F2 Initial Listening Impressions

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#181
Hi Rehad. Congrat's with your amp🙂 Yes R13 runs really hot.
The power of the factory F2 is 2x5watts. I believe the clone is pretty close to that. The AR speakers are famous for being a difficult load for the poweramp. They do sound pretty good though. I had a pair of AR91's long ago. My guess is that you will have better results with your F2 clone, using some more efficient speakers. Happy listening.

Steen.🙂
 
#182
steenoe said:
Hi Rehad. Congrat's with your amp🙂 Yes R13 runs really hot.
The power of the factory F2 is 2x5watts. I believe the clone is pretty close to that. The AR speakers are famous for being a difficult load for the poweramp. They do sound pretty good though. I had a pair of AR91's long ago. My guess is that you will have better results with your F2 clone, using some more efficient speakers. Happy listening.

Steen.🙂
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Rehad,

I second what Steen has said, this amp is rally for efficient speakers say minimum 92dB or higher if not the amp will easily clip.

R13 runs hot; it burns between 8 and 9W depending on circuit conditions and 2 amps bias, so make sure you have at least 12W dissipation capacity. :hot:
 
#183
Come to think of it, Rehad. You could change the feedback circuit back to the original Zen values and you would have a 2x10watt singleended amp with a regulated supply and with a little damping factor! It would be really great for those AR's as opposed to the F2 Clone! Make sure to up the rail voltage though, I think its about 32 volts!! Please read the Zen papers 😉
Let us know if you need more information🙂
Steen🙂
 
#185
F1, F2, F3 - looking for advises

I read with very much interest the listening impression on
http://www.diyaudio.com/forums/showthread.php?postid=683266#post683266
as well as
http://www.diyaudio.com/forums/showthread.php?postid=682980#post682980

I'm currently building a four way speaker based on
Fostex PA 38 for the bass
Fostex D582 for low medium
Fostex D232 as hig medium
Foster D825 as tweeter

I'm looking a firstwatt amps (i like the philosophy behind) to power each single driver since a active cross over would be used to have a quadri amp. As I undertood F1 and F2 are happy driving cross over less drivers which would be the case since each driver would have its own amps. And they are speacial products.

Woofer / bass section
I'm a bit scared to drive the bass with the F2 (5watts) but maybe it is a misconception of mine. The review seems to indicate F1 to drive bottom end. any advise ?

F2 seems to be hellacious fast when reading the F2 owner manual. Would it make it a good choice for the tweeter ?

And maybe using 2 F3 for the medium section.
It is difficult to say.

But any comment / suggestion would be most welcome.
 
#186
I suggest reading the Salt lake city shootout thread for further opinions...

I guess F2 would not be my choise for bass amp, F1 would be more apropiate.

F2 would be a good choice for mids... but it depends on system speakers as usual.

Let your ears decide....
 
#189
 
#191
During this summer i have built three of F2 Clone Amplifier . Even the electronic parts are not top quality the sound of the amplifier is near to high-end systems . I am driving Fostex Fe 206 full range speakers with the F2 , the details of mids and highs are quite well . You can hear every detail of the sound track . Really nice . As you know FE 206 needs some time to break-in . During the break-in period mids are above normal and it is of course undesirable . After the break-in period still the vocals are sometimes above normal . I have tried notch filter but it is not so good because of lowering the mids. Some time later i will try phase plugs . Will see what will happen with the phase plugs.

As of my experience F2 ampli with Fostex Fe 206 is producing very good mids and highs . Deep bass also is good . By the way i have tried Transmission Loaded box and also front loaded horn box for the FE206 . Transmission loaded box is better than Horn loaded as of bass sounds . What i can say for the weakness is the absence of the violent bass sound ( between 100hz - 300hz ). And of course undesirable high vocals . But as a summary the overall sound of F2 with Fostex FE 206 is no doubt a highend sound . I coudn't hear the same details in other "good hi-fi " systems priced between 3000-4000 usd.

Attached is my friend's system ( The below black ampli is a F2 built by me )

Regards
 

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#193
Actually we all need to thank to Mr Nelson , for having designed such a simple and very nice sound amplifier.

As for some details i have used a single 500VA toroidal transformer with thermistors in the power supply . Because of large capacitors the initial current is too high . To limit the initial power-on current i have used PTC thermistors as the current limiter . 47,000 uF x 2 Jamicon and 10,000 x 2 Daewoo capacitors used in the power supply board and also there is another 1000 uF at the amplifier board . I am not sure 104,000 MF total is enough or not ? And also different capacitors is good or not ? May be having too many small size capacitors is better. I didn't used metal oxide resistors in these amplifiers but now i think i should. ( Small differences come together and makes a difference )

🙄
 
#197
Hi,

I have tried wooden phase plugs on Fostex Fe206E . Phase plugs no doubt improved the sound quality . Harsh sounds on vocals gone . And there is no absence on mids and highs . I can suggest to use phase plugs for the FE206.

On the other hand i have noticed a resonance on 40hz-70hz sounds. Deep basses seems boomy. To understand better i have tried the Fostex's with other amplifiers such as Roksan Caspian and Classe Seventy, they don't have this problem , there is a noticeable difference with the Clone F2 . Is there anyone noticed this before .

I am suspecting the output stage of clone F2 . May be the Bleeding capacitors and the 15 Ohm resistor together with the Fostex impedance creates a resonance . Or this is a transformer problem.

Anyone have an idea ?

Thanks
 
#200
Thanks for your helps,

Actually i added 2 x 22ohm in parallel , it sounds better now . But for the highs i think there is nothing to do, for me this is quite fine . Mids and highs are very detailed and smooth .

On the other hand the tone of the amp is very similar to the Roksan Caspian M1 integrated . The only difference F2 is more sweat and warmer .

Fostex speakers are very transparent .If the amp has something different you can here the difference . I have tried a lot of amps with Fostex , until now i found Caspian and F2 are the better than others

Thanks Again
 
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