# Bypass cap´s for BYV27 and ground speaker basket´s?

#### mikaelmark

##### New Member
By default design´s for power supply section in a pre amp, headphone amp or a DAC and when replacing standard rectifier diodes 1N400x with BYV27-200, I use to solder a 0,1 uF capacitor for each diode to eliminate unwanted high voltage peakes and noise.

But as I´ve been told by a technically know how-person that those bypass cap´s should only been used for standard rectifier diodes, eventually also combined with a low ohm resistor i serial. If this mod are being used with the better and faster BYV27, there may be a worser result as there will be a small amount of quiscent/leakage AC current.

But as some designs already is equipped with BYV27 combined with 0,1uF cap´s, do someone have any thoughts about this mod - is it only for standard rectifier diodes so BYV27´s whould be used without those cap´s of will it also do fine with BYV27´s?

Also, the same guy recommended to ground all speaker basket´s, to eliminate electrical static´s that will occur from the coil magnet and he told the positive effect from this mod will be heard. Has someone tried it and have any experience about it? Should it be worth doing?

#### rjenkinsgb

##### Well-Known Member
1N4000 series diodes are quite slow and can, hypothetically at least, generate a small amount of noise from reverse current at each zero crossing.

The caps reduce or eliminate that. They are often used in RF designs but I've never seen them used in audio.

If you want to have a similar effect with the faster diode, use a proportionally smaller cap.
The 1N4000 series has a recovery time of up to 30uS, the BYV25 just 25nS. 100pF should have a similar damping effect as 100nF on the 1N4000.

To be honest, I don't think they are needed for audio either way. Decent post-rectification filtering with proper regulation and grounding should eliminate any supply noise regardless.

Re. speaker frame grounding - no chance. I think whoever "hears" any difference is hoping for some; it's like the reviewers that claim one make of digital optical cable sounds different to another, an absolute physical impossibility.

#### audioguru

##### Well-Known Member
Capacitors parallel with rectifier diodes were used 50 years ago in European audio circuits. Not anymore.
Speaker baskets do not collect static (unless an animal rubs it) and are not grounded.
Snake oil is used only by audiofools, not by audiophiles.

#### Nigel Goodwin

##### Super Moderator
Another reason (perhaps the 'real' one?) for the capacitors, is to possibly help with rectifier reliability, a capacitor across them also helps to reduce any in-borne high voltage spikes that 'might' damage the diodes - however, rectifiers die with or without the capacitors fitted, and I've no idea if it helps or not.

I suspect the real reason is that it's 'been done for a very long time', and people just copy it - perhaps it's introduced as needed in University courses?, simply because of that reason. I've never designed anything with the capacitors across the rectifiers, and can't see myself ever doing so - it's just something else to go wrong (and they do go S/C occasionally), and appears to give no advantage.

The speaker thing is ludicrous - and you certainly won't hear any difference, and there won't be any difference, however some speaker manufacturers have occasionally fitted a wire between one side of the voice coil and the chassis of the speaker, presumably simply to ground the chassis. Possibly this is what has created such a myth?.

#### unclejed613

##### Well-Known Member
i agree, grounding the baskets on speakers really does nothing. and in 40 years of work, i've only rarely seen bypass caps connected to bridge rectifiers, and as somebody mentioned, it's something done in communications equipment, not in audio equipment. if you really want to eliminate reverse recovery effects, silicon carbide rectifiers don't have any reverse recovery problems (in SiC rectifier data sheets, if Trr is listed at all, it's printed as "Trr=0"). they have a slightly higher forward voltage than silicon. either way, you won't change the sound of a piece of equipment by using bypass capacitors or special diodes. there are a lot of "audio urban legends", many of them are invented to part you and your hard-earned money.

#### Nigel Goodwin

##### Super Moderator
and in 40 years of work, i've only rarely seen bypass caps connected to bridge rectifiers, and as somebody mentioned, it's something done in communications equipment, not in audio equipment.
It was commonly done in audio equipment and in TV's, I've seen huge amounts of equipment that did so.

#### mikaelmark

##### New Member
Ok, here´s a link about Snubber mod (using a capacitor with a resistor in series before the rectifiers):

https://diyaudioheaven.wordpress.com...es/snubbering/

For my schematic; If I remove C301 - C304 and replace them with only one capacitor with a resistor in series between the transformers secondary AC, should they be soldered directly between and after the heat fuses RF1/RF2?

As there are 15VAC for secondary, should a 100nF with a 10Ohm resistor be fine or are there any better values?

