Author Topic: Sansui Amplifiers (Read 110634 times)

rascal101 · « **Reply #120 on:** Sep 22, 2006 at 10:51 AM »

Ok thanks. Will give it a go.

av_phile1 · « **Reply #121 on:** Sep 22, 2006 at 11:53 AM »

Quote from: JojoD818 on Sep 22, 2006 at 10:43 AM

Biasing your opts higher will guarantee a minimized crossover distortion levels but at the expense of heat dissipation.

Isn't that how they achieve class A-like operation on a push-pull class AB topology?

JojoD818 · « **Reply #122 on:** Sep 22, 2006 at 12:01 PM »

Quote from: av_phile1 on Sep 22, 2006 at 11:53 AM

Isn't that how they achieve class A-like operation on a push-pull class AB topology?

Yes it is. But with the anticipated heat dissipation. so more sinks, heftier tranny, sometimes more opt trannies, etc..

av_phile1 · « **Reply #123 on:** Sep 22, 2006 at 12:26 PM »

So I wouldn't be surprised if the previous owner of the Sansui in question increased the bias for each output transistor. I do recall a colleague from ages ago saying that increasing the idle current up to a certain level without unduly increasing heat beyond what the sinks can handle actually yielded smoother and fuller-bodied sonics. I suppose that would be true if the amp didn't have a good class A/B design to begin with.

Would like to hear your comment on this

http://www.websitetoolbox.com/tool/post/sansui1944/vpost?id=1219919

JojoD818 · « **Reply #124 on:** Sep 22, 2006 at 12:43 PM »

Quote from: av_phile1 on Sep 22, 2006 at 12:26 PM

So I wouldn't be surprised if the previous owner of the Sansui in question increased the bias for each output transistor. I do recall a colleague from ages ago saying that increasing the idle current up to a certain level without unduly increasing heat beyond what the sinks can handle actually yielded smoother and fuller-bodied sonics. I suppose that would be true if the amp didn't have a good class A/B design to begin with.

Would like to hear your comment on this

http://www.websitetoolbox.com/tool/post/sansui1944/vpost?id=1219919

It's true, incresing the idle current would yield better sonics especially if the amp is used in a fairly low level volume, rendering the sound reproduction in pure classA operation. Only when the volume is turned up when it will shift to classB.

I read the link you posted, and the guy's better off increasing the idle current since he said his amp has a huge heatsink and can dissipate the heat.

However, his question of why didn't the manufacturer set it at this position, and instead they set it at a lower current of 36mA per device is simple to asnwer, the manufacturer took into consideration the SOA and secondary breakdown parameters of the opt devices. Raising the opt's idle current also raises it's temp, which in turn derates the device, hence it's available power capability will also be reduced, the opt devices will blow up before the amp can reach peak/full power as advertised. He mentioned C3284/A1303 devices so it's no surprise that the manufacturer had to compromise.

As we all know MOSfets donot suffer from secondary breakdowns and as of the moment, there is only one bipolar transistor that is immune from secondary breakdown and its the Sanken 2SC2922/2SA1216 Silicon Epitaxial Transistors. These Sanken devices are the workhorse of some of the more expensive amps we see now.

av_phile1 · « **Reply #125 on:** Sep 22, 2006 at 02:20 PM »

Thanks for the confirmation of what I suspected.

I would imagine circuit designers in these brands will design their circuits around a given transistor or IC operating traits and optimize their use for the price objective they have to work within. And these are often made with a lot compromises here and there. A well informed or seasned DIYer would know how to lift those compromises and so come out with a modified rig that can be superior in many ways to the commercial orig.

JojoD818 · « **Reply #126 on:** Sep 22, 2006 at 03:29 PM »

Indeed. In fact, our very own Tony here buys every suitable heatsink he can find.

With this in mind, he can design the amp with extra C/W parameters so it can be pushed with a little bit higher idle current and still be able to provide extra power to the load while operating the opt devices within it's SOA.

I bet Tony's heatsink collection is a sight for sore eyes.

Cheers

av_phile1 · « **Reply #127 on:** Sep 22, 2006 at 04:39 PM »

I suggest he look into those water coolant systems used in super-moded Pentium PCs and how they can be applied to power amps. If I recall right, there was an expensive power amp using some sophisticated active cooling system other than typical convection.

