L-Adapter

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killie99

Member
Joined 2011
I built a little streamer using a couple of L-Adapters, Pi4 and an Allo DigiOne Signature, sounds superb :

digione_sig_1_inside_small.jpg

digione_sig_1_rear_small.jpg

digione_sig_1_small.jpg
 
L

lupoal

Member
Joined 2020
I have question (maybe a stupid one, sorry in advance)... with this power unit in would drive two tubes heaters, SRPP output configuration... the amp I'm going to duplicate, with the hope to improve, has the output tube filments floating, not elevated (here is the scheme) ...
in the description about how this L-adapter works I read: "C1 shunts for AC the LEDS+trimmer Vref system to ground. Thus the active elements noise finds an easier path to ground through it and filtering happens." ...
and the question is: then if I do not connect the DCout0 to ground this unit will not work? if this is tha case using a voltage divider connected to DCout0 from HV supply unit (I would use SSHV2 for that, two units one per chanel) could cause problems? suggestions?

thank in advance for help
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
You will obviously have to connect both output points to the receiving end (tube's heater circuit) but the return point (0) doesn't have to be system grounded (floating/DC lifted heater compatible). Indeed there's a return point marked with a general ground symbol after the diodes bridge on the original heater supply schematic link. Electric current has to return to it's source. Any circuit is a full circle. Hence the terminology.
 
G

Grarea

Member
Joined 2019
Hi,
this is such a great kit.
I am pretty new and ordered the full kit to reduce the risk of me making mistakes.
I know it has been said before, but what a great layout on the board etc.
Even I found it easy. Thank you so much. I am loving the flexibility of it.

Now, can I just confirm a couple of noob things please?
Am I right in thinking that I don't need to isolate the 5 heatsinks electronically as I am using the kit and sinking on board?

Also, should I be using a fuse between the L-Adapter and USBridge sig or Pi?
I don't see anyone else doing it. So I assume not.

Thanks again.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
Hi,
You can skip isolating the semiconductors from their onboard sinks BUT no chassis point should be touching them. Also don't ever probe them with something grounded etc. No use of isolation pads certainly improves thermal transfer but a bead of thermal paste is still advised to be used.
Fuses for the loading circuits will add some further voltage dropping resistance in the rail. Rail resistance modulates drop with load demand. You can try with them in the start and after everything works well and feeling secure remove or bypass them. Use the thickest gauge shortest run DC output power line cables applicable in any case.
 
G

Grarea

Member
Joined 2019
Salas said:
Hi,
You can skip isolating the semiconductors from their onboard sinks BUT no chassis point should be touching them. Also don't ever probe them with something grounded etc. No use of isolation pads certainly improves thermal transfer but a bead of thermal paste is still advised to be used.
Fuses for the loading circuits will add some further voltage dropping resistance in the rail. Rail resistance modulates drop with load demand. You can try with them in the start and after everything works well and feeling secure remove or bypass them. Use the thickest gauge shortest run DC output power line cables applicable in any case.
Click to expand...
Marvelous.
Thank you for that.
 
G

Grarea

Member
Joined 2019
I seem to be running a bit hot in comparison to others.
I bought the full kit from Tea Bag and sinking on board with those.
The sink is too hot to touch and according to my DMM, 70C (16C Ambient)
10V in 5VDC out.
Powering a USBridge Sig with it. Which then powers a Khadas Tone Board (which asks for a 500mA power supply )
I tried removing the KTB, but it only made a few degrees difference.
Would quite long DC cables cause it ? (I forgot you advised short as possible.)
 
Rush

Rush

Member
Joined 2009
Salas,

I am wanting to power a friends (and maybe mine in the future) PowerDac R. It works on 5 volt DC and a mere 0.25 Amps.
I don't know when to use this L-Adapter or when to use your UltraBiB SSLV 1.3.

What are your thoughts to use one vs. the other?

Rush
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
Grarea said:
I seem to be running a bit hot in comparison to others.
I bought the full kit from Tea Bag and sinking on board with those.
The sink is too hot to touch and according to my DMM, 70C (16C Ambient)
10V in 5VDC out.
Powering a USBridge Sig with it. Which then powers a Khadas Tone Board (which asks for a 500mA power supply )
I tried removing the KTB, but it only made a few degrees difference.
Would quite long DC cables cause it ? (I forgot you advised short as possible.)
Click to expand...
You need data. Measure the load's current demand with the DMM in series Ampere mode first. To see if its more than it should explaining the dissipated heat. Don't forget to place the red jack in the DMM's special socket for current measurement. Another reason would be having unnecessarily high AC secondary transformer leading to high DCin-DCout across the L-A even when the load's current demand is what you expected. You can verify the DC difference across the reverse protection diode D11. Do that when actually powering the application. If the mA consumption proves normal, augment the sinking because its much cheaper than changing the transformer.

*Any loss on the output cables is dissipated on the cables not on the sink. You can also measure the voltage drop across the beginning and end of the output cables while working. If its significant, use thicker / shorter ones.
 
