Stacking el2001s?
Aug 12, 2002 at 4:52 AM Thread Starter Post #1 of 17

andrzejpw

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Just wondering. .. when you guys "stack" buffers, what does this mean? Do you just put one over the other? Is this noticeable with el2001s?
 
Aug 12, 2002 at 5:16 AM Post #3 of 17

zbuddah

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thats exactly the way it is. One on top of each other, pin one to pin one etc. Just put a little solder on it to make sure it stays stacked. As to the sound, they say its sound better stacked but I can't compare since I started mine as initially stacked.
 
Aug 12, 2002 at 5:18 AM Post #4 of 17

andrzejpw

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hmm, so this is basically a 5 minute tweak that I could do If I got extra buffers?
smily_headphones1.gif


Do you just put it on the left/right buffer? Or does the ground one benefit as well?
 
Aug 12, 2002 at 6:03 AM Post #5 of 17

Tomo

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Hello,

I do not know about that. Your headphone impedance is 300 ohms. That is very high impedance. In such case, current capability improvements means very little.

In fact, 600 ohm headphones (mine!) can be wonderfully driven straight from opamps.

For these high impedance headphones, you should look for opamps with much cleaner gain such as OPA627. That might actually worth more to you. Adding extra buffer might not do anything but decrease your battery life. ... [Shrug] But who can be sure?

Grado headphones will definitely benefit from more current capabilities. But that's because it's impedance is 30ohms.

Tomo
 
Aug 12, 2002 at 6:54 AM Post #7 of 17

tangent

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There are a few different benefits from stacking buffers. One is higher output current, which is helpful for low-impedance headphones. This is what Tomo's referring to. I've stacked buffers to power low-Z unamplified PC speakers before, just for the hell of it...

But there's a few other factors to consider. One is the amp's output impedance. With one buffer, the output impedance of the amp is equal to the buffer's output impedance (10 ohms for the EL2001, 8 for the 2002). (Unless you add R8 or R9!) When you add a second buffer to each output channel, you divide the output impedance by 2. Add 2, divide by 3, add 3 divide by 4..., etc...

The lower the output impedance, the higher the damping factor of the amp, which increases the amp's control over the headphones, especially with the bass. I can personally attest that stacking a pair of EL2001s on the outputs of a META42 does make an audible difference with Senn HD-580s. (300 ohms) I tried 3 deep with these headphones, and that difference wasn't nearly as marked as the first level.

Another factor which I can't say much about is that stacking buffers reduces the load on each chip, which may help them to behave more linearly. Just a guess...

As for stacking the ground buffer, this is less important. However, it can help stabilize the rails. There is a procedure in the META42 documentation's tweaks section that tells you whether you need to stack this buffer or not.
 
Aug 12, 2002 at 1:45 PM Post #8 of 17

finleyville

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andrzejpw and I are both using the AD8610/20 opamp in our META's. Now I read somewhere that this particular chip doesn't really improve by stacking the EL2001's. Has anyone else found this to be true? What other buffers are available in the same price range as the 2001's? I know others have been tried, but I don't know their price points compared to the amount of improvement over the 2001's.
 
Aug 12, 2002 at 4:42 PM Post #9 of 17

morsel

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Finleyville, perhaps you are confusing output buffers with class A biasing of opamps. The AD8610/20 experiences only a modest improvement from class A biasing, but that has nothing at all to do with the output buffers, which are affected by headphone impedance. Also note that class A operation results in sweeter, less distorted highs, whereas stacked buffers provide tighter bass.

Stated generically, low impedance headphones will usually benefit more dramatically from stacking buffers, but even high impedance headphones experience some benefit. Using the EL2002 instead of the EL2001 will also improve sound but will draw 3-4x more Icq per buffer, so are typically used for AC powered amps.
 
Aug 12, 2002 at 9:17 PM Post #10 of 17

finleyville

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So how much are the 2002's? Is there any reason to populate all 3 buffers with the 2002's instead of leaving the Gnd buffer a 2001? I am only assuming that the 2002's also sound better stacked along with the 2001's.
 

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