Threshold S/500 bias set up anyone? - Page 2 - diyAudio
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Old 2nd August 2009, 09:54 PM   #11
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Default Ok, I know I blew it.

Although I did manage to get this amp up and runnin' by myself, I was under the impression that it was pretty much the way my old boss taught me, Stevie, he said, it's just an amplifier, find the bad parts and replace 'em. This has served me well most of my repair tech career. However, I was reminded of an experience long ago shortly after starting my tech life that I had with a McIntosh MC2300. One was brought into the store for service, one channel out, by a local bar that used it for low end on their system. This was my first Mac, so I decided to go to local dealer and pick the brain of their tech. He saw me comin a mile away and boy did he have a laugh at my expence. Either he thought his advise would eventually lead to me to bringing the amp to him to fix, ('cause ya know, he was the authourized repair tech after all) or he was a sadistic ba----d and just wanted to mess with me. Anyway, I wanted to order replacement parts from Mac for it, so I thought I'd just go over there to dealership and borrow a manual and write a parts order for them to sell me. He said that was just silly, "It's just an amp", "go over to Radio Supply (local parts house) and just buy ECG substitues for 'em. They'll work just fine!!" Well, you can guess, maybe, how much time and how many subsitute parts I went through before I realized the gain on some of the replacement driver transistors was soooo much higher than the specs for the original, that the amp was going into high freq oscilation and blowing up, again, before I got it half way up to power on the variac after replaceing all those parts....more than once, that's all I say. Guess what? I ordered all the parts from Mac, replaced the crap I had put in, and lowe and behold, it worked.
This is my first Mac all over again, only a little different. It's a Threshold, and I'm not familiar with them at all. Closest I ever got was fixin' a Nak PA-7 a few years ago. Anyway, I'm ready to eat my crow now, medium well please, and humblly ask again for any help you guys, who I know are here, are willing to share with an old fart who really doesn't know crap on this subject. Forgive me, this was an amp for me, first step in rebuilding my stereo that I was forced to sell over 4 years ago. NO SYSTEM FOR FOUR YEARS!!! You are amoung the only people on earth who really understand how anxious I really am to do this, and do it right. Thanks for being patient with me. Stevie
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Old 3rd August 2009, 02:58 AM   #12
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Talking My S/550E (cloned)

A couple of months for cloning this model

Original parts only solid state and resistors, I can't find 0.047uF yellow axial lead and 0.15uF orange (sprague)

Next week maybe complete with adjustable to class-a

Thanks
Anadigit
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Old 3rd August 2009, 05:38 AM   #13
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Anadigit, that looks like it could be the original! You did that board? Good job from the looks of it, great work! So are you building a compete S/550 from scratch? That's a hell of a tall order. Good luck. Do you have pics of entire amp, I saw the output section pic in your last reply, did you make that too?
Stevie
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Old 3rd August 2009, 07:13 AM   #14
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Schematic for your S500
Be carefull don't blow it or yourself up.

Cheers George
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Old 3rd August 2009, 07:39 AM   #15
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Exclamation Hi,

No, Geoge your schematic that's not S/550E, it's only S/550.
Take a look at OPTO of them !

Now I have original S/550E on hand, too

I took a photo from scratch S/550E and my Threshold Fet 10/E , I'm never build with a large or huge heatsink (it's only my plan)


Thanks
Anadigit
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Old 3rd August 2009, 09:54 AM   #16
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It's for Stevie, re the thread title.

Cheers George
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Old 3rd August 2009, 10:11 AM   #17
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Front End
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Old 3rd August 2009, 10:12 AM   #18
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Output Stage
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Old 3rd August 2009, 05:43 PM   #19
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Default Hey George and Anadigit

Thanks George, front end schematic tells me a lot about what to look at. Would really like to converse with someone who has experience setting up one of these, bias, and offset. They just really don't seem stable enough for me to believe that there is not something wrong still. Maybe I'm wrong, hope I'm not, but willing to be wrong and get schooled. Again, thanks for taking time to send me prints. Stevie
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Old 3rd August 2009, 05:49 PM   #20
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Hey ANADIGIT, so I guess it may take a while for me to learn how to read between the translation lines to understand your posts completely so here goes...That amp in last photo you built the "insides" of it? Then put it in old amp case? Let me know. Stevie
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