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Old 27th June 2002, 01:50 PM   #21
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I should have said unbalanced input. This is just tube lore. In a single ended topology only one active device (either solid state or tube) is present at the input and output. Most ICs that I have seen employ differential topologies. There could be exceptions?

Nice & simple topology for the headphone amplifier. How long do the batteries last?

Mohan
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Old 27th June 2002, 05:44 PM   #22
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By definition an opamp has + and - inputs. They can be implemented in balanced or unbalanced mode. Unity gain buffers have a single input but they are pure current gain devices.

Battery life depends on the capacity of the batteries, the current draw of the components you use in your amp, and the volume level you are listening at.

Alkaline 9v battery capacity is about 600mA hours. Rechargable 9V capacity is about 150mA hours.

The amp could draw between 10-20mA quiescent current, or even much more depending on configuration, but for battery operation you want to keep it reasonable.

I'll leave it to you to figure out how much current your headphones draw at your typical listening levels. I'm sure you can see that battery life varies widely because of all these factors.
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Old 30th June 2002, 11:13 AM   #23
hifiZen is offline hifiZen  Canada
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Mohan:

By "differential", i assume you mean "push-pull", and by "single-ended", I presume what you mean is something like the so-called single-ended class-A output topology seen on many older tube amp designs. In the opamp world, it's all about class-B these days, especially in an designs where power consumption is an issue. I highly doubt you'll find any single ended output stages on any modern opamp... There is, however, a trick for getting an opamp's push-pull stage to become a single-ended output stage. It requires the addition of a resistor or constant current source on the output to keep one output device turned on, and the other off at all times. But, I wouldn't recommend this for a portable application like this where you'll want longer battery life more than the small potential sound quality increase which may result from loading the output stage as such.

As far as inputs go, opamps are generally all "single-ended", except for some rare designs which employ complimentary differential pairs on the inputs. But, this really doesn't matter, since the small signal transistors will usually be in constant class-A operation at all times anyway.

Does that answer your question?

Morsel:

can you describe in a little more detail the sonic differences between the OPA134 and AD8610? I haven't yet had a chance to test out the 8610... Also, how would you compare it to the OPA627?

Thanks,
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Old 30th June 2002, 12:16 PM   #24
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Default Proof is in the pudding

I think that several things should be considered when comparing the sound quality of OP amps. These are the gain they are used at and the impedance of the input and feedback circuit. Perhaps also the supply voltage, load presented to the OP amp and the signal levels the OP amp is operating at. Some OP amps just work better than others in a specific circuit.

To generally say that one sounds better than the other without disclosing all the test, circuit conditions and other operating conditions may lead someone to the wrong conclusions.

The best way to evaluate the performance device is to use it yourself so that you have total control of all parameters. And even then the results can be misleading since we all have the tendency to hear what we wish to hear.

I would not recommend the OPA604 or OPA2604 for new designs. This part has been out for about ten years and I get the impression from the Burr Brown web site that they do not think about this part as highly as they used to. I still use these occasionally because they can withstand 24 volt rail voltages without difficulty and thus have increased headroom. Quite a number of my old designs used these parts and they can still provide excellent performance. They have never sounded muffled or bad in my system. I received a very nice Email one time from one of the Burr Brown engineers for using the old OPA2604AP in some of my DIY projects. This was very nice of him.

Some of the best OP amps ever produced are Burr Brown products. I have great faith in the Burr Brown OP amps and use some that are quite costly from time to time.

John Fassotte
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Old 1st July 2002, 09:55 PM   #25
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Thanks hifiZen. You have hit the nail right on the head. Exactly what I wanted to know about making Opamps work in Single Ended output mode. I shall try this out with AD8610. With analog circuitry, I always try to understand what the designer tried to achieve before I am able to convince myself that I can do better.

John,
With all due respect, Morsel was relating her experiences with Opamps and she is quite correct in relating her experiences and reaching a conclusion. It may not be possible to operate two different Opamps under the same conditions because the internal circuitry and active devices fabricated within each device may be different.

Morsel,
I have been using Stax SRX MKIII headphones for over 25 years. I use them for very critical listening to my amps, to adjust tracking angle on my turntable etc.. However, for extended listening sessions, I prefer my speakers.

Mohan
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Old 1st July 2002, 10:48 PM   #26
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Quote:
can you describe in a little more detail the sonic differences between the OPA134 and AD8610? I haven't yet had a chance to test out the 8610... Also, how would you compare it to the OPA627?
The AD8610 is more open, airy, spacious, and accurate than any of the Burr Brown opamps, and especially the OPA132/134 series, which are ok, but not top of the line. I don't use the OPA627 because it is an outdated, cantankerous, pricey opamp which enough people have compared to the Analog Devices opamps that I feel no need to go out and play with them myself. Of course, some people prefer the "Burr Brown sound".

Go search HeadWize and Head-Fi. You will find days worth of reading on opamp comparisons. It is like an unfolding story, as better opamps are discovered and/or released. The AD8610 is the latest and greatest in this saga. No doubt it will eventually be dethroned by an even better model.
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