[khaine1711]

Similar to what I feel about the impedance switch - unfortunately to me, as the sound getting thicker, the air/ss seems to narrow down, so I just stick with the L setting.
 
I'm not so sure about the feedback part though - just heard that both feedback and no feedback has their own drawnback, and one isn't exactly superior to another. Some of the very best amp I've heard have neg feedback (manley 300b/stingray/copland), while a few stuff  which boosts no feedback anywhere (*cough* audio-gd *cough*) isn't that special.
 
You're right about the caps, the stock coupling caps are two tiny poly caps (SCR poly cap, not exactly the best for this type of duty). Still pondering on which cap to replace though. Generally I like Jensen, but they tend to sound a bit "crowded" and might not be the best match with the Icon. Once I decided on a cap I'll report back (will be either Mundorf S/G/O or Jensen, or even Duelund)

 

[Xcalibur255]

You are right about the feedback issue, it is only one component of the larger picture that determines sound.  In my general experience the amps I have had which use negative global feedback just don't have the same sense of openess so I've come to shy away from amps that use it.  Some designs must have feedback in order to work properly, and some amps use it as a crutch to get away with bad design.  Because this is an all triode design I think it would have been possible to design it without any global feedback, but I'm sure David had his reasons for doing so.
 
My custom OTL amp has no feedback of any kind and it has the most open, transparent and uncolored sound I have ever heard from a headphone amp.  It puts you in front of the microphones, and at a fraction of the cost that most other amps in this league do.  I only mention this so people know my point of reference when talking about the Icon.  At any rate it is far too soon to judge the little amp, and I haven't even tried it with my LCD-2s yet.
 
At the end of the day the 6SN7 output stage is what drew me to this amp.  I was facing the choice of selling off my collection or finding an amp to use them in and I made my choice.

 

[Xcalibur255]

khaine, can I ask you what the value was on those coupling caps?

 

[khaine1711]

Quote:

khaine, can I ask you what the value was on those coupling caps?

0.33uF; 630VDC; tolerance is 5%. It's the same cap as this one. The one Icon offers as upgrade is Jensen Copper foil  (aluminum can with silver lead out) of the exact value.
 
 

I heard from a friend who build amp that this particular cap is not usuall for signal/coupling. He also hints at changing the resistors to better ones, but I'm not sure I'm confident enough to replace transistor inside the Icon chassis.
 
On an unrelated note, have you tried Glenn's OTL with the Hd800?

 

[Xcalibur255]

I haven't tried my own amp with HD800 (don't own them, went for the other end of the spectrum with the LCD-2), but Glenn himself has HD-800's and uses them to check when building his amps.  A number of other owners of his amps report extremely good synergy with both the HD800 and HD650.  This is one of those things that makes me question what I know about things like impedance matching.  Unlike most OTLs his design has an unusually low output imedance, something we were going for deliberately so it could drive phones like Grados or the LCDs well.  With 5998 tubes my own amp has about a 25 ohm output impedance which is pretty great for an OTL design, but in theory this should make it less ideal for phones like my Beyers.  Yet that isn't the case and the synergy between the Beyers and my amp is excellent, and so is the synergy between it and the LCD2s.  Honestly any quality well engineered headphones seem to sound their best on the amp, which makes me wonder why the whole impedance thing is up in arms all the time in the first place. 
 
Thanks for the info on the caps.  0.33 is not the value I would have expected, but then again I'm still pretty much a novice when it comes down to the details. 

 

[khaine1711]

Impedance matching is still preference I guess. I prefer my Beyer 600 ohm from a SS amp (low output Z). I tried adding 120 ohm (IEC standard), or using some high imp (various typical OTL amp) stuff but it didn't work for me. Sennheiser seems to hint at electrical dampening to change the signature in their hdvd600/800 too (43Ohm out I think?)
 
Thanks for the info on Glenn stuff, I might have to ... acquired one. I'm a fan of good OTL designs (Berning/Atma-sphere/Zana Deux).

 

[Xcalibur255]

FWIW the amp I have isn't made anymore.  He is doing a variation on it now I believe.  I brought about the version I have with the 5998 output, but both Glenn and I have had...... unfortunate things happen to our headphones due to these tubes developing shorts so he decided to move away from them.  He was working on a design using 6336 tubes for high power output that sounds really promising, but that'll be a pretty good size amp and a real room heater.  Of course you could always stick with the 6AS7, but honestly once we did the design mods the amp sounded so much better with the 5998 there was just no going back.  That tube is a sleeper.  People use them in 6AS7 amps not knowing their potential because the 5998 is starved of plate current in a 6AS7 circuit.  If you open it up and "let her buck" so to speak they are incredibly transparent tubes with amazing inner detail and completely liquid and effortless presentation.  Too bad they are so unreliable.  Still I love my amp and wouldn't give it up for anything.  I'm looking forward to having it back.
 
Anyway, apologies to all for the off-topic chatter.
 
