NEW OPAMP - Anyone tried JRC MUSES 8820 in OPA rolling?
Jan 28, 2011 at 8:27 PM Post #2 of 5
Jan 29, 2011 at 12:43 AM Post #3 of 5
I had a hard time getting this chip, a friend living in Tokyo sent me some after I pestered him to get me some - it was the JRC MUSES website that got me all excited to get hold of these - I didn't study the datasheet beforehand - dumb!
I tried the MUSES 8820 in a clone Beyerdynamic A1 amplifier I built that is originally based around the MC33078.
Given that the MUSES 8820 is a bipolar input (Ib=500na compared with LME49720 Ib=72nA!), it wasn't surprising that a DC offset appeared at the output of my amp - great! I need a DC Servo now to correct it!
Anyway, I took the A1 circuit into work and tested it on our Audio Pre System Two - The distortion was pretty poor rising from about 0.008 with the MC33078 to just under 0.09% with the MUSES 8820! It sounded a little bright on my Beyerdynamic T1s, I then tried my AKG K240s and K271 MkII's - pretty much the same results - bright, perhaps a little harsh sounding: What I heard wasn't an improvement to me. (With the LME49720 I hit the noise floor of the System Two!)
Looking at the datasheet, they are quoting all their performance figures with 2K ohm loads and the distortion performance only really looks good with signal levels above 1Vrms, the performance at 0.1Vrms looks lousy and seems to explain the results I saw in the measurements in my clone A1 amp.
The LME49720 is my preferred chip for my Clone A1 Amp circuit. IMHO from a Specmanship point of view, the LME49720 beats the MUSES 8820 hands down!
It seems the MUSES 8820 chip is pretty picky as to where you can put it in a circuit, or perhaps JRC have targeted it for specific applications - IMHO I can't see this chip easily displacing the LME49720 or the OPA627 for that matter; the LME49720 runs rings around it on price anyway – I ended up paying NZD$18.00 each for the MUSES 8820 chips!
Perhaps JRC will publish an application note that shows the "proper way" to use it? I bet ya they have already done that for the Japanese market and it will be in Japanese only!
Jan 29, 2011 at 7:54 AM Post #4 of 5
Stereophile reviews a DAC that uses this opamp.
Based on what I'm reading here, this chip may be great in certain specific uses, but apparently it isn't the sort of thing folks can just pop into their DIP socket. 
And thanks for the pointer to the OPAMP thread.  I'm afraid I don't have much luck using head-fi's SEARCH function to find what I'm looking for.  Typically it returns MANY pages somewhat related to what I'm trying to find... I dunno, the head-fi search syntax and I just aren't on the same lambda.
Jan 30, 2011 at 2:43 AM Post #5 of 5

Based on what I'm reading here, this chip may be great in certain specific uses, but apparently it isn't the sort of thing folks can just pop into their DIP socket. 


Totally agree; also the way you decouple the OPAMP, the type of capacitors and where they are physically located around the OPAMP makes the difference.


For example, decoupling the LME49720 (aka LME4562 - same die) with 0.1uF Film cap can give it a harsh sound in the mids and make it sound a little bright IMO.


Go back and change the capacitors around the circuit to something like 100nF (0,1uF) Multilayer Ceramic Capacitors (MLCC) (such as AVX SR205C104JAR) in parallel with 470nF MKT Film cap (such as EPCOS B32529C474J) I found the timbre or tonal character of the opamp to change quite a bit. 

I also quite like the combination of a 4,7uF 35V Tantalum (such as AVX TAP475K035SRW or VISHAY / SPRAGUE 199D475X9035C6VE3) in parallel with 1uF MLCC (such as AVX SR305C105K or MURATA RDER71H105K2K103B) is quite a sweet sound with the LME49720.


If your using the AD797,  this requires care when decoulping, it seems to work best with 100nF MLCC capacitors that are bypassed with 4,7uF 35V Tantalums that have a further 1,0 Ohm resistor in series with the 4,7uF cap - there is good reason for this to dampen the ESL (Lead Inductance) of this cap.

The AD Datasheet gives a lot of good pointers in using this fast OPAMP.

Also a 10nF MLCC cap across the +V and -V supply rails at the chip (you can solder it on top of the DIP package's PINs) tends to keep it under control, as well as the usual decoupling from +V to GND and -V to GND, as described above. The following gives an outline:


D1 and D2 are a good idea if your using two 9V Batteries to run the circuit - they prevent the opamp from destroying itself...esepcially if you try and run the opamp with, say, the -V Battery disconnected. A schottky such as the 1N5817 is useful for the more sensitive MOS devices.

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