JojoD818 · « **Reply #128 on:** Sep 22, 2006 at 04:47 PM »

Quote from: av_phile1 on Sep 22, 2006 at 04:39 PM

I suggest he look into those water coolant systems used in super-moded Pentium PCs and how they can be applied to power amps. If I recall right, there was an expensive power amp using some sophisticated active cooling system other than typical convection.

I see these during the haydays of cpu overclocking.

This could be the answer for those massive ss ClassA power amps, a cool amp to listen to while eating boiled eggs.

Seriously, I have yet to see an inspiration for such a project. Copper or aluminum billets are available which can be machined to provide water holes and the water flow can then be moved by an aquarium pump. Those mini radiators from scooters or those aircon evaporators can also serve as heat radiators. Wow!

av_phile1 · « **Reply #129 on:** Sep 22, 2006 at 06:53 PM »

Yeah, come to think of it, a 3/4 HP aircon is actually no larger or heavier than a Bryston or Perraux power amp. So if you can replace those bullet-proof heatsinks with a compressor motor and heat exchanger for even a 1/2 HP, you can have all the audio freon-cooled muscle while cooling some beer cans beside.

Rather than boiling your eggs on those massive heatsinks.

ATJr. · « **Reply #130 on:** Sep 23, 2006 at 09:55 AM »

Quote from: av_phile1 on Sep 22, 2006 at 06:53 PM

Yeah, come to think of it, a 3/4 HP aircon is actually no larger or heavier than a Bryston or Perraux power amp. So if you can replace those bullet-proof heatsinks with a compressor motor and heat exchanger for even a 1/2 HP, you can have all the audio freon-cooled muscle while cooling some beer cans beside. Rather than boiling your eggs on those massive heatsinks.

looking at the innards of the sansui 907, i'd say it has a freon copper tube with fin fan coolers, amps dating back to the 80's indeed have used this method, i can not now recall what model/s or makes those were...

ATJr. · « **Reply #131 on:** Sep 23, 2006 at 09:58 AM »

jojo,

i just got to hand it to you man,

you not only can make fine amps, but posts theories that are beyond arguing. keep it up....

sebman · « **Reply #132 on:** Sep 30, 2006 at 10:27 AM »

mga sansui gurus.. comment naman sa sansui au70.. oks ba tong vintage amp na to? thanks

sandawa · « **Reply #133 on:** Oct 01, 2006 at 01:56 PM »

I own an AU-70, which was made in 1965 before Sansui produced its classic AU-111 (also valve-based) and before it eventually shifted to solid state amps. The AU-70 is okay for me at low volume -- room level. With 25wpc output, it's not comparable with clean-sounding solid state amps I have. It has not been hooked in a system since 6 months ago for the simple reason I'm not a big tube fan: I have a dozen SS amp-driven systems all over my apartment unit, which to my ears any one sounds better than a system using AU-70. I had Radford and Scott 20 years ago but I prefer good dynamics, clean loud sound, which my tube amps, including the AU-70, couldn't deliver.

But if a good condition AU-70 is sold at P5K, maximum, I'll probaly buy it.

AEL · « **Reply #134 on:** Oct 07, 2006 at 01:04 AM »

Hi,mr.sandawa could you please comment sa sansui solid state receiver model 800 pamana sakin ng erpat ko imagine almost 40 years na gumagana parin paired w/ philips loudspeaker ganda parin tibay kaya partly i disagree na tawagin sansunog coz up to now di nag babago tunog and last thing i also have a 9090DB ang lakas at napakabigat magkano na value compare sa dalawang receiver maraming salamat ,ael

sandawa · « **Reply #135 on:** Oct 07, 2006 at 08:30 AM »

Sorry, I can only comment on gear I am familiar with. I haven't owned a Model 800 but I had a 9090DB (made in 1974 and rated at 125wpc) 25 years ago and it was really a good one. BTW, 9090DB is still selling at a good price in the US, a little less than $300, which is in the same price range as used Dynaco ST-70.

