For those of you who have ordered the SLB SR already, so sorry for not catching this error before producing the boards. If you have heartburn with your BD139 not having its back face the heatsink - let me know via PM and I will order you a v2 replacement board. But the v1 SLB SR boards are fully functional with Q5 orientation following pin 1 to the square pad.
Hi X,
Thanks for the SLB single rail doc's update info. As I want to buy a couple of these and you mention version 2 as having the fix done for Q5 orientation - when will these be ready for delivery from your Etsy store. I will hold off ordering till available.
Can you advise on this, thanks.
Thanks for the SLB single rail doc's update info. As I want to buy a couple of these and you mention version 2 as having the fix done for Q5 orientation - when will these be ready for delivery from your Etsy store. I will hold off ordering till available.
Can you advise on this, thanks.
Hi X,
Is there a formula to work out the AC volts in needed for a particular DCV out? I gather the normal forward voltage drop does not exist because of the new rectifier arrangement, and some volts are lost across the CX circuit. I was hoping to see in the first post a rule-of-thumb approximation for ACV in versus DCV out. For example, if I wanted a DC supply with +/- 28V or +/- 30V, then what ACV from the transformer would be required. Or is this info somewhere else?
Many thanks!
BK
Is there a formula to work out the AC volts in needed for a particular DCV out? I gather the normal forward voltage drop does not exist because of the new rectifier arrangement, and some volts are lost across the CX circuit. I was hoping to see in the first post a rule-of-thumb approximation for ACV in versus DCV out. For example, if I wanted a DC supply with +/- 28V or +/- 30V, then what ACV from the transformer would be required. Or is this info somewhere else?
Many thanks!
BK
Hi Bkdog,
It's approximate but go about it like this.
Decide what you need at the amp rail, say 28v. Under a Class A load of circa 3A, the voltage in an Antek sags quite a bit. Less so in other trafos. But a 300VA Antek will sag about 5v. Less is 500VA. The cap mx is about a 3v loss. The CRC is about 0.5v drop. The bridge is negligible. So add all of these losses to the voltage needed: 28v+5v+3v+0.5v=36.5v. That's what you need to be the nominal no-load voltage of the trafo. So now divide by 1.41 to get the AC volt rating of the trafo or 25.9v. The trafos come in specified increments and either a 25v or 28v will work. I would err on the bigger side and get a 28v 300VA. But if getting a 500VA, get the 25v. I have gotten the wrong one several times (like 3x now) and always too small, so I typically get the higher voltage one. It's easier to drop voltage than to make it.
Hope that helps.
It's approximate but go about it like this.
Decide what you need at the amp rail, say 28v. Under a Class A load of circa 3A, the voltage in an Antek sags quite a bit. Less so in other trafos. But a 300VA Antek will sag about 5v. Less is 500VA. The cap mx is about a 3v loss. The CRC is about 0.5v drop. The bridge is negligible. So add all of these losses to the voltage needed: 28v+5v+3v+0.5v=36.5v. That's what you need to be the nominal no-load voltage of the trafo. So now divide by 1.41 to get the AC volt rating of the trafo or 25.9v. The trafos come in specified increments and either a 25v or 28v will work. I would err on the bigger side and get a 28v 300VA. But if getting a 500VA, get the 25v. I have gotten the wrong one several times (like 3x now) and always too small, so I typically get the higher voltage one. It's easier to drop voltage than to make it.
Hope that helps.
A couple of warnings about constructing and testing the SLBs. Never connect them to a load without the large pass transistors plugged into the Molex jack. If plugged in, make sure the wires are wired correctly (trace each one yourself). If you do connect the load and apply power without the big C5200 or A1943 connected, all the current passes through the smaller TO126 transistor and the R15 resistor (which will smoke and then blow like a fuse). It's a good thing that it blows as it protects the BD139/140 from melting.
Other things to be careful of: make sure the BD139/140's are not installed backwards. The square pad is pin 1.
Make sure your electrolytics are not in backwards.
Both Vunce and myself have melted the 680R resistor leading from the BD139/140 because we forgot to connect the pass transistor (or did not connect it securely).
Other things to be careful of: make sure the BD139/140's are not installed backwards. The square pad is pin 1.
Make sure your electrolytics are not in backwards.
Both Vunce and myself have melted the 680R resistor leading from the BD139/140 because we forgot to connect the pass transistor (or did not connect it securely).
Yes, it was the ABBB stuff that prompted my post.
I would be interested in a single board SLB SR/MoFo but if it doesn't happen it won't be the end of the world as I already have my pairs of SLB SRs and DIY Audo Store MoFo boards.
I built up a pair of the SLB SR’s last night. Still need to connect the pass 2SA1943 BJT to some flying leads and the Molex connector. These are set up to handle any project up to 47vdc output. Will probably use them on some new MoFos next. CPU coolers ones this time with JPS64 PCBs.
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