Instead of IRFP150 would be option to use some other N channel MOSFET-s like Toshiba 2SK1530, FQA46N15, ECW20N20?
What are the sound sonic differences between F8 2SJ74 or using F8b 2SK170 version?
Is it also negative 2nd harmonic phase tuning or?
What are the sound sonic differences between F8 2SJ74 or using F8b 2SK170 version?
Is it also negative 2nd harmonic phase tuning or?
depending of xconductance difference to IRFP150, slight difference in THD, Spectra will stay the same; but nothing to write home about ....... in that range numbers are showing but no more than academic difference
much lower than it looks staring at goat (schm); in moments I have impression of slightly greater detailing but in next moment I know that such level of difference can't be judged by hearing memory
in short - that's same amp
certainly; nothing much is really changed, penthodes everywhere ........ and overall concept unchanged
It hurts a bit to pull out the M2X boards but I have no room for more large chassis.
M2X was (is) a nice amp. Here configured with Cedarburg.
Hope F8 likes its new "home".
It will take a while as I also will upgrade the chassis to use hex-screw rails insted of the old "self-cutting" screws. Some does not "bite" into the rail anymore.
The M2X chassis are mirrored because the boards was made that way. It should be ok with F8 boards as they so compact so wiring should be quite easy. Will probably mount both boards so input terminals are facing downwards in both chassis.
As you can see I like to use rail fuses. I tried to analyze what will happen if one rail-fuse is "burned". I don't think I will get + or - rail voltage to the speakers but bias will drop immediately to zero so no current can go to speakers (and amp will not be damaged either)?
M2X was (is) a nice amp. Here configured with Cedarburg.
Hope F8 likes its new "home".
It will take a while as I also will upgrade the chassis to use hex-screw rails insted of the old "self-cutting" screws. Some does not "bite" into the rail anymore.
The M2X chassis are mirrored because the boards was made that way. It should be ok with F8 boards as they so compact so wiring should be quite easy. Will probably mount both boards so input terminals are facing downwards in both chassis.
As you can see I like to use rail fuses. I tried to analyze what will happen if one rail-fuse is "burned". I don't think I will get + or - rail voltage to the speakers but bias will drop immediately to zero so no current can go to speakers (and amp will not be damaged either)?
Attachments
frankly, I didn't tried killing one rail
now, as you have inline fuses, connect dummy load, pull one fuse and observe what's happening with DVM across load
I believe - worst case is second fuse going south, but then you'll know
now, as you have inline fuses, connect dummy load, pull one fuse and observe what's happening with DVM across load
I believe - worst case is second fuse going south, but then you'll know
Think I have found the right spot to mount the F8 in the 5U chassis. Then signal input will be facing up (picture).
4AF fuses are sitting there in the moment. I don't use softstart for the 400VA trafo so primary fuse is dimensionen to be able to take the inrush current.
To not use rail fuses will be an easy change.
A dummy load between + and - rail. For 46V DC or so it would be 25-30 ohm or so. I wonder if I DMM reacts so fast so I can see what happens if I pull one fuse......maybe......
To check if I get DC out at speaker output with only one rail would it harm the amp if I power up the F8 with only one rail (+ or - rail)?
4AF fuses are sitting there in the moment. I don't use softstart for the 400VA trafo so primary fuse is dimensionen to be able to take the inrush current.
To not use rail fuses will be an easy change.
A dummy load between + and - rail. For 46V DC or so it would be 25-30 ohm or so. I wonder if I DMM reacts so fast so I can see what happens if I pull one fuse......maybe......
To check if I get DC out at speaker output with only one rail would it harm the amp if I power up the F8 with only one rail (+ or - rail)?
Attachments
dummy load (8R) at output of amp
I understood you - that you want to test output DC behavior in case of one rail fuse gone south
it could help if you have "max/min" function on DVM
400VA Donut - if you use bigger fuse than T2A5 (400VA/230V=1A74), you must use soft start
Ok, then I understand. When amp is finished and mounted then dummy load instead of speakers.
You don't think amp will break doing such exercise.....
I have DMM with peak memory function.
I will check primary fuse......my guess is that it is larger than T2A5.
During M2X development I had some mechanical hum from trafo now and then. It suddenly came and then disappeared.
I observed slight variation in rail when it happened. Even with mains DC-traps and regulated 230 VAC. I removed everything that could cause some voltage drop (soft start NTC was removed). I traced the "error" down to be the diodes / 30A bridges. Then I changed to diodes with very low forward drop and problem disappeared and amp totally silent. So that is the history about the "missing" softstart NTC 🙂
My own theory why trafo started to hum is that if some bridge didoes varies a bit in forward drop then this asymmetry can cause DC in secondary.
The variation in rails when it happened was some-+0.2V DC or so. A regulated 230 VAC was necessary to find that "error".
You don't think amp will break doing such exercise.....
I have DMM with peak memory function.
I will check primary fuse......my guess is that it is larger than T2A5.
During M2X development I had some mechanical hum from trafo now and then. It suddenly came and then disappeared.
I observed slight variation in rail when it happened. Even with mains DC-traps and regulated 230 VAC. I removed everything that could cause some voltage drop (soft start NTC was removed). I traced the "error" down to be the diodes / 30A bridges. Then I changed to diodes with very low forward drop and problem disappeared and amp totally silent. So that is the history about the "missing" softstart NTC 🙂
My own theory why trafo started to hum is that if some bridge didoes varies a bit in forward drop then this asymmetry can cause DC in secondary.
