Sansui AU-70 / TU-70 : my first Sansui tube adventure

[smurfer77]

I did get a chance to restuff the phonoboards before work this morning. I thought the phonoboard was one piece until I pulled it out and found them to be two cute dual mono boards. There you can also see the Ge Sony 2SB381 transistors. Looks like someone has been in here before me and replaced a couple of the caps.

I was planning originally to replace the small value caps too (the green guys), but there was an error on the schematic and I don't have all of the parts for now. Anyway, they should be more than fine so those are going to stay for now. FYI the error (or variation) is that my schematic shows a 0.06uF cap, but it is actually 0.006uF. So for now, it's just the electrolytics getting refreshed.

Tonight will reinstall these boards (not a big deal, but there is about 10 wires to makes sure I put in the right place) and see what I have missed elsewhere before doing final tests and putting the unit into service. There might be a couple of small value caps hanging out near front panel pots I missed.

EDIT: when i first tested the phono before recap, one channel was out. There is a switch on the back panel for switching impedance that needed a clean.

 

[smurfer77]

Another, and almost final, status update on the AU-70. I put the phono board back in, which is not that trivial if you aren't good with little fragile signal wires. I did have to fix a couple of the solder tabs on the PCBs that lost connection to the PCB - fortunately I did continuity checks of pins to pcb (and pin-to-pin - hey I make mistakes and those wires are close together!). Phono section is working great. I am not in a rush to replace those Ge transistors as my phono has very little hiss for now.

I replaced the shielded wires that were causing issues around V3 and the hum dropped off. Yet, I still wasn't happy enough with the hum. No matter how I adjusted the relevant hum resistor (the one of the right (looking at underside)), I had to chose between hum on V3 on one side, or a bit of hum upstream before V3 on the other wise. So I actually rewired more of the heater wires (previously I rewired a pair that runs around V3, but there are sets of wires carrying the AC to a tube on each side of V3 too), using common sense for layout and the situation improved. I tried a few different 12AX7 and things improved further (all of the 12ax7 I have a pre 70s so probably have the noisy non-spiral filatment so I'm going to grab a modern one, or a 7025, and see if that helps even further). Basically though, it's now hum free from volume 1 to 8 with tone defeat in or out, when monitored by headphones. I've hooked up to speakers and it seems I need to worry further. And I guess scope says it's in spec in terms of level of hum so I should not torture myself further and just let that last little bit of hum go (and see how the new 12ax7 helps later). (EDIT: now i have it hooked up to speakers in the listening room, the hum is obviously a no-issue, I can use all of the volume pot and don't hear anything from the listening position that is not very far away at all. In fact, even with my ear next to the speakers I don't hear anything until the pot is almost at full!)

I'm not replacing the hum resistors. The existing ones are working great (I used them a lot yesterday!) and have no signs of age. And, the subs I bought will not fit under the hood unless I take a hacksaw to them! Oops.

Only thing remaining is I need to do the power cable strain relief when the part arrives, and tidy up the power cable routing (now it's a bit messy, running across my bias pots). So while I'm waiting for a new V3 and strain relief, I'm announcing this one 'sorted'. So here are some PICS!

Here is a reminder/before-pic of how the unit came to me. Someone had replaced output coupling caps (red/maroon), two power supply caps (blue) and a bunch of little stuff here and there.

And here she is here, 99% finished. Still a bit of a rat's nest, but I'm sure you will agree it is a bit tidier.

Popping the bottom cover back on. I calculated those maximum cap sizes just right!

Okay, you might think the metal finish is a bit ugly, but it's just a healthy patina. Instead of doing my usual aggressive polishing, I was thinking that this amp has survived since the mid 1960s without any sign of the bad sort of oxidation, and didn't want to mess with that too much. So what I've done during the process is bath any metal part in mineral oil. It actually looks pretty cool with it's patina and some oil. I did that treatment on every exposed part/section multiple times over the last year.

The only thing I polished aggressively was the multi-cap cans, which was pretty much mandatory after the effort of restuffing those cans.

In this pic the phono board and preamp covers are on:

Front view and we gradually put her 'clothes' back on:

Putting the cover on:

And a couple of pretty pics to finish off.

Finally did something I have never done before... moved an AU-70 into my listening room. I really didn't want to taint my first impression with an out-of-spec unit. Am doing A/B versus my AU-777A right now as I type. I will post more on that in my AU-777A vs all contenders thread, but guys, I have TINGLES NOW. This is the mid-60s? No wonder this unit (and the AU-111) really installed Sansui as a hi-fi brand. Summary is, it is very very very similar in sound to the rebuilt AU-777A!

