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 Post subject: Sansui 3000/3000A upgrade driver boards
PostPosted: Jun Thu 21, 2012 6:46 am 
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Joined: Jun Thu 21, 2012 5:37 am
Posts: 15
Hello all,

For the last several months, I've been developing an upgrade driver board for the Sansui 3000/3000A receivers.

I won't go into detail, as that has been done many times, many places, including on antiqueradios.com, about that units infamous problems with thermal and DC drift. Those issues are near legendary. Having worked as a tech, between school stints, for a Sansui service center in the early '70s, I got a chance to listen to them after they had been fully and properly serviced and was always impressed with how good they sounded, especially right before they started a fire in any connected woofers! I also installed a number of Sansuis coupling capacitor retrofits and was saddened by the loss of performance, even though reliability was immeasurably improved by them.

Fast forward to 2011. One day while in a contemplative mood, perhaps in the throne room, I decided there was no reason why those receivers couldn't be updated, where they needed it, to become the product those old time Sansui engineers and management people always wanted them to be. I've been custom building audio equipment for installations for years, including amplifier, signal processors, speaker system arrays, etc. I had all of the tools. I had the skills. "We have the technology!".

I didn't want to make this a half baked perf board thingie, so I proceeded as I would for any commissioned development project, with the exception that it would be on my dime right up until I had product to peddle, which I do not have, at this time. (So, this can't be an advertisement! When I actually have something to sell, I will follow the proper procedures.)

Step 1:
Model the concept in X-Spice (Altium 2009).
Step 2:
Change mind and start over with different concept.
Step 3:
Get (2nd version) it to simulate with desired results.
Step 4:
Layout PCB (again in Altium 2009)
Step 5:
Make PCB on my CNC engraver. Stuff PCB. Install PCB in test 3000. Make changes needed to make it work. Make more changes so it won't blow up. Fix unexpected thermal consequences of circuit that provided DC stability. Sheesh!
Step 6:
Change PCB layout and make 2nd PCB prototype. Stuff and install PCB. Much better, except it motorboats. Damn! Cure is to change a couple of transistors (different package requiring change in PCB layout) and adding a bit of local NFB (more changes to PCB). However, kludging changes onto PCB #2 fixed its issues. This unit went into the listening room and survived the 24 hour "burn in" driving my Infinity RS2.5s, which are an impedance nightmare.
Step6.5:
Be blown away by sound of unit.
I did not expect the results to be this good!
Here's where I describe the new circuitry. The new board incorporates a servo amplifier that locks the output to 0 Volts DC (+- 5mV). It has thermal compensation for all of its on board parts and a thermal sensing transistor that is cabled to, and bolted on, the heat sink, which eliminates output transistor thermal run away. The surprising sonic performance comes in because of my decision to retain the original pre driver board, including the driver transformer. The new driver board reduces the load on the driver transformer, and thus the load reflected back onto the class A driver transistor, cleaning up that stage a bit as well as extending its response range. The major factor, I believe, was configuring the output as a current, rather than a voltage source. Virtually all of the great classic tube amplifiers were current sources and most of the speakers from that era, and through the mid '60s, were designed expecting that kind of drive. These amplifiers typically had damping factors in the 20s. Modern amplifiers have damping that is one or even two magnitudes above that. Speakers designed specifically for a highly damped (very low output impedance) amplifier sound great with them. Many speakers, especially older "classic" ones, were not and do not.
Step 7:
Changed PCB layout and made PCB #3 (production prototype), stuff and install in 3000. Take pictures at every step and document. Installation guider is being written based on this step.
Step 8:
Complete documentation, order boards and assemble kits.
I'm almost halfway through this step. Boards are ordered. Assembly procedures are still to be determined. Assembly guide is about 50% complete.

When Step 8 is complete, and I know what sort of costs I'm dealing with, I'll post a notice of availability on the sellers forum. There is a thread on this over on audiokarma.com that has been running for a while, if anyone is curious to learn more.

Thomas Garson
Aural Technology, Ashland, OR


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 Post subject: Re: Sansui 3000/3000A upgrade driver boards
PostPosted: Jun Thu 21, 2012 8:25 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11805
Location: Powell River BC Canada
Good luck with your project.

It would be nice to see a full run of IHF tests on the new circuit
along side the same run on the original Sansui version.