And how much Voltage should the snubber cap been rated at and what Wattage should the resistor be?

Should a MKP or Ceramic do best for this snubber?

Also, as I use an EMI(?) filter from a PC Power Supply 230VAC primary side; may the snubber mod interact with this filter so only one of them should be used, or is it ok to combine them?

#### rjenkinsgb

##### Well-Known Member
As there are 15VAC for secondary, should a 100nF with a 10Ohm resistor be fine or are there any better values?

And how much Voltage should the snubber cap been rated at and what Wattage should the resistor be?

Should a MKP or Ceramic do best for this snubber?
100nF and 10 Ohms should be OK.

Use a polyester or polystyrene cap, not ceramic, if you are trying to get the best noise reduction performance - multilayer ceramics can have some strange properties due to piezoelectric effects.

The power dissipated in the resistor will be trivial, a half watt or quarter watt will be fine.

It may reduce EMI but nothing should be able to get past the PSU filtering and regulation, regardless.

#### mikaelmark

##### New Member
100nF and 10 Ohms should be OK.

Use a polyester or polystyrene cap, not ceramic, if you are trying to get the best noise reduction performance - multilayer ceramics can have some strange properties due to piezoelectric effects.

The power dissipated in the resistor will be trivial, a half watt or quarter watt will be fine.

It may reduce EMI but nothing should be able to get past the PSU filtering and regulation, regardless.
I now gonna use an MKS 33nF cap and a carbon film 330 Ohm resistor for this snubber but I´m not quite sure what what rating the cap should be; may it be enough with 63 Volt MKS 02/K2?

My findings are due to a guy at another forum (prairedog) with a similar amp and also a DAC has been tested with different setups and measured with an oscilloscope, and the conclusion was as above:

" I took some 60Hz rectifier snubber measurements from both a homemade DAC and cheap chinese clone Lehmann headphone amp, similar to OP's project, and some breadboard variations.
For the Lehmann clone, transformer is Hammond 166J28 28VCT 1A, split-bobbin design, stock is four 0.1uF MKT across each (slow) 1N4004 rectifier, into 10,000uF filter caps for +/-18.5VDC typ. to the Vregs.
For the DAC which uses Hammond 166G25 25VCT 0.5A, split-bobbin design, four fast-recovery BYV26E rectifiers, into 3,300uF filter caps for +/-18.5VDC typ. to the Vregs. No capacitors across the transformer secondary or rectifiers. Very hard to see any recovery spikes on the scope, although they are still there.

With no capacitors at all, no ringing but a large fast spike about 20-30Vpk:
[IMG alt="Click image for larger version.
Name: No caps_xfmr_secondary TEK00027.PNG Views: 2 Size: 5.7 KB ID: 156649"]https://www.edaboard.com/attachment.php?attachmentid=156649&d=1574638209&thumb=1[/IMG]

Lowest cost but terrible for ringing is a capacitor right across the transformer secondary, or across each rectifier diode. OK for a car battery charger from 1976 but no good for a quiet PSU:
[IMG alt="Click image for larger version.
Name: 100nF across secondary TEK00032.PNG Views: 2 Size: 5.6 KB ID: 156650"]https://www.edaboard.com/attachment.php?attachmentid=156650&d=1574638219&thumb=1[/IMG]

RC snubber alone across the transformer secondary, I found 280-630R and 10-100nF was critically damped. A lower value of snubber resistor, i.e. 10R is too low and did not lower the circuit's Q so there is lots of ringing. 100nF is also on the huge side.
[IMG alt="Click image for larger version.
Name: Best RC snubber tuning 47nF 370R TEK00029.PNG Views: 2 Size: 5.7 KB ID: 156651"]https://www.edaboard.com/attachment.php?attachmentid=156651&d=1574638231&thumb=1[/IMG]

So my findings- fast-recovery diodes give a much smaller bump to the leakage inductance, and an RC snubber across the transformer tames the switching transients. The snubber values depend on the power transformer used and for audio 10-30VA around 28VAC like you'd find in a +/-15V power supply, around 33nF and 330R 1/2W. The cap doesn't matter if film or ceramic, although X7R have a large voltage coefficient. I use boxed MKT film caps rated 100VAC at least triple the operating voltage.

All this is relevant for a low noise mains PSU because the rectifier switching transients radiate EMI in the wiring and can walk through an electrolytic filter capacitor as their ESL is significant at RF frequencies. A linear Vreg has only a few kHz bandwidth. "

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