 

[_mano]

Well done, beautiful, very clean work.

 

[mozcho]

Used the ultrasonic cleaner on the knobs (and some AU-222 knobs). I actually ran the cleaner for a lot longer than I usually do and some of the black paint on the AU-70 knobs (in the tiny slot, indicating dial position), came off. So in the future I will just do a light ultrasonic (which I've never had trouble with before). Will repaint the slots that have been affected.

Hi Smurfer, ultrasonic cleaner - the one with a water tank to clean vinyl records? How many minutes do you recommend for an operation like this?

 

[mozcho]

I just recently found a blogger's review on some vintage amplifiers from Sansui and Luxman, it has the following praises for the AU-70. In summary, AU-70 excels at vocals and pop and rock music, but poor at classical piano and violin, and other instrumentals (emphasis mine):

"Its complement of tubes visually match many of today’s all-tube amps of the likes of FezzAudio, Unison Research, Manley, and newer competitors like Auris Audio. As I listened to the AU-70, I kept in mind the www.Sansui.us website’s one liner declaration that this kit excelled in vocals to the point where after one session with the Beatles LP or CD on the AU-70, one could never revert to solid state amplifiers ever again. Well, was it true to my ears? It scored roughly 60% on this claim.

I was bowled over with virtually all the vocals I played through it. Since mine were all CD, partial streaming (from Smart Phone via Bluetooth LOGITECH adapter/receiver with RCA connections) sources, the vocals were already rather
well refined in the recording studio. The AU-70 performed an additional miracle on all of them. On smooth jazz vocals of the likes of Nancy Wilson, Jeffrey Osborne, Kenny Lattimore, Frayne, Patti Austin, James Ingram, and Luther Vandross, the soul was reproduced with an added zing to it. Like the solid state Sansuis higher up on the technological rung, this was hard to explain except that the more emotive parts of singing grabbed me in an inexpressible way. When I switched to classic vocals of a Streisand, Karen Carpenter or Michael Buble, the AU-70 showed why it was a classic that has withstood the test of time: each of these singers demonstrated an expressive tinge that was at once intimate and underappreciated before. At some points, listening to great vocalists on the AU-70 beat even sitting in front row concert seats. It was that good! But I noticed I needed to keep the unique ‘presence’ switch on throughout to sustain the intimacy and warmth of the ‘Tubey sound’, while keeping the loudness switch off. I must however warn the reader that to hear this level of potential, I had all the 6AN8 and 12AX7 tubes replaced with mid-budget ones, and kept two of the stock 7189s, while switching two of the remaining 7189s for Mullard versions. I did not dare upgrade the tubes further having spent nearly US$190.00 on recapping and replacing the odd transistors. But the experience proved rewarding especially if one listened to vocals most of the time. What about instrumentals? The AU-70 excelled once again with the highly digitally recorded smooth jazz of the likes of Euge Groove, Everett Harp, Peter White, Joyce Cooling and Kenny G! The digital perfection of saxophones, guitar and booming bass were toned down in a sweet analogue-like manner. In fact I’d say the bass was beautifully rhythmic. If however, you are into classical piano and violin of the likes of Lang Lang, Jeno Jando, Vladimir Horowitz, Anne Sophie Mutter, or Midori, forget about the AU-70. The recordings universally sounded flat and lifeless even with the loudness and presence switches turned on. Mantovani, Paul Mauriat and Ronnie Aldrich sounded almost in limbo between mono and stereo. Instrumentals with lots of percussion recorded before the 1980s fared badly too. So this is a mixed verdict for the AU-70: great for all kinds of vocals and some very contemporary instrumental recordings, and probably will sound great with hard rock and pop as well, but ditch this for other instrumentals. Perhaps I’ll try the AU-111 when I have the funds! Two final operational warnings need to be heeded especially if you intend to acquire the AU-70. It runs very, very hot after just 15 minutes of operation so it is best to take the cover off even in winter indoor conditions, and keep a quite fan or airconditioner turned on during listening. Like all Class A tube amplifiers, there are characteristic light ‘popping’ and ‘ticking’ sounds as the tubes cool down after you power off the set." (https://easylisteninghifi.blogspot.com/2017/12/soundboxes-viii-mighty-little-wonders.html)

His review on AU-111 is of the highest level:
All instrumentals shimmered with a lively edge to them,...
What about the classics? ... Almost every recording has a concert like vibe to it. The AU-111 performed every aria, concerto and minuet effortlessly. If you listen occasionally to sung opera of the likes of Renee Fleming, Katherine Jenkins, or Sumi-Jo, this is the only amplifier you’ll ever need....
The Sansui AU-111 – made for musical preservation forever – and without peer for holographic realism!
(https://easylisteninghifi.blogspot.com/2019/09/soundboxes-xi-want-to-know-what-true.html)

I'd like to know, the OP and others who have compared both the AU-70 and the AU-111, do you feel the same as the above?

