F5 power amplifier

[tinitus]

I dont know, but I never had any problems with trafos up to 500va
But they were maybe 33V trafos, so less ampere
But 500va with such low voltage sure has much higher ampere

If anyone knows, I would like to know too
Does that make a difference ?

[udailey]

If you line your thermistors of 10R up in series you will get 20R, yes. But you wont get 15A you will still have 7.5A. If you put them parallel to each other you will have 15A and 5R. I am sure of the resistance part and not 100% sure about the current part but thats the way it makes sense to me.
If you put thermistors on the primaries then they clamp on the current from your house voltage. If you put them on the secondaries they clamp on the current from the stepped down voltage.
An example: If you have 3A at 240V coming into your transformer then you have 24V secondaries you can assume something around 30A on the secondaries. It matters where you put them if you only have a certain value. It doesnt matter so much if you can pick any thermistor you want.

[Nelson Pass]

You will want to use some caution putting power thermistors
in parallel, as they tend to current hog, that is to say that
one will get a little hotter, take more current, get a little
hotter...

[udailey]

That makes a lot of sense. Thanks Nelson.

[danieljw]

Hi Uriah,

I have used a sinlge 5 Ohm thermistor in conjunction with resistive/relay "soft start" circuit for 2kVa,

Recently i have been using a single thermistor for 500VA or less

and once again a soft start / thermistor combo for 600-700VA

The softstart circuits available at Ampslab have worked well for me.
There is alot of different options around.

I do understand your frustration but if you use a combo of a thermistor in the primary circuit of the power transformer and a soft start (resistive either power resistor or thermistor) i think you will find your problem disappears.

-Dan

[Brian Kingsbury]

Finaaaallly got my F5 working tonight!!!! I just need to say thanks to all the contributers here and especially Nelson for sharing your hard work and advice. I've never built an amp and am not an electrical engineer but all the info on these forums made it possible for me to finish without any (major) hiccups. I

I had to give up on biasing last night but got it down nicely tonight (<2mv DC on each output @ .600v bias)... It's definitely easier to bias if you have at least 2 multimeters .. and with hook probes so you can just hang em and turn the pots. I had to do it one channel at a time and with just one multimeter and it took longer than I had hoped since I had to wait for both channels to get hot before I could get a setting I liked.

After hooking up some crappy test speakers and quadruple checking (it's my first amp .. never can check enough :P) It's warming up again now and my first listen on my RBR's just sounds fantastic. All the glowing reviews have said it far better than I can but I'm extremely pleased. It's very neutral, the highs sound clean and airy, the bass is clean and deep and the owner is happy

I was worried it wouldn't be able to play loud enough (83db sensitivity speakers) but there's definitely enough volume from what I've heard so far. I haven't pushed it yet but just a quarter turn on my volume knob is plenty loud for casual listening.

Now to build a preamp .. using my old yamaha mid-fi receiver just doesn't do justice to the rest of my setup.

[danieljw]

well done brian

i will be the first to say

pics pics pics !! would like to see how it turned out !

-Dan

[tinitus]

Originally Posted by Brian Kingsbury

Finaaaallly got my F5 working tonight!!!!

Nice
Consider yourself lucky
A real good amp is worth a lot, and hard to find

Please try some of your less good recordings
I bet they too sound better than usual
Please report, I would like to hear of this

Managed to order my outputs today, and hope to join you soon

[Brian Kingsbury]

Originally Posted by tinitus

Nice
Consider yourself lucky
A real good amp is worth a lot, and hard to find

Please try some of your less good recordings
I bet they too sound better than usual
Please report, I would like to hear of this

Managed to order my outputs today, and hope to join you soon

I've been lucky enough to have frequent access to a friend's truly amazing reference system in the past that puts pretty much anything to shame. To put it simply, I thought hearing that setup had spoiled me for life.. and it's been hard for me to cope with mediocre audio ever since. I built the F5 in hopes of getting close to the feeling I got when I first heard that system. I had rest my hopes pretty high and expected to be somewhat pleased (it would certainly be better than what I had) but was a little afraid i would be let down when I compared it to that reference setup.

The F5 is the first component I've heard in a long, long time that gave me the same tingles I got when I first heard my friends system. It's definitely the star of the show in my humble setup. It excels at everything I've thrown at it so far, even the lesser recordings. The soundstage is huge and accurately seperates instruments and singers. There's so much more detail than I'm accustomed to that I find myself frozen listening to music I've heard many, many times before. I hear things that simply weren't there before and it's got me captivated to re-discover some of my favorite music. The tonal balance is perfect and uncolored. It just sounds like music.

I must say I had pretty high expectations going into this build thanks to all the rave reviews and successful stories from this forum. To avoid any possible let-down I bought some pretty pricey components since the parts count was so low. I used Fairchild output devices, Cardas wiring and binding posts, all the .25-.5w resistors are Tx2575 'nude' bulk foil resistors from texas components, a 600va Antek xformer and 90,000uf worth of nichicon kg super through caps for the supply. Total cost for the build was still <$400 because I was able to re-use an old chassis/heatsinks I had layin around.

This is the first time I've ever had a component in my system that I haven't found anything I'd like it to do better than it does. It's the complete package. It's truly world-class.

[Melon Head]

Originally Posted by CBRworm

Could someone that has an F5 simulation running tell me what will happen if one rail of the power supply goes open?

Thanks.

I get somewhere between 200mV and 300mV at the output.
That is with +/-35 V rails and 2.4A bias