[Zachik]

You always need just one more and you know this. Just one more...

I know!

In the words of Tom Petty..."Too Much Ain't Enough"

My limitation at this point is my rack space. No room for a 3rd rack (I have a giant one where all the amps live, and a baby one for my music server, NAS, and couple other components).
Tube amps take a ton of space... GOTL and 6EL3N amps already take a disproportional vertical space in my giant rack...

Maybe I should move to a house... $2600 for the amp + $1.3M ~ $1.5M for a house (in my area)... hmmm......

 

[whirlwind]

I know!


My limitation at this point is my rack space. No room for a 3rd rack (I have a giant one where all the amps live, and a baby one for my music server, NAS, and couple other components).
Tube amps take a ton of space... GOTL and 6EL3N amps already take a disproportional vertical space in my giant rack...

Maybe I should move to a house... $2600 for the amp + $1.3M ~ $1.5M for a house (in my area)... hmmm......

Ouch.

 

[L0rdGwyn]

Looking forward to (and fearing) the review by @Monsterzero
I know he is going to compare to his GOTL (which I also own).

Grabbing a notebook and pen, start writing 500 times: "I do not need yet another amp"...

We'll see how they stack up! Looking forward to it myself.

With my DAC chassis shipping today, I broke down the prototype on my protoboard to get started on the 45 amp prototype.

Before I did that, I made the change I mentioned on the output stage loading, swapped in the DN2540 as the bottom FET using my small form factor CCS PCBs. Running the stage as a hybrid mu follower, I expected further improvement in output impedance and that was the case, measured at 135ohm.



A few final random parts going in, got some nice plain silver feet and silver Amphenol RCA connectors to go with the silver chassis. I will be using ClarityCaps TOTL CMR series caps on the output.



Time to get to work on the 45 amp prototype!

 

[zach915m]

I got a chance to have the "Airmid" in house for a week or so - and I without a doubt can highly recommend it for ZMF's. I know @L0rdGwyn told me that it can change a bit in impedance output with different tubes, but the two sets I tried in it (6080 Amperex and the stock tubes) both sounded fantastic.

The one thing that that Airmid does right that stands it in front of the pack - is that is has a holographic, dimensional and forward mid range, that is coupled with resolution and low end weight. All of this works together in harmony to produce a cohesive and exciting sound, and I didn't have to work hard at tube rolls to find it. None of these strengths gets in the way of each other - which is also rare! While you can get to that spot with other amps many times, it can be after spending a lot on tubes and/or find the right headphone combo. The Airmid did this throughout the ZMF line-up really well, and quickly was a shop favorite among our other audiophile staff members.

We had the amp lined up with the Euforia and Glenn OTL. And while I definitely can never get into comparisons that say "one is better than the other" I can without a doubt recommend the Airmid among those amps, and I think out of the three, it's the easiest one to achieve a "ceiling" of sound that performs on the highest level of OTL amps.

So anyways - @L0rdGwyn is already building me a 45 based amp that I'm super excited for that he has mentioned here, if he wasn't, I'd already have put an order in for one of these as it's just that good! I really couldn't get over the "segmenting" of sounds that adds to the "3-d-ish-ness" of our headphones. It just makes you want to keep listening.

 

[Zachik]

We had the amp lined up with the Euforia and Glenn OTL. And while I definitely can never get into comparisons that say "one is better than the other" I can without a doubt recommend the Airmid among those amps, and I think out of the three, it's the easiest one to achieve a "ceiling" of sound that performs on the highest level of OTL amps.

Zach - can you elaborate a bit on the Airmid vs. GOTL?
Also, did you use the same tubes for both amps in the comparison, to make it more apples-to-apples?
(I know the GOTL uses 1 x 6SN7 vs. Airmid 2 x 6J5, but with an adapter it is easy to use 2 x 6J5 with the GOTL...)

 

[Monsterzero]

can you elaborate a bit on the Airmid vs. GOTL?

I compared them using the same rolls. There are some very obvious differences between the two.
I have used:
Kenrad 6j5+Bendix 6080
Sylvania green label metal base+ 5998
Tung Sol black plate+ 5998
GEC L63+ 5998

 

[Zachik]

I compared them using the same rolls. There are some very obvious differences between the two.

Awesome! Something to look forward to...

 

[L0rdGwyn]

I got a chance to have the "Airmid" in house for a week or so - and I without a doubt can highly recommend it for ZMF's. I know @L0rdGwyn told me that it can change a bit in impedance output with different tubes, but the two sets I tried in it (6080 Amperex and the stock tubes) both sounded fantastic.

