The Mighty AU-X1

[Vintagear]

I also notice how quiet the AU-X1 is, but didn't notice much if any difference in noise 'Jump off' // 'Jump on' with the controls set to 'normal' listening levels in each case. For me there was little or no difference in SQ with the Flat Amp in use (Jump off), or not (Jump on).

Can you try this test with headphones on your X1?

• With the amp power levels close to max, leave the jump switch off and with nothing playing through AUX turn the volume pot to the -10 db (or louder) mark. Do you hear anything at all?
• Then hit the Jump switch and can you detect a difference?

 

[Hyperion]

Unfortunately I can't try this for a while, my X1 is on the bench for a few component upgrades and rework, including the replacement of the last 'old' signal relay located on F-2774 PCB, which of course means dismantling the front of the amplifier. Rest assured I will try the above when it is finished.

 

[slimecity]

Hi guys - hope this hijack is OK - my question is so small that I dont see the point of starting a specific thread for it......

Im going thru and replacing all the zeners in the pre-stages of my X1 to try to diagnose a noise issue in the flat amp board.

The diode labelling for the F2819 flat amp board is a bit confusing. The SM lists D01-04 under "diodes." However the part numbers for these parts is RD6.2E (B) - that reads like a zener to me. This is confirmed by the schematic - which lists these parts with a zener symbol. But again, the actual silk-screening on the board lists these parts with a simple diode symbol - not a zener symbol.

These diodes in the F2819 board are all mounted in parallel with 100uF/10v electro blue caps.

A bit of confirmation from someone who has been here before would be great! thanks experts

 

[Vintagear]

Hi guys - hope this hijack is OK - my question is so small that I dont see the point of starting a specific thread for it......

No worries, I'm sure one of the tech experts will come along shortly and help you out.

Unfortunately I can't try this for a while, my X1 is on the bench for a few component upgrades and rework, including the replacement of the last 'old' signal relay located on F-2774 PCB, which of course means dismantling the front of the amplifier. Rest assured I will try the above when it is finished.

Thanks! Looking forward to it.

Here's what I hear:

• With the amp power levels close to max, leave the jump switch off and with nothing playing through AUX turn the volume pot to the -10 db (or louder) mark. Do you hear anything at all?

I can hear a faint hiss (steady and clean) that sounds normal to me. Much less hiss than other amps I've listened/tested in this manner (especially at that output level). Impressive in my book.

• Then hit the Jump switch and can you detect a difference?

I can hear a clear difference. On this setting suddenly I hear nothing, absolutely nothing. Even at a volume level high enough that my ears would explode if I were playing music. It basically sounds like headphones sound when they are not plugged into the amp at all. I literally mean there is ZERO noise. Amazing in my book.

 

[Multimode]

I agree with you. My 919 doesn't have more or less noise with the jump switch on or off. It does have a little more body (fleshed out) using the preamp (flatamp) section....

Exactly the same for me, and I prefer listening with the Jump switch off for that "more body" reason (good description!).

With the volume control on my (Hyperion reconditioned) AU-919 turned fully up, and Jump and input sources switched off, I can't hear any noise whatsoever unless I put an ear within two inches of either of the speakers' tweeters where I can just make out a very slight and steady murmur. Can't get much quieter than that!

 

[Hyperion]

The diode labelling for the F2819 flat amp board is a bit confusing. The SM lists D01-04 under "diodes." However the part numbers for these parts is RD6.2E (B) - that reads like a zener to me. This is confirmed by the schematic - which lists these parts with a zener symbol. But again, the actual silk-screening on the board lists these parts with a simple diode symbol - not a zener symbol.

Yes they are zeners, and I changed mine for direct (new) replacements. I am guessing my flat amp board is exactly the same as yours and if I noticed the symbol error I didn't pay any attention, because the schematic indications are so definitely requiring zeners in those positions. I am going to be taking a close look at the board sandwiched with the Flat Amp, (i.e. F-2774) so I can change the relay on it, when I do, I'll have a look at those symbols on the Flat Amp F-2819.

 

[Vintagear]

Can't get much quieter than that!

That’s what I would have normally thought but in my experience it does get quieter than that. That’s what is so amazing to me. When I put my ear within two inches of either tweeter with the jump off, like you I hear a faint hiss (I wouldn’t call it a murmur) but if I do the same with the jump on, I hear what I would hear if the amp were turned off- nothing. I’m sure the difference would be even more noticeable with very efficient speakers (>90db).

It’s not that the noise at the tweeter is high with the jump off, on the contrary. It’s much lower than say a restored Sansui 717 and I also found it to be lower than the Reference Class Marantz PM 14S which to me sounds like it has a higher gain structure. So the X1 is already ahead in that respect, but hit the jump switch and it’s game over - this amp is completely silent.

I know that while music is playing these are not huge differences but it’s just an observation on how an amp can go from already super quiet to totally silent. A testament to what they were trying to achieve when they designed this amp.

 

[Multimode]

I've now tried full volume on the AU-919 with Jump engaged. Absolute silence!

for spotting that with the X1, Vintagear, and I'm of course pleased that the down-a-level AU-919 gives the same result.

BTW, I used the word "murmur" earlier so as to try and convey that it was a very low and smooth sound, but I suppose it would have been more correctly described as a very faint hiss.

 

[Vintagear]

I've now tried full volume on the AU-919 with Jump engaged. Absolute silence!

for spotting that with the X1, Vintagear, and I'm of course pleased that the down-a-level AU-919 gives the same result.

