F5m kit

Ben Mah · 2024-03-23 7:38 pm

Push-pull versus single ended.

roger57 · 2024-03-23 7:49 pm

Got it now. So at 8 ohms, there's no difference in power.

TungstenAudio · 2024-03-23 7:57 pm

These amps certainly benefit from a strong power supply. The CLC configuration sounds like a good choice. I was reusing some existing boards, otherwise I would have built CLC.
When I use motor run caps, I look for 60 uF or better in CBB60, 250 VAC.

zman01 · 2024-03-23 8:09 pm

TungstenAudio said:
I am currently listening to my F5m with a recently completed upgrade to the power supply filters on each channel. Prior to this I was listening to a version of the Aleph J built with the simplified SS PCBs. And before that my F6 Diamond with the CineMag transformers..

All three of these amps sound more similar than different. They are all using high transconductance FETs in their output stage; some more so than others. My F5m and Aleph J SS now have very similar power supplies - a single transformer driving an enhanced Universal PS with separate motor run cap filtering in each channel.

The Aleph J has better rejection of the 120 Hz hum from the rectifiers. Once its motor run caps were in place, the imaging and soundstage were the equal of my best dual-mono build (the F6). Transparency was a revelation on some recordings. I needed extra time to find the right voicing to get just the right spectral balance. Obscure experimentation with Aleph coupling caps and tantalum film resistors, etc., nobody cares. But it became an amazing amp that I would happily live with indefinitely.

I have written about the F5m in the other thread, and it keeps sounding better. The motor run caps did their trick for the imaging. Instruments are fully detached from my speakers. There is a very slight residual 120 Hz hum; not something that bothers me when I’m in the room, just a nag at my OCD. Having said that, the F5m is slightly more laid back in its presentation. Bass extension is impressive, though it doesn’t call attention to itself. The bass of the Aleph J became a feature on some recordings. The F5m continues to excel with musical flow

Of the three amps mentioned, my F5m is using somewhat more conventional FETS. The FQA28N15 and IXTQ26P20P are a good pairing.
My recommendation is to build both or all three.

TA,

Thanks for sharing your impressions.

IIRC you have the F6 with diamond buffer running at higher voltage rails (+/- 27V?)

What about the F5M?

mkrawcz · 2024-03-23 8:09 pm

roger57 said:
I think I will build the F5m just because of the simplicity, and I'm intrigued by the feedback and comments in the thread. And, I've got a couple hundred 2SK170BL's so this is a good opportunity too use a couple.

My own subjective opinion is that, the F5M is probably the best cost vs performance amplifier I’ve come across. The sound quality you get for well under $500 in parts is crazy.

roger57 · 2024-03-23 8:16 pm

TungstenAudio said:
These amps certainly benefit from a strong power supply. The CLC configuration sounds like a good choice. I was reusing some existing boards, otherwise I would have built CLC.
When I use motor run caps, I look for 60 uF or better in CBB60, 250 VAC.

Yes, agreed. I ended up using the Antek AS4218 (400VA). I like the fact it has the static shield. With a solid central ground using a 4cm copper bus bar I can hear ZILCH noise, not a trace of anything from the speakers. However one of the Anteks is buzzing a bit so that's annoying, but not impacting the sound. Truly, I would find it hard to believe that the F5m could sound better than my beloved AJ's, but looks like yet another project is on the go...

roger57 · 2024-03-23 8:19 pm

mkrawcz said:
My own subjective opinion is that, the F5M is probably the best cost vs performance amplifier I’ve come across. The sound quality you get for well under $500 in parts is crazy.

Yes, the comments certainly point to this. And truly, NP would not put out a design that us audioholic crackheads wouldn't like, cost/performance notwithstanding. I just want to make sure it could sound better than my AJ's. Seems a stretch, but I am tempted to give it a go.

TungstenAudio · 2024-03-23 8:36 pm

My F6 Diamond is currently running on 26.5V rails. Soon to be upgraded to 29V with a transformer swap. Different boards are using FQH44N10 or IXTQ75N10P FETs Both of these sound great. Switching input transformers from Jensen to CineMag makes a bigger difference than switching the FETs.

I would expect the F5m to offer some advantages over earlier Aleph Js. It is a remarkable value in bang for the buck. Mine is running on 29V rails.

zman01 · 2024-03-23 10:15 pm

TA,

If I understand correctly:

1. Your F5M is running on +/-29V rails
2. You are using FQA28N15 and IXTQ26P20P in your F5M build

Am I correct in assuming that you are using the Toshiba / LSK JFETs for your F5M? Since rail voltages are high (+/-29V), what Idss value (in mA) are you using?

Good luck with the voltage rail increase with your F6 Diamond...

TungstenAudio · 2024-03-23 10:40 pm

Zman,

Correct on points 1 and 2.
My JFET front end devices are matched Toshiba K170 / J74 with an Idss higher than what is sane for my rail voltage. Right in the middle of V grade. I had to use 500 Ohm trimpots to dial in the correct Vgs.
So everything is running hot. Fun times.

If this is wrong, I don’t want to be right.

zman01 · 2024-03-23 10:47 pm

Fearless Amplifier Builder...

Have you considered heat-sinks for the JFETs? IIRC EUVL had some custom units made... however the orientation and spacing would have to match as they were built to cool a pair of 2SK170/2SJ74.

https://www.diyaudio.com/community/threads/the-next-best-thing-to-2sk389-2sj109.135154/

TungstenAudio · 2024-03-23 10:48 pm

Yeah, heatsinks on those JFETs would be nice 👍

zman01 · 2024-03-23 11:03 pm

Have edited my previous post an added the link for the thread where the JFET heat sinks were discussed.

TungstenAudio · 2024-03-23 11:23 pm

Thanks for that link.
I found some TO-92 heatsinks a while back. I have also considered using some thin copper tape. The JFETs are in contact with each other (using the older F5 PCBs). So I may have a couple options, but the inside of the amp isn’t a cool environment.

rayma · 2024-03-23 11:28 pm

It is, compared to the junction temp.

seventenths · 2024-03-24 12:42 am

TungstenAudio said:
Yeah, heatsinks on those JFETs would be nice 👍

I have some of the stamped steel sinks for to-92 and I'm sure they're adequate but those wire-cut units are just plain sexy. Jlcpcb offers machining services and based on the low cost of their PCB manufacture, I can't help but wonder what 100-200 lots of something similar would run. That's just curiosity speaking... nothing more