F5Turbo Illustrated Build Guide

On the Power Supply for the Turbo V2 vs the normal F5 build power supply, should the bleeder resistors be the same value? A note says they can change with PS voltage. I also noticed 6L6 added some optional resistors to the resistor bank in one of the F5T PS photos. Do you need additional resistors for some reason? If that info is buried in this thread somewhere, I apologize that I didn't see it or don't remember it. My photographic memory is out of film or the SD card is full depending on your generation.
 
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Nelson's design is for 7 0.47 ohm 3 watt resistors in between 8 10,000 mfd (4 on each side of the resistors). There is no bleeder resistor shown in the schematic.


FWIW, I used a 2.2K ohm 3 watt bleeder on mine.


"Power supplies like this have been described elsewhere, and there is nothing magic about this one – we are just scaling things up. The same Vishay rectifiers are used here, and you see that we are using lots more capacitors.The CRC filtering is still there to keep the supply noise lower, but the resistance has been lowered to 0.067 ohms to ensure low losses. You want CLC? Go for it."
 
F5 Turbo volume limiter and loudspeakers protection

Hello good people,

I need an advice and opinion about F5T. I have built a V3 version and it has immense power, but I have managed to burn my loudspeaker driver by accidentally using an interconnect line level cable (from preamp to power amp) with a bad contact. It only took one millisecond for the monster to deliver all the power and destroy the bass driver. The sound of the accident was very scary, but buying new bass driver was even worse.

The power amp is always at full gain and volume is determined by the preamp. I was thinking of installing a potentiometer on the input, to make it possible to put down the volume, however, I see that none of the papa Nelson's original amps have this feature! Actually I have rarely ever seen it in any high-end power amp.

The second option would be some sort of loudspeaker overload protection, but I wonder if that would harm the sound.

The third option would be to do nothing, except making sure to use good quality interconnects, but it's always a risk.

How do you people deal with this? Your thoughts and ideas will be highly appreciated, thank you!

Hazim
 
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So sorry to hear about your situation! :(

I admit to being a bit confused re: your diagnosis. What exactly was wrong with the interconnect? If the volume knob on the preamp (assuming a properly built pre-amp) was at a proper level, then the full signal will not reach the power amp.

With RCA, the faulty cable could either provide no signal or short the signal to GND.
With XLR (if you built balanced monoblocks), the faulty cable could provide no signal from in+ or in-; short in+ and in-; or short either/both in- / in+ to GND.

I can't envision how any of those situations would cause the scenario you described. Can you elaborate? Was the F5T only powering the bass speaker => biamping?

Potentiometers on the inputs may not prevent what you're describing, and I would imagine may not be an ideal solution (assuming DC was the issue and not some other issue).

There are quite a number of speaker protection devices; most claim to not harm the sound in any way. However, unless you're sure that the fault was due to DC ... again, it may not solve your issue.

Others may understand your diagnosis a bit better. I've considered adding DC speaker protection to my amplifiers, but since all of my pre-amps have a DC blocking cap on the output and/or the amps have a DC blocking cap on the input, I think there is little need in my situation.

Once again, so sorry to hear about your situation, and I hope to learn more from others also.
 
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If you lost ground contact, it happens more often then you think. I've had a friend who did the exact same thing, and the solution I gave him was to never power up the amp until all cables were connected and checked.

Accidents can still happen. The potentiometer is a poor solution, but you can envisage a soft mute, which attenuates the input by 20 or 30dB. Sort of like a standby circuit for a tube. This will render music inaudible, but boo-boos can be detected.
 
Thanks for the comments Perry.

I used bi-amp with F5T with an active crossover, and I had V3 for bass and V1 for highs. What happened in my case was that the ground of the RCA cable lost connection, and the input of the F5T V3 received a ton of hum through the signal line, without closed loop with the ground and practically without cable shielding.

I was picking something that I dropped behind the rack, I didn't even know that the RCA cable was faulty, but when I accidentally moved it, the ground lost connection, I got an extremely loud hum, so much that the bass driver exceeded its excursion - I literally heard the voice coil hitting the magnet. The driver didn't "burn" but the coil got physically destroyed.

I never listen to music on extremely high levels, but I like having large power reserves - so handy for dynamic swings, especially on bass, and V3 makes everything sound so effortless and easy. I don't have any problems with power amps or preamp or active x-over, in this case it was clearly a cable issue...
 
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Hi Sangram - Apologies if this is OT, but I can't seem to wrap my brain around the failure mechanism. I'd appreciate any insight as I learn. If the interconnect has no GND connection between the pre-amp and the power amp, how does the power amp receive a signal? Does the signal try to find a return through another path, and thus the fault?

Sorry for the silly questions, but even though I make every attempt to reduce risk, this is not something I had ever considered.

Thanks!
 
Trying to dot some I's and cross some T's here. Please tolerate cautious rookie questions!



On the new board is Q1.1 = Q3 on the BOM and Schematic = (2SK170BL)?



On the new board is Q2.1 = Q4 on the BOM and Schematic = (2SJ74BL)?



For non-cascode you need to jumper the top to the middle hole on Q7 and the middle to the bottom hole on Q8?


You also need to jumper the G hole to the LINK hole for a non-cascode single ended build?
 
to bullitt5094 #1232

Hello bullitt5094,


if you increase the amount of output-devices (=Mosfets) in your F5turbo-build,
then you need more 'juice' to drive them (higher capacitance....).
If you increase your railvoltages over the maximum ratings of your JFets, then you also need cascoding - BJTs.

Mr.Pass describes this in his F5T-article. ;)



Cheers
Dirk :D
 

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Found this... "The Q1.1 and Q2.1 position are left empty, they are there if you are going to make a huge F5T with more than 4 pair of output transistors, so you can parallel the Jfets and have more driver current."

It is really difficult to digest (and more difficult to remember) everything in this thread. Lots of confusing stuff with the different versions and different board versions that's involved. I am not an EE and not trained in electronics like most of you apparently are. What I am is very persistent! And for that I apologize.
 
to bullitt5094

Hello bullitt5094,


no reason for apologizing....;).


My F5T - monoblocks have been one of my first DIY-projects by Nelson Pass.

You can be sure that I had the same questions like you. And I was reading through the complete F5-T-builders-thread and the F5Turbo-article of Nelson Pass more than once.
Everybody will get to a point during an amp-project, when something is not clear.


Have fun with your build! If finished - have more fun listening to the F5T!


Cheers
Dirk ;)