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Sansui Au-a907dr vs Au-d907x

bolero said:
So if I had said "virtual grounds" it would have been correct?
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Since those virtual ground points are joined to the amp ground, they cannot be "separate".
However, if you want to have multiple/separated grounds, so be it.

DB-7 said:
Someone has held things back for far too long!
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No. It's not about revenge or anything. It's just about that the people who are reading around have the right to know that they are reading technically incorrect things that will put them on the wrong path.
Now whether this really concerns or not anyone reading that information, that's another story and not my decision.
That this is not usually happening around here (aka people being told that they are wrong), I also know that very well.
But such attitude really helps nobody, as when it comes to technical things a forum goes up or down by the knowledge level of its members. And troubleshooting amps and other devices is not poetry. Everybody knows this equally well as I do.
I just wanted to raise an alarm signal and that was it. Don't get me wrong, I'm not expecting people to do anything different tomorrow or after 10 years from now.

bolero said:
dual mono power supply design. Whatever that means...
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just google "stereo crosstalk meaning", there is plenty of information available
"In stereo audio reproduction, crosstalk can refer to signal leakage across from one program channel to another, reducing channel separation and stereo imaging." - wikipedia

crosstalk is what's happening in a shared power supply (between L/R channels) due to the finite resistance of the wires (depending on the internal wiring/traces) and the internal impedance of the power supply itself.
dual mono implies that there are separate power supply units for each L and R channels. in other words, no crosstalk which yields better separation.
not a night-and-day difference, if the shared power supply is well engineered. so the effect/size of the benefit for "dual mono" is debatable and depending on each particular implementation

For anybody wanting to learn but fearing formulas and "too many technical details" - then maybe check out this book:
Ethan Winer - The Audio Expert: Everything You Need to Know About Audio

Over & out
 
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rittmaster said:
It seems as though the tone has shifted a bit, but for what it's worth I just purchased the au-d907F Extra, restored unit with 90 day warranty from the seller/technician.

I'll be waiting for shipment notification over the next couple of days.

I also got word that my Thorens should be showing up in the mail before the weekend :rockon:

I appreciate everyone's advice and I'm looking forward to sharing lots of pics when it gets here and impressions after I get everything hooked up.
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Congrats! Cannot wait to see some pictures and read your impressions of that copper clad unicorn!
 
Moderator reminder: posts that are demeaning or insulting to specific users or AK members in general are prohibited by AK rules and will be deleted.
 
fojica said:
Ethan Winer - The Audio Expert: Everything You Need to Know About Audio
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Thanks for this. I've just ordered it. I'm becoming relatively comfortable with the mechanical part of repairing an amp - taking things apart, replacing parts, putting things back together, but I'm far from comfortable with understanding circuitry, reading/understanding a schematic vs. identifying and locating components in a service manual and on the amp, troubleshooting, testing, identifying and locating test points, understanding the working relationship of components to each other on a pcb, etc. Looking forward to any foundational fundamental understanding this may provide as I continue to learn the more technical details. And, as others have said above, I've enjoyed your contributions in the short time I've been around here. Please continue if you're so inclined.

@rittmaster Sorry your thread has been somewhat hijacked by the foregoing philosophical and technical discussions. Rest assured, however, we're all excited for your first (of many!) Sansui acquisition and look forward to its arrival and your upcoming experience and impressions. Let us know and, as always, pics or didn't happen!
 
@fojica that was all just a trick to get you back here posting again, I knew you'd take the bait ;)

good to hear from you again

The poor guy was just asking about differences between those amps: I wasn't directing anyone to do repairs & the concept isn't THAT far off.

All the best
 
There is important technical information that got deleted from this thread, before what is now post #35

"
"voltage supply rails" and "grounds" are different things.

since there are 2 separate voltage supply rails sets (+V/-V per channel), each of them must have that required "virtual ground" formed by the join of those two 6.8k resistors. The requirement for that "virtual ground" comes from the amp topology, as explained in the past.
but then both those virtual ground points are then joined to the "amp ground" - as it's a single ground in that amp (as in many others)
"

plus, without it the flow of conversation doesn't make sense
 
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Happy mail day today!

By the time I was able to take everything out and connect the speaker wires it was already 1030pm here, so I used headphones for my main testing, but all systems seem to be a go!

I tested with a 1khz sine wave, moved all of the dials around and hear no noises at all.

Main volume control is smooth as butter, the switches all have a satisfying chunky click to them. I’m over the moon!

I’ll play some Basie in the morning to see how things really are, and I’ll plan to spend some real sittin’ down time with a nice warmed up amp over the next few days.

Thanks everyone for your tips! I’ll keep this thread posted as I continue to set up (as you can see right now there is nothing in my room haha).

I posted in listening spaces about this too, but I also have the option to set up in a living room type space with a marvelous built-in - the issue is the cabinets are all covered in glass - should I quit this idea while I’m ahead? (Photo attached)

The nice thing about the built-in is it looks like I can put my components on those two main cubbies in the middle without doors (there are also speaker holes cut into them already). Also LP shelves!
 

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rittmaster said:
Happy mail day today!

By the time I was able to take everything out and connect the speaker wires it was already 1030pm here, so I used headphones for my main testing, but all systems seem to be a go!

I tested with a 1khz sine wave, moved all of the dials around and hear no noises at all.

