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|15th February 2012, 02:09 AM||#212|
"This is DIY. I view op amps the same way I look at a can of soup or a fast-food burger" NP
|15th February 2012, 03:44 AM||#213|
Join Date: Dec 2001
Location: San Francisco, USA
F-5 Turbo Circuit Boards moved here:
F5 Turbo Circuit Boards
|15th February 2012, 08:13 AM||#214|
Originally Posted by labjr
........Doesn't seem practical.
hehehehe, when has that stopped anyone around here?
Well you still have options.
1)Find out how much power you realy need (See Pano tread)
2)find out impedance of speakers and how much current you realy need
F5 current out = 2X bias current to stay in class A above that it will go in to class B
(this is as far as I understand things)
you can have for example 2 mosfets at 1.5 amps or 3 at 1 A
I think that altrought the sink dissipate same wattage the Junction themperature on the mosfet be lower. Let the sink go to 55 C
(Onother thing I have noticed is that after a 3 4 hour realy loud session sink felt some what cooler than idle Maybe insted of dissipating the Bias current as heat they where producing blifsfull sounds and running colder so Play loud )
Consider that Papa already said "they sound better at hi voltagge and Bias"
Papa also said Get heat sinks as big as you can aford.
Run at less than 1.3 A mosfet and you can hear it.
No point to go low voltagge your speakers will not ask the amplifier for uge current .
Say 16 V out on 8 homs speakers no mather what you will never ask more than 2 A
with 2 mosfets at 1.3 A on each rail you got 2,6 X2 A avvaliable
Yeah speakers are not resistors and impedence drop so you got a bit of head room
Any point going for 4 mosfets and 10 Amp current output.
So what options you got
P&P may be the killer but if you like same 300 X 400 x83 heat sinks like maine just PM
OR you could use a fan litle CPU coolers are capable to dissipate 100W of heat
Bolt one on the sink and run at low voltagge al you need is a spare mosfet a spare thermistor and a pot to make a themperature speed controlled Fan.
Even at very low speed difference is uge
Use wires to place mosfets on 2 sinks just make shure gate stoppers are soldered to gate pins duble cek you got no hi frequency oscillation or go balanced to double the power
OR like me wait for F6
Last edited by Bksabath; 15th February 2012 at 08:26 AM.
|16th February 2012, 01:55 AM||#215|
Should R26 in V3 be 10K? I simmed it with lateral MOSFETs and it looks pretty darned good! The Renesas will only do about 7A continuous, so it's not going to be as beefy as V3 -- but you don't need the diodes either.
Last edited by jackinnj; 16th February 2012 at 02:17 AM.
|16th February 2012, 04:33 AM||#216|
|17th February 2012, 10:06 AM||#217|
Apart of checking here and there, you can have your own math here.
Let's say we want the F5 turbo work at 50w@8ohm
Iout = √(50/8)
Ipeak = √2 X Iout
Ibias = Ipeak/2 = 1.8A
//F5 turbo is using 2 pairs of output drivers//
Each driver's current:
Ieach = Ipeak/2n
n = 2
Ieach = Ipeak/4
Vo = K x Ec = √(P x R)
Set K = 0.6
Ec = √(P x R) / k
when supplying +/- 35V rail, the current bias for each driver is roughly 0.8A
So you can have your own calculation to decide how to set the voltage supply and
current into the F5 turbo.
ps. Correct me if i have did the wrong calculation.
|17th February 2012, 11:23 AM||#220|
Join Date: Jul 2004
Location: Scottish Borders
I too get lost with the introduction of k.
Prior to that K, everything is correct.
Use peak output current and nominal load resistance.
3.54Apk * 8r0 requires an output voltage of ~28.3Vpk.
This is where the fudge factor k comes in.
What do we allow for the voltage losses through the output stage from Vrail to Vout?
I would guess a fixed value of 5Vlost rather than a proportion of the peak output voltage.
28.3Vpk + Vloss of 5V comes to Vrail of +-33.3Vdc. (for a ClassAB amplifier the rails need to be ~3V to 8V higher than the ClassA amplifier supply rails)
Once you have built the amplifier, you can measure Vlost and use that actual value for those devices and that peak output current from that PSU configuration for any future design or clone.
setting the device bias to 0.8A will result in the maximum ClassA output current being less than 3.2Apk.
Increase the bias to ~0.9A to achieve your desired 3.54Apk of maximum ClassA output current.
regards Andrew T.
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