Glenn OTL tube amplifier

Discussion in 'Headphone Amplifiers and Combo (DAC/Amp) Units' started by Vtory, Aug 21, 2019.

  1. Vtory

    Vtory Audiophile™

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    Thanks to @Phantaminum 's kindness, I can have this amp for the next couple of weeks. I didn't hear many things about this amp in sbaf -- there's only one outdated discussion thread (link). But have been curious because this is often mentioned in other forums in the context of zmf headphone pairing. Anyway he also loaned me a bunch of (really.. confusingly many!) tubes to test. Super excited.

    I will post more detailed impressions later. In the meanwhile, want to hear other folks' takes or impressions about this amp. Also open to any suggestion that can maximize my pleasure during the loaner period.

    By the way, this is the most bespoke audio product I've ever seen. No product homepage, intensive customization upon requests, extremely tube rolling nature (I was almost shocked that I didn't need all the sockets plugged), etc etc. I believe having a product page can benefit potential customers though.
     
  2. m17xr2b

    m17xr2b Friend

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    I heard the Glenn OTL at canjam London on the ZMF stand. It had a rectifier tube instead of hexfred, with an RCA 6F8G and what looked like Mullard 6080.
    Using my own HD650 I was very impressed by the top end I heard, very present with plenty of sparkle and detail, TOTL'ish.
    Nothing sounded even slightly wrong and I was thinking this is a worthy upgrade to my BH Crack.
     
  3. gaspasser

    gaspasser Flatulence Maestro

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    Thanks for doing this and I look forward to your thoughts. I’m intrigued by this amp and was reading through the massive thread at HF. I found it odd that it is hard to order one. I’m not sure, but it seems like everything is done through PM with the owner?
     
  4. Phantaminum

    Phantaminum Friend

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    Glenn is a low key guy. He won’t ever have a site up for his amp and does transactions through PMs. He’s a great guy to work with but transparency is a bit of an issue. He doesn’t have an excel document that shows what the status is for the build or where in the line you are at as a customer.

    There are a few personal reasons he works this way. I can’t really get into it because of the nature of them but I will say his amps are worth the wait. There is also a bunch of resources on Head-Fi and there’s an excel document with the different types of tubes the amp can use.

    If you have any questions on the amp or build I’ll be more than happy to answer them. If it’s a bit more specific like, different types of caps he offers, or transformers; you’ll have to send him a PM.
     
    Last edited: Aug 21, 2019
  5. gaspasser

    gaspasser Flatulence Maestro

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    Thanks for chiming in. Is there a standard configuration of this amp? I read that Glenn likes to utilize inexpensive tubes that many (like me) are noobs about. How did you figure out what configuration to get? I’ve never seen one of these in the wild. Did you get to hear one prior to ordering?
     
  6. Phantaminum

    Phantaminum Friend

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    Standard configuration would be one driver socket, two output power sockets, and one rectifier socket. This Is probably his cheapest build and pegs in around $800.

    Most will spring for the Lundahl transformer which lowers the noise floor and for the 6v/12/25v switch which both come in together at around $1200. Solid combination here and most won’t need anymore than this.

    My build has one driver socket, two c3g driver sockets (not really needed but extra if you want it), 6 power output sockets (really for running 6 x 6BX7/6BL7 tubes - think EC Super 7), the 6v/12v/25v switch, 5998 switch, hexfred rectifier (so I wouldn’t have to roll rectifier tubes) and a stepped attenuator which clocks in at $1600.

    If I could go back I would probably do without the c3g socket, only four power sockets, go with a normal but nice pot, and not get the 5998 switch. Glenn can also build the amp with whatever caps, pot, and transformers that you’d like.

    I talked to several people on the forum until I decided on this combination. Most of the people I received advice from, owned other higher end gear. They always gushed over this amp. Never got a chance to hear it but it was the best blind purchase I made.
     
    Last edited: Aug 21, 2019
  7. Vtory

    Vtory Audiophile™

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    That's good to know. I thought it a lot pricier -- as it sounds better to my ears (when paired with Verite) than it costs.

    Both Oblivion and this have surprised me, although there are different approaches (and perhaps different underlying philosophies). For 1200-ish usd, we may (mostly) get worse.

