SissySIT R.3

[chede]

twitchie (#479):

I have the amp in a 5U/400 chassis, with dual mono PSU, and I run a bias of about 1.85A; rail voltages +/- 25V. So, it takes a looong time to heat up fully, but then the heatsink temperature is in the range of 50 deg Celsius directly opposite the FET and SIT, and I can keep my hands for as long as I wish on the fins or the top of the heatsink everywhere.

The bias is nice, stable, and constant on both sides, and always has been; Zen Mod's new bias regulation scheme works a treat.
Bias varies with temperature or rail voltage fluctuations by maybe +/- 5%.


Best regards, Claas

 

[Zen Mod]

Chede

think of decreasing Iq to, say, 1A7 or even 1A6 ........ and I can bet that you'll not even hear difference

think of mosfet - with present state, dissipation is highish, and thermal interface must be perfect

 

[flocchini]

Claas

Enjoy the music

Best

Bob

 

[sp33ls]

twitchie (#479):

I have the amp in a 5U/400 chassis, with dual mono PSU, and I run a bias of about 1.85A; rail voltages +/- 25V.

Are those inductors you've added to the PSU? Did you go CLC rather than CRC?

 

[chede]

Yes, this is a CLC, dual-mono PSU.

Per channel:

- Toroidy audio grade transformers, 2 x 20V, 400VA
- simple standard bridge rectifiers
- 2 x 33mF per rail
- Hammond 156B - 1.5mH, 5A, 0.07R
- 2 x 33mF per rail
- 60uF motor run cap per rail to "cap it off"

In my M2 amp with "Stereo PSU" I have used Hammond 159ZL (2.5mH, 10A, 0.044R), but those were too big to fit 4 into one chassis ...

In my approach, I am going for a very low impedance of the PSU. That's why I have sub - 0.1R chokes there. Those filter better than your typical resistor value of around 0.1R in a CRC supply, and have lower impedance as well.

In my next "big" PSU, I will probably use DC-Link MKP capacitors instead of the motor runs. They are more compact, and you can fit more easily a lot of extra film capacitance to the PSU. In my tube amp PSUs, I'm already doing that. My EL84PP amp has only DC-Link MKPs in the B+ supply, no electrolytics.


Regards, Claas

 

[mattattnet]

I am going to start populating my SissySit R.3 boards, I will use the standard ZM specified dual mono power supply, unloaded rails are 25 VDC, and my THF-51s SITs are roughly matched from Watanabetomoaki. Chassis is 4U x 400mm swiss army knife type...

My question is: I can socket resistor sites, are there any sites recommended to socket to aid in fine tuning the operating points?

thanks,
Matt

 

[Zen Mod]

pretty much just Level shifter resistor (R115/215), if you want to achieve perfect symmetry of upper and lower mosfet Ugs

simple as this : assemble it, set everything

then measure both mosfet gate voltages (ref to output)

measure voltage across R115/215 , write here
we'll see is it for change or not

later just solder final resistors in pin sockets

 

[mattattnet]

thanks, ZM!

 

[Zen Mod]

 

[wirewiggler]

Teaser, finished the power supply now on to the amp. Upside down not shire why the site randomly turns pictures.

 

[Zen Mod]

 

[Vunce]

Super cool Bill!!
Are those 40mm Noctua’s?
Just a heads up, I’ve been playing around with added capacitance at the output of the MicroAudio SMPS-CLA supply with my M2. After all my grounding scheme tips and tricks were exhausted, I was still hearing a faint hum right at the speaker. I checked for ripple with my Fluke and was surprised to see 117mV. I added 22,000mF per rail and the ripple dropped to 43mV. The hum volume decreased also. Next setup will be a CRC for each channel, knocking the ripple down even further will hopefully eliminate all audible hum

The moral of my long winded story: leave yourself enough room inside the SissySit chassis for added capacitance.

Cheers!

 

[wirewiggler]

Iyep 40x10 they look like toys, not sure how much air they will move but with the bottom open I will get a pretty fair amount of natural convection. I have 2 of these to go with the amp I will defiantly measure ripple to compare.
Bill

 

[Vunce]

Perfect!
I’m using similar pcb’s.
Looking forward to seeing your progress on SissyS.

 

[Samuel Jayaraj]

Can anyone tell if there is an audible difference between the original SissySIT with ACS723-5A chips, R2 variation with 6N139 optocoupler and this R3 variant with LT3092+PC817s?

I have a pair of TH51-S and Lynn's SIT-3X PCB set, but cannot decide which one to venture with. I would like low DF as it matches my Fostex FE168ESigmas. Thanks for your inputs.

 

[Zen Mod]

Mighty Moi wrote several times that there is no audible difference between starting SissySIT, R.2 and R.3

(oh boy, how I like writing in third person )

 

[Samuel Jayaraj]

Thank you so much Zen Mod!!!

 

[Cresnet]

Teaser, finished the power supply now on to the amp. Upside down not shire why the site randomly turns pictures.

That setup looks so serious!

 

[wirewiggler]

Sammy,
Yes, this power supply as well as its SLB power supply will be the last power supplies I will build. All future amp builds will have to work with one or the other. The SLB has the advantage of being able to switch transformers for different voltages .
Bill

 

[Zen Mod]

just few teasers, not best angle for pic, but clear enough

finally found some brain to arrange with (one of) my winder(s) to have custom chokes for my concoctions


4mH, 0R15Rdc, good for 4A with no sweat

will use that (CLC) instead of usual CRC (R being 0R1/5W)

caps are 33mF

if CRC was good, this one is going to be goodgood