I too have learned a ton from this website and this thread in particular. Since my last post above, I have totally rebuilt my STASIS 2 that had the burnt-out channel with all new output devices, small transistors, cap upgrades throughout, emitter resistors upgrade, and more that I can't think of right now. At the same time I bought a Tektronic 465B scope that was in great shape and calibrated, a Hakko soldering station, a signal generator, a few more VOMs, lots of leads and uh, you know the rest. After that, I went though my other STASIS 2 with the same upgrades as above except for new output devices since the originals were all working fine, Both of the STASIS 2s are in daily use driving bi-amped Apogee Duetta Sigs . . . But did you think I would stop with that? Well, while I was on a roll, I got my hands on a STASIS 3 with a burned-out channel . . . it's totally rebuilt and upgraded now and sounds great! I even gone as far as to pick up a few dead middle-of-the-road pieces cheap on eBay as sort of a practice challenge. So far one pre-amp has me beat, but it's some sort of computer-controlled SAE thing and I can't find schematics for it. It looks like the proprietary CPU has issues, but I don't lose any sleep over it. I'm learning from it. I can always salvage the screws from it!
Yes, I too have learned a ton from you, Chris, and the guys here on this thread, and I know that I will learn more here in the future. THANK YOU!
PS: Yes Chris, I took your advice and used ON MJ21195 and MJ21196 . . oh so nice!
Yes, I too have learned a ton from you, Chris, and the guys here on this thread, and I know that I will learn more here in the future. THANK YOU!
PS: Yes Chris, I took your advice and used ON MJ21195 and MJ21196 . . oh so nice!
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So my amp is now, as it appears, is oscillating.. I have re-biased it with the aid of a variac... but when I try and just power it up with nothing connected at all (and no variac) it goes HUMMMMMMMM within about 5 seconds... and seems like the left channel is mostly lit up...
Should I be checking each zobel network?
It actually played for hours when I brought it up on the variac.. I used some cheap speakers and my cell phone as a source...
It absolutely HATES my tube eico 85.. wont even come up on a variac with it connected.. just screams bloody murder.. and the eico is working fine with my Aleph 3...
I dont have solid state pre amp to play with...
She played fine for years with no issues... but suddenly very unhappy with life.
Can you guys point me?
Should I be checking each zobel network?
It actually played for hours when I brought it up on the variac.. I used some cheap speakers and my cell phone as a source...
It absolutely HATES my tube eico 85.. wont even come up on a variac with it connected.. just screams bloody murder.. and the eico is working fine with my Aleph 3...
I dont have solid state pre amp to play with...
She played fine for years with no issues... but suddenly very unhappy with life.
Can you guys point me?
It seems odd that it would start oscillating on both channels all of the sudden. You know if you blow a rail fuse it will fully light up the LED display. Anyway, I take it that you are seeing the oscillation on your o'scope? If so, start by lowering the bias until you see the oscillation disappear. Then slowly bring up the bias on one channel. If it breaks into oscillation all of the sudden, and I don't have a schematic in front of me, but you probably have a small mica cap that across the output devices of one side of that channel finally went south.
Well, I think I resolved the power up humm issue... there was a 470uf cap on the right channel that either expired itself or when I put the cover on it pushed it in such a way that one of the leads partly pulled out of the cap.. when I removed it and tested it it tested bad.
I did replace the caps on the zobel nets but when I tested those caps they were dead on at .1uf. I also checked the resistors and they are fine... so now, no variac needed with my cell phone connected it plays fine.. though have only run it on and off for a few minutes.. but I was never able to get it to power up without the aid of the variac before I did the above...
but when I connect my eico HF85 tube pre amp to it it goes nuts.. loud bass sounding burst from both channels when I bring it up on the variac.. and I can unplug the power cord to the Eico and I get the same result.. If I disconnect the shielded RCA cables from the Eico it also starts up just fine (its not the cables obviously).
the eico plays fine on my Aleph 3....
Any thoughts here? I sold my Aleph so Id really like to make this work if possible.. it used to play on it all the time... but I did redo all the caps in the eico and I cant remember if I tried the 400a after I did that to be honest.. but pre the new caps in the HF85 Eico it played for years together with the 400a.
I tried no ground to the ac as well.. same issue..................... thats the only "mod" I made the eico.. I grounded the chassis.
Any thoughts here? I suppose Im out of my ability area and likely need a scope and experience at this point... I find it odd that with the power cord disconnected to the Eico I get the same result.. maybe the caps are bleeding down still? I dunno............
