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AU-517 vs AU-719 - a post-recap comparison

scottrt said:
The size and type of the main bypass caps will affect the sound: I really don't think increasing the value of the main filter caps has much if any affect. The Quality of the main cap would... that's why i stick with the Nichicon Gold Tunes whenever possible.
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I'm certainly leaning towards the Gold Tunes or some BHC caps. The BHCs have worked brilliantly in other amps that I have done, and they have much better longevity specs than most of the other caps out there (Eg. 16,000 - 26,000hrs vs 1,000 - 3,000hrs). They are very robust caps that just happen to sound great too.
 
About the AU-719 NOS driver boards. I bought them some time ago and also noticed the differences. As it turned out it's not a mistake, Sansui changed them for a reason.
Steph (steph_tsf), a guy from diyAudio forum was kind to explain it to me.

"The AU-719 schematic is a beauty, conceived in the golden age of audio amplification.

Don't worry too much about R1 becoming smaller. This may provide a tenth of decibel improvement in the signal/noise ratio when using the tone defeat feature, when the volume pot is at -6 dB.

Don't worry too much about R2 becoming smaller. The effect is to marginally extend the frequency in the ultrasonic range range and also marginally releasing the slew-rate limit that such low pass filter is introducing.

The change in the "diamond" resistors is more important. It looks like a typo error, with a permutation of their values. The bigger R20, R21, R23, R24 they are, the smaller becomes the differential "diamond" gain and the smaller becomes the "diamond" bias current. The other resistor, R22 changing from 150 ohm to 22 ohm, is to keep the "diamond" bias the same, after such dramatic differential "diamond" gain decrease. Maybe, they did it for improving the linearity at the expense of open-loop gain, following Matti Otala researches.

Worth having a look are R29 and R33. They remain unchanged ? I'm asking this because increasing them is also decreasing the open-loop gain. And also decreasing the driver quiescent current."
 
addr said:
About the AU-719 NOS driver boards. I bought them some time ago and also noticed the differences. As it turned out it's not a mistake, Sansui changed them for a reason.
Steph (steph_tsf), a guy from diyAudio forum was kind to explain it to me.

"The AU-719 schematic is a beauty, conceived in the golden age of audio amplification.

Don't worry too much about R1 becoming smaller. This may provide a tenth of decibel improvement in the signal/noise ratio when using the tone defeat feature, when the volume pot is at -6 dB.

Don't worry too much about R2 becoming smaller. The effect is to marginally extend the frequency in the ultrasonic range range and also marginally releasing the slew-rate limit that such low pass filter is introducing.

The change in the "diamond" resistors is more important. It looks like a typo error, with a permutation of their values. The bigger R20, R21, R23, R24 they are, the smaller becomes the differential "diamond" gain and the smaller becomes the "diamond" bias current. The other resistor, R22 changing from 150 ohm to 22 ohm, is to keep the "diamond" bias the same, after such dramatic differential "diamond" gain decrease. Maybe, they did it for improving the linearity at the expense of open-loop gain, following Matti Otala researches.

Worth having a look are R29 and R33. They remain unchanged ? I'm asking this because increasing them is also decreasing the open-loop gain. And also decreasing the driver quiescent current."
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Very informative information, thanks for posting.

R29 and R33 were unchanged at 120 ohm. The other differences were in R06 - 560 ohm in the original, 820 ohm in the new, and R14, 82 ohm in the original, and 420 ohm in the new. Also in the old, R43 was made up of two 56 ohm in series (112 ohm), and in the new one 120 ohm was used (schematic shows a single 120 ohm).

A question..... should both boards be bought up to the "new" resistor arrangement (currently both are as per the original arrangement that agrees with the schematic).

Edit.... the difference in gain betwen the "old" and "new" boards was approx 10db.

Cheers

John
 
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rasenthiran said:
Pete,

Do you use extra fan for cooling purpose for your AU 719??
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I do have a thin 160mm diameter fan which I have sitting on the amp above the driver boards. If I'm ever driving the amp hard when the room temperature is high (my Dynaudios are 4 ohm impedance) I sometimes use the fan. This is mainly because there is not a lot of space inside my entertainment unit, and if my sons/nieces/friend's children are visiting, the glass door stays closed. This limits air circulation. The fan helps massively in this situation. It's a low speed, slow flowing fan which helps the natural circulation of air through the amp via the normal convection process.
 
Thanks for the info Pete,I am using a blower fan but i had to place above the upper casing of the AU 719,It is located directly above both the AU 719 transformers,One of my friend said the vibration of the fan can caused difference in the sound quality which i am not sure..,You have any idea on this,The fan produce very low noise,but i am puzzled about vibration that can effect sound quality.
 
Generally-speaking, solid-state amps are not microphonic. Valve amps can have noise issues due to vibration though. How much vibration does your fan create? My fan creates minimal vibration and certainly has no adverse impact on sound quality.

Some might say that a fan placed in close proximity to the amp will cause electromagnetic interference. I haven't experienced any issues such as this.

Regarding your fan placement, the source of heat is generally the large heatsinks associated with the output transistors, rather than the transformers. You'd be best to try and circulate air over/through the heatinks rather than the transformers.
 
Nice post Pete-Mac, and I think a good comparison.
I'm running the 717 with a TU 919 in the dining room, it's a good combination.:music:
Nice pictures too. I suck at pictures.:tears:
 
I thought EPI was talking about the driver board differences :scratch2: I must admit I thought 10dB sounds like a big gain difference.

Question is, what is "bone stock" as both flavours of driver board appear to be valid, although different. :scratch2::scratch2:

I think we will have to wait for EPI... so its W&S :D
 
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Hyperion said:
I thought EPI was talking about the driver board differences :scratch2: I must admit I thought 10dB sounds like a big gain difference.

Question is, what is "bone stock" as both flavours of driver board appear to be valid, although different. :scratch2::scratch2:

I think we will have to wait for EPI... so its W&S :D
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I was talking about the driver board differences....because although mine is 90wpc...the au-9500 is much louder..and if I can pump up the db that would be superb....is this what you are saying?
 
EPI-Center said:
I was talking about the driver board differences....because although mine is 90wpc...the au-9500 is much louder..and if I can pump up the db that would be superb....is this what you are saying?
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Yep - but other than the driver board differences - which, unless your boards have been changed, or worked on to make the changes, I can't explain the difference you are noticing with your '719 vs '9500 - sorry. (unless you are under-driving your '719)

(for those who haven't 'fallen in' yet 'W&S' means Wait and See ! :smoke:)
 
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hi

Is there any way to address the glue problem for AU 719 without recapping?My AU 719 is still orginal and sounds good with no issue.

Thanks
 
Hi Bob,

I thought it shares the same issue since its from the same era,Does AU 719 have this glue problem??

Pete may be you can share some information since you have just recapped your AU 719,

Thanks
 
My 1980 vintage AU-719 doesn't have a drop of glue on any board or anywhere else inside. Maybe they stopped "gluing" after a certain date ? :scratch2:
 
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My 719 certainly has (or had!) the nasty glue.

I might check the serial number on the rear to see when it was built, and maybe we can all compare against each other.

I get the feeling that the early models had the glue and the late models did not, but we can confirm this soon.

The only way to remove the glue is to physically scrape it off the boards. To do this properly, you need to remove the caps which are being held in place by the glue. There are no other short-cuts for undertaking this process unfortunately :(
 
Second the statement on glue being in the 719 at one time as Tom's unit had it on the boards.
 
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