[leeperry]

be imaginative

besides they've never asked me any of these..

 

[shrisha]

Good for you. Bad for me

Not only imagination but knowledge about this stuff. I'm total noob on electronic field.

 

[ROBSCIX]

Quote:

Originally Posted by SpudHarris /img/forum/go_quote.gif According to ''HiFlight'' (My OpAmp Guru) this can't be acheived. He's the guy who let me into this little secret + OBCA (Output Bypassed Class A) which will only work with AD744's plus one other OpAmp (NE5534 I think).

The biasing only works with the AD744/NE5534 or the OBCA only works with these opamps?
I have never seen the OBCA idea, can you explain what is going on with that unit? -Very interesting BTW.

I appreciate your help and information.

 

[SpudHarris]

Quote:

Originally Posted by ROBSCIX /img/forum/go_quote.gif The biasing only works with the AD744/NE5534 or the OBCA only works with these opamps? I have never seen the OBCA idea, can you explain what is going on with that unit? -Very interesting BTW. I appreciate your help and information.

OBCA Only works with AD744's and NE5534's. The Class A Mod (2.2k Resistor between pins 6-7) works with any single OpAmp. Don't be fooled by my use of such mods as I'm not a techie by any stretch of the imagination, I just learned a lot from HiFlight (Ron Kerlin) on the P3 and P3+ threads that ran a while back.

When you get to a certain point in this hobby the cost of even small improvements in SQ can be disproportionate. The beauty of these mods is they are are cheap and if like most of us you have a critical ear they are so worth it. A little more body, depth and air for a few pence - bargain in my books.

 

[murrays]

Quote:

Originally Posted by SpudHarris /img/forum/go_quote.gif OBCA Only works with AD744's and NE5534's. The Class A Mod (2.2k Resistor between pins 6-7) works with any single OpAmp.

The "class A mod' can be adapted to work with dual op amps as well, as it is just a resistor (or Constant Current Source) from the output pin to either +V or -V supply pin. The pins are in different places for dual chips, and there's less physical space to fit the mods if you want to do it right on the chip/socket.

Remember, pretty much all of these op amps have a certain level of so-called "Class A' bias on their output stage by design. Check out the data sheet "quiescent/idle current" - typically 5 to 10 mA. This is fine for a buffered output into several K-ohms. I think Tangent's website has discussion of the higher biasing requirements for directly driving headphones.

Heh, my original LM1875 based headphone amp (from 1996) has about 70mA of standing bias - plenty for class A into headphones!

 

[majkel]

The only op-amp I know that improved from the class A biasing was OP27G. All modern op-amps are optimized to work without such tricks and the sound always gets worse. Sometimes there is a flaw in the signal chain which gives impression of improvement, kind of sweeter sound, but their virtual presence and spatial order gets worse. Some of the op-amps sound thin when biased this way, like LME49713.

 

[majkel]

I stopped using dual op-amps for multi-channel purposes. The crasstalk effects are too obvious for me since my amp and DAC use separate circuits for each channel. I am waiting for my samples from LT and I ordered some LME49710HA from Farnell. Should arrive tomorrow.

 

[murrays]

A quick question for those in the know - are dual op amps fabricated on one single wafer of silicon? If they are, then even if no circuitry is shared they will still be sharing the same substrate as well as their supply pins.

 

[majkel]

Yes, they are, and when you refer to the transistor count, it is not twice the single op-amp amount but less which means some circuits, most probably current mirror references, are common.

 

[ROBSCIX]

Quote:

Originally Posted by SpudHarris /img/forum/go_quote.gif OBCA Only works with AD744's and NE5534's. The Class A Mod (2.2k Resistor between pins 6-7) works with any single OpAmp. Don't be fooled by my use of such mods as I'm not a techie by any stretch of the imagination, I just learned a lot from HiFlight (Ron Kerlin) on the P3 and P3+ threads that ran a while back. When you get to a certain point in this hobby the cost of even small improvements in SQ can be disproportionate. The beauty of these mods is they are are cheap and if like most of us you have a critical ear they are so worth it. A little more body, depth and air for a few pence - bargain in my books.

Thx for the information. I appreciate it.
I consider my ear to be critical as I notice small changes in sonic signature.
I am always looking for upgrades even if they are smaller then others.
can you explain the point of the OBCA mods? -I am unsure what the point is of bypassing the output?

 

[ecclesand]

Quote:

Originally Posted by murrays /img/forum/go_quote.gif The "class A mod' can be adapted to work with dual op amps as well, as it is just a resistor (or Constant Current Source) from the output pin to either +V or -V supply pin. The pins are in different places for dual chips, and there's less physical space to fit the mods if you want to do it right on the chip/socket. Remember, pretty much all of these op amps have a certain level of so-called "Class A' bias on their output stage by design. Check out the data sheet "quiescent/idle current" - typically 5 to 10 mA. This is fine for a buffered output into several K-ohms. I think Tangent's website has discussion of the higher biasing requirements for directly driving headphones. Heh, my original LM1875 based headphone amp (from 1996) has about 70mA of standing bias - plenty for class A into headphones!

Interesting. So for a dual opamp...since there are two outputs, would you need 2 resistors...one from the +V to output A and one from the +V to output B? Or could you use one resistor and pigtail one end of it to both the A and B output?

 

[leeperry]

humm indeed, the THS4032 seems to sound seriously good to me! I will try the THS4031 later on...but my soundcard layout uses one dual op-amp per channel(AK4396), so it's not quite shared...

trebles are less muffled than the LME49722, but the SS is nowhere near as impressive...time to try the 49720HA again

 

[crapback]

For class A goodness I think i'll stick to my new hdams in my zero.

I like the earth in the dac better than the 797brz. The detail and imaging are great and the dynamics are so much better than the chip. I'm trying to think of a better way to describe the differences and I don't want to call the 7979b lifeless cause it is definitely not lifeless. I guess I have to say that the opa earth can be both in your face and laid back and everything in between while the 797brz just seems to sit more in the middle.

I have a compass on order that should be here within the next 2 weeks so I'll have a much better piece of equipment to test out some opamps in. For all I know, my opinions could be totally different with a different circuit.

 

[ROBSCIX]

Quote:

Originally Posted by majkel /img/forum/go_quote.gif I stopped using dual op-amps for multi-channel purposes. The crasstalk effects are too obvious for me since my amp and DAC use separate circuits for each channel. I am waiting for my samples from LT and I ordered some LME49710HA from Farnell. Should arrive tomorrow.

I am with you. I used to use the LME49720HA but found that a dual LME49710HA seemed to sound better in my gear so I started using those instead. When talking with people I would consider opamp experts they always tend to agree with this idea also.

 

[leeperry]

so what did they do w/ Andrea? ban his whole ISP or ppl using his web browser version?

ok, well the LME49720HA bass...amplified by the JRC4580 is just