[Saraya]

What is the key factor(s) to look for when considering the use of a stereo/speaker purposed amplifier, as a headphone amplifier?
 
I recently came across a Monacor SA-100, and having tested it, it does a good job to the point where I think it's better than my O2 amp.
 
However spec wise (as you can see below) it's not very forth coming with information.
 
Max. power     2 x 50 W_MAX
Stereo 4 Ω      2 x 25 W_RMS
Stereo 8 Ω     2 x 20 W_RMS
InputsPC:   140 mV/46 kΩ
CD:            140 mV/46 kΩ
aux:           140 mV/46 kΩ
player:       140 mV/12 kΩ (high), 25 mV/32 kΩ (low)
 
Frequency range      20-20,000 Hz
S/N ratio>          70 dB
Digital echo  -
Equalizerbass:   ±12 dB
Treble:              ±12 dB
Power supply     230 V˜/50 Hz/150 VA
Admiss. ambient temp.   0-40 °C
 
Connections:
PC: RCA L/R
CD: RCA L/R
aux: RCA L/R
player: 3.5 mm jack
speaker: spring-load. speaker term.
 
Any reasons why I should not continue to use it?

 

[Mr Rick]

  What is the key factor(s) to look for when considering the use of a stereo/speaker purposed amplifier, as a headphone amplifier?
 
I recently came across a Monacor SA-100, and having tested it, it does a good job to the point where I think it's better than my O2 amp.
 
However spec wise (as you can see below) it's not very forth coming with information.
 
Max. power     2 x 50 W_MAX
Stereo 4 Ω      2 x 25 W_RMS
Stereo 8 Ω     2 x 20 W_RMS
InputsPC:   140 mV/46 kΩ
CD:            140 mV/46 kΩ
aux:           140 mV/46 kΩ
player:       140 mV/12 kΩ (high), 25 mV/32 kΩ (low)
 
Frequency range      20-20,000 Hz
S/N ratio>          70 dB
Digital echo  -
Equalizerbass:   ±12 dB
Treble:              ±12 dB
Power supply     230 V˜/50 Hz/150 VA
Admiss. ambient temp.   0-40 °C
 
Connections:
PC: RCA L/R
CD: RCA L/R
aux: RCA L/R
player: 3.5 mm jack
speaker: spring-load. speaker term.
 
Any reasons why I should not continue to use it?

If it sounds good to you no one else's opinion really matters. Enjoy it in good health.

 

[sattech]

 If it sounds good to you no one else's opinion really matters. Enjoy it in good health.

 
+1
 
For 30 years, I've been using the internal Headphone amps in a lot of old Stereo Amplifiers; ROTEL, NAD and Marantz, Pioneer, Technics, Akai etc etc
The power amp section (and spec) is separate circuitry and amplifier topology, which has little to do with what sound you will get from the headphone jack.
With a good PSU and adequate filter caps in that PSU, like Rotel always build, any noise is limited to a minimum.
I think most of those silver face 70s flagship amps use passive switching (you can successfully operate switching selectors and a signal path through all the inputs and outputs without the mains power even connected). Even better if they have a "direct" button for true bypass, tp bypass any unnecessary circuitry, like a lot of Equalizers did then.
 
A lot of 70s and early 80s silver amps have excellent preamp boards in them for Headphone listening, provided you can minimise influence of active circuits (Bass, Treble, Loudness, Subsonic switching, Low/High pass filter switching etc) and get as flat as is possible with that unit.
With Bass and Treble indent potentiometers at 12 o'clock positions and "Loudness" switched off, theoretically, a high end 70s amp should be as "flat" as is possible.
 
It puzzles me why the transistor amps of the mid 70s to early 80s are so overlooked and why so many think that headphones need to be driven exclusively by a dedicated unit. These old beauties are now very cheap and easy to get hold of flagship models that were worth many week's pay back when they sold them.
If one checks out the circuitry, you will often find that pre-1990s models had a fairly good quality dedicated, often powerful and good sounding Headphone capability already on board.
 
Personally, I'm looking to some of the early 80s studio headphone amps, like a Tascam MH-40(B), as they were great.
Specs like these beat running a 300W ROTEL, just for headphones: http://www.manualslib.com/manual/712851/Tascam-Mh-40b.html?page=3#manual
4 channels is overkill, but when one like this shows up at the right price, I will be grabbing one.
 

 
 
Cheers!

 

[sattech]

I just checked out the price and spec of that Monacor SA-100.
http://www.monacor.co.uk/products/prosound-amplifier/vnr/254120/
Never heard one, so I could not possibly say, but maybe you've stumbled onto a winner there.
Maybe you've made a better impedance match for your headphones, as it does not strike me as particularly high end, but like we were saying, if it sounds good to you...
For that amount of money, personally I would be looking to a good quality 70s amp, that cost many times what they sell for now, the engineering inside a lot of those oldies is still up to spec. Picking up an old Luxman or something that was $800-1000 in the 80s, guarantees pretty good engineering and sound!!!
But that's just me...
 