Will your damping factor test be done at full power?
Attachment:
Sansui 3000 from book 099.jpg
Sansui 3000 from book 099.jpg [ 185.82 KiB | Viewed 3677 times ]

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VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
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 Post subject: Re: Sansui 3000/3000A upgrade driver boards
PostPosted: Jun Thu 21, 2012 9:53 am 
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Joined: Jun Thu 21, 2012 5:37 am
Posts: 15
I'm unaware of any IHF specifications ever published by Sansui for the 3000 or 3000A.
The only published value I've seen is a very vague 0.8%THD with no qualifiers. I suspect that figure was measured at 1kHz for 48 Watts into 8 Ohms.

Typical harmonic distortion performance with my driver board can be expected to be about 0.3% from 20 Hz to around 5kHz, gently rising to 0.8% at 20kHz.
The THD content is predominantly 2nd harmonic, as long as you stay below clipping, of course. The driver transformer does factor into the measurable performance and sound of the amp, which is what i expected, and wanted to retain.

I'm not promoting this conversion as turning a Sansui 3000 into a Krell. That's the last thing on earth I want to do and it isn't possible, anyway. My goal, realized in a slightly different way than anticipated, was to fix the inherent defects in the amplifier design of the 3000 without substantially changing its fundamental characteristics. After all, sterile sounding solid state amps are everywhere, and cheap. Why turn a vintage piece like a 3000 into something that sounds like the hohum 80s.

Damping factor:
Specified for 50Hz:
Rout=(Vunloaded/Vloaded-1)*Rload
DF=8/Rout

I typically determine what the output current would be for full power into a normal load, in this case 8 Ohms., which works out to 2.45 Amps r.m.s for 48 Watts.
In order to not abuse the outputs, enter into limiting or trigger protection, I load the output with the absolute minimum reasonable load, which for a 3000A, I would use 2 Ohms, and drive it, in this case, until I reach a current of 2.45 Amps r.m.s., which works out to 4.9 Volts r.m.s.
I unload the amplifier and note the changed output voltage.
Plugging in the values for the voltages and the known load resistor to the equations stated above, we can calculate the output impedance and damping factor for operation at rated current, which in my mind is a more valid measure.
For example, if the amplifiers voltage, in this case, rose to 6 Volts unloaded, the damping factor would be 20 for 2.45 Amps at 50Hz.
These are hypothetical numbers. I have not yet, but will, measure and publish, the DF of my modified 3000.

TG


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 Post subject: Re: Sansui 3000/3000A upgrade driver boards
PostPosted: Feb Sun 17, 2019 11:54 pm 
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Joined: Feb Sun 17, 2019 11:30 pm
Posts: 1
So, what happened? Is there a board or boards available to make the Sansui 3000A safe and good sounding?


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 Post subject: Re: Sansui 3000/3000A upgrade driver boards
PostPosted: Feb Mon 18, 2019 6:06 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11805
Location: Powell River BC Canada
The 3000 Sansui set speakers on fire.

Whatever you do with with one today, put a 1000 uFd capacitor in series with the speaker
output.

We sold the 3000 Sansui . I worked fine for for a long period. Then trouble started.

So Sansui issued a kit with capacitors and a bracket.

And here we are 50 years later.
Attachment:
Sansui 3000A specs.jpg
Sansui 3000A specs.jpg [ 104.19 KiB | Viewed 1366 times ]

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de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Sansui 3000/3000A upgrade driver boards
PostPosted: Feb Mon 18, 2019 8:27 am 
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Joined: Jun Thu 21, 2012 5:37 am
Posts: 15
If you don't care about the loss in sonic performance of your 3000A, go ahead and install output capacitors.
Make sure the capacitors are non polar, though, or use a pair of 2200uF in series, connected nose to nose for each channel.
They should be low ESR/low impedance types, not general purpose.
It will still overheat with inadequate ventilation as there is no thermal feedback to the driver circuit from the output heatsink.
It also will still not like 4 Ohms loads.

Don't get me wrong, I have great affinity for the 3000A. It was a landmark product for Japanese hifi, warts and all. There were a few serious gotchas in its electronic design, which my mods correct, making a thus altered 3000A a very worthy performer with the high efficiency (now very vintage) loudspeakers with which it was originally intended to be used. I have sold and shipped my modified 3000A units as far as Australia to like minded individuals.

TG


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 Post subject: Re: Sansui 3000/3000A upgrade driver boards
PostPosted: Feb Mon 18, 2019 4:30 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11805
Location: Powell River BC Canada
The model 3000 Sansui was direct coupled with no capacitors in the speaker leads. Solid
state amplifiers with capacitors coupling to output do not use non polarized types.

The requirement is the polarity be connected such that the voltage at the center
of the stack connects to the correct capacitor terminal.

