I am still assembling.
A jury rigged, uncased version may be running at the week end.
I am quite unhappy with the choices for C9 and C21 values. I expect to do a lot of swapping here after I hear the standard version.
What would you have placed instead of a Blackgate? And for C21, yes, we could have placed some film and foil or polypropilene.
C21 was supplied as type FKP2, a film and foil polypropylene.
Comparing the impedances of C9 and C21 at 10 kHz, C21 is 7200 times higher (77dB) so how can it influence the sound at all? At lower frequencies the difference is 10,000 times.
Andrew, I am curious about what is wrong with the value of C9 at 220uF.
Comparing the impedances of C9 and C21 at 10 kHz, C21 is 7200 times higher (77dB) so how can it influence the sound at all? At lower frequencies the difference is 10,000 times.
Andrew, I am curious about what is wrong with the value of C9 at 220uF.
Have you actually measured it? It is a very interesting fact that already hasn't arised...
BTW, my apologies about the C21 cap assumption. A big slap in my face...
i think there is a lot of room for personal judgment here. I like to have it flow through to the top side but I don't sweat it if it doesn't, as long as the solder joint is solid. Using solder with a low melting temp can help here. Generally I don't go to the top side and solder there - I just make one joint and go with it, if I don't think it is strong enough I suck off the solder and start fresh.
If you are asking have I measured the capacitor impedance, yes the graphs are in one of the PDF files I posted a while back.
My comment about the FKP2 was not intended as a slap, just a gentle correction.
The issue isn't the total capacitance of C9 and C21 in parallel, theoretically one could compute just using formulas and see C21 doesn't have a profound effect on the circuit.
I think the idea is that the bigger cap is electrolytic and has some real life downsides that may be audible but bypassing it with a better quality cap negates some of this. YMMV.
Right, the issue is not the total capacitance, rather it is the comparative ratio of the impedance each capacitor provides to the total current path. Stated another way, 99.99% of the signal current will flow through the Black Gate capacitor. Maybe you can explain how a small capacitor passing 0.01% of the signal can negate shortcomings in the larger capacitor.
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In attenuators I like to bypass the whole thing with 1M and higher resistors. Why does it sound better when the rest of the attenuator is total R of 6k? Who knows but the percentage is near nil. It makes a noticeable difference. Not the same as caps of course but just my analogy that I can draw from experience.
Uriah
Uriah
The C9 value comes directly from the Musical Fidelity A370 that inspired Mauro Penasa.
Sure it would be great if there's a way to reduce it to 10-22uF so we could manage to use a film cap.
In the MyRef Evolution Mauro fixed the problem using a DC servo instead.
Regarding C21: the value is strange, I agree, but I've tested several values and 22nF was the only that seemed right. (see: post1, post2, post3)
But that was with standard elcos, Black Gates usually works better without bypass...
I don't know a better cap in 5mm lead spacing...
And nevertheless it does... see the three posts I've linked.
Would you ever use a 1nF bypass between PS rails of an opamp?
Just yesterday tried it on a OPA827 and bass gained solidity and speed...
Those little value caps are strange evils...
Attachments
Regarding the opamp bypass, I usually use something in the range of 10nF - 100nF. But that is a different application not closely related to this discussion.
I didn't expect an explanation for the 0.022uF capacitor because logically it doesn't make sense that it should help. That said, it was part of the kit and I mounted it to the card with the rest of the parts. If it doesn't help it shouldn't hurt either.
I didn't expect an explanation for the 0.022uF capacitor because logically it doesn't make sense that it should help. That said, it was part of the kit and I mounted it to the card with the rest of the parts. If it doesn't help it shouldn't hurt either.
Would you ever use a 1nF bypass between PS rails of an opamp?
Just yesterday tried it on a OPA827 and bass gained solidity and speed...
Those little value caps are strange evils...
Yep. It might be a mystery to us but there is someone out there that knows exactly why these tiny values are making the difference. At least we can count on our ears to tell us when our experimenting pays off.
Uriah
C9 and C21 is a complicated topic, but, based on Bill P's findings and Andrew's and Regi's points, I think I see a resolution.
Mauro's original design did not have any bypass cap for C9; there was no C21.
C21 and most of the other bypass caps were added by Russ White of Twisted Pear when he designed these boards for sale to DIY'ers.
