F2 with SS.
I dropped in a South Semi R100 JFET this morning into an F2. About a 4 minute operation in my very proto looking F2.
Made music right from the start which is good. The previous bias setting had dropped from 14v to 10v. So I cranked it back up some, and listened for some time.
I think, with no other circuit modifications, there is a bit less gain, and the F2 sounds a bit 'cleaner' without sounding lean. I was driving a fostex ff85k in a bass reflex with only the 3x47r resistors on the output.
Might be far from optimal, but does appear to drop right in, replacing IRFP240.
I dropped in a South Semi R100 JFET this morning into an F2. About a 4 minute operation in my very proto looking F2.
Made music right from the start which is good. The previous bias setting had dropped from 14v to 10v. So I cranked it back up some, and listened for some time.
I think, with no other circuit modifications, there is a bit less gain, and the F2 sounds a bit 'cleaner' without sounding lean. I was driving a fostex ff85k in a bass reflex with only the 3x47r resistors on the output.
Might be far from optimal, but does appear to drop right in, replacing IRFP240.
Attachments
The F2's that I have updated with the JFETs need the
following changes:
R6 = 47k
C1 = 10 uF
Z1 removed
The potentiometer must be re-adjusted for minimum
distortion at 4.5 watts (symmetric clipping) and readjusted
after an hour.
The distortion results are typically a reduction from about 1%
at 1 watt to .25%.
following changes:
R6 = 47k
C1 = 10 uF
Z1 removed
The potentiometer must be re-adjusted for minimum
distortion at 4.5 watts (symmetric clipping) and readjusted
after an hour.
The distortion results are typically a reduction from about 1%
at 1 watt to .25%.
Papa,
Completed your circuit mods, made sense to remove R2 since it seemed a lonely soldier.
The unit now biases at 13v max (P1 full blast), and by ear (swag) I think the distortion seems to be less with bias at about 10v. Do you off hand remember the bias voltage you had? My distortion analyzer is only imaginary, so I was hoping for a best guess. I have no R13-15, but do use 10R 10W across a FF85k terminals.
I thought R4 could be set to 4.7k for more bias, but that seems to be going in the wrong direction.
Completed your circuit mods, made sense to remove R2 since it seemed a lonely soldier.
The unit now biases at 13v max (P1 full blast), and by ear (swag) I think the distortion seems to be less with bias at about 10v. Do you off hand remember the bias voltage you had? My distortion analyzer is only imaginary, so I was hoping for a best guess. I have no R13-15, but do use 10R 10W across a FF85k terminals.
I thought R4 could be set to 4.7k for more bias, but that seems to be going in the wrong direction.
I have tried it. The distortion is not as low as some of the other
parts, but that is to be expected. The capacitance is lower
though, and if you have a higher source impedance or simply
want more bandwidth, it might be preferred.
There are a couple of specific recommendations on the input
networks which will give you lower noise and so on. I'll
write them up from Sea Ranch later in the week.
post 325 regarding R100 semisouth in F2 - feb 2010.
does anybody know if there is anything more on this??
or is post 328 the answer??
Papa??
Ed
Last edited:
The F2's that I have updated with the JFETs need the
following changes:
R6 = 47k
C1 = 10 uF
Z1 removed
.
Hi,
Will 4.7uf caps for c1 give me enough bandwidth? I haven't thought about this stuff in about a year and am a bit rusty... |
Tea-bag, did you figure out the answers to your own question from March about the bias voltage? I also lack proper test equipment so will be tuning it by ear..
Well, regardless of the answers to the above, I think I'm going to swap in the jfets this afternoon. I'll let everyone know how it sounds!
Wicked1,
I changed R4 to 3.32k for sport. Still Bias'd at 10v, mostly because I perceive it to be a good value from both heat dissapation and sound. More bias might give a bit more body and less distortion from messing with amp's in general. I will tweak more once I get a scope home from work and learn to use it.
I changed R4 to 3.32k for sport. Still Bias'd at 10v, mostly because I perceive it to be a good value from both heat dissapation and sound. More bias might give a bit more body and less distortion from messing with amp's in general. I will tweak more once I get a scope home from work and learn to use it.
Ive got a scope and analog synth which will give me any shape wave at any frequency I need.
I can look for clipping, but how do I know when it's @ 4.5 watts?
Or, should I just hook up the scope, turn it up till it starts to clip (regardless of what the actual level is) and then adjust the pot till it's symmetrical? (my scope is old and uncalibrated, but I don't think that will matter for this.. I wouldn't trust it to measure voltages, but it draws waves well enough)
And, I'm guessing I hook up the scope across a 16ohm resistor @ the speaker terminals of the amp?
Thanks
I can look for clipping, but how do I know when it's @ 4.5 watts?
Or, should I just hook up the scope, turn it up till it starts to clip (regardless of what the actual level is) and then adjust the pot till it's symmetrical? (my scope is old and uncalibrated, but I don't think that will matter for this.. I wouldn't trust it to measure voltages, but it draws waves well enough)
And, I'm guessing I hook up the scope across a 16ohm resistor @ the speaker terminals of the amp?
Thanks