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Old 23rd August 2005, 07:06 PM   #11
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2 more N-channel MOSFET designs

Read the whole thread. Quasi may have made updates to those schematics in later posts.

He considers this to be his better design:
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Old 23rd August 2005, 07:21 PM   #12
cd-i is offline cd-i  Romania
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i know that i can't use the IRF's directly on the asp101 project. That's why i like the idea of building the creek amp

I am not so good in analog audio to modify an audio amplifier and get some performances too....

That's why i prefer to build one that is designed by somebody else and is tested.

Because blowing transistors is not funny at all and after some "sparks" it's becoming frustrating....
....I hope this thing works better than it looks....
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Old 23rd August 2005, 07:40 PM   #13
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That K6 SMPS is awesome. The price is too high for me, though.
Will you buy it, or build from schematic?

I'm using some Lambda 160W 50-0-50V 2A SMPS's to power an amp I'm working on. I'm getting these surplus for $25. Two of them in parallel, per amp. It's hard to find surplus SMPS's with useful voltages, so when I see them, I pounce.

I'm glad to see other diy-ers considering an SMPS for audio amps. I find they're such an elegant solution.

You just need to be careful with any load that may draw current peaks much higher than avarage current. A short 10A transient from a 5A X-former may dip the rail, often causing some clipping, but nothing more than that.

The same situation on an SMPS may cuse a dip in its auxiliary supply winding, which powers the primary side controller. Controllers sensing an under-voltage condition typically shut down the PWM until their supply returns to normal. The controller may wait up to a second before re-powering the primary.
Or it may go into reset, taking power from the mains resistor divider, then going through the soft-start sequence (2-3 seconds).

This can mean some gaps of silence in the middle of your music. Your guests may laugh at you, and refuse to attend your parties in the future.

I would modify any SMPS I use for audio to take it's controller supply from outside the SMPS, say from a separate, small 12V 100mA transformer/rectifier/filter cap supply.

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Old 23rd August 2005, 08:50 PM   #14
cd-i is offline cd-i  Romania
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yes indeed the k6 power supply is very well build. I payed some attention to that schematic and i'm pretty sure that you don't have to worry about that silence in your audio program because the supply is build around SG3525 controller which is a current controller which means that the end of a conducting pulse for a diagonal of the bridge is given by the current thru the primary winding of the transformer. The conducting cycle is initiated by the oscillator. Anyway you can find details about this controller in the datasheet. And as you said the controler is powered from a separate power supply. So the only effect that i see from the schematic is a drop on the output voltage. The regulation is somehow applied to both rails in this way the unbalance in supply voltage is avoided.

And to answer to your question, I intend to build that power supply from the schematic... beacuse it's very well documentedand i have the original layout which is essential in SMPS design. If you take a look at the schematic you will see that the number of turns of the transformers are noted. And the rest is like building a kit....

but in order to be able to use that power supply i need to build an amplifier. And if i find the right amplifier for my design and measure it's power requirements i will build that power supply.
....I hope this thing works better than it looks....
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Old 23rd August 2005, 10:00 PM   #15
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Duuh.. I'm a dog.

I didn't look closely at the schematic for the K6.

It does have a dedicated controller supply.
All the inductor turns, and even the ferrite core type is specified! It's the first time I see this on a schematic. These guys must have lost their freakin' minds!

OK, I think I'm gonna build this thing.

The surplus supplies I've been fiddling with are forward converter topologies, and are prone to occasional UVLO shutdowns, but the K6 is much better designed.

There's nothing like a full bridge to make a man feel like a king!

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Old 24th August 2005, 01:04 AM   #16
tlf9999 is offline tlf9999  United States
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Originally posted by funberry

my (highly subjective) observations on the design:

a) the VAS load during the + and - cycles is not symmetric: during the positive cycles, Q4 sees a Vbe (Q7) and Vgs(Q9. for now, assumes just one pair of output devices, Q9+Q12). during the negative cycle, Q4 sees just a Vbe (Q8).

What I usually do in cases like this is to use a resistor on the emitter of Q8 to reflect the Vgs of Q12. The resistor will be of the same value of the collector resistor on Q8. as Ic ~= Ie of Q8, the voltage drop off that emitter resistor will be very close to the voltage drop off the collector resistor which is identical to Vgs. That way, the Vgs of Q12 is "reflected" on the emitter resistor and Q4 sees both Vbe (of Q8) and Vgs (of Q12).

b) I am not quite sure the purposes for those two 100pf capacitors on b and e of Q7 and Q8.

c) I still don't like the idea of having two different rails. the amp will perform identically in sonic had you had one rail at the higher voltage. it will just be less efficient (big deal).

d) I acutally prefer current mirrors over CCS, if you have to waste two resistors (I would have use neither). a current mirror load gets you equally high gains, but allows the amp to run over a much wider voltage range.

My perference is to design as simple an amp as possible.
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Old 24th August 2005, 03:02 AM   #17
quasi is offline quasi  Australia
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Hey tlf9999,

The cct you have linked to is the first version of many updates in a very long thread.

Please look at the final version which was developed following a lot of input by many forum contributors.

I think you'll find that the final schematic is quite different to the one you have assesed.

In any case, no attempt should be made to build the schematic you have linked to.

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Old 24th August 2005, 05:55 AM   #18
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thanks for the clarification.
I did instruct the reader to follow the entire threads to check for updates.
I had 1 minute to write the message and run out the door. So I delegated the thread research job to the reader.

And you did mention in your post #1 that this was an invitation for comments.
Someone just has to read.

final schematic and board seem to at posts 157 and 166 of that thread.
Again, anyone reading this, read the entire thread, as there may yet be more changes.

I have a saying:

You can take a fish to water.....

but you'd better run fast, otherwise it's gonna die.

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Old 24th August 2005, 06:17 AM   #19
wrl is offline wrl  United States
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Consider building a Leach Amp.

I guess it uses BJT's but its got some of the best documentation around for how to build the darn thing. And its output is 120W per channel which seems to be what you're looking for.

Anything worth doing is worth doing right... and redoing to make it better... and again to fix it back the way it was.
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Old 24th August 2005, 07:31 AM   #20
cd-i is offline cd-i  Romania
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I think that Leach is a great amplifier but i'm afraid of using complementary output stages because of the transistors matching.

That's why i prefer to build something cuasicomplementary and with MOS-FET's because i have a bunch of IRF450 around and i would like to use them.

I like that NMOS schematic but the power level is too high for me,
and i wanna know if i can reduce the power level by reducing the supply voltage to something around 35-40 volts and building the power stage with only two pairs of transistors.
....I hope this thing works better than it looks....
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