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Old 28th September 2008, 08:30 PM   #11
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Any ideas on the self buffered dual op amp approach? I have a bad feeling the design of the virtual ground might not support another set of dual op amps that draw/output more power since it is based on the tle2426 divider with two capacitors in parallel in front of it. This amp is also biased into class A, I imagine with a resistor, which will also increase current draw, no?
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Old 29th September 2008, 12:24 AM   #12
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When you say "self buffered", do you mean with one half a dual feeling the other half of a dual, or having the two halves of a dual running in parallel? The second approach has some sort of merit....the first has perhaps a very small amount of merit in ensuring that the voltage amplification occurs cleanly, but in the end, the second half of the dual can't supply any more current than the first half could on it's own. In terms of power draw, I'd say it's not worth it.

Operating in parallel will allow more current to be supplied, which could be useful if you're using opamps with a low current capacity, however, in some cases it can make the opamp quite unhappy, making it unstable or causing it to get quite hot.

Biasing into class a will increase power draw, but, in the case of using low current opamps, will have the more serious effect of reducing the available current. If you've got an opamp which can supply 25 mA, and you bias it into class A by sinking, say, 10 mA, then you have in a very real sense now only got an opamp capable of supplying 15mA. If you were powering headphones with a low impedance, that would be a problem, but the senn's are nominally 300 ohms, so the opamps ought to be able to swing several volts even with only 15mA.
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Old 30th September 2008, 10:36 PM   #13
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Thank you for replying to my post. I am still learning this stuff and I expect I will be for a long time.
I believe I have an idea of what is going on with this design. The designer specifies that he implemented "Jung Multiloop Technology" on this amp. Since there are no buffers I imagine he has done this by using both sides of the op amp and buffering itself. Unfortunately, I do not know how to depict this but does this sound feasible? Are they any common schematics for a "JML" implementation using a single dual op amp? I suppose I would like to "unJung" it and work in a pair of single channel op amps. Perhaps there is some way to enhance the virtual ground design a bit by air wiring something to it and continue to use the JML dual self buffered op amps with a different op amp type installed.
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Old 1st October 2008, 12:38 AM   #14
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http://electronicdesign.com/Globals/...tent/1518.html is one of the original Jung Multiloop discussions, you might find it helpful. Also take a look at the schematic of the PPA, http://tangentsoft.net/audio/ppa/amp...schematic8.pdf

In more direct answer to your question: if you're clever about it, maybe you can.

http://cimarrontechnology.com/single...rpn020302.aspx

That adaptor will accept two single SMD opamps and convert the pinout to an ordinary dual opamp.

This version http://cimarrontechnology.com/single...npn021001.aspx will accept DIP parts if that makes you more comfortable, but you may struggle to find an appropriate buffer.

By populating the correct half (this, I imagine, would be the hard part) with, say, OPA627, as the amplifier, and the other half with, perhaps, LMH6321 (there's a little more work involved in this bit, the pinouts of a single opamp aren't quite identical to this buffer, just very close) you could have a properly buffered Jung Multiloop amplifier.

Problem is that the buffering opamp must have AT LEAST the same bandwidth as the amplifying opamp (and, of course, an equal or greater current capacity, or it rather defeats the point), but particularly fast opamps aren't terribly happy on that kind of adaptor.

http://cimarrontechnology.com/twopre...u-020302s.aspx

Since the OPA627 is rated for a reasonable current output of 45mA, you could use that adaptor, with two premounted 627's, with probably quite good results. Since it's probably among the cheapest ways to get two OPA627's, I'd recommend it even if you intended to remove one to use a different buffer.
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Old 1st October 2008, 11:56 AM   #15
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by espressogeek
The only particular flaw I can find is the amp gets a little harsh in the upper midrange at reasonable volumes using either my grados or senn 580s.
could that be the ear wax telling you it's time for a Spring Clean?
__________________
regards Andrew T.
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Old 1st October 2008, 05:29 PM   #16
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I don't by the wax thing. It sounded great in my little CMOY. I am going to review this a bit more. It doesn't sound to me like the use of JML in a dual op amp is really advantageous unless you are trying to gain the benefits of such a design with a low part count / foot print. At any rate, I'm just going to button this little amp up and give her a new home via Ebay or something.

I started working on my own amp on a rat shack board last night. I want to use a discrete buffer and a dual op amp. Then later on I'll add discrete output buffers. I think this will give me a good opportunity to gain more knowledge, understand basic electronic theory, and have a good time doing it. I think it is better to start fresh then try to tweak someone else's design when their board was not intended for doing so.

Thanks for everyone's feedback and I'm sure I will be "seeing" you in other threads.

Cheers
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Old 1st October 2008, 11:08 PM   #17
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Excellent plan - do keep us in the loop when you've got something to show off!
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