QLS QA-350 (Line Out) op-amp alternatives; other tweaks?

[hollowman]

The QLS-QA350 WAV player (similar to their 550 model but with Line and Headphone out sections) uses an AD8656 in its output. QLS claims to have rolled thru several op-amps before settling on this model. IMO, a huge setback to the QLS-350 topology is that there is only +5V to work with (that's what you get for using 7.4 Li-Po batts w/o dc-dc step-up).
On Head-Fi.org, I saw someone substituting what I think is an LT1364. The AD8656 specs + (single) supply 2.7 V to 5V operation; the LT1364 is a ±2.5V, ±5V, and ±15V. The Head-Fi poster claims the replacement (LT1364?) sounds "more sweet."

What do you folks think? Any better op-amp options out there, given the low supply-voltage one has to work with?

[EUVL]

Meridian 508.24 - modding opamps

Patrick

[hollowman]

LT6230 - 215MHz, Rail-to-Rail Output, 1.1nV/rtHz, 3.5mA Op Amp Family
Wide Supply Range: 3V to 12.6V

The QA350's 5V LDO will like this opamp. It's not too $, either -- hopefully, that doesn't mean it's "cheap" (i.e. lower-quality sound).

[hollowman]

From The Best Sounding Dual OPAs thread, LT1358:
LT1358 - Dual and Quad 25MHz, 600V/uS Op Amp - Linear Technology
Specified at ±2.5V, ±5V, and ±15V
Quite $$ ... $6.78 ... but may be good.

Also, OPA1642 which, too, was mentioned in the 'Best Dual OPAs' thread:
Precision Amplifier - Wide Bandwidth - OPA1642 - TI.com
WIDE SUPPLY RANGE: ±2.25V to ±18V
$1.45 ea.

The OPA1641 (single), OPA1642 (dual), and OPA1644 (quad) series are JFET-input, ultralow distortion, low-noise operational amplifiers fully specified for audio applications.

The OPA1641, OPA1642, and OPA1644 rail-to-rail output swing allows increased headroom, making these devices ideal for use in any audio circuit. Features include 5.1nV/√Hz noise, low THD+N (0.00005%), a low input bias current of 2pA, and low quiescent current of 1.8mA per channel.

These devices operate over a very wide supply voltage range of ±2.25V to ±18V. The OPA1641, OPA1642, and OPA1644 series of op amps are unity-gain stable and provide excellent dynamic behavior over a wide range of load conditions.

... and OPA1612

[SoNic_real_one]

+5V it is too close of the lower voltage limits of ±2.5V...
Personally I tend to belive that the AD8656 is hard to beat there. Maybe I would try the LT6230...

[hollowman]

Originally Posted by SoNic_real_one

+5V it is too close of the lower voltage limits of ±2.5V...

Yeah ... worried about that, too. FWIW, the LDOs are outputting 5.1v. The far more important issue is that OPAs tend to perform best near their MAX supply-voltage rating. The stock AD8656 has a MAX of 6.0V. So maybe QLS made a good (best?) choice after all??

[ferynov]

AD8656 in my personal opinion is good enough, I tweak other parts / recapping is worth ... my pic

[hollowman]

Ferynov:
I tried LT1364 but like the orig. AD8656 better. New QA350v2 uses high-current AD8397 for HO, but I've heard the AD8397 is better for LO, too (FWIW ... 8397 is 2x price of 8656). I never use QA350 HO so I don't really mod that section; but I will try 8397 for LO soon.

You put film (Wima) in signal path. Not really ideal. Best use Non-polar electros, esp. BlackGate (keep values at 10uF).

A small 33-100uF across opamp supply pins helps, too. Also, small high-quality electros (20uF Panasonic FM are okay) for Vin and Vout of 3.3v LDO for osc. help.

Damp osc. with rope-caulk or 'tack'.

Follow the Russian modder's suggestion in link noted earlier for other/more tips.

QA350 has pretty HQ stock parts, but I don't like tantalums. Some newer "wet" or "organic" tantalums (Kemet) may be better. Also, orig. Samsung ceramic caps (e.g. 0.1uF) may be bettered with film ... dunno for sure, tho'.

Note: Quality of electro cap is v. important: so Sanyo Os-con, Black-Gate are ideal.

[ferynov]

Since Blackgate are expensive / rare i better not use them, oscon are good...default in signal is elna silmic II 10uF/16v. who's better wima or elna ?i bet goes to wima,or vishay 1837. in here these part are rare. thanks for your suggestion.