• These commercial threads are for private transactions. diyAudio.com provides these forums for the convenience of our members, but makes no warranty nor assumes any responsibility. We do not vet any members, use of this facility is at your own risk. Customers can post any issues in those threads as long as it is done in a civil manner. All diyAudio rules about conduct apply and will be enforced.

F3 pcb group buy...

Status
Not open for further replies.
Jump to Latest
#201
R5 trimmer ? But that'll be for the jfet, and I'm assuming have no impact on the ac current gain ...

I'll have a go with the 3 1ohm resistors first anyway, and if I can't get 50% current gain, then I'll replace the resistor.

I went a bit overboard with the caps and psu 🙂
The board caps are Nichicon KZ caps, with a jensen 4 pole for the output.

The PSU is dual mono, CLC thang (33000uf, 2.2mH, 33000uf), and should hopefully kick some butt (just better not be mine !). The transformers have dual 18V secondaries, so the voltage should be well within the ballpark.

I've yet to wire this thing up, as I want to finish off my pearl phono preamp first 🙂
 
#202
Don't think the 50% thing is "fixed in stone" - can alter the sound a bit with less/more
May want to try Silmics for C2, C3 and C4 - I have some spares.
And the C9 can be a bit tricky - I'm using Phillips PP + Rifa styrene in series.
The 2.2mH chokes should be great (0.1R?)

All the best - amazing amp
 
#204
Apart from the above question,..
The 2 channels are playing just fine with my portable flac player.
When connented to my DEQ 2496/DCX2496 I get distortion at low volume.Must be something with ground I think.One channel has 0,7v at input,am I sopposed to take the loadspeaker between +46v and - output?
The LU1014 has 0,6v on source..
Is there a layout/gerber file for the PCB so I can print it out when messauring?
 
#209
first thing first ; isolate them ........
Click to expand...
Okay,that did it,plays fine after the DEQ2496,but a little low sensitivity,compared to my Symasym,cannot maXimaZe the F3.
I guess I could make a prestage with a 2sk389 in F3,thouts?

Anyway P1 is adjusted for half V+ at Q2,now what about P2?

I´ll throw in some pics later..
 
#212
Ovan-1.jpg


Fram.jpg


Notice the small Symasym..😉

F3 needs an extra gainstage,if I can found a schema with jfets..
A schema with 1-2 fets are welcome..with + and - supply..Or should I go single supply as F3 is singlesupply??
And P2 still not adjusted..🙄
 
#213
F3 more gain?

Ryssen,
Sometimes things don't go according to plan (!) but with a 1v input, the amp should put out the equivalent of about 15W into 8R speakers (about 1.5Amps) which should be enough provided all things are assembled correctly, and you're not using one of those complicated big loss passive crossovers - remember, this amp doesn't require a speaker to have a "flat Z" (constant load) to function properly.

A possible source of trouble may be the amplifier's low input impedance that can sometimes cause the signal source such as a CD player to not deliver full output, and the addition of a simple buffer to the amp's input will solve this, such as the one described in Nelson's B1 project (on the First Watt site)

I would also check that your Jfets have survived the "chassis connection" - all the info that you require is on the F3 manual or on this thread - it's not a complicated amp if you go about in a systematic way and if I remember correctly, the R0 Cct diagram contains the various cct voltages to check that all is functioning correctly and especially around the Jfet.
The speakers are connected to the amps output and the 0Volt (or central ground point) as usual, except the terminals are marked in reverse - it's a current gain amp

At low levels, this amp is excellent, particularly as you've added the choke into the power supply - I have used the amp to drive my AKG701 headphones (64R load) with excellent results with very soft and occassionally extremely loud volumes. No problems.

Hope this may be useful ...
 
#214
A possible source of trouble may be the amplifier's low input impedance that can sometimes cause the signal source such as a CD player to not deliver full output, and the addition of a simple buffer to the amp's input will solve this
Click to expand...
That might be the case,I willtry to connect my brute force tube pre inbeetwen and se how it goes.My portable flacplayer can drive it from the eaphones jack.

I would also check that your Jfets have survived the "chassis connection"
Click to expand...
Yes they did,but 1 Q2 died,so its replaced.

I have not seen anywhere how to set up P2,maybee i´ll read it again.


Edit:with the tube stage it plays loud as it should without dist.
Guess I have to carry the oscilloscope dowstairs to se how much signal it neds..
 
Status
Not open for further replies.
Top Bottom