Aleph 30 the best choice of C1 C2 C3 on brian gt PCB

[boywonder]

The same schemo as in post #1 in this thread. BrianGT PCB's. +/- voltage is about 13.8V. Outputs are IRFP240's running about 1.2A bias.

Mods so far: C1 and R10 removed, R14 and R16 reduced to 866R, C2 bypassed with .12uf MKP film.....

 

[Zen Mod]

observe 1nF caps in this schm

try them , one by one

btw. 13V8 is bit low , so maybe cleaning that ringing will do more harm than good

 

[boywonder]

C102? Where exactly should I try that in the mini-A schematic?

 

[Zen Mod]

you have 2 of 1nF there ; C102 and C105

in same places

 

[boywonder]

Thanks ZM! The BrianGT schemo (and my amp) already has the equivalent of C102 (it's labeled C5 on the BrianGT schematic).

I'll add the C105 equivalent to one channel and report back.

 

[boywonder]

Well, I added a 1nf C105 equivalent but no change in the square wave.......

 

[Zen Mod]

what's p-p voltage when you took that test ?

 

[boywonder]

about 20Vp-p. The amp clips with a sine wave at about 22Vp-p so just under clipping. The sq wave still has ringing at lower p-p voltages as well, although at lower voltages it has slightly less ringing. The pic is at 10Vp-p.

Would ferrites somewhere possibly help?

 

[tonimxp]

about 20Vp-p. The amp clips with a sine wave at about 22Vp-p so just under clipping. The sq wave still has ringing at lower p-p voltages as well, although at lower voltages it has slightly less ringing. The pic is at 10Vp-p.

Would ferrites somewhere possibly help?

Hi!Which is the maximum undistorted output signal with a sinusoidal input signal?
The output load is 4 ohms or 8 ohms?
Can you post the picture of the oscilloscope?
As I say this because in my first mini aleph powered with +18 V 0-18V I made ​​a mistake, I used the 0.33-ohm resistors instead of 0.47 ohms, the result was a distortion early at about 7w of power output.
I do not know if this information will be useful for you but i hope this.
this thread is getting more interesting ... thanks to ZM that is always available to answer our questions.

 

[tonimxp]

you have 2 of 1nF there ; C102 and C105

in same places

Do you know what are C102 and C105, why in BrianGT pcb there isn't C105?
C104 from 10pf to 15pf ?I imagine it could affect the frequency response!
If yes how to determine the right value?
hmmm...This caps are objects always the most mysterious!
This thread is getting more interesting ... thanks to ZM that is always available to answer our questions.
Thanks.

 

[Zen Mod]

now desolder both 1nF caps - they;re antioscillation thingie , observe that you don;t have oscillation ,and the fiddle with value of C4

try 15pF for start

 

[boywonder]

Hi!Which is the maximum undistorted output signal with a sinusoidal input signal?

22Vp-p

The output load is 4 ohms or 8 ohms?

I'm using an 8R 100W load resistor

As I say this because in my first mini aleph powered with +18 V 0-18V I made ​​a mistake, I used the 0.33-ohm resistors instead of 0.47 ohms, the result was a distortion early at about 7w of power output.

I have .47R source R's and clipping with a sine wave occurs at about 22Vp-p (about 8W or so) I'm assuming that this is reasonable with +/- 13.8V rails.

 

[boywonder]

now desolder both 1nF caps - they;re antioscillation thingie , observe that you don;t have oscillation ,and the fiddle with value of C4

try 15pF for start

OK, thanks. I'll report back shortly.

 

[tonimxp]

22Vp-p



I'm using an 8R 100W load resistor



I have .47R source R's and clipping with a sine wave occurs at about 22Vp-p (about 8W or so) I'm assuming that this is reasonable with +/- 13.8V rails.

The Power out with 13,8V is ok! I think too that the cause should be the C4/R15 conbinate values.I think too that you have to try to change (slightly)these values.

 

[Zen Mod]

R15 is defining CLG of amp

leave it as is

fiddling with C4

 

[boywonder]

Bingo!!

OK, that made a big difference. I paralleled another 10pf with C4 for a total of 20pf.

I'm starting to understand.......R15 is the feedback R and C4 is the compensation cap, correct? Now I want to play with reducing feedback........

So my new square wave would indicate a bit of HF loss, correct? Leading edge is a little rounded. Looks like for 100K feedback R, the optimum C is somewhere between 10 and 20pf. Of course my pf cap selection is a bit thin.....

Thanks ZM!!

 

[Zen Mod]

that's good

leave it as is

 

[tonimxp]

that's good

leave it as is

Hi!ZM what do you think about 15pf value i think it will/schould be perfect

 

[tonimxp]

OK, that made a big difference. I paralleled another 10pf with C4 for a total of 20pf.

I'm starting to understand.......R15 is the feedback R and C4 is the compensation cap, correct? Now I want to play with reducing feedback........

So my new square wave would indicate a bit of HF loss, correct? Leading edge is a little rounded. Looks like for 100K feedback R, the optimum C is somewhere between 10 and 20pf. Of course my pf cap selection is a bit thin.....

Thanks ZM!!

Hi! BW do you think that you will try with 15pF or not?

 

[boywonder]

Hi! BW do you think that you will try with 15pF or not?

If I had one I would try it......I'm going to do the other channel and listen for a while.

I'll order a few values on my next Digikey order.