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What issues with Pass Labs F5 power amp?
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Author:  natedog [ Sun Oct 15, 2017 12:05 pm ]
Post subject:  What issues with Pass Labs F5 power amp?

I've a clone F5 and it seems pretty good to me! Certainly some detail in music on open baffles that I did not usually hear with my tube and gainclone amps.
What are the down sides, from you users?

Ugly brute, unfinished, here's a pic...

IMG_3384.JPG [ 144.63 KiB | Viewed 1237 times ]

Author:  natedog [ Thu Dec 07, 2017 3:00 pm ]
Post subject:  Re: What issues with Pass Labs F5 power amp?

Ok, try to boot this interesting topic on!

Are any of you CAM'ers aware of this great (in my case DIY) amp?

It needs a recap soon:
at present there's 48,000 microf at each 'corner' - because there's 2 power supply boards, as it's a true dual mono version.

I read 30,000 microf at each corner is a minimum.
What do readers suggest? what brand of capacitors? what microf can I sensibly get away with [given I do not want to spend a thousand $$]?

Author:  dcrooks [ Thu Dec 07, 2017 3:19 pm ]
Post subject:  Re: What issues with Pass Labs F5 power amp?

I've never heard the F5, but the Pass gear I own (pre-amps) are keepers, and I have a half built Aleph 2 clone that I keep saying I need to get back to...

The only issue with these amps that I'm aware of, is heat. I see you have four little muffin fans, so you seem to be aware of this! If you're looking to re-cap the amp, I suggest you pay attention to the temperature rating of the caps as well. Most large electrolytics are rated for 85c, but you can also get them rated for 105c. Just like over-spec'ing voltage, increasing the temperature rating will lead to significantly longer lifetimes (I've seen figures as high as 10x).

Enjoy! Dave

Author:  ripblade [ Thu Dec 07, 2017 3:45 pm ]
Post subject:  Re: What issues with Pass Labs F5 power amp?

Hopefully dazed2 will post some of his experience as he's well qualified, having built both versions. I've heard them both and think very highly of them, both the design and his implementations.

Downsides? A lot of heat, mostly....

Author:  dcrooks [ Thu Dec 07, 2017 5:58 pm ]
Post subject:  Re: What issues with Pass Labs F5 power amp?

That's part of why my Aleph project is an on again/off again thing! I keep thinking I'll only run it in the winter, when the extra heat is not a bad thing! Why pay for electric baseboards? :D

Author:  AstroNewbie [ Fri Dec 08, 2017 5:28 am ]
Post subject:  Re: What issues with Pass Labs F5 power amp?

Neat amp. Did you build it yourself?

I'm a bit surprised it needs a recap soon. Anyway, the production F5 used 8 x 15000 uF
Panasonic caps, so your 30000uF figure is reasonable.

I too suggest getting 105C caps because of the temp involved. Make sure the voltage is adequate.
If you pick caps roughly the same physical size, the job should be pretty straightforward.

Some parts at Mouser: ... =Pricing|0

Downside as mentioned is the heat, though if it's running at the standard rail and bias, it's in the 140W range
and quite manageable.

Author:  Lutherton [ Fri Dec 08, 2017 6:17 am ]
Post subject:  Re: What issues with Pass Labs F5 power amp?

Since September 2016, I've had a DIY F5 in my system, purchased from a fellow CAMmer that no longer needed it. Don't know a whole lot about the innards, except that it's in the deluxe 5U case and built to DIYaudio/Nelson Pass specs. Speakers are Martin Logan Source electrostatics, which many will say aren't a good match. I say they couldn't be a better match. Preamps are a Meitner PA6i, and a Creek passive. Both mate well with the F5. I love the "passive pre" sound quality so much that I'm presently finishing up a Tortuga Audio kit, another passive using opto-couplers (LDRs) for switching and volume, which also has features lacking on both the Meitner and Creek.

Downside? None. Let me repeat that - NONE. Heat output, even in summer weather, is not a problem in the larger-than-spec 5U case. 25wpc is plenty, in my 16' by 25' room, sitting 9' from the speakers.

Upside? Well, all the superlatives apply, in spades. I have had many tube amps and preamps in my system, starting with an ARC SP3a preamp in about 1976. Thought I was a tubaholic, until the F5 arrived. Now I realize that I just love good music, and that tubes got me closer than solid state for many years, but not now, not ever again. I also have the Aleph J boards, but unfortunately this version of the amp is not compatible with the ML Source speakers so I have not bothered to switch.

All these years, I 'd thought that more better power, within reason, was best. Now, I'm certain that LESS better power, within reason, is Nirvana. Considering that it cost me less than the price of a premium interconnect, I don't see it ever leaving my home until after I do.

Author:  sasquatch [ Fri Dec 08, 2017 7:05 am ]
Post subject:  Re: What issues with Pass Labs F5 power amp?

Those muffin fans blowin up or down? Hopefully up drawing heat out.
Might work better bottom mounted blowin up since hot air rises.Less restrictive.

Just a thought.
Cool build.


Author:  japon [ Fri Dec 08, 2017 8:03 am ]
Post subject:  Re: What issues with Pass Labs F5 power amp?

Actually the fans will work better on top blowing up. To control directivity of airflow you need to suck the air towards the intended direction of airflow. Blowing towards an object creates dispersion. Sucking the air past a target area will stream the air at the intended target.

Author:  natedog [ Fri Dec 08, 2017 8:43 am ]
Post subject:  Re: What issues with Pass Labs F5 power amp?

Many thanks for all the good info, gents.

I see it will not, when the time arrives, kill me to recap this monster.

And the fans? I did not build the amp, the seller had them installed - they work, for sure.

Now to find someone who can fit me a face-plate. I was thinking alu, but then considered 3-part exotic wood might look better?!

Author:  AstroNewbie [ Fri Dec 08, 2017 11:39 am ]
Post subject:  Re: What issues with Pass Labs F5 power amp?

And on the sound of the F5, and other FW amps, Mr. Pass had this to say: ... ost3864501

Author:  dazed2 [ Mon Jan 01, 2018 9:21 am ]
Post subject:  Re: What issues with Pass Labs F5 power amp?

Just saw this now.
If you know the circuit and understand how its built, there are a lot of upgrades that you can do with the amp that can upgrade the stock sound.
First of all how big is the transformer? It does benefit from a hefty transformer.
Yes cap upgrade is also useful. You can pretty much put as much as uF of caps as you desire, it will help with punch and bottom end.
You can also upgrade resistors, especially along the signal path. It will increase resolution of the amp as well.

When you choose caps, try and get as low ESR as you can afford and because your caps are in a Class A amp look for higher temperature rated amps. 105C are better, 85C is ok.

Oh also, if possible there is a speaker protection circuit in the original design, if its in there, I would take it out. Does wonders for the sound.

Hope that helps...

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