D AMP is back !!!

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#45
Hi luka, here is simple schematic, describing measurement of output impedance. Note: sinewave gen must provide output currents up to ~1..3A.
 

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#48
Hi Luka,

My proto works with 330pF so don't worry about it ;-)

I'm looking for a safe way to drive output N channel Fets...
I've burnt several IR2113 and I'd like to find another solution...

I am trying fredos's model 1200 way to drive P and N channel fets but limited in power because of P channel poor specs...

If you have any idea
I think my problem is with bootstrap cap...
Help is needed !
thanks
 
#49
Fairchild FQA36P15, free sample on web site, matched with IRFP250 or IRFP260 work well, at a maximum of +/-70V. You will have to play a bit with gate resistor to match dead time to these device. Another way is to double IRFP9240 with same gate resistor and a IRFP260. I have do that for special order for a customer that use it bridged into 3 ohms for bass instrument with succes.

With this configuration, you will take advantage of adaptive dead time! You will like it!

Fredos
 
#51
+/-80V with switching power supply is not a probleme at this level. IR211X serie of driver are very sensitive to everything. I only use it in switching power supply for my HVI serie Amplifier. There are not enought rugged for class d amplifier. Yes I means 2 P channel with 1 N channel. Unusual, but work very well. At +/- 70V you can use with no prob the Fairchild I suggest you. At 36A iD, these device work well to 2 ohms per channel! Order it as sample from Fairchild! These series of amplifier are on the road for more than 10 years and still rock many bar and band! They only use cheap parts and are very reliable. This is what we can call a proven old design! 🙂. We will maybe release a new budget serie with this old design with these new Fairchild parts, under maybe 400$ each amplifier for 600 watts per channel. Like I told you, they use only easy avaible and cheap parts, that was not the case 10 years ago! Just follow exactly schematics for power amp section and you will not be dissapointed.

Fredos
 
#52
Hi Fredos,

thanks for your answer !
Gonna try with such device....

sound with your model 1200 front end and ir2113 was great i'm not disapointed at all ;-)

very excited to try your design very smart indeed the way you apply negative feedback to comp input ! seen nowhere else !
 
#54
fredos said:
I still use this technic in my lattest serie of amplifier! Sound great, work well and really stable! I did'nt find a better way from now!

fredos
Click to expand...


Did you measure THD/Freq plot? I think it's would be pretty flat, though claims about zero IMD fully marketing BS, obviously. BTW, the trick to have more loop gain with the same stability, does exist, i guess, that i see it.😉
 
#55
To add more gain, you need error amplifier that add delay in amplifier transient respond. Using comparator as error amplifier/comparator combo avoid this, at the expense of lower gain. That's why I claim that IMD is near zero! You can put a 20 Khz squared wave at the input and you will get a squared amplified wave at the output, with no overshoot! And yes, you definitively need lo pass filter at the input to avoid frequency over audio spectrum....Basicly, UCD work in the same maneer (no error amplifier), but in free running mode....Just dont use clock in my circuit and you will got same result!

Fredos
 
#57
The trick to make loop gain higher could be achieved by making the triangular smaller in amplitude. This could go ahaed with increased triangular linearity. Since a higher triangle voltage is desirable in practice - because it makes the modulation process less susceptible to EMC problems - we would have to make a tradeoff unfortunately.

Regards

Charles

Edit: And yes, stability could be improved by adding a resistor somewhere ! 😉
 
#58
We use a old calibrated HP analogue THD meter. We cannot under 0.01% of THD with accuracy. All of our amplifier are under 0.1% of THD at full power, and under 0.01% from 10W to full power, from 30-20 000 hz. We always got a dip at 6.3Khz, due to the feedback compensation. Under 10 watts, THD cannot be measured due to the residual noise at the output. Even with a 22Khz low pass filter, meter are unable to performe. I Know that for purist, these spec are not impressive, but my market is (hight) power amplification. And as Alexclaire said, he seem impressed by the overall sound quality of the amplifier, and all of our customer too.

Your right too that with lower triangle wave amplitude higger gain could be achieved, but under certain level, amplifier go out of stability. Low amplitude can be attained by placing physicaly on PCB the integrator capacitor and resistor really close to the input pin of comparator with good ground plane around it. Lower the value of the resistor and higger the value of the capacitor provide enought margin again EMI and stability.

Fredos
 
#59
fredos said:
We use a old calibrated HP analogue THD meter. We cannot under 0.01% of THD with accuracy. All of our amplifier are under 0.1% of THD at full power, and under 0.01% from 10W to full power, from 30-20 000 hz. We always got a dip at 6.3Khz, due to the feedback compensation. Under 10 watts, THD cannot be measured due to the residual noise at the output. Even with a 22Khz low pass filter, meter are unable to performe. I Know that for purist, these spec are not impressive, but my market is (hight) power amplification. And as Alexclaire said, he seem impressed by the overall sound quality of the amplifier, and all of our customer too.

Your right too that with lower triangle wave amplitude higger gain could be achieved, but under certain level, amplifier go out of stability. Low amplitude can be attained by placing physicaly on PCB the integrator capacitor and resistor really close to the input pin of comparator with good ground plane around it. Lower the value of the resistor and higger the value of the capacitor provide enought margin again EMI and stability.

Fredos
Click to expand...


nice if the sound great, by the way, not every professional class D amp can sound even decent (many people tell me, that Powersoft, Crest etc class D purchased for light weight only, but never for the sound), next for the decent THD spec, you need exactly those 6db of loop gain, that you lose in the your current design, with the same part count.
 
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