Single ended audio amplifier why need DC block

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Discussion Overview

The discussion revolves around the necessity of a DC block in single-ended audio amplifier circuits, particularly when converting a double-ended (BTL) circuit to a single-ended configuration. Participants explore the implications of DC current on speaker performance and the operational differences between amplifier types.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that connecting a single-ended circuit by shorting the spk- to ground results in muted audio, and questions the reason for needing a DC block.
  • Another participant explains that DC current through the speaker coil is wasted energy and that amplifiers typically use DC blocking or feedback to manage DC current.
  • A different participant suggests that the stress on the amplifier occurs due to low impedance to ground in a single-ended connection, and questions whether the BTL configuration cancels out DC current through the speaker.
  • One participant mentions that older transistor radios often used transformer coupling, which may not require a blocking capacitor.
  • Another participant clarifies that their issue is not related to muting the speaker output jack but rather obtaining audio through the use of a DC block.
  • A final post introduces a vague suggestion about balancing output DC without further elaboration.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and function of the DC block in single-ended circuits, with no consensus reached on the best approach or understanding of the underlying principles.

Contextual Notes

Some participants reference specific configurations and operational principles without fully resolving the implications of DC current in different amplifier setups. There are also mentions of older technology that may not apply to all current scenarios.

spid3rx
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Hello all,

This is my first post in this forum. Hope can get some constructive help from the community.
I did some testing with some radios which is actually a double ended circuit (BTL), meaning it has the spk+ and spk- port.

When I want to connect it as a single ended circuit, meaning the spk - short to ground, the audio is muted. The only way for it to work is by adding a capacitor in line with the spk+ which is the DC blcok. I search through the internet and found similar information saying that the DC block is required in order to work.

Can I know why ? what is the reason behind?
Thanks, appreciate the view and help.
 
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Any DC current running through your speaker coil is wasted energy, for a start - it's not part of what you want to hear.

Afaik, most amplifiers - even double ended ones - use DC blocking - or they will use feedback to eliminate any DC current through the speaker. Connecting one amplifier outlet via a very few ohms to ground will totally upset the DC conditions; the two outputs of a balanced output could be varying (in antiphase) between V++ and 0V (or between V++ and V--) and neither of the output halves is expecting to supply a lot of DC current to ground. Give the poor thing a break!:smile:
 
Thanks sphiecentaur.
The main reason for single ended connection, the audio amplifier sees a low impedance that is going to ground hence causing stress in order to provide higher current. Correct me if I am wrong :)

For BTL, even without the DC block, the speaker will work, is it been cancel off by the inverting spk- ?

This is a good information i manage to read through internet, just for comunity sharing :)
http://www.audiodesignline.com/howto/205601397;jsessionid=3FGICYURRJYADQE1GHOSKHWATMY32JVN?pgno=2
 
I hope these were not old valve radios they can present lethal voltages.

More recent, but still old, transistor radios usually had a transformer coupling to the speaker. In this case a blocking capacitor is not needed.

If you are talking about muting at the speaker output jack, some of these automatically switch out the internal speaker when you connect an external one.
 
its not old radio :)
I am not trying to mute the speaker output jack, instead I want the audio. this can be done with the help of the dc block.
 

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