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20th December 2012, 08:33 PM  #681 
diyAudio Member
Join Date: Aug 2008
Location: Toronto

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. 
20th December 2012, 10:17 PM  #682 
diyAudio Member
Join Date: Aug 2008
Location: Toronto

I think my numbers show peak Class A watts. RMS would be about 60 and 40.
Last edited by BigE; 20th December 2012 at 10:34 PM. 
21st December 2012, 12:11 AM  #683  
diyAudio Member
Join Date: Apr 2006
Location: MA

I am currently collecting parts for a V2. Could someone expand on the section of the F5T article below about the diodes? I am not 100% clear what is need to be done. I am thinking 32V rails and not sure of the bias.
Quote:


21st December 2012, 02:25 AM  #684 
diyAudio Member
Join Date: Aug 2008
Location: Toronto

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. Last edited by BigE; 21st December 2012 at 02:29 AM. 
21st December 2012, 02:51 AM  #685 
diyAudio Member
Join Date: Feb 2009

0.7A bias pr device, and 4pairs = 2.8A bias. 52V*2.8A*2=291W dissipation.
this will give you about 125W Class A power at 8ohms. transformer need to be a minumum of 600VA pr ch. 
21st December 2012, 03:26 AM  #686  
diyAudio Member
Join Date: Sep 2002
Location: India

Quote:
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. Quote:
Will be glad to see where I went wrong in this calculation. 

21st December 2012, 03:36 AM  #687 
diyAudio Member
Join Date: Aug 2008
Location: Toronto

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. 
21st December 2012, 03:46 AM  #688 
diyAudio Member
Join Date: Aug 2008
Location: Toronto

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. Last edited by BigE; 21st December 2012 at 03:50 AM. 
21st December 2012, 03:54 AM  #689 
diyAudio Member
Join Date: Feb 2009

1A pr device, 2pairs =2A bias. dissipation =2A*32V*2 = 128W pr ch. so minimum 250300VA transformer pr ch.

21st December 2012, 03:59 AM  #690 
diyAudio Member
Join Date: Sep 2002
Location: India

: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 120130W total. Also, during summer as is my practice with the F5, the bias will be lowered to prevent me from bursting into flames. 
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