I did replace the caps on the zobel nets but when I tested those caps they were dead on at .1uf. I also checked the resistors and they are fine... so now, no variac needed with my cell phone connected it plays fine.. though have only run it on and off for a few minutes.. but I was never able to get it to power up without the aid of the variac before I did the above...
but when I connect my eico HF85 tube pre amp to it it goes nuts.. loud bass sounding burst from both channels when I bring it up on the variac.. and I can unplug the power cord to the Eico and I get the same result.. If I disconnect the shielded RCA cables from the Eico it also starts up just fine (its not the cables obviously).
the eico plays fine on my Aleph 3....
Any thoughts here? I sold my Aleph so Id really like to make this work if possible.. it used to play on it all the time... but I did redo all the caps in the eico and I cant remember if I tried the 400a after I did that to be honest.. but pre the new caps in the HF85 Eico it played for years together with the 400a.
I tried no ground to the ac as well.. same issue..................... thats the only "mod" I made the eico.. I grounded the chassis.
Any thoughts here? I suppose Im out of my ability area and likely need a scope and experience at this point... I find it odd that with the power cord disconnected to the Eico I get the same result.. maybe the caps are bleeding down still? I dunno............
It looks like you are on your way to a resolution, but check the two 680pf caps circled in red. If one of those goes, it will oscillate . . . I don't have a clue on the Eico HF85 issue, but is there any significant DC offset coming from the HF85?
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Im gonna have to pull the channels out to check those caps.. in looking at my removed parts bag I see I did not replace any of those little caps. This was probably because I was told I did not need to in this thread.. so I may just order all those up and be done with it..
I see a range of .001-.044v DC on the outputs of my pre amp on my chinese fluke (tongue in cheek)... Not sure if that is a lot or not..
I suppose I could try lowering the bias... both sides were at about 45c when I last checked it which is the preferred method to set this amp up per Mr. Pass.
I wish I had another pre amp other than my cell phone to test..
I suppose I could build a passive pre and see what happens there. Im not sure if there is enough gain in the early 400a for that.
If you have any other ideas let me know.. otherwise I will maybe just order up all those little caps and have at it and see what happens.. maybe lower the bias too.
I with I had a magic bullet for the issue. These troubles can be caused by many esoteric issues. ie. I just repopulated a driver circuit board because when the unit got up to full temp. the speaker would buzz loudly. It was a 120Hz sawtooth on the output at about 1/2 v p-p and it went away when I removed the top and blew on the circuit. On the last go round of changing 3-4 transistors I found a fleck of plating hanging on a bent transistor lead. Some problems are just about perseverance. Sounds like you could have a ground issue that becomes an issue with that preamp. 400a is not known to oscillate like the Stasis circuits.
400A damage
At long last, i opened up my 400A which let out its smoke a few years ago. Two burned resistors, probably more damaged parts also.
I am going to close it again, but I think I have to get some parts ready, clean my desk, open it up again, and do the necessary surgery, and also some capacitor replacement. And also some good old Hoovering. I thought about selling the Hoover as it just collected dust....)
Wish me luck!
At long last, i opened up my 400A which let out its smoke a few years ago. Two burned resistors, probably more damaged parts also.
I am going to close it again, but I think I have to get some parts ready, clean my desk, open it up again, and do the necessary surgery, and also some capacitor replacement. And also some good old Hoovering. I thought about selling the Hoover as it just collected dust....)
Wish me luck!
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I'm going to go back through this thread and take notes on all the highlights. I know it's not exactly the same amp but the general troubleshooting should apply to a Threshold 4000.
What other threads do you suggest to a newbie about troubleshooting an amp such as the 4000? I've read through about everything I can find on the 400a and 4000.
Thanks for any and all suggestions....
What other threads do you suggest to a newbie about troubleshooting an amp such as the 4000? I've read through about everything I can find on the 400a and 4000.
Thanks for any and all suggestions....
Well.. Im back.. been awhile, alot has changed for me, mostly was in a bad motorcycle accident which changed my life as Im in pain 24/7 and have limited use of my right arm.. 2 avulsed roots (which means they were torn out of my spine in my neck). No sympathy required, I created this.
Im glad to see so many have found this thread useful.. it is sort of infamous and linked on many web sites. I read back and see what an a hole I was and have learned that while Im still the same a hole I dont type it. Im a little kinder of a person now as what happened to me makes me think about others and what they might be going through.
Now to the 400a I rebuilt.
About 7 yrs ago, before my accident something went wrong and I think it began to oscillate on one channel. As of late Ive gotten back into audio to entertain myself (im a recluse now).. Im thinking about repairing this unit again, though it will be painful to do but I can work through it. Will likely be a long project as I'll need to do the work when I feel up to it.