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Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
Rush said:
Salas,

I am wanting to power a friends (and maybe mine in the future) PowerDac R. It works on 5 volt DC and a mere 0.25 Amps.
I don't know when to use this L-Adapter or when to use your UltraBiB SSLV 1.3.

What are your thoughts to use one vs. the other?

Rush
Click to expand...
Its in the spec range of both. If opting for the Ubib it needs to be set at 0.35A constant current so to have 0.1A headroom for good Zout. In any case either L-A or Ubib are going to play a pre-regulator role and I am not sure how audibly better the Ubib can prove being a shunt and all that. In absolute terms being a fully fledged specialized reg it should have the performance edge when allowed to come through. Certainly hotter, but still manageable at this voltage and current range.
 
R

Robert2346

Member
Joined 2022
Salas said:
- We many times wonder what if that SMPS brick that feeds the Raspberry Pi or the mini PC or the MiniDSP or the Squeezebox or the DAC or the desktop Class-D amp etc. was a linear PSU? How such wonder boxes would perform without switching noise polluting their rail and most crucially their many times interconnected ground?

- What if we had a simple and strong linear PSU instead of fixed SMPS brick adapters that it could cover the voltage range for such applications by only setting it up with a jumper?

- Enter the L-Adapter. A versatile Sziklai pair stabilizer / capacitance multiplier based on LED voltage reference.

- Its output voltage is how many LED + trimmer minus one Vbe. Roughly 1.5V to 20V range. Move the jumper, trim Vout, ready. Connect the load.

- Is it any good? Yes its good. Not noisy at all and stable. For 1.5V input ripple it produces 1.5mV thick DC line. For 3 Ampere load it measures 0.02Ω output impedance. Which is flat and extended in frequency. When you pulse it the recovery is clean of ringing. Because there is no feedback between the output and the voltage reference. We want a general purpose PSU staying insensitive to random gear loading peculiarities.

- The recipe isn't anything new but the details are well researched. Low noise unity gain reference, but adjustable too. Which LED bar with which CCS experimentally chosen between many styles for very good Vref stability, what pair of transistors, the layout. Various ways to sink it, accepts quality TO-220 bridge diodes, two reservoir capacitors, fused like a Π filter. The board is 136mm x 63mm.

- What about its output current ability? Well, it uses a 15A audio amp grade TO-3P pass transistor. But that alone says nothing much. Its also the transformer the diodes the reservoirs the sinking the load's average consumption. Say up to 7.5A average can be catered for.

- For any light or heavy current application it takes that the chosen Tx the bridge diodes and the reservoir caps won't lose the plot for a target Vout. That's about rectification and filtering basics. It does not like less than 2.5V input-output voltage difference. That's the DC difference between C4 and the output. Can probe that between the fuse and V+ out. Or across D11. Although it keeps working on smaller differences it gets progressively goofy. If you see the LEDs dimming a bit its tell tale you crossed the raw DC section's losses good limit.

- Here is a schematic with typical reservoir caps values and some pictures. That soldering iron pulled 55W peak from the mains through the PSU to boot and idled at 12W. The scope pic displays Vin ripple on C4 vs Vout status captured at a point when the iron was still pulling hard to heat up started from room temperature cold state.

The Fluke reads C4's raw DC level in another picture. Started at 27V idle with worst loss of 4V during the soldering iron's boot cycle (trafo, diodes, rippleV). At 23V raw DC for 18V output to the iron, that trafo and reservoir caps passed the 2.5V Vin-Vout criterion by double margin. Other type & quality trafo or diodes could lose more or less steam of course. Higher value reservoir caps would achieve less ripple voltage but would also make the diodes work harder. Since the worst raw DC level sufficed, better not increase the caps value in this case.

The example has 4xMUR860 & 2x4700uF/35V B41231 EPCOS/TDK. Also a 38mm tall Q2's sink. Which sufficed due to the irregular current pull of the micro controlled soldering iron. Can it do an RPi3? Yes I tested it with Wi-Fi and streaming vids on the Raspbian OS. Can it do a 12V Windows 10 Cherry Trail mini PC? Yes I tested it. Watched a whole movie stored in a mechanical 2.5 inch USB Hard Disk attached to it. The PC was at the same time charging an OnePlus X phone from a spare USB output so I pushed it further. I now used lower voltage and smaller size transformers than that R-Core. EI or toroidal of average quality. They and the sinks sufficed again because of the irregular current pull of computers with idling gap periods. 45C on the 38mm 35C on the 25mm ones for the diodes. Minimal RPi use shouldn't need diode sinks at all.

- In the final black & gold boards there are actual Q1 Q2 designations. In the first photo of the green prototype you may spot Q3 Q4 instead. They are just a relic from an earlier schematic with extra parts due to various discrete CCS tests until ending up using IC1. Forget about those Q3 Q4 prototype marks.

- I will be editing & enhancing post #1 in later installments.

- 25/6/2019 Build guide added (includes circuit description & BOM) - attachments rearranged
Click to expand...
Hi there! Just became a member of this forum. HOW CAN I BUY THIS LPSU? I AM READY TO JOIN ANY GROUP BUY. Could someone please email me? Thanks
 
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