Attaching speaker to HK-828 voice recorder

[edwards.aus]

Hi all,

I want to build a voice record/play circuit using HK-828. I have attached the datasheet for convinience. I want to use Random Access Type (with 4 message recordings - (Pg 9 of HK-828 datasheet).

I was having some issues with choosing the right speaker. I have an 8Ω 0.25W rated speaker.

According to the datasheet (Pg 11), the speaker pins output a power of 1W to a 16Ω load.

Now, I want to use my 8Ω speaker for this circuit, but I cannot directly put it across the SP+ and SP- pins due to power mismatch.

To overcome this, I thought I might use a seperate audio amplifier. I thought I might work with LM386-N-1 (again datasheet attached for convinience). it is pretty cheap.

Basically I was looking at utilising Application circuit, Amplifier with Gain = 20 Minimum parts (Page 5 of LM386 datasheet). According to the HK datasheet, the Voltage output from the speaker pins is 1.4Vpp. So i might voltage divide with a pot as in the appln. circuit to get 1/10th voltage input and then amplifier gives 20 gain (prolly enough for me).

I have not yet built the circuit although I have bought the components. I am new to electronics and thought I might discuss this approach whether it will work or not.

Await reply in earnest.

Thanks,

Edwards

 

[transistor495]

Why can't you buy a 1W speaker?

 

[edwards.aus]

True. I could buy a 1W 16 ohm speaker...

But i have 4 8Ω speakers from previous applications and LM386 chips.

I thought maybe I could utilise the amplifier chip without compromising the workings of the voice recorder IC and spending money on an extra speaker.

Edwards

 

[transistor495]

True. I could buy a 1W 16 ohm speaker...

But i have 4 8Ω speakers from previous applications and LM386 chips.

I thought maybe I could utilise the amplifier chip without compromising the workings of the voice recorder IC and spending money on an extra speaker.

Edwards

A small 1W,16ohm(8ohm might work) won't cost more than 1USD and you may need to attenuate the speaker output of the board before feeding to LM386.

IMO, a new 1W speaker will give you more pleasant sound without LM386 and related problems. You're gonna study a great lesson if you go with this project

You can try some of your household electronics or neighbor side in search of a seconds 1W speaker.

 

[edwards.aus]

I absolutely agree with you that 1W speaker will give better sound... and would definitely be the way to go.

It's just that I picked up this project to understand the theory behind speakers and audio amps (which I am not much familiar with)

I did some research to come up with the idea that I posted above.

I was sort of hoping that someone who has experience with these matters might be able to confirm whether I am on the right track and advise me of any other pitfalls I should be on the lookout for.

you may need to attenuate the speaker output of the board before feeding to LM386

Yes, I suggested using a voltage divider to attenuate the signal to 1/10th (because the speaker pins output 1.4Vpeak-peak which are too high for the amplifier).

...and related problems...

Are there any other issues one should be on the lookout for?

Appreciate all the responses.

Edwards

 

[transistor495]

First you need to download LM386 datasheet and read it thoroughly. Then pick up the right circuit and post it here with necessary modifications depending on your requirement.

 

[edwards.aus]

First you need to download LM386 datasheet and read it thoroughly. Then pick up the right circuit and post it here with necessary modifications depending on your requirement.

Sure thing.... Here it is.

I have have 2 different sections : the recorder IC connected to the audio circuit. the connections Vin and common between the 2 circuits shown.

Edwards

 

[transistor495]

I've gone through the HK-828 datasheet. It rather looks like a bridged audio output with SP+ and SP- terminals without a common ground. So a normal attenuator cannot be used for connecting to LM386. Using a load lower than 8ohm impedance may damage the IC. 16ohm is actually recommended.

A coupling audio transformer may work here. However I won't recommend to continue this project because this would be a worst case of disturbing/damaging the IC having a bridge mode audio output

 

[audioguru]

Use a single output from the recorder, attenuate it with two resistors in series to ground (or a volume control pot) and capacitor-couple it to the input pin of the LM386 amplifier. The coupling capacitor is needed since the output pin of the recorder has a DC voltage on it and the LM386 amplifier's input must be at 0VDC.

A transformer is not needed.

 

[transistor495]

Wow great, I didn't even think about it.

 

[edwards.aus]

Use a single output from the recorder, attenuate it with two resistors in series to ground (or a volume control pot) and capacitor-couple it to the input pin of the LM386 amplifier. The coupling capacitor is needed since the output pin of the recorder has a DC voltage on it and the LM386 amplifier's input must be at 0VDC.

A transformer is not needed.

Hi audioguru and transistor495,

Your suggestion of using a single output from the chip to amplifier makes sense.

Thanks,

Edwards

 

[fodder128]

Call me old fashioned but why not use a transistor to drive the speaker output

 

[audioguru]

Call me old fashioned but why not use a transistor to drive the speaker output?

A simple single transistor will put DC on the speaker which wastes a lot of power and may damage or cause distortion in the speaker.
Usually an amplifier has a class-AB complementary pair of output transistors used as emitter-followers for a strong low impedance output.
Frequently an audio amplifier is bridged (two amplifiers driving each end of a speaker) which gives much more output power and then a single-polarity supply can be used without a big output coupling capacitor.

 

[balaramnutakki]

Where can i buy HK828

Hi,
I'm from Florida US Can u tell me where can i buy HK828? This is very urgent as my project due date is very close..

 

[edwards.aus]

Where to get hk-828?

Jaycar USA perhaps:

**broken link removed**