[Pageygeeza]

Avro Arrow you're a great man!
 
So it's kind of a DC to AC converter? Class A/B isn't it? 

 

[Avro_Arrow]

Thank you
 
The op amps are class A/B but the final stage amp is single ended class A.
The first op amp stage is the I/V converter and the second stage is the low
pass filter. You should be able to drive about 4 volts into your headphones
with this.
 
Quote:

Avro Arrow you're a great man!
 
So it's kind of a DC to AC converter? Class A/B isn't it? 

 

[nikongod]

I dont think that the feedback loops around U3 and U4 are set up properly.

 

[Avro_Arrow]

Ya, your right...see what happens when you draw something in a hurry in the middle of the night...
I guess I'll have to re-draw it.
 
Quote:

I dont think that the feedback loops around U3 and U4 are set up properly.

 

[Pageygeeza]

Thanks again, look forward to the end results.
 
Then I'll have to start some furious saving!

 

[Avro_Arrow]

I revised the original drawing.
 
Thanks to NikonGod for finding the mistake.

 

[mugdecoffee]

What everyone is trying to say about inverted and negative DAC outputs is that the L- output is always the negative of the L+ output (same with R+/R-).  If L+ is putting out the sine wave sin(2t), L- is outputting -sin(2t).  If at some point in time L+ is outputting 3V, L- is putting out -3V.  The same works for current output DACs.  If L+ is outputting 1ma, L- is outputting -1ma (or 1ma is flowing into L-).
 
Now, if you used a 4 channel amp (balanced and I think bridged too?), you amplify L+,L-,R+, and R- separately and the headphones are connected with a 4 pin connector.  So if L+ is 3V and L- is -3V out of the DAC and your amplifier has a gain of 2, you get on the output 6V and -6V and when you connect this to your headphones, they see a 12V difference.
 
All this means that there is no current flowing from the the signals into ground.  Instead, the L+ and L- perfectly balance each other so what one is outputting, the other is inputting.

 

[Avro_Arrow]

Well said!
 
Quote:

What everyone is trying to say about inverted and negative DAC outputs is that the L- output is always the negative of the L+ output (same with R+/R-).  If L+ is putting out the sine wave sin(2t), L- is outputting -sin(2t).  If at some point in time L+ is outputting 3V, L- is putting out -3V.  The same works for current output DACs.  If L+ is outputting 1ma, L- is outputting -1ma (or 1ma is flowing into L-).
 
Now, if you used a 4 channel amp (balanced and I think bridged too?), you amplify L+,L-,R+, and R- separately and the headphones are connected with a 4 pin connector.  So if L+ is 3V and L- is -3V out of the DAC and your amplifier has a gain of 2, you get on the output 6V and -6V and when you connect this to your headphones, they see a 12V difference.
 
All this means that there is no current flowing from the the signals into ground.  Instead, the L+ and L- perfectly balance each other so what one is outputting, the other is inputting.

 

[Spacehead]

use TPA6120 for this with DC servo?

 

[Avro_Arrow]

It doesn't really need a servo, once balanced, the DC offset doesn't drift very
much as long as you have all the mosfets on the same heat sink.
My Szekeres VE3 is never more than +- 1mV.
You are quite welcome to add the servo if you wish though...
 
Quote:

use TPA6120 for this with DC servo?

 

[Pageygeeza]

Mugdecoffee:  Thanks.  
 
I somehow had this idea in my head that the audio was produced differently, after it's now been drummed into me a few times now it's sinking in (that's what I get for not reading the manual.)  
 
It's all part of the learning curve, thanks for being so patient guys, I appreciate it!