Sansui AU-777A vs all contenders

Discussion in 'Exclusively Sansui' started by smurfer77, Nov 14, 2016.

  1. smurfer77

    smurfer77 AK Subscriber Subscriber

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    Surprised me those little Sony units. Aside from the unobtainium factor of the VFETs it's also worth noting that I did have to play around a bit with the power supply (voltage doubler) and the VFET positions/matching (very different pinch-off voltages, but I have two VFET amps so I could measure and match output devices a bit) to get nice & clean output on the scope. As I says, they are a bit 'specialist' :). Can't wait to get this TA-5650 up and running and see what that does.
     
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  2. smurfer77

    smurfer77 AK Subscriber Subscriber

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    I guess there should be pics of every amp I compare to. Here are some pics of the Sony amp. A bit naughty in the Sansui forum I know :). Notice the "VFET" on the front. Very serviceable as the chassis opens up like a clam with the front and rear tilting. What else... oh there is a voltage doubler on the power supply board that sees some hard work, and it supplies the gate voltages to the VFETs (without any voltage between gate and source they are full throttle). This voltage doubler is a section I will rebuild (I've already seen one hard working cap in the voltage doubler on my other Sony VFET (TA-5650) vent hard).

    [​IMG]

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    I promise I will compare to more Sansui soon, but I am finding it very exciting to find models in other brands to get excited about (I know there are many, but I haven't found many personally, but hey, I'm a Sansui guy!)... but there might be a comparison to a very cool Yamaha CA-1000 soon. This model has come up lately in some other discussion in this forum, with respect to the AU-999 mods as some of the mod adjustments are built in adjustment on the CA-1000. More on that later; actually I'm listening now to the yammy, but the amp is a new purchase and I need to check it over before I do the proper A/B... but I can tell you already it's a serious amp! Can you say "Variable loudness knob!"? (not something I have seen on sansui, but have on pioneer and others too.)
     
    Last edited: Jan 25, 2017
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  3. moefuzz

    moefuzz Active Member

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    I have seen variable loudness way back when.

    The inherent nature of a well designed loudness circuit is usually aimed at rolling off just as our ears inherent frequency response somewhat begins to flatten out at mid decibels. -Something that Sansui did very well.

    It seems to be that variable loudness could easily be used to overly compensate for something our hearing naturally does at moderate volumes.

    By the way, was that a glass cover I saw a few posts back?
    -pure sex


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  4. smurfer77

    smurfer77 AK Subscriber Subscriber

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    Did a fun comparison today. I stacked up the usual rack of AU-777A / AU-9900A / Sony TA-4650 / Eight Deluxe versus my ST-70 with VTA high-gain driver board. It is an amp a built from one of the Bob Latino kits when I first got interested in audio DIY a few years back. Now it is running soviet 6p3-se tubes (a kind of military high plate voltage EL34). The imaging and top and clarity and sparkle of that ST-70 has always been outstanding, but it can't compete on the mids and bass to the sansui units. So today I paired the ST-70 up with a Marantz SC-6 preamp. That sure helped the ST-70 along. Not quite the bass or mids of the AU-777A but very very good, no doubt.

    Oh and my AU-9900A has started having that leaky cap noise.... so listening to it in stock form has come to an end and it get's moved out of the rack and replaced by something else (probably a Yamana CA-1000 I'm working on) for a full recap.

    The news I was hoping to share today was the comparison of my rebuilt AU-777A to a stock unit. I grabbed a very clean one recently.
    [​IMG]
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    It is not mint, but has very minimal signs of use; the best unit I've seen. It is meant to be working properly, so I brought it up and sure enough there was sound on both channels. So I biased it up - all good. But when I went to adjust the main amp centre voltage I can see there is a problem. As you can see, if you inspect the oscilloscope, one channel is not 'pulling' no matter the adjustment... the 'pull' just doesn't turn on. As mentioned, biases up ok, and output transistors have just been pulled and nothing seems bad. So I wont be doing the stock/rebuilt comparison today, and I'm leaving on a work trip for a few days... so it might be the weekend after this when I get to poke around this 777A. The goal is to get this, and another stock AU-777A I have up to spec, and then compare the three; with new motorola output transistors in one of the otherwise stock units.
    [​IMG]

    On a final note, I think this makes it about 5% for the "fully working" amps I've bought to be actually working properly. How do non-technical folk survive?!
     
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  5. moefuzz

    moefuzz Active Member

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    Smurfs,

    How or what would an average owner hear/identify "leaky cap noise"???

