Questions regarding β22
Jun 28, 2007 at 10:41 PM Post #17 of 28
Quote:

Originally Posted by cotdt
as filters they seem to work just fine


I stand corrected then. I assumed that since they are undesirable in amplifiers the same would apply for filters. Either way, I do not require any here.

As for the previously mentioned film caps, is there a recommended size for these? I have seen everything from 0.47 uF and up.
 
Jun 28, 2007 at 10:56 PM Post #18 of 28
try it without the low-pass filter first. it seems to sound fine without the low-pass filter straight out of the DAC chip, but I couldn't get much volume out of it so it's not a proper evaluation.
 
Jun 29, 2007 at 7:41 AM Post #19 of 28
Quote:

Originally Posted by cotdt
try it without the low-pass filter first. it seems to sound fine without the low-pass filter straight out of the DAC chip, but I couldn't get much volume out of it so it's not a proper evaluation.


If you are talking about the WM8740, I'm guessing this is because it already has an internal low-pass filter. Its cutoff frequency of 195 kHz is a bit on the high side however. I had planned to add an external low-pass filter with a cutoff of 40 kHz.

You say you couldn't get much volume out of it, should I increase the gain of the beta22? I had planned to run with a gain of 2 (this is for balanced headphones), should I perhaps increase this to 5?

About the coupling caps, these form a high pass filter together with the coupling resistors. I had planned to set this at around 5 Hz. Is there a minimum size I can use for the caps? Good film caps become rather expensive as the size go up.
 
Jun 29, 2007 at 1:32 PM Post #20 of 28
Quote:

Originally Posted by Cauhtemoc /img/forum/go_quote.gif
If you are talking about the WM8740, I'm guessing this is because it already has an internal low-pass filter. Its cutoff frequency of 195 kHz is a bit on the high side however. I had planned to add an external low-pass filter with a cutoff of 40 kHz.

You say you couldn't get much volume out of it, should I increase the gain of the beta22? I had planned to run with a gain of 2 (this is for balanced headphones), should I perhaps increase this to 5?

About the coupling caps, these form a high pass filter together with the coupling resistors. I had planned to set this at around 5 Hz. Is there a minimum size I can use for the caps? Good film caps become rather expensive as the size go up.



The size of the cap only depends on the input impedance of the next stage (amp) and since you've got the B22 at 1M with the formula being f = 1/(2 * π * R * C), you can calculate it fairly easily.

f = 1/(2 * π * R * C)
f = 1/(2 * π * 1,000,000 * 0.000,000,47)
f =~ 0.338 Hz with a 0.47uF cap
or
f =~ 1.592 Hz with a 0.1uF cap
or
f =~ 3.386 Hz with a 0.047uF cap

Lots of options, but considering the price differences between the caps being only a buck or two, just grab whichever one and you'll get a pair of AuriCaps for around $25, well worth it.
 
Jun 29, 2007 at 4:28 PM Post #21 of 28
I know how to calculate the cutoff frequency for a filter.
smily_headphones1.gif
I wasn't sure if there was a minimum size for the capacitor. I assume there is not.

Is there a big difference between AuriCaps and Black Gate NX for example? The AuriCaps are quite a bit more expensive.
 
Jun 29, 2007 at 10:54 PM Post #23 of 28
If they are that much better then I guess I don't have much of a choice.
smily_headphones1.gif


Looking at the schematic for the beta22, I'm having trouble deciding what 100 uF and 470 uF electrolytic capacitors to use. Any recommendations? What should I be looking for? Low impedance, high ripple current?
 
Jun 30, 2007 at 12:06 AM Post #24 of 28
Quote:

Originally Posted by Cauhtemoc /img/forum/go_quote.gif
Looking at the schematic for the beta22, I'm having trouble deciding what 100 uF and 470 uF electrolytic capacitors to use. Any recommendations? What should I be looking for? Low impedance, high ripple current?


My advice is just to go with the recommendations at the β22 website parts list. There is no need to obsess about these caps as long as you don't use utter crap (and I wouldn't recommend those on the website).
 
Jun 30, 2007 at 10:08 AM Post #25 of 28
Quote:

Originally Posted by amb
My advice is just to go with the recommendations at the β22 website parts list. There is no need to obsess about these caps as long as you don't use utter crap (and I wouldn't recommend those on the website).


You want me to go with the recommendations on the website, at the same time as you wouldn't recommend those on the website? A bit contradictory don't you think?
smily_headphones1.gif


I have seen the list of recommended parts but it doesn't say why they are recommended. I assume these caps act as a buffer for the power supply, in which case low impedance is the most important factor? Low impedance means they can discharge faster, which is what you want, right?
 
Jun 30, 2007 at 11:07 AM Post #26 of 28
The way I read amb's comment was that he recommends you use the parts list on the beta22 site; you don't need to obsess about caps as long as you don't use utter crap caps, and he wouldn't recommend utter crap caps on his site for his parts list.
 
Jun 30, 2007 at 11:19 AM Post #27 of 28
Yes, what Nebby said.

While low ESR is a good thing, the circuit design of both the PSU and the amp is such that the small differences between any of the recommended caps will not cause any measurable or audible difference.
 

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