Threshold SA/1 monoblocks cap issues, perhaps?

Few weeks back I bought these monoblocks and added to my system consisting of Metrum Adagio, EAR 868L, Focal 1038BE and laptop working as a source which will be replaced with a custom made computer based transport in few weeks.

But these monoblocks seems to have few issues though the seller told me that everything was fine with these monsters.

1. There is big thump when I switch on these amps one by one and also within a second I hear a high frequency sound like "ptakk" from both sides. This sound is there while switching off the amp though less frequently and intensity IMO.

2. Initially I thought the sound is only while switching on and off but later I found that it is also there in between while the music is playing. This is more like "karr-karr" like.

3. One day I also heard it even when I switched off amp while rest of system was on. So I am thinking it might be due to leaky caps. All the caps look like in really good condition and seller told me that there is no need to chnage these as these have hardly been used. Even I use these for 20-30 min per day five times week.

4. Once I removed EAR868 from the chain and same issue was still there indicating EAR is not the criminal here. Adagi was working fine with Parasound Halo A21 which I had earlier before I added preamp and monoblocks.

I do not have much knowledge but I can learn quickly. Need the advise of experts as I really love the sound signatures of these monos.

Contact Jon Soderberg-Vintage Amp Repair. Awesome pair of monos don't risk em get them fixed.
Threshold SA1  Mono blocks used four 29000uF/75V capacitors on each  amp. You need to replace all 8 caps from both mono blocks.Diameter Is 3 Inches or 76mm. the best replacement is United Chemicon  36000uF/100V AT 95C or United Chemicon 33000uF. Cornell Dubilier is more expensive both caps are made In USA. This will solve your amp problems.
Unfortunately I can not contact Jon as I am from India. I am not sure if he can help from that much distance.

Replacing these caps is the easiest option for me as these are also available in India and price is approx. $450 for eight pieces. But I am not sure if it will solve my problem. Sometime it just might be fuse related problem.
E36D101HPN333ME92M   33000uF/100V 76mm  In diameter about 4 inches long you need longer screws 10.32 US standard. These you can get at mouser they will ship to India $240 plus shipping. 
E36D101HPN333ME92M   33000uF/100V 76mm In diameter about 4 inches long you need longer screws 10.32 US standard. These you can get at mouser they will ship to India $240 plus shipping.
So in your opinion fault is with caps? 
Mallory electrolytic caps electrolytic Is dried up since the caps were made In 1984. There Is a Threshold SA/1 on eBay for sale he replaced the original Mallory 29000uF caps with Cornell Dubilier 37000uF caps the results.
The capacitor upgrade is a noticeable sonic improvement particularly with the lower bass notes, very deep and tight. In parallel with the new electrolytic capacitors.
E36D101HPN333ME92M   will do the job lower price than CDE.
While back I did sell 36000uF/100V AT 95C 8 capacitors for SA/1 made by United Chemicon.
E36D101HPN333ME92M 33000uF/100V 76mm In diameter about 4 inches long you need longer screws 10.32 US standard. These you can get at mouser they will ship to India $240 plus shipping.

Can you please send me the link for these longer screws 1032 US Stnd.?

I do not mind paying more for higher priced CDE caps if they are significantly better than the ones recommended by you.
The guy on eBay replaced the the original Mallory CGS293U080X6L3PH with 37000Uf 75V he lowered the voltage by 5 volts not a good idea. The cap was 29000uF 80V. The last number 3PH means 1/4 28 screws bigger screws not a problem USA caps uses 10.32 screws and 1/4 28 screws about 20 percent.
 You want CDE 39000uF/100V price $120 each.37000uF/75V is $80 each. 100 percent USA made. United Chemicon is USA and Japan both are made in USA. 
United Chemicon 
E36D101LPN303UEA5M   30000uF 100V and E36D101HPN333ME92M 33000uF 100V is a good replacement. CDE and United spec is about the same. CORNELL is 3 times more expensive. Cornell is the worlds most expensive used by McIntosh/Ayre/Lamm etc.

I had a pair of McCormack DNA rev a monoblocks years ago that did exactly what you described. It all started when a speaker connection came lose and and was grounded and blew a fuse. I replaced fuse. From then on it made a loud thump when turned on then high pitch noise that went away in a few seconds, but I never heard noise while playing music. I lived with it for a while since I left amp on 24/7. I did end up sending off for repair because I was scared something may go wrong in the future. I was told it had something to do with what they called "the rail".

Several months ago I borrowed these amps from a local audio dealer in Minneapolis. They had been on consignment for $3k many months and I commented to the salesman several times that I should take these home and give them a try. Each time he politely told me to try other amps as in his view, these were not so good.....not at all incredible like many other used amps his shop had for sale over the last year, in particular, a pair of Goldmund mono amps that were sold for $4k in just a matter of days. But finally my curiosity got to me. He did however tell me not to do any critical listening for 24 hours. Once I turned them on, I was to leave them on.

I had been on the hunt for a solid state amp to drive a pair of Sonus Faber Amati Futura speakers for the times when I did not want all the heat from using CAT JL-3 amps. I tried Odyssey and Belles amps with marginal success with these speakers. The tonality was coherent but was rather flat dimensionally, and the bass was not at all powerful like I had heard these speakers at the Chicago dealer showroom with the dealer’s suite of multiple top-level amps and speakers.

