Headphone OPAMP recomendation for battery usage. - Page 1
Forum section: electronics / projects

author: BrianHG
author_rank: Super Contributor
timestamp: September 20, 2023, 09:06:41 pm
content: Ok, here is the blast. I have a worst case dual rail +7.5v and -7.5v battery supply.I need to add gain from a stereo line out of ~6db, or 2x, an input load of ~1k or 600ohm will do.I want a clean audio output at ~7vp-p (+/-3.5v), ~2.5v-rms driving >250ma load without distortion.Ok, I know how to use op-amps in analog circuits. I'm looking for a recommendation of the magic op-amp which will be crystal clear and not kill my batteries with too much background load. I also don't want any phase errors in the upper 10khz-20khz as well as any cross-over distortion whatsoever.

author: TimFox
author_rank: Super Contributor
timestamp: September 20, 2023, 09:15:47 pm
content: Is that 250 mA load at 2.5 V rms correct?That would be a 10\$\Omega\$ load impedance, which is typical of a loudspeaker.The NE5532 (dual) can drive a 600\$\Omega\$ load (more typical of a headphone) easily, and pulls typical 7 mA (quiescent) at +/- 7.5 V power; I believe that is for the two-channel device.Actual output current into a short circuit load is specified (at +/- 15 V) as typ. 65 mA (not specified at lower voltage).Any op amp will pull at least the output current from one or the other supply rail: 250 mA is rather high for battery power."None whatsoever" is not a specification: it is a pious wish.The usual methods to reduce crossover distortion increase the quiescent current draw, which is a reasonable tradeoff for audio applications, but problematic for low-power battery operation.What level of distortion and phase error is your specification?

author: BrianHG
author_rank: Super Contributor
timestamp: September 20, 2023, 09:46:04 pm
content: 3.5v / 16ohm = ~220maYes, I have low impedance earphones and I want my ears to burn without distortion.For 32 ohm headphones, I would still need a 110ma capable opamp.I would love ~0.01% distortion at full power, full bandwidth. However, for full power, I could tolerate 0.1% so long as 75% power delivers 0.025%.

author: BrianHG
author_rank: Super Contributor
timestamp: September 20, 2023, 10:05:03 pm
content: Awww, the OPA2677 was so damn close. It's limiting factor was the power supply of +/-6v. If it went to 7.5 through 9v, it would meet all my criteria on top of supporting 500ma.

author: BrianHG
author_rank: Super Contributor
timestamp: September 20, 2023, 10:09:47 pm
content: The Richtek RT9146/7 might do it. However, who is Richtek? Never heard of them. Can they be trusted?

author: John B
author_rank: Frequent Contributor
timestamp: September 20, 2023, 10:20:17 pm
content: 2.5V @ 250mA is 625mW of power. I look forward to seeing this Eardrum-o-nator 5000™

author: BrianHG
author_rank: Super Contributor
timestamp: September 20, 2023, 10:34:29 pm
content: Quote from: John B on September 20, 2023, 10:20:17 pmLOL... Yup, for a mixing consoles used by DJ's when mixing music at a live event. They want it LOUD and clear.(I know I said battery at the top...)Sanyo has their 'LA6501-TL-E' opamp, designed for headphones. It drives up to 1 amp and comes in a 5-SSIP / TP-5H package. But I can only buy Sanyo in bulk.

author: Benta
author_rank: Super Contributor
timestamp: September 20, 2023, 10:37:10 pm
content: Perhaps this one?https://www.ti.com/product/LM4952

author: TimFox
author_rank: Super Contributor
timestamp: September 20, 2023, 10:39:35 pm
content: Have you considered low-voltage power amp ICs such as the LM386N-4, capable of 1 W into 32\$\Omega\$ at total 16 V supply, with relatively high THD at full power, typical 0.2% at lower power?Philips has a whole "TDA" series of audio amplifiers for consumer applications:https://320volt.com/en/tda-serisi-anfi-entegreleri-dokuman-designers-guide/These devices are not for the audiophile community, but keep millions of teenagers happy.

author: BrianHG
author_rank: Super Contributor
timestamp: September 20, 2023, 10:49:36 pm
content: I think I might have a candidate: Analog Devices AD8397. 310ma, data sheet specs at 25ohm are impressive and it supports my voltage ranges. The gain BW flatness and final THD within spec should melt the audio power amp ICs. Though you do pay for it, 7$us each, which isn't an issue for me.

author: RoGeorge
author_rank: Super Contributor
timestamp: September 20, 2023, 10:59:09 pm
content: Quote from: BrianHG on September 20, 2023, 09:06:41 pmThis one was optimized as one of the finest headset amplifiers, see if it fits the other requirements for your circuit:TPA6120A2 High Fidelity Headphone Amplifier

author: BrianHG
author_rank: Super Contributor
timestamp: September 20, 2023, 11:05:02 pm
content: Quote from: RoGeorge on September 20, 2023, 10:59:09 pmThanks, that one did not show up in my digikey search.700ma per channel. Designed for 16ohm load and can go as low as 8 ohm. Though it does require 30ma quiescent current where the analog devices only requires 18ma, but I can live with that.The only thing I don't like is in the example circuits, they use a large series resistor at the output. I may have to experiment.

