Built a custom D8B external power supply

[arjepsen]

Sure thing. I also plan to post complete instructions and pictures of everything when I am done with the project. Should be finished by the end of August.

Vellemen Kit K 8042 - I had to build these up and purchase the optional heat sync separately. You have to be careful, because the PC board is very cheap and if your soldering iron is too hot and is exposed to too much heat while your waiting for the solder to wick, it will pull the copper trace right off the board. I bought 2 and screwed one up so now have to buy another, but for $10 I am not too pissed!

Since using a +/- 22 VDC power supply, you will need to the heat sync.

I will also post info on the power supply from TRC Electronics. It is a bit more expensive than the TRACO TXL 035-1515D, but worth it to ditch the big ass transfer that was in the d8b.

https://www.eio.com/products/velleman-k ... gJVU_D_BwE

Just a few notes:
I'm looking over the schematic for that velleman kit - essentially it is the same as the +/-16V supply in the d8b.
You mention a +/- 22V DC supply for it, instead of the transformer - I don't think that'll work. The circuit is aimed at getting an AC supply, so I don't think you'll escape the transformer with it.
Please correct me if I have misunderstood something.

[RJH_MUSIC]

That is what I thought originally, but the input side is designed for vdc, not AC, if I understood you correctly. When I connected the TXL 035 1515D, (which puts out +/- 15 vdc, it stepped down to +/- 12. So I need the +/- 22 vdc power supply to make it work.

[arjepsen]

I'm actually sort of fairly certain that it's designed for AC input.
You can see it in the specs here: https://www.velleman.eu/products/view/?id=353668
Also, if you look at the schematic at page 11 on the instructions: https://www.velleman.eu/downloads/0/ill ... _k8042.pdf
You can see it's listed as AC input.
Yes, it's possible to supply it with DC, and get DC out, but it's kind of like trying to regulate a voltage that is already regulated... And like you describe, it wont get you the +/- 16V you need.
It's possible that you could get +/- 16V if you supplied it with 22V DC, but there's a couple of problems with that.
First of all - I haven't been able to find a +/- supply above 15V, that provided equal current high enough, for both the positive and negative rail. At least not in a size that makes it a viable option.
Also, the regulation circuit is "eating" some of the current, so you'd have to find a supply that is beefy enough to both supply the current for the desk itself on top of the current eaten by the regulation circuit.

I finaly got around to install the codec card that I got from Bruce Graham (THANKS Bruce!!!) - and the good news is that I now have sound coming out of my desk. The bad news is that it's only coming out on the right channel.... the left channel seems to be dead, so I guess there's even more fried circuitry in there. This is with the +/- 15V supply (TXL 035 1515D), so it seems that we can get sound with it - but I still think it isn't powerfull enough to supply all the current needed when using multiple channels and effects. I think I'm gonna try to use a dual 22V toroid tranformer, and then make my own small circuit board, with the same regulation circuit used in the original power supply. My biggest trouble is to figure out exactly how much power the transformer needs to be able to supply. (my brother did also give me a 160VA tranformer that should work, but I think it might be possible to use a smaller one)
The other option would be to make custom +/- 16V smps supply, but I don't know enough about them to do such a project. (at least not yet).

[RJH_MUSIC]

Take a look at figure 12. The ac mains are connected to transformers. The outputs to those are connected to the inputs of the velleme kit. The max input is 24vdc. If I understand correctly, you want to connect 110 ac directly to the inputs? I am thinking it will melt. If none of this works, the alternative is to use the parts from the original d8b and just replace the +5 power supply. After all, the vellemen kit is really a miniature linear power supply, it just doesn't handle the +48.

[arjepsen]

Take a look at figure 12. The ac mains are connected to transformers. The outputs to those are connected to the inputs of the velleme kit. The max input is 24vdc. If I understand correctly, you want to connect 110 ac directly to the inputs? I am thinking it will melt. If none of this works, the alternative is to use the parts from the original d8b and just replace the +5 power supply. After all, the vellemen kit is really a miniature linear power supply, it just doesn't handle the +48.

No, I definately don't want to connect the 110V mains directly to the input - unless I'm being in a destructive mood...
Figure 12 actually says: "Absolute max. AC input : 2 x 24VAC" (not dc).
The figure shows a transformer (actually it shows two variants - a regular one, and a "toroid" transformer above that one), so the transformer should have two secondary windings (the outputs) of maximum 24V AC each (under load - it will usually be higher when the transformer isn't connected to a load).
The velleman board could be seen as two seperate circuits: The first one is a rectifier that converts the 24V AC to a DC voltage. The second part is the circuit with the two regulators (LM317 & LM337), that outputs a nice stable +/- 16V DC.

