A guide to building the Pass F4 amplifier

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soldersmoker

Member
Joined 2005
Thanks to both of you for all the answers. I forgot to mention that my speakers have a sensitivity of 97 dB/w/m, and they've been "okay" with a Darling 1646 0.75 (3/4 watt) wpc amp, though I feel like the Omegas really need about 5 watts per channel to satisfy my typical listening needs. That's the main reason I wanted to try the F4, more power, with as little change as possible to the source's and preamp's sound.

I feel a lot better now. I was feeling a bit of buyer's remorse after worrying that I had jumped on the F4 bandwagon without doing more due diligence in figuring out how it will probably work in my system. Lesson learned: worry less.

BTW, I owned a factory-built F6 and sold it after a few months. I was never 100% on board with its sound. I've read here and there that a few people like the F4 better. FWTW . . .
 
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cal3713

Member
Joined 2014
Also, I didn't have them in the room at the same time, but I prefer the F4 to an XA25 I tried out earlier this year.

Not sure these descriptors fit together, but I find the F4 somehow both transparent and sweet. My Coincident PREs don't impart sweetness on their own, so I do need a bit of sugar, as ZM likes to say. I guess that nice 2nd harmonic focused distortion that is documented by 6l6 on the first page is responsible...

Eric said:
You're quite welcome! The F6 has a particular "flavor" whereas the F4 is about as neutral as they come. I think you'll be set with 97dB speakers and the F4 - I knew the Omega's are a bit more sensitive, but am unsure how this varies with particular models.
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soldersmoker

Member
Joined 2005
I didn't mean to sound dismissive of the F6. It's obviously a very fine amplifier, but I'm partial to a bit of the (distorted?) tone of dem tubes. The OTL sound might be more neutral, a la solid state, when compared to some other tube topologies, but I really like how the LTA MZ2 sounds in my system. I liked my 2A3 and current 1646 SET amps, but the LTA I like even better.
 
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cal3713

Member
Joined 2014
For someone out there, I'm sure the F6 is the perfect amplifier. I personally was attracted to the simplicity of the F4's design and felt like it was a nice match to my speakers' decent sensitivity and flat impedance curve. I also liked this statement from Nelson:

"The combination of a simple Class A circuit operated without feedback and the good objective performance gives us a superb sounding amplifier. The low distortion, bandwidth extension, and high damping results in midrange clarity, treble detail, and control on the bottom end. While these are available from most good solid state amplifiers, the F4 also brings depth, imaging, midrange warmth and top-end sweetness.

Overall, it is one of the best sounding amplifiers, and if you can live with unity voltage gain in your amplifier, it is possibly your best choice."

soldersmoker said:
I didn't mean to sound dismissive of the F6. It's obviously a very fine amplifier, but I'm partial to a bit of the (distorted?) tone of dem tubes. The OTL sound might be more neutral, a la solid state, when compared to some other tube topologies, but I really like how the LTA MZ2 sounds in my system. I liked my 2A3 and current 1646 SET amps, but the LTA I like even better.
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Zen Mod

Zen Mod

Official Court Jester
Joined 2003
zenmod.in.rs/
Paid Member
gdglenn201 said:
Would anyone mind making some suggestions on chassis wire gauges and types solid vs. stranded etc?
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all power lines 1.5 or 2,5 sq. mm , more the merrier ; nice stranded ......... solid is no-no there , not overly clever when dealing with pcbs
input signal - I'm using 0.2mm dia solid core , silvered copper


SoundEros5 said:
Finally completed Pow Supply and F4 Boards. The less light up. However, I am reading .6 ohms across the .47 ohm resisters, and 0 VDC no matter how I turn the P1 variable resister. Any suggestions?
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tricky to read anything sane cross R source , when same is in circuit , not taking in account possibility that you either have lousy DMM or lousy battery in same

regarding Iq - ( voltage readout across Rs) - you need two DVMs - one across output to observe output DC offset , and second across any Rs , to read voltage , thus Iq

pictures could help , also some measurement values , not even mentioning how important is to point us to your ref. schmtc
 
6

66deg

Member
Joined 2016
Hello DIY collective,


I am in the process of collecting parts for an F4 build and would like to ask a couple of questions. Before we get to them; my proposed setup will be, ARC Ref 3 pre amp - F4 -speakers or ARC Ref 3 PREAMP - Flea watt amp (TU 8100 PCL86) combined with F4 - speakers.
In the second scenario with the flea watt amp I am not sure how they are conected together and I think the flea watt needs to see a load whereas in the first scenario it would just be connected as normal i.e RCA in, speaker binding posts out.

Could I ask how to go about the construction of a flea watt seeing a load

what parts would be required and secondly how it is connected.


My other question concerns the toroid, I live in France so our eletrical supply is 230V - 50Hz and I am looking to order from Canterbury Windings, I think TM160A is the right one but would like to double check;http://www.canterburywindings.co.uk/standard_range.htmlhttp://
If this is not correct I have the option of a custom build. http://www.canterburywindings.co.uk/ordering.htmlhttp://
If this is my best option could anyone advise me on what would be the specifications for a custom build.
Merci.
 
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