I'm sorry, I didn't mean to confuse the issue. I have not finished my SKA yet. That pic is of another amp I am just finishing. I just wanted to know it that wave form was what he meant. I will let you know if I get a similar problem once my outputs arrive.
Blessings, Terry
Now I have a free square wave generator. Thanks Bigun!
I attached the pics from the scope with 10pF cap. The scope gives 1kHz sine.I used the speaker as load so the voltage is only 4.60V (my ears can't stand a higher voltage-noise). All seemes normal, doesn't it?
One thing: after replacing the Rifa cap with a Wima the sibilance much reduced. But I still find the voices - particularly the female voices - a little hard, not smooth and polite as the original SKA. Could it be the 2SA/SC sound signature?
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Now I have a free square wave generator. Thanks Bigun!
I attached the pics from the scope with 10pF cap. The scope gives 1kHz sine.I used the speaker as load so the voltage is only 4.60V (my ears can't stand a higher voltage-noise). All seemes normal, doesn't it?
One thing: after replacing the Rifa cap with a Wima the sibilance much reduced. But I still find the voices - particularly the female voices - a little hard, not smooth and polite as the original SKA. Could it be the 2SA/SC sound signature?
That waveform looks pretty damn good, it would be great to see how it performs at higher frequencies and voltages. Maybe you could build a cheap dummy load to save your hearing - I just use a few cheap power resistors in parallel.
Can't comment on the 2SA/SC transistors sorry, as I've only ever used BC5XX.
Are there any differences between the power supplies of the original SKA and this amp?
Disclaimer: I've never built a SKA, I just recognised the symptoms you mentioned and thought I might be able to help.
That thought crossed my mind too, maybe the caps need some time to bed in.
After replacing the zobel cap the sibilance is gone.
The sound is still a little hard although much better. I'm trying different compensation caps, 15pf seems to tame the harshness but going higher it seems to kill the highs too much. I'm not sure if I let the 15pF in or reduce it a little more.
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Ii have got a problem with mine. It is drawing way to many amps. Did you build yours per the Jim's audio BOM? Can't seem to figure out what is happening. Pulling like 4amps per rail at only 15v. Just got through checking all the resistors and they are right on. Checking the devices next.
Thanks, Terry
I used Jim's BOM and no problems with it. Actualy, I solved the sibilance and hard sound problem, now everything is perfect sounding very good indeed!
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Paulo, very nice work, the project looks most professional. I think I'm going to source a good hi-end chasis and build my final version of my home theatre amplifier into it. I've never worked with a new good chasis before so it will be a treat. Then I'll have an excuse to build 5 amplifiers
I used Jim's BOM and no problems with it. Actualy, I solved the sibilance and hard sound problem, now everything is perfect sounding very good indeed!
What did you do to solve the sibilance problem?
That's very flattering, thank you Bigun!
Thanks Do!
Yes, it is!Hey, that's a Per-Anders Sjostrom softstart, same as I use in my SKA!
I first used a Rifa PHE450 as zobel capacitor and I was having a great deal of sibilance. Greg recommends a Wima MKP for this role. I changed this cap for a Wima MK10 and the sibilance was gone!
I don't know if the Rifa was bad or was just the way it sounds in that position, anyway the sibilance was gone when I changed caps.
Hi Terry,
Here (I used your pic) you have the cap that is part of the zobel network (RC).
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