I've been listening to the Icon for the last hour or so.  It took a big shift in sound about 30 minutes ago, the treble tamed way down and the soundstage let itself out a few belt sizes.  Just the chance I was waiting for.  I love actually listening to amps while they break in, they pretty much all seem to go through the same stages, but sometimes I can literally hear the treble setting down in the space of a single song and I love experiencing that.

 

[Painterspal]

My review is up - here. Hope you enjoy it - go easy on me!
 
I have some listening impressions based on actual tracks that I'll post at some point. I'll probably add some photos too.

 

[alvin sawdust]

Quote:

My review is up - here. Hope you enjoy it - go easy on me!
 
I have some listening impressions based on actual tracks that I'll post at some point. I'll probably add some photos too.

That's a really good read, thanks for taking the time.
What are your thoughts with it powering the LCD-2s?

 

[Xcalibur255]

I think it's noteworthy that all of the reviews so far have been amps which have the upgraded Jensen PIO coupling caps.  I am beginning to feel this is a very important thing for potential buyers to keep aware of.  The US distribution of this amp by Music Direct is only for the standard version so we can't get ahold of the version with the Jensen caps.  I feel I have enough hours on my amp now to be able to say this cap upgrade makes a pretty significant difference in the performance of this amp.  So far I'm consistently disappointed by how compressed, grainy and unnatural the highs are, and the whole sound in general is thin and edgy with the Beyers.  It sounds smoother with the LCD2's, but there is no transparency or realism to instrument timbres.  This is with some of the best NOS 6SN7 tubes around keep in mind.  I will grant running the stock 12AX7 is a bottleneck that I'm trying to keep aware of in my judgements, but until the new tubes I bought for this position arrive there is nothing I can do. 
 
What I'm hearing doesn't jive with the reviews, so I'm going to upgrade the coupling caps in my amp and put the theory to the test and find out.

 

[Painterspal]

Quote:

That's a really good read, thanks for taking the time.
What are your thoughts with it powering the LCD-2s?

 
Thanks - much appreciated. Actually, I thought it was fine with the LCD-2, in my view it drove them well. I can't comment on the sound specifically because I sold them some months ago. Others may want to chime in...

 

[khaine1711]

Well I think a cap change will do far more than any tube rolling - especially to a transformer coupled amp. Good thing is you can replace the caps yourself, and it's much cheaper than what Icon is charging here in the UK (of course it might not be as pretty). One of the reasons I didn't order mine with the cap upgrade.

 

[Xcalibur255]

Quote:

That's a really good read, thanks for taking the time.
What are your thoughts with it powering the LCD-2s?

It drives them well generally speaking.  There is enough current swing on tap for everything but very loud listening.  It doesn't sound off pace or lacking in dynamics.  The biggest issue is the bass, the lowest octave is pretty MIA probably due to the limitations of such small output transformers.  Bass notes don't seem to carry through with the sense of weight that the LCD-2 is so very good at conveying, the notes feel a bit hollow on the Icon.  The bass control is there, nothing sounds "one note" althought sometimes I feel like it just barely has a grip on that control if you know what I mean.  It doesn't sound dark or overly damped on the high end though, at least not with appropriate tubes.  The LCD-2s are painfully revealing of the amp's lack of inner detail and low level resolution, again I think those coupling caps are the major contributor to this.  A quick upgrade there and a quality driver tube and the amp will make a fine companion for the LCD-2.  I feel the synergy with the amp is actually quite a bit better than with my Beyer DT880s.  The Beyers sound too thin with anything other than the National Unions in the output sockets, but those tubes have quite a few weaknesses of their own so it is a compromise either way.

 

[Xcalibur255]

I've finally got a good tube for the driver socket, a triple mica black plate Sylvania 5751.  This was a major upgrade.  If any owners got their amp with the OEM Shuguang 12AX7 instead of the JJ tube project86 had in his review my advice is to get rid of it ASAP.  It seriously holds this amp back.  I was expecting an improvement when the Sylvania went in but not this much of one.  Gone is the edgy hifi-ish sound and in its place is the open effortless sound I expect from a good tube amp.  I still plan to do something with the coupling caps for curiosity sake but with this change the amp is now pretty nice to listen to.

 

[Painterspal]

Quote:

I've finally got a good tube for the driver socket, a triple mica black plate Sylvania 5751.  This was a major upgrade.  If any owners got their amp with the OEM Shuguang 12AX7 instead of the JJ tube project86 had in his review my advice is to get rid of it ASAP.  It seriously holds this amp back.  I was expecting an improvement when the Sylvania went in but not this much of one.  Gone is the edgy hifi-ish sound and in its place is the open effortless sound I expect from a good tube amp.  I still plan to do something with the coupling caps for curiosity sake but with this change the amp is now pretty nice to listen to.

 
Yes, reinforces my view that a good 12AX7 really makes a big contribution to the sound of this amp.