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

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#1,464
I am a newbie.
You can see the spaces between caps (C21, C22) and pcb in the image.
I wonder whehter it occures some problems?

slb.PNG
 
#1,466
#1,472
This is sort of an extension of my continuing saga of a Burning Amp that I have been working on for over a year. I have two SLBs in a dual mono config and the positive side of one of them is giving me ~41v unloaded while the negative rail is giving me ~38v. I am running a dual 28v secondary (actual is ~29.4 given high wall voltage) so I am expecting 38v from a working SLB. What could be wrong with the 41v side? Even though the light is lit and I get power out of it, something is not working. I sorta recall reading in this forum that perhaps the cap mx pulls about 3v, so maybe that isn't working? I get no smoke though and it has ran multiple times for an hour or more, so it at least partial works. Any thoughts on what to check?
 
#1,473
Have you adjusted the trimpot for max voltage drop? The range is only 2v maybe.

Is it reducing ripple? Measure the AC voltage ripple with DMM upstream of the BJT and downstream of it. If you have an Oscope check visually at level of ripple. If it’s working well there should be under 5mV rms ripple output under load.

Could your trafo windings by non symmetric? Try swapping the secondaries and see if imbalance flips.

Could your amp be drawing less current from one rail vs the other?

Some photos of your setup and sketch or diagram of how it’s connected and your amp would be helpful.

If it’s working, the large heatsinked BJT should be similarly warm.

Good luck.
 
#1,475
Thank you for the quick responses!

I tried adjusting the trim pot this morning and it barely made any difference, the greatest change was about .4 volts. So from 41.2 to 40.8.

I do not know where to check ripple upstream, but downstream ripple varies from 1.2mv to 1.8mv depending on the trim pot. Without load.

My transformer windings both measure 29.4v AC by themselves. When I swapped the secondaries the imbalance did not flip.

Under load the negative rail measures 34.2, same as the other power supply, while the positive rail measures about 36.6, about 2.5v too high, as expected given the imbalance.

You have helped me a few times early in the year when I had a strange tapping noise on my outputs. I solved the noise problem by replacing the output transistors, well, at least I did on the other channel which has proper voltages. I haven't tried this channel yet because the voltage offset is too high to zero out the DC on the output.

Here is the post with my layout drawing: Layout drawing

Here are pics of my amp from the BA-3 Build Guide thread: BA3 Amp Pics

I have more pics higher up on the same page.
 
#1,476
The issue is apparently related to the 2SA1943 cap mx transistor. Even though the power supply is working, when I swap the transistor between my two power supplies, the issue follows the transistor. My leads are soldered to the transistor so I would think that isn't the problem; I get continuity between the leads and the connector and the same .1 ohm resistance. I am ordering some new parts and will swap it out. Weird how it seems to be another transistor problem....this amp has been plagued by transistor issues. Could be me of course, lol, still weird.
 
#1,478
Could the failed transistor affect the range of trim pot - as in the trim pot has no effect at all? I was going to post on here just a quick update that everything is working on my amp at this point (besides the slightly high output voltage). The pulsing noise I was having earlier this year was narrowed down to some bad P channel parts in the output stage (whether they were bad before I got them or I damaged just the P channel parts, I don't know). Thank you for all the help you provided as well as the production and availability of this awesomely clean power supply.
 
#1,480
AKSA said:
Thanks for the photo - helpful, but I have the impression this has two independent secondaries, perhaps each 12Vac?
If so, as you mentioned, not enough volts. You need about 25Vac from each winding if you are using the SLB since it will drop about four volts.
Do you have a schematic and color code from the transformer manufacturer?

HD
Click to expand...
Hi AKSA!

I am resuming this project after a long hiatus. As you suspected, I had wrong transformers. I replaced them with Toroidys, 2X25V. I just performed a test measurement and I'm getting 35,5V and 35,6V on the output rails. Seem a tad high perhaps to me, but at least now the outputs are in agreement with each other. Am I back on track?
 
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