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| joeflorida Member Joined: Mar. 9, 2002 |  Message [#1] posted on: 03-11-2002 03:00 PM CST (US).   |  |  I am a newbie to electronics and high-end headphones. Thanks to Tangent for posting the DIY cmoy amp instructions. Without this easy to understand info, I would not know where to begin. In his "Notes on Audio Op-Amps", he made reference to the AD823 op-amp as the one to choose for the best performance, which is the one that I want to use. However, in the head-fi link in that article, Apheard states on 7-16-2001 that you cannot use the AD823 in a cmoy/hansen pcb. Can the AD823 be used in Tangent's cmoy amp? If so, are there any modifications needed to substitute the OPA2132 with the AD823? TIA, |
| antness Member Joined: N/A | Message [#2] posted on: 03-11-2002 03:05 PM CST (US). | | I think the problem would be that the pins on the AD823 are not each the same as the pins on the OPA2132. If this is the case, to use the AD823 with a premade hansen pcb you would probably have to solder wires from the pcb to different pins on the AD823 and not be able to mount it in the board |
| Possum Member Joined: N/A | Message [#3] posted on: 03-11-2002 06:58 PM CST (US). | | Actually, the pin layount on the OPA2132 and AD823 are the same. When I accidentally blew an AD823 in my Apheared #42 this past summer, I used an OPA2132 in the socket to test the rest of the circuit, and the OPA2132 worked fine. |
cmoy  Administrator Joined: Apr. 13, 1999 | Message [#4] posted on: 03-11-2002 08:31 PM CST (US). | | joeflorida, the problem is that the AD823 has less current drive than the OPA132/4. See this thread for more details: http://headwize....fnum=3&tid=2307 |
tangent Headphone Council Joined: Aug. 27, 2001 | Message [#5] posted on: 03-12-2002 02:01 AM CST (US). | | I did later test this after that post in the thread cmoy referenced, and the AD823 is indeed noticeably weak when driving low-impedance headphones. With Grados (32 ohm) the combination isn't unacceptable, but it's a weak enough performance to prefer the OPA132/134 family in this case. With higher-impedance phones like Koss KSC-nnn's (60 ohm) there's still a small amount of weakness left. With high-impedance phones (most Senns, AKGs...) the 823 sounds better to me than 132/134s. Still, driving headphones directly from this chip is very edgy -- you're running it at its very limit. They can even get a little warm. (Not hot, just warm.) Adding buffers relieves the load on the AD823 and allows them to drive even very low impedance headphones. That's one reason I'm so exited about the Apheared 42 boards that are being built right now. It sounds like an ideal matchup, on paper. |
| joeflorida Member Joined: Mar. 9, 2002 | Message [#6] posted on: 03-12-2002 05:22 AM CST (US). | | Tangent -- If I drive Senn 590's with the AD823 on your cmoy amp, will I have to make any modifications? Or, will I be better off with the OPA2132? |
| tangent Headphone Council Joined: Aug. 27, 2001 | Message [#7] posted on: 03-12-2002 04:04 PM CST (US). | | Having never heard 590s, I can only guess, but I think it will work fine. Again, doing this is a little on the edgy side. If this is your first amp, I recommend you get a 2132PA and maybe later upgrade the opamp chip. The 132/134 family is still very good. It's just that I think the 823 is better for some things. If you've already got a 2132 on hand, by all means, give the 823 a shot, because if you're unhappy you will have a "backup". Opamp rolling is all about experimentation. My web page certainly isn't the last word on the matter -- it's just some notes on my subjective experiences. Go with a 2132 if you want a low-risk, high-performance part. Branch out from there if you don't mind a little risk for the possibility of a higher payoff. |
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