Babelfish M25, SissySIT - general building tips and tricks

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Zen Mod

Zen Mod

Official Court Jester
Joined 2003
zenmod.in.rs/
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Robin De Wolf said:
It is R.2 and I have put a 0R1 resistor in line with negative rail from PSU across which is my DMM.
Click to expand...

Robin - with 68mV across 0R1 your'e at just 680mA of Iq

you need to dial higher Iq and only when you are having stable 1A4 or 1A5 , you can attend to dial DC output offset

so, figure of interest across your 0R1 is 150mV for 1A5 and later - 170 to 180mV
 
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Robin De Wolf

Member
Joined 2019
Exciting times, I am fiddling with P1 and P2 (in my lunch break, I couldn't resist the urge). Second channel will follow soon and this evening the crappy speaker test starts!
Offset keeps drifting between + and -30 mv, after lid on top and 30 min warmup I could not remember if I read it, but this is expected behaviour?

Thanks for your help so far ZM.
 
Zen Mod

Zen Mod

Official Court Jester
Joined 2003
zenmod.in.rs/
Paid Member
no worries Robin

everything up to 100mV (hot) is completely normal - fo any amp around, except can amps

so - just readjust it when amp is hot and forgetaboutit

R.3 is behaving better in everything, but that's - as I said - irrelevant

worth stating - again - that there is no sound difference between original, R.2 and R.3

I wish I had brain and cojones to invent R.3 right from the start but, hey , even OmniOmniZM is prone to learning process

:)
 
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Robin De Wolf

Member
Joined 2019
Allright, thanks William and ZM. I thought so, especially after seeing BAF 2021:

1640107104818.png


I have grown accustomed to my precious R2 already. Besides, you already comforted me when ordering that there are no audible differences.
 
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Robin De Wolf

Member
Joined 2019
Yes she has been singing for 3 hours straight! I lost track of counting;) She does need warming up quite a bit, because the difference between lukewarm and "can hardly hold hands on chassis" is quite big and the sound really opens up. It is very different from the Sony VFET. Highs seem much softer, lows more pronounced and detailed. As for image, I wouldn't know how to explain😅

I am still very surprised by the difference between this amp vs the F6 and the VFET. It will need and get many hours to pinpoint what it all is. First metric is of course fatigue, and there was none! So far I am very pleased.

Thanks ZM for this beautiful diy product, the build phase has been very enjoyable and with your instructions not too complicated.
 
R

Robin De Wolf

Member
Joined 2019
Hi ZM,

As I will be trying a different front end for my Vfet (pt2) amp, I will have Edcor 600:15k signal transformers to put in my SissySIT (Jensens are sold along with F6). After the exacto and wire mod, can I still use these after the mods or should I remove the wire and solder the exacto mod on the boards?

Thanks!

Robin
 
R

Robin De Wolf

Member
Joined 2019
So I installed the edcors, 10k resistor and 680pf cap, SIT connected again now with proper flying resistor. But guess what, I forgot to jumper the board where the 100r used to be. So upon power up I heard a loud buzz and SIT was already warm after one second because I turned it off immediately. I have been checking SIT and MOSFET mounting for isolation only to find out I forgot to solder a wire in R21/L21 when I was doing grocery's.

This must have been the cause of buzzing PSU, right? Hope I did not fry the SIT's..
 
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