Thanks for reminding me about my Sansui!!  If I am only going to listen for an hour, I hate to fire up the BA because I hate to turn it off...

Thanks to purrin, I've got caps to put in mine.  This project moves up the ladder!

Any reason you want to use speaker taps with the MadDogs?  They should rock fine from the HPO. 

That's one of the best parts about these vintage amps, they didn't have a separate amp for headphones, the HPO is tapped directly into the big amp.

If you hunt around you can find some speaker tap set ups on-line.  I know Fang sells one: http://hifiman.com/Products/?pid=104

Damn, I can see why people can really get into vintage receivers. The Sansui 5000A sounds great with the Mad Dog 3.2. I wish I had more orthos to try on it. You can tell it's not quite as clean and flat (FR) as some other amps (dedicated headphone amps or not), but there's still something about it that I really like. It sounds surprisingly clear and detailed, smooth, and powerful. Some people have said it's a warm receiver, but I'm not hearing that so much coming from the Leckerton UHA-6S Mk.II.

Out of curiosity, I took some RightMark measurements of the headphone out. Setup went PC with Auzentech Bravura, line out to the Sansui set at 24/96 with volume set at 4 (I believe the Windows volume controls the output voltage, because music clips after a volume of 50 or so, and 50 was too high for RMAA tests), and the Sansui HPO went to the line-in (set at 24/96, 100 volume) of the Auzentech Bravura using the stock T50RP cable.

More simply: Auzentech Bravura line-out -> Sansui 5000A -> Sansui HPO -> Auzentech Bravura line-in

The receiver is plugged straight into the wall. The PC is plugged into a surge protector that is plugged into the wall just above the receiver.

I know this isn't an ideal measurement setup, but I'm just working with what I have.

The first thing I noticed was that the FR was a bit tilted towards the treble with the tone knobs set at 0 according to RightMark. I had to adjust those to make the FR as flat as I could. The channel balance was also off a little bit, so I had to correct for that (I hope that's not a sign that I need to fix or adjust something in the receiver...it was a 0.2-0.5dB difference). Once I got the settings narrowed down as best as I could, I got the following results:

Overall:



FR:



Noise:



THD:



IMD:



DR:



Crosstalk:



IMD + Noise (Swept):



The FR looks worse that in is. There's some roll off at the top and bottom, but it's still relatively small (see the scale). Some of this is also due to my sound card. You can still hear the small differences in the FR when compared against flatter amps, but on its own is nothing to worry about. I'm guessing some vintage receivers weren't designed to be entirely ruler flat like companies focus on today...? I could be wrong. I messed with the tone knobs for a while and could not get a perfectly flat response. I can, however, get the treble response boosted up a bit. My ears just prefer it being toned down a tiny bit.

One thing that I noticed in the measurements was the 60Hz harmonic distortion and noise. I would think I'd hear humming (ground loop?) through the headphones, but they're nearly silent when plugged into the receiver. I get a low amount of hiss if I turn the volume up on the receiver with nothing playing. It could be that the noise and distortion is still too low to really hear, but I'm not sure. Could it be just be a byproduct of how I measured the HPO and not indicative of how a HP would really perform from the receiver? Or perhaps I'd just hear it as less "clarity" in the most heavily affected regions?

Discounting those 60Hz and harmonic spikes, the dynamic range, noise, and THD are at or better than -90dB above 300Hz. I& #039;d say that's pretty good for a 40+ year old receiver! Once you get to the upper mids and treble, it's pretty darn clean. Sounds that way too.

I'd be really curious to see how the Sansui HPO would measure given a proper setup.

All in all, I'm really liking it so far! It's in fantastic condition as well. I'll try to get pics up sometime.

You know, I was wondering that myself. I didn't see anything for it on the front, so I'll have to research that.

Even with the tone settings at 0, the RightMark measurement scale is so small for FR that it's really pretty much neutral either way. I just got it narrowed down a bit better from that is all.

Also, I'm still confused why the HPO's high impedance on the receiver doesn't mess up the sound of the T50RP/Mad Dog like many claim a high output impedance on an amp will do. A lot of the technical electronics talk just sounds like jargon to my ears, but the main problem is that I've seen about 5 different explanations as to why vintage receivers still sound good with certain headphones (seems to be orthos or HPs with flat impedance curves). Many of these explanations seem speculative, and maybe that's just how it is. But I do want to learn more about how amps work with headphones, and this is a particular question I've been wondering about.

That's the idea. Flat impedance curves mean a purely resistive load, meaning your load should be less sensitive to high output impedance. Think of it like you're driving a resistor, and then decide to put a even bigger resistor in series. All you have now is a bigger equivalent resistor. Meaning you might have to turn the volume up a bit to get more power into it, but it shouldn't change it's performance. Unless your amp can't handle the extra power you want from it, but that shouldn't be a problem.

If you were to have a load that wasn't purely resistive, it would be modeled by not just a resistor, but also by some capacitors, inductors, and extra RLC networks in parallel or series. Now if you try to put a resistor in series with that load, it would change the response. Hopefully I haven't just confused you further.