Thank you buzzforb. I misunderstood it as the opposite. How's your build coming along?
I could be wrong, but i think thats right. My build is slow because i am shipping F5T kits monday. I have the screwed up version close, but dont know if ill get to it.
Maybe poor implementation is better description. I got FE looking like F5T input with signal coming out of source and then in the output stage, I got the big 10uF caps instead of 1000uF's like Ilquam. It is CCS loaded LEd's fro bias voltage on output. Rs is 22R and gain is set at about 10. I am using laterals because they are close to SS in bias voltages and if i blow them up, I dont feel as bad.
Edit:
Why the need for large caps? Are they forming a high pass on top ot blocking dc through coils?
Edit:
Why the need for large caps? Are they forming a high pass on top ot blocking dc through coils?
Last edited:
secondaries are low impedance jobies
even if they're looking at 10K load (Pa sez that) , better to put nice biggie Silmic in series with them
bigger is sometimes better
even if they're looking at 10K load (Pa sez that) , better to put nice biggie Silmic in series with them
bigger is sometimes better
I hope you meant to say "Rs is 0R22". The large caps reduce the modulation of the bias voltage by the signal. I may have used excessively large caps, but I suspect 10uf is too small and will increase low frequency roll-off.
I just ran the simulation again and equation to calculate output impedance. Increasing Rs increases the output impedance, thereby decreasing the damping factor. Increasing Rs also lowers the voltage gain of the output stage, thereby lowering the open-loop gain. Is closed-loop gain is held constant then the amount of negative feedback is reduced which also decreases the damping factor. The 2 effects are not really multiplicative, but I do not have the equations in front of me that shows the general case with feedback.
lhquam. Thank you for the correct answer. I had the underlined backwards [reversed] in my head for a while. You have several variables to "juggle" to nail the optimal and final status of the amp. Based on past publications by Mr. Pass, and Mr. Rothacher, the general sound character of your amp is expected to be "pentode-like" versus triode-like if the output stage devices were SIT instead of JFETs. Have you built a SIT amp according to the Rothacher DIY?
I do not know if there will ever be a consensus on the "optimal" configuration of parameters. It will depend on personal sonic preferences.
My prototype uses SemiSouth SJEP120R100 JFETs.
The official schematic of F6 will embody design variables which express a unique sonic signature that is solely attendant to the preferences of Mr. Pass. He is listening to the voice of his assembled F6 through his loudspeakers [unknown make] playing his preferred music [unknown] in his music/test room of unknown dimensions, surface treatments; with or without suppression of standing waves etc. Thus, he has geared his F6 to his listening pleasure, plus the other important technical and business pursuits. He may already have cast his design in stone, and thus gave it Universality. What is the probability that the sonic signature of his official F6 is like that of a DIY build of F6 DIY using his schematic? I say very good to excellent. Fortunately, the above also holds true for your design, triode_al, buzzforb, bobodioulasso and countless others, as y'all have also tweaked your listening environment [and support electronics] which are an integral part and parcel of the sonic signature of the amp. There will be a lot flexibility in design to suit as underlined in your text. Just like the old classic [based on the wimdehaan-Tent Circuit] which came in many renditions and topologies!
Given the moderate (turn on) Vgs of the JFets, i think 0R22 for Rs is enough.
Olg isn't penalised too much allowing more feedback aiming to less distortion and a better damping factor etc...
But i might be wrong.
Olg isn't penalised too much allowing more feedback aiming to less distortion and a better damping factor etc...
But i might be wrong.
Last edited:
Correction: I am using SJEP120R100A JFETs. I do not know how they differ from to SJEP120R100 JFETs, but their data sheet says "High Performance Audio".
I think they are parts that missed the mark for switching purposes which they were made for.....I think.
I thank you for that suggestion.
The source resistor has two different effects:
The source resistor has two different effects:
- 1) degeneration - local negative feedback.
- 2) bias voltage stabilization - and ability to measure bias current.
and you can modulate them from bottom of Rs ....... or from top of Rs ....... or one from bottom and other from top ....... or the other way around .........
Nelson, a question for you please.
When you chose the impedance match to the primary of the transformer as input device, what guided you to 600 ohms? Will a higher impedance / inductance/ DCR cause undue distress? I have a pair of 2800 ohm split primary and secondary transformers, 48% nickle core and pin out to match the Jensen parts. I can also have 1200 ohms or 600 ohms or whatever is best. Can you provide some guidance please?
Bud
When you chose the impedance match to the primary of the transformer as input device, what guided you to 600 ohms? Will a higher impedance / inductance/ DCR cause undue distress? I have a pair of 2800 ohm split primary and secondary transformers, 48% nickle core and pin out to match the Jensen parts. I can also have 1200 ohms or 600 ohms or whatever is best. Can you provide some guidance please?
Bud
as my , always modest , chip in ..... ( just to mud the water before Pa's answer ) -
those so called 2K8 , instead of so called 600R , will present even more uniform load to input buffer while still having more than enough muscles to fed output gates
) -those so called 2K8 , instead of so called 600R , will present even more uniform load to input buffer while still having more than enough muscles to fed output gates
