MicroZOTL 2

tube burn-in is for real.... I should have taken my time before posting my previous feedback.
Indeed, checked it again yesterday with my HP50 and was surprised to find the sound pretty dark.... So switched headphones and checked with my HE5LE and now the sound is completly different from the previous day! The harshness is gone, warmth is there!!! have to do more listening but I can finally see the potential in this amp! I had regrets initially buying this amp... tried to love it... gave up! but with this tube swap am starting to like it. Now have to get a good PSU...

 

Tube burnin.... warmth.... Whaaaa???

 

yes man... strange.... but I'm pretty sure i don't have the buyer bias!

 

I ran this thing endlessly but didn't achieve satisfactory results until finding my LPS. Lucky you. In my case, treble issues could have been exacerbated by headphone pairings, I suppose.

 

I must admit, I was absolutely unaware of this forum - until I learned about the sorrodje mod for the HD800, read further and hit this thread. Being a microZOTL2 owner for a few months I find this thread very interesting and -while not sure I can add anything substantial- thought it would not harm if I wrote a few lines. Note, that I am not an audiophile and do have not enough listening & gear experience to make educated judgements. I just want to listen to music in a proper way

I am the guy with the slightly modded cover (posting #146), giving me more freedom to roll tubes. When I tested the ZOTL for the first time (stock tubes & PS) I noticed glare and unpleasant treble. However, I was familiar with that sound, as my previous amp (Feliks Audio Elise) showed similar symptoms when driven by the current production Tung-Sol from Russia. I was optimistic to tame that with some tubes I successfully used on the Elise (which I do not have anymore). My current favorite is the FDD20 replacing the 6SN7, taking away the treble sharpness and adding more power to the lower end. I am also powering the ZOTL via an SBooster LPS, which was highly recommended from the seller. I am 99% happy with this amp. It is powering the HD800 nicely - I hardly go beyond 50% volume. Some classical recordings or choir music need a bit more. Note, that the FDD20 seem to have a bit more gain than the 6SN7… Speaking of choir music - I like the other extreme as well. I used to be a metalhead and from time to time still listen to bands like Paradise Lost and Fear Factory. I have the FF Genexus album on my CalyxM and I have never heard it as precise and brutal as via the ZOTL. Maybe not the usual sample tracks but astonishing. Apart from that I enjoy a wide range of genres via the ZOTL and have not yet found a drawback.

Bass was and is my only nitpick - or maybe not? The ZOTL has less bass than the Elise with 5998 power tubes. But while the Elise with those tubes seemed to have a virtual loudness switch permanently set to ON, the ZOTL seems to be more honest. When there is bass in the recording the ZOTL delivers. Double bass on classical pieces and jazz music have a nice fundament. My two albums by Edgar Knecht sound great, punchy, natural and balanced. My Smashing Pumpkins recordings already reach the edge where there is almost too much bass. The only thing which is still lacking (even with the FDD20) is the sub-bass rumble in the Saint-Saëns organ symphony no.3 (Kansas City Symphony recording!). I heard (rather felt) that rumble strongly with the Elise/5998/HD800 combo and with the CalyxM feeding my InEar Stagediver SD-4 IEMs (moderately V-shaped). With the ZOTL is is still there but less pronounced. I borrowed a Behringer DEQ-2496 for a quick test and EQed the 20-50Hz region, which immediately brought back the rumble - but the overall result was not pleasing. So that specific tube (5998) does some magic but the FDD20 is very close. I think the ZOTL is just more linear but still able to reproduce it. I will see what different drivers will do. I have some Mullards, cheap Brimars and Tungsram which I need to check. I have tried the Amperex 7062 but still find the Siemens E81CC to give a crisper and more detailed sound.

I am also curious how different headphones will perform. The sorrodje mod is on the way - I hope that someday I will have an LCD 2/3/4 to test. From what I have read the ZOTL should be able to power them, right?

Cheers,
Torsten

 

The 7062 tubes are prone to being microphonic. It had become particularly bothersome on the desk at work. What I'd noticed is that the face plate actually rests on the desk, i.e. the chassis feet aren't tall enough to provide a gap there. Even vibration from typing was becoming problematic.

Enter a Composition notebook isolation device. And at least for now, problem solved. As an aside, as well, I'm not sure what the deal is with all the unused "amp" wiring inside the case. If we had truckers passing by, I wonder if I could overhear their conversations through my ZOTL.

 

My Elise had a constant 50Hz hum, independent of the volume setting. I tried everything possible to rule out that the cause is my listening setup and finally came to the conclusion, that it has to be the amp. As a result I was heavily flamed at the other forum. The ZOTL is totally quiet.

Not sure I understand the impedance explanation. Please correct me if I'm wrong: I was under the impression that the amp's output imdepance needs to be significantly smaller than the headphone impedance to prevent damping. Elise homepage says supported impedances are 32 - 600ohm, ZOTL seems to have an output impedance of 2ohm.

 

I thought we'd been using the larger feet longer, I guess not. We'll send you a pair of the larger feet now standard. Two pairs, rather.

 

Thanks, Will.

 

The feet on mine are also a bit too short (same symptom as bazelio's) but I have a sheet of expanded rubber between the ZOTL and the tube heaters' power supply.

 

We'll get some properly-sized feet sent to you as well.

I hadn't been aware of the notable variation in headphone impedances before, and the bass aspect is interesting. Those people who like their Audezes with OTLs must be waaarm and comfy.

 

Thanks Will!

I need to borrow some Audezes someday,,,

 

Planars impedance curves are pretty much flat, so the output Z is not so relevant in terms of FR for Audezes. The concern with planars is power transfer, though Audezes are efficient enough to avoid serious problems with most OTLs.

 

June issue of stereophile magazine has a review of the ZOTL2, including measurement results. It seems they used the switching PSU - I wonder how the results would look with a linear PSU...

 

no online version I guess?!
Am very interested in seeing the stereophile review. Apart from @bazelio and @Marvey 's reviews (which is inline with my own observations except that it really gets better with tube rolling in my case), it is only highly suspicious praise, praise and praise...

now there's also a review of............... different PSU.... even some that cost more that the Zotl itself.... no comment.

 

I received new feet from Will (thanks again, Will). The Composition Notebook is still needed. I might suggest looking for some kind of modest isolation type of feet, even simple rubber cones like on my ZDS. But I'm not going further with ZOTL changes at this point... on to a T3 project instead. @nephilim I am curious though - what are those power tubes in your avatar?

Regarding the HF thread.... yeah. No comment, either.

 

These are FDD20 - I enjoyed them on the Elise and they sound great on the ZOTL. Compared to the stock 6SN7 less harshness and a very welcome emphasis of the lower frequencies. Maybe not as crisp and detailed as the C3g but these are different beast anyway. Note, that the FDD20 require 12.6V and hence an additional power supply.

Regarding drivers the past week I listened to Tungsram ECC81: Very strong bass but muted treble and overall rather lifeless and dull. I switched to Brimar 6060 and immediately noticed a wider soundstage and a more balanced sound.

 

@nephilim
Do you have any 7062s to compare/contrast to the 6060s ?