Just a note about the Prelude/Meridian Opamp mod and Opamps in general
Mar 15, 2008 at 7:37 AM Thread Starter Post #1 of 12


100+ Head-Fier
Dec 15, 2007
When you remove the opamp and bridge the 3rd and 6th opamp input plugs the audio on the right channel is out of phase. This is something I discovered today after removing my opa637's.

Also I should mention that audio sounds much better with the opamps removed, even with the audio out of phase. It's unfortunate that there are so many problems when you remove the opamp though (volume being another problem)

Also I would rank the opamps I've used in this order

1. No Opamp
2. opa637
3. lm4562

I would call it a tie between the opa637 and the lm4562. Neither of them sound right though. The lm4562 sounds more balanced but colder, more artificial and very digital sounding. Very flat in other words. The opa637 is very airy, bright, and highly detailed but lacking in mids and swing. Treble is a little too sibilant and they make my Sennheisers sound similar to Beyerdynamic headphones. If I had to chose one over the other I would pick the opa637's since I found myself swinging my head to my music when I was using them but I still don't like the way they sound.

4. LT1361
5. LT1469
6. LT1364

The LT's are ok. The 1361s have very nice mids but they lack transparency highs and bass. The lt1469 is insanely detailed but lacks mids and base. You will the most minute details possible with the lt1469, if a fly farted in the recording studio, you will hear it, but it's really not a very enjoyable experience since it's so darn bright. The lt1364 is somewhere in between and doesn't really have any discernible stand out qualities.

6. lm2107

The lm2107 has very dark mids. People say it sounds like the OPA637 but I don't think they sound similar at all. It's just dark and recessed sounding. Not lively or airy like the opa637 and just not all that great.

I guess I will have to save for a decent discreet output dac if I want that no-opamp sound again without sacrificing the right channel.
Mar 16, 2008 at 6:54 AM Post #2 of 12
You can work around the out of phase issue by bridging the 3rd and 5th plugs rather than the 3rd and 6th. Whoever came up with this mod was pretty creative but not all that bright for suggesting people bridge out of phase.
Mar 25, 2008 at 8:26 PM Post #3 of 12

I have also done the opamp bypass on a x-meridian (shorting the non-inverting inputs with the outputs). The resulting sound is way better than any other opamp based system I've ever heard.

The total volume level reduction is significant. However, using replaygain and a powerful solid state amp (in conjuntion with the hot outputs of the x-meridian), I achieve a confortable level (80 db max) over a 250 ohms cans.

Sonically, the only opamp I heard that comes close to this setup may be the lm49720 metal can version (quite an improvement over the lm4562 ceramic which seems bright and harsh in comparison). I have tried several LT's, OPA's and LM's but they do not come close. Its sound is quite pleasing and neutral comparing, but comparing against the passive output, it is still a little bit harsh and "digital" on the highs.

Does anybody knows an external DAC for which the same opamp bypass can be performed but providing higher output levels? I suppose the DAC should be a voltage based one as the AKM in the auzentech cards to work. The other possibility is a dac with a fully discrete output. However, I am not aware of any DAC of this type with a reasonable price tag...
Mar 29, 2008 at 2:43 AM Post #4 of 12
THE LM4562 and the 49720 are essentially the same op amp, and yes the metal can versions of both these op amp's sounds closest to the no op amp mod. The metal can package is a real upgrade to the ceramic or plastic dip versions of these op amps, go for it.

Mar 29, 2008 at 8:17 PM Post #5 of 12
How much of a difference do you think the opamps make?
Is it something most people can score a 9/10 on a blind test?

Personally, I have to really listen for it if I want to hear a difference between 128kbps mp3's and lossless flac. If I was casually scrolling through my album, I would never notice if suddenly all my flac files were re-encoded...
If opamp rolling is like that, I don't really want to go through the trouble..
Mar 29, 2008 at 8:38 PM Post #6 of 12
depends on the type of music, and where its coming from, aka speakers or headphones, and you already know that some of them are more forgiving than others.
Mar 29, 2008 at 11:53 PM Post #7 of 12
Well I could notice right away with every opamp swap. It's similar to changes on an EQ graph almost I would say. If you switched out the LM4562 and used an LT1369 instead you would notice that the mids and the drums sound more 'in your face' and sounds funner than the LM4562 but at the same time you would notice a loss of detail as though a veil has been placed in front of the sound.

The opa637 is better to me than the LM4562 and it sounds more like the prelude without an opamp but it colors the sound a bit. Makes the drums stand out more and is a bit to bright at the top end. Sounds more natural than the LM4562 but the LM4562 is not as bright and sound more balanced, (albeit very digital sounding).

I guess it all depends on how much effort you put into focusing on your music. Maybe if you listen to single albums repeatedly it would be more noticeable than if you just shuffle through random mp3s. Its a pretty big change though, I would say. I would rate it maybe 6-7/10 for difference in sound quality.

These are all very noticable things to me and I don't consider myself a nutso audiophile (no offense to anyone
) that needs to have special silver cables or separate power supplies feeding my amp or anything.

I was never one to believe that spending big money on separate source components would make a huge noticeable difference but after using the Prelude sans opamp, and having to use opa637's instead because of volume issues, I am interesting in buying a discrete output dac now when I can afford one.
Mar 30, 2008 at 9:34 AM Post #8 of 12
Thanks.. I think I want to try the opa627's. I can get a pair of the AU' surface mounts for $20 shipped + brown dog adapters for a couple dollars extra. (anybody wanna sell me one for $5 shipped?
I don't want to pay $12 for a pack of 5 >_>)
It's a tad expensive, but there seems to good-sized base of people who agree that it sounds better than all the other alternatives.
Mar 30, 2008 at 11:15 AM Post #9 of 12
I have tryed 627 & 637.
637 is more detail, but less natural sound than 627.
627 is the best choice in my audio configuration.
I think, 637 is better if you want upgrade an standard Hifi equipement, but if you have an audiofil equipement, 6267 'll be better choice.

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