F5 power amplifier

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#11,670
Reibradi said:
Thanks.
The whole thing is just too big to be honest.
There should be a short, concise summary with the options and links somewhere.
Or did I not find it?
Cheers
Chris
Click to expand...

Maybe you can look at the most exelent 6L6 tread
and for $20US enhanced print wiew is absolutley super.(see donations)
and use your ignore switch so to get rid of the dross.

The most important thing is to get a copy of Nelson F5 write up and the Mighty Zen Bias guide.
 
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#11,671
Bksabath said:
Maybe you can look at the most excellent 6L6 thread
Click to expand...

Which can be found here - http://www.diyaudio.com/forums/pass-labs/188691-illustrated-guide-building-f5.html

As I say in the introduction, this is not the only way of doing it, merely the way I did it. (Heck, if I were to make another I would do it a bit differently! But that is the nature of DIY...) 😀 😀 😀 My biggest reason for making the post is because this thread has gotten ludicrously big and unwieldily.
 
#11,672
Yes threads are big but if you want to learn something...that is good news.

This is not a kit building site ...thank god !

Your effort is very welcome 6L6 and appreciated, after the amp has been discussed here in detail.

...and Bksabath makes a very relevant point....$20 gets you a very easy to view version of the thread !!!😀

DIY is not like taking a pill...it's the enjoyment of the journey...and there is some great company here for that.

😎
 
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#11,674
ClothEar said:
Mighty Zen Bias Guide? Where can this be found?
Click to expand...

It's in the middle of my build guide. It looks like this -

From Zen Mod:

dial both pots to 0 ohms ( check with ohmmeter )

place one voltmeter across PSU caps ( best between + and - of PSU) to observe max voltage of PSU

place one voltmeter at output - to observe offset

place one voltmeter across one source resistors of output mosfets ; it doesn't matter which one .

for test - slowly dial up Variac ( presuming that you have one , as man with many skills) up to full mains voltage , observing voltage at PSU ....... thinking about max cap voltage ( 25V as in FW ? ) , because with 0 Iq PSU is unloaded and voltage is maxed

if nothing is smelling - leave Variac at full mains ;

what's important - Iq must be very low , offset is irrelevant in this moment .

now turn one pot one turn ( assuming that you have multiturns )

then turn other pot one turn

observe Iq and offset

proceed one then second pot , again just one turn

observe Iq and offset

again one turn + one turn

now you are probably in range when you can see which pot is pulling offset in right direction - to 0 .

proceed iteratively with pots , while you set - say - 75% of desired Iq and zero offset

now - put lid on box and let it cook for a while - until yo get thermal equilibrium on heatsinks

it's best to use wire/clips to leave those voltmeters in place ;

open the lid , up bias to - say - 90% of desired one ,while maintaining offset

put lid on , let it cook

check ;

if all is OK - move voltmeters for Iq and offset to other channel and repeat procedure

use it few days at 90% of desired bias , then check and set to 100%

remember - temp. equilibrium with lid on is important
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#11,677
What grips this guy.

http://www.parttimeprojects.com/audio/diy/F5.php

One DIY-er really hated his F5.

I've just got the building bug, his comments almost steer me away from trying an F5.

I've got a DIY Aleph 4 (100W Class A / Ch) which I am very happy with. I just wondered if the F5 was better.

100W versus 25W might make the A4 an easier amp to use ????

Not quite sure of the sensitivity of my speakers, they are B&W 683's.
 
#11,678
He does not discuss the voltage gain though, which at 15dB, is surely more unusual than 25W. Many tube amps of such power live along medium sensitivity home speakers. Another 15 to 20dB of line level gain before the amp is needed for the system to feel normally dynamic on circa 90dB/W speakers. Max SPL could be compromised with 25W on such speakers, but average level ''bounce'' need not.
 
#11,679
B&W state
90dB spl (2.83V, 1m)
Click to expand...
but they don't seem keen on declaring what the nominal impedance of these speakers are
8? (minimum 3.0?)
Click to expand...
all available @
Experience the B&W 683 - Bowers & Wilkins | B&W Speakers

They seem to be 4ohms to 8ohms speakers that are 90dB/2.83Vac @ 1m.
The 4 to 8 will effectively reduce their sensitivity to ~ 87dB/W @ 1m.

They are also suggested as being compatible with 25W to 200W amplifiers.
The F5 being ~50W into 4r0 just sneaks into the lower end.

Worth trying, to see/hear how the Aleph compares to the F5.
 
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