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Old 1st April 2013, 03:12 AM   #1711
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Quote:
Originally Posted by Jallhalla View Post
Could I build a mild v2 turbo by using two pairs of mosfets and diodes over the resistors, but using only the original f5 18v psu transformer? Im building an f5 now, and Im already considering how to improve it.

If Im thinking correctly this would not give me an improvement in watts, but could make it a lot more powerful at difficuld loads?

Thanks for any thoughts on this!
As I understand the Turbo part is carried out by the diodes, thet kik in at hi voltagge so why do bother for 18 V trafos?

I am running twins on 26 V rails on 4 Homs speakers (nasty ones) and it is prety good.

IMO First decide what power you realy need
then build stock version to get taste of it
then based on that you are prety free to get up and up but ditch the 18 V traffo

About the considering to improve the F5 see abowe< build stock first>

PS the J fets can take up to 35 V rails before cascoding but cascoding only add further bonuses and the current limiters are not realy needed but get same speaker protection duda
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Old 1st April 2013, 09:06 AM   #1712
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Default F5, V1 PSU problem, getting 70V !

Hello

Turned on psu and amp circuits yesterday to start final set up and the little J74 / Q2 smoked, only on the left channel.
And for some reason the output from the PSU had doubled from 35 previously to 70v. I know that the little transistors have a breakdown point of 60v
Today I disconnected all 6 leads from the PSU to the amp boards. My simple test shows that I am getting +35 and -35 from the bridge rectifiers. Next test; positive lead from meter on + of PSU, and negative on PSU gives +70vdc, however placing black lead from meter on PSU GND result is 35vdc. What I have done wrong??
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Old 1st April 2013, 09:34 AM   #1713
Marra is online now Marra  United Kingdom
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I f I read correctly you're p/s sounds ok.With the leads across plus to neg will give 70vdc.Connect the black lead to the centre connection between the caps and move the red lead from pos +35v to neg will give -35 hence your 70v across +-. As to the smoking jfet some one with more knowledge will no doubt chip in.Good look.
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Old 1st April 2013, 09:39 AM   #1714
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Old 1st April 2013, 09:50 AM   #1715
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by Bksabath View Post
As I understand the Turbo part is carried out by the diodes, thet kik in at hi voltagge so why do bother for 18 V trafos?
...................
the diodes kick in when the output current demand rises too high, as determined by the voltage drop across the source resistor.
The diodes make more current available to the load by bypassing the Source Resistor.
The diodes help to reduce the voltage lost across the Source Resistor when high currents are demanded.

It does not matter whether a the PSU is +-20Vdc or +-50Vdc, the diodes turn on at high current demand.
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Last edited by AndrewT; 1st April 2013 at 10:05 AM.
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Old 1st April 2013, 09:58 AM   #1716
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hello
this my first post on diyAudio,
i hope my english level is good for tey to build an F5T.
i have already build uP and ugs .
i see this kit :
F5T Turbo Power Amplifier kit for sales ( i have a lot of irf irfp IRF9240/240) but spencer shop is closed .
have you another source for pcb ?
thank's
fgaston
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Old 1st April 2013, 10:01 AM   #1717
omishra is offline omishra  India
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I completed my dual mono vertical box. Running successfully at source resistor voltage drop 300mV(0.6A bias) per device. Thanks again NP, all FM here and buzzforb for semiconductors.

Power Supply, mains section. I used softstart and thermal cutoff from bay.
Image956.jpg

Closeup each toroidal transformer is 300VA, 2X24V secondary.
Image943.jpg

Partition separation - 7mm gap between open end of transformer mounting bolt and side panel. 5-6mm gap for power caps and side panel.
Image942.jpg

Other side of the partition, all power bank of DC voltages. I used 8 X 15000F per channel.
Image951.jpg

Closeup of power switch and reset switch for slow start. My amp does not power on automatically on mains supply reconnection. It needs push button trigger to switch on.
Image953.jpg

Both 75C thermostat attached to heatsink using spring taken out from cloth drying clip.
Image947.jpg

Closeup of mains earth ground isolator. Bridge connects mains ground to chassis at central mounting bolt and PS AGND comes from behind PCB at bottom.
Image948.jpg

Aluminum handles fitted with M4 SS bolts. Indicator 3mm red LED into hole with 2mm opening in top and 3mm from behind on face plate. LED hole filled with transparent hard glue.
Image949.jpg

Side view of complete box.
Image958.jpg
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Old 1st April 2013, 11:14 AM   #1718
Zen Mod is offline Zen Mod  Serbia
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that's Fugly!

mount lower and bottom plates (regularly looking as front and back ) via some spacers - to ensure some vertical air flow inside the case
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Old 1st April 2013, 11:17 AM   #1719
omishra is offline omishra  India
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Originally Posted by Zen Mod View Post
that's Fugly!

mount lower and bottom plates (regularly looking as front and back ) via some spacers - to ensure some vertical air flow inside the case
Thanks ZM! Yes there is some gap (~3mm) between top and bottom plate along with side panels.
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Old 1st April 2013, 11:18 AM   #1720
Rixsta is offline Rixsta  United Kingdom
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Hi,

Source = 1-3v
Speakers = 87db

So just wondering if i need a Pre as well as B1.
But also its possible he could connect up a quieter device, perhaps having that niam clone pre-amp would be good idea anyway.
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