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300B SET Design Project
http://www.diyaudioprojects.com/Forum/viewtopic.php?f=9&t=2699
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Author:  Woodo [ 25 Jun 2019, 16:46 ]
Post subject:  Re: 300B SET Design Project

Suncalc wrote:
This can be a problem if the secondary resistance is small. Sometimes this can be remedied by adding resistance to the outer legs of the secondary or shrinking the size of the first capacitor to increase conduction angle and shrink the current spikes into the first capacitor.

Matt, from the design guide my R-s is 74 ohms and peak supply resistance is 177. According to the 5u4g data sheet the minimum effective plate supply resistance at the section E-rms of 367 vac is about 60 ohms if these are the relevant figures. I could try either remedy though. Can you recommend any particular values to try for R and or C?

Author:  ILoveHiFi [ 26 Jun 2019, 00:55 ]
Post subject:  Re: 300B SET Design Project

If you increase the R, you reduce the ripple. But the voltage at the load reduces
If you increace the C, the voltage dosen't change but ripple reduces

Theres no harm with larger capacitors, the larger the better.
Only draw back is that it takes few seconds longer at most to charge or discharge them at intial startup.
This will not cause anny prolbems.

Author:  Woodo [ 26 Jun 2019, 06:39 ]
Post subject:  Re: 300B SET Design Project

edit, just a pdf as i couldn’t add the .xls. I’ll try and annotate it better. i don’t understand most of the formula as i only did a basic electronics course a long time ago so apologies for errors. Please make corrections or suggestions on layout. the highlighted part to reduce ripple with an extra 10uf cap i’m not sure i did right. it may need to include a resistor . Still looking at that. can try and model higher resistances and smaller C1 to see if that could help as Matt suggests though not sure where in the circuit to put them. I just played the whole of Crime of the Century by Supertramp and haven’t enjoyed it as much for years. Also a few songs i like off Too Stuffed to Jump by Amazing Rhythm Aces. Great sounding on this amp. I recall on the latter a few songs had some silky cymbal sounds which i don’t seem to hear anymore. They’re there but lower volume. my ears may be rolling off.

Author:  Suncalc [ 26 Jun 2019, 19:30 ]
Post subject:  Re: 300B SET Design Project

John; I'm having a hard time following your math. Can you attache an "as built" PS schematic?

Author:  Woodo [ 26 Jun 2019, 21:22 ]
Post subject:  Re: 300B SET Design Project

Suncalc wrote:
John; I'm having a hard time following your math. Can you attache an "as built" PS schematic?

It’s probably very likely i’ve taken a wrong turn and should keep the training wheels on. It will be a useful guide though to learn. I followed the schematic at page 33 of this thread viewtopic.php?f=9&t=2699&start=320#p28729 except as marked in the pic. Hope I am not torturing anything in the process.

Author:  ILoveHiFi [ 26 Jun 2019, 21:43 ]
Post subject:  Re: 300B SET Design Project

Just stick another 100uF in parallel and another 47uF if your concerned with the noise.
This will deffintly reduce the voltage noise further so you can now go and look for other prolbems if the noise is still unacceptable.

Author:  Woodo [ 26 Jun 2019, 21:59 ]
Post subject:  Re: 300B SET Design Project

Thanks that may well be a practical solution in the end. I see there are some dual can caps some of which I see used in designs on this site. Are there advantages using those?

Author:  ILoveHiFi [ 27 Jun 2019, 00:45 ]
Post subject:  Re: 300B SET Design Project

Depends on which one is easy to install for you and size considerations, just mind that some caps have the metal case connected to ground terminal of the actuall cap.
And if you use caps in series for the B+ there will be half the b+ voltage on the metal cap. Leave this exposed and it can be fatal.

But I thought in the PDF you already have achived noise levels within recomended specs, if so then therres no point in adding extra caps if the noise is still there.
But if your chasing extreme low noise then you need the extra caps to achive this

Author:  ILoveHiFi [ 27 Jun 2019, 02:46 ]
Post subject:  Re: 300B SET Design Project

Actually nearly all capacitors with any exposed metal will be likeley connected also to the negative pin of the capacitor, I had a shock once becasue I didn't realise there was HV on the cap shell.

Author:  Woodo [ 30 Jun 2019, 07:02 ]
Post subject:  Re: 300B SET Design Project

Woodo wrote:
edit, just a pdf as i couldn’t add the .xls. I’ll try and annotate it better. i don’t understand most of the formula as i only did a basic electronics course a long time ago so apologies for errors. Please make corrections or suggestions on layout. the highlighted part to reduce ripple with an extra 10uf cap i’m not sure i did right. it may need to include a resistor . Still looking at that. can try and model higher resistances and smaller C1 to see if that could help as Matt suggests though not sure where in the circuit to put them. I just played the whole of Crime of the Century by Supertramp and haven’t enjoyed it as much for years. Also a few songs i like off Too Stuffed to Jump by Amazing Rhythm Aces. Great sounding on this amp. I recall on the latter a few songs had some silky cymbal sounds which i don’t seem to hear anymore. They’re there but lower volume. my ears may be rolling off.

edit updated pdf of spreadsheet. I increased the voltage drop of the 5u4g according to the value in the power supply guide graph, the data sheets have various figures. work in progress still just to help me understand it better.

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