JojoD818 · « **Reply #136 on:** Oct 07, 2006 at 09:47 AM »

Quote from: TonyT on Sep 23, 2006 at 09:58 AM

jojo,

i just got to hand it to you man, you not only can make fine amps, but posts theories that are beyond arguing. keep it up....

tony,

thanks man

, it trully pays to learn from the best...

JojoD818 · « **Reply #137 on:** Oct 07, 2006 at 09:55 AM »

Sandawa,

Sir, may I suggest that you at least run those vintage tube amps once a month to keep the electrolytic caps in good condition. otherwise, if the amp has been shelved for more than 3 months then it may be wise to reform the caps first before operating the unit.

hope it helps...

AEL,

The term "sansunog" was coined when Sansui "radicalized" their design from the more conventional feedback design to their (as they say) "revolutionaly" concept of feedforward.

Most of the amps built before this transistion are made like battle tanks, strong enough to survive a world war. unfortunately, the newer amps have such weakness that a mere oscillation can blow up all the output trannies... hence the term, "sansunog".

Cheers

av_phile1 · « **Reply #138 on:** Oct 07, 2006 at 10:47 AM »

If I recall right, the very first Sansui models using their proprietary super feedforwrd circuits were stable enough and had the unparalled reputation for being the most accurate and neutral of SS amps at that time. I think the models were the AU-D9 and 11 models. With a power bandwidth and frequency response from DC to 300khz, with a deviation of no more that 0.01db at a THD of 0.005%, they were said to be one of the finest SS amps ever produced on earth, not only at that time, but pressumably for ALL time. (In contrast, the current Bryston SST line consdied the finest modern power amp has a freq response startng at 0.5hz to 100khz at 0.007% THD)

It was the succeeding models with "enhanced" super feedforward designs that got into oscillation problems that fried their transistors at the slightest excuse. But still, WHEN they worked, you got the best SS sound possible. And when they didn't work, they were often in the repair shops.

And promptly got the name "sansunog."

AEL · « **Reply #139 on:** Oct 07, 2006 at 02:49 PM »

To sandawa and jojo both of you thanx for the info. now i can say today that i am proud and happy to have this sansui receiver aalagaan ko lalo itong 9090db at 800 salamat uli,ael

sandawa · « **Reply #140 on:** Oct 07, 2006 at 05:16 PM »

I maybe wrong but if I remember correctly, the "Sansunog" term here was coined due to high rate of failure among Sansui amps and receivers that were common at the height of "Saudi days." The early OFWs brought home a lot of Sansui amps and receivers -- models starting with "A" for amps (not AU) and "R" (instead of "G" or "Z") for receivers. Those gear were made as part of component systems and accepted only 8 to 16 ohm speakers (better if used with the prescribed Sansui floorstanding compo units). I myself experienced one such failure, a few weeks after I hooked an AR speaker rated 8 ohms to an A-707 amp. The Audiolab Timog technicians told me later that AR speaker had an effective 6-ohm impedance. Some Sansui/Sansunog owners used Infinity, very popular during those days, rated 4 ohms resulting in breakdowns.

Take note that models A for amps and R for receivers hardly appear in existing Sansui directories, especially those released in Japan. This only shows the Japs sold inferior and cheap Sansui in the international market during those years to corner a good share of the newbie market, especially those who tend to favor "looks" over "sound." The hifi oldtimers here who saw those early component packages would attest how good-looking those systems were.

On the "feedforward technology", I'm not a technician but I've read somewhere it also involves high bias and thus Sansui hardly used class A description in its upscale amps even as most of their good amps run hot. There's only one major documented complaint on oscillation specifically model AU-X1 involving a unit acquired by BeatleFred the former moderator of Sansui forum in Audio Karma and his case spread like wildfire on the Internet. The feedforward technology was generally blamed for it -- the unstable bias or biased to the edge, whatever -- but BeatleFred admitted in his later post in AK and Classic Sansui forums that the unit he complained about seemed to be already defective when sold to him. After some research, the seller of that problematic AU-X1, he concluded, had cases of disposing altered/modified units not only of Sansui's but Accuphase's as well. Take note that Beatle Fred has two AU-X1 units and that he never had a problem with the older one.

