[kazaakas]

I just received this amp and before plugging it in I was already impressed by its rock-like sturdyness.
Since my Q701 is taking a long time to arrive I decided to check it out with my current HD555 headphones, and I surely am impressed already!
Really clean sounding amp, I like it. Also hooked the RCA output up to my crappy 2.1 speakers and they sound better than ever before!
I'm wondering what kind of replacement opamp I could get for it. I like the uncolored, transparent nature of this thing so I'm kinda looking for a general improvement in detail, so not really change the signature, any suggestions? OPA602, OPA627, OPA827 or LME49990? All these seem to be generally liked, but I can't really seem to find any kind of comparison, of course it's all opinion, but still... Price isn't much of an issue as long as its < $30 which almost every opamp is if I'm not mistaken.
 
Quote:

will the amp affect anything plugged into its L and R output in the back? like speakers?

I can tell you from personal use: Yes the amp will output an amped signal to the RCA outputs on the back when there is no headphone plugged in

 

[Xymordos]

Actually the amp outputs signal anyways when headphones are plugged in...

 

[kazaakas]

Quote:

Actually the amp outputs signal anyways when headphones are plugged in...

Just checked and I'm 100% sure mine doesn't

 

[Xymordos]

Really? Mine isn't the 2012 version, so it might be different. But many times I left my speakers on while listening to headphones and wondered why my headphones had such massive sound stage...

 

[Chris J]

Quote:

Really? Mine isn't the 2012 version, so it might be different. But many times I left my speakers on while listening to headphones and wondered why my headphones had such massive sound stage...

 
I have the 2011 model, RCAs output sound whether or not headphones are plugged in.
 
But I have noticed that volume drops if I plug a source into input 1 and switch to input 2 when I am also listening to source 1 via my amp & speakers.

 

[Xymordos]

Sorry I didn't really understand what you just wrote :\
I never used both inputs though.

 

[Chris J]

Quote:

Sorry I didn't really understand what you just wrote :\
I never used both inputs though.

 
Maybe I should expand:  my CD player has two outputs.
I send one to my stereo pre-amp
I send the other to my mighty, mighty Matrix M. It is plugged into Input 1. There is nothing plugged into matrix input #2.
When I listen to my CD player thru my stereo pre-amp and switch Matrix to Input 2 the pre-amp volume drops!

 

[Xymordos]

That's really odd o.O. With nothing plugged into input 2, shouldn't it just cut the circuit to the m-Stage?

 

[Chris J]

The sound level coming out of my speakers drops a small amount when I switch the Matrix inputs!

Not the sound coming out of the headphones. The sound coming out of the headphones drops to Zero.

 

[Xymordos]

I would suggest emailing the makers of the m-Stage about this in case it is a sign of a defective product :\

 

[Chris J]

I don't flip the input switch to input #2.
That solves the problem to my satisfaction.

 

[otherlives]

Bought one of these to pair with HD650's.  Seems like there are slightly better choices on the market, but for the price and the fact I needed something that would be a *portable* desk amp that I could throw in my bag and carry between offices I figured this was pretty good.  It looks like the two preferred options for setting up this amp are the LM4562 at 18 gain or the class A biasing 627's?

 

[Xymordos]

I've compared 627sm, 637sm and 49710HA, and I still found that the original 2134PA sounds the best. It just sounds...matching with the amp. The other opamps do give a different sound, but those sounds doesn't seem to be flowing with this amp.

 

[Chris J]

I like the LM4562 with gain on 10 dB, but in the interests of "full disclosure" I should point out that I have deleted the input cap.
I use Q701s with this amp....................90% of the time!

 

[Guess?]

A-class OPA627BP with shunted input caps gives me what I need.