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Old 23rd May 2012, 06:16 PM   #261
cdfac is offline cdfac  United States
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hi all,

i would like to build a "basic" V2 (32V rails, 4 outputs/channel) but i have a few questions before i commit. if i missed these being answered elsewhere, apologies. i have tried to read quite a few thread pages on the Turbo.

1) if i do the 0.3V "scaredy-cat" bias Nelson suggests in the write-up, what kind of Class A power am i looking at?

2) related to that question is, how much heatsinking will i need? i would appreciate any suggestions, particularly regarding domestically available stuff. in my basic F5, i'm running 6" lengths of the 10" stuff from Heatsink USA, and it seems to be enough, but i'm unsure how dissipation will change with the V2. at first glance, if the Class A power from 0.3V bias is similar to the basic F5, then i'd probably want at least a little extra to account for the extra MOSFETs and diodes.

3) i've done some poking around, and it appears the F5c board can be used without too much trouble for the simpler Turbos, as Nelson mentions. would that be the case for a V2 like i'm planning? except for P3, which i don't mind leaving out, i suppose the only trickiest part will be fitting in the diodes. can they be mounted with extension leads?

i should note i am flexible with bias -- 20-25Wpc in Class A is enough, frankly. i'm mostly looking for the extra headroom i get from having 50Wpc on tap because my speakers are probably not quite sensitive enough for my F5 as it is (sealed 3-way bookshelf, exact sensitivity unknown), and also a bit difficult to drive in the bass -- i usually only use a few watts, but i don't want to be clipping the big transients. plus, the V2 sounds more intriguing than just building the higher-wattage F5c.

thanks for the help!
-Chris

Last edited by cdfac; 23rd May 2012 at 06:20 PM.
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Old 23rd May 2012, 06:22 PM   #262
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by SteveHolt View Post
.....
Where would you recommend I connect the LED's to please? and what voltage rating?

Kind regards

Steve
between + and gnd

rule of thumb for series resistor , when common type LED is used - use 100R for each volt in PSU ; example - use 2K2 for 22V

500mW resistor is usually fine

if too bright , just double value

I made complete 'ritmetic for LED , but now I'm lazy to find it , or type again
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Old 23rd May 2012, 06:27 PM   #263
6L6 is offline 6L6  United States
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As for heatsink requirements, look at the original F5 manual for a good hint --

(From the F5 manual) (Bold is mine)
"At 1.3 amps per channel, you will see idle heat dissipation of 62 watts. To keep the tempature rise of the heatsink to 20deg C. above the ambient temperature, you will want a heat sink rated at about .6 deg C./watt for each transistor. An example of this would be a chunk of finned aluminum, with a series of 2" fins attached to a 8"by 6" base. You will need 2 per channel."


So - There it is. A 8x6 inch finned heatsink for each transistor. That doesn't count the heatsink requirements of the bias diodes. Obviously a forced cooling system can be smaller.

Knowing this, the answer to the question that you are thinking is, Yes, the amp is going to be big.
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Old 23rd May 2012, 06:46 PM   #264
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with 0.3V across 0.5ohm resistors you have 0.6A pr device.
so 1.2A bias. thats around 23W classA in 8ohm. and with +/-32V rails. you will have dissipation of around 80Wpr ch.
to calculate heatsink you use accepted temp rise, devided by dissipation.
f.ex: 25C rise / 80W = 0.31C/W p ch.
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Old 23rd May 2012, 06:49 PM   #265
cdfac is offline cdfac  United States
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Quote:
Originally Posted by 6L6 View Post
As for heatsink requirements, look at the original F5 manual for a good hint --

(From the F5 manual) (Bold is mine)
"At 1.3 amps per channel, you will see idle heat dissipation of 62 watts. To keep the tempature rise of the heatsink to 20deg C. above the ambient temperature, you will want a heat sink rated at about .6 deg C./watt for each transistor. An example of this would be a chunk of finned aluminum, with a series of 2" fins attached to a 8"by 6" base. You will need 2 per channel."


So - There it is. A 8x6 inch finned heatsink for each transistor. That doesn't count the heatsink requirements of the bias diodes. Obviously a forced cooling system can be smaller.