 

[mozcho]

Hi, hope to hear some sharing on the above...

 

[GrisPato]

Hi, hope to hear some sharing on the above...

Realise, I don't own or had the privilege to even listen to the AU-70 and AU-111.
So this is generalising comparing equipment.
I, for myself, are really distrustful of reviews that go into extremes about differences when comparing equipment. Especially when, to me it's really contradicting.
An electronic device is not aware of what it is processing/ amplifying!
Taking the review you give, how can an amplifier that sounds so good ( superlatives everywhere) with voices, sound so bad with instruments (piano,violin) that will demand the same quality in reproduction. How can all the dynamics and subtleties of a voice be reproduced but not with a violin?? In the extremes described??
An amplifier is accurate and has its own sound signature in a certain frequency band or not, sure, but not depending on if it's a violin or a guitar or a voice, or even more strange, digital or analogue source material.
This also would be limited to the overall sound signature, more warm signature can balance better with more cold/harsh recordings ( digital!?). But this is not devidable into digital/ analog in absolutes.
Just my opinion, but you asked for one

 

[Sansuiman]

^ one would surmise the quality of the recordings comes into question. Obviously some recordings - irrespective of media - are better mastered than others. That having been said, I also think some reviewers/critics of gear get a bit too caught up in feeling they have to present an extensive word salad of explanation to justify their positions, or risk losing relevance to those who value their proclamations.

After all; a simple statement of "it sounds really good" will not carry much weight. Not when compared to a flowery, descriptive multi-paragraph dissertation on what are really a bunch of subjective impressions dependent in some way on every component in the source and signal chain; the room, and probably even the disposition of the listener on a particular day.

 

[GrisPato]

I also think some reviewers/critics of gear get a bit too caught up in feeling they have to present an extensive word salad of explanation to justify their positions

Just had that same problem this week when an AK member asked me if the AU-D707 I recently restored was better then the AU-719 I restored before.
The thing is, that for me just connecting the amplifier, put on some music, sitting down and listening, it was clear from the first tone it was better. Just the energy of the music communicated alone was enough.
So, then how to tell about that, it's even more a feeling, how the music touches you.
For that I can understand a little the word salads.

 

[Hyperion]

Sometimes when one is comparing two amplifiers one after the other, you know the sources and the speakers are the same. But there is just something about the presentation of one which excites and pleases you more. Sometimes making you want to turn it up a bit, other times directing you to a particular piece of music which you are sure will sound wonderful. It's those kind of 'epiphany moments' that I think we all strive for, you know, the ones that make you want to hear all your favourite music again because of the greater pleasure of listening to it.

 

[GrisPato]

the ones that make you want to hear all your favourite music again because of the greater pleasure of listening to it

Well said, yes!
I have been wondering lately about the influence of restoring amplifiers on the way you judge them and listen to them. I am sure for me it creates a bias towards how you listen, expectations. But it also changes the perspective to a more pragmatic view.
You start to understand what makes the amplifier so you look less for magical properties in the sound, still a little magic there.

 

[_mano]

Simply for me, when the hair on my arms starts to stand up.

 

[smurfer77]

I just recently found a blogger's review on some vintage amplifiers from Sansui and Luxman, it has the following praises for the AU-70. In summary, AU-70 excels at vocals and pop and rock music, but poor at classical piano and violin, and other instrumentals (emphasis mine):

"Its complement of tubes visually match many of today’s all-tube amps of the likes of FezzAudio, Unison Research, Manley, and newer competitors like Auris Audio. As I listened to the AU-70, I kept in mind the www.Sansui.us website’s one liner declaration that this kit excelled in vocals to the point where after one session with the Beatles LP or CD on the AU-70, one could never revert to solid state amplifiers ever again. Well, was it true to my ears? It scored roughly 60% on this claim.

