F5 Turbo Builders Thread

[Rush]

Advantage i200
got nice features, like remote adjustable level on all inputs seperately
and you can write your own names on all input sources

unfortunately...it does not work without the remote control, which ofcourse wears out, and is stupidly expencive
or maybe it has develloped yet another 'failure'

maybe its at the end
I also have the matching CD player
so its a dilemma

Sell the CD player while you can. You can do better with a Mac Mini and a Ayre QB9 (SE or Balanced out).
Gut the amp and make a pretty F5T balanced in its place.

Rush

 

[schaume]

Where did you find that case, it's quite nice?!

 

[jacco vermeulen]

VT4C

 

[Rush]

VT4C

211

 

[Rixsta]

So what happens if output transistors go up in smoke or die in the amp ?

will it output DC to speakers? and is there any other way to protect speakers other than fuse and relay protection ?

 

[AndrewT]

A crowbar across the amplifier output. This must be preceded with fuses either in the supply rails and/or close rated fuse in the transformer primary.

 

[Rixsta]

Ok, yes will add fuses on rails as well as primary.
My guess here is that as soon as there's a fault those will blow as amp will be drawing too much current.

This sounds like good protection, perhaps DC would go to the speakers for a tiny fraction of a second, or fuse may blow before that.

I don't expect my F5T to fail but just incase.

what did you mean by a crowbar AndrewT ? thanks

 

[AndrewT]

Crowbar = A circuit that shorts the output to ground to force the speaker damaging voltage down to near zero.
But it draws enormous current while the smoothing discharges and will virtually guarantee destruction of the output stage.

 

[Rixsta]

I see thanks, good protection for speakers but pretty nasty for the OP stage.
How can we work out how many amps output power that can be delivered ?

Im debating buying Speaker protection board from ebay but need to know if 15Amp is ok.

15A Current relay Speaker protection board Kit for DIY kits | eBay


Thanks

 

[AndrewT]

The BIG problem with conventional mechanical relays, is that when the isolator is REALLY needed, the relay contacts can arc and/or weld and not achieve the open circuit that the speaker requires.
One needs to check the DC rated breaking capacity. It is usually very much lower than the AC rated breaking capacity. And it is worse for inductive loads, i.e. speakers.

Read the Thread about SS relays, Mooly ?

 

[Rixsta]

Yes, I remember reading you saying this on another post somewhere.

Thanks Im thinking of going this way with good relays OR just putting appropriate fuses on the secondary AC or after Caps DC ?

Im Presuming with the right fuses, they would blow fairly fast and the speaker may see DC for a second or two.

Atleast fuses are some form of protection without having to worry about sound quality issues.

 

[WalterW]

Two questions:
- When I power up my new F5Turbo v2 it consumes around 300 Watt total and after an hour or so they stabilize around 350 Watt ( that is the bias I set them to when they were hot). Is this a too big difference ?
The R11 and R12 resistors which are in series with the NTCs are already lowered to 1k21 instead of 2k2. Should I lower them further or even short them?

- One transformer starts sometimes humming for a few seconds, or a minute and then the hum dissapears slowly. With a cold and warm amp, very unpredictable... The amps bias and powerconsumption does not change when humming.
I noticed this behaviour already testing the transformers without load.
What is the reason of this? What can be done?

Walter

 

[6L6]

Your power consumption seems normal.

The important question is what is your measured cold bias and what does it change into when it's warm?

 

[ijscobar]

Walter, what kind/brand/rating transformers are you using?

 

[oiphy]

- One transformer starts sometimes humming for a few seconds, or a minute and then the hum dissapears slowly.

dc in mains?

 

[vdi_nenna]

Transformer Rating

When building the v3, it's recommended to use a transformer with twice the rated VA. I have two Antek AS-4218 rated at 400v or approx. 11A each.
With secondaries in serial for 36v, will the secondaries deliver half the current?

Will the transfos be enough for mono block v3 F5? Would 5-6 amps be enough to drive 1 channel to 100w?

Thanks,

Vince

 

[WalterW]

Walter, what kind/brand/rating transformers are you using?

Two new Amplimo's 98016 : 625VA, 2 x 25V, 2 x 12.5 A, made in UK.
Total of 1.25 KVA for 320 Watt class A dissipation.
So 4 times the dissipation, which is good according to Papa

 

[WalterW]

- One transformer starts sometimes humming for a few seconds, or a minute and then the hum dissapears slowly.

dc in mains?

DC in the 230 Volts? Is that possible?

 

[oiphy]

afraid so.

DC in the 230 Volts? Is that possible?

yep..... and it saturates the trafo so it starts humming..
there's an easy fix with two diodes and two caps I believe... edit : AndrewT posted a link to it a while ago...


edit: http://www.federalpacific.com/literature/drytrans/10transformernoise.pdf maybe some help here

 

[WalterW]

Your power consumption seems normal.

The important question is what is your measured cold bias and what does it change into when it's warm?

Hi 6L6,

I measured cold exact 0.2 volts over the 0,1 Ohm resistor in each PSU rail.
So cold 2.0 Ampere = 1.0 Ampere per MOSFET.
Over the P channel 0.22 Ohm sourceresistors I measured 0.217 V and 0.212 Volt, so that's indeed around 1 Ampere / MOSFET.

When the Amp is hot, I measure 0.252 Volts over the 0.1 Ohm PSU resistor, so my beloved 2.5 A per rail. The 0.268 V and 0.262 Volts over the sourceresistors confirm this. Around 1,25 Amp / MOSFET.

So that's what the bias changes from 20 degrees Celsius to 52 degrees Celsius.
Is that too much?