Hello guys. I have built a dc coupled two stage DAC output like from the schematic. In the original version I had 10H 120ohm choke, and the last two capacitors were 330uf electrolytics and resistors 470 ohm.
It played really well, but I thought I can make an improvement.
I was suggested by a friend to replace the last elcos with 20uF foils.
I also replaced 470ohms for 1k2 for better filtraton and time constant with the smaller capacitors.
I fired it up and.... everything cleared up a bit, highs were better, the usual improvement when you replace electrolytic with foil. But the energetic deep bass that I was proud of are not here so good.
I thought why?
First reason will be that the B+ voltage for 6N2P will be slightly lower, but I dont trust that 1 volt difference can be so big in sound.
Than I replaced the chokes. (every time I added bigger choke to a power supply, sound was again more dynamic and energetic). This didnt improve the energy.
The other reason can be simple:
simply that the new caps can not store so much energy as the big elcos....
But Im still confused.
In my power amp, I have driver stage which draws 5mA. And totally doesnt matter if the filtration paper in oil here is 5uF or 10uF or 15uF. Even if I increase the dropping resistor a bit, no difference in sound.
I simply dont trust that Ive moved the operating point too far from the original, by having a 5 volt loss for the 6N6Ps and 1 volt difference on 6N2P. Or do you think it can be the case?
They are schematics.
Thank you very much for help. Best regards, Michal
It played really well, but I thought I can make an improvement.
I was suggested by a friend to replace the last elcos with 20uF foils.
I also replaced 470ohms for 1k2 for better filtraton and time constant with the smaller capacitors.
I fired it up and.... everything cleared up a bit, highs were better, the usual improvement when you replace electrolytic with foil. But the energetic deep bass that I was proud of are not here so good.
I thought why?
First reason will be that the B+ voltage for 6N2P will be slightly lower, but I dont trust that 1 volt difference can be so big in sound.
Than I replaced the chokes. (every time I added bigger choke to a power supply, sound was again more dynamic and energetic). This didnt improve the energy.
The other reason can be simple:
simply that the new caps can not store so much energy as the big elcos....
But Im still confused.
In my power amp, I have driver stage which draws 5mA. And totally doesnt matter if the filtration paper in oil here is 5uF or 10uF or 15uF. Even if I increase the dropping resistor a bit, no difference in sound.
I simply dont trust that Ive moved the operating point too far from the original, by having a 5 volt loss for the 6N6Ps and 1 volt difference on 6N2P. Or do you think it can be the case?
They are schematics.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Thank you very much for help. Best regards, Michal
Last edited:
Hi Michal,
There is one part of the schematic of your power supply i do not understand. The filament of the AZ1 is connected to the 4 V tap on the power transformer like it should be. But what is the meaning of the part parallel to the 4 V tap, from which a lead goes to the first cap and the choke? Is that part a centre-tapped or variable resistor? And if so, what is the value of it?
Greetings,
Robert
There is one part of the schematic of your power supply i do not understand. The filament of the AZ1 is connected to the 4 V tap on the power transformer like it should be. But what is the meaning of the part parallel to the 4 V tap, from which a lead goes to the first cap and the choke? Is that part a centre-tapped or variable resistor? And if so, what is the value of it?
Greetings,
Robert
These are two 10 ohm resistors in series, the ends are connected to AZ1 filament and the middle is the part which continues to the supply - first cap and choke, etc....
Now I have tried this: replacing 1k2 resistors with two 5H 50ohm chokes, adding 330uf electrolytic in paralell to the 150uf electrolytic, and replacing the AZ1 for AZ4 which is stronger rectifier. Nothing helped. The bass is still weak and lazier than with the 330uf electrolytic in position of the 20uF oil caps.
OK, so the 2 x 10 Ohm draw an extra 0.2 A from the 4 V tap. Just to be sure: Is the 4 V tap rated for at least 1.3 A ?
Yes, the rectifier is heated properly. I have checked that. I simply cannot go back to the punchy good bass whet the last caps were 330uf biggies. Ive made a lots of changes but no good ... Maybe I can go back to 470 ohm resistor instead of the 1k2.
Experimenting again. Im where I was. Az1 rectifier, last stage is 470 ohm plus the 20uf ollie. This sounds best, bass is maybe liitle bit better but not on the levels where it was with the elcos. Maybe I can try lower, I have nice 170 ohm wirewounds laying around. I can also bypass the 20uf ollies with some 10nf silver micas to better HF filtering.
Its interesting, that by sonic comparison, the cap probably need to be charged fast (becahse due to low capacity it discharges also fast). But calculation with time constant shows the opposite 😀
Its interesting, that by sonic comparison, the cap probably need to be charged fast (becahse due to low capacity it discharges also fast). But calculation with time constant shows the opposite 😀
