Avondale Schottky Full Wave Bridge Module.....(Bargain)
- Thread starter dazz lee
- Start date
Richard Lines
pfm Member
Dan,
I'm not an EE so forgive any 'stupid' questions.
I can see that active rectifiers have some potential advantages but I understand that they have act as a 'snubber'?
As I understand it Avondale don't use any kind of snubbing in their systems.
Is 'snubbing' a good thing or a bad thing or is this one of those 'subjective' things?
Regards
Richard
I'm not an EE so forgive any 'stupid' questions.
I can see that active rectifiers have some potential advantages but I understand that they have act as a 'snubber'?
As I understand it Avondale don't use any kind of snubbing in their systems.
Is 'snubbing' a good thing or a bad thing or is this one of those 'subjective' things?
Regards
Richard
Snubbing means damping. If you need it then it's great and if you don't then don't bother.
Sometimes switching diodes or FETs can cause either the transformer, the large PSU caps, or large inductors to ring exactly like a bell.
There was a little active device designed over on Diyaudio called the Quasimodo that you can wire up to your traffo to make it ring, it then gives you the correct cap and resistor values to critically damp the ringing (to snub out the noise)
These recent SMT Shottky diodes might be so fast that ringing can't occur (at least at audio related freqs) - just my working hypothesis, although I could be talking nonsense.
A lot of the Active evangelists are maintaining that active rectifiers can't 'ring' / cause ringing.. There's a short gap between the FETs switching and that's where I suspect problems might occur.. Depends on how fast your FETs are and size of Traffo/ caps/ inductors
Sometimes switching diodes or FETs can cause either the transformer, the large PSU caps, or large inductors to ring exactly like a bell.
There was a little active device designed over on Diyaudio called the Quasimodo that you can wire up to your traffo to make it ring, it then gives you the correct cap and resistor values to critically damp the ringing (to snub out the noise)
These recent SMT Shottky diodes might be so fast that ringing can't occur (at least at audio related freqs) - just my working hypothesis, although I could be talking nonsense.
A lot of the Active evangelists are maintaining that active rectifiers can't 'ring' / cause ringing.. There's a short gap between the FETs switching and that's where I suspect problems might occur.. Depends on how fast your FETs are and size of Traffo/ caps/ inductors
davidsrsb
pfm Member
Diodes conduct for a short time after the voltage across them reverses. Ordinary diodes have to sweep out the minority carriers in the junction. This leads to a big current glitch, with harmonic content beyond audio and triggers LC ringing. Some premium silicon diodes have better turn off behaviour, quicker and smoother. Schottkys don't have these stored carriers, but do have significant capacitance, so a little pulse can still happen.
Richard Lines
pfm Member
I have a Quasimodo kit and a PCB here but was advised not to bother with them so I haven't built the kit - I ordered the kit having become aware of the thread on the diyaudio forum.
I noted the forward voltage on the SMD rectifiers was circa 0.265V.
Regards
Richard
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Looks about that for me
Richard Lines
pfm Member
Good evening all,
As a matter of interest the MBR20200CT I removed had a forward voltage of circa 0.325V - I really do need to get out more.....
Regards
Richard
As a matter of interest the MBR20200CT I removed had a forward voltage of circa 0.325V - I really do need to get out more.....
Regards
Richard
davidsrsb
pfm Member
That drop is the forward voltage. Reverse voltage is the voltage across the diode when it blocks conduction, 20V or whatever
Hardly seems worth making a change, the SMT ones are MBRD10200CT
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laverda
pfm Member
Fwd threshold voltage
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Richard Lines
pfm Member
Dan/ Graham,
I'm aware the both the SMD and PTH devices are both dual diode devices.
Dan - on paper the argument would be why bother indeed - I'm after confirming whether there might be a sonic difference
Regards
Richard
I'm aware the both the SMD and PTH devices are both dual diode devices.
