help me in trouble shooting my design

muting transistor

hello guys
iam eletronic student ....currently i doing project with audio amplifier and LED.

i need to design a 0.5w audio amplifier with mute and volume control....the design should allow user to select two different bandwidth....selected choice must be indicated visually using LED...the power supply is +- 12V ...the leval of baseband signal is 250mv pk to pk at 1khz...

components should be used ...MicroA741. TDA7052A, regulator (LM78, L05), transistor 2N2222......

my group was able to design a circuit for our topic...we think there could be some minor faults in ckt.we are supposed to use only 1bandpass filter..and v should not use it for music.now the main problems in our ckt are:

*only two switches must be used,but in our ckt we don't knw which one 2 omit as there are 3switches.

*what is supposed to be done in between the frequency supply and the music's BJT?whether a resistor or some other device to be used there?

*when we test our ckt,do we need to test part by part(op-amp by op-amp)or we can directly patch up the whole things and test for the output?

we have attached two ckt diagrams with this post..the one with red circles was done by us(which is 2 b corrected)
If the other one is more accurate and workable than ours..pls try 2 modify it for us.
pls kindly reply to me ASAP..it would be really helpful if do this favour for us. Thanks in advance

designing 845 amplifier

holy christ !!
all well said,but not drawn well !! would you mind getting the schematics done in some s/w tool.I undertsand it is an acamedic stuff,but still you could have done it in some basic free downloadable softwares.
I doubt,whether you can get any help,with the manner you have posted it.

microa741

Hi!

I agree with the last post on this thread unfortunately - I can't read it!!!

However, the solution is fairly simple! Use 4066 analogue-switches in the signal paths to change over between the different bandwidth amplifier sections, using a group of sections with their control inputs inverted (1 transistor inv) to represent the Normally-open sections of your Signal Changeover switches!

You can link the inverted control i/ps of the '4066s to the NO contact of a single DPDT panel-switch section, and the non-inverted control ip/s to the NC contact of the same DPDT panel-switch section with the common going to the positive supply.

The second DPDT switch section can then control your panel indicator LEDs as desired!

However, if your design assignment ***specifically states*** only two switch sections are allowed in the signal-path (wether mechanical or '4066 type) then its permissible to use a unity-gain summing-amplifier in the o/p side of your bandwidth-filters with one c/over '4066 or mechanical switch section switching between them on the input sides of your filters!

Unfortunately I've not got a scanner to hand at work, so I'll have a go later tonight with a circuit-idea for you!

Chris Williams

Why are there two threads for this project?
I answered the other thread here:


Moderator, please merge both threads into one.

Hi!

Sorry - I hadn't realised this thread had already been duplicated! For what its worth, here's the circuit idea as promised based on member "audioguru's" suggestions!

Note! The speaker should be 16 ohms for 12V operation - I'd got the '7052 circuit from an Elektor Book and they'd got it wrong!

Chris Williams

I don't think we should do ALL the homework for school kids.
We should just give a few hints and let them work it out.

I really appreciate chris and audioguru for their patience and assistance, for having a look at the weird schematiics posted.
k_e2,lucky this time..better post in a good manner next time.

thanks guys........

Kavi i also doing this project. but my friend found a mistake in sheet 2 where the +12V switch closed,the transistor will be in saturation mode and there will be current in Ic. if this is the case there will still be current passing thru towards the 100k volume.pls reply as we have doubts too

falcoz said:

Kavi i also doing this project. but my friend found a mistake in sheet 2 where the +12V switch closed,the transistor will be in saturation mode and there will be current in Ic. if this is the case there will still be current passing thru towards the 100k volume.pls reply as we have doubts too

Click to expand...

The collector is at 0VDC and the emitter is also at 0VDC so the transistor will not have any collector current. The transistor shorts the AC signal to ground when it is turned on during muting.

But if the collector signal exceeds a negative peak voltage of about -6V then the collector-base junction will be forward-biased and conducting and the base-emitter junction will conduct with avalanche breakdown causing severe distortion.

Hai guys...
May be any kit from United7 technologies mentioned here may help you. More kits list may be found at www.united77.com/projects.htm

Remote Audio Board ………………………...….1185/- (INR)
This microcontroller-based kit is intended to work as an add-on to audio power amplifier. Motorola's MC68HC705 microcontroller and TDA7315 audio controller provide standard functions such as volume, bass, and treble using remote control. A LED panel gives status indication. Number of ICs used: 6.

Remote Control Digital Audio Processor ….. 1860/- (INR)
This infrared (I R) remote controlled digital audio processor has four stereo input channels and one stereo output. The processors in this system control various functions of each channel and output them to your audio amplifier.

Good luck

Audio thanks bro.so the diagram basically can work? hope u can give us some advice.thanks alot bro

The muting transistor turns on and off so fast that a "click" will be heard in the sound. To eleiminate the click you need to detect a "zero crossing" and switch the transistor on or off at that time. Some digital volume control ICs do that.

All muting circuits I built ramped the attenuating transistor slowly to eliminate the "click".