I'd like suggestions regarding the capacitors outlined in red. Is there an advantage going with polarized electrolytic caps
like THESE versus big film caps like THESE?
I asked in the tube forum regarding the RIAA caps but if anyone here wants to chime in about those as well, I'd appreciate the information.
Phono-stage
like THESE versus big film caps like THESE?
I asked in the tube forum regarding the RIAA caps but if anyone here wants to chime in about those as well, I'd appreciate the information.
Phono-stage
The advantage for electrolytic supply caps is cost and size, dramatic difference in fact. But lifetime isn't so great.
The caps used in an RIAA equalization circuit should be film caps, note, need to have stable values, not be microphonic, not be polarized.
NP0 or C0G ceramics are acceptable, no other ceramics are.
The caps used in an RIAA equalization circuit should be film caps, note, need to have stable values, not be microphonic, not be polarized.
NP0 or C0G ceramics are acceptable, no other ceramics are.
Parenthetical -- LED's in that design can be bypassed for lower noise. They are low enough impedance that they shouldn't "hang". A shame to throw away some of the noise advantages of the triode strapped D3a.
SY wrote an interesting DIYAUDIO article https://www.diyaudio.com/community/...a-thoroughly-modern-tube-phono-preamp.163570/ which used the D3a as the input. He discusses the reasons that LED's are preferred to the RC combination.
Nevertheless, I did some measurements of triode strapped pentodes, and found that the LED biasing was somewhat noisier than the plain vanilla RC for biasing. Given the noise on most LP surfaces, you may not be able to "hear" a difference.
I would suggest reading SY's article, try both methods, report back.
I've read his article but will re-read it at your suggestion. Still would like additional specific suggestions regarding capacitor/resistor choice.
Wading in a capacitor discussion thread is something I try to avoid, but here are my thoughts. I'm wondering what the point of diminishing returns is here. You say size is not a concern, but you also say you're a novice builder. If you're asking about putting three of the large film caps in a phono preamp, that is going to be a lot to fit into a chassis -- unless you simply want it to be big as a design statement. Ripple obviously isn't a problem here with all your choke-filtering.
We do have very low-ESR electrolytic capacitors these days, and you could parallel two or three of them to get the value you wanted, further decreasing overall ESR by putting them in parallel. The smaller size would make your layout more flexible, which could turn out to be an advantage in a circuit where you want low-noise. I have seen people cause unexpected problems by trying to shoehorn large parts into a build.
If you look at the product description for these film caps, you can see that they are intended for heavy-duty applications like power inverters, solar energy, automotive charging, etc... where their low ESR, non-polar, and long-life characteristics present advantages, being crucial to power networks. But do you need that in a phono preamp?
We do have very low-ESR electrolytic capacitors these days, and you could parallel two or three of them to get the value you wanted, further decreasing overall ESR by putting them in parallel. The smaller size would make your layout more flexible, which could turn out to be an advantage in a circuit where you want low-noise. I have seen people cause unexpected problems by trying to shoehorn large parts into a build.
If you look at the product description for these film caps, you can see that they are intended for heavy-duty applications like power inverters, solar energy, automotive charging, etc... where their low ESR, non-polar, and long-life characteristics present advantages, being crucial to power networks. But do you need that in a phono preamp?
This is like asking if the Pope sh*ts in the woods. A Catholic won't find it very funny, but a non-Catholic will, regardless of the truth.
First, here's my two cents:
My own personal experience with film vs electrolytics:
I built a Bottlehead Crack and "upgraded" the final PSU cap + the output caps to be humungous film capacitors. The moment I turned it on after the upgrade, I told myself it was a huge difference. Eventually I started to question this. So after a year of having them installed, I replaced all of the caps with electrolytics. Couldn't hear a difference.
TL;DR Do whatever is going to help you sleep at night--if you're convinced film caps will make a big difference, you'll need to use film caps whatever anyone else says.
I've tried to suggest a "middle ground" approach above. The idea with using 630V when all you need is ~250 V for the capacitors is that the higher voltage ones will be "higher quality" and will "sound better." In my latest amplifier build, I used "budget" Cornell-Dubilier film caps for signal coupling purposes at the 1 KV rating. They cost me less than $10 a pop and, as far as I can tell, sound great. That said, I haven't spent $500 on other caps and double-blind A/B tested them to determine if I could squeeze .1 - 5% "better sound quality" out of them.
First, here's my two cents:
- It looks like the schematic says you're running a B+ of 180 Volts. You can dramatically lower the size of the film caps necessary if you lower the voltage rating on the caps to 250V.
- I doubt you will hear any difference between quality electrolytic or quality film caps. I also highly doubt you will perform a double-blind A/B test on yourself to figure it out.
My own personal experience with film vs electrolytics:
I built a Bottlehead Crack and "upgraded" the final PSU cap + the output caps to be humungous film capacitors. The moment I turned it on after the upgrade, I told myself it was a huge difference. Eventually I started to question this. So after a year of having them installed, I replaced all of the caps with electrolytics. Couldn't hear a difference.
TL;DR Do whatever is going to help you sleep at night--if you're convinced film caps will make a big difference, you'll need to use film caps whatever anyone else says.
I've tried to suggest a "middle ground" approach above. The idea with using 630V when all you need is ~250 V for the capacitors is that the higher voltage ones will be "higher quality" and will "sound better." In my latest amplifier build, I used "budget" Cornell-Dubilier film caps for signal coupling purposes at the 1 KV rating. They cost me less than $10 a pop and, as far as I can tell, sound great. That said, I haven't spent $500 on other caps and double-blind A/B tested them to determine if I could squeeze .1 - 5% "better sound quality" out of them.
I have made decisions regarding the caps. I chose the Panasonic EZP series for the first two caps in the power supply and a pair of Mundorfs dual caps for the ones closer to the tubes. I've built, from schematics, a similar phono-stage, two identical pre-amps and a couple of mono-block SET amps. I AM a novice when it comes to understanding how circuits operate but my mechanical skills are somewhat adequate.
I checked the B+ on the first phono-stage I built like this and the voltage went to 270VDC for a few seconds until it settles to just over 220. PSUD shows it should produce 180VDC but IRL, I get 220 which brings into play another set of variables. I figure I need to have caps rated for greater than 250V because of this.
You are right I will not do a double blind test of the caps! I do appreciate your post.
What does TL;DR mean?
I use the 75uf 600v polypropylene film caps I get from Apex Jr on eBay for a great low cost power supply cap. They are $5 each! You can get four for the price of one you listed. The power supplies I’ve built with them are great giving more detail and weight to the sound due to low ESR. If room is no problem use them and never worry about electrolytic caps wearing out again.
I should have looked at those. The thing is, with this build, the cost of a $25 cap vs a $5 cap is not important as I just need a couple. Now the specs sure come into play! That is exactly what I was interested in.
I meant to come back and revise my comment after considering that the B+ voltage may exceed 250V upon turn on, but got distracted by work!
"TL;DR" -- "Too Long; Didn't Read"