The one thing that that Airmid does right that stands it in front of the pack - is that is has a holographic, dimensional and forward mid range, that is coupled with resolution and low end weight. All of this works together in harmony to produce a cohesive and exciting sound, and I didn't have to work hard at tube rolls to find it. None of these strengths gets in the way of each other - which is also rare! While you can get to that spot with other amps many times, it can be after spending a lot on tubes and/or find the right headphone combo. The Airmid did this throughout the ZMF line-up really well, and quickly was a shop favorite among our other audiophile staff members.

We had the amp lined up with the Euforia and Glenn OTL. And while I definitely can never get into comparisons that say "one is better than the other" I can without a doubt recommend the Airmid among those amps, and I think out of the three, it's the easiest one to achieve a "ceiling" of sound that performs on the highest level of OTL amps.

So anyways - @L0rdGwyn is already building me a 45 based amp that I'm super excited for that he has mentioned here, if he wasn't, I'd already have put an order in for one of these as it's just that good! I really couldn't get over the "segmenting" of sounds that adds to the "3-d-ish-ness" of our headphones. It just makes you want to keep listening.

Thanks for the feedback Zach! Much appreciated.

Speaking of the 45 amp, I cleared my DAC circuit off my protoboard yesterday, spent the whole morning stuffing PCBs for the ancillary circuitry for the 45 build.

With all of that out of the way, the rest will come together quickly, should be able to have a listen either tonight or by midday tomorrow at the latest.

 

[zach915m]

Zach - can you elaborate a bit on the Airmid vs. GOTL?
Also, did you use the same tubes for both amps in the comparison, to make it more apples-to-apples?
(I know the GOTL uses 1 x 6SN7 vs. Airmid 2 x 6J5, but with an adapter it is easy to use 2 x 6J5 with the GOTL...)

I compared them using the same rolls. There are some very obvious differences between the two.
I have used:
Kenrad 6j5+Bendix 6080
Sylvania green label metal base+ 5998
Tung Sol black plate+ 5998
GEC L63+ 5998

Probably best to defer to Monster for roll comparisons as I didn't have the exact same tubes in both at the same time and listened more for enjoyment than comparison.

The Gotl and airmid are alike in their effortless portrayal of sound via an OTL vehicle. You wouldn't be able to go wrong with either, I think the airmid is quieter and less suseptable to noise than my gotl, the gotl I have does have more tube choices but I'm not sure thats always a good thing!

 

[L0rdGwyn]

I got the ZMF 45 amplifier prototype up and running. It's a mess of alligator clips, sort of a complex build.



Nothing is ever perfect the first time though, have a left channel hum to troubleshoot in the morning. Sometimes a side effect of poor layout when building on a piece of plywood.

Brought my Audial DAC downstairs for a listen. Best word I can use to describe this amplifier is holographic, expansive three-dimensional soundstage. Really impressive on first listen, will be better when all is quiet though

 

[Xcalibur255]

My advice to Zach is to start scouring eBay for the right unicorn pair of globe 45s now. They are unquestionably worth it, and the things they do better than their ST counterparts will probably play to the strengths of ZMF headphones too. The only reason I take my Ken-Rad UX245s out of my amp is so I can have that incredible "wow" moment again when they go back in.

 

[L0rdGwyn]

My advice to Zach is to start scouring eBay for the right unicorn pair of globe 45s now. They are unquestionably worth it, and the things they do better than their ST counterparts will probably play to the strengths of ZMF headphones too. The only reason I take my Ken-Rad UX245s out of my amp is so I can have that incredible "wow" moment again when they go back in.

Once I track down the hum gremlin I will try my globe Sylvanias!

 

[L0rdGwyn]

Okay, hum gremlin found. As expected, it is due to the layout of my protoboard, magnetic field from the mains / bias / filament transformers being picked up by the left input tube, long alligator clip cathode leads not helping LOL. I ruled out all other causes first moving along each stage of the amplifier - also put DC on the heaters of the input tubes, which will be in the final build, I was running them on AC for convenience in the prototype.

But ultimately picking up the left input tube socket with the connections attached and moving it around revealed the problem. Interestingly, the little bias supply transformer puts out a hefty magnetic field. I moved it further away and rotated it 90 degrees, which got the hum down to near inaudible levels. It will be killed completely in the final build in which the layout will be optimized for low noise.

So in go the globe 45s.



Holy moly, it's going to be very hard not to build one of these for myself.

 

[L0rdGwyn]

Whoops, duplicate post my test subject (aka girlfriend), was very impressed, she said something along the lines of "the imaging is amazing", nailed it!

 

[Zachik]

All this amp talk makes the wait so hard until @A2029 finally start working on MY amp!!!
Just couple more parts, and couple more people ahead of me in the queue...........