Best Audio Chip For.......

[Space Varmint]

If you get feedback in that way, then it's because your design is completely useless - it's absolutely impossible in anything like a correct design.

Oh you loved saying that. Actually this design is patent worthy I do believe. The whole receiver has 12 transistors and the LM386 chip. Really it is only 8 transistor stages in the radio section. Two of the transistors are for the pair in a differential amplifier and a Darlington pair. The two other transistor are for the AGC which works. No Op Amp. I know it works because I have a pot in it and if adjusted wrong you can hear the signal shut off. It is driven from the output of the IF and is IF AGC meaning it shuts it's IF off. So it is single conversion and uses a 455KHz ceramic filter for selectivity. Performance. Performance is great. Very clean for being all in one small box. This is why I have to keep the IF level down so that I don't get high frequency parasitic oscillations. What is unique is that I can make a small adjustment and pick up SSB & CW with no beat frequency oscillator. I could also do it by adding a switch to drop out the IF section and run the output of the post mixer amp straight into the audio. So think about it. Really it is only 8 transistor stages and 2 transistors for the AGC. 8 transistors into an LM386 chip for short-wave reception. I can pick up ham operators meaning allot transmit only 50 watts or so. Also it is not susceptible to 50 ohms input and a long wire antenna gives a good match. The only thing it needs is a little more audio. It will drive a speaker but really need headphones for true operation. Still it is all in one box with no shielded sections. That is why it was necessary to DELIBERATELY suppress the IF level. So when it encounters any sort of odd oscillations, it will automatically turn the gain down for normal reception.

 

[audioguru]

If the power buss is not filtered well enough then of course it might cause oscillations in the circuit.

A few people on this forum are deaf and I can't remember if you are one of them. The 0.45W max output from an LM386 amp is plenty for a single non-deaf person. 4.5W will sound twice as loud. I don't know if your radio has enough gain to produce weak distant stations at a loud enough level.

 

[Space Varmint]

If the power buss is not filtered well enough then of course it might cause oscillations in the circuit.

A few people on this forum are deaf and I can't remember if you are one of them. The 0.45W max output from an LM386 amp is plenty for a single non-deaf person. 4.5W will sound twice as loud. I don't know if your radio has enough gain to produce weak distant stations at a loud enough level.

Well it's short-wave. So small signals like even 5 watts are common. Even your Broadcasts are commonly from other parts of the planet and so if the propagation is low, the signal will be weak. Nothing like local AM & FM broadcast which aren't nothing but the same old songs anyway...lol. Short-wave is informative. But yes, with short-wave it is usual especially with weak signals coming in to hear that staticky hiss from running the IF or IF's with lots of gain. But really with the headphones it will practically make your ears bleed so I think I can get away with a bit more power from an audio chip to achieve the results I am after. I think I have plenty enough IF.

 

[Ubergeek63]

See? That's what I'm talking about. So what would give me 4.5 watts? I might get some feedback...right?

are you familiar with the term decibel?

the ear is logarithmic... that means it takes five times the power to sound twice as loud...

West Labs Guitar Amplifiers - Pots

in other words 4.5W sounds a LOT louder than 1W on paper than it does in your room.

Dan

 

[mneary]

Well it's short-wave. So small signals like even 5 watts are common.

The distinction between power and gain has become blurred here. A 5W amplifier and a 500mW amplifier will have the same output until 500mW is reached. If 500mW is loud enough with a strong signal but isn't loud enough with a weak signal you need more gain, not more power.

 

[audioguru]

An LM386 amp usually has a gain of 20. If one capacitor is added then its gain is 200.

 

[Mikebits]

The distinction between power and gain has become blurred here. A 5W amplifier and a 500mW amplifier will have the same output until 500mW is reached. If 500mW is loud enough with a strong signal but isn't loud enough with a weak signal you need more gain, not more power.

Hehe, sounds like a chemistry limiting reagent experiment.

 

[Space Varmint]

An LM386 amp usually has a gain of 20. If one capacitor is added then its gain is 200.

