I can’t rely on Tangent’s Notes on Audio Op-Amps too much, because he tested those Op-Amps in CMoy circuit. They might sound differently in my headamp, because of the Jung’s multiloop configuration (like in Pimeta) and jfet cascode class A biasing (like in PPA). Another thing, I might have different taste than him
The power supply for the headamp is regulated using LM2941 and LM2991 set at precisely +7.2 and -7.2 volts (14.4 volts rail to rail).
I will try more Op-Amps as times and budget permits
Amplifier : 'My Modified Pimeta Clone' DIY HeadAmp
Source and Headphone : Panasonic PCDP SL-CT810 and Grado RS-1
CDs : Ultimate Demonstration Disc from Chesky Records, Women of Song from Chesky, Best of Audiophile Voices, Jennifer Warnes – The Hunter, and some other CDs.
So, I tested them with bright, lively sounding, and very revealing headphone. And for my taste of music, vocal is very important. I like thick and warmth midrange.
There is no exact measurement to describe how audio equipments sound. All measurements are subject to personal taste, so this Op-Amp comparison is only sharing of my experience with those Op-Amps, with hope there will be readers benefit from it.
Very bright and lively sounding Op-Amp. The treble sounds a bit too dominant. Very good detail and imaging. I love the transient and impact of the AD8620. My only complain with this Op-Amp is the treble, a little bit too sharp, and the color tends to the metallic sound.
The good : Bright, very good detail, lively sounding, the most transparent sounding so far.
The bad : Treble can be sharp and harsh with bright headphones.
Application: Not to be paired with bright headphones. You might get ears fatigue. Probably good for Senns, but not for Grado. I still can enjoy it with my RS-1 though, but only for certain recordings. Very good detail and resolution will reveal recordings flaw. So, this Op-Amp is only for good recordings.
Sweet, but veiled sounding Op-Amp. It’s sounds the other way of AD8610. Not bright, veiled, with poor detail. There is no way you will get ears fatigue with this Op-Amp, but you might get bored. It is not a lively sounding Op-Amp. It is not bad, it has a nice color of sound, just a bit mellow with strong Burr Brown’s laid back signature. Some people might like it.
The good : Sweet, warm, never sound offensive, good for long hour easy listening.
The bad : Poor detail, veiled, mellow, far from lively.
To be paired with very bright and lively sound headphones. For those who like long hour easy listening, this Op-Amp might be the choice. As it will hide many details, it might be good to listen poor recording with this Op-Amp.
Very nice natural sounding Op-Amp. I like its treble. Not too bright, just nice. It has the laid back Burr Brown sound, but light not as strong as the OPA2604. It is not very bright and lively, but not heavily veiled either. For Senns it might sounds analytical, but for the lively sounding Grado, it makes the Grado sounds well controlled. I can use this Op-Amp for a long hour listening with Grado without getting ears fatigue. Good detail, but not as good as the AD8620. The midrange and bass are slightly thicker than the AD8620 which are nice. Overall, I like this Op-Amp in my headamp paired with Grado, it sounds natural and really ears friendly. I can feel a lot of 'air', like listening to the singer in open air. When you listen to my amp with this Op-Amp, it is not a WOW, but its sweet, and you might wear the headphone longer. I just miss the lively sounding and transparancy of the AD8620 a little bit.
The good : Natural and sweet. Very nice treble, good midrange and bass.
The bad : Not as detailed as the AD8620, and slightly slow in transient and impact.
To be paired with bright and lively sound headphones. Very nice for long hour listening, better than the OPA2604. As it is not highly revealing amp, it forgives flaw in recordings. I might put this OPA2228 permanently in my ‘Pimeta like headamp’, it is very nice to be used for listening my ‘non audiophile’ CD collections.
Putting this Op-Amp in Pimeta doesn't change it's sound characteristic a lot. Just a tad more transparent (only a tad) compare to CMoy. I would say that this Op-Amp has the worse imaging than others that I have tested. Very narrow, narrower than my PCDP output. Very narrow space between the singer and the musical instruments, sometime feel like putting my head in a bucket. It only good in bass, nothing else. So for some music from MIDI, which doesn't need imaging at all, this Op-Amp is fine. It has big bass and thick midrange, which is good. The treble is a bit 'short', means bell's sound will sound shorter than the AD8620 or OPA2228. Ok, I have no intention to make it sounds like a bad Op-Amp. OPA2134 is a good Op-Amp, very DIYer friendly, and they have nice sound color of which I like. My complaint is only the narrow imaging, that's all.
The good : Big bass and thick midrange. Nice color of sound.
