F5 Turbo Builders Thread

Official Court Jester
Joined 2003
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Many thanks.
I now have transformer/rectifier/4x 68,000 U32d in seperate box and 8x 22,000 Kendeils in amp box.
There are a few issues relating to this build of which I am uncertain.
a, which box should house the R.
b, how much R is recommended (I have some 0.47 1%,3w dales).
c, at which position on the power supply ground, should the,
bridge/thermistor be returned to earth.
d, with respect to the above power supply, what amp rating of plug/socket should be used to connected box 1 and 2 together.

At the risk of sounding like a complete lunatic, the above build is running as well as the one described at #4991



a. irrelevant
b.I'll use 3 of these in parallel , per rail
c.central GND point , which is usually exact middle of last caps in filter ; that is usually point where I connect all GNDs
d. at least 5 times Iq
 
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c.central GND point , which is usually exact middle of last caps in filter ; that is usually point where I connect all GNDs
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Do not take your reference point to the PSU Zero Volts. That is where the worst charging current pulses pass through.

Use a wire to bring the PSU Zero Volts to the Main Audio Ground (MAG) and take all your references from this MAG.
For least interference the PSU to Amplifier cable should be a twisted triplet with the +ve , ZeroVolts and -ve all close together to minimise LOOP AREA.
 
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Its said that the F5 Turbo is more laid back than the original F5 but when I heard it my ears heard more power and authority (which really nocked my socks off!) , if the F5 Turbo was too laid back does anyone know for what reason or what part of the circuit would be responsible for that ? someone else said that the original F5 more neutral which I guess is a good thing!
 
Well the V2 literately blew my mind, Im hoping to build one again one day for myself rather than for my friend :D but I saw this post on Fet audio about a version of Turbo V3 that has less output transistors... interesting ?!

F5T Turbo Power Amplifier kit for sales << FET Audio | Hi-End Audio Projects

Also he is using an inductor on the PSU which seems to reduce noise and ripple I guess, he also said that the cascade transistors lowered the noise levels nicely so I might try with them, but am worried if I build with that perhaps the sound will not be as mind crushing as without (I doubt it!), also interesting the use of Toshiba 2SC2705Y outputs over the IRF-P pairs.

So hmm yeah, Im wondering if to build the V2 or V3 when (one day) I can afford it :)
but lets start somewhere, Chassis and PSU that will do.
 
Its said that the F5 Turbo is more laid back than the original F5 but when I heard it my ears heard more power and authority (which really nocked my socks off!) , if the F5 Turbo was too laid back does anyone know for what reason or what part of the circuit would be responsible for that ? someone else said that the original F5 more neutral which I guess is a good thing!

Reduced feedback in turbo. Needed for stability with more mosfets and rail voltage. Also increases gain.

Regular F5 is more lively if kept within its power and current comfort zone.
 
MUR3020W VS MUR3020WT-N3

Hi all! First I want to thank everyone and especially Mr. Pass for your generosity of time, teaching and engineering skills. I'm still pretty green but have successfully built a B1 buffer and Pearl 2 to drive my beautiful Mcintosh MC-30's into my Klipsch Cornwall III's.

I'm happy as a clam and very grateful for everyone's contributions.

I'm building an F5T v2 and am stumped about the diodes. Is there an issue with using MUR3020WT-N3's in the amp stage instead of MUR3020W's?

Looking at the spec sheets the only difference appears to be that the WT-N3's have a 22ns recovery time vs the W's at 35ns. I'm not seeing any info regarding the impedance of these diodes.

Would I need to modify the value of the source resistors?

My gut is saying that faster is better, all other things remaining the same. Is there any reason NOT to use these? Aside from the price? Mouser is selling WT-N3's for double the price of the W's.
 

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accidently doubled PSU voltage on F5 (42V per rail) for a short time. everything looked like normal, no smoke. then I fixed PSU and have got normal voltage about 22V and started to fire up.

got 0V on R7 R8 (jims audio F5kit) with 0 resistance on P1 P2. but increasing resistance on P1 and P2 didnt get any effect, still 0V on R7 R8, no heat from mosfet at all. then saw some little smoke from two amp boards separately. now I have 15-20V directly beetween 1 and 3 pin on mosfets, depending on P1 P2 resistance. 0 DC output, no heating.

what I have to check firstly?
thank you.
 
accidently doubled PSU voltage on F5 (42V per rail) for a short time. everything looked like normal, no smoke. then I fixed PSU and have got normal voltage about 22V and started to fire up.

got 0V on R7 R8 (jims audio F5kit) with 0 resistance on P1 P2. but increasing resistance on P1 and P2 didnt get any effect, still 0V on R7 R8, no heat from mosfet at all. then saw some little smoke from two amp boards separately. now I have 15-20V directly beetween 1 and 3 pin on mosfets, depending on P1 P2 resistance. 0 DC output, no heating.

what I have to check firstly?
thank you.

Did you accidentally "double up the voltage" by not having a negative rail but instead having two positive rails?
 

Some food for thought:

I believe there is no cascode on the Jim's Audio board. Your jfets saw 44V...2sj74 is probably done. But this might be good news...since I doubt that the Jim's audio Jfets are genuine. I'd start by desoldering those and testing them. Apologies to Jim's Audio if they are genuine.

Then I'd move on to the Mosfets...the N side had reverse voltage on them. I'd remove them and test...I don't know if Jim's audio matches the mosfets. They need to be matched. So maybe a blessing in disguise again if you bought a kit with unmatched fets.

If you are using the diodes test them too.

Also test the trimpots by measuring the change in the resistor they parallel to see if they work.

And lastly...did you applied positive voltage to every cap on the negative rail? Was reverse voltage applied to the caps?

This would make me worried about the caps. I'd replace any caps on board and test the PSU caps....you might need a cap tester. But you might be OK...hard to know. It depends on how tough the caps are and how long they had reverse voltage.

And don't feel too bad about it. These things happen. Consider it payment for a better understanding of how this amp works.