[francisdemarte]

 
Keep in mind also that depending on your opamp, distortion can also be caused by having too LOW a gain. Some opamps require a minimum level of gain to work properly, they are not unity gain stable. Consult the opamp's datasheet to see if they require min. gain.
 
If you roll opamps, I suggest keeping a minimum gain of 10. 

 

[Elar]

Quote:

Given the way the system works, my suspicion would be that at a certain level of gain we are starting to creep out of class A mode and back into class AB mode.
 
If you are already running in AB - as in when the unit is in stock configuration - there would not be an audible threshold of change.... but with Class A on OPA627, as we drop back to AB mode the difference is much more obvious...
 
Just a guess - some work with multimeter/CRO would be required to confirm it...

What gain do you personally suggest that I use if I go for class A? I am planning to do so later on, after I get a good picture of M-Stage's signature. Atm I am using 10 gain and have the volume usually at 12 o'clock. After listening the amp for some time, I would say that what I would like to improve in it is the soundstage. I have read that some people want to bring the "image" forward, but I want the opposite, especially in some particular recordings I would like the singer to be a little bit further away from me, sometimes it feels that we are so close that I can feel his/her breath in my face. But then again some live recordings I have have  huge soundstage, so maybe it depends on the recordings.

 

[AlfBaxter]

Quote:

Given the way the system works, my suspicion would be that at a certain level of gain we are starting to creep out of class A mode and back into class AB mode.
 
If you are already running in AB - as in when the unit is in stock configuration - there would not be an audible threshold of change.... but with Class A on OPA627, as we drop back to AB mode the difference is much more obvious...
 
Just a guess - some work with multimeter/CRO would be required to confirm it...

Quote:

What gain do you personally suggest that I use if I go for class A? I am planning to do so later on, after I get a good picture of M-Stage's signature. Atm I am using 10 gain and have the volume usually at 12 o'clock. After listening the amp for some time, I would say that what I would like to improve in it is the soundstage. I have read that some people want to bring the "image" forward, but I want the opposite, especially in some particular recordings I would like the singer to be a little bit further away from me, sometimes it feels that we are so close that I can feel his/her breath in my face. But then again some live recordings I have have  huge soundstage, so maybe it depends on the recordings.

See dlaloum's post on p.75. There he reports that several opamps, including OPA627, have odd high frequency spikes at 0dB gain, which are smoothed out at higher gains. If you want a more recessed sound, with deeper soundstage, you might well like the OPA627 not in class-a. Although it is hard to imagine you won't prefer it in class-a once you try it!
 
@dlaloum: are you suggesting that above a certain gain level, the opamps are no longer in class-a? If that's true, then 10dB would be the ideal setting, as many seem to have discovered. The extra detail that some claim to perceive at 0dB would be the HF distortion you found in your RMAA analysis.
 
For my part, I find the Matrix (OPA627, class-a) fatiguing and a little harsh at 0dB, much smoother at 10dB gain. Distortion of existing high frequencies can sometimes sound like additional detail, but it's still bad.

 

[ninjikiran]

My opamp is running class A @ 10gain as well though so its something in his chain more than likely. 
 
Quote:

Given the way the system works, my suspicion would be that at a certain level of gain we are starting to creep out of class A mode and back into class AB mode.
 
If you are already running in AB - as in when the unit is in stock configuration - there would not be an audible threshold of change.... but with Class A on OPA627, as we drop back to AB mode the difference is much more obvious...
 
Just a guess - some work with multimeter/CRO would be required to confirm it...

 

[dlaloum]

Quote:

@dlaloum: are you suggesting that above a certain gain level, the opamps are no longer in class-a? If that's true, then 10dB would be the ideal setting, as many seem to have discovered. The extra detail that some claim to perceive at 0dB would be the HF distortion you found in your RMAA analysis.
 
For my part, I find the Matrix (OPA627, class-a) fatiguing and a little harsh at 0dB, much smoother at 10dB gain. Distortion of existing high frequencies can sometimes sound like additional detail, but it's still bad.

 
Hmm - my own listening seems to tend towards 10db gain...
 
My RMAA testing says - definitely NOT 0db gain
 
This is using my Revox 3100's (DT880/600 OEM circa 1986).
 