Hopefully some will still be willing to help me. I now have an oscilloscope that might be helpful by the way.
So first question; I threw away my variac in a moving tantrum... what size do I need? Is 5amp large enough? I presume my concern is inrush current..I know the fuses are 5amp.. so is 5amp enough? By the way, I need to open it up but I think I soldered in 2 inrush devices (cant remember what they are callled due to memory).. but they are black. Will this do the job?
https://www.amazon.com/YaeCCC-Transformer-Variable-Voltage-Regulator/dp/B076Y2XHRS/ref=sr_1_1_sspa?dchild=1&keywords=variac%2Btransformer&qid=1620579716&sr=8-1-spons&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExTTdUU0kzREJKWFZCJmVuY3J5cHRlZElkPUEwNzc0MTg3M1M3MTA0SkJESEFVQiZlbmNyeXB0ZWRBZElkPUEwMjcyNTM5WE5HUEFBM0lBOUpMJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ&th=1
I think once I have a variac again, due to all I learned here, I can fix it myself. this thread goes over almost ever detail.. pretty neat.
Question #2: the one regret I have on my rebuild is not replacing the bias pots. They were finicky when I did the bias if memory serves (which was also damaged so thank goodness this thread is still here) and I dont want to go through that again especially with my hand being somewhat shaky now.. so can someone help me source new pots for it that will solder right in? I need to try and find the schematic.. I remember I had it and the bias adjustment instruction printed out and I put them in the same bag as all the old caps which I still have... somewhere.
I now have a nice DAC and am interested to see what she sounds like. Not too mention, what a waste sitting in the floor of my closet.
-Barchetta
Im glad to see so many have found this thread useful.. it is sort of infamous and linked on many web sites. I read back and see what an a hole I was and have learned that while Im still the same a hole I dont type it. Im a little kinder of a person now as what happened to me makes me think about others and what they might be going through.
Now to the 400a I rebuilt.
About 7 yrs ago, before my accident something went wrong and I think it began to oscillate on one channel. As of late Ive gotten back into audio to entertain myself (im a recluse now).. Im thinking about repairing this unit again, though it will be painful to do but I can work through it. Will likely be a long project as I'll need to do the work when I feel up to it.
Hopefully some will still be willing to help me. I now have an oscilloscope that might be helpful by the way.
So first question; I threw away my variac in a moving tantrum... what size do I need? Is 5amp large enough? I presume my concern is inrush current..I know the fuses are 5amp.. so is 5amp enough? By the way, I need to open it up but I think I soldered in 2 inrush devices (cant remember what they are callled due to memory).. but they are black. Will this do the job?
https://www.amazon.com/YaeCCC-Transformer-Variable-Voltage-Regulator/dp/B076Y2XHRS/ref=sr_1_1_sspa?dchild=1&keywords=variac%2Btransformer&qid=1620579716&sr=8-1-spons&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExTTdUU0kzREJKWFZCJmVuY3J5cHRlZElkPUEwNzc0MTg3M1M3MTA0SkJESEFVQiZlbmNyeXB0ZWRBZElkPUEwMjcyNTM5WE5HUEFBM0lBOUpMJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ&th=1
I think once I have a variac again, due to all I learned here, I can fix it myself. this thread goes over almost ever detail.. pretty neat.
Question #2: the one regret I have on my rebuild is not replacing the bias pots. They were finicky when I did the bias if memory serves (which was also damaged so thank goodness this thread is still here) and I dont want to go through that again especially with my hand being somewhat shaky now.. so can someone help me source new pots for it that will solder right in? I need to try and find the schematic.. I remember I had it and the bias adjustment instruction printed out and I put them in the same bag as all the old caps which I still have... somewhere.
I now have a nice DAC and am interested to see what she sounds like. Not too mention, what a waste sitting in the floor of my closet.
-Barchetta
Yes, a 5A variac is fine.
I'm glad you're okay now. I'm also in pain 24/7 after I was rear-ended ant 100 km/hr while I was stopped on a highway. The other guy didn't even hit the brakes. I have a good understanding of what you are dealing with.
You have help from many people, and I am glad you have a 'scope now. Makes everything easier.
Yes, change the trimmers for bias current.
-Chris
I'm glad you're okay now. I'm also in pain 24/7 after I was rear-ended ant 100 km/hr while I was stopped on a highway. The other guy didn't even hit the brakes. I have a good understanding of what you are dealing with.
You have help from many people, and I am glad you have a 'scope now. Makes everything easier.
Yes, change the trimmers for bias current.
-Chris