If building an F5T, the bias limit is determined by the diodes Vf. If you want to increase or lower bias, you must also change the source resistor values. If not using diodes, it is a non issue.
Buzz, I am using the diodes and the source resistor that was in your premium GB.
Based on that which is in your experience the maximun mV that I can reach during the bias?
Based on that which is in your experience the maximun mV that I can reach during the bias?
I would max it out at between 380 and 400mV across the across the source resistors until you get the temperature performance stable. You can bump it a little after that, just be careful. This amp can get away from you faster than most if you have it biased too high and the diodes cut on. Highest I have had mine is 420mV.
Noted... I will not go more then 470 mV as mentioned on the FirstWatt article.
Thank for the advise
Thank for the advise
I have mine set to the middle, hope this wont be a problem. I will be firing up with a variac, like I did with "regular" F-5. Is this sufficient sans light bulb tester? Or is this amp so twitchy the pots must be zeroed even with variac?
Thanks,
Russellc
Folks:
Can someone explain the purpose of Q1.1 and Q2.1 to me? I understood that cascoding helped to spare Q1 and Q2 from having to bear voltages beyond their meager capacity, which is why Q7 and Q8 are in the circuit. What do Q1.1 and Q2.1 add, and are they required in all implementations of the F5T?
Regards,
Scott
Can someone explain the purpose of Q1.1 and Q2.1 to me? I understood that cascoding helped to spare Q1 and Q2 from having to bear voltages beyond their meager capacity, which is why Q7 and Q8 are in the circuit. What do Q1.1 and Q2.1 add, and are they required in all implementations of the F5T?
Regards,
Scott
In a build with lots of output fets there is a possibility to run out of oomph in the driver stage. The .1 Jfets allow paralleling for the reason AudioSan mentions, and also if you need more current to run lots of output mosfets.
Remember this design can scale up towards the ridiculous - especially in terms of how much heatsink you need... 🙂 🙂 🙂
Great meeting you at Burning Amp, It's always nice to attach a real face to a forum member. 😀
Remember this design can scale up towards the ridiculous - especially in terms of how much heatsink you need... 🙂 🙂 🙂
Great meeting you at Burning Amp, It's always nice to attach a real face to a forum member. 😀
AudioSan and 6L6:
Thanks for the explanation!
6L6:
Not to go off-topic (very much), but I also enjoyed our conversation at Burning Amp and appreciated the time you took amidst the bustle to hang out. I'm already looking forward to next year....
Regards,
Scott
Thanks for the explanation!
6L6:
Not to go off-topic (very much), but I also enjoyed our conversation at Burning Amp and appreciated the time you took amidst the bustle to hang out. I'm already looking forward to next year....
Regards,
Scott
What are the source resistor values?
Did you finish your biasing meanwhile? What is the result?
Did you finish your biasing meanwhile? What is the result?
As per original schematic: 2 resistor 1 ohm in parallel.
I complete the biasing at 360 mV. Right channel is stable while the offset of the left is not so stable. Rechecked after 1 week and the offset value move from 0,2 to 17 mV. Re-biased at 0,0 mV and I will re-check time to time.
The result? Astonishing... 😱 I was expecting a good result but, togheter with the DCB1, the whole setup is fantastic. The only flaw... trafos are slightly humming
I complete the biasing at 360 mV. Right channel is stable while the offset of the left is not so stable. Rechecked after 1 week and the offset value move from 0,2 to 17 mV. Re-biased at 0,0 mV and I will re-check time to time.
The result? Astonishing... 😱 I was expecting a good result but, togheter with the DCB1, the whole setup is fantastic. The only flaw... trafos are slightly humming
Ok, thanks Emyeuoi. What kind of trafos do you use?
As per original schematic: 2 resistor 1 ohm in parallel.
I complete the biasing at 360 mV. Right channel is stable while the offset of the left is not so stable. Rechecked after 1 week and the offset value move from 0,2 to 17 mV. Re-biased at 0,0 mV and I will re-check time to time.
The result? Astonishing... 😱 I was expecting a good result but, togheter with the DCB1, the whole setup is fantastic. The only flaw... trafos are slightly humming
Two Primerose toroidal 600VA 24V to get 32 Vdc rial. 2 separate PSU each one with the softstart.
The caps are nr. 8 22.000 50V for each PSU. Those caps was part of the F5T Premium kit GB organized by buzzforb that also included the parts for the PSU (the caps, the bledder and filter resistors and the diodes). The PCBs are from TeaBag... Thanks TeaBag 
.... and Thanks Buzzforb
.... and Thanks Buzzforb
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Those transformers are not supposed to hum. Do you have DC blockers on the primary side of the transformers? The hum could be caused by DC on the main supply line.
Those trasformers are not supposed to hum but they hum. I [just] replace the transformers 2 weeks ago and the hum disappear... is a mechanical hum
😱 Oi! Not good. Did you specify that the windings must be dipped to dampen mechanical vibration? It should be standard with these big VA transformers I believe.
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