Keep your eye on these posts, meanie - they're happening fast! LOL...
And thanks of course for sharing your experience. Although I love the idea of monoblocks, I am hoping to solve my issue instead of having to re-engineer the amp around the problem.
Yes. 3.3k is still ok. Basically anything between 2k and 3.3k. 2k would be better though.
Yes.
If you use current regulating diodes then anything between 5mA and 8mA.
If you go with current regulating diodes it might be worth getting some prototype board with sockets just to test correct orientation of all parts together beford soldering them in.
Last edited:
I replaced 6V8 Zener with 3LEDs, just to please 2 picodumbs 
Less bias drift during varm up.
R7, R8: 3K3
R1/R2:0R56/0R47
bias: 0,6V
When I first built it I went with R1/R2:0R47/0R47 but needed more 2H. Not noticeable change with 0R56. 3'rd dominate at 1V in and with 2V in 2'nd gets dominate. With Iron Pumpkin with no harmonics to speak of, fantastic pre by the way, I like to se if there is other mods I can try for other coloring sounds.
What about the mod 0R1 source resistors? Even less harmonics? How about bias volt over 0R1?
Other comments or ideas are welcome.
Less bias drift during varm up. R7, R8: 3K3
R1/R2:0R56/0R47
bias: 0,6V
When I first built it I went with R1/R2:0R47/0R47 but needed more 2H. Not noticeable change with 0R56. 3'rd dominate at 1V in and with 2V in 2'nd gets dominate. With Iron Pumpkin with no harmonics to speak of, fantastic pre by the way, I like to se if there is other mods I can try for other coloring sounds.
What about the mod 0R1 source resistors? Even less harmonics? How about bias volt over 0R1?
Other comments or ideas are welcome.
Attachments
Last edited:
Yes, please! FWIW, my personal goal would be a bit more power into lower impedance loads, but all trials to learn are appreciated. I'm just now beginning to get comfortable with an oscilloscope and REW. I find this fascinating.
Pico's Magic F6 Trick
Green LED References
R7 Anything between 2k and 3.3k
R8 Same as R7
Q1 IRFP250 (do not use IRFP150), - IRFP140 might be suitable but this has not been tested as yet.
Q2 IXTH64N10L2
R1 0.22 Ohms
R2 0.22 Ohms
R3 100 Ohms
R2 Anything between 20 and 23 Ohms
Bias around 1.5A to 1.75A
This will get you J2/Aleph J like operation without needing to degenerate - but also with the additional benefit of Class AB operation.
Absolutely
Green LED References
R7 Anything between 2k and 3.3k
R8 Same as R7
Q1 IRFP250 (do not use IRFP150), - IRFP140 might be suitable but this has not been tested as yet.
Q2 IXTH64N10L2
R1 0.22 Ohms
R2 0.22 Ohms
R3 100 Ohms
R2 Anything between 20 and 23 Ohms
Bias around 1.5A to 1.75A
This will get you J2/Aleph J like operation without needing to degenerate - but also with the additional benefit of Class AB operation.
Last edited:
This is what F6 has always done.
Transitioning into Class AB from Class A is always better than hard current limiting. This is what F6 has always had over Aleph J and J2, nothing new.
Aleph J and J2 just hard current limit, not good for difficult loads.
Here you can have it all.
Zero degeneration
Similar single ended operation to J2/Aleph J
No hard current limiting into difficult loads
It's a win/win
Just to clarify IRFP250 must be VISHAY
Last edited:
Last edited:
My parts are here and I’m soldering tonight! But before I do I want to make sure I have this right. Are the LEDs in my picture oriented in the right direction on the PC board?
Attachments
The cathode is pointed in the opposite direction to a zener.
So turn them 180 degrees.
So turn them 180 degrees.
An externally hosted image should be here but it was not working when we last tested it.
Last edited:
F6 Channel A issue
About one month ago I finished the build and dialed in BIAS (0.5V) and OFFSET (few mV) to constant levels. Lately, channel A started to show quite a drop in volume after some 20 minutes from powering up. If I crank up the volume the channel starts to work again; however, with reducing the volume the issue reappears. Both channels are dead quiet at the speakers. Any ideas what or more specifically which (heat sensitive) component might cause this issue? I hope it is not the Jensen transformer, as they are currently out of stock at the DIY audio store. Any feedback would be appreciated.
About one month ago I finished the build and dialed in BIAS (0.5V) and OFFSET (few mV) to constant levels. Lately, channel A started to show quite a drop in volume after some 20 minutes from powering up. If I crank up the volume the channel starts to work again; however, with reducing the volume the issue reappears. Both channels are dead quiet at the speakers. Any ideas what or more specifically which (heat sensitive) component might cause this issue? I hope it is not the Jensen transformer, as they are currently out of stock at the DIY audio store. Any feedback would be appreciated.