[edulov]

There are several threads about this amp. Actually its very good, my old Senn HD430 (600 ohm) is a perfect match. Koss Pro 4AAT (250ohms) also sounded better. I even do not need more then 1/3 of the volume for Senn!
But you should understand, that if yours came with stock Chinese 6JP valves (tubes) - they are really bad.

 
I found and ordered other pairs of fine tubes quite cheap. Like day and night. Great improvement in highs, mids and especially lows and bass extension. Additionally I’ve got better soundstage. Not in width (left-right), compared with my main amp, but in depth (in front-behind).

Later I shall order more valves to choose from and after selecting 2 best options I plan to play more, switching op amps (DIP8 package).
Stock ones are good compared even with mid-class amps and very decent compared to HiFi amps.
So all parts of "modding" is for people who do not believe much in recommendations and want to hear it personally. This cheap but good amp is a perfect option for this.

 
BTW (Its not very strict thou) I found some “hardcore” hardware threads (in English and in Russian) which actually say that one pentode valve per channel sound much better then one twin-triode per channel. Cleaner, more natural, better soundstage and more power to drive hard cans.
 

 

[DangerClose]

Anyone know the power consumption on this or similar?  I don't think it's Class A.  I'd like to leave it on 24/7 but not if it uses a lot more power and creates a lot more heat than a typical little 10 watt amp.

 

[edulov]

PSU - 6V DC, 2A, so max consuption is 12W, but even for 600ohm 1/4 of volume is quite loud, so I doubt that you will use more then 5-7W
 
The problem is not a consumption itself. Tubes/valves work fine several amount of time. Regular 6j9p works about 500 - 1000 hours.

 

[DangerClose]

Thanks.  Current prices on replacement stock tubes is as low as $1, but replacing them every month would still get annoying. 

 

[edulov]

The "thin ice" here is not actually that valve will stop working. They degrade with time, may be unevenly. So the sound will change. In this amp valves are used for buffer, so your hearing will adopt to the changes in 24/7 sessions while the amplifier will keep working. I mean that you'll need to check the sound from time to time and replace valves upon your hearing criteria.
 
BTW, I will check some relatively cheap valves later (in July) and on the opposite side - one very long life reference, "looking" at their sound.
Very soon I plan to try 3 another op amps. Not the newest ones, but all of them received positive reviews and now they are really cheap, hoping that rolling cheaper tubes and op amps will provide stunning results. Fingers crossed.

 

[edulov]

I'v got a question on tube rolling, also I have some general comments and results of op amp rolling. Thus I'll post them here.
Philosophy.
It does not matter how many times it was said or written, people still think that getting HQ is possible only from costly units. Gear is very important, especially for good headphones, especially high impedance ones (250 Ohm and above). But the result highly depends both on components quality and electrical/electronic design. Amplifier in mention has a simple, robust and smart design, so SQ mostly depend on components. Valve/tube is used as a buffer for inverse op amp connection where the buffer actually is a dynamic closed link which defines a big “cut” of SQ pie. But it also means that rolling op amp may improve or damage SQ. And – more rarely dynamic electrical connection between valve and op amp is unbiased giving sound artifacts and/or additional noises.
The other side of the mirror is more complicated. SQ is flexible. Some elements like details, resolution, wide soundstage always count. Many other elements, especially quantity of bass and treble as a control over them are subjective. So I’ll mention only undeniable improvements.
 
Rolling tubes.
Before anything else please understand that 6ж9п valve have many direct analogues and highly compatible ones also. Due to fabrication processes and materials they are not identical, so the devil hides in details. But first of all here is a list of all references, especially if you will look for them at eBay:
6ж9п, 6j9p, 6g9p, 6zh9p, 6ж9п-Е, 6j9p-e, 6g9p-e, 6zh9p-e, 5A/170K, 6688, 6688A, CV3998, CV6189, E180F
Adding suffix letter usually means long life version of tube, also with refined specs.
Since I wanted to keep “playing” with this amp for some time, I tried some, definitely good options, but will continue testing after finding valves at reasonable prices.
 
At the moment I checked just 3 of them, but all - very good ones:
- General Electric 6688, US
- RCA 6688A (made by Mullard)
- Amperex JEP-6688, CША
 
If you want studio-type sound you need GE. Detalization, resolution, separation of instruments, soundstage – exceptional. BUT! They do have bass extension w/o good punch and density. It does not mean that you will get problems with lows, since they are fully controlled. Just not too much. So this valve is not for bass heads.
RCA and Amperex JEP are very similar. Just a little bit less of “open air” but much more prominent lows. Overall control is equal, punch and density. With one small detail – Amperex offers even bass density up to the lowest extension, while RCA offers less “body” at low-low bass. But once again, it will be important only for a hardcore bass head. Also RCA has lesser depth (not width) of soundstage, but you will need very good open cans to capture that. That’s why I am using Amperex JEP.
A bit later I’ll try “normal” Amperex, comparing with JEP version and RCA’s once again.
 
