BA283 Fabio Out - debugging help required

[Guest]

I just finished wiring up Fabios BA283 output stage only boards and have a few questions
This is my first hit at debugging audio signals - PSUs no problem - this a bit out of my depth

Here is the schem and layout

http://www.groupdiy.com/index.php?topic=5335&postdays=0&postorder=asc&highlight=ba283&start=0
I have it on t bench (well a desk) and am feeding it 24v from a homemade Bench PSU
I am feeding a 1v sign wave from a signal generator and measuring the 1v sign wave on a scope
I am using the second probe on the scope to poke at the various bits of cricuit to see what comes out (before I plug it in)
The scope shows absolutely fine up to a point
then I start seeing a small square wave (the gate of the transistors?)
And just before the feed to the transformers there is a quick wiggly shallow line vibrating like mad
The output from the transformer is roughly the same

The scope shows a sine wave from R14 all the way to the beginning of R15
There is no sine wave after the R15 (in fact not at all after lower leg of R15) - signal tester proves there is a connection though

I jumpered RGx and put a switch at Gain to Rg
RV1 has no effect on anything on the scope
Just out of interest - do both bolt holes on the T03 need to be attached to the circuti or do I isolate one (?) - there are solder rings for both on the board
Anything else I need to check?

 

[Guest]

Pretty please

 

[Guest]

Solved
Both T03 holes needs to be done ie not isolated
It helps if your Output transformer is connected properly (ie 2 and 4 connected on a LO1166)

As well as the T03 getting hot - C17 gets really hot - is it because it is close to Q4?
My C17 is 25v (as per BOM) and is quite big due to being an Elna Cerafine

 

[kiira]

[quote author="uk03878"]Solved
Both T03 holes needs to be done ie not isolated
[/quote]

Hi. Could you explain this a little more? On a T0-3 the case is the collector (is that right?) .. so that means that you need to isolate anywhere it could contact the circuit except the 2 mounting holes, and the traces the contact?

The layout of your board looks different too, on mine Q7 is actually mostly under Q6. I'd put Q7 on the other side of the board? - ??? for anybody.

thanks,

Kiira

 

[Greg]

Nice work, uk. I did the same thing in the past. On the TO-3, the case is the collector, so the standoffs can't isolate the case from the circuit. It's common for Q6 to generate some heat, so make sure you have a heatsink on it. I don't think C17 should be getting warm.

 

[Guest]

This isn;t the board I have as well - Q7 is more vertical (although thats for a different transistor that I don't use so nothing is fitted - I hope)
Yes - I was meanign the two screw holes - (the case collector) they do need bot to be incontact with solder pads ont he bottom (for some reason I only thought on needed to be) - but the PCB traces want both
I gave them both and it works

My scope went though the roof - I was sooo happy to see the amplifcation of the input sine wave

I put all the resistors for the gain on a switch and put a 50k pot at the front as well
Interesting seeing what the RV1 bias pots does - I am a bit thick so I can onyl tell you what I see
When rotated the sign wave starts to square off at the bottom - at full or is that minimum all I see is a little bump ont he top of the wave - then it goes into a normal wave when I twist RV1 then it squares of at the bottom

I just set it to the best sine wave I could - I had to back of the 50K pot and take the resistor switch down a step to do this (I figure I am seeing the amp distorting)
Oh - I love this...
everyday is a school day

 

[Greg]

Isn't the "volume" 5K, not 50K?

 

[Guest]

I took it from the comment "50k is sweeter" from Steffen's - make up gain on his pultec
I am also goign to bung a 31267 before the pultec
So not really a gyraf pultec more of a "throw everything together and see what happens passive EQ"

 

[Greg]

Gotcha... I didn't know you were using this as make-up gain for the Pultec.

 

[safe as milk]

hi
guys, sorry to jump on your thread(cool info by the way),
but im just about to stuff a load of fabio's 283's,
what heatsinks are you using? underneath ones or sharkfin on top?

cheers

 

[Greg]

I've used both... both work fine.

 

[Guest]

I am using the one on top (because I had problems trying to find an underneath one that didn;t go over the transformer solder pads)

 

[safe as milk]

thanks a lot for that,
i think ive found the one from your bom greg at rs
there not cheap when u want a dozen or so are they.

cheers

 

[Guest]

£3 each from most places I think
I got my from ebay

Still not sure about them - cos you can;t use the mica heat transfer pads - so I guess you have to smear thermal glue stuff evrywhere ins ead (not nice looking and probably not healthy when you smear it with your fingers)

 

[Guest]

£2.35 at rapid
http://www.rapidonline.com/productinfo.aspx?kw=heatsink&tier1=Electronic+Components&tier2=Semiconductor+Hardware&tier3=Heatsink&tier4=TO-3+Heatsink&moduleno=77179

Although I wonder how good this one if from bardwells
http://www.bardwells.co.uk/detail.asp?stockid=SEMH05&ref=search%2Easp%3Ft%3D%26qfcode%3D%26catid%3D%26manuid%3D%26keywords%3Dheatsink%26minprice%3D%26maxprice%3D

5 for a quid

 

[safe as milk]

hi
ive ordered them 3quid ones from rs,
which side would u put the mica sheet? under or over?
i got a bag of them to try, will be cutting them to fit t03,
i bought them for t220 packages but it might work?
havnt opened up my grease pot yet, got that mess to look forward to!

how's yours sounding now?

cheers

 

[Guest]

[quote author="safe as milk"]hi
ive ordered them 3quid ones from rs,
which side would u put the mica sheet? under or over?
i got a bag of them to try, will be cutting them to fit t03,
i bought them for t220 packages but it might work?
havnt opened up my grease pot yet, got that mess to look forward to!

how's yours sounding now?

cheers[/quote]
You can;t put the mica sheet over cos of the bump of the trannie can
I guess you shouldn;t put it under - cos it means that you want heat transferred to the PCB
I do have T03 mica pads - but no they don;t work over (they crinkle and then I thought - stop - you are being f***g stupid)
I then stuck it under
(and now I relaise that is perhaps nto a bright idea)

Haven't had any time to progress it any further
Next stage is connect up pots and switches to the pultec boards
Off board switches - using uninsulated spade terminals to connect

 

[Greg]

For the one on top, I just used some thermal compound. No problems as far as I can tell.

I had an old BA183 and that's where I got the heatsink that mounts under.

Check out the 4th pic:
http://www.groupdiy.com/index.php?topic=17697&highlight=1272

 

[safe as milk]

cheers greg
i think mine are the same?
rs part number 402-989

sorry :roll:

 

[Guest]

Broadvision session displays no data - give us the part number and we will search
I did put systems in for RS - but not that pile of sh*t