Realistic STA-90 Amp Circuit A-Z

[videolady201]

Where to Look Qvox

Somebody please tell me where to look in the schematic for the Qvox mode control. I must be blind...

That is the same issue I have. I don't see anything in the circuit. It must be the way they are connecting the speakers through the speaker selector switch. There are only two amps in this unit and they can't do two different sounds to two different speakers at the same time. I think it must be through the selector switch. I will find out, I will trace the unit backwards from the output terminals and see where each ends up with the selector in the Qvox mode.:scratch2:

 

[terra1]

...

 

[Metalownz]

I think what makes this unit sound so good is its simplicity. Alot of higher powered receivers are more complicated in their designs. This receiver has the power of a receiver almost twice the power. I think Sansui had to have made this model because it looks like the 881. Ive compared it with a Marantz 2240B and a Yamaha CR-640 and it seems ALOT more powerful then those units.

 

[videolady201]

STA-90 Power

I think what makes this unit sound so good is its simplicity. Alot of higher powered receivers are more complicated in their designs. This receiver has the power of a receiver almost twice the power. I think Sansui had to have made this model because it looks like the 881. Ive compared it with a Marantz 2240B and a Yamaha CR-640 and it seems ALOT more powerful then those units.

I agree. I have noticed that this unit, when it clips, it does so very slowly. Many others really clip fast once you reach full power. The one I have starts to show clipping at 52 watts into an 8 ohm bench resistor. Once it starts clipping it just changes the shape of the tips on the scope. They just start to lay over. As you keep driving the power, the tips just lay over more, up to around 24 volts a channel! After that the true clip, flats on the sign wave, start to show up!:yes:

 

[BinaryMike]

This sort of output limiting could be caused by beta droop in the output stage transistors. By the way, I've been fooling around with a circuit that can add soft clipping functionality to any amplifier. PM me if you want the schematic.

 

[Metalownz]

Wow Videolady, thats pretty impressive for a 45 watt per channel receiver. You really have to try this receiver with a LAB-400 turntable. Man they sound sweet together!

 

[videolady201]

Phono Stage

Wow Videolady, thats pretty impressive for a 45 watt per channel receiver. You really have to try this receiver with a LAB-400 turntable. Man they sound sweet together!

That's what I am using! I have a Shure V15 on the LAB-400 with the STA-90 and it does sound Sweet!

 

[Metalownz]

Wow really??! Im using a Pickering V-15 Micro IV on mine. Like i said, the phono section sounds amazing in the STA-90. It seems like the LAB was meant for this receiver. I may swap the LAB-400 with my Technics SL-1800 to see how that sounds.

 

[krimney]

Thanks......

You've all given me one more project to play with. I've used an STA-90 in my garage for about 4-5 yrs, and since my recent move to a condo, in my storage unit in the parkade. I cna't get amy FM signal in the basement so have it hooked up to an old cassette deck and some minimus 7. maybe I have to dust it off and bring it upstairs for some serious listneing.

funny it should be compared with the older sansui, i brought an 800 into the house today for a dust off.....

I wonder if it's an acident these particular units have stuck with me through the yrs when so many other units have not.....

 

[Metalownz]

Its like in the closet good sound. I traded a Marantz for my STA-90 and while alot of people thought i was crazy, i dont regret the decision at all. Yeah the Marantz has more value, but i like the phono section and power more in the 90.

 

[Metalownz]

And you cant beat the fact that it has REAL metal knobs and a REAL wood case. Not vinyl.

 

[videolady201]

The Real Thing

And you cant beat the fact that it has REAL metal knobs and a REAL wood case. Not vinyl.

That's right. It looks great, It tests great and best of all, it sounds Great!!:yes:

 

[Metalownz]

Yes indeed it does! And you have to love the orange lights. How many receivers actually use orange as indicator lights you know.

 

[HomeBody]

Its like in the closet good sound. I traded a Marantz for my STA-90 and while alot of people thought i was crazy, i dont regret the decision at all. Yeah the Marantz has more value, but i like the phono section and power more in the 90.

Ah Man...that speaks VOLUMES right there...
Ya just can't help but love the ol'Shacks of yesteryear.

 

[AnalogDigit]

I just bought a STA 90 off of eBay. I done a little research why this receiver is so sought out over. Found out it got raved reviews in Stereo Review in March, 1976, the receiver has a 4 gang AM section, Q-Vox, and excellent phono section. 45 watts per channel is not bad neither.

When I get the receiver, I will connect it up to my Nova 7B speakers that I have. To make room, I will maybe get rid of my Yamaha receivers.

 

[videolady201]

STA-90 Info

AD Sheet from 1976!

 

[AnalogDigit]

Bought a STA 90/ 2000

The STA 90 came yesterday via UPS ground. I opened the box, and it was packed with newspaper! :nono: There was some damage to the bottom and the sides of the wood case. Fixed the problem with the damage on the bottom with a rubber mallet. Looked inside, there were a lot of dead spiders and cobwebs. Looks like he had the receiver in storage in his basement for a long time. Vacuumed the cobwebs and spiders out. Cleaned the metal where the tuning dial moves, since it was sticky. AUX indicator light is out, which is an easy fix.

Powers up fine. All controls work, volume control needs a shot of Deoxit. Sounds very nice hooked up to my Nova 7B speakers and with Minimus 7's. AM sounds very good.

My only problem with the receiver is that it FM receives all stations, but the signal meter hardly moves and most of the stations I do receive are in mono. I live in the Chicago area, so there should be no problem receiving stations very strong with a dipole antenna. So the FM might need adjusting. Is this an easy fix or do I have to take it in?

Was thinking of putting this receiver with my audio/video setup in the living room. It would work nice with my Minimus 11 and 7 speakers.

Also, I picked up a STA 2000 receiver from AK'er Markthefixer last weekend. He repaired the FM section of the receiver. Clean inside and out, the receiver looks like it came from a Radio Shack store from 1977! Sounds really great. Thanks a lot Mark, your the best! :thmbsp:

 

[HomeBody]

That's a sweet lookin' call girl, that there STA-90-
Hmmm...:scratch2:
You & Video have up and done gots me ahuntin' forza 90 unit.
I'll never catch up.

 

[terra1]

Cleaned the metal where the tuning dial moves, since it was sticky. AUX indicator light is out, which is an easy fix.

Powers up fine. All controls work, volume control needs a shot of Deoxit. Sounds very nice hooked up to my Nova 7B speakers and with Minimus 7's. AM sounds very good.

My only problem with the receiver is that it FM receives all stations, but the signal meter hardly moves and most of the stations I do receive are in mono. I live in the Chicago area, so there should be no problem receiving stations very strong with a dipole antenna. So the FM might need adjusting. Is this an easy fix or do I have to take it in?

Have you checked the how to clean a analog tuner thread in Tuners? That might be worth doing to see how she responds.

Otherwise it would be worth have a tech do a full alignment and adjustments.

 

[AnalogDigit]

Have you checked the how to clean a analog tuner thread in Tuners? That might be worth doing to see how she responds.

Otherwise it would be worth have a tech do a full alignment and adjustments.

Thanks for the info. It might just need a good cleaning. It was pretty dirty on the inside.