Op amp rolling.
Fooling with operational amplifiers is not so popular, since most amplifiers have them soldered.
 
Our amplifier comes with DIP8 chips package and beds, so you can exchange them easily. But beware, you need electrical compatibility. That is why not all op amps in DIP8 package will fit (electrically). Also you must read corresponding threads since op amps are not equal. Many provide sound coloration. I prefer neutral sound without rolled-off higs and lows, so my list of candidates (considering prices and packaging) was quite short. I made it after harvesting forums in different languages. Take into account, that I am giving description how they sounded with my favorite tubes, but please believe me, my opinion virtually coincided with other people impressions from other amplifiers and sound cards.
 
First of all, the factory installed NE5532 are old as mammoth ****, but in a well designed amplifier they offer very good balanced sound. Just a slight roll-off in treble and a little softness of treble too. Talking about preferences it makes NE5532 a perfect choice for many-many people, especially if they are sensitive to highs. It should be clear: a bright track in bright hp’s will sound bright, but not killing your ears.
 
AD823ANZ is old also, but still very popular. Their sound character is not for my needs, but I can hear it w/o any hesitation. The sound reminds a magnetic tape, in a good sense. Sound is calm and clear, light in mids. Good bass control, some punch. Not much of body in lows, resembling magnetic tape sound even more. Slightly harsh treble, but only for high treble, so you’ll need special tracks and hp’s to hear that. The greatest negative for me (also reminding tape sound) is decent, but much narrower soundstage, compared to 5532. Only a hint of depth. It was noticeable even in fine closed cans, not only in a HiFi open ones.
 
LME49720NA. Can’t say anything bad. As promised it offered incredible detalization, resolution and huge soundstage. Perfect control and balance everywhere. But this op amp has slightly different electric specs, so using it with my tubes caused little but clear “over” sound, like some derived noise, so I had to reject it. I was afraid it could happen, so I’ll try it with another tubes posting additional comments later. BTW – some people may call this sound a little bit clinical, which is not good for easy-going listening.
 
LT1364CN8. It has a love-or-hate comments, showing that electric design affects its selection. In our case it is love. Studio, balanced sound w/o any imperfections. Great resolution and bass control. Top notch, honest treble. So some tracks could become too bright for you. Soundstage – wow! On a verge of placebo, comparing with LME. Absolutely natural sound of live instruments and vocals. A tad less detalization compared to LME, but captured that because I knew what might happen. You will need very good cans and quite specific tracks to hear such a difference. And the most important – no bias problems with my tubes.
 
Beware! If you will choose "dark" op amp with bass-oriented tubes, the sound will float too far from being natural. Better find good bass heavy cans, keeping amp with balanced sound but extended lows. Combining op amp and tubes with rolled-off and "soft" treble also won't do any good.

 

[edulov]

P.S.
 
Try to buy a batch of 3+ tubes, especially the used ones.
1) As a backup
2) If L/R sound different, 3 tubes give you 3 combinations to try
3) Golden pins are better, indeed, but for much higher frequences (MHz). So there is no need to pay extra for the same reference. Magic happens inside the valve.
4) When amp is ON, moving the box and touching tubes will couse "ringing" sound. A cuple of seconds is fine. But if "ringing" is long, or worse - permanent, try to check if the tubes were firmly installed first. If installation was correct - locate the ringing tube and replace it.

 

[DavidK35]

Could not resist, ordered one today, for desktop system. Plus some US NOS 6688A tubes.

 

[edulov]

Simple suggestions:
1) Compare the sound of the stock tubes against another amp, the good one. And only afterwards try another tubes.
2) In case of Panasonic RP-HTF600 & AKG 271 cans you will hear improvements, but not so much for lows due to their FRC's. In my setup AKG 271's lows got some body (not a placebo) and much better bass control, but it was happening with all my cans.
 
I'll apreciate if you can share the results comparing the sound of NS-08E with Little Bear.
 
Another comment, comparing my Topping TP32EX with Fiio E10K(line output)+Nobsound NE-08E. There are small differences, I can describe them, but the biggest difference was in the perception of the sound space created by headphones.
 
For Nobsound I've found myself inside bigger hall, and more surprisingly the sound was more clear, like the walls were covered by marmol providing more reflextions. BTW, the use of GE tubes gave sensation of the huge hall, (Not the size of the soundstage, but how do you interpret the imaginary sound space).
 
For Topping I feeled that walls were draped by thick cloth. Also a big-big hall, just smaller then others.
 
