Babelfish XA252 / Babelfish XA252 SIT / Babelfish XA252 SET

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#741
I also used the bias-circuit with the LT3092 from Zen Mod in my build. Worked from the first start like a charm!
And the IXYS-MosFets are not easy to be kept in the 'playfield'. My ones are biased to 2.6 - 2.7 A.
I only have another frontend which is very close to the VFet-frontend (a kind of cascoded BA-3 - frontend).
These amps are very nice sounding 'beasts'. Lots of power and control.
Cheers
Dirk
 
#742
I put the test rig in a case and it is sitting at about 43c. I need to evict my AJ and give the XA252 passive cooling + babysitter.

David Bowie has never sounded so good.

Shutdown behaviour is not very good, I am getting 3 thuds (not quite AJ thud level). I am disconnecting the speaks before shutdown until I work out what is going on. Have I made a Frankenstein XA252? I will post my KiCAD schematic and layout later.
D79400AB-57D1-4C7B-AB3F-F3A8A966C1E9.jpeg
 
#743
dunno Bubba

mine (any of 3 iterations) are behaving

if there is no signal, can't see nor hear neither powering On nor powering Off

that mild it is

though, in general - for good behavior it isn't just schematic, in some cases it is also how pcb routing is done

problem with my pool of knowledge is - it isn't overly organised, so I'm not exactly able to express what is important and what is not

in short - can't help much with pcb design, if it ends that your schm is correct
 
#744
Hopefully it is a correctable mistake in my schematic. If it is my layout I will have to buy some professional boards designed by someone who knows what they are doing. I was inpatient and really wanted to make a XA252. At least my pucks and speaks have not blown up or caught fire yet. I only started DIY audio during lockdown and was bored (one good thing about COVID).
 
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#748
Zen, since we are on the topic of PCB design, I see there is no ground plane. On some boards I see them, others I don't. How do you decide whether to use one or not?

Also, I notice that on your boards, the components are spaced very closely together. Other boards I see them far apart with long traces. Is this to reduce noise, crosstalk etc?
 
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#750
Mikerodrig27 said:
Zen, since we are on the topic of PCB design, I see there is no ground plane. On some boards I see them, others I don't. How do you decide whether to use one or not?

Also, I notice that on your boards, the components are spaced very closely together. Other boards I see them far apart with long traces. Is this to reduce noise, crosstalk etc?
Click to expand...

well, I'm not really aware of any good comprehensive tutorial for drawing pcbs, even if there are certainly some and certainly good ones

as I said - from various reasons it is not easy for me to make any longer, while still comprehensive, tutorial on subject .... mainly because habits I have are result of years of collecting crumbs and forming ideas of them; my ideas - not saying those are proper, but they're certainly working for me

anyhow - some components you must spread due to thermal reasons ( say output devices)

if you can keep anything/everything close - keep it
differentiate power traces from signal traces
recognize all routes (traces) being susceptible to capacitive coupling; same for current pulses
differentiate GND routes regarding signal and power
differentiate senses
recognize routes critical to oscillations ( connected to susceptible ones above, but not only)

keep them all fatest you can

double power ones - to top and bottom wherever you can

etc etc

ground plane - who cares, as long construction isn't MC, MM or digital

how to learn PCB design - take confirmed and good project and study it; there are myriad of Papa's pcbs around - real gems with which you can learn what's important and what's not

I'm deliberately doing many things different, simply because I'm Chicken and I started doing my own pcbs ..... when - yesterday? ........ comparing to Papa
 
#751
Very cool. Thank you for the mini writeup. I have a lot of Mr Pass's PCBs. I have been looking at them here and there as I start to play with drawing up PCBs. It is yet another interesting aspect of this hobby.

I am going to pull a few out tonight and look at them.

Thanks again 🙂 👍
 
#756
zeners 22V are there to keep voltage across LT3092 in safe range

Vmax for LT3092 is 40V

if rails are 35V, that's 70V window

5 volts or so across CMirror transistors and all series resistors

1V2 across 120K reference resistor

less 2*18V zeners, ends with ~28Vdc

using 22V zeners means ~20Vdc

not critical at all, did put them on above list as difference to ref. schm

frankly, voltage of cascodes being first thing possible to make difference in behavior, if culprit is in schematic and parts values
 
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#758
Mikerodrig27 said:
Very cool. Thank you for the mini writeup. I have a lot of Mr Pass's PCBs. I have been looking at them here and there as I start to play with drawing up PCBs. It is yet another interesting aspect of this hobby.

I am going to pull a few out tonight and look at them.

Thanks again 🙂 👍
Click to expand...
Another thing to keep in mind - the final size/format you’re after can have a big influence on layout. Conversely, if you don’t really have a specific target size, you can let the layout determine the final dimension.
 
#759
Letting the parts dictate the size is what I have been doing. I tend to like to layout things in a way that makes them easy to work on. so space parts out a little etc. However, it seems that keeping traces short and some parts close is also a design advantage so.... Lots of little battles.

I drew up the XA252 mosfet non-SET version just for fun a week or so ago. Just to practice. Now I get to go back and look for all of the little flaws. Drawing this particular amp was surprisingly difficult as I didn't really refer back to Zens for parts placement. I wanted to wing it and see what I came up with. I ended up with a few vias. There are a lot of traces crossing back and forth. Also, auto-routing wasn't ready for Mighty Zen's creation.

I have the real thing so this was just purely an exercise to learn how to use the program. 🙂
 
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