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The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB

If you connect this toroidal up to a standard silicon bridge and CRC supply, is there still buzz? In general, the SLB will help make a trafo quieter.

One reason for buzz is if it is operating too close to its design margin. I like to run them 2x to 3x over sized. So for dual AN, with SLB we are talking about 110w per channel or 220w total. So 2x is 440VA and 3x is 660VA. A 500VA seems like it should be good.


Paid Member
2014-01-26 8:20 pm
Just a quick question…

I can hear my toroid transformer hum when connected to the SLB and when adding the second SLB two secondary 3-4 the hum just gets louder.

My initial thought is I had possibly too much DC on the AC line but just a mere 1.5mV would never bother my toroidy transformer. I also checked some other things. If transformer is not connected on the secondaries, it is totally silent. Now I will try a different PSU for testing.

In the meantime, I’m thinking it is the snubber at the AC input on the PSU… I’ve added the default BoM values, but those are most likely not optimized at all for this transformer and it is making it hum. Do you think it is worth removing the snubber or I’m wasting time? I’m thinking wrong value here can only cause issues like ringing, etc…


Hi Do,
Are these SLB's used with your AN amplifier? Didn't this setup work fine with a different trafo, but now with the Toroidy there is hum? I'm just trying to get the whole picture.

I believe this is an 800VA trafo so definitely not underpowered.
Here's what I've tried

- DC blocker, but result was the same
- No load, the transformer is barely audible, you have to put your ear on it.
- Ideal bridge rectifier (LT4320), SLB PSU = loud hum under load
- Ideal bridge rectifier (LT4320), linear PSU = loud hum under load
- Regular bridge rectifier, linear PSU = loud hum under load
- Transformer shield connected or not to chassis ground = loud hum under load

Humming noise seems to only come out from where the cables exit the transformer.

I've contacted Toroidy to know what they suggest. I think this is a defective transformer. I never had a single Toroidy transformer make any noise under load or any PSUs.
So... Good news!

I must say Toroidy stand behind their products and offer impeccable customer service!

They sent me a battery of tests to do, which I did and return the results to them. Then they asked if I could send the transformer back for further testing at their facility in Poland. I explained that shipping cost from Canada to Poland and also to return to Canada is going to be quite prohibitive, mainly due to weight... So I offered them a counter offer, where I will order the same transformer, only the encapsulated version and pay the difference with shipping. They concluded it was a good idea and accepted the offer.

Now, I should be getting this new transformer in 2-3 weeks, hopefully.


I hope this works out for you Do! FWIW, my only experience with Toroidy is with their Supreme fully encapsulated and fully potted variety. My reasoning was simply because shipping costs are so high from Poland to North America that you might as well buy the best for a small upcharge (at least to me).

I don’t do DIY to hit a budget to be honest. I do it because the products I build aren’t available commercially in the manner I want it to be built or in the execution. The thrill of course is in the journey.

Hi Anand,

My thought process is a lot like yours as I never look at building amps on a budget and although I put a cover on the amp chassis to hide the internals, I always make sure it looks good. Call it OCD maybe but I’m like that… LOL

I’ve build 3-4 amps with Toroidy Supreme transformers and several more with the Audio non-encapsulated transformers and never had a single issue until now. I usually use the non-encapsulated transformers when space is an issue, because the encapsulated version is quite larger and heavier. Toroidy assured me they’re very similar transformer, aside the capsule and whatever they use as filling. For sure the Supreme is super quiet even under heavy loads. That chassis I have is badly designed as internal space and after measuring it should fit but I’ll have to do some extra work.

Anyways, with Class A amps, I’ll only order encapsulated transformers going forward.

Good news. Today I finished installing and testing the two single-rail SLBs in my Fokin project. I set them up so that I measure 3.1V across the pass transistor protection diodes (it actually fluctuates about 0.2V or so either side of 3.1V) and used a test load to pull about 1.7A through the SLBs - all seems good.

I'm using a 500VA 30VAC transformer and output voltage is spot-on at 39VDC. Transformenr is silent.

No prob X. Here's a picture of the testing:


and this shows the general arrangement of the Fokin chassis, one SLB for each Tokin 2SK180.

So I bought a single rail SLB. I plan to use it for the F3 build and maybe a Tonkin SIT build if it uses a single rail voltage like the vfet lottery kits. For the F3 it appears we want +46V. I am doing monblocks, so my choices from Antek of 200VA with 36V secondaries, or 300VA with 34V or 35V secondaries. I could use both secondaries or I could get a transformer with a smaller secondaries and run the secondaries in series.
I got a question from a member on what to do if one wants to use a single rail SLB at 6A.

The SLB’s were nominally designed for 5A so 6A is only a bit higher. The main thing is the ripple current on the first cap as that can heat it up. Also, the dissipation across the R of the CRC. The specified caps currently have an 8A rms ripple current rating and are 15,000uF. The first one takes the brunt of the ripple. Look for a cap with a higher ripple current (say, 10A) or same (8A), but smaller capacitance value of bulk cap value. So look for 10,000uF cap with maybe 8A ripple current rating on first cap. Keep second one as is. Your output ripple after CRC will go up a bit, but I think the cap multiplier will smooth most of that out. If you are feeding a balanced amp like SuSyLu, it has good PSRR by topology. However, it’s important that both legs of amp be fed by an identical supply ripple so that common mode ripple can be subtracted out in the amp. If using two single rail SLBs on a balanced amp, tie their outputs together with a big low impedance wire to ensure the voltages are the same. For the the resistor calculate dissipation and maybe make a 4 resistor series parallel array to dissipate more heat. Since you can dissipate more heat, you can compensate for smaller first cap with slightly larger resistance. Right now it is 0.1ohm, maybe try 0.15ohm or 0.22ohm but 10W worth of dissipation rating.
I just finished a dual mono BA-3 build at 32v (actual 34.5v) and am experiencing a tapping noise from the speaker on both channels. The noise is not volume dependent, present whether inputs are shorted or connected to preamp, nor related to AC Hz....it's at least 200 beats per minute. There is no DC on speaker out. After a few posts on the BA-3 forum, the members suggested I ask here as it is believed to be from the power supply. The amp is fully biased but I am actually getting about 34.5 volts from each SLB as the Antek transformers (3228's) are not sagging as much as expected. In addition, none of the LEDs light up even though I am getting stable and identical + and - voltage from both boards. I cannot imagine that I installed all 4 leds backwards, so I am thinking the problems are related. The BA-3 front end and the neg speaker posts go to the grounds on the SLB, which then goes to chassis/earth ground.

What could be the problem and where do I begin troubleshooting?