F5 power amplifier

[AndrewT]

Checking that you have wired up the mains plug correctly, wired up the transformer correctly, wired up the PSU safely, wired up the amplifier safely, assembled the amplifier safely.

Go and read some, or many, of the posts describing the bulb tester operation and use.
Question:
How can you be a Member here for 30months and not have bumped into "mains bulb tester"?


BTW,
I have never blown up or damaged or smoked, any equipment whether wired up wrong or not, that was powered via the bulb tester.
That is not the same as saying one can never damage equipment via the bulb tester. But I am fairly sure that all wiring and assembly faults in power amplifiers can be detected without damage if the bulb tester is used and a voltmeter is then used to check all operating voltages, before direct power ON.

 

[dungdochi1978]

the same

Thanks for all your advice.

What still confuses me is the bulb tester. I know it functions as a current limiter. But what exactly am i testing with it?
And what should i be looking at when i power up with the tester (aside from smoke, fire & explosions) ?

they want to confirm make sure max current give out to load(will be speaker) with increase temp ...check what happend with all parts,V,I,dirtor..But remmember that ohm of bulb is not 8ohm.Dont mind it try this and you will get experience.( R5,R7,R8,R6,R1,R2 ,R11,R12) better bigger and you wont care about change value by temp.
Do everrything if u want.

 

[dungdochi1978]

Better they need make amp with 1 device (charactic of this device must be hight quality no have dirtotion,V-I,Temp ,high gain ..stability all time) .

 

[studiostevus]

Ok guys. I have started and biased the amp! No smoke no explosions.

Unfortunately the front and back panel are at the cnc mill, so everytime i walk past the amp, the bias moves a couple of mV due to temp variations... Does it make sense to already start listening to it? Or will that be a waste of time?

 

[Zen Mod]

if you made it (biasing procedure) with lid on while cooking , then everything is OK

 

[MaHo]

bias setting problem

Hello

I build F5 regular without changes, I set bias with no problem to aprox 540mV and offset 5mV, I run amplifier with speaker for cca 40h no problem sound was amazing, temperature was OK no problem to hold my hands on heatsink for log time. Yesterday when I power on amp /after resting more then 16 hours and cooling to room temperature/ fuse blou out. I check everything, found nothing wrong use bulb tester ans bulb light on and dont turn off,

I try reset bias tur pots to 0 ohm and no problem amp run OK no problem with fuse I reset bias recheck and everythig run OK, but after turning off and cooling to room temperature I try to power ON with bulb tester and ligh is still on

this is my first project. I think there should by problem with termistor, which after cooling down change bias and put to much curent thrue source resistor. I am not sure.

My knowledge is very limited
thanks a lot for your help

Martin

 

[Zen Mod]

it's likely just low fuse value

do you have 10R NTC inline with mains ?

 

[MaHo]

yes NTC in mains i have
fuse is 1.25A slow blow
first week was no problem with powering on

Now when I disconect amp from PSU powerig on is no problem PSU give +/-24.4V

thanks

 

[Zen Mod]

VA of xformer and filter capacitance ?

in an case - double that fuse

 

[studiostevus]

I am experiencing the same, a 2A fuse does the trick.

With the bulb tester and 2 channels connected, I see the PSU struggling to get above ~12.5VDC. Without bulb there is no problem and everything is working fine. Also cold but only with one channel there is no problem. Just the combination of cold, 2 channels, and lightbulb are tricky...

Is it because when cold more current is passed?

--- 400VA, 94000uF per rail

 

[MaHo]

500VA 2x 18V
66000uF per rail

 

[Chris Goldring]

Single Supply?

Hello,

just wondering, is it possible anyway to run the F5 on a single supply?
(48V instead of +-24V)

Happy listening! 🙂

 

[Zen Mod]

it is , in few different ways .

but - with slightly revised sch , either of amp or supply itself

for later , take a look at Quad 606 PSU

 

[Zen Mod]

500VA 2x 18V
66000uF per rail

3A15 , slow blow

 

[Chris Goldring]

it is , in few different ways .

but - with slightly revised sch , either of amp or supply itself

for later , take a look at Quad 606 PSU

Okay,

I would like to put the positive +48v at one "IRFP source-side" and ground at the other Source adding an output capacitor about 10mF or so at the Drains, using a single secondary winding rectified and smoothed to one rail +48v..

But i'm unsure how that will effect the VAS/input stage and the feedback network.

 

[Zen Mod]

I'll answer tomorrow , with best option

 

[Zen Mod]

look at attached schm

make your PSU in same manner , with two bjt's potential divider

feel free to use slightly stronger type of bjt's , something in range of BD139/BD140 , but with higher beta

that solution , even if compromise comparing to regular FW PSU , is certainl bettr than messing with amp circuit itself , thus decreasing it's PSRR

 

[regal]

Is the F5 a goood choice for these new ortho headphones that need 2W across their 38 ohm voice coils? So roughly 9Vrms with 238 mA.

 

[Zen Mod]

make some mini version

and be careful with that axe , Eugene ........... 9Vrms will not fry just your ears ..........

 

[jackinnj]

Is the F5 a goood choice for these new ortho headphones that need 2W across their 38 ohm voice coils? So roughly 9Vrms with 238 mA.

Take a look at Dick Marsh's new headphone amplifier in Linear Audio "A Headphone Buffer/Amplifier and Auto EQ for Headphones" -- sims out really good down to 30 ohms.