I just purchased a very nice looking ST-90 (overpaid) that was purchased on physical appearance. Cosmetic wise it is perfect. Internally it all looks original. Every works including lamps but I did need to clean the controls for the scratchiness. While in there I saw some very slight bulge on the main filter cap so I replaced both with new “audio grade” from Mouser. I notice the treble range control is limited in response unlike the bass control and the treble is just not quite right and this was there even before the filter cap replacements. . The loudness button can be over burdensome so I need to run it off. Any ideas on cause or should I just shotgun recap and see where it goes? I want to hear the “wonderful sound” others have mentioned but this unit does not sound a bit like my STA 2080.
Realistic STA 90 mid-range / treble no quite right.
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Kind of figured I would start with a full recap. Trying to locate a schematic and service manual now. No visual signs of overheat or discoloration on the carbon resistors. Kind of leery of changing much other than full recap until I get the needed schematic. It’s a beautiful looking vintage piece.
Lavane
Lunatic Member
It can be difficult to find schematics for RS gear. I finely found them for a couple pieces I have, but arent very high resolution. The controls themselves that Foster used weren't that great. I've had various issues with RS controls. Volume controls that don't track evenly with one channel coming up before the other when turning the volume up, balance control issues, selectors, etc. I've found cleaning them can even cause more problems somerimes. Adding Fader Lube does help aftesometimes. Though. Try flipping your selector switch back and forth a few times see if that does anything, along with the balance control.
But replacing those old general purpose capacitors they used a lot is a good idea. There my be some week transistors in the treble part of the tone stack I guess. If it uses two single or a single dual OP amp maybe test them.
Oh and mark the PCB with a sharpie marking either the positive or negative side of the electrolytic caps before you replace them. Foster made plenty of mistakes with the silk screening on there PCB's.
But replacing those old general purpose capacitors they used a lot is a good idea. There my be some week transistors in the treble part of the tone stack I guess. If it uses two single or a single dual OP amp maybe test them.
Oh and mark the PCB with a sharpie marking either the positive or negative side of the electrolytic caps before you replace them. Foster made plenty of mistakes with the silk screening on there PCB's.
If you can't find the service info drop me a PM with your e-mail address. My first real stereo bought with my own money was a STA-90. Served me well for many years.
I too recently bought a near perfect one that I will re-furb someday. I'm probably past the mid-life crisis, so it must be reliving my youth.
Depending on what transistors are loaded in yours there may be a few or a bunch that are on the replace on site list.
Yes, at age 73 I am definitively reliving my youth but I can hardly call 73 years "mid-life". Thank you for the offer on the offer but I did finally locate and have the service manual and a letter size schematic that I will have to magnify to read. What is remarkable is that the more I use this the better it sounds - Very mellow and balanced. Is it possible the electrolytics are coming back after years of the unit being silenced? Do they somehow come back? If so I cant imagine how fine this unit will be after full recap but I love the fact that it is current an untouched virgin but for the filter caps. Even original bulbs.If you can't find the service info drop me a PM with your e-mail address. My first real stereo bought with my own money was a STA-90. Served me well for many years.
I too recently bought a near perfect one that I will re-furb someday. I'm probably past the mid-life crisis, so it must be reliving my youth.
Depending on what transistors are loaded in yours there may be a few or a bunch that are on the replace on site list.
cademan
Lunatic Member
Maybe check HiFi Engine site for free schematics and/or look to see if both are available.
Usually, an updated version of a particular model will usually have something following the original model number. For instance, the original STA-90 might have an updated version known as the STA-90(A) or some other suffix.
Usually, an updated version of a particular model will usually have something following the original model number. For instance, the original STA-90 might have an updated version known as the STA-90(A) or some other suffix.
cademan
Lunatic Member
I am curious. When I read that you saw some bulging caps, I thought of the plastic caps on top of those big power supply electrolytics. They were probably okay as it takes a lot of steam and heat to make one of those things bulge.
Did you have this treble problem before you recapped?
Did you have this treble problem before you recapped?
Unfortunately HiFi Engine is not accepting new members and you can not download docs without a membership. Wish they would start accepting new membership as I have been waiting for three months so far.
The large main caps were bulging (small bulge) at the rubber bottom and only very slightly at the top
Attachments
Yes, same issue prior to these two caps. Expect I will do a full recap but it would be so nice to have a “virgin” receiver as the rest is mint.
Beautiful sound has returned. Most caps replaced. I am slow and methodical with horrible eyesight. A lot of the small transistors replaced that were known for issues. The treble control is now working as it is supposed to. The deep rich tube like sound is back. Now to find someone to align to tuner. Color me VERY VERY pleased. I like this one better than my STA-2080:and my STA-2300. What a great performer at only 45 watts.
Your sta2080 was one of the best
I like it better than my Mac 1900 or my carver hr772 , especially for classic rock the Mac is better for jazz or more mellow listening !