I've had the amp for about a month now. Like other impressions I've read, they work real well with low impedance phones. I'm enjoying the RS1 (flat pads) with them right now. The sound I'm getting is fantastic. I've never felt like the music was in my head, just in my face. I haven't tried tuberolling yet, but I have a few on the way. Tube world has a nice chart of different characteristics.



I'll have the CV4003 Brimar, Amperex Bugle Boy Holland and a Mullard long plate sometime this week, basically one from each section. There are lots of tubes on eBay which is where I found mine. I'm not really around to watch the auctions so I just use BIN. They were around $20-$30 each, which wasn't too bad for me. There are some lots listed with a variety of tubes, they might be a bargain. Audiotubes has some more info on the 12au7.

I've been using the GS1000 with the EF1 as well. I found them a bit harsh sometimes, so I was wondering if the Brimar CV4003 would help out.

Has anyone tried op-amp swapping? I can't seem to find much info about that... I'd be interested in trying if I knew what to get and where.

I just ordered the ef-1 for my akg 701s last night. Cant wait to get! Thanks Mecc for the tube chart.

Ask Hiflight about opamps. I would like to know what other op-amp options there are as well. How can you tell if op-amp will work with ef-1? what specs do you look for?

Just to make sure, the switchable op-amp in the output stage is a dual-channel type in DIP package right?

Given this unit a quick listening to Cinematic Orchestra, but not for too long as it's NY eve, and the missus has only so much patience, and it's very smooth and involving. Very nice early, early impression it's given me.

I've been looking forward to receiving this.

I've received two of my tubes this week. Mullard long plate and Brimar CV4003. Both were heavily oxidized. I didn't do a good job cleaning the Mullard long plates. I spent a few sessions with them (was wondering why it didn't sound too good). I gave it two treatments of deoxit prior. I had to resort to using a more abrasive method involving an eraser and it worked pretty well. All the black/dark stuff is off the pins are more shiny. I'll give them a listen later. I notice they have a weird startup effect. The bottom of the tube flashes once up once when I turn the amp on then goes away.

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Yes! I've spent several hours with the CV4003 and it did a lot for the GS1000. My opinion on the GS1000 is that they are weirdly enhanced headphones. It has a smile face for it's presentation. The bass is bumpin, mids are slightly recessed, and the highs are sparkly. Pretty unnatural. Here's what the CV4003 did for me.

Bass: It's still groovy, detailed and ample. Just less in the way.
Mids: I was not expecting this since there wasn't a description mentioning anything with the mids, but I found the mids to be more pronounced and very 3D like. I'll go as far as to say the vocals I'm hearing are around K1000 levels, except smoother and warmer. The vocals are more forward and that's a good thing here.
Highs: They are a lot softer. They don't pop out like What before. If you listen to the GS1000 at a very low level, you'll notice how the lows and highs really stand out. Very unnatural. It's better now.

Sibilance: This is a weird thing for me. Some songs sound great, no prob. Others with a slight emphasis on s, sh, ch. The CV4003 seems to have softened up (somewhat) the minor sibilance I was experiencing. There are songs that sucked before, they still suck, just not as bad. It could very well be the song itself that's poorly recorded.

The GS1000 sound I'm hearing now is more neutral and close to being where I'd want them to be. I'm not expecting K1000 realism, especially with a $300 amp. I just want to alleviate more of the sibilance. Maybe the GS1000 are just revealing and I have to deal with it. I'm going to try messing with cables and changing sources. I have a feeling upgrading my source will give me good results, but I don't want to upgrade unless it will give improvements in every area (not just get rid of the harshness at the expense of detail).

I tried the RS1 with the CV4003 and had some not so good results. The bass was very thin as well as the mids. Vocals were a bit sharp and too much in my face. Kind of distracting and hard to get away from. This was with bowls. Pads made the RS1 sound congested, dull, and the soundstage went into my head.

Haven't tried the ESW10, yet. I think the RCA cleartop the EF1 came with is a very good tube for them.

I have an lm6172 and lm6171 also I have 8610/8620 on adapter that fit my go-vibe 5s wondering if i can swap out the 8620 for op275? or the lm6172? I believe those are the 2 channel op-amps right?

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relax, just rock it back and forth a bit and push a little and it will go in as long as pins are in the right orientation.

make sure the pins on the tube are straight, and line up, then gently rock the tube back and forth and push in. The socket is designed to flex a little.

It is possible that our shipping department put a wrong tube in the box. Would you please make a picture of the tube that you received？

Yeah, maybe make a tracing of the socket with a pencil onto a piece of paper, do the same with the tube, and you'll know the answer if the pins literally don't line up. But sockets can be a bit stiff.

I'm seriously considering getting this amp for my hd600s. If I get the rca cleartop, would I be fine or do you guys suggest changing the opamps. Ive already read recommendations for the ad743

I received my EF1 yesterday, and I've been burning it in/listening to it since with my Denon D2000. Haven't been this satisfied with audio gear since I upgraded from Sony boombox to Celestion speakers/Onkyo receiver during college many moons ago.
I'll post some pics/impressions in a few days.

The price is back up to USD$399.

Would it be possible to simply replace the OPA275 with an OPA627?