I have been considering trying some tests using my Koss Pro4/x - which at 250ohm requires more current and less voltage.... This means that the system will be further into its class A biased voltages.
 
With the Revox (and any higher impedance headphones) you need more voltage.... this makes it more likely that you will leave the class A operating voltage range.
 
If you increase the gain - you increase the end voltage, and are likely to also exit class A mode...
 
So ...
1) 0 gain is not great - definitely more grunge/hash.
2) excess gain is likely to move back into class AB mode (also undesirable)
3) Increased bias current, will enlarge the class A envelope - in exchange for additional heat
     this may be possible with some opamps and configurations - a side by side adapter could be fitted with a heatsink
     Doesn't look good for top/bottom adapters -as heat dissipation is problematic (anyone want to build some heatpipes?)
     Metal Can opamps may handle this better as they can dissipate heat more effectively
 
In any case with the JTAM OPA627 module and class A socket - I think 10db is optimal when using my 600ohm HP's.
 
I haven't had time for more extensive testing (the tests take a LOT of time)... and sometimes I do like to just listen to Music..... oh yeah that's right - that was the whole point of the exercise....
 

 

[roob]

I've noticed a slight hiss in my amp... Is this normal?

 

[dlaloum]

Quote:

I've noticed a slight hiss in my amp... Is this normal?

What headphones are you using?

 

[Jibbie]

There could be a hiss if you are using very sensitive headphones and the gain setting is too high.
Quote:

I've noticed a slight hiss in my amp... Is this normal?

 

[XTTX]

I had hissing (low level of noise) as well; however, I resolved this by getting an external DAC. Not sure if it was necessarily the DAC that fixed it, but immediately afterwords, the noise was gone.

 

[roob]

I'm using my K701's at 10dB gain. I think the hissing becomes more noticable when the amp has been on for a while...
I'm also using my D4 as DAC aswell as my X-Fi, and switching between the modes/unplugging etc did not remove the hiss.

 

[nycbone]

Is the m-stage lineout signal influenced by the volume control or is it just a loop out? The literature says it can be used as a preamp - just checking.
 
Thanks.

 

[JoetheArachnid]

Quote:

Is the m-stage lineout signal influenced by the volume control or is it just a loop out? The literature says it can be used as a preamp - just checking.
 
Thanks.

Is there actually a point to having an output that isn't a pre-out? If it had a line-out you'd just be paying $250 for a female-female RCA connector. Not trying to be rude, just wondering if there's genuinely any use in this. With DACs/transports I understand; amps... not so much
To answer your question, yes it's a preout. Project86 mentioned its use as a preamp for his speakers in his review.

 

[nycbone]

 

[nycbone]

 

 

[Elar]

A few questions about some things that are not that clear about opamp and the class A mod. About opamps, as I understand it, if they are dual I can just remove the existing one and insert another 8-DIP opamp. If they are single then I need this BrownDog single-to-dual opamp adapter. Questions:
 
1. Is there any other similar (or better) adapter available from other sellers (Digi-Key, Farnell, Mouser, Newark). I am asking because I want to make one big order with all the opamps and other stuff that I need.
 
2. Should I solder to that adapter two 8-pin DIP socket (like this or this) and then mount to each one single opamp (like OPA627)? Or should I solder directly to that adapter the two single opamps, and if yes, what type of opamps should I buy for that (are they called soic?)?
 
With class A mod things are even more complicated for me. First of all, from what I read in this article, there are different ways to make an opamp class A. From what I understand, the best method is the third one, the JFET Cascode. I really don't have a clue how all that work (the soldering needed will be done by a friend of mine with better soldering skills that my own, which is none), so if someone can summarize it a bit and point out what component exactly are needed to archive it, that would be great.
 
With that done, if I use a dual type opamp, I guess the thing to do is to take one 8-pin DIP socket (like the two models I mentioned earlier), and make it class A (I am thinking more about adding resistors here, I don't know if the JFET method works differently). Then putting this socket above the one existing socket in the amp and the opamp in it. Is there any way to avoid using this additional socket (by adding the transistors directly to the amp socket or to the opamp itself)?
 
If single opamp are used, the question is if the transistors cannot be added to the BrownDog adapter directly, or do they have to go to each socket that will hold each opamp?
 
Sorry if I don't make too much sense with some of my assumptions, doing my best to understand how these things works. Thanks.