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metaphile 8th August 2019 09:12 PM

Solved the hum!
1 Attachment(s)
Sorry for the rapid fire posting (can you tell I'm excited?!), but I seem to have solved it.

The ground from the L channel PCB (which, recall, has nothing landed to it) was passing right over the Antek torroid. I unplugged this from the SLB ground hub AND I moved both it and the L channel speaker ground as far away from the torroid as possible. They both still land on the SLB hub. This seems to have solved the hum issue.

Photo attached.

Wahoo! Thanks all for the quick help. Now I can nicely dress the cables :D.

Vunce 8th August 2019 09:43 PM


Originally Posted by metaphile (
Sorry for the rapid fire posting (can you tell I'm excited?!), but I seem to have solved it.

Wahoo! Thanks all for the quick help. Now I can nicely dress the cables :D.

Excellent work Metaphile!!
It’s very satisfying to tame the “HUM” beast, we’ve all been there :rolleyes:

When you clean up all your wiring make sure to twist all of the AC wiring, primary and secondary side of the Trafo.

Enjoy your new F6!! :cheers:

xrk971 8th August 2019 10:34 PM

Nice work! Glad you got it fixed so quickly.
Enjoy the hum-free music.

Do twist the primary red/black wires when you get the chance. That will help too.

A hum free Aleph J by evanc and a hum free F6 by metaphile. 2 quiet Class A amps courtesy SLB in one day. That’s a pretty good day.


evanc 9th August 2019 02:29 PM

Nice work metaphile

You guys are making it easy to get great results. Plus I cheated by making mono amps.

xrk971 9th August 2019 03:09 PM

Yes, monoblocks are usually easier to get silent. A lot of it still depends on good star grounding topology practice though.

potstip 9th August 2019 07:27 PM

Hello SLB looks promising. I have few questions.

1. The issue here below Tom mentioned is affect SLB? Supply Filtering and why Capacitance Multipliers are NOT the Answer

2. Is there any reason commercial amp pioneers such as (goldmund, accuphase, Pass, krell, MF, gryphon, burmester...) using mostly crc instead of cm or regulated ps. And many out there and i also hear that there is sonic improvement when they replace regulated ps with simple CRC. There must be something affect sound instead of ripple, i mean some smps have great ripple performance but not a common choice for amplifiers.

Thanks in advance.

xrk971 9th August 2019 08:27 PM

For Class AB amps with a high intrinsic power supply ripple-rejection ratio (PSRR) a cap multiplier isn’t necessary as the amp takes care of the ripple induced hum. So using just a CRC provides the cost savings and a very low impedance current supply is presented to the amp.

For a pure Class A amp where the bias current runs at it maximum despite whether or not any music is playing, these amps have a well defined maximum current they need - it’s the same all the time. Many of these amps, including many single ended Class A, have no PSRR to speak of: that is, ANY ripple on the supply rail shows up as audio signal on the speaker. This is the ideal situation to use an SLB or “ripple eater” based power supply. The SLB provides the amp with the PSRR it lacked.

However, as Tomchr points out, the cap multiplier may be more prone to mains input voltage variations to induced hum. I haven’t experienced this with the SLB - but a good things that helps audio sound quality is a good UPS - it provides active mains voltage stabilization and cleans it up to remove spurious motor induced noise from heavy equipment connected to the mains. The UPS also does a very good job cleaning up EMI/RFi contamination of the mains.

The SLB is probably not needed for a typical Class AB amp with circa -70dB or better PSRR. But for most pure Class A amps we find on the forums around here, it does a great job of forcing convenience and ultra low ripple. 5A is the maximum current it was designed for and still run optimally. 5A is a lot of current and you won’t get hot rectifiers and their associate headroom loss using the SLB.

Shawnstium 9th August 2019 08:27 PM

Rod explains some of the drawbacks of a Cap Mx here Capacitance Multiplier Power Supply Filter

Also, the Cap Mx in that tube amp uses a MOSFET, which Rod also touches upon in that article.

potstip 11th August 2019 05:06 PM


Did you have a chance to try ideal bridge rectifier with SLB ps?

SLB is SMPS right?

What is the model of owon ossiloscope you used to measure 1mV ripple?

Did you have a chance to measure peak to peak ripple instead of rms?

xrk971 11th August 2019 05:08 PM

SLB uses ideal bridge rectifier via LT4320 - that is the core of the SLB to give DC from AC secondaries of a linear transformer. The results presented are with a linear transformer not a SMPS.

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