Regulated +80V Supply ....

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#2
Looking at your other thread I'm assuming the 80 volts regulated is at very low current ?

If so a simple zener regulator is ideal (3 series connected 27 volts zeners) fed via a resistor. A small cap is placed across the three zeners to maintain a low impedance clean supply. The resistor value is calculated by knowing the voltage feeding the chain (which has to be higher than 80 volts) and the max current the regulator has to supply.
 
#3
Mooly said:
Looking at your other thread I'm assuming the 80 volts regulated is at very low current ?

If so a simple zener regulator is ideal (3 series connected 27 volts zeners) fed via a resistor. A small cap is placed across the three zeners to maintain a low impedance clean supply. The resistor value is calculated by knowing the voltage feeding the chain (which has to be higher than 80 volts) and the max current the regulator has to supply.
Click to expand...

Yes I think so, it's at ver low current as it is to supply the VAS. Can I found somewhere a principal schematic?

Or does it makes sense to use a regulater like the LM317 ...?
 
#6
Like this. Resistor is calculated with ohms law to allow a few millamps to flow in the zeners.

eg, 100 volt unregulated. R=V/I so R=(100-81)/0.01 which is 1900 ohms. Use 1800 ohms as preferred value.

So that allows 10ma to flow in the zeners. The load (the amp) draws from that 10ma. If the load were 5ma then the zener current would reduce to 5ma with the above values. Always allow at least around 5 ma to flow in the zeners at all times.
 

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#8
The zener type shunt regulator takes some beating with its low output impedance. I think they will give the cleanest possible supply.

The TL783 is an interesting choice but not without precautions. This type of regulator needs a minimum load applied at all times in the region of 15 ma (absolute minimum) so that could make it more inefficient than the zeners.
 
#10
I was just looking at the circuit for the Nytech.

There's nothing to stop you using a "double" zener regulator. Use an 80 volt one as mentioned and add a 50 volt one for the bias network fed from the 80 volt one.
 
#11
Something like this.

The important question is, what is the regulated 80 fed from ? In other words how much headroom is there as the 80 volt regulated must start out as something higher than 80 volts and that really determines the value of the resistors used. R6 would need to be lowered slightly to allow for the zener current. The zeners can be any values that add together to give the required voltages. Depends what is available.
 

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#12
Mooly said:
Something like this.

The important question is, what is the regulated 80 fed from ? In other words how much headroom is there as the 80 volt regulated must start out as something higher than 80 volts and that really determines the value of the resistors used. R6 would need to be lowered slightly to allow for the zener current. The zeners can be any values that add together to give the required voltages. Depends what is available.
Click to expand...


Hi Mooly,

thanks for your tips. My idea is, not to change the the schematic of the 602 in the first step. I want to setup a PSU with a regulated and an unregulated +80V supply.

I'll use 120VA Toroids with 58V / 0V. This will result in 83.5V ...... Each chanel will get one Toroid. The PSU-Board I will prepare is a dual rail design.

Even if it is a little bit small, there is enough place for some Zener and 2 small caps.

Have a look: http://www.diyaudio.com/forums/solid-state/214899-diy-project-nytech-cpa602-today.html#post3093309

What is your proposal for the rectifier diodes? The idea was to use good old 1N5404 ..... or better MUR XXX?

Ingo
 
#13
If using 1N5404's I would add a small snubber (say 3.9 ohm 1watt carbon or metal film and a 0.1uf in series across each secondary winding close to the diodes).

There are many newer types of diode (FRED... fast recovery epitaxial) but I don't know any device numbers from memory for those.

Only having around 83 volts (from the 58 Vac tranny) could be a problem. That supply (I take it it feeds the main amp too) will dip under load and the differential between 83 and 80 volts isn't enough for "safe" design with the zeners. The resistor feeding the zeners would be low value (say 250 ohm). If the supply dips a little the zener current drops and may even drop out of regulation. If it goes high (mains on a good day, say giving 87 volts) then the zener current will increase to around 25 ma.
 
#14
We are just sitting togehter to discuss the idea.

Our solution is to change the regulated path to 54V and adapt at least the resistors in the VAS to get the right bias.

So there is enough difference between regulated and unregulated voltage for the zeners.

Are the diodes MUR860 ok for the PSU?
 
#15
The data sheet shows they should be OK.

You would have to draw out what you propose regarding the VAS and resistors.

If you can not get enough differential then another possiblity is to keep the second zener option that I showed (the zeners across C2) and replace "R" (the unmarked resistor I drew) feeding the chain with a normal diode to help isolate the stage from variations in the supply feeding it. The voltage across C6 would then be fairly constant and not pulled down as the supply dips momentarily.

Note... the two zeners I mentioned and where I said "add a 50 volt one for the bias network". You would need to measure the voltage at that point first to determine the zener required. The 50 volts I mentioned was from looking at the "50V" marked on the circuit but I think that refers to the voltage rating of the cap... it's just written a long way from it 🙂
 
#18
The early AKSA used a diode a resistor (100R as far as I can remember) and a cap to "decouple" the supply from the main voltage. As the absolute voltage is not so important here as long it is near 80V, I think this could probably be a first step here (for your Nytechs), you could add the zeners maybe later?
 
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#19
lohk said:
The early AKSA used a diode a resistor (100R as far as I can remember) and a cap to "decouple" the supply from the main voltage. As the absolute voltage is not so important here as long it is near 80V, I think this could probably be a first step here (for your Nytechs), you could add the zeners maybe later?
Click to expand...


Good Morning lohk,
I remember this proposal from our discussions. How would it look like? 😕 It can be realized with the same PCB as we need for the Zeners, or?
Maybe you make a small sketch for the "mechanical Ing" ...
Regards
Ingo
 
#20
NRWler04 said:
Please see the updated schematic for the PSU with regulated and unregulated +80V Rail ....
Please give me your comments ....
Click to expand...

Basically OK but the concern over headroom for the regulated supply remains.

The maths says that 58 volt AC will give 82 volts DC (and we haven't considered rectifier losses in that). In practice a 58 volt tranny may give nearer 60 or 65 volts when lightly loaded. What happens when heavily loaded ? It also should work reliably under all possible mains voltage tolerances.

A couple of options...

You could lower the regulated supply to say 75 volts or even a little lower. Although that would slightly lower the maximum output swing it would have little impact in practice.

Another option is to use a simple voltage doubler to generate a high voltage rail and then zener regulate that to 80 volts. Two caps and two diodes are the only extra parts.

The resistor feeding the LED may be to low. High brightness LED's only need a milliamp or less.
 
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