I choose to reopen this thread since the amp is playing music again. The information might turn out useful for somebody else.
Well the owner of the Stasis brought it to a guy with some experience in repairing amp's. You wont beleive it, but the cause of all the problems was simply the 3 electrolytics on each pc board!
The guy soldered in 3 new caps per channel and the amp sounds just great again
I just went and visited my old friend and I was just surprised that the solution was that simple. It just goes to show that when you have trouble with an old amp, swap out the caps The diode bar had a bad solder somewhere so thats working again too Thats what you get for trying too hard to find some failure. No need to change all the output devices and everything else with them. The repair costed the owner something like 50 bucks.
Happy ending indeed.
Steen.
Well the owner of the Stasis brought it to a guy with some experience in repairing amp's. You wont beleive it, but the cause of all the problems was simply the 3 electrolytics on each pc board!
The guy soldered in 3 new caps per channel and the amp sounds just great again
I just went and visited my old friend and I was just surprised that the solution was that simple. It just goes to show that when you have trouble with an old amp, swap out the caps The diode bar had a bad solder somewhere so thats working again too Thats what you get for trying too hard to find some failure. No need to change all the output devices and everything else with them. The repair costed the owner something like 50 bucks.Happy ending indeed.
Steen.
steenoe said:You wont beleive it, but the cause of all the problems was simply the 3 electrolytics on each pc board!
The guy soldered in 3 new caps per channel and the amp sounds just great again
That's true also of many PC board failures. Lytics are the week components on any electronic circuitry.
My son gives away many fine PC boards including motherboards and video cards, I just replace the caps and they have a second life on one of my computers. No matter how much you pay for those components they are dead in 3 or 4 years for that reason.
One interesting fact on my son’s last video card acquisition, all caps were rated at 125V never saw that before and it also sported some OsCon caps - which might not be that uncommon this days.
Threshold Help
The outputs will give you the most trouble. You need to use Motorola output devices or risk lots of oscillation. Replace the small caps on the driver cards with some nichicon 470 u, 16V
47uF 63 or 100V
The main caps are probably worn out too, but you should be able to at least make it work. Lift the emitter resistors and measure with a diode checker to determine which output devices are bad.
JOn
The outputs will give you the most trouble. You need to use Motorola output devices or risk lots of oscillation. Replace the small caps on the driver cards with some nichicon 470 u, 16V
47uF 63 or 100V
The main caps are probably worn out too, but you should be able to at least make it work. Lift the emitter resistors and measure with a diode checker to determine which output devices are bad.
JOn
Jon, Nelson, or anyone, I have a pair of Stasis 2s that I will be using to power my bi-amped Apogee Duetta Signatures (directly coupled to each driver, electronic crossover only).
Both amps have a little more DC offset than they should:
Amp #1: R= 0.215 Vdc L= 0.140 Vdc biased to 42-43 degrees C.
Amp #2: R= 0.095 Vdc L= 0.070 Vdc biased to 47-48 degrees C.
Also, I replaced all the electrolytics both big (4 x 22000uF) and small (Blackgates) on both amps.
Both of these amps sound great especially now that the electrolytics have replaced, but even when using amp #2 to drive the tweeter sections, that small amount of DC offset causes the tweeter ribbon to move out of it "home" position. Previously, I used a Threshold S-150 Series II that has a DC offset low enough(L=0.050Vdc R=0.045Vdc) not to adversely effect the tweeter ribbons.
Question: How can I lower the DC offset of my two Stasis 2 amps? Is this a sign of other aged components that are in need of replacement? If so where should I start?
Thanks
Forrest
Both amps have a little more DC offset than they should:
Amp #1: R= 0.215 Vdc L= 0.140 Vdc biased to 42-43 degrees C.
Amp #2: R= 0.095 Vdc L= 0.070 Vdc biased to 47-48 degrees C.
Also, I replaced all the electrolytics both big (4 x 22000uF) and small (Blackgates) on both amps.
Both of these amps sound great especially now that the electrolytics have replaced, but even when using amp #2 to drive the tweeter sections, that small amount of DC offset causes the tweeter ribbon to move out of it "home" position. Previously, I used a Threshold S-150 Series II that has a DC offset low enough(L=0.050Vdc R=0.045Vdc) not to adversely effect the tweeter ribbons.
Question: How can I lower the DC offset of my two Stasis 2 amps? Is this a sign of other aged components that are in need of replacement? If so where should I start?