author: BrianHG
author_rank: Super Contributor
timestamp: September 20, 2023, 11:38:19 pm
content: I guess I will target the TI amp:https://www.digikey.ca/en/products/detail/texas-instruments/TPA6120A2DWPR/1670531For the battery version, I guess I will just use 2x9v lithium rechargeable cells.

author: dobsonr741
author_rank: Frequent Contributor
timestamp: September 21, 2023, 12:10:21 am
content: BUF634 +your fav audio opamp. A lot written about in hi-fi forums. I have a commercial battery op headphone amp with 634 in it. It sounds very good, silent, powerful enough.

author: magic
author_rank: Super Contributor
timestamp: September 21, 2023, 05:46:18 am
content: Which 16Ω headphone needs 2.5V RMS?Whatever you do, mind power dissipation. 250mA with 5V dropped across the chip is not negligible. Your supply rails are a bit high for this.Quote from: RoGeorge on September 20, 2023, 10:59:09 pmIt's a DSL line driver marketed to audiophools. Needs the output series resistor for stability, but maybe a DIY air coil could work as well. Search DIYAudio, it's a popular chip.Quote from: BrianHG on September 20, 2023, 10:49:36 pmAnother one that audiophools played with a lot, I seem to recall it was also difficult to stabilize.

author: BrianHG
author_rank: Super Contributor
timestamp: September 21, 2023, 06:12:28 am
content: The 1amp capable Sanyo part I listed above has a beefy heatsink. Same with the BUF634 bipolar 1x class AB follower bufferamp, except that one is something like 10$ a piece and it is mono. Yes, the cheaper BUF634s are available in SMD, but those could get toasty.

author: gamalot
author_rank: Super Contributor
timestamp: September 21, 2023, 06:34:02 am
content: I built this TPA6120 based headphone amp for my K712 many years ago, I'm very happy with it and I still use it every day. You can consider using two or more TPA6120s in parallel if you need to drive very low impedance loads.

author: Zoli
author_rank: Frequent Contributor
timestamp: September 21, 2023, 06:51:46 am
content: Kevlar/Mithril armour is on, so I just leave the link here:http://nwavguy.blogspot.com/2011/08/o2-details.html

author: edgaras006
author_rank: Contributor
timestamp: September 21, 2023, 07:28:07 am
content: Everybody going crazy, for low distortion, forget that you have to consider whole signal chain, but bottleneck is the speakers or a headphones majority of the time. Distortion spec of 0.5% is very good one. Having that said LM380 (not LM386) or TDA2822M would do for me, for audiophiles TPA6120A2.

author: RoGeorge
author_rank: Super Contributor
timestamp: September 21, 2023, 08:30:09 am
content: Quote from: BrianHG on September 20, 2023, 11:05:02 pmApart from the datasheet example, TI did an evaluation board for TPA6120, where the output series R is 4 times smaller than in the datasheet example (linked in the product pagehttps://www.ti.com/product/TPA6120A2). I guess the series R also plays the role of a DC current limiter, to protect the headset in case the final stage of the amplifier fails as short circuit to one of the power rails.When the chip was launched, there was yet another PDF written like an application note, with more details about the current feedback advantages and other design choices (including that R). It's been 10+ years since, and apparently that PDF is no longer linked in the product page.

author: Terry Bites
author_rank: Super Contributor
timestamp: September 21, 2023, 11:13:37 am
content: Tinitus and deafness at a reasonable cost?You might want to parallel up some choice opamps to get the 300mW.OrA composite amp lets you create the power level you want.Us a low distortion low noise amp with a power bufferHave a look at the LT1010 datasheet page 1 for an example

author: edgaras006
author_rank: Contributor
timestamp: September 25, 2023, 09:24:16 am
content: Quote from: Terry Bites on September 21, 2023, 11:13:37 amI have not been there, but at certain volume brain waves might start resonating with audio signaland then epifany comes.

author: JerryC
author_rank: Newbie
timestamp: January 05, 2024, 03:01:24 am
content: The best tradeoff between idle current, output power and THD that I have found after a lot of research is OPA1692. Using one chip per channel (the two halves paralleled, with 10 ohms per side on the output) I measured 140mW into 32 Ohms at 0.004%THD, or 80mW into 16 Ohms at 0.006%THD. Total idle current 1.3mA (2x650uA). Loud enough to blow my ears off playing bass guitar in earbuds. If you need more power than that, use two chips per channel (4 opamps).