MagnumOpus & The B1

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M

MagnumOpus

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Joined 2011
I am trying to figure out how to choose a power transformer.
I have ordered the Velleman K1823 for regulation and the datasheet states that to get an output of 18-22vdc I need a 50va 24vac transformer. Seems odd since I've seen others use 15va 9vdc x 2...is there any kind of formulae to calculate the desired transformer according to the vdc you need?

http://www.vellemanusa.com/downloads/0/illustrated/illustrated_assembly_manual_k1823_rev3.pdf

Edit: I had sourced a power inlet somewhat locally (Inside Norway, atleast :) ), but then I see this: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=817-1599-ND

Any reason I shouldn't use this? I'd prefer this over the other because of the filter...
 
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6L6

6L6

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AC volts multiplied by 1.4
Then subtract 1 volt for diode drop
will give you DC at the rectifier.

A 9+9 transformer with secondaries in series will give 18AC

18*1.4 = 25.2v

25.2-1 = 24.2v DC at the inlet of the regulator.

The Velleman regulator uses a normal LM317 circuit which needs about 2 volts input more than output, meaning that you should have a good adjustable range of about 18-22volts, perfect for a B1
 
M

MagnumOpus

Member
Joined 2011
6L6 said:
AC volts multiplied by 1.4
Then subtract 1 volt for diode drop
will give you DC at the rectifier.

A 9+9 transformer with secondaries in series will give 18AC

18*1.4 = 25.2v

25.2-1 = 24.2v DC at the inlet of the regulator.

The Velleman regulator uses a normal LM317 circuit which needs about 2 volts input more than output, meaning that you should have a good adjustable range of about 18-22volts, perfect for a B1
Click to expand...

Thank you! But what about the VA, 15, 20, 30 or 50? Whats the difference?
 
M

MagnumOpus

Member
Joined 2011
Ok. I am about to order some missing stuff. Can someone please confirm somethings for me, so I don't make any more mistakes?

Transformer: 20va 2x24.

PEC pot: If I decide on dual mono's do i go with log or linear?

Fuse for power entry module? I have this one at hand: Digi-Key - CCM1822-ND (Manufacturer - PS0S0S000)

I will either use this (if I can figure out how to hook it up)
or another one without power switch, that one also with fuse holder up to 10A.

What type fuse do I need?
 
6L6

6L6

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Transformer - 24v is much too high. Get something around 18v, Dual or single secondary. 20VA is fine.

PEC - Log is probably better, but if you can't get them, linear will be ok.

The power entry is nice!

Fuse - 1/2A fast will be good. "The fuse holder can hold two 1/4” x 1-1/4” (3AG) or 5 x 20mm (metric) fuses." (from the datasheet) It also goes on saying that there is a shorting clip to make it use only one fuse.
 
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A

AndrewT

R.I.P.
Joined 2004
The transformer for Salas type shunt regulator should be 15+15Vac for a +-10Vdc supply.
24+24Vac will give a very high voltage across the smoothing capacitance.

The fuse for 20VA transformer is roughly 3 * 20VA / Mains Power supply voltage
115Vac 20VA requires a fuse >=T500mA.

20VA 15+15Vac will allow 2/3Aac from each secondary.
The maximum continuous DC current available from that transformer feeding a capacitor input filter is ~1/3Adc.
I and a few others recommend that for cooler running the continuous DC current should be reduced to ~50% of the maximum rating, i.e. 1/6Adc or ~160mAdc continuous from each winding.
 
6L6

6L6

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AndrewT - He is not using a shunt reg, but a LM317 connected as in it's datasheet. I don't know if that is much different that the shunt reg, but it does mean that he is aiming for 18-20vdc as a supply voltage, to power the stock B1.

Also, he being in Norway, he has 240v mains. Does that change the fusing requirements?
 
A

AndrewT

R.I.P.
Joined 2004
for normal regulator that can work effectively with a lower input to output voltage overhead, the standard advice is select a transformer Vac to match the output DC voltage. For +-10Vdc select 10+10 or 12+12Vac. At higher DC voltages the transformer can be voltage downrated by 5 to 10%. At lower DC voltages the rectifier drop becomes significant and the transformer voltage needs to be increased by 1 to 2Vac, i.e. for +-6.3Vdc use 7Vac or 8Vac.

BUT YOU MUST calculate the heat dissipation requirements when mains voltage is at maximum tolerance.
You may have to check that ripple voltage does not allow the regulator to "drop out" when mains voltage is at lowest tolerance and load is drawing maximum current.

The stock B1 is powered by a single ended/polarity supply of 18Vdc.
This needs a single 18Vac transformer or a 9+9Vac transformer for a regulated 18Vdc.

Yes, a 220/240Vac supply has a different fusing requirement from a 110/120Vac supply.
 
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M

MagnumOpus

Member
Joined 2011
6L6 said:
Also, he being in Norway, he has 240v mains. Does that change the fusing requirements?
Click to expand...

230v mains.

Using the Velleman K1823 reg.


Ok, getting 10pcs of 5x20mm 0.5A fastblow fuses.

20va 18vacx2 in the shoppingbasket :)

Also, I am still not sure about using a toroid, and have found a wallwart (18vdc) but all the connection jacks I can find is rated 12vdc, I don't get it..can I use this?
 
M

MagnumOpus

Member
Joined 2011
There, finally decided on what to order..man, I can be indecisive sometimes, but this is too much :)

I went for the dual mono pots (going against what was previously "decided"). Figured I wanted to try something new.

Found som nice knobs from Kilo International too: Digi-Key - 226-2002-ND (Manufacturer - ML-90-1-5)

I got some parts for a JDS Cmoy also. Gotta have something to do, while I decide on transformer power or wallwart :D

Thank you again, 6L6, Andrew T, Aurora B, Marra and everyone else who has helped me through these headaches :)

I am learning something everytime you answer my questions, and you answer everything. Awesome, just awesome.

I think I am starting to understand. ( I am slow learner when it comes to stuff like this)

But is alot of fun. Except part sourcing, thats a major pain....

So, now all I need is the rest of the psu and a chassis + some rca's and hookup wire:D
 
A

AndrewT

R.I.P.
Joined 2004
before you put in the 4 "amplifier" jFETs, power up and check the input and output voltages of the regulators.
Check the voltage going to the coil of the delay/muting relay.
When you are satisfied these are correct, then fit the last 4 jFETs.
Power up and (set to mVdc) check output offset. Set to mVac and check output noise.

Connect your source/s and check if the noise on the output has changed.
 
M

MagnumOpus

Member
Joined 2011
Got mail from Digikey today, so I'll be putting together the JDS Cmoy and the rest of the B1, less the chassis and plugs. The volume knobs were abit smaller than I imagined, but will hav to do.

Been looking at other options for an amp also, since there might be some difficulty sourcing the F5 boards... There really are to many to choose from. The Beta 22 in power amp config looks good. The Audiosector kits also. The Beta24 is a monster and look way to complex....
 
M

MagnumOpus

Member
Joined 2011
6L6 said:
Problems getting F5 boards? Just get the ones from Peter Daniel/Audiosector. It's a great amp.
Click to expand...

I beleive I mailed him about that a while ago, and he said (though I might remember wrong) that he only had the psu boards left in singles...

I could always get the ebay ones though, but goes heavily against my morals to buy those. I'll ask around in the sales/swap section and the diy forums in Norway, perhaps someone have a spare set.
 
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