F2 with 12V supply

[Ipanema]

Hi Mr. Pass,

Since I enjoy your F2 amp so much, I'm planning to build one for my car. May I know how much power can I expect with 12V car battery? Or which other current source amp of your design is more suitable for low supply voltage? FYI, I'm planning to match it with Fostex Fe-126/7 speaker.

Thanks a lot.

 

[winslow]

You are going to have to build some sort of switching power supply to get the + and - rail voltages...or use 2 batteries and reference power the opposite on one of the batteries, but you couldn't listen and charge the batteries while driving.

That and I don't think you have the proper space for those drivers to get any kind of lowend from them.

But I'm more of a car audio guy than a home guy, and those are my 2 cents.

 

[Ipanema]

winslow,

Agree that SMPS is a better solution, but I do not have the experience building that. I'm thinking of using F2 in bridge mode in order to increase the output power if there is no other suggestions coming in.

The fostex will only provide midrange and high frequency at the front. Subwoofer at the back will supply the low end grunt. Is this feasible?

May I know why fostex is seldom use in car audio?

Thanks.

 

[kilowattski]

IRRC the F2 uses a single 24 V power supply. The reason Fostex is never used in automobiles is that they are designed to be used in single driver horn speakers.

 

[Ipanema]

Hi kilowattski,

I'm aware that both are not designed for car use. I believe they will work in a car, but not sure how well will it be. But from replies, it doesn't sounds like a good idea.

Thanks.

 

[Magura]

Fe 166e has been used in horns in cars before with some success.


Magura 🙂

 

[woody]

I realy don't think the f2 will like operating on a 12 v supply.
Mosfets usualy need some voltage to operate best. If you look
at the capacitences of a mosfet they gets higher the lower
the drain source voltage and tend to get verry high below
6v.

I haven't heard of anyone building it but Andrew Cirnoff sp?
(one of my many spelling errors) had an interesting fet amp
for car use. It used an inductor as the current source. But
then geting a good 3a low dcr inductor at about 500mh is
another problem!

 

[Ipanema]

I just browse through Passdiy website. It looks like ZV5 or Babo version of ZV5 might be suitable for use in 12V supply due to the almost rail to rail ouput swing. But I'm afraid that this design might clean up the 2nd harmonic that I so love in the F2. hhmm...dead end again...

 

[winslow]

I put Mini-A boards into my Monolithic A501 heatsinks and power supply. PS needed a lot more filtering but sounded good...not that the A501s were bad to begin with.

But I wouldn't recommend doing that to such a hard to find amp like the Monolithic.

Maybe find another car amp that has the rail voltages you need and use it for the PS?

 

[Ipanema]

Good idea. Save alot of trouble this way. I'm heading to junkyard now...hehe..

 

[Nelson Pass]

Well, the problem is that the FETs like to have some Drain-Source
voltage, like 4 volts or more. So most of the time we design the
supply at 4+V more than we want for peak swing, and this is just
throw-away voltage.

A car has a 13.8V supply. Subtract 8 volts, and you have 6
volts left, or 2V rms - less than a watt into 8. And that's ignoring
the drop across any Source resistors.

 

[Ipanema]

Mr. Pass, may I know what's the reason to have 4+ volt margin for mosfet Vds? As for as I know, the upper swing is limited by RdsON of IRFP240 X bias current, which should be very minimal for large current.

Do you have any suggestion on how to migrate F2 sound into car?

Thanks for your inspiration. 🙂

 

[Babowana]

... the reason to have 4+ volt margin for mosfet Vds?

For the operation outside ohmic region, I think . . .

 

[Ipanema]

Hi Babo,

Thanks for sharing. It does make sense from the graph.

The only option for me right now is to get some old amp from junkyard and replace the internal organ wtih those of F2. 😀

Regards.

 

[MikeW]

Looks like a job for power J-fets.

 

[Nelson Pass]

They have a similar characteristic in this regard.

 

[EUVL]

Build a DC/DC converter using an LT1680 and you can get 48V 5A without too much difficulty. Problem solved. Perhaps a cap multiplier after a L-C filter to get rid of the 100kHz ripple ??

🙂


Patrick

 

[MikeW]

They have a similar characteristic in this regard.

Depending on the Vgs?😕

 

[Ipanema]

Speaker recommendation

Build a DC/DC converter using an LT1680

Thank you. This doesn't look too complicated at first glance. I might give it a try. 🙂

Guys,

Can you recommend a speaker system that will work well with F2 in a car? I propose FE126/7 as front speaker and subwoofer at the back but was shoot down by the caraudio guys because they said Fostex are not built for car environment. At home, I love to listen to my Coral Flat8A in a big bass reflex enclosure. Any idea?

Thanks.

 

[Magura]

I haven't heard of anyone building it but Andrew Cirnoff sp?
(one of my many spelling errors) had an interesting fet amp
for car use. It used an inductor as the current source. But
then geting a good 3a low dcr inductor at about 500mh is
another problem!

Winding such an inductor is sure possible, I have made something similar for a hefty power amp.


Magura 🙂