I can't see any difference between that one and most recently posted schmtc, in opening post of Babelfish M25, SissySIT - general building tips and tricks
regarding that ........ all I can add (as maybe missing info) is that I'm using specifically PC817C opto
Thank you ZenMod. I used 10R on both rails and monitored Iq on positive rail. Held up well with low offset for several minutes. Only the 5W resistors got quite hit.
I bypassed the resistors and had the full voltage of +-24.46 Volts, Iq was 1.4A, monitored on Ammeter, when the Mosfet burned.
You may have made a mistake on the PCB. Easier to use tested one from ZM.
if it was steady at 1A4 ....... something else is wrong
silly mistakes are possible even when you have zillion years of experience - maybe you had something critical in heat transfer and isolation arrangement
as I wrote - I had problems with second channel during T-Bed assembly ; first channel was sorted completely , every part position checked and finalized , even THD measurements completed ....... then , with second channel I couldn't bias it
I already had thoughts that pcb is having some mistake ( L and R aren't the same , logically) , when I realised that I mounted pair of IRFP240 , instead of IRFP240+IRFP9240
Silly ZM
Referring to schematic in post #118, R15 is 220E, but in the build guide it is 270E.
I had 220E on hand and used it. Would that make a difference? Asking, to be sure.
Quite sure that PCB is correct. I was not patient enough to allow for thermal equilibrium; set Iq too quickly. Also need to recheck thermal arrangements. Will report back. Thank you.
I had 220E on hand and used it. Would that make a difference? Asking, to be sure.
Quite sure that PCB is correct. I was not patient enough to allow for thermal equilibrium; set Iq too quickly. Also need to recheck thermal arrangements. Will report back. Thank you.
I removed the Output Mosfets and powered up the board. With P1 setting of 0E, the voltage at the junction of R15, R16, R17 measures 1.246 Volts. I turned up P1 slowly and the junction voltage increases smoothly. I measured upto 1.275 Volts and stopped. Even without the Output Mosfets, offset can be set to zero.
So I am sure that I wasn't patient with Iq setting. Thermal Transfer issues didn't seem to exist, which I checked before dismantling the output stage from the heat sink.
What should the minimum voltage be at the junction of R15, 16, 17?
Thank you.
So I am sure that I wasn't patient with Iq setting. Thermal Transfer issues didn't seem to exist, which I checked before dismantling the output stage from the heat sink.
What should the minimum voltage be at the junction of R15, 16, 17?
Thank you.
A quick update. Yes, as ZenMod had suspected, mine was indeed a thermal arrangement issue. Metal surface of the Mosfet was not in proper contact with the heatsink.
Fixed fresh pair of Mosfets. Now all is well.
Minimum Iq is 1.05Amps. It won't get any lower. It depends on Vgs of the devices. Offset can be nulled very smoothly.
But the build up to set Iq, takes a little more than a minute and during this time, offset begins from above 10 volts before settling down to zero. One reason for this is also because the regulated supply I am using, ramps up slowly, after power on.
Don't those of you who have built the M25 experience a turn-off, turn-off thump. Delay, Speaker protection?
Fixed fresh pair of Mosfets. Now all is well.
Minimum Iq is 1.05Amps. It won't get any lower. It depends on Vgs of the devices. Offset can be nulled very smoothly.
But the build up to set Iq, takes a little more than a minute and during this time, offset begins from above 10 volts before settling down to zero. One reason for this is also because the regulated supply I am using, ramps up slowly, after power on.
Don't those of you who have built the M25 experience a turn-off, turn-off thump. Delay, Speaker protection?
it's smooth as baby's butt and harmless as ice cream , once connected to proper PSU
one need to know what is gained and what are complications , when using particular lab supply
I personally prefer donut with rectifier and caps via Variac , when dealing with output stages , leaving lab supply for sissier loads
one need to know what is gained and what are complications , when using particular lab supply
I personally prefer donut with rectifier and caps via Variac , when dealing with output stages , leaving lab supply for sissier loads
Arrggh! I cant decide whether to do Sissy or M25 first. I have the SITS, Kit and my M2 in hand. I thought I had decided to do Sissy first, but now am waffeling. A Question or two:
1. If I convert my M2, will I miss standard version when driving simple easy speaker loads? It is one of my favorite amps, I have spare complete boards, built with edcors and toshiba Jfets all mounted. This is how much I like this amp!spare boards ready to go, or to build extra amp...like I need that!
2. I intend to buy another of zenmod's Sissy/M25 kits for other amp version, but I also think I should get another pair of SIT of same measurement as I already have, either as spares, or somehow I feel other shoe hasnt dropped for some upcoming PaPa kit in store....
3. SIT-3 seems to use Semisouth devices, (tailored to Papa's specs) and I have a set or "regular" Semisouth with Vfet kit....can these outputs be some how used for a different SIT-3 clone in future? Or should I shut up and use them for Vfet project?
Thanks all,
Russellc
1. If I convert my M2, will I miss standard version when driving simple easy speaker loads? It is one of my favorite amps, I have spare complete boards, built with edcors and toshiba Jfets all mounted. This is how much I like this amp!spare boards ready to go, or to build extra amp...like I need that!
2. I intend to buy another of zenmod's Sissy/M25 kits for other amp version, but I also think I should get another pair of SIT of same measurement as I already have, either as spares, or somehow I feel other shoe hasnt dropped for some upcoming PaPa kit in store....
3. SIT-3 seems to use Semisouth devices, (tailored to Papa's specs) and I have a set or "regular" Semisouth with Vfet kit....can these outputs be some how used for a different SIT-3 clone in future? Or should I shut up and use them for Vfet project?
Thanks all,
Russellc
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Also, I have heard several drone on at SissySit's wonderful spooky character, could someone who has finished M25 talk about there experience sonically with it? I feel since most ( but not all ) of my speaks are an easy load, so am thinking SissySit may provide more immediate "new amp" gratification? Eventually will build both, but which first is freaking me out.
I need a good slapp'n or advice...maybe both,
Russellc
I need a good slapp'n or advice...maybe both,
Russellc
1. simple easy .... difference there will be ..... but mostly due to superduper Mighty ZM buffer , not OS itself (which would have nothing to fret about) ...... but I can't say will you like it more
2. always warm around heart when having some stash in drawer
3.care to clarify that a little , can't follow you there ...... dunno of any VFet kit with Semisouths in ?
easy load ......... well
with my Tanns and RCA , B. M25 is doing most of the work as space heater , while guys listening Dynaudio Contour 1.8 are simply spooked with sound
if you need another M2 , slightly better (than original one) for your needs - then build B. M25;
if you don't need another M2 at all , do not
in that case - it's clearer ...... you have enhanced mode parts (SJEP) , while for any iteration of SIT-3 you need depletion mode part (which would be SJDP)
what final result would be , dunno ....... but - that's easy to try in SissySIT circuit , if one is having depletion mode Semisouths ...... which I don't have