What speakers do you have? Mine are New Large Advent and the 1.5&2.2k were good in my setup.Yes lower the 1.5 and see what happens,once you get it tuned it will be worth it.
My speakers are very efficient modified LaScala horn speakers. When I lost one channel I thought oh s**t I have done blown some jfets then I thought it might be my preamp when I ruled the amp out and then it came to me blown fuse. I keep my speakers fused with a smaller amp fuse then specified. Never blows listening to music but quickly burns out in case of turntable needle drop etc...
Being 'one' of those a bit erm.. dissapointed with MY F6 build's actual sounds.. through MY 95 db speakers (5.6 ohm av impedance according to those who Have measured such)
Thin and a bit dull to my ears, not quite equalling the affordable / humble pedigree amp that preceded it.
Which is back in place .
Although one thing that did/does seriously impress/please with the F6 is it's total utter complete silence through the speakers Very nice.
I'm thinking I might experiment a bit with this PF.
Happy to try and get My F6 to the 'keeper' stage.
I can't seem to open the above file though.. It seems as a simple asc file... sigh.
But Win 10 is proving annoyingly recalcitrant. Suggestions ?
thanks
Last edited:
Rated for 8 ohms but like most speakers it can be all over the place. Since I have a 1 ohm 10 watt I think I will give it a try.
Those are very efficient speakers,all I can say is experiment.The LTSpice sim only allows me to check loaded vs. unloaded voltage,however someone more experienced with it may be able to do more. That is how I came up with the resistor values.
Success with the 1 ohm resistors. Just a touch too much uncontrolled bass with a bass fiddle so I may want to lower it some more. I am very impressed with the sound, much more like some of my SET amplifiers. Short duration of listening time and the amp has not even warmed up for best sound but it sounds altogether different in a positive way.
Thats great news.I found that letting it warm up made all the difference.Much better bass control,better imaging more precise instrument placement in the soundstage. Electronic music sounds incredible, seems the dynamic range is better.BTW,what do you have your bias set to?
The bass did seem to tighten up as the amp warmed up so for now I am going to listen some more with the 1 ohm resistor installed. Totally different sounding amp now. For me it has improved the F6 and made the sound much more to my liking. Others may prefer the sound as it was with their speakers. Speaking from just a short listening period the amp now does not appear to be as quick with it's sharp quick bass but it sounds so much better in the mids. It sounds much more like the M2 with PCF injected which was my favorite FW with my horns. You may lose some of the detail with PCF if you like such an amp and the F6 is one of the best detailing amps I have heard but just too sterile sounding for my taste. With PFC it has more soul. All this I have said may change after more listening this is just my first impressions
It has been awhile since I built the F6 but if my memory is correct I biased it at .700V. I started at .500V and really did not hear any difference in the sound increasing the bias as other FW amps did.
It has been awhile since I built the F6 but if my memory is correct I biased it at .700V. I started at .500V and really did not hear any difference in the sound increasing the bias as other FW amps did.
As I wrote in one of my threads about PCF, it is a very delicate matter to optimize the amount of PCF. I highly recommend a 100 ohm or 200 ohm 2 watt potentiometer parallel over the R-sense (1 or 1,5 ohm power resistor) with the mid-tap on the potentiometer connected via the 2200 ohm resistor to the input J-Fets.
It is like a tone-control but with a whole new vector of adjustments to the character and sound of the amp. From plain and dull all the way to incredibly "nervous", alive and aggressive.
For playing Skinny Puppy, Meshuggah and Skrillex at loud levels I prefer more PCF as it tends to accentuate the aggressive and hard hitting nature of that kind of music. For playing soft piano based Jazz I want to decrease the amount of PCF to lower distortion and emphasize the unhindered effortless organic character of a simple single stage class A amp.
Cheers,
Johannes
It is like a tone-control but with a whole new vector of adjustments to the character and sound of the amp. From plain and dull all the way to incredibly "nervous", alive and aggressive.
For playing Skinny Puppy, Meshuggah and Skrillex at loud levels I prefer more PCF as it tends to accentuate the aggressive and hard hitting nature of that kind of music. For playing soft piano based Jazz I want to decrease the amount of PCF to lower distortion and emphasize the unhindered effortless organic character of a simple single stage class A amp.
Cheers,
Johannes
Very interesting observation.With my setup the detail is much greater and it seems quicker,bass is tight and multi layered,I can hear deeper tones.Mids for you and me are excellent.As you said and I agree it has more "soul".So I guess resistor values are speaker specific ? It makes me wonder with Nelson's F7,as it is sold to accommodate not just one speaker.Maybe there is a middle ground set of resistor values.My bias is the same as your. One last thing,have you re-routed your capacitor negatives to include the source resistors in the feedback loop as I have?Before I did this I found it sterile and kind of lifeless to my liking.
Last edited:
I wondered myself after finding I needed less PCF with my speakers than you did yourself how Nelson balanced the PCF in his F7 to accommodate any and all speakers the F7 could be used with. As you said he probably had to seek a happy medium. Diyer's will be able to adjust the amount of PCF to suit their specific needs. I have not configured my caps to include the source resistors. I like using a tube pre with generous amounts of 2nd harmonics so I see no need to do so. I may try my excellent BA3 configured preamp I have with the F6 with PCF and see what the difference is now using it. I like Johannes idea of using a pot where adjustment of the amount of PCF is available. When I tried using Johannes PCF circuit it was with the PCF injected after the jfets not before as I did with your circuit.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.