    I was planning to try at least three different tube configurations tonight (currently using Tung Sol 7236 powers and Tung Sol 6C8G driver), but the "one more song" effect is delaying my schedule. Can't stop listening. Oh, well.
     
  8. gaspasser

    gaspasser Flatulence Maestro

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    I am trying to triangulate how this amp sounds. Have you heard (and can compare with) known OTLs such as ZDS or BHC, etc.? I looked through some of your posts on HF and get the sense of excellent soundstage and layering. I don’t lurk around at HF enough to know the value of the other opinions there.

    It seems the amp pairs well with high impedance headphones. Other than that, any specific pairings you like beside 650/Auteur/Verite?
     
  9. Phantaminum

    Phantaminum Friend

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    Never heard the ZDS and it's been years since I heard the BHC.

    I'll try my best to explain what it sounds like and hopefully with Vtory adding more information you can get a better picture.

    I'll start off with the drawbacks:

    • It doesn't have that crystalline/clear sound you get from an OTL like the Feliks Euforia. Depending on the tubes you can get very close and you won’t notice this if you haven’t experienced other higher end OTL.
    • It can at times sound a bit slower than full OTL amps. This can be remedied with different tubes.
    • You’ll find it difficult to find tubes that are dead quiet in this amp with 6AS7G/6080 tubes. This isn’t like the Euforia which has a dead quiet background even with some of my noisier tubes. The Russian 6H13C and Cetron 6336 are dead quiet with all driver tubes.
    • Because of the tube hum it’ll suffer a little in microdynamics.
    • I want to say that the image is very solid on the GOTL but the outside edges aren’t as defined as like the Euforia. What I mean is that the note density is very solid but the delineation sometimes suffers on this amp on very busy passages. Separation is done better on the Euforia with cheaper tubes but can be mostly alleviated with higher end tubes. (This is being very nit picky of me)
    Positives:
    • It is very transparent to tube changes. You can mix and match all types of tubes to get the tone/timbre/speed/sound stage/tone/timbre you want.
    • 6v/12v/25v switch allows you to roll all types of driver tubes. If you don’t want to pay for a 6SN7 Sylvania Bad Boy at $200 then buy the 12SN7 version at $60.
    • With most power and driver tubes, it throws a pretty wide sound stage with good depth. With better tubes you can get this sound stage to be quite large and very deep.
    • Layering - one of my favorite things this amp does. It allows you to hear into the music and you can tell where a person/instrument is in relation to another. In front, above, behind.
    • Great note texture. This may be a strange way to explain this but when a bass guitar is played, it feels like you can feel the front and back of the string.
    • This is one of the few amps with the cajones to bring some serious body to the HD800. If you want to hear some great mid/low end bass on this headphone, this is a good pairing.
    • It can run Planars with 6336 tubes but the notes aren’t as delineated as on a high quality solid state.
    • It has more body than a normal OTL and can bring some nice sub bass rumble if that’s what you’re looking for.
    It’s an authoritative amp with the right tubes and can sound lean and lithe with a different set of tubes. With most tubes its south of neutral. Its warm, always has strong note density. It’s a very involving amp and you get immersed in the music. It throws up big images. I feel like I’m not doing a great job of explaining but I have to say that if I had to choose any amp between $1000 - $2100 price range I’d always pick this amp.

    In terms of pairing I settled in on the HD650 and ZMF cans as they give me everything I want in a headphone. The only other headphones I’d buy would be the Aeolus and HD800. The HD800 really surprised me with it sounding far from lean on this amp. The mid came forward and not one thing in the treble bothered me. I also had great success with the Aeon Open Flow pairing but thought the Ananda/Ether 2 pairing were ok. Hope this helps.
     
  10. Walderstorn

    Walderstorn Friend

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    Tons of info and it was pleasant to read. I have one question though, what does the 5998 switch do?
     
  11. m17xr2b

    m17xr2b Friend

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    The 5998/WE421A tubes are not 100% identical to the 6AS7G so the switch changes the operating point to it's most linear I think, not a big deal. Still, Glenn will never ever use the 5998 due to multiple failures and headphones going pop on startup. He has the worst luck, recently one of his GEC 6AS7G died, unlikely to be the amp itself.

