Question about OPA627 in the 'Max' modules

Thanks for the question, Covenant.

Hmm,, not sure about this ... Lemme check with HeadRoom audio engineers and see what they have to say. I'll reply again shortly w/ any news.

Cheers,
Jorge
HR Sales/Product Manager

.......OK -- Here's Joe W., HeadRoom Audio Engineer, reply to the questions:

1. The low-bass issue you describe, Covenant, could be due to the 637 being used very close to or at it's bare minimum gain. Unlike the unity-gain stable-operation of the 627opa, the 637opa requires a minimum gain of 5. This is due to the lower amount of compensation in the 637. If the amp design uses a gain close to this bare minimum, there may indeed be serious stability issues that are negatively affecting the audio performance. That's just a guess though... The low-bass problem may perhaps be more implicitly due to the actual topology design of the amplifier. Again, that's just a guess. There are many places where audio anomalies can creep in some DYI designs. Many times, poor bass performance is initially blamed on a poorly regulated power supply (as it's modulating with the audio) and not necessarily the amplification circuit. That would also likely be a good place to examine.

2. The M^3 is a completely different kind of amplifier compared to HeadRoom designs. It uses an active ground channel for return currents coming back from the headphones. Our HeadRoom amplifiers all use traditional 2-channel amplification with a passive ground plane. I make no claims as to which is better or worse but the 3-channel (active ground) amplifier can certainly be much harder get working properly. Furthermore, since the M^3 is not solely made by one "manufacturer", there's also the specific implementation of that user's personal amplifier to consider.

3. Nope. They measure +/- .5dB down to 10Hz or so. Most headphones don't get anywhere near that low.

Cheers,
HeadRoom Engineering Dept.