First Watt F7 review

[Juntuin]

if we are speaking about something having resemblance of F5 , for starters you need zero resistance in JFet drains

Yes we are, and thanks ZM! (I never built F5 myself, my first one were Aleph 5)

 

[oreo382]

BL grade fets came finally. One pair ids 8.06 and second pair 8.35.

I'm very close to fire it up, hopefully not literally. I just don't get one thing that I really should understand; measuring resistance from bias (and offset) trimmer pot center pin - JFet drain, should my initial setting be max (500R in this case) or 0R? My guess is 0R, but I wan't to be sure.

Try 100 ohms on the K170 500 ohm pot and 200 ohms on the J74 500 ohm pot.8 ohms on the K170 side of the 20 ohm pot which equals 12 ohms on the J74 side of the 20 ohm pot.

 

[Juntuin]

8 ohms on the K170 side of the 20 ohm pot which equals 12 ohms on the J74 side of the 20 ohm pot.

This is very useful, thanks!

 

[oreo382]

This is very useful, thanks!

You are welcome.I'd shoot for about 1 amp bias,the 500 ohm pot settings will get you close to that.Let the amp warm up before adjusting too much.

 

[Juntuin]

Got it up and running 🙂 impossible to do any critical listening since I don’t have any complete speakers available atm.

 

[jugi63]

Great job, Jutuin! 🙂

 

[Juntuin]

Great job, Jutuin! 🙂

Thanks Jugi

 

[bregargasper]

I have just purchased a few pairs of 2sj162 2sk1058 fets from aliexpress for way cheaper than I expected. I am curious if they will work at all and even if they do, will they behave as originals or are they just a generic mosfet with a name engraved on the case. [wiki=https://www.aliexpress.com/item/33019677789.html?spm=a2g0o.productlist.0.0.5e9d563b8493cd&algo_pvid=aab08a85-8da8-4ba1-8e68-00d3cc10d5c8&algo_expid=aab08a85-8da8-4ba1-8e68-00d3cc10d5c8-0&btsid=9a4a9c5d-d633-4dee-8745-5d89c2ac34c1&ws_ab_test=searchweb0_0,searchweb201602_1,searchweb201603_55]%[/wiki]

 

[Juntuin]

How high you have biased your F7’s and how it have affected sound? Amp sounds good now but at 1A bias it’s getting barely warm.

 

[Sangram]

I have just purchased a few pairs of 2sj162 2sk1058 fets from aliexpress for way cheaper than I expected. I am curious if they will work at all and even if they do, will they behave as originals or are they just a generic mosfet with a name engraved on the case.

Just from the feedback on the item page, looks like they are fake.

We still get the last batches of those devices in India, but verified genuine parts are hard to come by now. The last lot I picked up will probably be the last ever, the packaging is correct but some of the verification code and batch markings are missing.

Fortunately I still have a small number of known good Hitachi parts left, and a few pairs of the Renesas devices well. Enough to finish a 3 pair F7 this year.

 

[ggetzoff]

Hi,
In progress of trying out F7, I don't understand anything about anything, but my friend helped me out with this one.
It seem that I have only V-grade J-fets available. Is BL-grade required on this one? I think that about 8mA idss would probs be best choise, these are just so hard to find nowdays.

I know there will be couple of others obstacles before I have working amp 😀

Well, I would disagree, you know how to use a computer and post here....😀

 

[bregargasper]

Just from the feedback on the item page, looks like they are fake.

We still get the last batches of those devices in India, but verified genuine parts are hard to come by now. The last lot I picked up will probably be the last ever, the packaging is correct but some of the verification code and batch markings are missing.

Fortunately I still have a small number of known good Hitachi parts left, and a few pairs of the Renesas devices well. Enough to finish a 3 pair F7 this year.

I was too excited to even read the reviews at the time of purchase 🙁 I can still (mis)use them in other projects or tests 😛

 

[Antoinel]

Question?

The attributes of Positive Current Feedback [PCF] are well established and are highly regarded by audiophiles. I've experimented with PCF in amps unrelated to diyF7. The subjective sound from the same loudspeakers [ADS L730] is different with and without PCF.

Can one consider the subjective sonic effects of PCF a beneficial distortion?

Best
Anton

 

[Soundhappy]

The subjective sound from the same loudspeakers [ADS L730] is different with and without PCF.

Can one consider the subjective sonic effects of PCF a beneficial distortion?
Best
Anton

PCF incrase loudspeakers damping factor 🙂 Laterals sound better with

 

[Nelson Pass]

I don't think I would have bothered, but the laterals in the F7 only gave a DF of 5
with the minimal feedback I had.....

 

[Soundhappy]

http://www.firstwatt.com/pdf/prod_f7_man.pdf

In the F7 manual damping factor is specified >100 🙂

 

[Sancho49]

And by that you mean this orange path?
So even if there is a ground loop, the induced hum is minimal just
because of the distance of this ground loop from the transformer?

And what about the loudspeaker ground current?
As I simulated this layout it turned out that even 1A from the output
current can flow via the RCA interconnect ground wire around the channels.
Isn't this causing some distortion modulating the original signal via the unbalanced connection?

Hi Everyone,

I've try this DIY F7 (Dual PSU) amplifier without succes ...
Separated power supply, but 80v AC on the chassis without protective earth connected : but very low noise on output

With protective earth connected, huge 50Hz noise on speakers ...

Do you have find the ground loop problem on this amp ?


Thank you Community

 

[Sancho49]

 

[Sancho49]

I use this board : (Please remove it if *illegal*)

 

[ksJPN]

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.