BTW, I used the word "murmur" earlier so as to try and convey that it was a very low and smooth sound, but I suppose it would have been more correctly described as a very faint hiss.

That's great! Anyone with one with a restored 919 or X1 should give it a try. Just be sure to raise the volume higher when you use the jump switch to be ensure that you are comparing equivalent SPL. I actually played test tones and tracks to lock down the same SPL dBs with the two settings (Jump Off/ Volume Lower & Jump On/ Volume Higher) so that I knew where to set the volume for each to be sure I was comparing apples to apples.

It would also be great if someone could compare the noise floor of the two settings on a bench .

 

[Multimode]

I understand about making the comparisons at the same SPL dB, however I used the full volume setting for both tests (Jump Off and Jump On) as it was simpler to do and gave the 'worst case' answer.

My thoughts are that the 'same dB' test is primarily for academic interest whereas the 'full volume' test is a quick check for any noise-creating problem within the amplifier.

 

[Vintagear]

I understand about making the comparisons at the same SPL dB, however I used the full volume setting for both tests (Jump Off and Jump On) as it was simpler to do and gave the 'worst case' answer.

My thoughts are that the 'same dB' test is primarily for academic interest whereas the 'full volume' test is a quick check for any noise-creating problem within the amplifier.

I agree that it is simpler to do and will definitely give you the worst case scenario for each setting but I think that method would also give the Jump On setting the clear advantage because it is not amplifying the signal as much and thus will have less noise.

So while that method shows that Jump On is quieter, IMO it doesn’t really confirm that Jump On is quieter than Jump Off at the equivalent output level (which rules out amplification differences and increase in associated noise that comes with higher output) which is what I guess I was getting at.

 

[lbcgav]

Here is a picture of the modification - sorry a bit dark

View attachment 1055568

And another - to give a better view of the connections.
View attachment 1055570

So, you have to cut the track that joins the gate of FET01b to the junction of R43 (2.2Ω) & R44 (20KΩ), then bridge that cut with an added 0.33µF capacitor. Then join the isolated gate pad (of FET01b) to the output of the head amp with an added 1MΩ resistor. (shown sleeved in the above pictures).

For the 0.33µF I used Mouser No: 505-MKP20.33/100/5

Any questions - just ask.

I just did this mod on my AU-919 and it worked perfectly. Thanks again for showing this in such a clear manner that someone with such little electronics knowledge as myself can achieve success.

 

[Ronito6]

I just did this mod on my AU-919 and it worked perfectly. Thanks again for showing this in such a clear manner that someone with such little electronics knowledge as myself can achieve success.

Glad it works!

In the name of clarity and giving credit where it is due.

This mod was created by an engineer in Germany by the name of Martin Kuehne.
Mr Kuehne's initial report http://ftbw.de/xp/amplifier-xp/sansui-au-x1-01.html

In 2015 it was Harolda who found Mr. Kuehne's website where he presents his solutions, and reported it in this thread http://audiokarma.org/forums/index....-output-transistor-replacements.684619/page-4

Hyperion was the first person to suss out Mr. Kuehne's description, and he was the first to show how to do the modification.

All thanks goes to them!

 

[Ronito6]

I just did this mod on my AU-919 and it worked perfectly. Thanks again for showing this in such a clear manner that someone with such little electronics knowledge as myself can achieve success.

I forgot to ask, any pics of your work possible? This modification was designed for the AU-X1's EQ boards. It would be great to see how you applied this modification to an AU-919.

I'm sure many 919 owners would love to see your work, AND you would be the first to show how to do this mod on a 919.

 

[lbcgav]

I forgot to ask, any pics of your work possible? This modification was designed for the AU-X1's EQ boards. It would be great to see how you applied this modification to an AU-919.

I'm sure many 919 owners would love to see your work, AND you would be the first to show how to do this mod on a 919.

Here is the page where I show the work. See posts 85 and 93 for details: http://audiokarma.org/forums/index.php?threads/replacement-filter-caps-for-au-919.831517/page-5

 

[Ronito6]

Here is the page where I show the work. See posts 85 and 93 for details: http://audiokarma.org/forums/index.php?threads/replacement-filter-caps-for-au-919.831517/page-5

Thanks and amazing work at applying that Kuehne mod to your AU-919!!

Another first!

I suspected that the Kuehne modification could work on other amplifiers. Thanks for proving my suspicions correct.

 

[lbcgav]

Thanks and amazing work at applying that Kuehne mod to your AU-919!!

Another first!

I suspected that the Kuehne modification could work on other amplifiers. Thanks for proving my suspicions correct.

Thank you, but any praise really needs to go to Hyperion for clearly showing it on his AU-X1 and confirming that what I was proposing to do on my AU-919 wouldn't ruin it.

 

[slimecity]

I just picked one of the many X1 threads to post this. I have my X1 up and running thanks to Kevzep. The flat amp and driver boards are all go - and all of the amp (except for all the phono boards) have been recapped and sorted. She is sounding absolutely mighty.

So a question - only one of my MM boards has this ceramic on the back. Was the consensus to remove these for improved stability?

thanks!

 

[Hyperion]

Was the consensus to remove these for improved stability?

It was, Mr Kuehne said leaving them in made his example less stable, on reading that, I had no hesitation taking them out of mine.

An extract from his article:
"Obviously, ceramic capacitors between one of the operating voltages and the cooling angles had been retrofitted on the MM modules. After their removal, the continuous oscillation of the final stages was gone with the cover sheet attached."

 

[slimecity]

Good stuff - cheers John