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F5Turbo Illustrated Build Guide
F5Turbo Illustrated Build Guide
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Old 12th October 2019, 08:31 PM   #581
thompsontechs is offline thompsontechs  United States
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Quote:
Originally Posted by 6L6 View Post
Very nicely done!!

Congratulations! You have a very lucky friend.

Make sure you listen to it a home for a while, you know, for “quality control” reasons.

YA, I think a couple months of QC is required! How much should the offset move around when you are playing music?


Thanks for the compliment!



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Old 12th October 2019, 08:46 PM   #582
Zen Mod is offline Zen Mod  Serbia
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F5Turbo Illustrated Build Guide
you can't measure offset while playing ........ eyes and brain are rarely in sync with amp and readout

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Old 12th October 2019, 09:33 PM   #583
thompsontechs is offline thompsontechs  United States
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Quote:
Originally Posted by Zen Mod View Post
you can't measure offset while playing ........ eyes and brain are rarely in sync with amp and readout


I wasn't so much measuring it as looking at the way it reacts when music is playing. Okay, I was measuring/monitoring it.
It really does sound great, I haven't hooked it up to my main speakers. Highly modded Tekton DI and PAP Horn1s. I figured if it blew or DCed my drivers, it will be an old pair of Fluance and not the 8k Horns lmao.



It's more a thing, of wanting to know if this is a normal condition.

Last edited by thompsontechs; 12th October 2019 at 09:57 PM.
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Old 12th October 2019, 09:37 PM   #584
6L6 is offline 6L6  United States
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Yes, offset does move with a signal, so don't worry about it.
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Old 12th October 2019, 09:59 PM   #585
thompsontechs is offline thompsontechs  United States
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Originally Posted by 6L6 View Post
Yes, offset does move with a signal, so don't worry about it.

Roger that, and thanks.
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Old 12th November 2019, 01:51 AM   #586
airborne11b is offline airborne11b  United States
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Noob here. Can anyone give me the lowdown on matching FETs for a F5T v3? I have ordered a matched quad JFET set from the store but I still need the 8 - Bipolar and 16 - MOSFETS. i read in the First Watt article that the bipolars are not critical but have not read much about the necessity of matching the MOSFETS.
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Old 17th November 2019, 12:50 AM   #587
WKCox is offline WKCox  United States
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Quote:
Originally Posted by airborne11b View Post
Noob here. Can anyone give me the lowdown on matching FETs for a F5T v3? I have ordered a matched quad JFET set from the store but I still need the 8 - Bipolar and 16 - MOSFETS. i read in the First Watt article that the bipolars are not critical but have not read much about the necessity of matching the MOSFETS.
Nelson's MOSFET matching tutorial from the First Watt website:
http://www.firstwatt.com/pdf/art_matching.pdf

Reliable eBay seller for matched MOSFETs here:
IRFP240 / IRFP9240 Complementary Matched Groups | eBay
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Old 17th November 2019, 01:16 AM   #588
coolnose is offline coolnose  Europe
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Quote:
Originally Posted by airborne11b View Post
Noob here. Can anyone give me the lowdown on matching FETs for a F5T v3? I have ordered a matched quad JFET set from the store but I still need the 8 - Bipolar and 16 - MOSFETS. i read in the First Watt article that the bipolars are not critical but have not read much about the necessity of matching the MOSFETS.
You might want to contact our member "h_a" before reaching out to ebay or other as well...
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Old 17th November 2019, 01:29 AM   #589
coolnose is offline coolnose  Europe
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Quote:
Originally Posted by airborne11b View Post
Noob here. Can anyone give me the lowdown on matching FETs for a F5T v3? I have ordered a matched quad JFET set from the store but I still need the 8 - Bipolar and 16 - MOSFETS. i read in the First Watt article that the bipolars are not critical but have not read much about the necessity of matching the MOSFETS.
You might want to contact our member "h_a" before reaching out to ebay or other as well...
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Old 14th January 2020, 04:02 AM   #590
alexkosha is offline alexkosha  United States
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F5Turbo Illustrated Build Guide
Recently, I decided to increase my BIAS voltage since previously set 360mV gave me about 40 deg C on my heat sinks. New value equal to 420mV is empirically found and allowed me to set my monoblocks to about 55 deg C (21-22 deg C ambient temperature). So, I locked it with 420mV which is 3.6A CC in my case with 4 pairs.
Now, where it is getting interesting…
I used FFT to see how they behave and I found huge noise on both units (Left and Right blocks). I suspected my FFT measurement setup for GND loop and tried to find the source of it. Nada… Replaced cables on my FFT setup with nice and professionally assembled Mogami. Same noise. Please see attached images. (I change Fs size and FFT on “No Noise” image to match my RMAA setup. Is it still good representation of FFT). Went into amp and tried to find some GND loop/s there. Also nothing suspicious. I use Rod Elliott’s method of GND elevation and I also removed 10R. Based on many feedbacks, it is still safe with ying-yeng diodes (35A rectifier bridge) since it will allow current to meet Earth in case of catastrophic failure of the circuit. So and technically, it is simulated like no GND connection, but I still got same noise… Same issue when input signal came from preamp that I know for the fact it is very clean. Previous BIAS showed same noise.
So, I decided to try input isolation transformer (Jensen JT-11P-1HPC ) and that is finally defeated my noise issue.
I lost 100kHz FR linearity.., and about -0.5dBv at 20kHz which is no one can hear any way.
Personal appreciation to Salas and L6L for tremendous support during my troubleshooting.

P.S. Please understand that I described my personal case only. Your device is possibly totally fine.
Attached Images
File Type: jpg Noise.jpg (183.8 KB, 50 views)
File Type: jpg Isolation_transformer.jpg (280.8 KB, 49 views)
File Type: jpg FR.jpg (134.5 KB, 49 views)

Last edited by alexkosha; 14th January 2020 at 04:05 AM.
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