Dan - on paper the argument would be why bother indeed - I'm after confirming whether there might be a sonic difference
Regards
Richard
laverda
pfm Member
Another thumbs up for the FWB2...I dropped a pair in my Phono Stage PSU the Pearl II by N PassDIY. The PSU is a duel mono stand alone unit using two 2 x EI 0.75VA = 24-0-24 AC through a pair of miniCAP6's ending up with 35-0-35 raw DC feeding the Pearl II on board regs.
I wasn't sure if the PSU upgrade would transfer through the Pearl II on-board caps & regs, I'm pleased to report it did.
I removed the existing diodes from the miniCAP6's and retro fitted the AA FWB2's through the miniCAP6 mounting hole (via some stand offs) with flying leads to the PCB.
The sonic results are quite substantial. Allowing low level detail retrieval to be presented, with more clarity and presents than I was listening to before. The highs are cleaner crisper, mids have more texture and there is more weight to the lower registers.
I wasn't sure if the PSU upgrade would transfer through the Pearl II on-board caps & regs, I'm pleased to report it did.
I removed the existing diodes from the miniCAP6's and retro fitted the AA FWB2's through the miniCAP6 mounting hole (via some stand offs) with flying leads to the PCB.
The sonic results are quite substantial. Allowing low level detail retrieval to be presented, with more clarity and presents than I was listening to before. The highs are cleaner crisper, mids have more texture and there is more weight to the lower registers.
Did this get solved?
Richard Lines
pfm Member
I believe so yes - it does seem that Graham (and his customers) believe so also.
I did hear differences (improvements) with the SMD FWBR in place. My next stage will be to listen to the new version CAP6 at some point which is obviously designed to be used with the MBRD10200CT. I will have the original, FWBR 'bodged' and the new CAP6 to compare.
I should have the wherewithal to do so in the next few days although there are other things I also need to be getting on with.
Going from there to nowhere I note AA are now supplying the CAP6 with 12,000uF capacitors fitted. Ironically I noted that 12000uF/ 80V capacitors can be bought more cheaply than 10,000uF/ 80V jobbies!
Regards
Richard
All, What device surface temps are you getting from these SMT diodes/ rectifiers?
I'm trying a pair of the FWB3 items in a Pass M2 with a single CLC supply - they are getting 'quite hot'
8x 33,000uF caps configured in pairs, bias is 1.3amps *2 channels. Might be asking too much, although 100degC diode case temps are within limits
Have I missed something? I might start by reducing the bias, see what rectifier temps that gives me
I'm trying a pair of the FWB3 items in a Pass M2 with a single CLC supply - they are getting 'quite hot'
8x 33,000uF caps configured in pairs, bias is 1.3amps *2 channels. Might be asking too much, although 100degC diode case temps are within limits
Have I missed something? I might start by reducing the bias, see what rectifier temps that gives me
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Richard Lines
pfm Member
Dan,
No idea TBH.
Mine are on amplifiers driving the two Isobarik woofers so I’d expect them to be working for a living.
I’ll take the lids off both amplifiers this evening and see what temperature I can see both with my IR hand held and I can also stick the FLIR camera on them.
This will, obviously, only show the temperature on the upper surface of the FWBR.
Regards
Richard
No idea TBH.
Mine are on amplifiers driving the two Isobarik woofers so I’d expect them to be working for a living.
I’ll take the lids off both amplifiers this evening and see what temperature I can see both with my IR hand held and I can also stick the FLIR camera on them.
This will, obviously, only show the temperature on the upper surface of the FWBR.
Regards
Richard
laverda
pfm Member
All, What device surface temps are you getting from these SMT diodes/ rectifiers?
I'm trying a pair of the FWB3 items in a Pass M2 with a single CLC supply - they are getting 'quite hot'
8x 33,000uF caps configured in pairs, bias is 1.3amps *2 channels. Might be asking too much, although 100degC diode case temps are within limits
Have I missed something? I might start by reducing the bias, see what rectifier temps that gives me
I think you may be asking a lot without any heat sinking. My F5T rectifiers ran quite 'hot' (to hot to touch) even bolted to the chassis floor and the heat build up over time would dis colour the plastic boots on the spades connections.
Bit of a testament to these little SMD's.
