[KurtW]

Battery life will depend on the capacity of the battery and the power consumption of the amp. The power consumption will be a function of all of the circuitry as well as the output power used. For example, biasing the op amp into Class A takes some current, as do the output buffers and the power supply buffer.

I measured the last two META42s that I built, both with the AD8620 op amps running in Class A. One had double EL2001 buffers and measured 12.3mA and the other had triple buffers and measured 13.6mA This is a static measurement taken with a battery putting out 10.0 volts. When I listen to music at my typical levels with low impedance headphones the current goes up around 0.5 to 1 mA. The Plainview battery is rated at 170mAH, so with music I would expect to get around 13 hours from the double buffers or 12 hours from the triple buffers. Your battery may be different. This seems about right based on my experience but I've never timed it. With the AD845 you'll get a little less than half of this.

According to my calculations, the DT770 Pro would require 2 volts RMS to achieve 105dB SPL, so 7 volts should be fine with either chip. This is 4mA of current draw, so the above amp with double buffers would only last 9.5 hours with the 8620 and 5.4 hours with the 845.

 

[purk]

Kurtw,
Which sound better b/w the AD845 or AD8620? Can u describe their differences? Thanks. I had about 6 or 7 hours on my Tangent META42 with AD845

Purk

 

[KurtW]

Purk, as I've indicated before, I've never heard the 845 so I can't comment on the sound. I originally tried the 8620 because several people liked it better than others they tried. I've been so happy with the 8620 for portable 9v operation that I've not been tempted to try anything else. Maybe you can get a chance to try it out in your Meta, assuming you have a socket for the op amp and can find a 8620 that's mounted on a adapter board to try.

 

[Taphil]

I'm using the AD845 right now but will switch it to the AD8620 as soon as I receive it from Tangent, so I can let you know by the end of the week.

With the AD845 and HD600, I can get over 10 hours on a Plainview 9V before it quits, but I notice the sound quality goes down a bit before that point, so I usually change the batteries at around 8 hours or so.

 

[tangent]

Quote:

I don't think (from what I've read) that the AD8620 is unsuitable for 9V operation, even though at least one person (Tangent, I think) wouldn't recommend it.

I've repeatedly stated that I've got distortion on my torture test up to 10V, but people keep misapplying that info. (Some times I'm part of "people", I admit it.) The torture test is done with a CMoy amp, with low-impedance (64 ohm) headphones that are relatively inefficient (need over 1V RMS to reach max loudness) with a particularly difficult piece of music. Also, because that music has an overall low recording level except for the peaks, I probably tend to listen to it at higher levels than I would for most music. This test is designed to drive an amp into clipping. (You can read more about the test here.)

In the real world, things aren't that tough. Most people either use high-efficiency low-impedance headpones (e.g. Grado, Koss) so the load driving characteristics of the op-amp don't matter so much, or high-impedance headphones which allow the op-amp to perform better. Or, they use a buffered amp design like the META42 where the op-amp has an ideal load: linear and very high impedance. Also, my CMoy test amp probably allows greater ripple on the power rails than a better amp would, which affects clipping behavior.

Recently, I re-tested this chip for voltage performance in a META42, and was able to to take it safely down to 6V with my HD-580s. I've recommended in the past that you skip the AD8620 for single 9V operation, due to my earlier CMoy tests, but these new tests have changed my mind for buffered amps like META42s. That's why Taphil is getting an AD8620 -- he's got a 1x9V META42 that currently has an AD845 in it. I tried it, and felt safe recommending that he change chips.

Quote:

What is the better of amp for portable application, given one 9 volts battery? The AD845 or AD8620?

For a META42, I would happily use either. The choice between them comes down to...

Quote:

Which of the two sound the best?

The AD845 has the incredible smoothness of the higher-end AD843. By sacrificing some of the higher current draw of the AD843 (10mA @ idle/chip vs 13mA for the 843) and voltage limitations it loses a fair bit of the detail. The overall effect is smooth and easy to listen to, but somewhat veiled.

The AD8620 is an incredible chip. It sounds very close to the AD843, just not quite as good. I've heard others reverse these two chips in audio ranking, so take this as my opinion only. I'm not alone in my opinion, though.

If you want lots of detail without harshness, the AD8620 is a good choice. Also choose the AD8620 if power draw is important. If you want a super-smooth sound (not quite tube-like, as it doesn't have the midrange bloom of the tube amps I've heard) and are willing to sacrifice some battery life and detail to get it, the AD845 is your choice.

 

[purk]

Tangent,
Thanks for a very comprehensive information. Thanks!

Purk

 

[andrzejpw]

Very nice information tangent! This really opens up a whole new world of possibilities with the 8620. . . smaller cases, etc!

 

[kelly]

andrze
I think you've already seen it but Kurt is using the AD8620 in his single 9v META42s in the little blue transparent cases. It seems quite doable at least.

HeadWired got hold of one of these amps from Kurt recently so I'm hoping to meet up with him for lunch sometime and check it out.

 

[JMT]

I've built a couple of the single 9v configs with the 8620, plus I have been using the 8620 in my travel amp. Battery life is acceptable, especially considering the improvement in sound.

 

[purk]

JMT,
How many hours did u get on your AD8620 with one 9V batt? Thanks

 

[HappymaN]

KurtW: Ever thought of using this heralded AD8610 in your Corda Blue?

 

[puppyslugg]

Quote:

KurtW: Ever thought of using this heralded AD8610 in your Corda Blue?

Don't know about kurtw, but I have.

As well as the ad843 and opa627/37.

BTW: ppl recommends the ad8620 for battery use and ad843 for ac.

 

[ablaze]

so where does the 8610 fall in the whole range, in terms of acoustics?

 

[HappymaN]

I wonder what the sonic benefits of using an Analog Devices chip would be? For the Corda HA-1 that is.

 

[JMT]

Quote:

Posted by Purk How many hours did u get on your AD8620 with one 9V batt?

I haven't really kept track. However, I have only changed the battery twice (as I recall), and even at that it didn't need changing. Keeping in mind how much I travel, and how much I use this amp, the battery life is acceptable. If I had to guess, I would estimate that I get around +/- 15 hours.