[Tom-s]

Even more details plus a better defined and more pronounced bass were the most noticeable improvements. I paid 15€ for the 6080WB Raytheon "tested by Bendix" and 40€ for the Bendix. For that money, it's worth it.

 

[Solarium]

Any comparisons of the Crack-a-two vs the Crack w/ speedball yet?

Does anyone own a Crack 2? I'm debating whether to upgrade to that or the Elise.

 

[ClintonL]

Where'd you get the tested by bendix one btw? Can't find one on ebay.

 

[larcenasb]

I was reading page 205 of this thread, about padding the volume pot for more breadth and fine-tuning of the volume. I just want to get this right before I start soldering. Anyone with experience, I'd really love to get your affirmation and any tips. Thanks!
 
http://www.goldpt.com/mods.html
 
I don't have experience reading schematics, but from what I'm seeing from the link: in order to pad my Alps Blue Velvet 100K pot to get -20db of attenuation and not change the input impedance, I should, 1.) de-solder the wire from the "in" of the pot, 2.) solder an end of an 82.5K (1/2W okay?) resistor to that wire, 3.) solder the other end of the resistor to the "in" terminal of the pot and also to an end of a 10K (1/2W?) resistor, then 3.) solder the other end of the 10K resistor to the ground terminal of the pot. And do this separately for each channel. Is this correct? Thanks so much!

 

[ScottFW]

^^^ Sounds like you've got the right idea. I also have the Blue Velvet 100K pot and usually stay towards the low end of the range w/ HD650s, I just never felt like padding the input since mine measures very evenly between both channels even at the low end of its range.
 
1/2 watt resistors are overkill, 1/8 W will do fine, and the Vishay / Dale RN55 series are an inexpensive and sonically neutral option.

 

[larcenasb]

Thanks ScottFW. Although, I already have 1/2W resistors. That's okay right? Or should I buy the 1/8W? Thanks again for your help. Take care.

 

[ScottFW]

By all means, use 1/2 watt if that's what you already have, it's no problem.

 

[deserat]

Step one.  Crack meets Acid and Bath Salts.  ( ok, the only salts I actually had in the house were himalayan pink )
 

 

[larcenasb]

In the process of upgrading my crack further. I want to replace the last capacitor in the power supply, I have a question though:
 
What should yield more benefit, a 1000uF 250V electrolytic (from BHC or Rifa) or a 220uF 250V film capacitor (from Solen)? And why?
 
They're about the same size, thanks for your time.

 

[grausch]

Based on my understanding, higher capacitance may lead to more bass, but the Crack is already pretty well optimised, thus most of the uF above 220uF may not have any effect (other than the caps taking longer to discharge). There is some math on the Bottlehead forum which will allow you to calculate the corner frequency (I believe it is called this) and Paul Joppa has commented more than once that the final PS cap is part of the audio chain. My own interpretation would be that changing the capacitance on the final PS cap may lead to more / less bass. However, my understanding of this is purely based on forum discussions, so take it with a grain of salt.
 
Almost everyone believes that film caps offer a genuine sonic improvement, thus it may make more sense to go for the film.
 
My own build has the first 2 PS caps upgraded to 470uF electrolytic caps and I have a 270uF film cap as the last cap. Tough to say if there are any improvements since A/B comparisons are tough to make while working on the Crack. However, due to the increased capacitance, the audio takes about 7 seconds before it fades out once I switch the power off.

 

[tomb]

Sorry - just saw this in passing.  The corner frequency has nothing to do with caps in the (Power Supply) PS.  The corner frequency occurs because the impedance of a pair of headphones combines with the amplifier's output capacitors to form an RC circuit.  An RC circuit, depending on configuration, will filter out certain frequencies.  In the case of output capacitors on a DAC or headphone amp, they filter out bass.  The circuit phenomenon is dependent on the values of R (the headphone impedance) and C (the output capacitor).  Increase either one and it will move the "corner" of where the bass has dropped by -3dB further down in the frequency range.
 
For instance, if you combine a 32 ohm headphone with an amp that has 220uf output capacitors, you will lose some bass.  With a headphone of 300 ohms, 220uf capacitors will push the bass drop below 20Hz so you won't hear any lack of bass.  That's one of the reasons (among others) that people say OTL amps are bad for low impedance headphones.  You can up the size of the output capacitors, but they are typically very large and expensive at the high voltages of a tube amp.
 
In terms of a PS, a film cap may be there specifically to tame higher-frequency transients (hash or even preventing oscillation) that may be coming off of the power supply.  Film capacitors have little to do with removing ripple and hum - that is performed by the electrolytic(s) in the power supply.  Replace the film cap with an electrolytic and you may be increasing the power supply noise, not improving it.

 

[larcenasb]

Thanks grausch, yeah I use 600ohm AKG K240s, the bass is just fine on mine. But I've read others who've replaced the caps with higher uF caps and saying power delivery increases and background is blacker. Did you notice that at all?
 
Thanks for the thorough explanation tomb! I understand better now. However, did you mean "Replace the electrolytic cap with a film cap and you may be increasing the power supply noise, not improving it."? Based on what you said about film caps having nothing to do with removing ripple and hum, that makes sense -- was that a mix-up?
 
So, my understanding now is that electrolytics are important in a PS to remove ripple and hum, so replacing them with film outright is not a great idea -- but bypassing with film is good as it can add a bit of smoothness to the de-rippled and de-hummed signal. Is that fair to say?

 

[mcandmar]

Larger capacitance can reduce the ripple level by smoothing out the 50 or 60hz mains frequency of the power supply, which translates into less audible hum. A stock crack does a perfectly acceptable job of this so adding more capacitance isn't really going to do anything for you. If anything it may be a disadvantage as you are putting more of a strain on the power supply having to charge up such a large reservoir, especially on startup. IMO a 1000uf 250v capacitor is way too large and not really suitable for this application. If you did want to filter more hum there are much better ways to do that instead of bulk capacitance, i.e. use chokes in the power supply, or add another resistor and capacitor stage to the power supply.
 
All capacitors have a bit of resistance and inductance, a film capacitor is closer to a perfect capacitor in that it has much lower values of each than an electrolytic capacitor. In theory using a 220uf film cap could give better high frequency response and dynamics, but i stress the "theory". I used a Solen 220uf film cap in my crack, and honestly i cant say if it does make a difference or not.
 
A 220uf electrolytic and a 220uf film cap with do roughly the same job at smoothing ripple in a power supply. I think what tomb is referring to is small value film caps that are commonly used in circuits to target certain frequencies, which isn't applicable to a stock crack circuit.
 
In short the big electrolytic is a bad idea, the film cap may be an advantage, but i really don't think its worth the cost. I would buy a nice set of output caps or tubes instead

 

 

[grausch]

  Thanks grausch, yeah I use 600ohm AKG K240s, the bass is just fine on mine. But I've read others who've replaced the caps with higher uF caps and saying power delivery increases and background is blacker. Did you notice that at all?

 
Can't say I did. My stock Crack was pretty damn good with absolutely zero issues. My biggest issue was when I rebuilt the Crack and had a flaky solder at at T13 which is one of the legs of the final PS cap. That made the Crack sound flat and is why I believe the last PS cap influences the sound, although tomb's and mcandmar's explanations are most probably correct and mine not.

 

[larcenasb]

Thank you grausch and mcandmar, I definitely learned a lot from your answers! I bought Cree Schottky diodes for the power supply and will now plan to get Dayton 100uF 250V output caps. Later on, maybeeee I'll get Mundorf 220uF electrolytics for the power supply just for kicks. Thanks again for your time and help. Happy listening and take care!