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Threshold S500 optical bias - filter caps and bias - experience so far
Threshold S500 optical bias - filter caps and bias - experience so far
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Old 20th February 2018, 09:18 AM   #1
eswaroop is offline eswaroop  United States
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Default Threshold S500 optical bias - filter caps and bias - experience so far

Iíve had an S500 for almost 8 years now - all stock no mods- used to run lukewarm at best and itís been in storage for a while - I decided to hook it back up when I got myself a pair of Polk LSIM707s.

I finally got around to adjusting the bias ( thanks to a helpful forum member! and got it up to about 45 degrees stable each side on the heatsinks.. ) sounded a lot better - clearer and open and it made it to the top of the list in terms of listening quality

Two issues Iím running into - I decided to give it new filter caps and bought KEMETs newest line of ALS80s - 43000 uf +- 20% 100 volts ( ALS80A433NF100 KEMET )

Swapped the old ones out - and the amp sounded different - not as much base or depth anymore.. let the caps reform over a few hours and no luck! I swapped the original MEPCOs back in and it sounds great again - I did slow reform the Mepcos over several days a couple of years ago - maybe that helped - so not sure which way to go - should I upgrade to PeH169s or just leave it as is?

Secondly - when I raised the bias settings to 49 degrees stable - the amp sounded completely off - base was gone and It was somewhat shrill at best.. volume was lower and everything sounded frizzled.. is the best way to put it - I have the optical bias versions that are supposed to be stable to 49 degrees?

I dialed the bias back to 44-45 degrees at the heatsinks and the amp sounds fine again - any pointers on where to go from here ?
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Old 20th February 2018, 09:43 AM   #2
Zen Mod is offline Zen Mod  Serbia
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Threshold S500 optical bias - filter caps and bias - experience so far
you tried it all ......... dial to where it pleases you most

regarding new caps - you can't expect to hear their regular performance for at least 100hrs ......
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Old 20th February 2018, 04:55 PM   #3
RobertS61 is offline RobertS61  Netherlands
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you tried it all ......... dial to where it pleases you most
Subzero
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Old 22nd February 2018, 10:48 PM   #4
eswaroop is offline eswaroop  United States
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Thanks.. did not think caps needed 100 hours to break in.. will try that. Also if I were to upgrade the diode bridges, is there a recommended spec / p/n to go with new ones? I've heard IXYS FREDs, etc..
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Old 23rd February 2018, 12:19 AM   #5
analog_sa is offline analog_sa  Europe
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Threshold S500 optical bias - filter caps and bias - experience so far
Quote:
Originally Posted by eswaroop View Post
should I upgrade to PeH169s
Тhe PEH169 do sound better than the ALS. Keep in mind that they are definitely upwards tilted tonally, not thin or bright, but definitely not bass-masters.

Once tried them in a S300 and the result was pretty much what you describe, with improved clarity from the midrange and up. Highs were indeed better, but tonally the change was not pleasant.

From the currently manufactured caps i have had good luck with EPCOS-TDK, B41456B9479M. Excellent bass, dynamics, soundstaging.
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Old 23rd February 2018, 12:59 PM   #6
eswaroop is offline eswaroop  United States
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Default Reform higher voltage caps at rated voltage ?

Is it possible that the new caps (100V rating ) should be first fully reformed to the 100V rated voltage before putting them in as they would never experience the full rated voltage directly in the amp at 75-80 volts ? Maybe once fully reformed they have a better performance or capacity ?




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Subzero
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Old 8th April 2019, 10:31 PM   #7
Mikerodrig27 is offline Mikerodrig27  United States
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Eswaroop, I wanted to see if you ever solved the problem?
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Old 13th April 2019, 02:21 AM   #8
eswaroop is offline eswaroop  United States
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Eswaroop, I wanted to see if you ever solved the problem?
Yes - reformed the original caps over several weeks and multiple cycles and they sound the best - they tested better for leakage, which was amazing considering a 40 year old cap -they were built well I guess !
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Old 13th April 2019, 05:57 AM   #9
Mikerodrig27 is offline Mikerodrig27  United States
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From what I hear, these Threshold amps are almost indestructible. I just picked up a S/500 with the optical bias a little over a week ago. Just today I picked up a Adcom GFP-565 preamp which will let me use the Threshold for the first time once I hook it up. Glad to hear you got your amp sorted.



People have talked about having success with using larger caps. I suppose you just have to use the right one. Maybe Cross that bridge when you really have to.
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Old 13th April 2019, 05:57 PM   #10
Nelson Pass is offline Nelson Pass  United States
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Threshold S500 optical bias - filter caps and bias - experience so far
Quote:
Originally Posted by eswaroop View Post
Yes - reformed the original caps over several weeks and multiple cycles and they sound the best - they tested better for leakage, which was amazing considering a 40 year old cap -they were built well I guess !
I did a rebuild of 40 year old Stasis 1's. The power supply caps were
perfect. Not so with the tantalums used for supply bypassing on the
control logic.
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