine in the shop, it wasn't quite enough in a friends larger/noisier/softer surfaces home. Running it at 5v (adding a step-up) should help.

...It appears that voltage has no noticeable effect on maximum volume. The only difference when running this setup at at 5.2v (VS 4v) is a slight decrease in current. I don't have an averaging multimeter, but it looks like ~.035 VS ~.045a at max volume (i.e. ~.18 watts for both). The maximum volume with both voltages (same song) was ~74db (1M from 1 speaker).

While I like the red board, the last ones (right) I got appear to be mistakes. I'm not sure about the caps, but the 47k ohm input resistors amount to 0 input gain (same resistance as the green board pot at its lowest setting), i.e. significantly lower amplification. Replacing the 47k ohm resistors with 10k fixed the volume level. I'd like to try something a bit smaller than 10k (e.g. 8.2k), but the next one down I had was 4.7k and that was too low.

I've been playing with more powerful amps and haven't compared the various 8403 boards, e.g. the simple green board or the one with volume control (no obvious +/-'s after brief tests of both).
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TPA3110 15W Amplifier

TPA3110 15W AmplifierThe 15 watt specification is for 8 ohm speakers and running the amp at 16 volts (operating range is 8-18v). My tests are at 9v, where the maximum for my 4 ohm speakers appears to be around 7.5w (5w for 8ohm). Producing 7.5 watts appears to require around 1 amp of current (@9v).

My current testing testing (of the pictured TPA3110/KRC combo) only shows that the amp is incredibly efficient, in the same ballpark as the PAM8603, over 34hrs of runtime on a 2.5ah 18650... The measured current draw is ~50ma at the testing volume. That seemed really low, but the DigiKey Battery Life Calculator says I should get 35hrs at 50ma. I have no idea how that translates to output power, but it cannot be much if it takes 1000ma to produce 7.5w.

The amp sounds good and the default gain is right where I want (just below center for everyday listening). With a full battery (~4.2v), I can crank it up without anything cutting out. However, as the battery voltage drops, cranking up the volume starves the bluetooth and it drops. Bluetooth drops permanently when the battery reaches 3.25v (exactly).

...I'm not sure why bluetooth drops when it should be getting at least 3.25v (its min), but after adding a 5v step up for the bluetooth I'm able to max the volume regardless of battery voltage. The maximum reasonable volume for the testing setup seems to be around 87db, ~8db higher than with the Sanwu 3w.... Adding the 5v step-up reduced runtime from ~34hrs to ~24hrs. Comparing the current draw I got ~100ma w/ step-up and ~70ma w/o. The two differences are consistent (~44%), but seem like an awful lot. I tried a completely different 5v step-up module and got the same result (~100ma). I also had similar losses when running the Sanwu 3w off a 5v step-up

TPA/KRC with different amp step-up boards (no KRC step-up):
9v2016.5 15:151.3ah60xx
The last one confirms my first test (>34hrs/~50ma) with the same setup. It looks like the inline volt/amp meter could be using as much as 10ma. I have no idea what the clock timer, running off a 1.5v step-down, might be using.

At 33 x 25 x 3.5mm, it back-to-back pairs nicely with the KRC bluetooth board. Of course the audio out/in pins aren't in the same order, but two of them can line up pretty darn close. At least for my current uses, having the speaker connections at the same end is also a plus.

...The current setup replaces a 2016.5 charger/step-up with a small 9v step-up that is back to back with a 03962A charger. This setup is more compact and gains a protection circuit.

...Using a 12v wall wart, with a 5v step-down for the KRC, works well - noticeably more power (and noise/pop at startup).
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PAM8610 10W Amplifier

PAM8610 15W AmplifierThis board is sometimes advertised as 15w because that is the maximum output with 4 ohm speakers and running the amp at 12v. it's 10w for 8 ohm speakers. It looks like the maximum for 9v and 8ohm speakers is about 5 watts. That could mean that, like the TPA3110, the max for 4 ohm speakers is ~7.5w (@9v).

At 30 x 25 x 2.5mm, its pretty much the same size as the TPA3110 and back-to-back paring with the KRC bluetooth works here as well (image). While I was liking this board, it has taken a back seat since I got the TPA board. The gain on this board is just too high for driving 4 ohm speakers with 9 volts. It also appears that this board is not as efficient as the TPA, at least on the low output end.
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Comments [ new ]

Re: Bluetooth and Amplifiers
Posted by Andrew L on Monday, 02-Dec-2019

I have the HW-332-C8. It had too loud voice prompts and also the music played was too loud. After a bit of research I found out that the gain of the PAM8403 is determined by the input gain resistors. On these boards they are R1 and R2. Originally my board had soldered 1kOhm resistors. I tried couple of values and settled on 100kOhm. The voice prompts are still a bit loud, but overall 100kOhm is a nice compromise.

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Re: Bluetooth and Amplifiers
Posted by Dave L on Thursday, 13-Jan-2022

Another comment about the HW-332-C8 gain being too high motivated me to check my Sanwu boards. The SW-HF43 v1.1 that caused me grief has 1k gain resistors (R1/2), the SW-HF43B v2.0 that I like has 10k. The later is in line with my finding that 10k was pretty good on my PAM8403 board (the amplifier chip on these boards). Andrew needing 100k indicates that there might be some other differences between the HW-332-C8 and SW-HF43(B) boards.

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Re: Bluetooth and Amplifiers
Posted by Adam on Tuesday, 22-Jan-2019

Hi Dave!

I have a question: can I connect two 3 watts speakers, one 10 watts and one 12 watts in series to the amplifier (HW-332-C8). Each speaker has 4 ohms. And can the 3 watts speakers be in pair with the 10 or 12?

Thanks for Your advice


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Re: Bluetooth and Amplifiers
Posted by Dave L on Tuesday, 22-Jan-2019

Theoretically, the HW-332-C8 can output 3 watts per channel with 4 ohm speakers. That's barely enough power to drive one speaker per channel. I'm pretty sure it wouldn't even work with speakers in series (2x4 ohm = 8 ohms).

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Re: Bluetooth and Amplifiers
Posted by Octavian B on Wednesday, 12-Jan-2022

Hi, Dave, I'm new to this, I've just try the cheap board HW-332-C8 and the power-up message is annoyingly loud. Is there any chance to lower the message or mute it forever? The LED indicator is enough to know when the device is connected.
Thank you in advance.

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Re: Bluetooth and Amplifiers
Posted by Dave L on Thursday, 13-Jan-2022

See above [link]. You could try Andrew's solution and replace R1 and R2 with 100k resistors (a PITA) or buy the SW-HF43B version.

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Re: Bluetooth and Amplifiers
Posted by Octavian on Wednesday, 26-Jan-2022

Thank you, I've changed the two resistors with 100K and it is much better now.

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