My best chip to buffer and couple the OPA627 - diyAudio
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Old 2nd March 2014, 08:28 AM   #1
ygg-it is offline ygg-it  Italy
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Join Date: Feb 2008
Post My best chip to buffer and couple the OPA627

The preamp section of my vintage Class A Musical Fidelity A120 (which I have renovated with new 105 caps), is based on two opamps (from TL084 chip): buffer and variable gain stage, and I replaced the gain stage with the top in class OPA627.

OPA627 is surely a fantastic chip, but given its well known personality (tonal richness), I found very difficult to couple with other chips and obtaining a colorless preamplifier.

I have tried all the following dual opamps combined with OPA627, and frankly I was giving up to the OPA (and to my 60 USD paid for them genuine) until I finally tested the little-known LT1498.

Several opamps excellently played but all of them produced a hole (gap) or a resonance (peak) somewhere in the audio band when coupled with OPA627.

The risk is that OPA627 could be too bright and not pleasant if bad coupled.

The only one who produced a flat neutral buffering for the OPA627 was the LT1498. This is quite slower than the competitors (only 6v/us slew rate), but it passed anyway the bi-tonal 19/20kHz IMD test that I always use in these cases (negligible audible 1kHz tone till to the clipping when I play two 19kHz and 20kHz mixed traces).

LT1498 has a 110dB of PSRR and I verified that the ones who sound better show the highest ratio (>100dB).

The winner combination of LT1498+OPA627 sounds less fatiguing than all the others: warm throughout the spectrum, very detailed, with full bass response, clear mids and sweet hights. Soundstage is wide and 3D is quite realistic. Last but not the least, no hissing (Ssssss).

All the benefits of the OPA627 are fully maintained at 100%.

Herebelow my test: more asterisks, better coupling with OPA627 in my opinion (remember: I'm measuring appreciation of the combo, not of the chip alone).

The chip is used as a buffer in inverting configuration with gain of -1 and 47kohm of feedback resistor:

Listening test (my opinion):

LT1498 + OPA627 ***** (the winner)
LT1361 + OPA627 ****
LT1355 + OPA627 ****
AD826 + OPA627 ***
LT1208 + OPA627 ***
LT1358 + OPA627 ***
LME49860 + OPA627 ***
LME49720 + OPA627 **
LM4562 + OPA627 **
LT1364 + OPA627 **
AD827 + OPA627 **
OP249 + OPA627 **
OPA2132 + OPA627 **
OPA2604 + OPA627 *
AD823 + OPA627 *
LT1352 + OPA627 *
LM6172 + OPA627 *
LT1112 + OPA627 failed IMD test (too slow)
OPA2107 + OPA627 failed IMD test (too slow)
AD812 + OPA627 oscillates

OPA627 + OPA627, not tested

Curiosity: I waited for several years and at the end I decided to buy it: I'm now a new fan of the OPA627, but still I think that performance does not justify the cost of two opamps + adapter. I had to purchase it on an official catalogue distributor, given the fact that the OPA627 is prone to being a counterfeit when bought through alternative channels.
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Last edited by ygg-it; 2nd March 2014 at 05:07 PM.
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Old 3rd March 2014, 04:57 AM   #2
jcx is online now jcx  United States
diyAudio Member
Join Date: Feb 2003
Location: ..
I like the TPA6120 CFA amp - many CFA DSL driver chips may be equally good but the TPA6120 has full audio specs in its datasheet

Walt Jung has written about these multiloop op amp circuits with CFA output buffer stages for audio line driver applications

you can add gain inside the global feedback loop if you understand the stability requirements
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Old 22nd August 2014, 12:55 PM   #3
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Join Date: Jan 2013
Location: Tehran

The sound of music ,live!!!

opa2604(I/V) --->lme49860 --->muses01 --->OPA627

Magic make no sound /Sound Stage dreamy and dark and deep ... 3D... fuller Bass ... vocal live!!!

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