After I built my first amps and started experimenting with different components, I noticed a strange distortion on female vocals and some instruments. It sounded like a weird, out-of-phase kind of thing, very fleeting and subtle, but real. Dario was experimenting at the same time and recommended a certain cap for C9. I tried that and the distortion did not go away; it might have gotten worse. Dario recommended the current small value for C21. I tried that and the distortion went away. At the same time, I replaced C9 with a Blackgate. The sound became beautiful, no other way to describe it. I had made the rookie error of making two changes simultaneously, so I never was certain that the distortion was caused by C9, or by the interaction of C9 with a larger value C21. I was never completely satisfied with the small value of C21, but my amps sounded so good that I quit experimenting.
I now believe that C21 is such a small value that it has very little, if any, effect on the overall sound of the amp, other than that it might have no effect at all. Perhaps Mauro's original design was the best (as we have determined again and again). Bypass caps are always a tricky affair, and perhaps the best bypass is none, especially directly in the signal path.
A larger value C21 would probably introduce the same distortion, no matter how "good" a cap is used for C9. I believe the quality of sound from this amp is the result of the quality of C9, the Blackgate. That might sound like voodoo to you tech guys. Prove me wrong, and we'll all be richer for it: no more $7 caps at C9.
Simple experiment: leave C21 out and listen. I'm not gonna do it first.
More complicated experiment: different C9's. Been there, tried that. Blackgate's are legendary for a reason. I wish someone could make them again, or something else that sounds as good.
Peace,
Tom E
Mauro's original design did not have any bypass cap for C9; there was no C21.
C21 and most of the other bypass caps were added by Russ White of Twisted Pear when he designed these boards for sale to DIY'ers.
After I built my first amps and started experimenting with different components, I noticed a strange distortion on female vocals and some instruments. It sounded like a weird, out-of-phase kind of thing, very fleeting and subtle, but real. Dario was experimenting at the same time and recommended a certain cap for C9. I tried that and the distortion did not go away; it might have gotten worse. Dario recommended the current small value for C21. I tried that and the distortion went away. At the same time, I replaced C9 with a Blackgate. The sound became beautiful, no other way to describe it. I had made the rookie error of making two changes simultaneously, so I never was certain that the distortion was caused by C9, or by the interaction of C9 with a larger value C21. I was never completely satisfied with the small value of C21, but my amps sounded so good that I quit experimenting.
I now believe that C21 is such a small value that it has very little, if any, effect on the overall sound of the amp, other than that it might have no effect at all. Perhaps Mauro's original design was the best (as we have determined again and again). Bypass caps are always a tricky affair, and perhaps the best bypass is none, especially directly in the signal path.
A larger value C21 would probably introduce the same distortion, no matter how "good" a cap is used for C9. I believe the quality of sound from this amp is the result of the quality of C9, the Blackgate. That might sound like voodoo to you tech guys. Prove me wrong, and we'll all be richer for it: no more $7 caps at C9.
Simple experiment: leave C21 out and listen. I'm not gonna do it first.
More complicated experiment: different C9's. Been there, tried that. Blackgate's are legendary for a reason. I wish someone could make them again, or something else that sounds as good.
Peace,
Tom E
it will develop a small value of AC voltage across it.
I decided to join the Group buy and accept the kit as it was offered.
That was an informed decision and I have no regrets.
Except, I ordered chassis the day before the kit arrived. The smoothing caps + PCB thickness is only 1mm less than chassis height. Oops.
Can you explain why does it develop a voltage?
You're lucky for the chassis trouble. You could try slightly shorter standoffs for the board, if you still have spare clearance.
Regards,
Regi
There won't be any room for stand offs, unless they are <0.95mm high.
I envisage a double layer of thick insulating tape to keep the soldered pins from touching the aluminium chassis floor. But, will the lid fit without buckling or crushing?
The input cap passes frequencies that will develop a voltage across the feedback cap.
That combination of 2u2F Obligatto and 220uF Black Gate guarantee that.
Reducing the input cap to 1uF gets close to filtering the problem LF, but why pay for 2u2F Obbligato and leave it in the packing?
Maybe add 75k//100k (Rin~43k) to make the input filter more effective.
Or double up the 220uF BG with a cheap 220uF, or replace with a 470uF or .... , there are many options to prevent AC across the feedback cap.
That's why I bought two kits and two PCBs.
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I had finished populating the boards and tested it. Everything seems to be functioning as it should but I found the gain to be pretty high. I am using a B1 and i can hardly turn the pot more than 9 o'clock. On my other amp, I can easily listen at 12 o'clock. I think the gain was listed as 31, which is very much higher than I really need. Could I possibly lower the gain, or perhaps I made a mistake somewhere?
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