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

[xrk971]

I typically use an NTC like 8D-20 between IEC line and trafo primary. That works pretty well as it has about 10ohms resistance cold. Takes about a minute to warm up to 0.5ohms nominal value once hot. Simple and passive.

 

[astromo]

I typically use an NTC like 8D-20 between IEC line and trafo primary. That works pretty well as it has about 10ohms resistance cold. Takes about a minute to warm up to 0.5ohms nominal value once hot. Simple and passive.

From Post #1, Advantages:

7. As icing on the cake, the SLB provides a smooth slow ramp up to prevent mains current overload and tripping fuses, plus, it eliminates turn on speaker pop

.

xrk971, so you're recommending an NTC as well? Contradiction? What's the nuance?

 

[jhofland]

Perhaps I can help. Without some sort of soft start there will be significant currents required to charge the main caps in the SLB. The output of the SLB, on the other hand, does have a ramp up due to the relatively long risetime of the control voltages that are part of the of the so called capacitor multiplying circuits.

 

[Shawnstium]

The components of an electronic inrush current limiter and cap Mx are very similar, however the 60,000uF of CRC filtering is before the cap Mx. If you’re using a small (<300) VA transformer you can probably get away without using a soft start method, but the current surge is still stressful to your fuses and transformer.

 

[xrk971]

The NTC reduces in rush current to energize the magnetic core of the trafo. Also, as Jhofland mentioned, the bulk caps before the cap Mx need to charge up.

 

[astromo]

Perhaps I can help. Without some sort of soft start there will be significant currents required to charge the main caps in the SLB. The output of the SLB, on the other hand, does have a ramp up due to the relatively long risetime of the control voltages that are part of the of the so called capacitor multiplying circuits.

The components of an electronic inrush current limiter and cap Mx are very similar, however the 60,000uF of CRC filtering is before the cap Mx. If you’re using a small (<300) VA transformer you can probably get away without using a soft start method, but the current surge is still stressful to your fuses and transformer.

Got it. Thanks.

Item 7 that I quoted could go with a reword to avoid misunderstanding. Ideally a wiring overview, typical schematic for those coming in cold..

 

[Dadbeh]

You can go as high as 32v, but don’t exceed it. (Maybe 2v or so above might still work, but 32v or less is guaranteed safe).

this is the excellent instructions that came with the gainclone LM3886 that I am building and it clearly says that the power supply vontage can be as high is +-42v just like I originally said, is it possible that the 32v was for the LM3875? the instructions are so detailed that it is hard to think there is a mistake there. instruction pdf file is attached.

 

[Vunce]

Dadbeh,

If you reference the Texas Instruments data sheets for the Overture amplifier series LM3875, LM3886, etc...
The absolute max voltage with input signal is +/-42v. You would never want to run these chips that high. No “extra” power, but a lot of extra heat

 

[xrk971]

Go by manufacturer’s data sheet which says max supply (with signal present on inputs) is 84v absolute or +/-42v.

These can be run single supply with output cap, which is why they say an absolute voltage.

https://media.digikey.com/pdf/Data Sheets/Texas Instruments PDFs/LM3875.pdf

 

[Shawnstium]

Item 7 that I quoted could go with a reword to avoid misunderstanding. Ideally a wiring overview, typical schematic for those coming in cold..

Don't forget that input fuse too!

 

[xrk971]

For those of you whom have placed orders for the SLB dial rail, I just got word that the boards will be delivered to me today. So should be sending out soon.
Thanks for your patience.

 

[meanie]

SLB is alive!
With load of about 1.5A, not much room for voltage adjustments.

 

[Vunce]

Nice work meanie
There is approximately 1V of adjustment.
What amplifier will you use the SLB with?

 

[xrk971]

Very nice work, Meanie!


You will want to adjust it for about 3v of dropout under higher loads for max ripple reduction. Under 1.5A load, probably will be less.

 

[meanie]

Was able to set the voltage at +/-23.0 Vdc at SLB output, against CRCRC's +/- 23.1Vdc now.
Its powering M2X now. I will do listening test in this config for the moment.

An externally hosted image should be here but it was not working when we last tested it.

 

[meanie]

The SLB was meant for the USSA5 eventually.

 

[xrk971]

Was able to set the voltage at +/-23.0 Vdc at SLB output, against CRCRC's +/- 23.1Vdc now.
Its powering M2X now. I will do listening test in this config for the moment.

An externally hosted image should be here but it was not working when we last tested it.

That’s very interesting that the CRCRC has similar voltage drop relative to a SLB! Same trafo?

You should hear some marked improvement in the level of background noise and hum with no signal. Should be super for USSA5 as well.

 

[meanie]

Yes, its the same 18-0-18Vac trafo.

Just realized one single SLB with proper sized VA trafo is more than enough to power a stereo class A power amp. I barely feels any heat from the SLB unit.

I love the USSA5, was trying to make it more refine by using SLB, i hope.

 

[meanie]

However my newly purchased 500VA 24vac trafo, end up with too much voltage at the output of the SLB. With about 4A load, its rails is still at +/- 29Vdc!

Now don't know what to do with the 2x500VA trafo ....

 

[Vunce]

Meanie,
Are you using the active rectifier option with Prasi’s CRCRC PSU board?