[Greenears]

  A pair of preamps for level matching are needed too. You can usually find inexpensive used ones on eBay. It helps to get the same make and model.

I don't mind doing that but I was hoping the sources would have volume controls and I could use that to adjust the levels.  Otherwise they will say something like "your pre-amp colored the sound and invalidated the test"   Sources and DACs are a big part of the test for me, as well as speakers.  However I think I have a reference source with volume control, the problem is how to get material onto the second source.

 

[bigshot]

Not all sources have adjustable line out levels. If you are using a preamp as a switcher, it will use the same volume for both.
 
It's no trick to make an audibly transparent preamp. You can get tons of them at ebay for around $30 or less.

 

[Don Hills]

...  
It's no trick to make an audibly transparent preamp. You can get tons of them at ebay for around $30 or less.

 
The hard part is determining which of them are audibly transparent, short of buying them all and testing them.

 

[bigshot]

I have yet to find a solid state preamp that isn't audibly transparent. It's very simple to determine. You take two preamps and feed the same signal into them. Level match and switch. If there is no difference between them, you are good to go.

 

[Greenears]

OK, so let me summarize to see if I got it right.  If I want to compare two power amplifiers A/B, I bring in my 2 preamps, use a Y cable to feed the two preamps, then each preamp into each power amp being tested, then into an A/B switch into one set of speakers.  I guess it's not a great example since power amps should be unit gain on the voltage out, but anyway just in case there is attenuation you use your SPL meter to calibrate both sides to the same volume.
 
To be double blind, I guess you need a second disinterested party to do the switching, and purposely randomize it. 
 
Is that the gist of it?

 

[bigshot]

Comparing two power amps would involve putting a switch box between the amps and the speakers. For comparing headphone amps, you would switch between the headphone output. Comparing sources would mean taking the two outputs into a preamp to balance the line level, then into your power amp and switch there. It all depends on what you are comparing.

 

[Greenears]

Right ... so I guess you are saying an A/B switch and 2 preamps is enough to put any gear in the chain under test.  My only question is about Y cable on an output, like say when you sending a single source into two devices.  Won't the naysayers say that negates the test?  I ask because it is not so common to find two matched sources you can test easily, like say two high end CD players.  If I'm testing something downstream best to take the source out the equation.

 

[Rajikaru]

   
Please recommend the names of these items (SPL meter and A/B switch) and generally where I can get them.  I already know I'm in for a bit of an odyssey since audio stores are not set up to enable A-B comparisons ... surprise surprise.  But I think A-B testing is doable with some perseverance.

 

 
Here's what I use - it's an Extech 407730 meter. There are more expensive and accurate type 2 (or type 1) meters available, meant for industrial/lab use. But for checking the relative volume between two amps out of a headphone, I think this does just fine. I just take several readings back and forth with a noise track to be reasonably confident the levels are matched. 
 

 
In case anyone was wondering about the green light in background of the above image, I'm listening to this unannounced portable amp (minus the front panels) right now. Linkin Park's Papercut sounds so satisfyingly fast and furious on my Audio-Technicas (It's been a long day at work hahaha.)
 
No idea what the amp is going to be called eventually, but right now, I'm calling it the Objective 2's Baby . 

 

[stv014]

It might be more reliable to measure the voltage (while playing a test tone) on the headphones with a splitter and a multimeter. Or just the unloaded amplifier output voltage when sources are compared.

 

[Rajikaru]

  It might be more reliable to measure the voltage (while playing a test tone) on the headphones with a splitter and a multimeter. Or just the unloaded amplifier output voltage when sources are compared.

 
That would be the most accurate method. 
 
Is there a specific multimeter you would recommend for measuring output voltage and output impedance? 

 

[bigshot]

Accuracy can be a rabbit hole. You have to keep perspective on *why* you're doing the test in the first place. It isn't to get accurate abstract measurements. It's to determine the effect something has on listening to music on your system. If you want to precisely measure a subtle difference, that can be very complicated and involved. But it isn't a heck of a lot of work to quickly patch two things into a switcher, do a ballpark level match and determine that the difference doesn't amount to a hill of beans.
 
Most audiophiles who sweat "the last 1%" haven't even taken the time to address the broad strokes issues yet. It's best to work from the biggest issues down to the smallest. If you do it the other way around, you'll find that you're wasting your time on things that wouldn't even exist if you had simply addressed the large scale issues first.

 

[Joe Bloggs]

When it comes to headphones, I think it would be simpler to take it as given that an entry level source, DAC and amp of adequate power will be able to drive your headphones transparently and move on to choosing your headphones... (or shaping them, as I do )

If it's a matter of loudspeakers, invest in sound treatment at the first reflection points and then a flagship AV amp that has sophisticated loudspeaker calibration, eg Audyssey XT32.

My humble opinion is you're usually up a certain creek without a paddle if you're having to depend on the different sound "signatures" of different boutique source components to make or break your audio experience. If you need to change the sound of your music, change it for real (using DSP).

 

[bigshot]

I'm with you 100% on all those points.

 

[NLNH]

subbed 

 

 

[bigshot]

Welcome to the party, NLNH.