Reducing Voltage in a safe way.

[darkm4n]

I'am not intersteed in modifing the kit board , i'am interested in a simple voltage reg for 40 V or what resistors i have to add on the 55 + 55 - rails to decreas at 40 V + and 40 V - , i assume the resistors should have a big wattage but .. i don't know the value and wattage .

Thanks

[millwood]

Originally posted by darkm4n
i'am interested in a simple voltage reg for 40 V or what resistors i have to add on the 55 + 55 - rails to decreas at 40 V + and 40 V - , i assume the resistors should have a big wattage but .. i don't know the value and wattage .

Thanks

I doubt you will be successful with resistors. The current drain from the PS will be dependent on output power (which fluctuates a lot). Using resistors essentially turns a good PS in to a very bad PS.

As to regulated power supply, a linear regulated PS will require a lot of heatsinking in this case (think about how to dissipate 7ax15v), and as will most regulated power supplies, transient responsess suffer big time.

One (far less than optimal or even desirable) is to use a switching supply for this. I am not aware of one off-the-shelf product to handle your situation but I am sure you can get a switching controller and stack a mosfet to it to make it work. Alternatively, you can build one. One idea is to use a mosfet as a switch to charge up (or cut off as the situation maybe) the output rail. but I haven't sketched out it.

If you don't want to touch the amp, your best bet is to get another transformer.

[darkm4n]

What is the required wattage for the resistors ?

[Christer]

Resistors won't work unless your load has a constant current
consumption, since the voltage drop over the resistors will
vary with the current according to Ohms law. I understand
the kit is a power amp, so presumably you don't really need
a regulated supply. The simplest solution then is probably
to use an emitter follower to drop the voltage and use a
zener diode to set the output voltage.

Anyway, whatever method you use, you will have to drop
15V, which means you must disspate 15W per Ampére. Are
you sure you want to do that? For high power the best
solution is to get another transformer that has the correct
voltage.

[darkm4n]

Is there any chanse with a voltage regulator , from 60 V to 40 V ?? There is one scheme on page 1 , what is you opinion ??

[markp]

The schematic I posted is the best I've found for high current and high voltage regulation. If you can't find the 1k trim pot I would hestitate to build any high power project though. These are deadly power levels!

The 350w is obtained by bridging the two channels of the amp. I still think it is on the optomistic side! Remember to use only 8 ohm speakers as a bridged amp see it like a 4 ohm load.

[darkm4n]

That 1 K trim pot it's a simple pot , but it's small , right ?
Like this one ? http://www.vitacom.ro/pictures/cerm.jpg

On .. how many amp's can handle that voltage reg ?

[markp]

Originally posted by darkm4n
That 1 K trim pot it's a simple pot , but it's small , right ?
Like this one ? http://www.vitacom.ro/pictures/cerm.jpg

On .. how many amp's can handle that voltage reg ?

Use one of the little square ones and single turn is just fine. 1/2 watt is plenty.It can handle about 10 amps(very conservative) for each output transistor used. Just use as many as you would like.

[peranders]

darkm4n, forget all about voltage regulators.

You have these options:

1 Analyze the amp if it's possible to use it at +- 50 V (maybe with modifications). 50 volts aren't very high so I see not so big problems to make it work at this not very high voltage.

2 Change transformer

3 Choose an another amp or amp design

[janneman]

Originally posted by Christer
Resistors won't work unless your load has a constant current
consumption, since the voltage drop over the resistors will
vary with the current according to Ohms law. I understand
the kit is a power amp, so presumably you don't really need
a regulated supply. The simplest solution then is probably
to use an emitter follower to drop the voltage and use a
zener diode to set the output voltage.

Anyway, whatever method you use, you will have to drop
15V, which means you must disspate 15W per Ampére. Are
you sure you want to do that? For high power the best
solution is to get another transformer that has the correct
voltage.

darkm4n,

If this is a toroid xformer, wind some wire on it, and put that in series with the primary. Depending on the phase, you either get MORE or you get LESS sec voltage. Test is with the bare xformer, not connected to anything on the sec side. Make sure you use isolating tape before and between windings. Start with say 20 windings to determine the amount you need. After you're done, isolate it again, this is mains live voltage.

Now, this is possible, but with all due respect, following this thread, you need to decide whether you are really ready to tackle a high-power bridged amplifier. I would advise you something less powerfull and less complex. Why not try one of the ZENs? There are many people doing that so you will have expert advise at every step.

Jan Didden