Crack;Bottlehead OTL
Apr 26, 2015 at 5:14 AM Post #6,857 of 12,297


In the last two days I have bypassed the 100uf mkp solens I'm using for coupling caps with 1 uf, k73-11 PETP kommiekaps which I then bypassed with 0.1uf vishay-roederstein mkp 1837 bypass caps. I noticed a slightly wider soundstage with improved dynamics and bass extension. Earlier today I replaced the last electrolytic in the power supply with a 100uf obbligato PSU film cap; having already installed a choke. Haven't given it a proper listen to identify any changes. Next week I plan on bypassing the remaining electrolytics with china film caps.

Then my dad's friend offered to make me a new case for my crack, one that is both wider and deeper, designed to accomodate a speedball board, second choke, more film caps in the psu, schotkky diodes, and a switch board to change bias' so I can run 12au7 or 12bh7, pilot light all while still being a perfect fit for the plate so it can continue to be gravity mounted.

I can't wait for summer, I will post many project updates with pics.
 
Apr 26, 2015 at 2:58 PM Post #6,858 of 12,297
Ok so I really want somebody to please explain to me or point me to a post that can explain the importance of the uf rating on caps. Do you have to replace the output caps with two 100uf caps or what will the effect be if you use one with a much lower uf? and what is the point of bypassing caps? How does that work? Sorry for all the questions I just really want to understand this and will appreciate a response a lot.
 
Apr 26, 2015 at 7:39 PM Post #6,859 of 12,297
uF is the value of the capacitor. Larger number mean more capacitance. Not always better. Circuits are designed using a particular value for a reason. Often the size chosen is a compromise between several diverse constraints. Here is some reading to further your knowledge:
 
http://en.wikipedia.org/wiki/Capacitor
 
Apr 26, 2015 at 8:00 PM Post #6,860 of 12,297
  Ok so I really want somebody to please explain to me or point me to a post that can explain the importance of the uf rating on caps. Do you have to replace the output caps with two 100uf caps or what will the effect be if you use one with a much lower uf? and what is the point of bypassing caps? How does that work? Sorry for all the questions I just really want to understand this and will appreciate a response a lot.

 
Since you mention the output caps specifically, the 100uF output cap forms a 1st order high pass filter where the impedance of your headphone is the load. The formula to calculate the resonant frequency of this filter is fc = 1 / (2*pi*R*C), where R is the load resistance, or the impedance of your headphones, and C=100uF.
 
In the case of the popular HD600/650, they are rated at 300 ohms, so fc = 1/(2*3.14159*300*100e-6) = 5.3 Hz.
 
This means at 5.3 Hz, the frequency response is down by 3dB, which is known as the cutoff frequency. It doesn't mean there's no signal below 5.3 Hz as there is a gentle roll-off below 5.3 Hz. 
 
Note: In actuality, the impedance of your headphone varies with frequency so this formula is only an approximation. 
 
So if you cut the output capacitance in half, your f3 doubles to 10.6 Hz. Although this might not sound bad at first glance, you have to realize that the frequency response starts to roll off much higher than the f3 frequency, so to maximize the (low) bass response you want to make the output cap large. Note also that if the impedance of your headphones is much lower, that also raises the f3 frequency.
 
Explaining a bypass cap is more complicated. Large electrolytic caps have rising series resistance as frequency rises, and this resistance could be significant enough at higher frequencies to be audible (attenuation of highs). A common way to combat this is to place a small film cap in parallel that has much lower series resistance at high frequencies. It's been debated whether this actually helps, but there's plenty of anecdotal evidence that it does.
 
Apr 27, 2015 at 6:09 PM Post #6,862 of 12,297
Speaking of caps I've been looking into getting some polypropylene ones for my build. After doing some measurements it looks like Solen 250v 100uf will fit nicely in the stock base mounted to the chassis.
 
Whats the best way to mount them? I was thinking of using some sort of bracket with double sided tape and zip ties and was curious if anyone had any good recommendations.
 
Apr 27, 2015 at 6:13 PM Post #6,863 of 12,297
  Speaking of caps I've been looking into getting some polypropylene ones for my build. After doing some measurements it looks like Solen 250v 100uf will fit nicely in the stock base mounted to the chassis.
 
Whats the best way to mount them? I was thinking of using some sort of bracket with double sided tape and zip ties and was curious if anyone had any good recommendations.

 
Quiet a few me included have used "self adhesive cable tie mounts" plenty to choose from on ebay etc 
 
Apr 28, 2015 at 1:49 AM Post #6,866 of 12,297
Apr 28, 2015 at 2:44 AM Post #6,867 of 12,297
Most zip tie mounts have a screw hole in the middle. After you pick your spot and stick them down, just drill straight through the aluminum with a small bit. Pop in a screw and nut = no falling off.
 
Apr 28, 2015 at 2:55 AM Post #6,868 of 12,297
^ ^ even better. You don't want something falling loose. Things do warm up in there.
 

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