Hi Merlin,
while I agree that a snubber is not required when using active rectification, there's still evidence by some enthusuasts with high resolution equipment and speakers, that snubbers with active rectification often yield an audible (not dramatic!) positive effect on the sound stage imaging, spaciousness and localisation "illusion".
Given that snubbers literally require just a few cents investment, they are not a waste in my opinion, but an optimisation, avoiding unwanted spurious effects...
Regards,
Winfried
while I agree that a snubber is not required when using active rectification, there's still evidence by some enthusuasts with high resolution equipment and speakers, that snubbers with active rectification often yield an audible (not dramatic!) positive effect on the sound stage imaging, spaciousness and localisation "illusion".
Given that snubbers literally require just a few cents investment, they are not a waste in my opinion, but an optimisation, avoiding unwanted spurious effects...
Regards,
Winfried
Hi Winfried,
There is something not good with active rectification & snubers, Tibi pointed not to use snuber due to mosfet capacitance, others pointed for HV to change the standard capacitors used in Quasimodo (thanks Mark Johnson), I'm not sure what's happen but using Tibi HV active rectification & standard capacitors values 10nF & 150nF to dampen the PT ringing with the scope I needed 9k1 (value too high) so it's possible using snuber we do some kind of filter that makes the sense of high resolution but only is a supposition. I'm waiting Mark Johnsson answer to clear all my doubts.
Bst
Felipe
There is something not good with active rectification & snubers, Tibi pointed not to use snuber due to mosfet capacitance, others pointed for HV to change the standard capacitors used in Quasimodo (thanks Mark Johnson), I'm not sure what's happen but using Tibi HV active rectification & standard capacitors values 10nF & 150nF to dampen the PT ringing with the scope I needed 9k1 (value too high) so it's possible using snuber we do some kind of filter that makes the sense of high resolution but only is a supposition. I'm waiting Mark Johnsson answer to clear all my doubts.
Bst
Felipe
Hi Merlin, it great that you have benefitted from using the active bridges and it's interesting that there seems to be some interference between the transformer's snubbers - Tibi uses very high quality devices and he's probably right about this too.
What you can do if you feel like a search "back in time" is to find the thread about using a single high quality capacitor to 'tune' the secondary winding, a different thing altogether than 'snubbing the ringing'
If you add the details of your transformer(s), I'll have a look at the results I kept from the old "Prometheus" site days and F5 amp power supply experiments to give you a starting point - it could be interesting ....
We're still on what's called "Stage 4" lockdown here but the spring season change should make some improvements.
What you can do if you feel like a search "back in time" is to find the thread about using a single high quality capacitor to 'tune' the secondary winding, a different thing altogether than 'snubbing the ringing'
If you add the details of your transformer(s), I'll have a look at the results I kept from the old "Prometheus" site days and F5 amp power supply experiments to give you a starting point - it could be interesting ....
We're still on what's called "Stage 4" lockdown here but the spring season change should make some improvements.
Okay, with the single winding of 150v x 0.2A = 30va (approx.) so at a guess, you're looking at something about 3.75nF across the sec winding, but if the transformer is a toroid, the value will be a bit higher.
This is a 'try-it-and-see' exercise so start with around 3nF and increase in steps of 0.1nF using plug/socket (and measure each of the caps) - the higher voltage will restrict the range of propylene caps and it is a very tedious exercise - when you get close, the sound of your amp/preamp/etc will change it's tonal balance quite noticeably.
Nobody was quite sure what is the exactly mechanism at play here (many theories, few certainties) but this surfaced about 10 years ago - it originally appeared many years ago in the "Radiotron Designer Handbook" and according to the best guesses back then, is to alter or create L/C resonances of the secondary windings but not sure if the behavior of the LT bridge will change this - a challenge, if you will …
I remember trying this out on the secondary windings of the 2 x 18v 300VA transformer of my F5 amp at that time and could alter the sound from the typical slightly aggressive sound to a mild laid back much heavier bass sound of a typical Marantz amp - a really amazing transformation.
Something to distract you while the restrictions of this Covid bug are in force.
This is a 'try-it-and-see' exercise so start with around 3nF and increase in steps of 0.1nF using plug/socket (and measure each of the caps) - the higher voltage will restrict the range of propylene caps and it is a very tedious exercise - when you get close, the sound of your amp/preamp/etc will change it's tonal balance quite noticeably.
