REVIEW: Head-direct.com HiFiMan EF2 tube Hybrid Amp with USB DAC - Page 65

Ya, I'm not sure the order, or if it really matters in a device like this. I have removed the tubes completely before and the device still works, with much less volume of course.

That leads me to this question, has anyone removed the op-amp before?

I do want to remove the opamps. But don't want to brake it..

I've removed the tubes with the same result..

Is it possible we can change the op-amps in the EF2A to get a different sound signature or a better sound stage ?

Loving my EF2A, it's gotta have at least 500 hours on it. Just waiting for Mullard tubes to arrive, really looking forward to that

I emailed them a while back about the opamp and the response I got was that the opamp is not in the signal path. The amp is discrete transistor and tubes.

So is the op amp in the EF2 responsible for the solid state amplification?

Computer noise from USB input when using CD input

I'm getting some irritating computer noise from my iMac when not using the USB input with the volume at 12:00 (my favored level) or greater; the noise coincides with moving browser windows around, minimizing/maximizing windows,

I've tried reducing and muting the volume of the mac; I've also tried going to mac audio settings and switching audio output from USB to internal speakers. Ironically, the noise does not occur if I am switched to the USB input. It seems the only solution to avoiding the electronic noise while using the CD input is to remove the usb cable or reduce the EF2 volume to below 12:00.

Is the DAC to blame? I'm considering a uDAC if it might help.

*Note: I had this same problem with a Mac Mini and an old HP desktop.

Sounds like a grounding fault to me. My EF2 is not doing this. Try a different RCA and USB cable.

Wouldn't be the DAC as you said your not using USB.

if i plugged this dac via usb to my laptop, would i sitll need a headphone amp? what about a preamp?

The EF2 has a DAC yes, but it also is a headphone amp, that's it's main feature.

Ya, think of it as a headphone amp that happens to have a DAC as a bonus feature.

Got the Mullard tubes today! \o/

Out of the box impressions in comparison to stock tubes, with the Denon AH-D2000 (obviously subject for change):

- Soundstage got quite a bit wider
- Separation of instruments increased
- Highs became way more controlled and enjoyable, was slightly too sharp before
- Mids seem a bit more controlled as well
- Lower frequencies of the bass seems a bit recessed at the moment

All in all, these are out-of-the-box impressions, nothing more, but even if they were to stay at this state I'd consider them an upgrade in comparison to the stock tubes.

Thanks for the advice guys, really looking forward to "hear" them grow as they go through burn-in

According to the email I got from them, no. It is responsible for no part of the amping at all. The solid state amping is done by discrete transistors.

From them:

No, there's just the vacuum tubes for voltage gain and the transistors (just look inside) for low impedance phones.