Main volume control is smooth as butter, the switches all have a satisfying chunky click to them. I’m over the moon!

I’ll play some Basie in the morning to see how things really are, and I’ll plan to spend some real sittin’ down time with a nice warmed up amp over the next few days.

Thanks everyone for your tips! I’ll keep this thread posted as I continue to set up (as you can see right now there is nothing in my room haha).

I posted in listening spaces about this too, but I also have the option to set up in a living room type space with a marvelous built-in - the issue is the cabinets are all covered in glass - should I quit this idea while I’m ahead? (Photo attached)

The nice thing about the built-in is it looks like I can put my components on those two main cubbies in the middle without doors (there are also speaker holes cut into them already). Also LP shelves!
Click to expand...

Beauty! And even more impressive to see the AU-D907F Extra in it's native habitat.

My two cents for the listening space options would be the first open room. And maybe you are already aware, but you'll definitely need a rug or rugs and some furniture and or acoustic paneling to quiet the room down. Proper room setup is more important than the equipment. Excuse me if you already know all this.

If you are comfortable taking the cover of the amp off - we'd love to see shots under the hood!

Again - congrats!
 
rittmaster said:
Happy mail day today!

By the time I was able to take everything out and connect the speaker wires it was already 1030pm here, so I used headphones for my main testing, but all systems seem to be a go!

I tested with a 1khz sine wave, moved all of the dials around and hear no noises at all.

Main volume control is smooth as butter, the switches all have a satisfying chunky click to them. I’m over the moon!

I’ll play some Basie in the morning to see how things really are, and I’ll plan to spend some real sittin’ down time with a nice warmed up amp over the next few days.

Thanks everyone for your tips! I’ll keep this thread posted as I continue to set up (as you can see right now there is nothing in my room haha).

I posted in listening spaces about this too, but I also have the option to set up in a living room type space with a marvelous built-in - the issue is the cabinets are all covered in glass - should I quit this idea while I’m ahead? (Photo attached)

The nice thing about the built-in is it looks like I can put my components on those two main cubbies in the middle without doors (there are also speaker holes cut into them already). Also LP shelves!
Click to expand...
Yeah, baby! That was fast - like magic fast! Beautiful amp. Looking forward to seeing your setup come together. What are your speakers?
 
JimEGR said:
Beauty! And even more impressive to see the AU-D907F Extra in it's native habitat.

My two cents for the listening space options would be the first open room. And maybe you are already aware, but you'll definitely need a rug or rugs and some furniture and or acoustic paneling to quiet the room down. Proper room setup is more important than the equipment. Excuse me if you already know all this.

If you are comfortable taking the cover of the amp off - we'd love to see shots under the hood!

Again - congrats!
Click to expand...
Thanks!

Yes, I’m aware of the basics of room treatment. The tricky thing about this first room is the floor is tatami mat which is a huge sound absorber by nature… and the sliding doors are wood, but lined are lined with a paper-like material (I’m not entirely sure what that will do the sound).

If I go with this room I’ll definitely plan on some hard surfaces like small tables and potentially a kotatsu (a table affixed with a blanket and heating element for winter) for a mix of reflection and absorption.

The glass window is covered by more sliders with washi paper. Lots of variables…

I potentially have one more room available to set up in with hard flooring and some shelving (without all of the glass everywhere), but that will depend on how we purpose the rest of the unit.
 
petesui said:
Yeah, baby! That was fast - like magic fast! Beautiful amp. Looking forward to seeing your setup come together. What are your speakers?
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Yeah, baby is right! Shipping domestically here (with the exception of very long distances like Hokkaido or Okinawa) typically only takes two days max from shipment.

I think the seller was very prompt in his packing and shipping - the amp is super, super clean too. I get the feeling the restoration was not very long before it was put up for sale.

The speakers are JBL S2600 ! Domestic market system from 1993-4(??) based on the Everest. They have a sibling S3100 with a larger woofer and different driver, but the 2600’s are much easier to come by and much more affordable.
 

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I’ll see about opening it up after I get things a bit more set up.

For now though, these are from the listing (hopefully it’s the same amp haha).
 

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I’ve had both, worked on both, and compared them back to back. How good one sounds vs the other is critically dependent on their respective conditions. The adjustments and condition of the contact points being especially critical. Recapping becomes a consideration moreso with the D907x depending on its condition and usage history but it could easily be just fine in that regard. At first I thought the Alpha might sound better but as I further dialed in the d907x, the tables turned. I think Petesui ended up with my d907x. It's definitely an amp I would like to revisit once I get through a pile of amps here and find them new homes; I am absolutely buried with Sansui's. In the end, I found the d907x to have the best balance of qualities of all sansui's I've heard. You can't go wrong with it but whoever has / will work on it better know what they are doing or you could be fooled into thinking its not a great amp. I have the alpha 907 MR and it's a magical amp but it really showcases any flaw in the source material. With exquisite material it may be superior in some respects like ultimate detail, resolution, and delicacy in the high frequencies, but it doesn't seem to have much "warmth". I also have the 907F Extra. Superfeedforward is quite a different sound signature and very worth exploring. The realism and naturalness of the sound is unparalleled in the sansui lineup but the highs do come across as slightly soft and muted compared to non SFF designs. Also, the build quality of the F extra has some serious deficiencies; be gentle on that one! I can really hear the difference between the different models and that's why I've pretty much had.....too many of them let's say.
 
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