Actually it is a nice combination, since some music styles sound more lively and natural with Topping, others - in Nobsound.
 
So for now I'd love to get an indication which hybrid/tube amp (valve+op amp rolled may be) can offer the effect of big!!! hall with wooden walls. Reasonably priced of cause.
 
Since I've heard music in different ambients, I am quite sure about my impressions.
 
Cheers!

 

[edulov]

Finally made a comparision between
1) JEP Amperex 6688 - my favourite
2) Amperex 6688A - the goal of comparision, NewOldStock, US made
3) RCA 6688A by Mullard
 
The main idea was to compare how "special" Amperex go against regular ones and another fine valve pair.
For good or for bad the summary of the sound signatures and dufferences is short and simple.
 
1) most control over bass; dense, punchy lows everywhere; extended lows; exact reproduction in all FR range
2) less control over bass, dense (less at low bass), punchy lows, but more boomy then 1); details, resolution - they have it, but overall sound is "smoother"
3) slightly less control over bass, dense (less at low bass), punchy lows; details, resolution - they have it, but overall sound is "smoother"
 
For me:
1) goes ranked as the best between tubes rolled by me
3) Have 2nd place, good for relaxed music listening, not getting heavy in bassy tracks
2) Ranked 3rd, good for relaxed listening to music, more for bassheads
 
P.S. for "experts" who might doubt Fiio 10K capabilities. DAC part of the device is very good, so presence of linear output is a gift of gods. You  can use it as DAC/AMP outside home with normal hp's and connect better AMP to it at home for better cans.

 

[DangerClose]

Not only is there not a 1/4" jack on this, but the 1/8" jack is recessed, so typical 1/4" to 1/8" headphone adapters won't fit.  Bad news for my K701.  
A couple of my 1/8" headphones barely fit too.  An extension adapter cable works, but I need to try a shorter one since my 10-foot one hurts the sound quality. 
 
It should go without saying that an electronic device should be in a secure spot.  This one lets you know when it's not by giving a pinnnggg sound when bumped. 

 
I think the headphone output ohms is pretty high.  Without a gain switch, this isn't an ideal amp to use with easy-to-drive headphones anyway.
 
Gets kind of hot.  I'm thinking about cutting a few air vents in the top.
 
It softens the sound.  I had no plans on tube rolling with this, but you say the stock tubes are really bad.
 
I'm trying to figure out if the tubes can be bypassed.  It looks like they can, but I'm not a circuit board whiz.

 

[edulov]

1. Bad design of the front panel (with deep holes for connector cables ) complicates connections, but there are different long tip jacks just as the fine thin cables. I have both options.
2. Amp have so much power that I don't need any gain switch, volume knob is enough.
3. Stock tubes are so bad, that any other will be better. I saw a lot of them quite-quite cheap, even from fine makers. Beware of the differences in bass and bass extension.
4. Electric scheme of this amp REQUIRES some element as a buffer in a "closed-loop" connection for inverse op amp use. This buffer is made on the basis of the other solid op amp (like the finest soundcards and other amplifiers due to size restrictions) or using vacuum valve (triode or pentode). Better say that without it things just won't work for this electric design.
 
BTW, tube rolling is one of the funniest parts, while using a vacuum or hybrid amps.

 

[DangerClose]

  2. Amp have so much power that I don't need any gain switch, volume knob is enough.
 
4. Electric scheme of this amp REQUIRES some element as a buffer in a "closed-loop" connection for inverse op amp use. This buffer is made on the basis of the other solid op amp (like the finest soundcards and other amplifiers due to size restrictions) or using vacuum valve (triode or pentode). Better say that without it things just won't work for this electric design.
 

 
It could use a switch to lower the power so the volume knob is more useful and in its best zone.
 
I know the tubes are required as it is, but you're saying the tubes can't be bypassed with a soldered wire somehow, at all.  There's pins on the tubes that aren't connected to anything.  Some circuit guys chatted a little about it and said it should be easy to bypass the tubes, but they only looked at it casually.
 
I like it overall as-is, I'm just wondering how it might sound without the tubes, and also thinking ahead to if I use it a lot and start wearing out tubes constantly. lol.

 

[edulov]

Tubes/Valves (or op amps in similar designs) are functional in this electric scheme, so w/o it in the best case scenario you won't get enough power to drive high impedance headphones. For me it is one is the most important specs of this amplifier, equally important to the possibility to roll both tubes and op amps.
 
Since you ignore rolling and don't need so much power - why did you bought this amp in the first place?

 

[DangerClose]

   
Since you ignore rolling and don't need so much power - why did you bought this amp in the first place?

 
Who said I don't need so much power. I just don't need so much power all the time.