    I suspect it would be sawtooth wave whooshing or soft fuzz/static but just speculating as I am more a mechanical kinda guy than an electro-tech. Seems to me it would be saw waves-ish as the capacitor failed to control the sine? But as most of you guys know, Us Mechanical guys tend -more often than not- to use a hammer [​IMG] to determine why something won't work and sometimes it has even helped diagnose things (like my milwaukee cordless drill that I lovingly refer to as planned obsolescence) [​IMG]

    and then there was the time back in the 80's when my cheap car cassette deck ate my favorite un-replace-able tape (it was from a recording studio session) and that cassette deck quickly felt the wrath of my L78-15 Michelin truck tires from the F150. [​IMG]..

    ... That too sounded like sawtooth waves ?

    [​IMG]






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    Last edited: Feb 15, 2017
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  6. moefuzz

    moefuzz Active Member

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    This will be interesting, hopefully you will be able to 'stress' test them...

    I remember seeing articles where they compared amps by running them into clipping then measuring
    the time it took for them to settle back down at just below clipping. Most amps were quick to regain composure under load.

    ...But some amps - transistors do not want to settle back into their groove once you've pushed them over the edge.
    I had a harmen cardboard once that would not come back around unless you reset/turned it off.
    ok, I admit it wasn't HD's best amp but you would think that an amp should sort itself out quickly once you have toned the volume down to 10 or less watts and that thing would not.

    Anyway, it will be interesting to see a comparison of OEM's versus replacements.



    EDIT: My thoughts are that A transistor is only as good as it's ability to remain stable
    before, during and after being pushed to the Edge of the Cliff and Back...






    moe of the north

    :lurk:


    =======================================================

    Sansui is a Hell of a Drug


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    Last edited: Feb 15, 2017
  7. avionic

    avionic " Black Knights" Subscriber

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    Or your favorite 9900Z...:biggrin:
     
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  8. smurfer77

    smurfer77 AK Subscriber Subscriber

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    In this case kind of like an alien yawning or someone opening and closing a rather large creaky door. Failing transistors can sound like that too....
     
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  9. bsandovalb

    bsandovalb AK Subscriber Subscriber

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    Smurfer, what differences do you find (sonically) between the au-777 and au-777a? I havebeen amazed by the little brother (au-505), and eas wondering how each compare against the other in music reproducton.... thanks!
     
  10. smurfer77

    smurfer77 AK Subscriber Subscriber

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    I've been holding of giving comments/comparisons until I'm sure the units I'm listening to are up to spec. I do have an AU-777 but it's got some issues.... but i can tell you it IS going to be very good. in fact it was listening to this 777 in the workshop that made me go ahead and grab a 777A and rebuild it while I fix up the 777. The 505 is an amazing unit, as you probably know, most closely related to the AU-555A. I could easily live with the 505/555-A (they are slightly different but I tend to lump them together)... it has some magic. The 777 variants just have more (for me, and with my speakers at least...). It was the 555A that got me into Sansui in the first place.
     
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  11. GPS16

    GPS16 Active Member

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    Hi Smurfer,

    that's a cracker!!! One of those "difficult to describe, but you know it when you hear it" situations.

    I remember one of the operators at work coming into the Maint Dep and asking if someone could look at the machine she was an operator for. She said it "sounded like a cow". All the engineers laughed but when I got close to the machine it definitely went "Moo"!!!! It turned out to be duff bearings on a cooling fan!!!!

    GPS16
     
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  12. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Will have a 555 non 'a' version in the collection once I get the time to go get it. Still has the original blue film, (one owner unit), over the front panel. After a rebuild will add my thoughts as to its sound as well against the heavy hitters, of course with the stuff lined up for service might be a while and no I do not want to tackle another 9900z anytime soon :)
    -Lee
     
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  13. smurfer77

    smurfer77 AK Subscriber Subscriber

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    I hope you enjoy the regular AU-555. I have tried one, and also listened to my friends and it is my least favourite of the 222/555/777. In fact, it's probably my least favourite AU I've heard. Not saying it was bad, just not amazing like the rest IMO. Also, a bit bass light until you crank it up, and yet not trebly shy, which made it worse. Sounded fine at high volume though - things seemed to balance up in terms of tone. But hey, maybe both units I tried had issues that I didn't know about. (FYI, both were stock)
     
  14. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Weak output coupling caps will cause that for sure, intend to uprate them and replace along with signal transistors and caps before giving it a true listen. Happen to have a nice restored tube receiver to compare it against with Klipsch speakers. Should be interesting to add to the thread once done.
     
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