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As ZM alludes, the R550 would be a good choice. You simply
have to bias it with a lower impedance input network, probably
dividing the input resistancees by 4 or so. You can also
consider upping the bias currents.
considering that you need certain amount of Iq through them ( even using '550) - it's hardly wise to make another power amp in disguise
.....
Hi ZM,
O.K. I begin to understand better now, what you mentioned, I looked at the diagrams. The Iq needed for the 550 to work properly would be higher than 100 mA I suppose ....... that is what you meant with "Power Amp". And what Nelson says in his soft way I had to consider upping bias.
But I suppose the SK2013 (Juma uses) could be more suited, correct...?
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correct ; they're more suited if you're counting on lesser needed bias for fancy shmanzy sweet spot , but only comparing them and 550's in exact circuit will tell ;
Problem is that we don't have curves for low current region for these critters , so - it's hard to predict anything "from paper"
but I know that you're already grown DIY-er , so I have no doubts that you'll spend afternoon or two on that dilemma
tip : I saw somewhere schematic of Be Yamamura's WOT preamp , made with Toshiba mosfet
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%.
Hi,
I dropped in couple of SemiSouth 120R100s today into my DIY F2 clone, and with mods recommended above. I hooked it up and the bias (voltage at Gate of SS 120R100) is at 2.9V. I adjusted P1 back and forth and the voltage does not change much, hovering around
2.8V- 2.9 V. What could be wrong?
It seems to play music fine though. The current source Mosfet (IRFP9240) seem to run a little hotter also. Anybody has any idea ?
Hi,
I dropped in couple of SemiSouth 120R100s today into my DIY F2 clone, and with mods recommended above. I hooked it up and the bias (voltage at Gate of SS 120R100) is at 2.9V. I adjusted P1 back and forth and the voltage does not change much, hovering around
2.8V- 2.9 V. What could be wrong?
Measure at Drain pin (center) to ground point on schematic.
If bias is too low here <10v, I would replace pot with 10k, instead of 5k. Or replace R4 with a higher value.
I changed R4 to 3.32K, able to bias up to 16v.
I still settled for 12V, seem to agree with the heatsinks a bit more.
I also tossed the Peter Daniel boards because I was getting hum, and built another set point to point on some perf boards.
I let her run in for a full day. I used silimics on input, and as a bypass on the 15000uf output cap.
Hooked it with a 10R-10uf across speaker outputs, the 47rs are omitted.
This gave me a favorable sound I liked.
although the soundstage wasn't perfect, what I got was some real spooky inner detail, on strings, and depth of location of instruments. Apparent speed of the cones was equally good.
The 4-5W can present some limitations of dynamics, but I was really impressed by the tone of the amp, and it's precision. The sweet top-mids and highs are very impressive on the R100.
I ran this on a lowther in an open baffle, When I can get around to it, I want to see how it does on a smaller 4" full range speaker in a simple bass reflex enclosure. This will give me some idea of the low end on this beast.
Keep in mind, these are my impressions, on my clone, other users may see something else.
Newbe F2 build
Hi,
I am new here and would like to build F2 (thanks tea-bag for JFETs). Would somebody be so kind as to summarize all main points of building F2 - e.g. components types/sources, initial debug/tuning, etc.? I am planning to buy boards from Peter Daniels, but it would be good to have some starting info in one place - it would benefit other people as well.
What is idle current of this amp? Is there a possibility of powering it with batteries (e.g. Lithium polymer - 24V/10-15Ah pack)?
Also, anybody tried using it with Audeze LCD-2 (50 ohm)? Do the load resistors need to be changed for this from 15 ohm to 50 ohm?
Thanks,
Vladimir
P.S. I have some basic electronics knowledge (i.e. soldering/assembling somebody's circuits, maybe some tweaking), but not an expert in amp design.
Hi,
I am new here and would like to build F2 (thanks tea-bag for JFETs). Would somebody be so kind as to summarize all main points of building F2 - e.g. components types/sources, initial debug/tuning, etc.? I am planning to buy boards from Peter Daniels, but it would be good to have some starting info in one place - it would benefit other people as well.
What is idle current of this amp? Is there a possibility of powering it with batteries (e.g. Lithium polymer - 24V/10-15Ah pack)?
Also, anybody tried using it with Audeze LCD-2 (50 ohm)? Do the load resistors need to be changed for this from 15 ohm to 50 ohm?
Thanks,
Vladimir
P.S. I have some basic electronics knowledge (i.e. soldering/assembling somebody's circuits, maybe some tweaking), but not an expert in amp design.
