[ProTofik]

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.

 

[Fred_fred2004]

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

 

[ProTofik]

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.

 

[Fred_fred2004]

Spot on

 
cheers
FRED

 

[ProTofik]

Just replaced with 7.5K resistor and it's great.
I also noticed that output impedance dropped from 0.51[size=small]Ω to 0.13[/size][size=small]Ω.[/size]
 
[size=small]If I will ever have more questions about my CMOY I will post in this thread.[/size]

 

[Zigis]

Better change 10K to 1k-2K

 

[ProTofik]

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?

 

[Fred_fred2004]

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

 

[ProTofik]

So my cmoy can work on 12v without a problem?

Do I need to disconnect batteries when connecting power supply?

 

[Fred_fred2004]

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