korben69 said:
udailey said:
I think the pot value is 100k as this matches the input impedance. Anyone feel free to correct me if I am wrong.
for Zin = 100k the source impedance (Rs) is usually better if it is below 10% of Zin.chrismercurio said:
i.e Rs=<10k is better for Zin=100k.
The maximum source impedance of the pot follows this rule: Rspot<=[pot value +Rssource] / 4. Assume source is 1k.
pot=100k gives Rspot<=25k25
pot=25k gives Rspot<=6k5
pot=10k gives Rspot<=2k75
Use either 25k pot or 10k pot.
I prefer the lower value since a source impedance of 6k5 will result in a treble cut filter if there is significant capacitance following the pot. Anything approaching 500pF will be significant.
i have a friend that just built a F5--he can't get it up to full bias on both channels- he runs out of pot. i have a similar problem with my F4-one side biased up fine but the other side wide open was at 90% bias-so i just turned the good side down to match it. could this be caused by a gross mismatch in the jfets??? is his F5 and in my F4 we just picked the jfets from a pile--didn't match them. I have a F5 that i matched the parts and it biased up just fine. anyone have any suggestions??????
bubba177 said:
increase drain resistors ( in parallel with pots ) for ~25% and you're there
quick 'n' dumb solution ....... if you don't want to pick jfets with higher Ids
He runs out of pot? there's the problem .
You shouldn't mix solder smoke with pot smoking.
LOL sorry bout that couldn't resist.
You shouldn't mix solder smoke with pot smoking.
LOL sorry bout that couldn't resist.
thanks zen !!!! -we were leaning that direction or changing the jfets-mucho gracias for the advice
amp-guy said:
hey - we are here in PASS forum ............ so - running out of pot is just out of question ......
Biamp F5 F4
I know this is a few days old but I saw your post. I've been thinking of doing F3 and F5 with a DCX - F3 on ribbon tweeters F5 on midrange panels. Just curious about how you like you're set up and why you choose the F4 F5 combination
Tom
tms0425 said:
I know this is a few days old but I saw your post. I've been thinking of doing F3 and F5 with a DCX - F3 on ribbon tweeters F5 on midrange panels. Just curious about how you like you're set up and why you choose the F4 F5 combination
Tom
Re: Biamp F5 F4
Honestly I just like the versatility of the F4's for many speaker situations and they sound very good no matter what I throw at them. The F5 is just a very transparent and pristine amp without any harshness or glare ideal for the upper frequencies in my setup. It just sounds right harmonically. A stock DCX is not pleasant at all, but with the mods mine has I think it comes closer to what the amps themselves are capable of.tbrooke said:
hi andrew
no rose coloured specs mate just common sence
its much easyer to set up an active system with lower and upper amps that are the same gain and spec than to use different amps and know they are not working together 100%
eg different gain ,td specs ,slew rates etc
no rose coloured specs mate just common sence
its much easyer to set up an active system with lower and upper amps that are the same gain and spec than to use different amps and know they are not working together 100%
eg different gain ,td specs ,slew rates etc
I have seen several posts about bridging the F5 but is what about paralleling the output into a 4ohm load? I assume the distortion curve would resemble the 8ohm but are there other benefits...better bass, higher output, etc. ?
hi mate
yes 8 is a bit much
i might try building 4x to start with and biamp the system to see how it goes and build the other 4 channels whilst im deciding if i like what im hearing
ive only let the magic smoke out of one amp ive built so far and it scared the !@*# out of me big flames and explosion
my tip for the day is do not run a ska gb300 with more than 3mv bias
yes 8 is a bit much
i might try building 4x to start with and biamp the system to see how it goes and build the other 4 channels whilst im deciding if i like what im hearing
ive only let the magic smoke out of one amp ive built so far and it scared the !@*# out of me big flames and explosion
my tip for the day is do not run a ska gb300 with more than 3mv bias
Zen Mod said:
hey - we are here in PASS forum ............ so - running out of pot is just out of question ......
Thanks Zen. Swapping the Fets with higher Ids did the trick. now have ample pot!!!! and bias to boot!! Thanks for timely advice (and humor)
increek22 said:
it's still not too late !
you can put some resistors instead of jfets ......... and have more fixed gain ......... as gain
Re: Re: Biamp F5 F4
I finally got an F5 running in the main rig.
I too am impressed by the lack of glare of any sort here.
In my system, it seems very relaxed, and soundstages, images or whatnot in a very 'crisp' or detailed manner.
It also seems to 'control' the music very well, so there is no garbling of difficult passages. I will admit, I didn't listen too long or even critically, and have yet to throw lots of music at it.
I would agree it sounds very similiar to an F4, but possibly with an edge on 'control'
tms0425 said:
I finally got an F5 running in the main rig.
I too am impressed by the lack of glare of any sort here.
In my system, it seems very relaxed, and soundstages, images or whatnot in a very 'crisp' or detailed manner.
It also seems to 'control' the music very well, so there is no garbling of difficult passages. I will admit, I didn't listen too long or even critically, and have yet to throw lots of music at it.
I would agree it sounds very similiar to an F4, but possibly with an edge on 'control'
labjr said:
Yes. 2SK170BL (complemented with 2SJ74) however I am a little suspicious about the range of Ids I measured with a batch of 100 parts purchased from Futurlec.
Ids ranged from less than 2 to more than 17 ma. I thought they were supposed to be 6 - 12 ma but there were none in that range. Maybe they had been picked over or maybe my measurement technique isn't quite right. But my F5 boards are biased and playing audio. Now for some serious listening - which is what all this is about isn't it?