Class-d amp running at +-45V

Tried to run the prototype on +-45V. Works fine but, I need to add more dead time. It runs so hot without a heatsink that the PCB warms upp and thereby warms up the thermistor used in the over heat security circuit, and this is when it is just mounted on the PCB and not in connection to mosfets or anything! :roll:

Class-D Amp version 3 running

Well it’s been some time since I started working on my third version of my class-d design. It has taken some time to make work reliably.

I had designed without any means of additional dead time than is provided by the gate diodes and resistors. This is simply not a way to go. The output simply got too hot. So I had to add a little board with dead time control build around a 74HC86.

Another thing which has played me for years, is getting the amp to start up when either there is no signal on the input or the output is not connected. After many trials, I have now implemented a new concept, but it has still problems to start oscillating without either input or output connected. But test shows that it dosen’t do any harm to the amp, and that it starts when it is connected. So this is it for now.

I have now designed a new PCB and will send it for production at Olimex. Will also try to conect it to a larger power supply ad test it at max out.

Stay tuned :)

Version 3 working


USB DAC for 15 Euro!

Bought myself a little Christmas present.

Want to see if I can get a little less noise when listening to music on my PC.

Ordered a little Bur Brown PCM2704 based DAC board on eBay (here). It’s actually amazing what you get for 15 Euro!

It has a precision clock based on a +-25 ppm 12 MHz crystal oscillator, and it even has a pulse trafo equiped S/PDIF output.





Looking forward to testing it :)

There is simply no way I could buy the components and PCB and make it myself for this price!


Class-D, New revision, New PCBs

Class-d, new PCBTime to do an updated version of my class-d amplifier. Last revision was more of a prototype, with a mother board where all the switching and output filter was placed, and a daughter board where the modulator was placed. This allowed for playing a lot with the modulator, but now it is time to integrate it all on a single smaller PCB.

Where the mother board measured 8 x 10 cm, the new PCB only measuers 5,3 x 10 cm!

There will be components on both sides. All the smd components will be on the under side, and the larger through hole components will be on the top side.

Additionally a few bugs have been fixed, and the possible voltage till be higher. I also want to test some new MosFets, namely IRFB4229, which will be especially good for subwoofer usage …. these FETs are good for staggering 91 A!!!

Will be interesting to see, whether it performes as good as the last ……

Stay tuned ;-)

New PCB, both sides seen

PC-Speaker measurement

Made the first frequency response measurement of my PC-Speaker today. I used HOLMImpulse for the measurements. I just placed the mic at the place where my head is usually situated in front of the PC. So it ia a near field measurement, with all the garbage around the speakers, screen, coffee mug etc. This is ofcourse not the best environment for the measurements, but I like to get the in room, in place response and not something more stylistic.

Frequency response Dec 31. 2010

It’s not too bad, but on the other hand it could also do with a lot of work.

I’ll need to measure the driver units including filter one by one to se how they roll off. It could seem the the tweeter it a bit to high in level, and that tweeter and bass not overlap enugh around 2 kHz.

Well, no surprise, as I just found two coils and two capacitors in the drawer and fitted these as the filter. Stay tuned ;-)

AceBass up and running

AceBass circuit on small PCB

AceBass circuit on small PCB

Finally got the PCB for my AceBass circuit populated with components. It has been in my drawer for some time, but now it is time to do something about it.

…. and it actually works like a charm.

I used my small 6.5″ Peerless woofer (which I use for my PC as sub) just for the initial trails, just to test out the concept:
I have the driver in a small 11 liter closed box, which has been used together with a Linkwitz Transform circuit.

After some calcualtions and some simulation in WinISD, I decided for the following parameters:
Parameters before:     With AceBass:
Cms = 1.0166
Mms = 18.5
Rms = 1.5239
Fs = 36.7
Qts = 0.59
Vas = 28.5
  Cms = 0,6
Mms = 80
Rms = 30
Fs = 23.0
Qts = 0.32
Vas = 16.8

Don’t think you will find a driver with these parameters in real life 8-)

In the WinISD simulation below  it is seen how the driver now goes down to some 28 Hz before rolling off. The green line is with the AceBass circuit, the yellow is without.

WinISD with and without AceBass

The circuit it self is almost identical tothe one showed in AES paper by Karl Erik Ståhl, but with values calcuated to fit the small Peerless driver:

AceBass Schematic

AceBass Schematic

You can also download a pdf version of the schematic here … it’s a bit easier to read.

For the calculations I used a small Excel sheet, which can easily be used for calculations for other drivers .. download it here and a tutorial or step by step guide here

Here is a picture of the small subwoofer. The vent used is 4 cm wide, and 34 cm long, so it needs a bend in the box to fit …. until I get that it has to just point out of the box!

IMG_0596 (Large)

So what is the conclusion?

Well, it works, and the small peerless wofer now goes down to 28 Hx in a quite small box. The circuit needs a little more amplification, as the sub is now a little to week in amplitude with the small 2 way speakers I use. This should be easy to fix (fixed by changing R13 from 22k to 10k). Otherwise I think I’ll try it out on some larger speaker as well, and with a larger amplifer. The one I use is just some 25W. I will also have to do some measurements to verify that it actually works as prescribed. But this is a good first step ;-)

PC Speakers

PC SpeakersI have for a long time had some drivers that was intended for some small PC speakers. I got the units on sale some years ago. The Tweeter is a Seas 25TFFN, and the bass is probably a Peerles OEM product 13 cm, with a coated paper cone.