Nobody was quite sure what is the exactly mechanism at play here (many theories, few certainties) but this surfaced about 10 years ago - it originally appeared many years ago in the "Radiotron Designer Handbook" and according to the best guesses back then, is to alter or create L/C resonances of the secondary windings but not sure if the behavior of the LT bridge will change this - a challenge, if you will …
I remember trying this out on the secondary windings of the 2 x 18v 300VA transformer of my F5 amp at that time and could alter the sound from the typical slightly aggressive sound to a mild laid back much heavier bass sound of a typical Marantz amp - a really amazing transformation.
Something to distract you while the restrictions of this Covid bug are in force.
I don't think anyone ever got close to that - I think a professor in Italy at one of the Universities did quite a lot of work on the hypothesis but this didn't evolve into a clearly defined theory. The ham and amateur radio guys of my youth used to do these sorts of things quite a lot but the knowledge has got lost in time, I think.
The article appeared as "Copyright 2001 Promitheus DIY" and the link I have from back then (2012)says 'http://mitglied.multimania.de/Promitheus/tuning a power supply transformer" - I've never been able to track it down since and I don't know if the name 'Promitheus Audio' is the same person.
Oh, should mention, the 150 odd volts means you need higher voltage caps like Wima propylene, etc - the Rifa styrenes that I used don't reach those voltage.
The article appeared as "Copyright 2001 Promitheus DIY" and the link I have from back then (2012)says 'http://mitglied.multimania.de/Promitheus/tuning a power supply transformer" - I've never been able to track it down since and I don't know if the name 'Promitheus Audio' is the same person.
Oh, should mention, the 150 odd volts means you need higher voltage caps like Wima propylene, etc - the Rifa styrenes that I used don't reach those voltage.
That's what I'd do - getting a selection of caps about this size might be a problem but I used those screw down sockets and added multiples of caps in parallel - messy and boring but worked quite well.
I think the Nicholas of Promitheus Audio (De) is the originator of the article - he seems to be big in transformers, TVAs, etc and a couple of write-ups mention the transformer tuning technique.
I think the Nicholas of Promitheus Audio (De) is the originator of the article - he seems to be big in transformers, TVAs, etc and a couple of write-ups mention the transformer tuning technique.
Good luck with trying just the caps on the secondaries - you might need to go well outside my suggested starting size but be methodical about it and write the different attempt down - I didn't at the start and kept on repeating myself.
About the use of snubbers with the Active bridges, probably no answer as the behavior of the new rectifier method doesn't excite the same 'noise' in the transformer windings so there's really not much for the capacitor/resistor networks to do - ie. no need for snubbers.
While you're playing around with this area, if you haven't tried adding a resistor between the active bridge and the first cap, insert one in series and see if it changes anything - it may do nothing as the new rectifiers produce a much smoother power supply ripple that some people don't actually like in their systems.
About the use of snubbers with the Active bridges, probably no answer as the behavior of the new rectifier method doesn't excite the same 'noise' in the transformer windings so there's really not much for the capacitor/resistor networks to do - ie. no need for snubbers.
While you're playing around with this area, if you haven't tried adding a resistor between the active bridge and the first cap, insert one in series and see if it changes anything - it may do nothing as the new rectifiers produce a much smoother power supply ripple that some people don't actually like in their systems.
Hello Folks ! good news! 
international shipping has finally begun, so I am going to go ahead with this GB
LT4320 RECTIFIER AND LT4320 CRC PSU GROUP BUY - Google Sheets
I plan to begin sending paypal invoices 10 a day. Once payment is made, shipping will happen at the earliest opportunity (due to plenty of rush at poastal office).
All updates will be available in the google sheet above.
I know its quite delayed, but better late than never
.
If someone would like to withdraw, please let me know (or forever hold your peace...).
regards
prasi
international shipping has finally begun, so I am going to go ahead with this GB
LT4320 RECTIFIER AND LT4320 CRC PSU GROUP BUY - Google Sheets
I plan to begin sending paypal invoices 10 a day. Once payment is made, shipping will happen at the earliest opportunity (due to plenty of rush at poastal office).
All updates will be available in the google sheet above.
I know its quite delayed, but better late than never
.If someone would like to withdraw, please let me know (or forever hold your peace...
).regards
prasi