The variation in rails when it happened was some-+0.2V DC or so. A regulated 230 VAC was necessary to find that "error".
if you use separate secondaries and bridge per secondary, with GND established after the bridges, then there is no possibility for DC on secondaries
that's especially important with amps intrinsically having unequal rails loading, as is SissySIT, as extreme case example
practically - any amp having non-symmetric current distribution between rails is presenting problem for more common Center-tap PSU arrangement
think Aleph, any DEF
even F8 is in that category
that's especially important with amps intrinsically having unequal rails loading, as is SissySIT, as extreme case example
practically - any amp having non-symmetric current distribution between rails is presenting problem for more common Center-tap PSU arrangement
think Aleph, any DEF
even F8 is in that category
I have separate secondary's and bridge (4 x diodes) pr secondary and GND after the bridges.
I just got everything solved with the low forward voltage drop diodes. Then I got a higher rail voltage of course.
Then I have no good explanation why the special diodes solved the problem.
Will see if I can get 2.5A TT fuses or I can re-establish NTC softstart.
I just got everything solved with the low forward voltage drop diodes. Then I got a higher rail voltage of course.
Then I have no good explanation why the special diodes solved the problem.
Will see if I can get 2.5A TT fuses or I can re-establish NTC softstart.
as I said, with separate secondaries and bridge per secondary, there is no way of getting DC practically "reflected" back to secondaries
no use of obsessing what was exact reason with old bridges; maybe one of the bridges was malfunctional, maybe you have/had unfortunate combination of all factors leading to ringing ( snubbers could help), but you solved it
now, difference in resulting voltage between classic diodes and low drop ones is practically negligible/irrelevant; with 18Vac secondaries output voltage is 24Vdc nominal ( taken from unloaded PSU measurements) and who cares are you at 22V2dc or 23V2dc ........... I would be puzzled if I measure 26V6dc from 18Vac secondaries, but anything less is fine with me ......... because I'm cheapskate, using 25Vdc declared caps
no use of obsessing what was exact reason with old bridges; maybe one of the bridges was malfunctional, maybe you have/had unfortunate combination of all factors leading to ringing ( snubbers could help), but you solved it
now, difference in resulting voltage between classic diodes and low drop ones is practically negligible/irrelevant; with 18Vac secondaries output voltage is 24Vdc nominal ( taken from unloaded PSU measurements) and who cares are you at 22V2dc or 23V2dc ........... I would be puzzled if I measure 26V6dc from 18Vac secondaries, but anything less is fine with me ......... because I'm cheapskate, using 25Vdc declared caps
I have ordered 5x20mm 2.5A TT fuses. 4A T (double fused) installed in the moment. I can't remember how many different values I have tried to find the smalles value not breaking during inrush. I think there is a good chance that 2.5A TT can work.
I have two other donut based PSU's that just plugged into to wall (unloaded) starts humming randomly. It is like random "waves" coming in. That I hate about these "donut" trafos. Sometimes a DC-trap helps but not always. I am sure donut is ok with no loose windings etc.
Iron pre donuts are silent which is nice. Smaller is better here........
I have two other donut based PSU's that just plugged into to wall (unloaded) starts humming randomly. It is like random "waves" coming in. That I hate about these "donut" trafos. Sometimes a DC-trap helps but not always. I am sure donut is ok with no loose windings etc.
Iron pre donuts are silent which is nice. Smaller is better here........
excluding DC on mains, proper Donut is buzz free, simple as that
if there is buzz, Donut isn't proper, whatever name is printed on
if there is buzz, Donut isn't proper, whatever name is printed on
Had to come back, been listening to this amp for the last 3 days. Sounds absolutely incredible, there is something about the imaging of this amp. I was never a fan of my previous backup speakers(B&W 602) and I cant believe how incredible they sound with the miro ad1862 dac, iron pre and babelfish f8. I could honestly be happy(is that a thing for audiophiles) with this setup. Now I just have to rebuild my previous favorite XA252, I love this amp, but there is just something about it sending 40VDC to speakers that bothers me, LOL.
Thank you Zen Mod for making this version, been waiting for a F8 something for awhile.
Thank you Zen Mod for making this version, been waiting for a F8 something for awhile.
A quick question for you ZM. What is the recommended pot settings for initial start up?
For the offset pot TP1 (500R for Semisouths), I assume mid position for the wiper would be a good starting point.
For the bias Iq pot TP2 (200R) - where should the wiper be for the initial start up?
Apologies if you have answered this, but I could not find details in the thread.
Have resistors loaded so far.
For the offset pot TP1 (500R for Semisouths), I assume mid position for the wiper would be a good starting point.
For the bias Iq pot TP2 (200R) - where should the wiper be for the initial start up?
Apologies if you have answered this, but I could not find details in the thread.
Have resistors loaded so far.
mid is OK for both trimpots
I presume you're familiar with usual two DVM setting procedure?
chill up man, it's ZM here...
I presume you're familiar with usual two DVM setting procedure?
chill up man, it's ZM here...
Thanks for the reply ZM, yep have 6 Fluke DMM's - so I can monitor everything. Close as possible to OVDC across the output and 1.8 Adc through R17//R19 (0R6 total) = 1.08VDC. Slowly adjust to let the channel warm up, then final adjustment after a good hour or so.
yeah, that in short, numbers checking
Iq is dead stable from start, DC Offset benign slide in temperature domain
Iq is dead stable from start, DC Offset benign slide in temperature domain