ISD1700 help !!

[Agent36]

Hi Russ,
I was wondering if you could give me some advice on the 1700 series audio chips.
I have built a couple of proto crcuits using surface mount isd1740's in push button mode to start with. I can record, fast forward and play with out any problem.
I would like some tips on how to remove the pops at the start and end of the recording, along with the back ground hiss. Such as circuit design and layout to enable me to get the best from these chips. I have added a lm386 audio amp using an old winbond application sheet. I have both the main application sheets.

Any help to be very much appreciated.

kind regards Nick

P.s If any other forum members have some advice I would be please to hear from you too.

[RussMartin]

I would like some tips on how to remove the pops at the start and end of the recording, along with the back ground hiss.

Are you recording from an audio line input or from a microphone? You might try an "anti-pop" resistor across the input. To reduce the hiss, try a low-pass filter.

How are you configuring the APC register?

At what frequency are you running the ISD?

Such as circuit design and layout to enable me to get the best from these chips.

Pay especial attention to bypassing (lots of it!) and to power and ground routing.

I have added a lm386 audio amp using an old winbond application sheet.

I would like to see a copy of that old application sheet if possible.

[Agent36]

Hi Russ,
Here is the info you asked for;

APC Register: Not sure if this can be done without spi mode. So its a No

Freq: Running at 8KHz going to up it to 12K when I get the right value resistor.

LM386 Application diagram: Here is the link www.quasarelectronics.com/ds/isd-ab6a.pdf
I used this when using the 1200 series chips, so tried it on the 1700 series, connecting it to the spk outputs. Have changed the circuit to the minimum parts diagram with a gain of 20 from the LM386 data sheet, and connected this to the AUD/AUX output.

Mic input: I tried it using the anain (with FT low) as per example #2 then I tried decoupling the Mic- to earth using a 0.1uf cap and a decoupling cap on the Mic+ to the source with a 1k resistor on the isd side between Mic+ and Mic-.

Did some more searching on the net and found the ISD-COB17xxx demo board user manual, this includes a circuit diagram and pcb layout. I am in the process of drawing a PCB board using this as a guide on a single sided PCB. If it would help I could try and up load the layout for you to look at. I would buy one as a trial but there not for sale in UK and postage is a bit steep from USA.

I hope I have provided all the info you asked for..

What sort of quality have you managed to get from these chips? Is the LM386 the right choice of amp for the ISD 1700?

Kind regards Nick