Bluetooth impedance question

steven94

AK Subscriber
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In another thread someone asked about hooking up BT To his amp. The amp has only 1 pair of speakers out and no headphone jack. I suggested a speaker switch box with impedance protection. I know if you run 2 pairs of 8 ohm speakers the impedance drops to approximately 4 ohms. My question is what happens when you hook up 8 ohm speakers to output #1 and a bluetooth transmitter to output # 2. What is the impedance of the BT transmitter and would this set up work with out damaging anything?I did read somewhere that the transmitter could be as much as 200 ohm load but can't confirm anything. Thanks in advance
 
You mean running a Bluetooth transmitter from the output of the amplifier?

Assuming so, a Bluetooth transmitter is typically intended for line level inputs, which would normally be relatively high impedance, like 10k ohms. I would expect to see a 200 ohm load from some headphones, but not from a Bluetooth transmitter.

However, an amplifier's speaker output can seriously overload and/or damage the line level input of a typical Bluetooth transmitter. A pair of resistors can be used as a voltage divider to reduce the voltage to safe levels for both headphones and Bluetooth transmitters. See, for example, https://diyaudioheaven.wordpress.com/tutorials/power-amp-adapter/

Better still would be to run the line-level source input to the amplifier to the Bluetooth transmitter, instead.
 
Thanks Dave . the OP of that thread has a Jolida 202 there are no line level out only speaker out. If there is not a BT that can work on speaker out put then I think the only way is a switch box and wire the speakers in.
 
I would think that at worst. a pair of speaker to line level converters would then do the trick.

In fact, if those converters are high enough impedance, he might not even need an impedance matching switch box. But, I have no idea what impedance they would be.
 
Thanks Dave . the OP of that thread has a Jolida 202 there are no line level out only speaker out. If there is not a BT that can work on speaker out put then I think the only way is a switch box and wire the speakers in.
A speaker-to-line-level converter is necessary if the user must use the speaker output of the amp. However, it would be better to run the input to the amplifier -- the source -- into the Bluetooth transmitter instead of the amplifier.

Nothing is gained by running the Bluetooth transmitter from the output of the amplifier, but there's a slight risk of damaging either the Bluetooth transmitter or the amplifier if something goes wrong.

In general, the (relatively) high power output of an amplifier should be used only to run speakers, not run line level devices, if at all possible.
 
Bluetooth is digital, over a radio. If a Bluetooth transmitter uses speaker-level inputs, then it must be using a high-impedance load to sample the speaker-level inputs digitally, without drawing significant current from the amplifier, similarly to a subwoofer with speaker-level inputs "sampling" the signal in the analog domain, but with analog-to-digital conversion added.
 
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