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F4 power amplifier
F4 power amplifier
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Old 9th September 2019, 06:04 AM   #4471
Zen Mod is offline Zen Mod  Serbia
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F4 power amplifier
reg. 1) - assuming all mosfets are being polite , open exactly at 4V of Ugs , it gives difference of 6V8-4V=2V8

2V8 across 0R47 source resistor is almost 6A

that being tripled , roughly 18A as peak current at one side of swing

welding time!

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Old 10th September 2019, 11:28 PM   #4472
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Default Mono Balanced Operation

I have just completed biasing of a second F4 amplifier. Now I wish to wire them up for mono balanced operation. I read and re-read Nelson Pass's Operation and Service Manual and found cviller's succinct description (#2789). But I'm still lost.
Is there a diyAudio member out there who can enlighten me with a more detailed walk-though on how to do this?
I'm using a Benchmark DAC3 HGC with XLR output as an option. By the way, the sound quality of a single F4 is spectacular. I've gone the route of 91A 300b tube amps and, more recently, the F6 a beautiful design. But the detail of the F4 is the best by far. I just need a little more power for my Dick Olsher's OB design using SAL speakers. How beautiful they are!
DIY all the way!
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Old 10th September 2019, 11:39 PM   #4473
Zen Mod is offline Zen Mod  Serbia
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F4 power amplifier
have XLR panel jack on back of each stereo F4

wire pin 1 to (any) RCA jack GND

wire pin 2 to hot of Right channel RCA jack

wire pin 3 to hot of Left channel RCA jack

connect XLR-XLR cable to output of your preamp

other end of cable connect in XLR jack on back of F4

positive output of Rch is your positive speaker wire connector

positive output of Lch is your negative speaker wire connector

do the same for other channel amp
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Old 11th September 2019, 12:21 AM   #4474
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So simple. And a breath of fresh air.
Thank you Zen Mod!
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Old 11th September 2019, 01:05 AM   #4475
Zen Mod is offline Zen Mod  Serbia
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F4 power amplifier
OB are for Sissies!

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Old 11th September 2019, 01:53 AM   #4476
6L6 is offline 6L6  United States
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F4 power amplifier
The benchmark will output 27.5 dbu, that’s 18v rms and will give you approximately 25 WPC...







...which will never clip.



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Old 11th September 2019, 09:11 AM   #4477
Zen Mod is offline Zen Mod  Serbia
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F4 power amplifier
why I'm instantly seeing autoformer inserted there ?

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Old 11th September 2019, 11:28 AM   #4478
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I enjoy F4 very much. I switch back and fourth between M2 and F4. I use a dual PSU in external chassis. I guess the cable from psu to amp has some impedance. The motor run capacitors in F4 chassis makes the bass vibrant. On the other hand the treble in my Cornwalls take dive above 14k-16k. Especially after a while, warm tweeters?
I don’t know if a small capacitor in parallel of the motor runs affect the frequency. Bollocks or fact, could it be advised to put for example a 0.1uF in parallel to motor runs in F4? If so would any of Rifa paper-metal, Wima MKS4 or Kemet rms(pps) be good choice? Just to keep a low impedance?
PSU-caps: peh200 15kuF, esr 12-16mOhm, esl 22nH.
Motor runs in F4: 40uF(to low but doing some good work).
Help me to to think here

I have also considered a super tweeter and read, or heard, somewhere that F4 likes ribbon tweeter over dome(?)

Considering buying one of these super tweeters:
Fostex T90A
Viawe Audio GRT-145
I am grateful for any idea or advice.
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Old 11th September 2019, 11:55 AM   #4479
Zen Mod is offline Zen Mod  Serbia
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F4 power amplifier
why thinking at all - just put those 100nF caps and sleep better**

regarding supertweet - you need efficiency , so Fostex could be better than ribbon

if ribbon , think about second cheapest Fountek , first with Horn - around 100-120E pair in Eu

edit: found the type : Fountek NeoCD3.5H

edit edit: ** even if I think that only sleep is going to be better
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Last edited by Zen Mod; 11th September 2019 at 12:03 PM.
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Old 11th September 2019, 12:30 PM   #4480
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Nice! Going for sleep and super tweeter. I will read about the horn.
Thank you, mighty ZM!
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