By the way guys, what should be the optimal choke value for 24V 2.5A MOFO? 50mH? Or higher is better? I'll try another inductor and see. What's the benefits of going higher inductance? Lower distortion?
Thanks guys!
Thanks guys!
> 24V 2.5A MOFO? 50mH?
50mH will support 8 Ohms down to 26Hz. It is plenty big for any system of this power level.
The choke is not a "low pass", it is not choking your highs.
It has capacitance but at 8 Ohms even 1uFd is barely tolerable and even a physically huge choke won't be 2,000p[/u]Fd, 500 times higher. (MOSFET Gate capacitance is more likely than choke capacitance.)
Source impedance driving the Gate should be under a few K Ohms. 4K makes a 20KHz low-pass. Most solid-state preamps are much-much lower than this, though few have the Volts to drive a 24V Mofo to full output. A low-current 6B4 may be a few K Ohms.
50mH will support 8 Ohms down to 26Hz. It is plenty big for any system of this power level.
The choke is not a "low pass", it is not choking your highs.
It has capacitance but at 8 Ohms even 1uFd is barely tolerable and even a physically huge choke won't be 2,000p[/u]Fd, 500 times higher. (MOSFET Gate capacitance is more likely than choke capacitance.)
Source impedance driving the Gate should be under a few K Ohms. 4K makes a 20KHz low-pass. Most solid-state preamps are much-much lower than this, though few have the Volts to drive a 24V Mofo to full output. A low-current 6B4 may be a few K Ohms.
PRR if this was inductor loaded common source amp your calculations would apply but I believe when used as a source follower things may be drastically different. Just look back at the article and you see the amp is only down about 1/3 db at 20 hz.
Try to use another type of blocking capacitor to see if that influences the sound. I like the Philips axial type, to me that was the best on the SEWA. Greetings
BTW i can provide a full test when i'm in a position to secure a clean part of the work station.
I hope soon. 🙄
I hope soon. 🙄
Hi guys,
I did some test yesterday. Surprise surprise...
I tested it from from 10Hz till 200kHz sine wave and sees NO drop in output - no attenuation even at near 200kHz. 1kHz square wave looked perfect from 2Vpp to 20Vpp.
Still, I did some further listening test and still preferred the 6B4G tube SET - it has more transparency, more forward image, and more air on the high frequencies.
Now I gotta see if the output coupling caps (Nichicon KG Super Through) are to be replaced with something brighter/airier sounding. Any recommendations for e-caps with better highs? Gaborbela mentioned SEWA - can't find it here. I'll try a smaller cap too, perhaps 10,000UF is too much.
The other option i see is to just eliminate the output-coupling altogether - by custom making a 1:1, 2.5A air-gap output transformer. About U$490/pc I checked. Not too bad and I get to eliminate the caps. Only down side is the waiting time. May be long.
Will post some pics when I get them.
Rgds.
I did some test yesterday. Surprise surprise...
I tested it from from 10Hz till 200kHz sine wave and sees NO drop in output - no attenuation even at near 200kHz. 1kHz square wave looked perfect from 2Vpp to 20Vpp.
Still, I did some further listening test and still preferred the 6B4G tube SET - it has more transparency, more forward image, and more air on the high frequencies.
Now I gotta see if the output coupling caps (Nichicon KG Super Through) are to be replaced with something brighter/airier sounding. Any recommendations for e-caps with better highs? Gaborbela mentioned SEWA - can't find it here. I'll try a smaller cap too, perhaps 10,000UF is too much.
The other option i see is to just eliminate the output-coupling altogether - by custom making a 1:1, 2.5A air-gap output transformer. About U$490/pc I checked. Not too bad and I get to eliminate the caps. Only down side is the waiting time. May be long.
Will post some pics when I get them.
Rgds.
Maybe what you perceive as more “airiness” or “transparency” is something related to inherently higher harmonic distortion in 2nd and 3rd harmonic is 6B4G SET vs what MOFO has? MOFO is zero feedback amp so should have very good imaging as spatial detail.
You should try other types of caps on the output.
To me, this type was far the best with SEWA, I tested several audiophile caps. Need a week or so to burn in and please pull off the plastic from the cap.
Not much change in my health, at least I attend a therapy group (7 weeks more) where they try their usual treatment. Until now I just took medication for sleep, not to feel dizzy all day, faint or avoid blackout & collapse (maintain the symptoms) In case if I could not sleep for a couple of days I start blackouts, etc. 😱
To me, this type was far the best with SEWA, I tested several audiophile caps. Need a week or so to burn in and please pull off the plastic from the cap.
Not much change in my health, at least I attend a therapy group (7 weeks more) where they try their usual treatment. Until now I just took medication for sleep, not to feel dizzy all day, faint or avoid blackout & collapse (maintain the symptoms) In case if I could not sleep for a couple of days I start blackouts, etc. 😱
Attachments
not freq. linearity issue , just fact that you prefer even more 2nd harmonic in THD spectra, than MoFo is having
try listening with switched polarity of speakers , maybe you'll like it more
try listening with switched polarity of speakers , maybe you'll like it more
you can try 1000uf or more DC link cap , big expensive cap at first but the sound worth it. in theory you will have -3db at 20hz but in fact the Bass seems mre powerfull and fast 🙂
You could also try building Korg Nutube pre and use that with MoFo. It works better than expected with MoFo and will give more 2nd harmonic.
MoFo vs VTL ST-80
That's very interesting. Going to try flipping at speaker.
The VTL ST-80 (push-pull) has the ability to extend or reveal the harmonics in say a piano chord. There's better sustain and the harmonics are more apparent. The same goes for reverb. Changes the performance space.
Another nice thing VTL does is magnify the size of instruments and vocals. Depth is nice too, although the MoFo can do depth well.
Aside from these traits, the MoFo and VTL are very much the same, although they are important differences in my opinion.
That's very interesting. Going to try flipping at speaker.
The VTL ST-80 (push-pull) has the ability to extend or reveal the harmonics in say a piano chord. There's better sustain and the harmonics are more apparent. The same goes for reverb. Changes the performance space.
Another nice thing VTL does is magnify the size of instruments and vocals. Depth is nice too, although the MoFo can do depth well.
Aside from these traits, the MoFo and VTL are very much the same, although they are important differences in my opinion.
Psycho-acoustics, now that's a different field altogether. Lol...
Take care Garbobela! Will try BC caps next.
Take care Garbobela! Will try BC caps next.
"Sold out"??
Dang. I was really looking forward to my first attempt at an amplifier.
Apparently, I'm not so smart, and already ordered components, not thinking that I should have checked for the BOARD FIRST.
#facepalm
I guess I can spend the next week reading the other 208 pages of comments.
Many thanks to Mr. Rothacher and all those who chime in here to help.
Kind regards,
Drew
Dang. I was really looking forward to my first attempt at an amplifier.
Apparently, I'm not so smart, and already ordered components, not thinking that I should have checked for the BOARD FIRST.
#facepalm
I guess I can spend the next week reading the other 208 pages of comments.
Many thanks to Mr. Rothacher and all those who chime in here to help.
Kind regards,
Drew
because humor is still big thing here in Papaland
when it stops being that, bye bye ........ who needs serious amps ?
when it stops being that, bye bye ........ who needs serious amps ?