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Getting stereo from two MC34119 ICs

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kevinkirkp

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I am designing a circuit right now which takes stereo from a source and amplifies it to drive small speakers. The chip I am using is a Motorola chip MC34119. Currently I am using one chip, where left and right input are connected to the Vin pin and then the ground is going to the ground pin on the chip. On the other side of the chip (output side), I have VO1 and VO2. VO1 is the amplifiers output. VO2 has the same output as VO1 but is 180 degrees out of phase with VO1. for now, I am driving one channel using VO1 and VO2. Let me tell ya, this chip is awesome. I am only using Vcc of 3.0volt and this puppy rocks! Sound is great. Plus I think it was only drawing like 25mA. Not bad!

My problem is that I have no idea what to do about getting two channels working with a chip like this (by adding a second chip for a second channel). Input isnt a problem because i have one Vin for each chip. For output, I have a VO1 and VO2 for each chip, thus four outputs. but the stereo 1/4 jack only has three (gnd, left, right). Do you think I can just not use VO2 and use the VO1's for left and right and then use ground for output ground? I am probably missing some fundementals here. I tried to connect the two VO2's together for gnd on the plug and then VO1's for left and right channels. It drew a lot of current plus I am not convinced that is the solution.

I already know what you are going to say. Why am I not using LM386 for this? I dont like LM386 because Vcc has to be higher. I want to power this thing from Vcc of 3volts for this particular application. LM386 is much easier to work with though and I dont have this particular problem with having four output pins a stereo jack.

Thanks for your help,
Kevin
 

Sebi

Active Member
When You can use only 3pin jack for speakers, use LM386 it also works with 3V supply. MC34119 is a bridge amplifier, don`t connect any out to GND or supply+, it`s dangerous for chip. Other possibility: a serial condenser for one output (as LM386) and speaker to GND. This is half power out.
 

kevinkirkp

New Member
I am not sure that LM386 is an option at this point. I will have to put it back onto a proto board and see if it will work with 3v in this application. The nice thing about the Motorola chip is that I can effectively double the amplification because I am using VO1 which is in phase, and VO2 which is 180 degrees out of phase but equal in amplitude. That is a correct assumption, right?

I will give LM386 another go. I am afraid that I am going to have to use 9volt to get decent results.

Thanks,
kevin
 

pkshima

Member
if i recall correctly, ... lm386 (basic version) works on 4V-18V.
too lazy to check out its datasheet though. :roll:
 

bogdanfirst

New Member
thats the problem, 4-18 volts...
and i made an amplifier with lm 386, for a 8 speaker, works neat for voltage of 9-12v and good quality, but if you lower the voltage you get some distorsioins.
try tea2025 3-18olts and good quality, 3 wats i think,
did you connect the speaker to the 2 outputs? like one speaket contact to VO1 and the other to VO2?
i am not sure that you get a 180degree out phase.....
 

kevinkirkp

New Member
Yes, it would work if I connected it to standard speaker wire, but the problem I have is that i have to use a stereo jack (female). That presents a problem because I have 4 leads to go to three contacts on the stereo jack. I have noticed the same thing with the LM386 (distortion at lower voltages).

The chip i am using does have 180 out of phase if with V02. It is always there (no way to disable that). It is definetly a good thing for the performance of this chip though.
 

bogdanfirst

New Member
connect the bigger contact to the ground of the circuit and each of the other one to one amplifier and the other to the oter one.
 
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