Thanks
Forrest
You will find a schematic at www.passlabs.com/np
On it you will find at the negative rail a 300 ohm resistor
between the negative rail and the emitter of an A42 transistor.
Adjusting this value slightly will alter the offset.
On it you will find at the negative rail a 300 ohm resistor
between the negative rail and the emitter of an A42 transistor.
Adjusting this value slightly will alter the offset.
Stasis Offset
It is also possible to match up the differential pair of transistors. The available parts are A 18. A pair of 6571 was often used during the manufacture of these units. If one of these devices is damaged, the offset will go out of spec. I always look for less then +/-50 mV
JonS
It is also possible to match up the differential pair of transistors. The available parts are A 18. A pair of 6571 was often used during the manufacture of these units. If one of these devices is damaged, the offset will go out of spec. I always look for less then +/-50 mV
JonS
Jon,
Listening to Stan Getz and Astrud and Astrud Gilberto via iTunes (MacBook Pro) through a 400A (picked up a couple months ago) with Hafler 101 and a pair of Dynaco A-25s. Vintage system sounds quite nice with the 400A on AR-3as and Klipsch Forte IIs. Have not hooked the 400A to the "The AR turntable" or the small Maggies or the Infinity Primus 360s on the other end of the living room yet.
Question re powering up the 400A: I did not realize that I should have (or should I have not)cycled the power switch on the front panel on the 400A a number of times with the power off before firing it up for the first time (I don't have a variac). The first couple of times I powered the 400A up I heard (and saw) sparks from the front panel switch. The amp now is left with the front panel power switch in the "on" position and I power it up through a Discwasher 'Spikemaster' and all sounds OK to me. Should I continue with this set-up or am I asking for a disaster?
I'm also running a small (Honeywell) fan just at the edge of the 400A for cooling and am wondering if the differential in cooling between the edge with the fan vs the other side could create pproblems over time? The temp without the fan does not seem excessive (using the fingers on the cooling fins for ten seconds test)
I'm located on St Simons Island, Georgia but used to teach occasionally in Citrus Heights at the University of New haven (Connecticut) when they had a campus in Citrus Heights.
Sorry if this post is in the wrong 'pew' but was hoping to get your take on this, Jon. Thanks . . .
Pre- Threshold 400A - Klipsch vintage system is at:
http://forum.stereophile.com/photopost/showphoto.php/photo/903/password//sort/1/cat/all/page/1
Listening to Stan Getz and Astrud and Astrud Gilberto via iTunes (MacBook Pro) through a 400A (picked up a couple months ago) with Hafler 101 and a pair of Dynaco A-25s. Vintage system sounds quite nice with the 400A on AR-3as and Klipsch Forte IIs. Have not hooked the 400A to the "The AR turntable" or the small Maggies or the Infinity Primus 360s on the other end of the living room yet.
Question re powering up the 400A: I did not realize that I should have (or should I have not)cycled the power switch on the front panel on the 400A a number of times with the power off before firing it up for the first time (I don't have a variac). The first couple of times I powered the 400A up I heard (and saw) sparks from the front panel switch. The amp now is left with the front panel power switch in the "on" position and I power it up through a Discwasher 'Spikemaster' and all sounds OK to me. Should I continue with this set-up or am I asking for a disaster?
I'm also running a small (Honeywell) fan just at the edge of the 400A for cooling and am wondering if the differential in cooling between the edge with the fan vs the other side could create pproblems over time? The temp without the fan does not seem excessive (using the fingers on the cooling fins for ten seconds test)
I'm located on St Simons Island, Georgia but used to teach occasionally in Citrus Heights at the University of New haven (Connecticut) when they had a campus in Citrus Heights.
Sorry if this post is in the wrong 'pew' but was hoping to get your take on this, Jon. Thanks . . .
Pre- Threshold 400A - Klipsch vintage system is at:
http://forum.stereophile.com/photopost/showphoto.php/photo/903/password//sort/1/cat/all/page/1
Attachments
Isn't more useful to substitute this resistor with a 300 ohm trimmer so you can adjust DC with it. What a hassle to alter a static 300 ohm resistor or match those 6571 or A18 transistors. Why not a dc servo circuit incorporated? Why a impossible to operate 1 turn biastrimmer.... SorryYou will find a schematic at Sorry, this page isn’t available | Pass Labs
On it you will find at the negative rail a 300 ohm resistor
between the negative rail and the emitter of an A42 transistor.
Adjusting this value slightly will alter the offset.
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