symmetrical 400 problem...bias setting

Status
Not open for further replies.
Jump to Latest
M

Mattyo5

Member
Joined 2002
#1
Ok, I'm having trouble setting the bias on my aussieamplifiers symmetrical 400. There is NO mV across the source resistors (emmitor resistors) at all, no matter how much I turn the pot. Now, i built monoblocks...and both are behaving the same way. weird huh? I get almost zero mV offset...2 mv or so, and I do get sound out of the outputs...although it is quite distorted (either driver stage or preamp driving the speakers). There is voltage on the rails...and also taht rail voltage is getting to the mosfets...irfp240 and 9240. Any ideas where there is a bad solder joint or a bad connection? I have brought back the pot to zero ohms, per instructions, and measured 4.7k across q10's base and collector...again...per instruction... i have not check all the Anthony's checkpoints, but the ones I did check came out just fine. any ideas at all why no current is flowing? thanks!

-Matthew K. Olson
 
#2
Hello Matthew,
I am at the end of my re-construction of this amp with 2x300 VA toroids and the caps you sent me 😀 , and it works just fine....

Unfortunately today I can't access the net from home😡 , but when I get home I'll check if I had to make changes to get it work and tomorrow will post the reply.

Are you using Anthony's pcbs or did you make them yourself?

Cheers

Andrea
 
#3
Thanks Andy. The power supply works great...no problems w/ rail voltage...just don't know where I went wrong. I did "alter" the traces a tiny bit b/c i drilled some holes in the boards to be a little bigger. :-D So I'll go back this afternoon and make sure that I did everything ok. But still, i'm pretty sure I checked that stuff. Anyway,......i just need someone to look at the schematic and see where ....around the pot somewhere...I may have messed up a trace so I know what I'm looking for. Thanks! Later!

-Matthew K. Olson
 
#6
Ok....its 6kohm resistance between the c and e of q10 (bd139). I'm getting only about 1 volt across the gates....but everything...all of Anthony's checks are fine. The pot works...there are no shorts that I can find, and all of the voltages are correct...except the gate voltage. (too low). Not only that...but its the same voltage for both monoblock amps, and no matter how much I turn the pots....the voltage stays at 1v across the gates ...easier to check...the outside of the ZD3 and ZD4....that run to the input resistors. .99v. I checked to see if the zeners were backwards, they are not. The bd139 is wired correctly...the main drivers get barely warm...bd139 does not. It handles rail voltage no problem....hmm...what else. This is gonna drive me nutso. I can change out the bd139's...just to make sure that they are ok...but would 2 of them be bad?...in both amps? too weird! any any any ideas????

-Matthew K. Olson
 
#8
All is better!! Ok, for anyone doing the anthony holton symmetrical 400 amplifier...uh...the pinout on q10 is out of order. the collector on the bd139 does match up w/ the board....as does the emmiter and the base...BUT...the order on the board is cbe...rather than the rest of the board which is bce. Its weird...but as long as you are VERY careful to place the bd139's collector, base and emmiter leads (flying leads) in the right placed...everything is ok.

i hope its ok to post this link

http://www.farnell.com/datasheets/43480001.pdf

its to the bd139 pdf file.... this is to help anyone w/ the same troubles. Later!

-Matthew K. Olson
 
#10
Took me 8 hours to figure it out though. What a drag. If i thought Anthony would respond...I'd email him about it and tell him to post it on his site. Its just NOT cool that the base and collector are switched and in a different order than EVERY other transistor on the board. not cool at all. Thanks for the help though! later!

-Matthew K. Olson
 
#11
It is cool that you have it working, though! Just a layout issue, the base is in the middle so it can connect to the wiper of the potentiometer. (My sym amps are doing fine, and ironically I made the same mistake earlier and blew some stuff up.)
 
#12
I understand that they layout works out better...but DANG...he needs to put a note in the contruction notes since that actual layout is different than the pinout. I also know that Anthony has pretty much jumped off the planet ...Anthony, please post here and prove me wrong....but still. I hope that whoever else builts this amp notices :att'n: that CBE and BCE are DIFFERENT LAYOUTS!!! and careful attention needs to be payed as to where this goes. I have had zero zero zero problems other than this, and from reading this board...now...after knowing what to search for...I realize I'm not the only one. Boy is the bass on these amps SWEET. Later!

-Matthew K. Olson
 
#13
To be fair, the construction manual says: "Q10 will need flying leads soldered from the Base, Collector and Emitter pins of the BD139 to the appropriately marked pads on the PCB shown as Q10." And also, "For the time been temporarily wire up Q10 via flying leads. Making sure that you match up the Collector, Base and Emitter pinout’s on the PCB, with the Collector, Base and Emitter pinouts on the BD139." I know, it's sort of unfortunate he isn't very communicative anymore.

But, that's water under the bridge! Yes, the amps can really kick.
 
Status
Not open for further replies.
Top Bottom