[bgpaladin]

Hi,
 
I bought a JDSLabs headphone amp awhile ago and thought it was great! I got interested and tried to build a CMOY amp according to Tangent's tutorial. Using an OPA2227PA (from the JDSLabs amp)  the sound is OK, although not quite as good. However, when I try an NE5532, TL072 or JRC4560D I have terrible problems.
 
When I check the power supply with no op-amp plugged in, my 9V battery splits accurately into +4.5v and -4.5v, as expected.
 
However, whenever I plug in one of the "inferior" op-amps, I get big voltage swings and soft and badly distorted sound.
 
eg.
 
No amp           9.4v          +4.7v     -v.7v
 
OPA2227        9.39v        +3.39b   -5.93v       sounds OK
 
NE5532          9.42v        +7.44v    -1.50v       medium volume, distorted
                                                                  when I put one thumb on the underside covering soldered pins 1-4 and the other
                                                                  thumb covering pins 5-8 the volume increases and the sound improves a lot.
                                                                  Checking the voltages again, while touching the connections, the voltages are
                                                                  closer, but still no where near equal.
 
                                                                 I plugged this op-amp into the JDSLabs and got good sound and equal voltages:
                     9.08v        +4.55v     -4.53v
 
 
JRC4560D      9.40v        +0.88v    -8.60v      sound is absolutely dreadful - very soft and distorted.
 
TL072N          9.42v        +1.20v    -7.99v      reasonable loud, but very distorted   
                                                                Touching the underside of the board helped here, too. Connecting a 1M
                                                                resistor between pins 8 and 3 (8 and 5 also helped) improved the volume and quality
                                                                a lot. The harder I pressed, the better. 0.1uF capacitors did nothing
                                                                (I wasn't sure if my fingers were creating capacitance or resistance (or both)). 
 
I checked everything as well as I could. All resistors and connections seem OK - I don't know how to check the capacitors.
 
In frustration, I built a second Tangent amp and got pretty much the same sound output, although I didn't bother to check for voltage swings, as I was in too much of a bad mood. It seemed clear I was stuck with the same problem.
 
One thing I did notice - I used cheap op-amp sockets bought from EBay. The NE5532 seems to fit fairly snugly, but the others quite loose. All are tight when plugged into the JDSLabs socket. Could this be the problem? I am getting connections through to the amp, though, as I checked connections to the top of each pin.
 
I hope someone can help or offer advice. Surely I'm not the first novice to encounter these problems.
 
Thanks in advance for your help.
 
Regards,
Mike

 

[Soymilk]

first (i have to ask) are you putting the opamp in in the right orientation?
 
also, what virtual ground are you using? the basic two resistor voltage divider one? what gain do you have in the gain loop?
 
depending on how neatly you put together your circuit, a picture of it may help as well.

 

[nikongod]

If you used a resistor based rail splitter it is normal for the voltages in a Cmoy to come up unequally. 
 
If they come up unequally enough

the opamp runs too close to the rail and then life starts to really suck.
 
Replace the rail splitter resistors with a tle2426 (or newer device if thats whats popular) and you should be rocking.

 

[bgpaladin]

Thank you Soymilk and nikongod!
 
It did not occur to me that wide variations in voltage through the rail splitter resistors were "normal" in amps not using a tle2426 (after all, the split looked good until an amp was plugged in). I was convinced the problem was somewhere else.
 
I tried connecting two 9v batteries in series, using the center as ground and all four amps worked perfectly. I must say, though, that the opa2227pa sounded best to my ears, followed by ne5532, jrc4560d and the tl072. All sounded fine, though.
 
Tomorrow I'll look at how to modify my two amps to add the tle2426, as I'd prefer to use only one 9v battery for each. Next I need to figure out how best to put them into the Altoids tins I got for them

 
Thanks again - much appreciated!
 
Mike
 
PS. I think I might get hooked on this!

 

[nikongod]

unless you are really crunched for space 2X9V>>1X9V

 

[bgpaladin]

I tried the TL2426 and it fixed the problem - perfect voltage split between the audio channels. Two 9v batteries do sound a bit better than one, but the difference is fairly small. I think I'll stick with the single battery, though, in order to use my Altoids tins.
 
Thanks again for the quick and helpful device.
 
Mike