It sure sounds like the problem is in the power supply and not in the amplifier.
You want it to be slow. Standard CRC has circa 30,000uF to 44,000uF bulk cap per rail. The SLB has only 30,000uF before the CapMx pass transistor and a small one after. The pass transistor probably cuts off the 30,000uF before it can naturally fully decay. If you added a 22,000uf bulk cap after the Cap Mx, it may slow it down enough that you won’t hear the thump.
Might want to think about SLB design modifications which prevent the output from collapsing while there's still many many coulombs of charge in the 30,000 uF capacitor upstream. Arranging the Sziklai compound-pass-transistor so it doesn't cut off is one possibility and I imagine there probably are a few others too. Maybe @keantoken invented something useful in his Sziklai based K-multiplier: (link to non-diyAudio website) that you could copy.
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Is the Aleph somewhat unique in this regard, or would this be an issue in most FW/Pass Class A amps?
The SLB does not have this issue driving the F6, nor the Alpha 20 (not First Watt). I could try it on the M2 boards if you need to know. I currently don't have them installed in a chassis, but could swap them in.
Don’t bother. I’ve used the SLB with M2X and had no turn-on or turn-off issues.
Nah, no need to check. I was moreso curious how likely this would be to impact my upcoming SissySIT build. 😛
Apologies if this has already been covered in this thread, but I just wanted to double check that I've got the layout correct here for the pass transistors.
Square pad == Base (pin 1)?
And, is my diagram correct for wiring up the Molex adapter?
Square pad == Base (pin 1)?
And, is my diagram correct for wiring up the Molex adapter?
Well, it seems I got the pass transistors right since it's playing beautiful music right now -- if I hadn't got it right, it wouldn't work at all, right? Hopefully. 😂
The great news is that it seems to have solved my low-level humming issue (probably due to low PSRR in the amp). Getting around +/-23.3VDC with 20VAC 300VA Anteks.
The great news is that it seems to have solved my low-level humming issue (probably due to low PSRR in the amp). Getting around +/-23.3VDC with 20VAC 300VA Anteks.
Hi Sp33ls,
Glad you got it working! The fact that the low level hum is gone and the voltage appears to be correct means it is working. The transistors should be warm but not hot. If it was mis-wired it would not work or you would have smoke. Many SE Class A amps don’t have the best PSRR so the SLB will help to make the background quiet. Is that a speaker protect or soft start board you have mounted next to it?
Glad you got it working! The fact that the low level hum is gone and the voltage appears to be correct means it is working. The transistors should be warm but not hot. If it was mis-wired it would not work or you would have smoke. Many SE Class A amps don’t have the best PSRR so the SLB will help to make the background quiet. Is that a speaker protect or soft start board you have mounted next to it?
Works it does. I'm very thankful to everyone who helped make this one possible, too. I love not being able to discern whether the amp is on or not when your ear is pressed to the speaker cone lol.
Correct! Neurochrome goodies. Recently picked up the ISS (soft start) to go alongside the speaker protection, and I'm very happy with both.
@xrk971 have you played around with adding an additional cap bank at the output of the SLB for extra bulk storage? I've seen it suggested and was curious about adding some (like 15mF per channel).
I do indeed have a slight shutdown thump (it'd be easy to live with, tho).
I may try adding a bulk cap to each rail and see if that helps. Shouldn't be any potential downsides other than additional cost, yeah?
Sigh, so I let the magic smoke go tonight...
I somehow managed to forget to connect Q10 after double-checking my connections... >.>
R13 was burned and measured 15R less than it should.
I've since removed R13 and tried to remove that scent with isopropyl. Burnt resistors is a strong scent lol.
R17 seems to still measure about 5R (in circuit). I also removed D3 & R7, and both still appear to be fine, but going to replace them both anyhow.
Is there anything else I should replace while I'm at it, or do you suspect R17 took one for the team?
The good news is that swapping in my other SLB board results in the amp working as expected.
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Well, I replaced R13, only for R17 (4R75) to start smoking after being on for about 5-10m.
I ended up replacing it a 2W 5R1 I had lying around. Haven't had any issues thus far with this 2W in now.
I'm guessing when R13 went out, it must've also damaged R17 -- even if it had still measured alright.
Btw, what is the intended wattage for these locations? Just to make sure I didn't grab the wrong wattage...
I ended up replacing it a 2W 5R1 I had lying around. Haven't had any issues thus far with this 2W in now.
I'm guessing when R13 went out, it must've also damaged R17 -- even if it had still measured alright.
Btw, what is the intended wattage for these locations? Just to make sure I didn't grab the wrong wattage...