Knowing this, the answer to the question that you are thinking is, Yes, the amp is going to be big.
yes, you read my mind that 8x6 recommendation is assuming full Class A bias, right? i guess then my first question is the next one after that, which i might be able to answer myself. if i ignore the bias diodes (as i'm not sure what their effect on the biasing process is), 0.3V across 0.5R of source resistance should give 0.6A per transistor, or 2.4A per channel. that's nearly double the original F5 per above, so i would guess that translates to roughly 40Wpc Class A.

another question, then. does the V2 need to be biased at least to 0.3V to take advantage of the diodes? as i said above, i don't need quite that much Class A, particularly because it makes the enclosure design that much more complicated (i.e. large).
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Old 23rd May 2012, 06:55 PM   #266
cdfac is offline cdfac  United States
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Quote:
Originally Posted by AudioSan View Post
with 0.3V across 0.5ohm resistors you have 0.6A per device.
so 1.2A bias. thats around 23W classA in 8ohm. and with +/-32V rails. you will have dissipation of around 80Wpr ch.
to calculate heatsink you use accepted temp rise, devided by dissipation.
f.ex: 25C rise / 80W = 0.31C/W p ch.
thanks, that last part especially helps clarify my requirement. but don't you have to multiply the 0.6A times the four devices per channel in the V2 schematic? or can you safely run 32V rails with only a pair of devices if you limit bias to 1.2A per channel? my speaker load is 4 Ohms nominal with a dip to between 2.5 Ohms and 3 Ohms in the bass range, so i don't want to make life too hard for the outputs.
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Old 23rd May 2012, 06:59 PM   #267
6L6 is offline 6L6  United States
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If you ignore the bias diodes you are kinda sorta not really building an F5turbo...

Nelson repeatedly says that for best sound you want to run as much bias as possible. Running more bias helps with the transients, and that seems to be your concern. Perhaps a speaker that's more efficient as well?

The additional output devices of the turbo instead of the 'classic' F5 will help with the current required of the lowish-impedance speakers. Don't worry about it.
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Old 23rd May 2012, 07:08 PM   #268
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Quote:
Originally Posted by cdfac View Post
thanks, that last part especially helps clarify my requirement. but don't you have to multiply the 0.6A times the four devices per channel in the V2 schematic? or can you safely run 32V rails with only a pair of devices if you limit bias to 1.2A per channel? my speaker load is 4 Ohms nominal with a dip to between 2.5 Ohms and 3 Ohms in the bass range, so i don't want to make life too hard for the outputs.
orignal F5 has 1.3A pr device
this is a push-pull
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Old 23rd May 2012, 07:32 PM   #269
cdfac is offline cdfac  United States
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Quote:
Originally Posted by AudioSan View Post
orignal F5 has 1.3A pr device
this is a push-pull
ah yes, i get what you're trying to say now, sorry.

Quote:
Originally Posted by 6L6 View Post
If you ignore the bias diodes you are kinda sorta not really building an F5turbo...
i only meant ignoring their effect on the bias calculation. i guess if they don't conduct until above the bias point, then they don't come into the calculation.

Quote:
Nelson repeatedly says that for best sound you want to run as much bias as possible. Running more bias helps with the transients, and that seems to be your concern. Perhaps a speaker that's more efficient as well?
a more efficient speaker may come along, but right now i like what i've got. and i'm sure Nelson is right about higher bias in general. at the same time, i'm still trying to balance trade-offs here. but i can see now that the V2 with a dissipation target of somewhat better than 0.31C/W per channel (as outlined by Audiosan) is quite doable.
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Old 23rd May 2012, 09:00 PM   #270
gl is offline gl  United States
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Quote:
Originally Posted by 6L6 View Post
If you ignore the bias diodes you are kinda sorta not really building an F5turbo...
Hi 6L6,

I'm not sure I'd agree. I think the diode thing has become larger than life because of this forum.

What I get from reading the article is Nelson offering the widest variety of choices for hopping up the F5 - different power levels, different topologies, and different costs to the widest group of people. Lots of options, lots of choices, right to the of the article.
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