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.
Subjectively speaking they give more depth, definition and a bit better dynamics. It's impossible to do a quick A-B comparison but I've been listening with the LM4562's in there for a couple of years and I do like the discrete Op-amps a bit better. For about $16 bucks I recommend them. I have no idea whether they're better than something like the Burson discrete Op-amps but IMO they're better than the LM4562's which in turn are better than the stock Op-amps. The only bummer is having to wait around four weeks or so to get them. I call it a nice plug in upgrade.