Could you show me this capacitor? Another thing that is very apparent is the box. I have taken an off the shelf radio and hooked my output to it's speaker and it was louder than anything I could come up with. It was plastic. I still would like a little more audio but there are some things I will say about the radio. This radio will not produce static with no signal. Almost like squelch. Therefore it is very efficient. I revamped it a bit for maximum performance but I do believe I have a patent here. I dropped a transistor and went to a single transistor mixer. Being short-wave you still need about 10 foot of wire but this thing picks up signal everywhere and like I said, with no signal there is no output. I don't know what to call it but I have disproved some conventional radio theory. It is possible to drive the IF level up to where it will do some feedback like a regenerative receiver. What this will do is allow for CW and SSB reception. The whole radio is 6 transistors stages but using 7 transistors because of a Darlington amplifier I needed to come off the back end of a 455KHz ceramic filter. And then the audio chip and this thing picks up stations everywhere and has no audio hiss that wastes audio power. It just goes silent with no signal input.

*edit

Just to be fair I will say this. There are some draw backs to this design. Especially if I use a ground wire but not so much so if I don't, but it has a tendency toward intermod. If a station is very very strong than you may here it a bit under the station you are tuned to. It is possible to adjust it out but maybe not completely. This could possibly be reduced by using a better front end transistor as Mike pointed out. It also is susceptible to receiving harmonics which can also be adjusted out or in. Since I want a low part count, I do not intend to configure the local oscillator to cover the whole band. So it is possible to make an adjustment where I can receive at double the intended frequency. Also it could be considered an advantage for normal Short-wave listening because if a station changes frequency, in some cases you can tune around and detect the band the new frequency is on and if the intermod is present you can move to the frequency by the strength of the intermod.

 

[Mikebits]

Could you show me this capacitor?

See pins 1 and 8 of diagram.

**broken link removed**

 

[audioguru]

The capacitor between pin1 and pin8 boosts the gain 10 times.

 

[rekent]

audio, what do you think of the TDA7494 for a headphone out with volume and audio passthrough chip?

 

[BrianG]

What about one of those Velleman 7W mono kits based off the TFA2005 IC? Not the best quality, but better than the LM386. And if you feel adventurous, you can rearrange some stuff and make two kits into a single bridged output for more power.

 

[audioguru]

audio, what do you think of the TDA7494 for a headphone out with volume and audio passthrough chip?

Why use an amp designed for a 28V supply and 8W output?

 

[audioguru]

What about one of those Velleman 7W mono kits based off the TFA2005 IC? Not the best quality, but better than the LM386. And if you feel adventurous, you can rearrange some stuff and make two kits into a single bridged output for more power.

There is no TFA2005. The TDA2005 is a dual amplifier and the datasheet shows it bridged. It has 11 pins.

The newer TDA7240A is also a bridged amp iC with the same output power but its case has only 7 pins.

 

[BrianG]

There is no TFA2005. The TDA2005 is a dual amplifier and the datasheet shows it bridged. It has 11 pins.

Sorry, that was a typo. I meant TDA.

Not saying it was the perfect choice, but the Velleman kit would have all the components and PCB ready-to-go if that's what the OP wants.

 

[rekent]

Why use an amp designed for a 28V supply and 8W output?

The data sheet shows the supply range as 11-35V with a max of 40. My circuit is supplied with 15V. And also, the University has these that I can get free.

 

[audioguru]

The data sheet shows the supply range as 11-35V with a max of 40.

Be careful the high power does not blow up your hearing and blow up your headphones.

 

[rekent]

Be careful the high power does not blow up your hearing and blow up your headphones.

It will work ok though, I just need to watch how high I turn the volume pot?

 

[audioguru]

It will work ok though, I just need to watch how high I turn the volume pot?

You turn the volume pot down to half so normal signals are not too loud. But when you apply power or turn off the power it might cause a 5W POP.
The input cable might come loose and cause a 5W HUM. Then Good Bye hearing.

 

[rekent]

You turn the volume pot down to half so normal signals are not too loud. But when you apply power or turn off the power it might cause a 5W POP.
The input cable might come loose and cause a 5W HUM. Then Good Bye hearing.

Do you have a suggestion for a chip that provides essentially the same function that will work with 15V supply that does not have as high a danger to hearing and equipment?