Cheers.

 

[ProtegeManiac]

 
However spec wise (as you can see below) it's not very forth coming with information.
 
Max. power     2 x 50 W_MAX
Stereo 4 Ω      2 x 25 W_RMS
Stereo 8 Ω     2 x 20 W_RMS
InputsPC:   140 mV/46 kΩ
CD:            140 mV/46 kΩ
aux:           140 mV/46 kΩ
player:       140 mV/12 kΩ (high), 25 mV/32 kΩ (low)
 
Frequency range      20-20,000 Hz
S/N ratio>          70 dB
Digital echo  -
Equalizerbass:   ±12 dB
Treble:              ±12 dB
Power supply     230 V˜/50 Hz/150 VA
Admiss. ambient temp.   0-40 °C
 
Connections:
PC: RCA L/R
CD: RCA L/R
aux: RCA L/R
player: 3.5 mm jack
speaker: spring-load. speaker term.

 
That's an understatement - none of those have anything to do with the headphone driver circuit.
 
Quote:

  What is the key factor(s) to look for when considering the use of a stereo/speaker purposed amplifier, as a headphone amplifier?

 

It depends on the circuit but some headphone amps' headphone outputs are basically some kind of separate amplification circuit that isn't very good. Another thing to look out for is the output impedance on the headphone output. I had a NAD304 before and even the auxiliary headphone output on my Marantz CD60 (which might also be a 120ohm output, which is standard back then) was a lot better with my HD600, better (more neutral) than a Little Dot MkII actually. Both equally sucked on my SR225 - and you'd think speaker people who just want to add a headphone for night listening would be OK with Grados, given how they're usually the ones most tossed around speaker forums as a nice option (well, maybe with their iPods). 
 
 
 
Quote:

 
I recently came across a Monacor SA-100, and having tested it, it does a good job to the point where I think it's better than my O2 amp.
---
Any reasons why I should not continue to use it?

 
If it sounds better than your O2 then just keep using it, unless it's too big for where your system is.

 

[Saraya]

Thanks all, good information and appreciate the support. So far it still sounds a bit better on all music types. What I think I might do next is reset any EQ that I have in the audio system and then try again with a direct comparison. My AKG 602 and the O2 never did sound right straight out of the box.
 
 
My concern with using a 'stereo' type amplifier was that it might be dangerous to the headphones. I've noticed that when I turn them off, there's a little pop and then a brief sucking noise in the cans before it goes silent. Also when I have the volume down, there's a faint hiss/buzz when using the Monacor that doesn't exist with the O2. 

 

[ProtegeManiac]

 
My concern with using a 'stereo' type amplifier was that it might be dangerous to the headphones.

 

What? Headphone amps are stereo. You either have surround amps, like HT receivers; stereo for 2ch (which is almost all audio-only applications); or you have mono, like this...

 

 

 
 

 
I've noticed that when I turn them off, there's a little pop and then a brief sucking noise in the cans before it goes silent. Also when I have the volume down, there's a faint hiss/buzz when using the Monacor that doesn't exist with the O2. 

 
Some headphone amps can have the same or similar issues too - the original Schiit Asgard had some kind of turn-on pop on the K701/2 initially for example. Schiit has since fixed that problem.

 

[Saraya]

   

What? Headphone amps are stereo. You either have surround amps, like HT receivers; stereo for 2ch (which is almost all audio-only applications); or you have mono, like this...

 

 

 
 
 

Rather in contrast to 'headphone' amplifiers, like the O2.
 
 
 
 
 

 
 
Some headphone amps can have the same or similar issues too - the original Schiit Asgard had some kind of turn-on pop on the K701/2 initially for example. Schiit has since fixed that problem.

 
Though is it actually a problem to the life span of the headphones?

 

[kramer5150]

plug it in.
 
whichever sounds best is the winner.

 

[ProtegeManiac]

  Rather in contrast to 'headphone' amplifiers, like the O2.

 
They're all stereo; I'd distinguish them with terms like fullsize (speaker) amps, desktop (headphone) amps, portable (battery-powered headphone) amps.
 

 
Though is it actually a problem to the life span of the headphones?

 
Schiit insisted before it won't be that big of a problem, and they added the relay circuit mostly because of the insistence and widespread perception that it would. I don't care either way because I always unplug my headphones before I switch off the amp, then plug it in after switching on (not that my Cantate.2 has that problem, but I really just do that - I might forget to unplug the power strip during a lightning storm for example, and those are frequent here along with blackouts that can render the power strip useless, so in such a scenario at least my headphones aren't attached to anything hooked up to a wall outlet).

 

[Saraya]

I might start doing that then, thanks for the suggestion.