The bad : Poor imaging.
I think this Op-Amp need bright, transparent, and wide imaging headphone to balance it's narrow imaging characteristic. This Op-Amp is a NO NO for people who demand good imaging, probably another good alternative for those who like music from MIDI / electronica, and like BIG bass.
This Op-Amp dethrone the OPA2228. It sounds much better than the OPA2228. It has the AD signature, bright and fast. What I like most from AD8066 is the BASS. It has excellent bass, bigger than the OPA2228 and AD8620, and it goes lower. It has very good low bass. For comparison, OPA2134 also has good bass, but more to the mid bass, while AD8066 has better overall bass. My headamp is DC coupled, so it takes all frequency from DC. If yours is AC coupled, you might not be able to hear or feel the excellent low bass from the AD8066. Try 'The Hunter' from Jennifer Warnes to test the bass.
If OPA2134 'KICKS' then the AD8066 'KICKS' and 'SHAKES'
This AD8066 is not only good in bass. It also has excellent imaging, about the same as the AD8620. I love the treble which is a tad smoother, more 'airy' than the AD8620 which I often feel a bit sharp. So the conclusion is, excellent Op-Amp, very neutral, excellent bass, crystalline clear mid and treble (very good transparancy), excellent imaging, fast and detailed.
The good : Excellent BASS, fast, detailed, good imaging, with a pleasant 'airy' feeling. This Op-Amp really brings music to life.
The bad : Depend on personal taste, might be too bright for some people.
Eventhough I think this Op-Amp is an excellent general all-purpose audio Op-Amp for any headphone, but it tends to sound bright. With good recordings (non-metallic treble recording), this Op-Amp sounds very good with my RS-1. AD8066 is very revealing, you will hear any flaw of poor recording. For poor recording, OPA2228 might still preferable.
I agree with most of the DIYers that said that this OPA637 (and OPA627) is one of the best Audio Op-Amp. It is the most expensive as well . I didn't have enough time to listen to it, just a few tracks of Chesky Demo Disc, so my comment here will be based on mine and my brother comment (I bought the OPA637 for him). I use this Op-Amp in the amp I made for my brother, which in theory has the same circuits as my headamp.
It sounds Very Very Very natural. Almost no coloration, very musical with high listening pleasure. It has thick bass and midrange, with just the right level of treble for my Grado RS-1. The imaging is excellent. Comparing with AD8066, the AD8066 is a tad brighter, and slightly has more space in between the singers and the musicians, but the different is subtle. The OPA637 has the laid back Burr Brown sound which I like, but it is very minimum comparing with other OPAs.
The good : Very neutral and musical. Thick bass and midrange with transparant treble. One of the best Audio Op-Amp.
The bad : Probably a little dark for dark Headphone, slightly laid back sound which might not suit some people.
The best general Audio Op-Amp. Highly recommended for Grado users, or other bright sounding headphones. For Senns users, please audition before you spend the money for this Op-Amp.
If you like Burr Brown sound but OPA627/637 is way out of your budget, try OPA2107. It has the color of the expensive OPA637. So far amongs the other OPAs I tested, this is the one that is close to the OPA637, but it doesn't have the superb detail and the good imaging of the OPA637. It has a natural-dark sound, with very good bass and midrange, the treble is fine, but not as transparant as the ADs. It also has the BB laid back signature, more laid back than the OPA637 and OPA2228. I rolled back and forth with OPA2228 (which I like for being very warm and sweet), OPA2107 sounds more natural, faster, with more accurate and better imaging. But it is a bit darker than OPA2228. So for it's price, between the OPAs, it sounds right. More natural & faster than OPA2134, OPA2604 & OPA2228. Compare to the AD8066, I prefer the AD8066 for having better imaging and more transparant treble.
The good : One of the best Burr Brown Audio Op-Amp for the price. Natural-dark sound good for bright headphone such as Grado. Excellence Bass and Low Mid, very tight and thick. It sounds musical and enjoyable, good for long hour listening
The bad : Dark sound not good for dark Headphone. Laid back sound which might not suit some people. The imaging is narrower than the AD8066 (but wider than the OPA2134, OPA2604 & OPA2228). The treble is a bit too dark for me, not as transparant as the AD8066.
Good general Audio Op-Amp for it's price, recommended especially for those who like the dark and laid back Burr Brown sound. Recommended for Grado users, or other bright sounding headphones.
Now I'm still using the AD8066 in my Amp, so far it is the best sounding Op-Amp for me.
Thanks for reading this long post
Flavors of Audio Op-Amps
Edited by bpribadi, 05 October 2005 - 01:35 PM.