my 1st ever D-amp, WORKING!!!

Please, attach a schematic if you want a suggestion.

Hi,

I'd appreciate you linking to the thread which my schematic was posted to rather than uploading it from photobucket.

If you read the threads you got those from and I trust you have, you'll see part selection is very important in obtaining best performance, and I'd given a few good hints as to what matters where, so I hope you kept with that in your selection.

You lose me with your first post. "There was obviously some problem with the circuit, so I redid it with Kartino's layout".

What was wrong with the circuit is that you first used 30V 8amps as your first test without optimising the values for your given components. Changing the layout alone will do nothing for this, although a decent layout is obviously equally important, and I'm not sure this is it. The values you see on my circuit were what worked best with simulation, and not intended to be "real world" values, so they'd require changing in some places, I think I mentioned all this in my original thread though.

Now you're using lower voltage and have apparently limited the current to less than an amp (how you did this we don't know).. I'd say it is the lower voltage that's saving you though, given your selection of caps high currents will still flow through the outputs if you raise the voltage level.

At this voltage level you should be able to obtain mosfets that run perfectly cool and without the use of a fan. This of course has to do with component selection, and not just the mosfets, but the entire circuit really.

There are certain things in Kartino's circuit I can't vouch for, which could be causing your problems, as well as the layout of the PCB.

Without seeing your exact circuit with component selection it would be pointless to comment further on where your slight distortion is comming from, could be anything, I'd start with a half decent supply though, half wave?? noooo.


At least measure your DC offset, and start adopting some troubleshooting procedure that will allow you to make sense of things as opposed to changing your layout immediatly after the first problem.

If you want to perfect this at those voltage levels, you're simply going to have to become familiar with optimizing it based on the components you chose, and that also includes the possibility of re-evaluating your choice of components. It is more important to use components that are right for the job over what is more easily available.

That's really all I can help you with, it took me nearly two years to get as far as you've come with it in less than a month, but being given that doesn't really allow you to just build it and go, you'll have to become familiar with it enough to be able to tweak and optimize it based on your design choices.

. So you're in for a bit of work and learning yet, and I know it's worth it, you probably have found this out yourself already, despite the zzzzrrrtttt sound, I bet it is uniquely pleasing in a kind of high end way?

The IRFZ48 you are using for lower side is almost 5 time slower than the IRFZ44 you are using for the high side. It will therefore see a higher loss than the high side.

What switching freq are you running at?

If the MOSFETs are heating up without load, I'm not so sure you got the timing spot on. (If your PSU heats up, I think you have some shoot throught)

You should use the same mos for upper and lower, as a start. Then adjust the deadtime (better starting with too much delay as a start until everything else works).

Check all waveforms on a scope.

Have you checked that you don't have any DC on the output?

Does the filter heat up as well?

Uhhhh huh..... uh huh...


Watch what happens now when you go and up the voltage to +-30Vdc...

Also watch what happens when you put your new mosfets on...

We'll see who's got who.

At least you've picked up a few things on how to tweak it, but do not neglect the rest, the balance resistor in the current mirror is a good way to tune the overal driver response/and deadtime, along with the value of the turn on bias resistor and series gate resistor.

You lucked out that this worked so easily for you, but things are going to change, so enjoy this for now

It is alright to run it without the input stage, but there are good reasons to have it, it's a matter of complication I suppose.

Do you have a scope to work on this with? It would make life easy.

You have to watch the values of the gate drivers as it can easily load down the driver voltage supply.

You cannot substitute the schotty baker clamps with a single diode, it won't work properly. I've gotten around that problem of not having shottky's by using a dual diode version which I've posted many times as well, so you can dig that up and it should help you further.

Keep us posted, how is it sounding now anyway?

Chris

Hi Raff,

So many smash.... hmmmmm...... seem you are very happy....

How the sound at low volume. Did you use volume control separately as suggested? Deep bass is it? I thought!

Coil heat? Use bigger wire. Did you use core from PC PSU output filter?

If the coil is heating up without signal/load, it is because of core losses.
The wire seems more than ok for a 10W amp, don't think it is due to copper loss.

When you switch to the 30 V DC PSU, does it get even a lot hotter? ... it will if it is due to core loss.

Go for a Micrometals material 2 core.
You can get them from Parts and Kits

I use T130-2 for my amp and it significantly reduced both heat and distortion. (used some SMPS core I just had in the drawer)

On Micrometals homepage you'll find a program to calculate number of windings, loss etc.

You should get hold of a scope to check all signals, frequencies etc. ..... though simulating is the way to go for sure, you still need to check everything after assembly, as simulation and calculation is one, reality something else

No the coil should not be hot.
How do you know it should be around 25uH ..... it could be any value if you don't know the core material

(to correct my own post before ..... the SMPS cores I had in the drawer was the ones I used before, which heated up and added a lot of 3. harmonic distortion. ....... what I'm trying to say is, DON'T just use a core from an old SMPS ..... it is almost for sure not suitable for this use ...... SMPS (normally) does not run at the high switching frequencies we want for a class-d amp!)

... and get a scope