This is what I am thinking of building:
1) 4 devices per channel
2) 0.63 amps/device (total 2.52 amp bias)
3) 36 VAC transformer (approx. 46 volt rails)
using a 1.5 KVA transformer. This gives about 118 wpc class A.
If you use a 24 VAC transformer, I figure that 1Kva ought to do a stereo amp at this bias current, and give you about 80 wpc.
1) 4 devices per channel
2) 0.63 amps/device (total 2.52 amp bias)
3) 36 VAC transformer (approx. 46 volt rails)
using a 1.5 KVA transformer. This gives about 118 wpc class A.
If you use a 24 VAC transformer, I figure that 1Kva ought to do a stereo amp at this bias current, and give you about 80 wpc.
AndrewT, I have a spreadsheet for this now.
It says that an amp can be made with these parameters:
1) Vsec : 40 VAC
2) Vrail : 52 VAC (1.3* Vsec)
3) Ib : 0.7 A per device
4) Ibt : 5.6 A ( 8 devices * Ib )
5) VAbias : 582.4 ( (2 * Ibt) * ( 2* Vsec) )
6) VAcool: 1164.8 ( 50% transformer load at idle )
7) Wpeak: 291.2 ( Vrail * Ibt )
8) Wrms: 145.6 ( Wpeak/2 class A)
9) Wab: 291.2 (twice Wrms)
10) VAab: 582.4 (twice Wab, not 1.5)
11) Total VA: 1164.8 ( VAbias + VAab)
Note that this is the identical figure to VAcool -- that level of VA to allow the transformer to run cool. It is also exactly 8*Wrms.
So, you can make
A 145.6 Watt mono amp with 8 Fets, 52 volt rails, 40 volt secondaries biased to 0.7 A per device with a 1.2Kva transformer. Or this could be a stereo 72.8 watt class A amp. It dissipates 582 watts at idle.
If you have a 34 Volt secondary, and get 44.2 V rails, 0.7A, you can make a 123.76 watt monoblock or 62 watt stereo amp from a 1Kva transformer. It dissipates 500 watts at idle.
A 1A bias and 34 VAc secondary will need a 1414 VA transformer for a 176 W monoblock or 83 watt stereo amp. It dissipates 707 watts at idle.
A 1A bias and 36 Volt secondary will need a 1.5KVA transformer to produce a 98.6 watt stereo amp, or 187.2 watt monoblock. It dissipates 750 watts at idle.
The dissipation is VAbias.
I think these numbers are OK, but as usual, I will take NO responsibility for their accuracy.
It says that an amp can be made with these parameters:
1) Vsec : 40 VAC
2) Vrail : 52 VAC (1.3* Vsec)
3) Ib : 0.7 A per device
4) Ibt : 5.6 A ( 8 devices * Ib )
5) VAbias : 582.4 ( (2 * Ibt) * ( 2* Vsec) )
6) VAcool: 1164.8 ( 50% transformer load at idle )
7) Wpeak: 291.2 ( Vrail * Ibt )
8) Wrms: 145.6 ( Wpeak/2 class A)
9) Wab: 291.2 (twice Wrms)
10) VAab: 582.4 (twice Wab, not 1.5)
11) Total VA: 1164.8 ( VAbias + VAab)
Note that this is the identical figure to VAcool -- that level of VA to allow the transformer to run cool. It is also exactly 8*Wrms.
So, you can make
A 145.6 Watt mono amp with 8 Fets, 52 volt rails, 40 volt secondaries biased to 0.7 A per device with a 1.2Kva transformer. Or this could be a stereo 72.8 watt class A amp. It dissipates 582 watts at idle.
If you have a 34 Volt secondary, and get 44.2 V rails, 0.7A, you can make a 123.76 watt monoblock or 62 watt stereo amp from a 1Kva transformer. It dissipates 500 watts at idle.
A 1A bias and 34 VAc secondary will need a 1414 VA transformer for a 176 W monoblock or 83 watt stereo amp. It dissipates 707 watts at idle.
A 1A bias and 36 Volt secondary will need a 1.5KVA transformer to produce a 98.6 watt stereo amp, or 187.2 watt monoblock. It dissipates 750 watts at idle.
The dissipation is VAbias.
I think these numbers are OK, but as usual, I will take NO responsibility for their accuracy.
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Hi
I'll be using similar capacitance level (though my rails are lower) - 22000uF x 8 and 10000uF x 8. The first bank will be as per the V2 power supply recommendation, the second bank is twice as beefy. I am not sure that with the higher rails a similar capacitance will be sufficient.
Yes. 25V minus the margin of error for mains voltage, which is never 230V.
I'm running two pair outputs for V2 (no diodes), not four pair. At 1A per device and two channels, that's 8 devices x 1A x 64 = 512VA dissipation and doubled it for safety (though I know 2x is a little skimpy). That's how I got the 1KVA figure.
Will be glad to see where I went wrong in this calculation.