I was bowled over with virtually all the vocals I played through it. Since mine were all CD, partial streaming (from Smart Phone via Bluetooth LOGITECH adapter/receiver with RCA connections) sources, the vocals were already rather
well refined in the recording studio. The AU-70 performed an additional miracle on all of them. On smooth jazz vocals of the likes of Nancy Wilson, Jeffrey Osborne, Kenny Lattimore, Frayne, Patti Austin, James Ingram, and Luther Vandross, the soul was reproduced with an added zing to it. Like the solid state Sansuis higher up on the technological rung, this was hard to explain except that the more emotive parts of singing grabbed me in an inexpressible way. When I switched to classic vocals of a Streisand, Karen Carpenter or Michael Buble, the AU-70 showed why it was a classic that has withstood the test of time: each of these singers demonstrated an expressive tinge that was at once intimate and underappreciated before. At some points, listening to great vocalists on the AU-70 beat even sitting in front row concert seats. It was that good! But I noticed I needed to keep the unique ‘presence’ switch on throughout to sustain the intimacy and warmth of the ‘Tubey sound’, while keeping the loudness switch off. I must however warn the reader that to hear this level of potential, I had all the 6AN8 and 12AX7 tubes replaced with mid-budget ones, and kept two of the stock 7189s, while switching two of the remaining 7189s for Mullard versions. I did not dare upgrade the tubes further having spent nearly US$190.00 on recapping and replacing the odd transistors. But the experience proved rewarding especially if one listened to vocals most of the time. What about instrumentals? The AU-70 excelled once again with the highly digitally recorded smooth jazz of the likes of Euge Groove, Everett Harp, Peter White, Joyce Cooling and Kenny G! The digital perfection of saxophones, guitar and booming bass were toned down in a sweet analogue-like manner. In fact I’d say the bass was beautifully rhythmic. If however, you are into classical piano and violin of the likes of Lang Lang, Jeno Jando, Vladimir Horowitz, Anne Sophie Mutter, or Midori, forget about the AU-70. The recordings universally sounded flat and lifeless even with the loudness and presence switches turned on. Mantovani, Paul Mauriat and Ronnie Aldrich sounded almost in limbo between mono and stereo. Instrumentals with lots of percussion recorded before the 1980s fared badly too. So this is a mixed verdict for the AU-70: great for all kinds of vocals and some very contemporary instrumental recordings, and probably will sound great with hard rock and pop as well, but ditch this for other instrumentals. Perhaps I’ll try the AU-111 when I have the funds! Two final operational warnings need to be heeded especially if you intend to acquire the AU-70. It runs very, very hot after just 15 minutes of operation so it is best to take the cover off even in winter indoor conditions, and keep a quite fan or airconditioner turned on during listening. Like all Class A tube amplifiers, there are characteristic light ‘popping’ and ‘ticking’ sounds as the tubes cool down after you power off the set." (https://easylisteninghifi.blogspot.com/2017/12/soundboxes-viii-mighty-little-wonders.html)

His review on AU-111 is of the highest level:
All instrumentals shimmered with a lively edge to them,...
What about the classics? ... Almost every recording has a concert like vibe to it. The AU-111 performed every aria, concerto and minuet effortlessly. If you listen occasionally to sung opera of the likes of Renee Fleming, Katherine Jenkins, or Sumi-Jo, this is the only amplifier you’ll ever need....
The Sansui AU-111 – made for musical preservation forever – and without peer for holographic realism!
(https://easylisteninghifi.blogspot.com/2019/09/soundboxes-xi-want-to-know-what-true.html)

I'd like to know, the OP and others who have compared both the AU-70 and the AU-111, do you feel the same as the above?

My bullshit meter is going off the chart when I read those comments . Be very careful when reading opinions of others; you don't know their testing conditions, whether they really heard something different or whether the imagined it (which might effectively be a 'real' difference for them, but not for you perhaps).

The AU-70 and AU-111 measure very similarly. To me, in blind A/B tests, they sound similar too. I can tell the difference between them. I might even prefer the AU-70! That's personal taste though, rather than a criticism of the AU-111. But the idea that the AU-70 is good for one type of music but not for another doesn't sound right to me; the AU-70 (and AU-111) have very flat EQ and good dynamic performance.

My opinion. Disregard those things your read. Or at least treat them cautiously, especially when people speak of large differences. They are highly suspicious, and often a result mainly of best personal bias.

Lastly, neither of the amps are class A.

 

[GrisPato]

Nice reply. And my apologies for polluting your thread a little ...
As you say, I don't like to base my opinion on what other people say, especially not when it ends in contradicting extremes.
I do like to hear what you just told us, I nice impression of your listening experience.

 

[mozcho]

Realise, I don't own or had the privilege to even listen to the AU-70 and AU-111.
So this is generalising comparing equipment.
I, for myself, are really distrustful of reviews that go into extremes about differences when comparing equipment. Especially when, to me it's really contradicting.
An electronic device is not aware of what it is processing/ amplifying!
Taking the review you give, how can an amplifier that sounds so good ( superlatives everywhere) with voices, sound so bad with instruments (piano,violin) that will demand the same quality in reproduction. How can all the dynamics and subtleties of a voice be reproduced but not with a violin?? In the extremes described??
An amplifier is accurate and has its own sound signature in a certain frequency band or not, sure, but not depending on if it's a violin or a guitar or a voice, or even more strange, digital or analogue source material.
This also would be limited to the overall sound signature, more warm signature can balance better with more cold/harsh recordings ( digital!?). But this is not devidable into digital/ analog in absolutes.