Here is a couple of examples from back then.
Attachment:
Sansuit Green OTL theory.jpg
Sansuit Green OTL theory.jpg [ 52.28 KiB | Viewed 1346 times ]


Attachment:
Sansui green 5000X output.jpg
Sansui green 5000X output.jpg [ 148.93 KiB | Viewed 1346 times ]

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de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Sansui 3000/3000A upgrade driver boards
PostPosted: Feb Mon 18, 2019 5:38 pm 
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Joined: Jun Thu 21, 2012 5:37 am
Posts: 15
Sigh, the reason for non polar capacitors is that if the 3000A output is in good working order and properly adjusted, there is no DC voltage offset to provide bias for a normal (polarized) electrolytic capacitor.
The capacitor is to protect the speaker and outputs in the inevitable circumstance where the output voltage substantially drifts off of zero.
Which way that will go is entirely unpredictable, hence needing the capacitor to work with either polarity bias.
If you have access to the Sansui docs that came with the capacitor kit, read them. They attempt to explain this.
Don't take my word for it. Ask any EE, electronics tech or experienced ham (Ham in the classic sense of the word, not just any person who can afford to buy a radio and can fill out a license application.)

TG


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 Post subject: Re: Sansui 3000/3000A upgrade driver boards
PostPosted: Feb Mon 18, 2019 9:19 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11805
Location: Powell River BC Canada
wedweb wrote:
So, what happened? Is there a board or boards available to make the Sansui 3000A safe and good sounding?


Post a photo of your receiver, front and back, showing what model you have. Also post a photo of
the inside of the bottom of the unit, and the top of the chassis with all covers removed.

-Do you have the operating manual and service manual, and the warranty card ?
These are often in the cartons of units stored for long periods. Where was the unit
purchased?

Some data still remains.
49 years ago, there was much chatter from Sansui.
Attachment:
Sansui green  i.jpg
Sansui green i.jpg [ 67.46 KiB | Viewed 1332 times ]

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de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Sansui 3000/3000A upgrade driver boards
PostPosted: Apr Wed 24, 2019 8:35 pm 
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Joined: Apr Wed 24, 2019 8:29 pm
Posts: 1
Are you around? I would like to upgrade my father's 3000.


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 Post subject: Re: Sansui 3000/3000A upgrade driver boards
PostPosted: Apr Thu 25, 2019 11:50 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 20713
Location: Utica, NY 13502 (USA)
OldZofTorC wrote:
Are you around? I would like to upgrade my father's 3000.
Please contact the seller directly via PM or email. Buying and selling is not allowed in the discussion forums.

Dave


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 Post subject: Re: Sansui 3000/3000A upgrade driver boards
PostPosted: Apr Thu 25, 2019 2:29 pm 
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Location: Warner Robins, GA
Seems like this board fixes the actual problem versus simply masking it with a capacitor.


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 Post subject: Re: Sansui 3000/3000A upgrade driver boards
PostPosted: Apr Thu 25, 2019 4:13 pm 
Member

Joined: Sep Thu 23, 2010 6:37 am
Posts: 11805
Location: Powell River BC Canada
Welcome to the forum. The best way to proceed is to to do this:

Post a photo of your receiver, front and back, showing what model you have. Also post a photo of
the inside of the bottom of the unit, and the top of the chassis with all covers removed.


Sansui produced several receivers that had a model number starting with 3000

more than 50 years ago.

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Sansui 3000/3000A upgrade driver boards
PostPosted: Apr Fri 26, 2019 7:26 pm 
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Joined: Feb Thu 24, 2011 1:29 am
Posts: 3158
Location: Now outside Dallas, TX - with bobcats and coyotes and more! Oh my!
tgarson wrote:
Sigh, the reason for non polar capacitors is that if the 3000A output is in good working order and properly adjusted, there is no DC voltage offset to provide bias for a normal (polarized) electrolytic capacitor.
The capacitor is to protect the speaker and outputs in the inevitable circumstance where the output voltage substantially drifts off of zero.
Which way that will go is entirely unpredictable, hence needing the capacitor to work with either polarity bias.
If you have access to the Sansui docs that came with the capacitor kit, read them. They attempt to explain this.
Don't take my word for it. Ask any EE, electronics tech or experienced ham (Ham in the classic sense of the word, not just any person who can afford to buy a radio and can fill out a license application.)

TG


Do you expect the single-ended power supply to, in a DC sense, reverse polarize a capacitor that's connected to ground on one end and 0 to +VCC volts on the other?
Maybe I missed something, but, I don't see a need for a bipolar capacitor here (in the image above).
I do see that the capacitor may lose it's polarity due to a lack of bias. In that case, I suppose that it could eventually short.

If it was (or is) a bipolar supply amp, then it most certainly needs a bipolar cap.

Edited - lack of clarity

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