Having problem with LM380 Intercom diagram

[younggun38]

Hello,I am new to this forum and very new to electronics.I am trying to learn as much as I can,but I am the type that only after I actually complete a task will I understand it completely.I bought an LM380 kit to build an easy intercom circuit(It says great for a kid or beginner,so I really feel like a moron).The Schematic shows a simple transformer symbol as T1=25:1.The part that is confusing me is the kit does not come with a transformer.The only thing I can figure is I could use one of the potentiometers,which the kit did come with.I know this is probably a simple question to answer,but I have searched the web for two days and can't get a clear answer of whether or not a potentiometer would work or what the difference between a step down transformer and a pot is.Any advice would be helpful.I attached the schematic for this circuit.Thanks in advance.INTERCOM 2(a).jpg

[Minion]

Did the kit come with a relay ??

[younggun38]

It came with 2 Pushbutton, SPST Momentary,switches.It came with many capacitors,resistors,pots,4 transistors.The kit is for a variety of circuits,but I wanted to do the simple intercom first.At least I thought it was going to be simple.Like I said I am very new to circuits.

[jaycee]

The kit should have come with a transformer unless they have changed it. the 25:1 transformer is there to act as a step-up transformer to allow the speaker to be used as a microphone.

[Mooly]

It's a real pity these circuits and kits are so hit and miss especially for a beginner.
That transformer is crucial to the design as Jaycee points out...
Have you got a link to the kit so we can have a look

You ask the difference between a pot and transformer.... well the short answer is they are two totally different things.
The pot allows you to "tap" of a voltage along the length of its carbon track using the middle terminal or "wiper. It can never increase the signal level.
The transformer can provide a voltage gain... in your case from the tiny voltage the speaker produces as a microphone into something larger that the LM380 can work with... but you don't get something for nothing doing that, but that's another story.

[younggun38]

Here is the link to the kit and parts.NightFire Electronic Kits : (#1415) LM380 2.5 Watt Audio Power Amplifier Kit - $8.25 don't know why my last post did not show up,so if this gets posted twice I am sorry.Thanks for the info. so far.I don't feel quite as stupid knowing that I am supposed to have a transformer to complete this.If anyone knows of a link to a simple circuit I can build with these components,I would greatly appreciate it.If not I have seen other schematics of this same intercom except they use a transformer from Radio Shack #273-1380.If I have to I will order this part and complete the Intercom with it and the other components from the kit I bought.

[Bone]

This is not a kit as such, just a collection of components which includes a LM380.
No circuit diagrams are supplied with it and there appear to be no recommended projects for it only suggestions. It is up to the buyer to decide on a circuit and obtain those parts which are not supplied.

[jaycee]

I'm wondering if a small "Output" type transformer you find commonly would work here

[Mooly]

Sorry for not replying earlier...
First off it's worth having the data sheets for parts handy, and for ic's these often give applications too... I see where your circuit came from now,
http://www.datasheetcatalog.org/data...r/DS006977.PDF

Data sheets from
LM380 Datasheet pdf - Audio Power Amplifier - National Semiconductor

It might be worth experimenting... if you can get an old scrap ancient transistor radio, the old 6 transistor types of 40 years ago lol, these had small trannys in them for matching the speaker to the amp... probably just right for your project.

[younggun38]

Originally Posted by Bone

This is not a kit as such, just a collection of components which includes a LM380.
No circuit diagrams are supplied with it and there appear to be no recommended projects for it only suggestions. It is up to the buyer to decide on a circuit and obtain those parts which are not supplied.

The parts did come with schematics and the Intercom was one of them there is a pdf on their website that shows the projects that can be made with the LM380.I don't have a problem ordering a transformer,but it is very confusing to a beginner to be given a bunch of parts and schematics and then not have the right parts for the schematics sent.I am sure there are a dozen circuits that can be built with these components,as I said I have about ten different schematics sent with the parts,but the only one that interested me was the intercom.I am going to order the Transformer used in the other schematics for this circuit which steps 8 ohms up to 1kohm.I am determined to build this now.I have seen other more advanced schematics that show an Intercom system without Transformers built with the LM380,but they take many more components and I am just trying to get one circuit to work and then I can understand more about how circuits work than if I read 10 manuals,that is how my brain works.Once the circuit is done I will understand the opamp's and other components purposes much better.Thanks for all the help and advice.It has saved me many days of searching the internet.