SissySIT R.3

tnx Grimberg :)

first thing - be sane enough to remember to order some, when ordering parts
second thing - order few more, so you can cut them in adequate length, for squeeze work
third thing - be careful when working with them, if you loose them on the floor, chair is having 6 double wheels, each of them being equally ruthless; so order even few more

because of third thing ( done first few more than few times), I'm always in need to do it again

me being even more clumsy, with age

:clown:
 

sp33ls

Member
Paid Member
2018-04-06 7:09 pm
USA
I was reading a few of Papa's white papers on the FW site, specifically finding the "sweet spot," VFETs and triodes.

It got me wondering (dangerous thing) about the role of temperature and THD with this amp (IRF & THF-51S). Measurements on first page show little to no difference, tho I can hear a difference between cold vs warmed up.

And how does the harmonic distortion spectra shift with bias -- hotter equal more sweet? >:)

Pa's comments regarding negative vs positive phase were also interesting. I'm guessing the SissySIT is tilted towards negative 2nd/3rd? Guessing so because the sound field and sense of space is greater than what I've heard before, and the presentation isn't very "forward" and in your face. Just a wild guess.

I suppose this is the "art form" for voicing the amp which the Mighty ZM has generously provided.

Also, burn-in seems to be quite real. I've experienced a similar sensation with brand new amps where the first couple hours (t0) are a taste of what's the come, then it takes a turn for the worse, then gradually comes back to t0, eventually blossoming into its full glory. I think I'm experiencing a bit of that right now.
 

Vunce

Member
Paid Member
2014-01-26 8:20 pm
LI, NY
Well. First impressions are that this this stupid spooky. :0

Honestly, setting the pots went without a hiccup, tho trying to access them with my super tight monoblock build was challenging. Managed to hit 199.5mV & 20mV without a problem. Let amp sit for 15m or so before setting offset. The LT4320 PSU boards deliver +/-26VDC to R+/R-.

View attachment 1049958
View attachment 1049962
I can only hear a faint hum with my ear right next to the woofer (both channels). Honestly, I'm surprised that it's not more noticeable given my small chassis. I'm glad I went with shielded donuts, tho I'm wondering if I may be able to almost eliminate it completely by moving some wires around?

Also, I'm currently using a 3A fuse in line of each donut (as well as 2x 6AT at IEC). Was wondering if I need to bump that down to 2A5?

I'm very impressed with the bass out of this thing given it's 'only' 20-30W.

The organic tone and spooky realistic nature is reminiscent of some SETs, but with the added benefit of solid state bass. :)

Thanks for answering my numerous questions, as well as the creation of this beautiful beast Mighty ZM! And, of course, we must blame Pa for our greedy addiction. I'm super grateful that this community exists.
Really nice build sp33ls (y)
Working with the new slim monoblock chassis must have been tedious at times, Bravo! The Lottery VFet case was slim enough for me, LOL
 
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just wait, you are still not pi$$ing full (destined) amount of Thinner :rofl:

all graphs you can see are delivered with amp in temp. equilibrium;

I don't care how they are looking when amp is cold, but as I said oomphteen times - I'm not waiting to enjoy my music until amp is fully warmed, I'm enjoying my music right from the Switch On - try doing the same, life is too short to be wasted on irrelevant rituals ....... besides - music is already there, recorded, take the spirit and just go with the flow

now, SissySIT is, intentionally or not, proper PoorMenSub for SIT-3, meaning - it's brain-obliging THD Factory, 2nd dominant, negative phase

ahem, slight difference in sound of amp being cold vs. full hot - most likely culprit is increased thermal distortion ..... meaning - distortions invoked by minute temperature changes in part itself are, by logic, much greater in system not yet reaching it's temp. equilibrium

I reckon - absolute value of these changes is not changing in two extremes, but its relative value is much smaller when everything is Bloody

TEMP.jpg
 
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jcon2

Member
Paid Member
2004-04-14 8:14 pm
Seattle
I was reading a few of Papa's white papers on the FW site, specifically finding the "sweet spot," VFETs and triodes.

It got me wondering (dangerous thing) about the role of temperature and THD with this amp (IRF & THF-51S). Measurements on first page show little to no difference, tho I can hear a difference between cold vs warmed up.

And how does the harmonic distortion spectra shift with bias -- hotter equal more sweet? >:)

Pa's comments regarding negative vs positive phase were also interesting. I'm guessing the SissySIT is tilted towards negative 2nd/3rd? Guessing so because the sound field and sense of space is greater than what I've heard before, and the presentation isn't very "forward" and in your face. Just a wild guess.

I suppose this is the "art form" for voicing the amp which the Mighty ZM has generously provided.

Also, burn-in seems to be quite real. I've experienced a similar sensation with brand new amps where the first couple hours (t0) are a taste of what's the come, then it takes a turn for the worse, then gradually comes back to t0, eventually blossoming into its full glory. I think I'm experiencing a bit of that right now.
Congrats on your sissysit build. Excellent job getting everything in the chassis!. I think that you will enjoy even more as time goes by. I have put 100+ hours and my build and enjoy it more and more. Find that low volume listening is exceptional as detail is not as compromised as other amps.

I considered using the L aluminum mounted to the sinks as it would be soo much easier adjusting bias and offset. Can understand why Nelson went that route. Particularly in this amp with only 1 mosfet using UMS. Also would have allowed placing of L lower on sinks giving the Sit more room to be centered on the sink. Oh well, Next build. Just ordered some 2sk182's as I suspect Papa or ZM might have another gem for us. Still not sure what to do with my pair of semisouths. I'll keep my eyes open as "buddha is everywhere".:yes:
 
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Analogico

Member
2015-12-27 10:05 am
ZM,

I plan to build, for my SissySIT, a dual mono CRC power supply with 4 capacitors per channel ( 2 caps before the R and 2 caps after).
Which of the following options would you choose?
  • 4 x 47000uf caps per channel
  • 4 x 33000uf caps per channel
  • (2 x 47000uf) + (2 x 33000uf) caps per channel
Thanks.
 

sp33ls

Member
Paid Member
2018-04-06 7:09 pm
USA
In the context of a dual mono PSU (230V), what is the most suitable option to use CL-60 thermistors as a softstart?
  • One CL-60 before both transformers
  • One CL-60 before each transformer
I ended up doing one CL60 for each primary line (red), so 4 CL60s since I have dual primaries and dual mono.

I saw a website where they offer to improve your First Watt amp via a series of tweaks. One of which was removing the CL60s. Not sure how that would make a difference when you've got 100k+ uF stored in cap banks lol
 
I opted for one CL-60 in total for my dual-mono SissySIT (230 V; 2 x 400 VA; 528 mF in total). My reasoning is that the amp draws less than 1 A from the wall in steady-state, and I want to have enough current flowing through the CL-60 that it gets hot enough, so that its resistance drops more and I have lower impedance on the primary side. Works absolutely fine, and I have a fuse of 1.6 A or 2.0 A in the IEC inlet, so the CL-60 is still providing enough of a soft start.

Regards, Claas
 
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