F4 power amplifier

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analogair

analogair

Member
Joined 2005
Actually the MF A1 has specs that says 2 x 20W into 8 ohm Class A, but im sertain they only go about 8-10W in Class A...

The Audiovector 4 have been put away in my basement and have been replaced with a pair of B&W Matrix 801 Series 2

I know they should be rated as having a sencitivity at 96dB/1m/ 8w

I somehow am pretty sure that the are harder to drive than that, so if someone have some real life specs on my new used babys. :cannotbe:

But i can actually turn the knob almost to 11 o'clock before the sound turns muddy and uncomfortable.

Just before that it is actually pretty loud, but not as loud as i would like it to be for some sorts of music (read.. Roger Waters, Dire Straits, Thin Lizzy, Midnight Oil, Queen...etc...) :D
 
lykkedk

lykkedk

Member
Joined 2002
have you headphone output on your CD player?

try to feed Babelfish from that output,just for test.....then tell us what you hear.
Click to expand...

I just tried that :) Look's like we have a winner here !

The soundpressure, is louder now, maybe 3/5 maybe even a little more !!! Of what the speaker's usually are playing when driving near to the max, with my leachamp. So i guess Magura is right when telling me, that the preamp is the problem.
 
Zen Mod

Zen Mod

Official Court Jester
Joined 2003
zenmod.in.rs/
Paid Member
lykkedk said:


I just tried that :) Look's like we have a winner here !

The soundpressure, is louder now, maybe 3/5 maybe even a little more !!! Of what the speaker's usually are playing when driving near to the max, with my leachamp. So i guess Magura is right when telling me, that the preamp is the problem.
Click to expand...


correction:

"So i guess steen is right when telling me, that the preamp is the problem
:devilr:

anyway-change the spks

:darkside:
 
doggy

doggy

Member
Joined 2004
A30 vs F4

I am attempting to build the F4 point to point. Waiting for parts from tech diy, the rest I sourced from digikey. Has anyone compared the A30 to the F4, and what would the differences be? I would assume less gain with the F4; and perhaps more transparency? With my fostex fe108ez-mcm 8"combo horn I have lots of power with the A30 and very enjoyable.:)
 
lykkedk

lykkedk

Member
Joined 2002
Actually i was looking at youre post,but it doesent come clear to me, how much current / voltage each mosfet must swallow :hot:

I am just preparing a setup for matching mosfets... Se this LINK

So i would just like to know the voltage / current, for correct matching. (And to test the heatdissapation too)

Jesper :)
 
cviller

cviller

Member
Joined 2005
lykkedk said:
I am just preparing a setup for matching mosfets... Se this LINK

So i would just like to know the voltage / current, for correct matching. (And to test the heatdissapation too)

Jesper :)
Click to expand...

About the matching, unless you let your devices reach temperature equilibrium, the timing is crucial. You need to run the devices for the same amount of time. I doubt it will be a good idea to use a heatsink, since it will take ages to heat up and make it harder for you to ensure consistency in your measurements.
 
lykkedk

lykkedk

Member
Joined 2002
CViller.

I would like to try something out, about the heatdissapation :eek: About the matching i know that i will have to wait the same time every mosfet.

But I am still not getting this clear :xeye: If 250mV is flowing through the 0,47ohm resistor it sure gives the 500mA, but then if the mosfet is run at 10v it's only about 50w each, is that right ? Sorry i can't see this as easy as you can :cool:
 
cviller

cviller

Member
Joined 2005
lykkedk said:

But I am still not getting this clear :xeye: If 250mV is flowing through the 0,47ohm resistor it sure gives the 500mA, but then if the mosfet is run at 10v it's only about 50w each, is that right ? Sorry i can't see this as easy as you can :cool:
Click to expand...

You have 3 N-channels each running at 0.5A and 22.75V and the same goes for the P-channel devices. (If you have 23V rails)

Does that answer your question?
 
steenoe

steenoe

Member
Joined 2004
lykkedk said:
CViller.

I would like to try something out, about the heatdissapation :eek: About the matching i know that i will have to wait the same time every mosfet.

But I am still not getting this clear :xeye: If 250mV is flowing through the 0,47ohm resistor it sure gives the 500mA, but then if the mosfet is run at 10v it's only about 50w each, is that right ? Sorry i can't see this as easy as you can :cool:
Click to expand...

Jesper, the 10V is the value that the smaller fets are matched with (IRF610). Usually the 240's are matched at around 13-15V. You can choose to match them at 0,5A if you like, just adjust the series resistor accordingly. This would be closer to real life for Fet's, sitting in a F4.

Steen:)
 
lykkedk

lykkedk

Member
Joined 2002
Yes, tnanx Cviller, but i throught they was run at 10v each...

Well thats gives me a 11watt heatdissapation continuesly. My setup is with a 10ohm resistor which gives about 22watt running at 15v, is it ok, to lover the voltage to e.g 11v when matching, for getting about 11watt ?
 
cviller

cviller

Member
Joined 2005
lykkedk said:
is it ok, to lover the voltage to e.g 11v when matching, for getting about 11watt ?
Click to expand...

Sure it is. What you do is you find a suitable psu with a voltage X and your transistor will take about 4V from that and the you find the needed series resitance R to get the correct current Y.

R=(X-4V)/Y

In your case:

R=(11V-4V)/0.5A = 14ohm
 
lykkedk

lykkedk

Member
Joined 2002
I tried to make an experiment, with some 'U' shaped 230x50x50x4 Alu. profiles.

The output voltage from a 5A PSU is 12.65, when loaded.
The Series resistor is 9,5Ohm which gives me 12,65v-4v / 9,5Ohm = 0,9A load for the mosfet.
The series resistor swallow 6v and gives the resistor a load of 6v / 9,5Ohm = 0,63A, which is not important in this case...

Please tell me, if i am wrong here :angel:
 
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