[lehtinel]

Allright, bare with me here. An engineering student for two years back in 2001-2003, never did anything practical over there, Im ashamed to say I've forgotten most of the theory we got or atleast it's buried somewhere in the back of my brain.
 
But anyway, lets cut to the chase. I built the Cmoy amp according to Tangentsofts excellent instructions, using the recommended capaciotor and resistor values, OPA2132P etc., the only big difference is the protobord I used. It has three connected rows, so I had to modify the layout to work.
 
Allright, all set up, theres sound, no distortion, no noticeable weaknesses in sound either, but, I can measure a huge difference in voltage at the caps, +2.7V / -6.6V and sone 1.4 - 2V at the IC V- and V+ pins. Also, if I disconnect the battery - the signal still plays trough, should it be doing this? 
 
A picture (no closeup though, my macro lens is some 500km away) from this morning.
 

 

[nikongod]

secret club

 

[lehtinel]

Cheers, plugged out my OPAMP and measured voltages again, now it gives me +9v an -0v so everythings on the plus side. I noticed I have soldered the IC socket with the notch upwards, but still I had my chip installed with the notch pointing down so by all logic I should be fine there. 

 

[Soymilk]

the socket orientation has nothing to do with anything, it is simply a socket, nothing more, nothing less.
 
if your cmoy isn't powered but it's still playing, that would lead me to believe your output is directly connected to your input. recheck your layout.

 

[gimble]

"My circuit isn't doing what I expected it to, but I triple-checked the schematic / got it from a reliable source!"
 
Cont test time. Make sure the physical circuit matches the schematic.

 

[lehtinel]

Quote:

the socket orientation has nothing to do with anything, it is simply a socket, nothing more, nothing less.
 
if your cmoy isn't powered but it's still playing, that would lead me to believe your output is directly connected to your input. recheck your layout.

 
Jup, I kinda guessed the socket doesn't do more than lead the signal through. Will have to check the input / output coupling thing.
 
Thanks
 

 

[lehtinel]

Allright dudes, friday evening fine-tuning, no stress. I got the voltage settled at 4.5 for both sides, nice, it was probably a bad soldering problem that bridged in the power section. 
 
The sound is improved a lot, but, theres a constant hiss or buzzing sound. And the amp music still plays trough if I remove my battery. I can't find any bridge between input / output that would cause this.

 

[lehtinel]

Okay, got the buzz fixed and now it doesn't even play trough when I take the battery out - but, the sound is very muddy...hmm
 

 

[Avro_Arrow]

Can you get a good picture of the top side so we can see how it is all wired up?
 
See how much you learn by doing these simple projects..?

 

[lehtinel]

Allright, found my extension tube so: 
 
 

 
And yes, it's intresting indeed and very nice to learn.

 

[Avro_Arrow]

You don't have those 100nF caps across any of your resistors do you?
You might have made a low pass filter...
Those 100nF caps should go from the power supply pins
on the OPA to ground.
 
I'll keep looking but check those caps first.

 

[lehtinel]

Mmm...in the Tangentsoft guide the 100nF caps are in line with R2 and the OPAMP first and second (input) rows. a detail of my underside: 
 

 

[Avro_Arrow]

I see, you are using the 100n as an input cap. I think
it is too small, it should be more like 1uF. But that
is my opinion and the 100n will not cause the problem
you are having, just poor bass. I also think that a
gain of 11 is too high. Maybe reduce to 5 maximum.
A 2K feedback resistor and a 500R gain resistor
would do the trick. A input resistor of 10x volume
pot value (100k to 200K) and an input cap of 1uF
will make a nice sounding CMoy. An optional
source resistor around 400R would balance it out.
Tangents tutorial is a great place to start but I think
the values he has there could use a little tweaking...

 

[lehtinel]

Allright, well, I've been tinkering around and I can't get the sound decent enough. What I've got at home partvise is 470nF 250V capacitors and I could switch R3 and R4 to 4.7kΩ for a gain of 3. Now the cans Im currently on are Koss Porta Pros at 60ohm but my main cans are Sennheiser HD600 so will the low gain cause problems there?
 

 

[Avro_Arrow]

Rfeedback = Rgain would be a gain of two.
The Koss Porta Pro's would be right at home with
a gain of two. The Senns would want a little more
voltage. Depends on how loud your source is.
You can always put in a switch to change the gain,
build a variable gain or just built two different
CMoys...they're are cheap enough...
 
Anyway, back to your problem...
It's kinda frustrating when a circuit this simple doesn't
work. Either it's wired wrong or the op-amp is defective.
All I can suggest now is to check your work again, draw
a schematic based on what you built and compare it to
the one on tangents tutorial and if all else fails, change
the op amp.