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Mcoy and lm386 Amp problems

post #1 of 18
Thread Starter 

I have attemped to build 3 headphone amps now and every single one has had the exact same problem. After everything is hooked up and everything is soddered down i get a huge hiss in the output . I have messed around with the grounds and everything and have yet to do anything that has fixed it. I have made a varient with a virtual ground and one without one. And they have all had they same problem.you can hear the original signal slightly but only the main notes such as bass and such. I have checked the grounds, ive changed out capacitors and resistors and it didn't do anything. Any ideas of what to do would be much help.

Thanks.

post #2 of 18

You might need to give more details of what your trying to build, pictures are a big help

 

cheers

post #3 of 18

Maybe they're not the real Cmoy?

 

w

post #4 of 18

They may not be the real McCoy either. 

post #5 of 18
Thread Starter 

Sorry i typed wrong, i meant the cmoy amp. But the other amp i made i made on a breadboard and took it apart. im going to build the cmoy amp on bradboard and see if it changes any. I'm going to see if it has the same problem on a breadboard. 

post #6 of 18
Quote:
Originally Posted by Dnaudio View Post

Sorry i typed wrong, i meant the cmoy amp. But the other amp i made i made on a breadboard and took it apart. im going to build the cmoy amp on bradboard and see if it changes any. I'm going to see if it has the same problem on a breadboard. 

 

 

If you've had the same problem on three builds, it sounds like there is a mistake you are repeating

 

I would not build another amp until you've got it sorted

post #7 of 18
Thread Starter 

i built the cmoy amp on a breadboard today and got to almost play right, however, im having problems with cutting out, and it sounds like typical brocken cable "water" sound, sloshly like. I messed with the power circut caps and it sounds much better but it still sounds way off

post #8 of 18

Have you done Tangent's troubleshooting thingies? 

 

What Gain did you use? 

post #9 of 18
Thread Starter 

Yes i did the troubleshoot, without a resistor on the output all i get is popping noices, Gain is set to 11 i have also tried different gains but nothing helped. Checked the chips, they are fine. I'm using two Opa227 one for each channel. im using a 8 ohm speaker for testing.

post #10 of 18
Quote:
Originally Posted by Dnaudio View Post

Yes i did the troubleshoot, without a resistor on the output all i get is popping noices, Gain is set to 11 i have also tried different gains but nothing helped. Checked the chips, they are fine. I'm using two Opa227 one for each channel. im using a 8 ohm speaker for testing.

Have you tried a higher impedance load, with lower gain?  Low impedances presented to high gain circuits almost always result in an increased noise floor.  The 227 is a pretty stable chip, it can handle gain settings lower than 11.


Edited by kramer5150 - 4/6/13 at 9:23am
post #11 of 18
Thread Starter 

i did try a higher impedance, it sounded better but then turning the gain down made the amp sound worse, the increase of impedance worked slightly but it also exponentially decreased the volume output. 

post #12 of 18
Quote:
Originally Posted by Dnaudio View Post

Yes i did the troubleshoot, without a resistor on the output all i get is popping noices, Gain is set to 11 i have also tried different gains but nothing helped. Checked the chips, they are fine. I'm using two Opa227 one for each channel. im using a 8 ohm speaker for testing.

 

Could you detail your troubleshooting procedures and results? 

How did you verify that the chips are fine? 

 

Why would you burden the Opa227 with an 8ohm load when the datahsheet makes no mention of low-impedance load driving abilities? 

Why would use a functional speaker (I'm assuming its functional) to test something that may blow up and destroy more gear? A 32, 120, or 300ohm resistor is fine. 

Alternately use a set of VERY cheap headphones in the 32-300ohm range. I save the headphones they give you on the plane just for this...

 

Quote:
Originally Posted by Dnaudio View Post

i did try a higher impedance, it sounded better but then turning the gain down made the amp sound worse, the increase of impedance worked slightly but it also exponentially decreased the volume output. 

 

This is contrary to everything I have ever experienced with any amp, but also quite intriguing. 

 

You know how a picture is worth a thousand words?

Could you post hi-rez pictures of both sides of your board? 

Dont worry, head-fi will host any jpg up to 10mb. 

 

 

An amplifier whose output decreases as load impedance increases could be quite useful. 


Edited by nikongod - 4/6/13 at 1:17pm
post #13 of 18
Thread Starter 

I'm sorry i miss typed yet again or just failed to mention, i have had a resistor on the output in series to increase the impedance of the speaker, the speaker is a small test speakers used in alot of cheap kits. Also correct me if I'm wrong but isn't doesn't a smaller resistance= a smaller load i might have got them mixed around. Because with all my experience a lower impedance sub will be louder than a higher impedance sub. I know the chip is good because i have 2 of them and have swapped the other one in, i got the 1 later than the first one so it is mostly unused.

post #14 of 18

now I get it. 

 

The series resistor will help to keep the op amp happy with regards to load impedance BUT it may screw you for voltage output depending how loud you want the speaker to go, and how large the series resistance is. Making the series resistance larger WILL reduce output volume from a speaker BUT it will require more voltage. You may be running the op amp out of voltage - again depending how large the resistance is. 

 

I should note that with few exceptions I prefer headphone amplifiers with a bit of output impedance. How much do you have? 

 

In what way did turning the gain down make the amp sound worse?

post #15 of 18
Thread Starter 

When i turned the gain down the sound became more distorted, in other words, the "wattery" sound gets more intense, when i think about it, the highs sound good and bass sound good but there is no mid at all. I've tried many different output resistors. Any other suggestions.

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