According to this, with 2 devices ( 1 N and 1 P ) each device biased at 1.3 A ( so the pair has 2.6 amps) my spreadsheet shows 27 watts , 108 Watts dissipation and a 216 VA transformer ( For one channel ) 16 VAC secondary and 20.8 V rail.
http://www.firstwatt.com/pdf/prod_f5_man.pdf
In your example, if you calculate using 8 devices at 0.7 A each ( 5.6 A) you get a 250 Watt peak = 5.6 * 5.6 * 8 , which is 125 Watts RMS.
The dissipation is 582.4 watts which is 5.6 * Vrail_to_rail as in Andrew's example.
http://www.firstwatt.com/pdf/prod_f5_man.pdf
In your example, if you calculate using 8 devices at 0.7 A each ( 5.6 A) you get a 250 Watt peak = 5.6 * 5.6 * 8 , which is 125 Watts RMS.
The dissipation is 582.4 watts which is 5.6 * Vrail_to_rail as in Andrew's example.
Sangram
According to the spreadsheet, you are exactly correct.
24 V secondaries
31.2 V rails
1 Amp/Device * 4 devices = 4 Amps draw.
Gives 64 Wrms per channel, using a 1Kva transformer. (1024 VA would be exact)
It will double in A/B and idle at 50%.
Ignore my previous post. It is exactly the right size.
According to the spreadsheet, you are exactly correct.
24 V secondaries
31.2 V rails
1 Amp/Device * 4 devices = 4 Amps draw.
Gives 64 Wrms per channel, using a 1Kva transformer. (1024 VA would be exact)
It will double in A/B and idle at 50%.
Ignore my previous post. It is exactly the right size.
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:whew:
I am aiming for more voltage swing, so the 'stereo' is only indicative. In reality I will be running in balanced configuration (this 8device/1A bias/1KVA supply is for 1 channel) with another exact monoblock for the other channel. The power output target is ~80W in Class A and maybe 120-130W total.
Also, during summer as is my practice with the F5, the bias will be lowered to prevent me from bursting into flames.
I am aiming for more voltage swing, so the 'stereo' is only indicative. In reality I will be running in balanced configuration (this 8device/1A bias/1KVA supply is for 1 channel) with another exact monoblock for the other channel. The power output target is ~80W in Class A and maybe 120-130W total.
Also, during summer as is my practice with the F5, the bias will be lowered to prevent me from bursting into flames.
1 Amp/device and two pairs = 4 devices = 4 amps.
4*4*8 = 128 W PEAK = 64 W RMS. Choose Between 6 and 10 times RMS value for transformer VA.
Lets choose 8. 8*64 = 512 VA. PER CHANNEL. A 1 Kva is required.
Check:
VA due to bias for one channel 4A * (32V *2) = 256 VA. But this runs the transformer at 100%. Run transformer at 50% instead. Use 512 VA PER CHANNEL. Requires 1Kva.
Check again:
Va due to bias = 256 VA as above. Power is 64 W RMS Class A as above. Allow 128 W A/B, and double for headroom = 256 VA. Vbias = 4 A * 64 V rail to rail = 256 as above. Add Vbias + Headroom = 512 VA PER CHANNEL. Requires 1 Kva.
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Looks like I'm almost in the right spot, and with a small bit of room for upping bias?
There is the thorny issue of matching halves and getting it to sound right. I will be using two mono amps running from a fully balanced source - another aim is to convert later for active crossovers and biamping, so - not the F5X style balanced topology. My cases have been designed to accommodate I/O panels to make the configuration flexible for more applications than a monoblock.
AudioSan,
From the F5 manual:
"For this sort of circuit, a 1.3 amp bias means that the amplifier will operate Class A to 2.6 amps of output current. To understand this, imagine a condition where Q3 and Q4 are
idling at 1.3 amps, so that all the current is going from the V+ voltage rail to the V- voltage rail, and none is going through the loudspeaker."
I read that as 2.6 amps (the total bias through all devices) from V+ to V-. That's also the calculation in AndrewT's post.
Are we both incorrect? The numbers agree perfectly with transformer VA = 6-10 Wrms -- actually perfect at 8 x Wrms.
.
From the F5 manual:
"For this sort of circuit, a 1.3 amp bias means that the amplifier will operate Class A to 2.6 amps of output current. To understand this, imagine a condition where Q3 and Q4 are
idling at 1.3 amps, so that all the current is going from the V+ voltage rail to the V- voltage rail, and none is going through the loudspeaker."
I read that as 2.6 amps (the total bias through all devices) from V+ to V-. That's also the calculation in AndrewT's post.
Are we both incorrect? The numbers agree perfectly with transformer VA = 6-10 Wrms -- actually perfect at 8 x Wrms.
.
1kV is good for V2. 1.5kv or dual 800vA is good for V3. Calculations are inundating the thread and going nowhere and confusing folks.
Btw, I am using 400Va for V2 and only have very tiny hum, from very tough performance, from TOO small toroid. My amp is biased at 1a per fet and shockingly enough, the whole thing is working with a 2A fuse on it
Sounds good too. How many f5T have been built?
Btw, I am using 400Va for V2 and only have very tiny hum, from very tough performance, from TOO small toroid. My amp is biased at 1a per fet and shockingly enough, the whole thing is working with a 2A fuse on it
Sounds good too. How many f5T have been built?