BTW, I have an AU-X11, which is almost the same as AU-X1 (except for my unit's wood side panels and a different heat-sink layout.) A friend here in Davao also owns an AU-X11. That model does run hot, like class A, but we never had a problem with it.

scofield · « **Reply #141 on:** Oct 07, 2006 at 07:12 PM »

Yung sansui A-5 ko pala "sansunog"? hehehehe bigay nga sakin ng uncle ko ito, saudi boy yun nung araw. kaya rin pala nahihirapan ako hanapin yung sa net ang specs nya.

pero ok naman hindi pa naman nasusunog, mas maganda pa tumunog kesa sa receiver ko in stereo setup. nakakabit ito ngaun sa infinity primus line speaker.

JojoD818 · « **Reply #142 on:** Oct 08, 2006 at 09:58 AM »

Gentlemen,

Let's not forget that oscillation problems in a power amp can also be caused by conditions other than it's design topology. When conditions are right for an oscillation to occur, then all hell break's loose.

Sansui Power amps has been a part of the colorful history of home hi-fi, let us not concentrate and burden ourselves with such problems. If your particular model is working fine then you should consider yourself lucky that you have experienced a better part of audio history and most of all - enjoy your Sansui Amplifiers.

Cheers

ATJr. · « **Reply #143 on:** Oct 09, 2006 at 10:12 AM »

re: feedforward technology

this was brought about by the fact the at high frequencies, there is a delay in the negative feedback circuit , error voltage from the output ciruit arrives a bit late to the input stage negating its usefulnes, and so to address this issue, feedback from the output is cutoff at high frequencies and instead taken from and earlier stage other than the output, say VAS of first predriver stage, where the transistors used are faster than those of the ouput stage.

prof. leach adopted this in his 4.5 version of the leach low-tim amp and likewise the latest iteration of his super leach amps all because accroding to him it made sense...

re: SANSUNOG,

saudi amps when used sensibly can last a long time, the problem is with the users who do not know any better and went on abusing the poor amps! since many replacement parts available in raon were of dubious quality and more often fakes, repairs can sometimes become a nightmare. that is why the term sansunog.

parasmi · « **Reply #144 on:** Oct 20, 2006 at 07:48 PM »

check this out

this is as mint as it can get

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=320037783300

and the mother of them all...AK guys drooled at this one

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=150024175595

karipas · « **Reply #145 on:** Feb 26, 2007 at 11:34 AM »

Quote from: karipas on Sep 13, 2006 at 08:55 PM

Hi Sir, I have the same problem with my amp a Sansui AU Alpha 707, from what I know, this is a result of the circuit protection unit activating because it senses something wrong in the amp to avert further damage.

"Mga masters" can you help us on the most probable cause of this problem, my amp stops after I played a few songs.

Thanks.

Hello Sirs: Sandawa, Av_phile, Tony and all,

Finally I had my Sansui repaired, I returned it to the pier and told them that I got the amp from them 3 years ago, after 2 days the amp was repaired. According to the technician he just replaced a malfunctioning transistor at the pre-amp section. I paid 350 pesos for the repair, I think I was charged too much for a small transistors but I was happy with my amp working again.

Thank you all for the advises.

Below you can see the happy amp:

ATJr. · « **Reply #146 on:** Feb 26, 2007 at 12:10 PM »

pwede na ibenta yan, then get yourself an onkyo or a pioneer para maiba naman ang experience...

karipas · « **Reply #147 on:** Feb 26, 2007 at 03:30 PM »

Sir Tony,

Thanks. Actually I sold my Onkyo Integra to a colleague (who is also one happy owner of that amp till today) to get this amp because I do not have enough funds at that time but should I come across again with an Integra (817 RX) of the same condition of my previous amp I will surely buy it....as it was my first amp then and actually that is how the surplus amp thread of akyatbundok started.

OT, Sometimes we joke that because of him its difficult now for us to look for gems at the pier but on the otherhand we know for a fact that he helped a lot of people by him starting the thread especially for people like me at that time was starting the hobby.

ATJr. · « **Reply #148 on:** Feb 26, 2007 at 08:49 PM »

you can also try those shops in cubao along aurora blvd. near isetan...

dana · « **Reply #149 on:** Feb 27, 2007 at 09:29 AM »

OT:

Sir TONY...paistorbo, sent u a pm...tnx