    If it was me I'd get SS rectification, octal and C3G input(great tubes, can't get enough of them), and just two output tubes instead of 6 to keep the cost down. Standard power transformer, alps pot and jupiter caps. Should run a bit over 1K.
     
  12. Phantaminum

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    Nothing, lol. It was supposed to give the correct (higher voltage) to the 5998 tube so that in theory it would sound the way it should (better). Myself and several others that have ordered it can’t tell a lick of a difference. So Glenn decided not to offer it anymore but I think it was the idea of someone else who had initially requested it for his amp.

    I did have a thought. I do follow GrizzlyBeast and what he enjoys sounds wise I find myself in the same mindset. From his description of the A&S Mogwai SE it seems to sound very similar to the Glenn OTL with possibly a cleaner/clearer sound.
     
  13. Walderstorn

    Walderstorn Friend

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    If i remember correctly the Mog SE is around 2500/2800? For twice the price would it still be justifiable? Not as much tube rolling as well.
     
  14. ColtMrFire

    ColtMrFire Writes better fan fics than you

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    Looking forward to reading how it compares to 3F.
     
  15. Vtory

    Vtory Audiophile™

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    After rolling 6 different power tubes, I found my top 3 favorites as the followings:
    • GEC 6080 : If I have to choose only one pair of power tubes, it will be 6080. Not very sure if my satisfaction came from tube per se, amp-specific synergy, or gear/pairing-specific one.
    • 6BX7 (six of them) : 6 glowing tubes were visually satisfying. A bit too much gain for Verite. But can stack against 6080 (actually sound similar) in sonic quality.
    • Tung Sol 7236 : A little more relaxed and rounded than the two above. Solid second choice for a different taste.
    Other tubes tested include Tung Sol 5998/6AS7G, Svetlana 6H13C.

    Having 6080 fixed, now I'm exploring drivers. It will need much more time, as I have roughly 17 driver tubes sitting around me! My temporary favorite is Siemens C3G though.

    I've never imagined I could enjoy tube rolling this much.

    I am still identifying amp's fundamental character regardless of tubes paired. Hope at the end of tube rolling adventure I can confidently say how this amp sounds.
     
  16. m17xr2b

    m17xr2b Friend

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    The GEC 6080 is usually found in top 3 to top 5 6080/6AS7G tubes. None of the US manufactured tubes have that sort of sound. Satisfaction is from the tube itself here, not the family. The 6080 family of tubes is pretty unremarkable overall.
     
    Last edited: Aug 24, 2019
  17. totlsota

    totlsota New

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    I am considering a Glenn at the moment. One of the major alternatives is the Feliks Euphoria (or Elise even). I found this post very interesting. @Phantaminum you said you would choose the Glenn every time, but was interested in any more on the Euphoria downsides perhaps? I know this is the Glenn thread here, so apologies and please recommend a better thread if this is not the right spot!
     
  18. Phantaminum

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    I’ve posted my thoughts on the Euforia and GOTL here:
    https://www.superbestaudiofriends.o...eliks-audio-euforia-headphone-amplifier.8065/

    If you have any other comparison questions send me a PM.
     
    Last edited: Sep 1, 2019
  19. Vtory

    Vtory Audiophile™

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    Glenn OTL tube amplifier short review

    Pros: tastefully exaggerated dynamics, great staging and texturing, very sensitive to tubes
    Cons: rough highs, a little loose bass, not desktop friendly

    Introduction

    I’ve been enjoying the Glenn OTL amplifier (on a loan from @Phantaminum; henceforth referred to as GOTL/gotl) for roughly half a month. I deeply appreciate his kindness to let me test his baby for such a long time. As I posted earlier, there are only a few of sbaf friends who own this amp atm.. And most owners rather kept silent. The greatness of this amp might be partly proved by super rare chance to pop up in the used market. But I was curious anyway.

    All I heard are legit. This amp is another undervalued (in sbaf) masterpiece, and should be viewed in line with any well-received tubes. Particularly for this pretty affordable price range. I really like Oblivion for its performance at only $1.2k .. and never imagined I had to add another great value proposition candidate.

    Associated Gears
    • Gustard DAC-X26 + U16
    • ECP Ravenswood DSHA-3F
    • ZMF Verite and Autuer

    Appearance and first impressions

    The appearance is more in line with utilitarianism. It’s build quality is quite good, but clearly lacks aesthetics of sleeker looking amps such as Oblivion. Just personal preference. Nothing wrong. If it’s a 5k-10k-20k luxury product, I might nitpick but that’s not the case this time.