The units are mounted in a small closed box.

Next step will be to measure and to make a crossover. I will go for something easy, maybe just 1. order, to save money and time.

They are hooked up now, the bass only, and the sound is actually pretty good.

Speaker standing next to PC

At the moment I’m driving the speakers with my mini class-d amps, having some 25W available.

Look here at my new toolshop :mrgreen:  …  just finished it all here last week. Damn it’s good to have a nice place to work in the evenings and weekends ….

Tool shop

Stay tuned :)

Mid driver upgrade from ScanSpeak 13M Kevlar to Dayton RS125

Top box with Dynaudio Esotec and Dayton RS125

Having burned one of my midtone drivers, a renowned ScanSpeak 13M 8636, which has served me well for many years.

As I have been thinking about making some all brand new speakers full range ribbons) I was not really willing to pay the 200 Euro a new SS unit costs.

Actually I find it a rather steep price no matter what, but it is actually quite good.

But instead I looked at alternatives, well knowing that just changing a driver for something else is not that easy without also changing the filter.

After reading some (I already knew a lot of drivers ;-) ) I chose to try out the Dayton RS125. It has a alu cone and is quite we’ll build, and has gotten some good words on the way from many sides (like ZaphAudio).

Physical size, and at least the senility matches that of the ScanSpeak unit.

ScanSpeak vs. Dayon (1)ScanSpeak vs. Dayon (2)I of course changed both left and right side drivers :)

The new Dayton driver looks like a million, and seems to be extremely well built. The price is less than 30 Euro, which is almost too good to be true …..

So you would of course expect  the new drivers to perform mediocre, compared to the ScanSpeak units.

Well, firstly it is a bit difficult to compare two speakers with days between, relaying on your memory. On the other hand I have had the speakers for some many years that I know their sound, so I think a comparison is on order.

I just changed the units, knowing well that I would have to make measurements, and probably make modifications to the filter.

But putting on some very well known music, I was quite stunned. The sound was less edgy, had a much better defined room, deep and wide, and a lot of clarity and stability in the instruments. The sound did not have the very forward sound of the ScanSpeaks (which has also been a little to much in your face).

Damn, this was really good. But I was also somewhat puzzled, how would the measurements look!!

I used HolmImpulse measurements program ( super cool and free measurement application), and was again surprised.

I have always had a 2 db raise in the upper mid with the ScanSpeaks, but now the response was almost flat ….. can you be more lucky? :)

Frequency responce left channel main with Dayton RS125 (Large)

The response is in room, so don’t look too much at the bass, but look at the response from 500 and up …. not bad at all :) :) :)

Seems that I don’t have to fiddle with the filter after all. Cool.

So what is the conclusion. Well, if you have some fine working ScanSpeak 13M’s in your system, I would by all means recommend to upgrade to a pair of Daytons. You will not regret it …. and for that price!!!!

Some will probably have to modify the filter to make it work, but I actually doubt that it will be hard to make it work. So go do it! :)

Dayton rocks :)  

The response is in room, so don’t look too much at the bass, but look at the response from 500 and up …. not bad at all :) :) :)

Seems that I don’t have to fiddle with the filter after all. Cool.

So what is the conclusion. Well, if you have some fine working ScanSpeak 13M’s in your system, I would by all means recommend to upgrade to a pair of Daytons. You will not regret it …. and for that price!!!!

Some will probably have to modify the filter to make it work, but I actually doubt that it will be hard to make it work. So go do it! :)

Dayton rocks :)

Before with the ScanSpeak 13MAfter with the Dayton RS125

ScanSpeak 13M/8636 Burned

ScanSpeak 13M Kevlar ... burned ...Testing my Class-d amp …. which now sounds really, really good ….. was on the other hand too much for one of my mid drivers …

The problem is that it just sounds so clear, that it dosent sound as loud compared to when the sound is distorted …..

Damn … ScanSpeak 13M Kevlar gone for good …. Worth some 200 Euro L

Guess my speakers were up for some changes … but not just now ….

Will change both ScanSpeaks mids to some Dayton RS125’s instead … much cheaper and maybe as good …. We’ll see ….. size seems to be total drop in, but I will probably have to make changes to the filter to make it work properly J

Stay tuned …

Class-d Amp listening impressions

IMG_8485 (Medium)

Have now tuned the stereo version somewhat.

It’s running 300 kHz, and is able to put out some 150 W in 8 ohm, though I have not tried yet to test it to the limit.

It is build into an old Yamaha box, using a 3 x 35V transformer of a decent size and 2 x 10.000 uF capacitors.

But that’s just tech talk … how does it sound?

Well, I’m comparing it to a big class AB amp based on LC Audio’s The End. It’s a 180 W version with 2 massive 800 VA transformers and 4 x 22.000 uF RIFA capacitors.

An amplifier that has been my faithful amp for a long time.

In comparison, I find the new class-d amp more precise. Not cold or harsh, but just more precise.

It’s easy to pinpoint the actors on the stage, and it “quiet” around the different instruments.

The End amp, as my wife put it; is more hazy! It leaves an impression of more spaciousness, but it is not as easy to locate exactly where the actors are standing on the stage.

I think it will take a bit getting used to, but it quite definitely have potential …. And I still have a number of possible improvements up my sleeve ;)