board power supply question

  • Thread starter Thread starter Foamfoot
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Foamfoot

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Hey ya'll,
As I mentioned on a couple of other threads I have a carvin mx1688 mixing board. It works pretty well for me, although the transformer has an anoying hum to it (transformer and rest of power supply are internal). I tightened all the screws that mount transformer and tighten bolts on transformer itself. It did help a little. I also replaced all the caps in the power supply section.

I remember Jim Williams or someone commenting on these Carvin boards on a forum one time and he said the power supplies in the Carvin boards are almost like toys. Don't remember for sure who said that but whoever it was suggested to get a beefier external supply.

Now, the other day I was at a friends house and he gave me a Fender Power Supply for a Fender Mixing Board (external supply-cpsm-4). I think it goes to a Fender board like a m-5200 or something like that. Anyway, this ps is definately beefier and when I turn it on it is dead quiet.

Here's my question. The carvin calls for +15/-15 vdc. When I measure off of the Fender ps it is putting out about +17/-17 vdc. Is this too much of a difference? Also, for the supply for phantom pwr even on the supply itself on it says it puts out 48v (normal), but when I measure off of that particular leg off the pwr supply I get about 58.6 vdc. (????)

I would like to use this pwr supply (cause it's beefier and quiet) but not at the expense of blowing my board or some mics. Any help/info would be appreiciated.

Let me know if I need to post this somewhere else. Just thought I would start here.

Thanks for any input.
 
Those voltages might drop once a normal load is put on it but you'd have to know what the current draw is from the boards circuitry to simulate an equivalent dummy load to retest the voltages with.

Cheers! :)
 
You could start from scratch and build your self an outboard power supply for your carvin. You sound bright enough to get the job done.
 
The Ghost of FM said:
Those voltages might drop once a normal load is put on it but you'd have to know what the current draw is from the boards circuitry to simulate an equivalent dummy load to retest the voltages with.

Cheers! :)
Click to expand...

That's probably a good idea. I was just wondering how tight the tolerances were. You know, if a few volts either way would make or break the deal.
 
moresound said:
You could start from scratch and build your self an outboard power supply for your carvin. You sound bright enough to get the job done.
Click to expand...

Well.......I probably know just enough to screw something up good. The Fender Pwr supply seemed like a quick, easy fix. Then again, those quick easy fixes usually don't turn out that way, do they? Thanks for the reply.
 
If only the transformer is humming the internal leaves may have lost the dipping resin from age and they are vibrating. Make sure it's that, and maybe you can easily replace just the transformer.

For a long time I made audio transformers for Klipsch audio. They were used in their crossover networks. We used an advanced resin to prevent leaf vibration which would occur if a Klipsch speaker (prior to our product supply to them) was overpowered.

As Jeff said loads reduce the voltage to the useful levels. Get the current draw and you may be able to use that transformer.
 
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Foamfoot said:
That's probably a good idea. I was just wondering how tight the tolerances were. You know, if a few volts either way would make or break the deal.
Click to expand...

A couple of volts up or down shouldn't be disastrous but the over voltage on the phantom power supply is worrying to me. Beyond that, I don't know if replacing the entire power supply based on someone's subjective opinion that the original design was a cheap one might not be something to take as absolute gospel. After all, the unit is what, 30 years old and it's still working! If the design was as pathetic as described, would it have lasted this long? Replacing the transformer I could maybe see doing if the hum/vibration is bothering you but changing everything without hard proof of the need to do so seems a bit much.

Cheers! :)
 
GCalo said:
If only the transformer is humming the internal leaves may have lost the dipping resin from age and they are vibrating. Make sure it's that, and maybe you can easily replace just the transformer.

For a long time I made audio transformers for Klipsch audio. They were used in their crossover networks. We used an advanced resin to prevent leaf vibration which would occur if a Klipsch speaker (prior to our product supply to them) was overpowered.

As Jeff said loads reduce the voltage to the useful levels. Get the current draw and you may eb able to use that transformer.
Click to expand...

That sounds like (leaves vibrating) exactly what is happening. Tightening helped but I guess you can only go so far. Thanks for the info.
Will the vibration make the transformer eventually fail or is it harmless, other than annoying?
 
I'm not sure if it's actually harmful but I suppose if it vibrated hard enough and long enough, it might wear the insulation down to the point where the coil would short. But that could be a factor of years to make it do that.

Cheers! :)
 
It is harmless. Just a result of electrical current passing through it for a long time and the heat degrading the resin.

EDCOR may have a suitable replacement. If you sent that unit to them I am sure they could easily duplicate it.

I have a link for another good transformer maker I will have to find.
 
The Ghost of FM said:
A couple of volts up or down shouldn't be disastrous but the over voltage on the phantom power supply is worrying to me. Beyond that, I don't know if replacing the entire power supply based on someone's subjective opinion that the original design was a cheap one might not be something to take as absolute gospel. After all, the unit is what, 30 years old and it's still working! If the design was as pathetic as described, would it have lasted this long? Replacing the transformer I could maybe see doing if the hum/vibration is bothering you but changing everything without hard proof of the need to do so seems a bit much.

Cheers! :)
Click to expand...

Point taken!! I think you are right. I think I'll try to find another transformer. The board seems to work fine. It's just that hum can get a little anoying at times. Don't it hear when music is playing. Hey, I just answered myself. Play more music and hum is gone!!!

Thanks guys. I really appreciate your input.
 
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