    The unit I borrowed had a stepped attenuator, but during my evaluation, I found continuous and minute adjustment of potentiometer could work for me better by comparison in dialing in volume sweet spots.

    Sound

    First of all, let me be clear that this amp is VERY responsive to tube rolling. Maybe the most sensitive among I’ve ever experienced. Likely intentional. This could be the opposite approach from Oblivion (claimed as less $$$ part-dependent). And for this reason, it took me awhile to distinguish gotl’s character from what attributed to tubes. Fortunately I could test a bunch of driver and power tubes -- 21 sets -- thanks to the owner. It really helped.

    So, how does this GOTL sound? In short, it’s very engaging and introduces lots of fun regardless of tubes plugged. My general impression is that it's not a kind of ‘doing everything right’ amps (Oblivion belongs to this camp) but rather ‘maximizing what it can do well’. It has a certain set of drawbacks (at least to my ears and tastes), but I almost didn’t bother during my time with gotl.

    This amp has a little forwarding highs and very good midrange. Tonality feels like a little mid-centric. The overall timbre is well extended and a bit distant in a positive way. Maybe with a slightly exaggerated sound in terms of dynamics and texturing.

    The bass and lower mid are quite neutral and unobtrusive, although bass appears to be a little lacking and less controlled than my reference point (DSHA-3F) as well as Oblivion that I recently evaluated. No it doesn’t have lame bass. I hear the amp produces deep bass when the music calls for it. But I typically prefer things tightened a little more (but not too much). Also note that I am using ZMF cans (mostly Verite for this amp) which aren’t usually seen as power-hungry monster. GOTL can have a lot of power and high gain. Insensitive transducers might be better to pull the most out of it.

    Upper mids and highs of GOTL strive for drama, not naturaliness. I found this amp produced fantastic imaging and soundstaging -- remarkably exciting, wide, and deep. I am not sure if the reproduced sound is truer to the recorded signal. Instead, gotl does open up the sound in the manner how I enjoy my favorite tracks. In other words, GOTL acts like an “expander” or “enhancer”. Unfortunately all such greatness comes with a bit rough and hard sounding, particularly compared to the DSHA-3F (and even politer Oblivion).

    I don’t want to specifically describe tube to tube impressions in this review as tube rolling wasn’t conducted in a fully comprehensive way. Nevertheless, there are a few sets of tubes I really like over the others, which all synergize with GOTL extremely well.

    • Mullard ECC35 (driver)
    • Siemens C3G (driver)
    • Sylvania 12SN7GT Bad Boy (driver)
    • GEC 6080 (power)
    • GE 6BX7GT (power)
    If I own my unit of GOTL some day, these tubes will definitely be prioritized. Possibly starting from C3G + 6080 combo.

    Compared with other amps I own or have relatively fresh memory about, the Oblivion is really an interesting contrast: it is politer, more natural, and does a better job of resolving microdetails, busy passages and delicate decays. GOTL easily wins in both microdynamics and macrodynamics though, nearly making Oblivion boring (which is not indeed) by comparison. The DSHA-3F is simply better to me. Weirdly it combines all the good things of completely different both worlds of Oblivion and GOTL. And in every criterion, DSHA 3F is more refined, more effortless, and has more sense of easiness.

    Closing thoughts

    Honestly I am starting to think that I don’t deserve DSHA-3F (too much overkill for me). Before the two recent amps I tested, I didn’t think much that way, as there were simply no cheaper alternatives making me happy enough. However, recently reviewed Oblivion and Glenn OTL, while both meaningfully outshined by 3F, taught me my satisfaction threshold could be at a much lower price point, with only a few negotiable compromises. For my situation giving most of the audio time to SR1a (followed by Verite), downsizing dynamic headphone rig is very, very tempting. Will I replace 3F with GOTL? I don’t know yet. We will see.

    Again, thanks very much for this opportunity, @Phantaminum . You succeeded in making me begin a second thought!
     
  20. ColtMrFire

    ColtMrFire Writes better fan fics than you

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    Feel free to send it my way...
     

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