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ISD 1700 series minimal sound

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hack

New Member
I'm using a new chip I bought the other day. It's the ISD1790. This is supposed to sample at 12kHz and at that rate will provide 60 seconds of recording and playback. (90 seconds at 8kHz)

I'm wondering if anyone has tried this. The datasheet for this chip is really sparse. Not nearly as good as the ISD 2500 series datasheets.

Problem I'm having is that the sound is really really quiet when I play it back through a speaker. The docs suggest I use an 8 ohm speaker. When I do I can barely hear the sound I recorded into the chip.

I'm recording through the analog input where I have a jack connected straight to my computer headphones.

Operationally this seems to be working fine. I would like to be able to use the chip without an amp - but I don't know if I'm going to be able to now.

Has anyone else used this chip? Any ideas?
 

Sceadwian

Banned
Did you say you're using computer headphones to record to the audio in? Headphones make REALLY crappy mic's.
 

hack

New Member
Meant computer headphone jack on my laptop.
 

Sceadwian

Banned
Might mean the input impedance for the analogin of your chip is low. It really should drive it okay though. You might want to try an audio impedance matching transformer and see what results you get. It's kind of hard to tell if the output is the problem or if the input is. Do you have an old sound card floating around that has a speaker out instead of a headphone jack?
 

audioguru

Well-Known Member
Most Helpful Member
The impedance of the line level input is 42k ohms so a headphones output has a nice low impedance to drive it but probably doesn't have enough signal level since max input is 1V.

Make a two-resistors attenuator for the headphones output and feed it through a coupling capacitor into the + pin of the mic input. Then you will have plenty of gain and will also have automatic-volume-control.
 

kool_rider007

New Member
reply to hack's question

hello hack. i am using ISD 1760 for my final year project. even i faced this problem.
either u can take the output signal and feed it into a low cost low-voltage audio amplifier like LM386 M1 to get a better sound quality

or

u can take the output signal, pass it through a simple potentiometer circuit, and then feed it to the speakers. it worked out for me.
 
Last edited:

ROSSi

New Member
Hi, I'm doing my Final Year Project for my last year in this school. I have some diffculties finding the ISD1760 SMD diagrams. Do you have any references or website, that you can introduce me?
 

Boncuk

New Member
Here is an ISD17XX series datasheet with all necessary information.

Boncuk
 

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