This made sense.

Just my opinion, but you asked for one

English is not my first language, not sure if I got it right. Those quoted opinions are not mine, I read them somewhere. I have doubts or unsure, I don't know so I asked. I'd like to believe that it's the message that got shot, not the messenger.
I like AK because of the nice community spirit, and the vast pool of collective knowledge available, and, usually I got helpful and friendly tips/advice whenever I asked for help. Maybe this is no exception.

 

[mozcho]

My bullshit meter is going off the chart when I read those comments . Be very careful when reading opinions of others; you don't know their testing conditions, whether they really heard something different or whether the imagined it (which might effectively be a 'real' difference for them, but not for you perhaps).

The AU-70 and AU-111 measure very similarly. To me, in blind A/B tests, they sound similar too. I can tell the difference between them. I might even prefer the AU-70! That's personal taste though, rather than a criticism of the AU-111. But the idea that the AU-70 is good for one type of music but not for another doesn't sound right to me; the AU-70 (and AU-111) have very flat EQ and good dynamic performance.

My opinion. Disregard those things your read. Or at least treat them cautiously, especially when people speak of large differences. They are highly suspicious, and often a result mainly of best personal bias.

Lastly, neither of the amps are class A.

When I first read them, I have doubts but I couldn't be sure because I don't have the AU-111 to compare with, so I asked here as I recall your excellent works on some of the AU series. Thanks for the sharing.

 

[GrisPato]

This made sense.


English is not my first language, not sure if I got it right. Those quoted opinions are not mine, I read them somewhere. I have doubts or unsure, I don't know so I asked. I'd like to believe that it's the message that got shot, not the messenger.
I like AK because of the nice community spirit, and the vast pool of collective knowledge available, and, usually I got helpful and friendly tips/advice whenever I asked for help. Maybe this is no exception.

For shure no shooting messengers !
I think in the end we al read at times the review (listening experience) of other people about equipment that has our interest or which we own and listen to.
The very subjective nature of listening to music will always give us ( at least me ) some need for verification of what we hear or think to hear.
I mean if we are a 100% sure why would we bother with someone else opinion.
So for that reason the reviews you quoted were potentially interesting.
The review just triggered what I have against most, extreme differences. Is like a review I was reading recently, don't now the brand anymore, poweramplier, was so much better than the previous poweramplier of this model at low frequencies.
So I went reading the review of the same reviewer of the previous iteration of this amplifier. Was the best ever low frequency he ever heard. So now this new one put shame to the best he ever heard?
I think they should start using dB for improvement scale. So is it 10 dB better, or 0.01 dB. Because I don't know what they mean with best, better and so forth. For me, the 30 years I have been reading reviews (at times) or the qualifications of private people describing the advance of audio quality and I listen to my Sansui from late '70, early '80 we should be out of this galaxy already, or 1,000,000 Bell in gain of sound quality .
But I like the personal descriptions of people about there equipment.

 

[mozcho]

For shure no shooting messengers !
I think in the end we al read at times the review (listening experience) of other people about equipment that has our interest or which we own and listen to.
The very subjective nature of listening to music will always give us ( at least me ) some need for verification of what we hear or think to hear.
I mean if we are a 100% sure why would we bother with someone else opinion.
So for that reason the reviews you quoted were potentially interesting.
The review just triggered what I have against most, extreme differences. Is like a review I was reading recently, don't now the brand anymore, poweramplier, was so much better than the previous poweramplier of this model at low frequencies.
So I went reading the review of the same reviewer of the previous iteration of this amplifier. Was the best ever low frequency he ever heard. So now this new one put shame to the best he ever heard?
I think they should start using dB for improvement scale. So is it 10 dB better, or 0.01 dB. Because I don't know what they mean with best, better and so forth. For me, the 30 years I have been reading reviews (at times) or the qualifications of private people describing the advance of audio quality and I listen to my Sansui from late '70, early '80 we should be out of this galaxy already, or 1,000,000 Bell in gain of sound quality .
But I like the personal descriptions of people about there equipment.

So true. Reviewer is probably the easiest title to be self-proclaimed, I wish I can have the wisdom to differentiate an opinion or a review. The blend and balance of subjectivity and objectivity makes this hobby so fun and also frustrated at times