Like I mentioned, you could hook a 22V DC supply to the inputs of the velleman board - but such a 22V DC supply would also be a combination of a rectification and regulation circuit - so it would be kind of redundant and a very inefficient way to end up with the +/- 16V.
You might actually simply use the regulation part of the circuit, to bring down the +/- 22VDC supply to 16V - but like I mentioned, that +/- 22V supply would have to be able to supply enough current on both the positive and negative rail.
As I mentioned, I haven't been able to find a +/- supply above +/- 15V, that can supply enough current like that.

So the more I look at it, the more it seems to me that the original circuit used might simply be the best option. The question is whether I can find a better transformer. I'd like it to be small of course, but it also have to be able to supply enough power, so I'm trying to figure out how much might be needed.

(I hope I'm not coming across as a wise-ass here... that's definately not my intention!!)

[doktor1360]

So the more I look at it, the more it seems to me that the original circuit used might simply be the best option. The question is whether I can find a better transformer. I'd like it to be small of course, but it also have to be able to supply enough power, so I'm trying to figure out how much might be needed.

(I hope I'm not coming across as a wise-ass here... that's definately not my intention!!)

Ideally, perhaps getting one wound to the proper spec(s) - mercury mags will do it for ya, but most likely won't be all that cheap... but it'll be damn good. You'd have to place a courtesy call to see if it's in your budget, they'll do it I just haven't a clue what it'll cost in the end. I'm sure there are other vendors available that'll wind you some iron, you'd just have to go about the due diligence...

At any rate, just payin' it forward : https://www.mercurymagnetics.com/commercial-industrial/

You knew it was coming, so here it is:
[Standard Mgmt Disclaimer] - "Your actual mileage may vary..."

[RJH_MUSIC]

LOL.... No, not at all being a wise-ass. I am soaking up all this info... since I am not an engineer, I am going off my memory of what my father taught me years ago. So the more the better. I did find a +/- 22 DVC power supply from TRC. waiting for it to be delivered. I will post the part # when I get home tonight. Interesting I had the same thought, of just replacing the huge heavy transformer in the d8b with a newer smaller one. and using the original Linear Power supply board. I even emailed Electronetics, the company that made them to find out what the specs were, but they are so old, they could not find the model # in their database. I ohmed out the huge thing and it puts our several voltages. the two red wires put out 60 vdc. I thought it would be +48 vdc but it was not.

[arjepsen]

LOL.... No, not at all being a wise-ass. I am soaking up all this info... since I am not an engineer, I am going off my memory of what my father taught me years ago. So the more the better. I did find a +/- 22 DVC power supply from TRC. waiting for it to be delivered. I will post the part # when I get home tonight. Interesting I had the same thought, of just replacing the huge heavy transformer in the d8b with a newer smaller one. and using the original Linear Power supply board. I even emailed Electronetics, the company that made them to find out what the specs were, but they are so old, they could not find the model # in their database. I ohmed out the huge thing and it puts our several voltages. the two red wires put out 60 vdc. I thought it would be +48 vdc but it was not.

Haha - I very much did the same thing
Today I put a scope on the transformer - weirdly the voltages doesn't change much between being loaded and not being connected...
It seems to have an amplitude of a little under 30V. I think a transformer rated for 22V output (under load) will work.
The tricky part is as described how much current it should be able to provide. There's a hint there, since there is a 3.15A fuse on each line, so I'm guessing: 30 * 3.15 = 94,5 VA rating for EACH line. That's like almost 200VA total.... wow - that's a bit big.... My twin brother gave me an old 2 * 22V 160VA toroid made by Talema - I might try to use that one and hope it can handle it. It actually isn't all that much smaller that the original trafo - just a flatter...

[arjepsen]

btw, what are the exact specs on that supply you found? You may want to check how much current each rail can handle - most supplies seem to have a quite lower rating for the negative rail!

[arjepsen]

Hmm.... I just looked over the datasheet for the +/- 15V supply we've messed with so far - it actually can provide up to 1.5A on the negative rail, and 2.4 on the positive. This might actually be enough...
Yes it isn't 16V, but last I measured the original supply, it actually didn't reach 16V either....