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Old 19th December 2008, 11:16 PM   #1
msb64 is offline msb64  Canada
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Smile Threshold Mods or Upgrades

Just wondering if anyone out there had some mods or upgrades for Threshold amps? I currently have an S/300 Series II, an S350e and an S/500 with the e topology upgrade.
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Old 20th December 2008, 12:13 AM   #2
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I've got two S-500s. They're good on low frequencies, but get somewhat cloudy or veiled at higher frequencies. I tend to use them on my woofers or subs most of the time.
Adding film caps--I used a handful of 4uF polypropylene caps I had on hand--as bypasses to the power supply caps went a long way towards opening up the mids and highs. At one point, I added enough extra power supply capacitance to bring each amp up to a quarter-Farad...helped very nicely with the subs I was running at that time.
There are some tantalum caps in the front end that I replaced with polyester caps, not so much as a sound quality issue (they're part of current sources, as I recall), but because one of the tantalum caps failed. Film caps tend to last a while.
I'll try to roust a brain cell or two and remember what else I've done.

Grey
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Old 20th December 2008, 12:24 AM   #3
msb64 is offline msb64  Canada
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I noticed that too, nice unit for bass but not the best for mid/highs.
I am using a Pooge2 modified DH200 for the mid/highs right now. Figured it was a good time to recap my S350e now, as it "came apart" Mods would be very easy now. Once this one is done, I can move onto the S500e, as funds permit.
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Old 20th December 2008, 01:54 AM   #4
spind is offline spind  Canada
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Belated welcome to the forums! Nice amps!!!! Cool location , well actually quite cool these days

Steve
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Old 20th December 2008, 03:29 AM   #5
msb64 is offline msb64  Canada
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Thanks for the welcome!
Definitely a cool start to our winter, an excellent reason though to work on various indoor projects such as audio/electronics.
I really like the older Threshold amps, and ended up picking up all 3 for less than the cost of a new S300 way back then.
I might have a spare Threshold amp to part with later on too.
I am thinking of putting the money into parts to build a musical concepts equipped Hafler amp.
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Old 20th December 2008, 08:30 AM   #6
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I have a S300mk2 sitting in a cupboard. Quite useless sonically, even for bass. The heatsinks and casing are probably the only redeemable parts and it may nicely house a 30-40W class A amp.

The only reason i haven't reused the casing already is the power tranny. If i could figure a way to non-destructively remove the potting i would rewind the secondaries to a lower voltage. Any suggestions how to do this?
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Old 20th December 2008, 03:09 PM   #7
msb64 is offline msb64  Canada
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Seems a shame to cannibalize a decent amplifier like that, especially considering it is still worth about $1000 US or more on the used market in North America. I'm sure someone out there would love to have it, and then you can use the money to buy the parts or equipment you need. Your location might be a issue though, I imagine shipping costs would be a little bit pricey. The DH series Hafler amps are not the most revealing amplifiers either in stock form, but boy do they come alive when upgraded. I wonder if the same is true for the Threshold amps? I did notice the 500e has much tighter, sharper and more defined bass than the 300 Series II, the 300 sounded kind of muffled and rumbley (word?) in comparison. Just out of curiosity, do you know what the secondary voltage on that torroid is? Chances are someone could also use that as is too.
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Old 20th December 2008, 08:07 PM   #8
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Quote:
Originally posted by msb64
Seems a shame to cannibalize a decent amplifier like that, especially considering it is still worth about $1000 US

When i last looked they seemed to go for around $700-800. I can't get a nice case and heatsinks for this amount. Plus i hate any kind of metal work. Most other types of work too I would very gladly reuse the transformer though. I think it outputs around 62v per rail dc so maybe 43v ac.

I tried some half-hearted passive parts upgrades and none brought a worthwhile improvement. Bypassing the main filter caps sounded outright bad with a wide range of bypass values. Replacing the NFB polycarbonate decoupling cap with a polyprop sounded marginally better. I guess good main filter caps will have a more substantial effect but that's a couple of hundred spent on a probably lost cause. If i get the energy to break the transformer potting i might turn it into an F5. The Threshold internals may be of use to someone looking for a nice PA amp.
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Old 20th December 2008, 08:43 PM   #9
msb64 is offline msb64  Canada
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Just out of curiosity, and if you don't mind me asking, what type of equipment were you using when evaluating the changes?
Source, preamp, speakers, cables etc.
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Old 25th December 2009, 10:12 PM   #10
msb64 is offline msb64  Canada
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I ended up replacing all of the electrolytics in my S350e, and added Vishay MKP1837 .01 mfd bypass caps, it did make a very noticable difference in the top end. I will be hanging on to this unit now as a backup unit for mid/highs.

I also have an S300 MK2 that I replaced the electrolytics in, as well as adding Vishay MKP1837 and some used Wondercap bypass caps, and I also increased the large ps caps from 29K mfd to 45K mfd caps that I had on hand. I brought it over to my buddies Infinity RS1 system and it easily outperformed his stock S300 amps. About 6 people were on hand to compare the units, and all picked the tweaked MK2 as superior in sound performance.

The Vishay MKPs are nice inexpensive bypass caps that anyone should be able to afford. The Wondercap Ultimas though are no longer available, so I am going to order some Sonicap Gen1s and Gen2s to try out.
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