SIT-3

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#42
30V4pp@8R

/2 = 15V2peak

/1.41 = 10V75Vrms

P=(10V75rms^2)/8R= 14W4
Pa declared it as 18W jobbie and it certainly is, but at some higher THD level

for Pleasure Device, as each of FW SIT amps is, you need adequate speakers - both efficient and sensitive (not same thing and rarely achieved in same time)

then you'll use few Watts and you'll have plethora of dynamic reserve

be happy - you snatched a Gem, speakers are easier to get
 
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#43
If that's the case then it would be even less at 13.65 because the load was 8.46. Is this what are others getting with their SIT-3?

13.65 seems a bit low and that would be right with what i was thinking about driving my speakers. I know them well and it sounded like 10-12 to me.

@Zen my Tekton DIs are easy to drive....
 
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#45
The right channel is the strongest at 30.4Vpp the left a bit less. The line is running at 123v. As for distortion, it will be a couple days until I get some cables in to measure that, but I don't see it making 4W more out of it, it's right on the verge of clipping maybe slightly into clip were i measured it.

Sounds fine, just sounded tome like it was down a bit and the measurements seem to back that.
 
#46
thompsontechs said:
If that's the case then it would be even less at 13.65 because the load was 8.46. Is this what are others getting with their SIT-3?


13.65 seems a bit low and that would be right with what i was thinking about driving my speakers. I know them well and it sounded like 10-12 to me.


@Zen my Tekton DIs are easy to drive....
Click to expand...

I believe you

in same time, speaker declared as 98db and 400W of max power ...... that is not sounding as speaker being delicate device, which SIT-3 deserves

high power handling gives impression of basically PA drivers used, and there is a price when you have necessary greater mass of copper in VC, which dictates heavier VC former, sturdier spider, heavier cone .....

see what type of speakers are using other users of FW SIT amps
 
#49
regarding power declaration - try to test it at 2% THD

now, we are used that Pa is often (in most cases) under-declaring power ratings of PL amps

with FW amps, in most cases he is either punctual, or rounding figure by smidge

though, knowing nature of SIT amps ( and I'm not blaming anyone for not knowing that) things are not overly easy nor overly uniform ......... while parts (SITs) having own spread of characteristics, there is no loop NFB to equalize that , while if there is any factory setting procedure done ( and it is) , main goal certainly isn't power range but uniform THD Spectra

pretty much each SIT amp is unique beast .... be it factory one, or made in DIY action

that's my opinion;

now, what your expectations are, as paying Customer, I can't say nor mess with that
 
#50
Let me do some more testing... Nelson, Is there anything you wish me to test voltages on internally, or no?

The right side tested at 30.4Vpp the left at 28.8Vpp, both right on the verge or slightly into clipping the load was a non-inductive resistor 200W at 8.4 ohms. Rigol DS1504 scope for the measurements.
 
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#54
poseidonsvoice said:
Here are the Sphile measurements for reference:

First Watt SIT-3 power amplifier Measurements | Stereophile.com

Best,
Anand.
Click to expand...

I found that last night, but thanks for posting it... Looking at John's measurements, put things in perspective. I'll have the cables today to do the same tests here. I think it will be on par with what John got.

Let's see what we see... the only other thing is to match the L&R and measure at the same distortion for output. Both sides seemed to be pretty close when at lower levels, but get more variance L-R as the input/output is increases.

The ruff numbers I got was 12.34 on the left and 13.65 on the right, a difference of 1.41W at clip. Again those numbers are ruff as the clip was done by eye and could be off a watt or more, so let's see what we see when I get the Quant going later today and tomorrow.
 
#55
Extreme_Boky said:
Maybe Iq needs to be fine-tuned..?
Click to expand...

indeed, let's get some solid numbers before, but yes, I think this might be the case.

I think that will, likely, be the only thing needed as i think the numbers will be close to what John A was seeing.

Nothing sounds wrong, it just seemed to me, it was a little light on power. I have powered the Tekton's with 5-10 Watts before, but it's been some time. It's possible, or even likely, that I was misremembering the output and sound with those lower output devices.

One thing has never been in question and that is that the sound is very good.

JT
 
#56
FYI, original DEFiSIT, having less than 10W at astronomic THD level, is not perceptually going out of steam, not just feeding big honkin' DC Tannoys in sorta big room, but also Dynaudio Contour 1.8, in somewhat smaller room

just speaking about concept ...... and uniqueness of same

THD here (post #8), even if you can't tell that I'm official source in any way or meaning

one of these days I'll repeat those measurements , just for fun - to remove that weed from graphs

edit: following logic of how things are done, I would except similar THD Spectra and levels - at 1W or so, but I wouldn't be surprised to see some difference up, at max level; settings are usually done at 1W level
 
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#60
Okay, the right side was 24mV or so the left was 0-3mV. I tweaked them for even clipping on both channels, now both sides are under or just over 1mV and the output for both channels is dead nut the same 30.4Vpp

Thanks Pops, good call. It's hard to believe because we are talking about very very tiny adjustment. The amp was as OT when I did the adjustments too. I'll check it later to see if there was any drift, but it appears solid when looking at it.
 
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