Scryer ... or how F8 met Mighty SissySIT

[Plott]

Many thanks!

Yes, practically the same, mine arrived via big river from China.

 

[Zen Mod]

my amp pcbs are all applicable to UMS, while my HA! pcbs are applicable to Modushop base plate - hole raster being 10mm

 

[Plott]

Of course, but in this chassis (Mini Dissipante) they couldn't be centered 🤪
That's why I use the plastic thingies.
It's just me, I like symmetry

 

[Zen Mod]

Symmetry is overpriced

even in case o SuperSymmetry, we strive to spoil it - to get dominant 2nd

 

[Plott]

PSU is up and running, please note the small blue led
No smoke, of course

 

[Plott]

Not exactly for this amp, but maybe for all of our 25w amps: I have "high performance" heatsinks with 0.3K/w @300w, 300 mm long, 100 mm high, the fins are 85 mm long. Could they be used for our amps, one per channel?
Thanks in advance!

 

[Zen Mod]

me visual type

pics please

 

[Plott]

Sure:

 

[Zen Mod]

one per side, just right about for regular FW format

say, no more than 100W of heat, rather cozy for 80W

mentioned 300W, who knows what criteria was that

 

[Plott]

Ok, thanks!

...and... one channel in on
Rails under load @+/-23.6v, DC offset 21mV.
But I can't bias higher than 165 mV across 0.11R, which means 1,45A
I let it cooke now for a while, but this values are stable since 20 minutes.

 

[Plott]

DC offset 10mV, great, Iq is still @1,45A, can't adjust higher.
I mean it's fine, but the amp can't develop big heat
The heatsink is hot, but I can leave my hand on for a long time.
Edit: in the max ohmic position of the Iq pot at the start there was 59 mV across the 0.11R group.

 

[Zen Mod]

change level shifter resistor to lower value

100R or 82R

back down with Iq prior to change

change

re-set

 

[Plott]

Many thanks! Okay, R134, I got it.
Will do it tomorrow or so.

 

[Zen Mod]

another way is to decrease value of R116, first lower standard value
so, 910R or 820R

though, if you give me present gate voltages of M101 and M102 - both ref to output node, I can give you exact/best recipe

 

[Plott]

Thanks MZM - looking at this schematics shows what the problem is.
I'm working with the schematics in your post #7 https://www.diyaudio.com/community/threads/scryer-or-how-f8-met-mighty-sissysit.388550/post-7078144 where the value of R116 is 1.3k instead of 1k in this new schematics 🤪
So I will simply change to 1k and I'm sure it will work and heat properly

 

[Zen Mod]

there is a link in post #1, pointing to final schm

always check my posts #1, who knows what new edit is waiting there

 

[Plott]

🤪

 

[Plott]

Okay, the changes are (but please correct me if I'm wrong):

R116 - 1k (was 1.3k)
R130, 131 - 6k8 (was 4k7 - smd-parts, I suppose there are the correct ones on the board?)
C109 - 100p (was 120p - smd-part, so same as before?)

So in fact I only have to change R116?

 

[Zen Mod]

just change R116 to 1K

gimme gate voltages of said mosfets, now or after the change, noting set Iq

 

[Plott]

Okay, thanks.