I was on the lookout for Plinius 102/103, BAT 600/655 and Symphonic Line RG1/4/7/Kraft amps. But all of these are hard to find so I finally decided to just give the SA/1’s a try. My room has three 20A circuits. Each CAT amp uses one circuit and the rest of the audio system along with a couple of floor lamps uses the third circuit. I disconnected the CAT amps and plugged the SA/1’s into those circuits with Dream State Dream Catcher power cords.

Upon power-up, each SA/1 had a low-frequency thump, not loud, but still noticeable. And unlike all other amps I had tried, there was a 60 HZ hum that I corrected by putting a cheater plug on one amp....not a solution I like to use for the long term but it was ok for the audition. There were no other noises at power-up, or buzz or hiss from the speakers. The system was dead quiet with no source and volume set very high (preamp is Aria WV5).

I played some music briefly to assure all was working and then did not listen until the next day as instructed by the salesman. The amps remained powered on. I checked the heat sinks late that night and they were cool to the touch which was a great surprise as I expected them to be at least warm during the idle operation.

The next day I was eager to try out the amps. A quick no-source test showed silence with the volume control very high. And the envelope please.......

....I have tried many amps, solid state and tube, with dynamic and electrostatic speakers, and never, I mean never, experienced an amplifier that was so forward in the mids. We typically associate brightness or fatigue with exaggerated treble, but not in the mids. Piano strikes were horrible, ringing, fatigue. The top frequencies too were exaggerated but this was moot with the midrange coverage. I tried multiple LPs, and switched to digital (Lampizator B6) and after just an hour or so, I could not listen to these amps any more. However, with all of the above "negative" observations, the bass performance was as outstanding as I heard at the Chicago dealer. These amps took control of the woofers like no other solid state amp I had tried at home up to that point. This was mighty impressive but moot based on the rest of the amps’ performance. I left the amps on for another 24 hours and tried again the next night. A quick listen here was all it took to confirm the sonic signature of these amps was the same.

When I took the amps back to the store, the salesman asked me about my observations. When I replied with my comments of midrange and treble forwardness and fatigue, he and his associate looked at me and both nodded. What once (30 years ago) may have classified this amplifier as the state of the art, well, unless this is to be used as a bass amplifier, I would not consider it. There are far too many amps at a fraction of the cost here that far outperform the SA/1’s. And with their size and weight, this requires even more justification to own these amps.

After this experience, I tried a VAC 70/70 which was wonderful in all but the lower bass as this amp has no chance at all to drive the Amati woofers. I then tried Wolcott P220 mono amps which drove the woofers very well but not quite to the level as the SA/1’. The Wolcotts, even with their mediocre resolution, were impressively tonally coherent. A return to the CAT JL-3’s and everything special about these speakers returned.

A few months later, just last week, I tried a Symphonic Line RG1 and this was absolutely stunning with the SF speakers. WOW would be an understatement. Still not the last word in bass like the CATs or SA/1’s but very impressive and awesome clarity.

I don’t know the age of the caps in the SA/1’s I tried, but the power supply with its ability to continuously drive the very demanding woofers in the SF Amati speakers indicated no issue here.

With all of the discussion in this thread about capacitors, perhaps the OP’s amps indeed need the caps replaced. But based on the previous post, I would not be in a hurry to invest in cap replacement. Instead, try some other amps before any additional expense is made to these amps.

One final thing: these amps are meant to be left on unless not used for long periods of time.  Turning them on and then off an hour or so later, will never give you any chance to hear what a component is all about.  The salesman made this very clear to me.  Only exception here is for tube power amplifiers which should ALWAYS be turned off when you're away.
Could be a combination of getting a thump, on start up and interconnects, power cables, speaker wire crossed and talking to each other. I would go through process of elimination outside of amp. Have you left amp on for long period of time to see if it clears up, if you don't trust to leave it alone don't do it. Unplug amps turn up volume leave for a day. Check fuses inside and outside of amp, make sure they are getting good contact they could have been in a not so perfect environment in storage and have corrosion or rust at contact point on fuses. Make sure fuses aren't stressed and correct value. Start at iec wire solder joints for good contact or altered ground wire going to power supply. Look for any loose or bad solder joints with magnifying glass or loop through out amp. Google what a bad cap looks Iike they do more than just swell. I find it odd two different amps are doing the same thing, certainly getting noise from both speakers while playing music. You will figure it out, those are very nice amps good luck.

Read thread a little better, I wouldn't just start throughing parts at it, that could get costly.

Never left the amps on for more than 30 minutes. The amps are connected to voltage stabilizer and power conditioner and I turn off everything after I am done playing music. I only have about 30 minutes for music 5 days a week.

Amps ere bought at end of this February.

At no point all the wires cross or come close to each other more than their respective inputs/ouputs behind all my equipment.

I have spare Parasound A21 and I prefer the sound of monoblocks.

BTW some renovation work is going on in our home and early next week I would check few internal parts though I doubt I can find a faulty piece.

I know this is an old thread. Does anyone here know the rail DC voltage is on these amps? I am thinking of changing my S/500 to strictly a class A amp and would need to reduce the voltage from the 76vdc it runs at now. 

Thank you