I have a couple of spare ALF pairs if you decide to go for these rather than the Exicon.
I have built my version of the F7 as well.I can say it is the best sounding amp of the F6,M2 and AlephJ I have also built.How much that has to do with speaker/amp pairing I do not know. My speakers are Energy 22 Reference Connossieur's---86db,2 way with 7" woofer,3/4" dome tweeter. The sound is airy,vocals are crystal clear,soundstage is very wide.Bass is deep and tight.I biased mine at 0.95 amps.I had higher Idss jfets (13ma and 11ma) (j74&k170) respectively.My jfet source pot is set at 14 ohms K170 and 6 ohms J74. I came up with that from my spice sim.Don't know what the actual harmonic ratio is but I'm happy with the sound.The cool thing is you can pick from what you think is "The" F7 and try different combinations.Nelson has given us enough info to at least make something that works and sounds fantastic.Pretty darn good for not giving up the official schematic I'd say. Thank you Mr.Pass.
Oreo382,
I'll be attempting a "smoke test" soon of your F7 sim.. Power supply is wired up. Need to test it first, then latest circuit mods/adjustments.
I'll name it the EFF SEVEN!
Vince
Vince,
Hope all goes well. Hope the "smoke" stays where its supposed to.
Hey, I thought this was a family show?
Ah, WTF!
(Please note: I'm not thumbing my nose at the mighty F7. Far from it. If it's as good as oreo says it is, that's some accomplishment considering the company it keeps. I have a loaner diy M2. We shall see! All good stuff!
The latest mods I mentioned make the big difference,although with your jfet Idss's you'll have to play around with that part I think.
It's been a while since I made this amp (I had just a tiny ZMs help, he dropped a very few breadcrumbs), and have as same impressions as oreo382. One of the finest amplifiers I have ever made.
Now, do not have spectrum analyser, will try something with 2 PCs and RMAA or ARTA when I catch time, but how the things gone for me in setting this amp:
Initially I set pot in middle of jfets to 50%. Set Iq 1A3 with simultanous trimming first two pots (F5 setting like). Fired up amp and got this,,,, so so strange soung, it was like you placed speakers in a barrel 3m deep and then its just mummling. Yeah you hear the sound, but everything got sooo mummly,,,
So I get to another idea, I reverted 2 pots in gates of laterals to 50% their values, and then trimmed jfet pot to get 0V at output. Position was, somewhere as oreo said, 14/6. Then I set bias to 1A3 via 2 remaining pots, and voila! As said, one of the finest amplifiers I have ever made.
Now, do not know even how the output order of harmonics look like, neither did I get the schematic right, nor component values right, just I know this what I built sounds pretty damn good.
Anyway, I still think mr. Pass reads what we are doing here and laughs at how creative, or non-creative our diy minds are
Thanks mr. Pass for your commitment to diy community. Waiting for official schematic some day to see how far / close we were
Now, do not have spectrum analyser, will try something with 2 PCs and RMAA or ARTA when I catch time, but how the things gone for me in setting this amp:
Initially I set pot in middle of jfets to 50%. Set Iq 1A3 with simultanous trimming first two pots (F5 setting like). Fired up amp and got this,,,, so so strange soung, it was like you placed speakers in a barrel 3m deep and then its just mummling. Yeah you hear the sound, but everything got sooo mummly,,,
So I get to another idea, I reverted 2 pots in gates of laterals to 50% their values, and then trimmed jfet pot to get 0V at output. Position was, somewhere as oreo said, 14/6. Then I set bias to 1A3 via 2 remaining pots, and voila! As said, one of the finest amplifiers I have ever made.
Now, do not know even how the output order of harmonics look like, neither did I get the schematic right, nor component values right, just I know this what I built sounds pretty damn good.
Anyway, I still think mr. Pass reads what we are doing here and laughs at how creative, or non-creative our diy minds are
Thanks mr. Pass for your commitment to diy community. Waiting for official schematic some day to see how far / close we were
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It's been a while since I made this amp (I had just a tiny ZMs help, he dropped a very few breadcrumbs), and have as same impressions as oreo382. One of the finest amplifiers I have ever made.
Now, do not have spectrum analyser, will try something with 2 PCs and RMAA or ARTA when I catch time, but how the things gone for me in setting this amp:
Initially I set pot in middle of jfets to 50%. Set Iq 1A3 with simultanous trimming first two pots (F5 setting like). Fired up amp and got this,,,, so so strange soung, it was like you placed speakers in a barrel 3m deep and then its just mummling. Yeah you hear the sound, but everything got sooo mummly,,,
So I get to another idea, I reverted 2 pots in gates of laterals to 50% their values, and then trimmed jfet pot to get 0V at output. Position was, somewhere as oreo said, 14/6. Then I set bias to 1A3 via 2 remaining pots, and voila! As said, one of the finest amplifiers I have ever made.
Now, do not know even how the output order of harmonics look like, neither did I get the schematic right, nor component values right, just I know this what I built sounds pretty damn good.
Anyway, I still think mr. Pass reads what we are doing here and laughs at how creative, or non-creative our diy minds are
Thanks mr. Pass for your commitment to diy community. Waiting for official schematic some day to see how far / close we were
I measured my jfet pots with an ohmmeter(power off!) and set them to 14/6. Powered on and fiddled the 2 drain pots(per channel) to get 0.95A and 0V output offset. I had put a 0.1 ohm resistor in the +VE feed to each board so I could measure the bias current, mV(resistor)/0.1 ohm=bias current.I am glad I used 20 turn pots because the bias and offset adjustments are sensitive,lots of back and forth to get it right.Initially I had too low value for my input and PCF resistors which gave me about 600khz bandwidth.I raised these to get around 100khz.As well with the 600k bandwidth I had the bias at around 1.2 amps and found the sound compressed.After replacing the resistors,lowering the bias the sound opened up,very airy vocals and I found the vocals to be easily understood.Some amps I have listened to smear the vocals,not so with this one,that is very apparent immediately.
I see. I understand that there is no way that an exact F7 schematic could be obtained. But I was wondering about the guesswork F7.
Anyway, I will have to wait. But, since I want badly to build this amp, I would like to purchase the output MOSFETs for a start (I already have a number of K170 and J74 JFETs). I searched for the original ALFET lateral MOSFETs, just to find out that they are discontinued. So, my only choice is to get the Exicon replacements. Just to be sure, I see that the Exicon equivalents are the ECX10N20 and ECX10P20. Right?
Start with Nelson's writings, then study positive current feedback, and it will become fairly obvious how to build your own.
The Exicons are fine.
