9K PSU transformer question/problem

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Rob Flinn

Well-known member
Joined
Jun 3, 2004
Messages
5,207
Location
Between Sussex, UK & Aude, France.
I just got my pair of 9k`s running. Very nice sound !

However, I have a slight problem. I`m using a 0-18v, 0-18v 15VA torroidal transformer, & its getting hot. How hot you ask ? Too hot to touch is the answer.

Now I guess it 7.5VA per winding, which to me means it should be able to supply 416mA per winding. With the number & type of chips on the 2 boards I`m surprised at the current draw. Its not a problem to stick a bigger transformer in there, but I just want to check if this sounds right or whether I`ve got a problem.
 
Great rob... yeah... 9k sounds really good...
No trafo problems here... i've used a toroidal 30V...
But i've powered only 1 preamp at time... just to test them...

I have a strange hum (pre are mounted on a alu plate at the moment) around 160-300HZ... it doesn't seem to be a trafo related problem...

Maybe just a ground problem...

P.S.: if i disconnect everything from the input, i have no noise at all !

Have you some hum on yours ??
 
Neeno

I have no hum problems here. I only connected the + & - PSU rails to the boards & connected the zero through the star ground (near input sockets). The star ground is then connected to the boards via the input sockets. This seems to work well.
 
I'm a little concerned about this too, having bought one of those neat (but small) Canford torroids with a 48v winding in addition to the +-15.

Not sure what to make of it but the MAT02 spec says absolute maximum power dissipation is 1.5 W (and assuming 40V accross it)
each of the 5 5534s max is about (guess)300mW (given15V each rail and 10mA)
say the same for the 052
then another two 5534s on your balancer card.
Thats (an unlikely looking)3.9 W per channel, so depending on how bad my 5534 guess was, that would make it pretty warm, but not dangerously. What happens to the current without the Mat02 ?

I'm still waiting for mine from Analogue :sad:
 
Thing is it`s not just the pull from the semiconductors but also what the regulators are burning up as well

I thought about this & realised I`m talking bollocks.

Most of the current drawn by the regs does go through the circuit & very little current goes through the reference leg of the regulator.
 
> I'm using a 0-18v, 0-18v 15VA torroidal transformer, & its getting hot. How hot you ask? Too hot to touch is the answer.

Disconnect the rectifier and let it cook an hour. Does it still get hot?

Small power transformer design is a lot about cheap. One way to be cheap is low primary inductance, which passes a lot of line current, and heats the winding even if you are not drawing any power out.

"Too hot to touch" is too-hot, in my humble opinion. But insulation has got a lot better since the days we used ground up bugs dissolved in gin. Modern poly-whatever insulation will stand heat your finger won't take.

> MAT02 spec says absolute maximum power dissipation is 1.5 W

You never want to run a low-noise device anywhere near its rating.

Mike-input transistors more often run 1mA to 3mA and 6V to 18V across them: 0.006W to 0.054W each, only 0.1 Watts per can. That's not where the power is going.

So you are looking at about 55mA or 1.7 Watts per channel. 2 channels? 110mA or 3.4 Watts.

> 0-18v, 0-18v 15VA ... I guess it 7.5VA per winding, which to me means it should be able to supply 416mA per winding.

0.416A AC. Safe DC current is about half that, say 200mA.

So right here, we see the transformer is working a hair over half its rating. It isn't load power that is heating it.

> also what the regulators are burning up as well. very little current goes through the reference leg of the regulator.

I don't have specs handy but ref current is like 0.015 Watts. Skip it.

The regulators DO "burn" the difference between the raw 18V*1.414= 25VDC and the 15VDC output. 25V-15V= 10V, 10V times 110mA is 1.1 Watts in each regulator.
 
I got my caps from about 3 different suppliers in the UK over a period of about 6 months, so its difficult to say which ones came from where. I did manage to put plastic caps in most places, but in some instants this requires an extra hole being drilled in the boards to accomodate component lead pitches that were realistic. Some of the component values seem to be impossible to get with the pitches that are on the board.

I`m just off out to dinner with my Mum & bro but I can try to take a picture when I get back, so you can see the caps to give you an idea of what I used.
 
Heres a couple of pics. I used an old computer hub box with a new 19" panel bolted on the front.
ssl%209k.jpg

ssl%209k%202.jpg
 
What's everyone doing with the 15volts if +-18 is your only main supply? Regulator, voltage divider? Also, is there any way to get the file for the pcb because I looking for a different pcb with different dimensions and the power/input/output pins on one side for my application?
 
If you look in my pictures you can see that I just used 2 of the PSU boards.

The right hand board in pics does +-18v & 48v. The left hand board does +-15v, & I used the other 48v slot on this board to make a +12v supply(using an extra mains transformer & 7812). This is because my phantom & phase are switched using 12v relays. These are mounted in the back of the case next to the XLR sockets on a piece of veroboard. The 12v is a bit of a kludge & the regulator goes in back to front with the pins bent about, but it works ! The 7812 needs a heatsink if all relays are energised at once.
 
I'm trying to put inside a console that has +-18volts and 48v at the connector but no 15volts. Also, is it possible to receive the pcb file to resize pcb and change pin location? :green:
 
If you`re not installing too many 9K boards you could make a small pcb that would regulate the +-18v down to +-15v with 7815 & 7915 regulators. With my 2 channels the 15v regulators do get warm but not excessively, so if your supplying 40 channels for your home built large frame consul you will have to work out an alternative regulator. The LM388K springs to mind.

I bought my boards from Gustav & he supplied a PSU board with each 9K board, so I had the required boards to do what I needed.

I think you can get the PCB files for the PSU but I`m not quite sure where they are, Maybe someone else can help with that information.
 
Sorry if I've missed something here, but why do you need to drop the +-18V supplies down to +-15V supplies for the 9K?

Both the output balance PCB and Main PCB's have +-18V..... Is this incorrect?

Thanks,

Steve.
 
not to hijack but,
how many 9k channels can be powered by 1 psu board? i was hoping i could use one of the 9k psu boards to power a Green pre.
thanks
 
blade sg, 5 seperate voltages are required; plus and minus 18V for the NE5534s and Mat02, plus and minus 15V for the TLO52 and 48 for the phantom.
 
Thanks Jonathan. Is it OK (I think this is what Rob is referring to?) to use the 2nd PSU PCB with 7815 and 7915 regulators to supply the TL052 IC's?

If so does this PSU PCB need to be modified at all other than the Regulators for +-15VDC?

Thanks,

Steve.
 
[quote author="Jonathan Hayward"]
then another two 5534s on your balancer card.
[/quote]

Is this a typo......? I thought they had to be SSM2142 IC's here or do the 5534's work here?

Thanks,

Steve.
 
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