some power amplifier recomendations

cd-i

Member
2005-08-21 10:15 pm
Hello,

I want to build a power amplifier for using it at home and i need some recomendations on schematics.

I don't need something too powerful, i think something around 100 - 120 watts is enough for me. I also want the amplifier to have MOS-FET's on the output.

Browsing on the internet i found the A and T labs webpage and i think that their K9 project is ok.

http://www.a-and-t-labs.com/products.htm

If anyone know something about that amplifier because the schematic looks good at first sight. But i wanna know some ratigs about how it sounds, not only some specification and waveforms.

I should mention that i am not so experienced in audio designs (i built some amplifiers but nothing special).

Thanks in advance
 

funberry

Member
2005-08-17 3:23 pm
The K7 looks good.

What do you feed it?

I wish they had shown the bottom side of that PCB also, so we can duplicate it.

It seems like a pretty good desig, hard to beat that. There were a few MOSFET designs around the forum, look up postings by member "quasi", and they should come up.

creek amp

I'll try to dig up others.


Cum e vremea in Timisoara?

Adrian
 

funberry

Member
2005-08-17 3:23 pm
What can I say, I'm partial to quasi-complementary symmetry, at least with MOSFETS.

The supply chain for true-audio complementary MOSFET pairs is too strangled. Scarcity, high prices, few players, high counterfeit presence, I don't want to go near that market. I stick with N-channel, all the way.

Plus there are many authors who affirm there is no real compelling sonic advantage to a MOSFET amp vs bjt designs. And I can get complementary power bjts' at prices I find acceptable.
I know, this can start a long FET vs bjt argument.

Most emerging semiconductor technologies are plagued by the same inherent challenge in audio design: The initial lack of available complementary devices. That's where IGBT's are now.
( I wish I could find a quasi-comp design using IGBT's!, these things are so rugged)

Ok here's another:

citation amp


Adrian
 

cd-i

Member
2005-08-21 10:15 pm
hello,

Yes i like the design of the k7 amplifier too but unfortunately the layout presented on the web page, besides the fact that is incomplete, is also designed for their custom enclosure.
I have an enclosure from an old romanian amplifier and i can not use that layout. I know that a good layout is essential but i have to redesign it in order to fit my enclosure. The space is very tight in there because i intend to build 4 amplifiers in the same enclosure and power them up with the switching power supply they used in their k6 project.

Anyway this project is in a very early phase and i only have ideas of what i want to stick in that enclosure...

So if anyone can give me some tips and ideas please HIT ME !!!


p.s. hehe o surpiza placuta. La Timisoara vine toamna...

( nice suprise. The fall is coming in Timisoara...)

Daniel
 

cd-i

Member
2005-08-21 10:15 pm
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....
 

funberry

Member
2005-08-17 3:23 pm
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.

Adrian
 

cd-i

Member
2005-08-21 10:15 pm
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.
 

funberry

Member
2005-08-17 3:23 pm
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!

Adrian
 

tlf9999

Disabled Account
2005-05-25 2:25 am
none
funberry said:


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.
 
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.

Cheers
 

funberry

Member
2005-08-17 3:23 pm
Quasi

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.

So...
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.

Adrian
 

cd-i

Member
2005-08-21 10:15 pm
hello,

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.