Project files: LME49600-based headphone amp

When I built the LT1210-based preamp I thought I set a record for longest wait between making a PCB and actually trying it out. I am happy to say that the record has been broken with this – a headphone amp based on the LME49600 buffer IC, which I apparently did back in 2013 but haven’t managed to assemble and test until now (!).

What is it?
This is a small universal preamp/headphone amp based on two single opamps of your choosing and two LME49600 buffers. The basic circuit is shown in the datasheets of several opamps intended for audio as well as the LME49600 itself. With the right opamp to suit your preferences it does sound very good – in fact I think that for many people this would be all the headphone amp they really need 🙂

The board is (nearly) all SMD with a mix of 1206 and 0805 parts (plus the ICs of course). This isn’t one of those layouts that I am incredibly proud of and so I might return to it at some point. However, it is still a good amplifier and as it seems to work as it should I thought I’d make it public as-is.

How big are the boards?
The board measures 2.55″ x 1.575″ or app. 40 x 65 mm.

What is the status of the boards?
The published layout is version 1.1. I’ve tested the v1.0 board and it works well, but I made some small changes afterwards (mostly to the silkscreen).

Does it use any special/expensive/hard-to-find parts?
No, not really. The long wait means that the LME49600 chip has been both EOL’ed and resurrected in the mean time, but it should be available from the usual safe sources (Mouser et al). The higher-voltage LME49610-version is gone, but if you have or can get genuine ones they will of course work. The BUF634F in TO-263 package should actually work as well (up to +/-15V), but I’m not sure it’s cheaper than an original LME. The opamps can be (pretty much) anything you like, but note the comment below on DC-offset.

Anything else I need to know?
A couple of important points to note:

• There is no DC offset compensation here at all, so be careful with using bipolar opamps and/or sources with DC offset on the output. I use OPA1641 JFET opamps and with the inputs shorted I get less than 0.5mV DC on both outputs. There is a negligble turn-on and turn-off thump as well but overall nothing to worry about.
• The board is intended for driving headphones, so there is no resistance in series with the output (just the buffer’s internal output impedance).
• The board is a little bit cramped when soldering, but if you start by soldering the opamp, then the passive components, the buffer and lastly the leaded components you should not have any significant space-issues.
• The board is hardwired into high-current/high-BW mode so the power consumption is a bit high for batteries, but other than that there should be no issues with just about any PSU you can think of.

Downloads:
Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.