Snubber cap

Jens · « **on:** 10 Jan 2003, 08:42 pm »

Hugh supplied a 220 NF snubber cap with my AKSA Nirvana 55 watt kit. According to the instructions it is supposed to be connected with a 100 ohm resistor between the two mains wires.

What does the resistor do? Why not use the cap alone?

I've seen elsewhere that a 47 nF cap is suggested without the resistor (not specifically for the AKSA, though).

I've connected the snubber cap as indicated in Hugh's instructions, but I am still getting a bit of contact noise (light switches) through sometimes.

Hugh or anyone - suggestions are welcome!

Cheers,

Jens

AKSA · « **Reply #1 on:** 10 Jan 2003, 08:57 pm »

Hi Jens,

The resistor limits current in the even the cap fails.

The purpose of the cap is to knock the edge of high frequency transients which find their way from the mains into the toroids. It's not completely effective, but it does some good and it tends to prolong the life of the switch as well since this is a highly inductive load with considerable effect on power factor (phase angle between current and power - current lags voltage).

Power supply rejection ratio of the AKSA is fairly low because of the resistive feed to the input and voltage amplifier stage. Unfortunately everything I have done to improve it effects the sonics; this appears to be one of those intractable compromises, but I continue to work away at it.

Cheers,

Hugh

Jens · « **Reply #2 on:** 10 Jan 2003, 09:15 pm »

Hi Hugh,

Well, that means I could omit the resistor, because I am using a socket with built-in mains fuse.

Would there be any effect of changing the value of the cap - up or down?

Apart from that you are right - please do not do anything that impairs that angelic sound

Cheers,

Jens

Grumpy_Git · « **Reply #3 on:** 27 Jan 2003, 02:26 pm »

Hmm, I'm just on my way to connect the modules up for initial biasing and I dont have a 100ohm resistor sitting round.

Also, I can't find any reference to the cap in my literature, where is this info and how is the cap and the resistor supposed to be connected.

Can I ommit this resistor for the moment till I can get to a shop to buy one.

is a standard half watt resistor fine??

Nick.

blizzard · « **Reply #4 on:** 27 Jan 2003, 03:29 pm »

Hi Nick,
I have the earlier version of the AKSA 55. But, in my assembly instructions on page 2 -- figure 1, there should be two diagrams of the power supplies. Both of these show the cap and resistor connected across the switch.
I don't know if the version 2 instructions have this figure on the same page. But, it should be in you power supply diagram.
Hope this helps,
Steve

PSP · « **Reply #5 on:** 27 Jan 2003, 05:49 pm »

Nick,
If you leave out the snubber (cap and resistor) you can get some significant arcs in your power switch due to the inrush when the amp is switched on. A few months ago, some AKSA 100 builders that missed that little detail in the power supply schematic were burning out power switches fairly quickly.

The resistor can be a cheap carbon comp, and I'd guess (I deifinitely don't know) that it's value isn't super critical... so if I had anything between 47R and 200R, I'd put those in and use them until I could get a 100R or Hugh says it's OK.

Good luck,
Peter

AKSA · « **Reply #6 on:** 27 Jan 2003, 09:41 pm »

Folks,

The action of the snubber is a little subtle; it quenches arcs arising from the inductive kick back of the transformer when the power is switched OFF!!

If you delete this from the circuit it will have almost no effect on the sonics.

This reduces switch wear at switch off. The resistor is not critical, as Peter suggests, 47-200R is just fine. Any 100R resistor, including carbon comp, is adequate for this, but it's mains potential so do take care to insulate it!

Cheers,

Hugh

dayneger · « **Reply #7 on:** 28 Jan 2003, 05:12 pm »

While hunting for solutions to various buzz and hum problems in my Foreplay I ran across references to HV snubbers (RRSF), which are supposed to supposed to reduct diode reflections back into the transformers.

Here's a cool little animation showing the circuit and how to stick it into the Foreplay:
http://home.att.net/~joemacjr/diyproject/foreplay.html#

then hit "noise & hum" followed by snubbers.

I was wondering if something like this would be helpful (or even relevant, for that matter!) in the AKSA power supply?

Thanks, Dayne

PSP · « **Reply #8 on:** 28 Jan 2003, 06:32 pm »

Hi Dayne,
This question is definitely on my "to do" list, but it's not high priority.

My '55s have extremely low levels of hum and buzz (my ear within an inch or two of the tweeter for buzz, woofer for hum, any further away than that, no problem). Someday I may get around to putting snubbers on to see if I can get rid of that buzz, but that is simply ego talking... the level of noise I have is inaudible a foot from the speakers, irrelevant for music by any standard.

My TLP (as readers from HD will remember) had hum issues when I had it in the same chassis as the AKSA amp torroids, and before I used good coax between the attenuator and the TLP input. I tried all manner of snubbers during that hum war, and there was no effect that I could hear. Currently, I'm putting my TLP in a seperate chassis, and if I have residual hum or buzz in that setting, I'll first try shielding, then try snubbers again. (and someday, it will be a GK1

)

Short answer, I would definitely not add snubbers first.. I'd listen to it stock for a while, assess, discuss any issues here first, and then move forward slowly (so we know what the problem was, and what was required to fix it).

By the way, If you put a shorting plug (RCA male with some resistor, say 75R - 5K, I've seen varying recommendations, not sure that it matters, connecting RCA hot to ground) into the AKSA inputs, the noise you hear (precious little in my case) is due to the AKSA.... look at wire dress, twisted signal and twisted AC wires, AC well seperated from signal, ground loops, etc.). Then you can move the shorting plugs to the Foreplay inputs... if there is additional noise, it is likely coming from the FP, or from ground loops that include the FP chassis.

Good luck,
Peter