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Few questions about CMOY

post #1 of 10
Thread Starter 

Hello.

I just finished my first CMOY using this guide. The only modification that I made was that I used 2 batteries and LME49720HA opamp.

 

Q1. What will happen when batteries will run low? Would the amp just stop playing?

Q2. The amp is a bit too loud for my liking. How can I lower the gain? I guess I need to change some resistors.

Q2.1 What gain setting does this amp have by default? 3X, 4X, 5X?

Q3. How can I make it run out of power supply? Do I just connect AC/DC 9-10V adapter instead of batteries? If so, how many amps this power supply needs to have?

 

Thanks.

post #2 of 10

1. BAtteries going low - it will distort and sound horrible

2. change the 1K resistors the gain at the moment is (10K/1K)+1=11  increase the 1 K to say 4.7K  (10K/4.7K)+1=3.12

3. see 2

4. yes just use a decent DC power supply, a cmoy uses very low power (10-20mA) so nearly any supply will be plenty

 

cheers

FRED

post #3 of 10
Thread Starter 

Thanks for reply.

 

If I understand it correctly replacing the R3 resistor with let's say 7K resistor would give me 2.42X gain, right? (10K/7K)+1 = 2.42

 

I'm kind of guy that doesn't like loud music.

post #4 of 10

Spot on smile.gif

 

cheers

FRED

post #5 of 10
Thread Starter 

Just replaced with 7.5K resistor and it's great.

I also noticed that output impedance dropped from 0.51Ω to 0.13Ω.

 

If I will ever have more questions about my CMOY I will post in this thread.

post #6 of 10

Better change 10K to 1k-2K

post #7 of 10
Thread Starter 
Quote:
Originally Posted by Zigis View Post

Better change 10K to 1k-2K
Sorry, I already changed R3 to 7.5K.

I have another question. I don't have any 9-10V DC power supply and I don't want to spend money on it.
I happen to have 12DC 500mA power supply. I guess I need to put some resistor in series to drop it to about 9,5V. My question is what resistor do I need?
Edited by ProTofik - 4/7/13 at 5:30pm
post #8 of 10

Changing R3 works perfectly so don't worry,

 

just use the 12 volt supply, if anything it will be better :-)

 

I regularly use supplies from 12-24volts

 

cheers

FRED

post #9 of 10
Thread Starter 
So my cmoy can work on 12v without a problem?

Do I need to disconnect batteries when connecting power supply?
post #10 of 10

Yes I would disconnect the batteries, 

 

wire up a DC socket with a switch or use the 2 diode trick look here

 

http://www.tangentsoft.net/audio/cmoy-tutorial/tweaks.html#dcjack

 

cheers

FRED

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