Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: deltaunit on April 18, 2011, 03:21:37 AM
-
Has anyone experimented with upgrading the PS caps, either with higher quality electrolytics or larger sizes?
I understand that lowering the size with have a negative audible affect due to the ripple getting through but are there any disadvantages to fitting larger caps, will they have an increased smoothing capability?
I'm interested in hot-rodding my amp up so am interested to hear if there are any benefits of upgrading these caps.
-
Capacitor values in the power supply are specifically chosen to filter out certain frequencies of noise. When replacing caps, I stay as close to spec as possible. I am a firm believer that Doc and Paul are much smarter than I am, and they chose those values for a reason.
-
You mean like this? I cant say exactly how much of an improvement is was, since I built it initially with the cap in place. I was said earlier that upgrading the final cap in the power supply would improve the performance significantly, so I did.
-
That's the type of thing! Well, I hadn't thought of going that large but yes! :)
I'm getting access to an oscilloscope in a couple of weeks and was just wondering if the larger the caps the better the smoothing or if there were any drawbacks of going large...?
I'd also be interested to know why the main improvement is to be made on the last cap in particular, rather across the board (expense?) or on the first taking the largest ripple...
-
The output audio current flows through the power supply, mostly the last capacitor, as well as through the output coupling cap and the output triode. So the final power supply cap should, in theory, be as important as the output coupling cap with regard to the sound of the amp. This is a characteristic of cathode follower circuits, such a the Crack and the Foreplay.
-
An alternative to bigger 'lytic caps might be to try a film bypass cap across the last filter cap.
-
Thanks Paul, I think I understand you, it's the quality of output on the last cap that matters most in the PS caps, improvements further up the chain could be lost otherwise.
Are there any drawbacks or benefits to increasing a smoothing reservoir sizes, in general?
I am planning on upgrading the coupling caps to some big polyprop caps at some point, the reason I'm asking about the PS caps now though is that I might be able to sneak some free components from RS!
I have my eye on a military spec 6080 too. Lot's of fun this Bottlehead project :)
---
Ah, thanks doc that confirms my suspicions! I was thinking that a big reservoir further up the chain and a very high quality last cap might be ideal, but not knowing anything about electronics (yet!) the hq bypass sounds like a good idea. I might do both!
One of the great things about your kits is the amount of new stuff you learn - thanks again.
-
In a two capacitor power supply the first cap sees horribly lumpy DC. It does filtering/smoothing for that. There is no need to buy a better sounding cap for this position. The second does a little smoothing and is the source of energy for the tubes if it is a two stage filter.
In two or three cap power supplies the last capacitor is the energy source for your tubes. The energy release (lower ESR caps and higher uF) is important here.
I'm also a big fan of the bypass cap that Dan mentions.
After last weekend I also think that you could use a choke to replace the resistor between the first and second cap in the power supply. The DC resistance of the choke should be similar to the resistor. The inductance will block high frequency noises that a resistor will pass on like a piece of wire.
-
I have two cracks, one "stock",one speedballed. Both have these Jensen caps in the #3 cap position , in the "stock"crack I put a even larger cap in the first position. This cap is however a 350uF cap (I understand this is a deviation from the original design). I put it in as a experiment, because it was cheap from a surplus shop. And I like the results. I ALMOST like it better for simple music (instrumental, solo vocal). It really surprised me at first, but I soon realized that the speedballed version did more complex passages better. Could this cap have changes things for the better?or am I imagining?
-
I post this with some frequency: "I never met a power supply improvement that was not also a sonic improvement."
-
An alternative to bigger 'lytic caps might be to try a film bypass cap across the last filter cap.
I like the idea of the bypass, any recommendations for this? I was thinking of one of those Russin PIO or teflons to bypass the Erse cooupling caps...
-
I would try both, even at the same time. First the PIO then add the Teflon. You can try this with jumpers to see if you like the sound first then solder them in if they appeal to you.
-
Thanks.
I am planning on using 1.0uf for bypassing the Erse output caps. What would be a good range for bypassing the PS cap? Prolly 400V for both.
-
Anything at the 250V range or higher will be safe. I bought groups of KK PIO and Teflon caps. I have used a 2.2uF and a 0.1uF both bypassing power supply caps.
Again, try it with jumpers first to see if it sounds right.
-
OK Thanks, sounds like a plan!
-
Check out this sitehttp://humblehomemadehifi.com/Cap.html (http://humblehomemadehifi.com/Cap.html)
Look at the comments for the Vishay MKP 1837. I ordered some and plan to test them in a crossover network.
John
-
Check out this sitehttp://humblehomemadehifi.com/Cap.html (http://humblehomemadehifi.com/Cap.html)
Look at the comments for the Vishay MKP 1837. I ordered some and plan to test them in a crossover network.
John
The reviewer certainly seems to like them, but it looks like they are only rated to 160V (at least in so far at what's available on mouser and partsconnexion). Per Grainger's post, bypass caps in the crack power supply should be in the range of 250V or higher.
-
I said that 250V or higher "would be safe." I don't know what the power supply "floats" to before the tubes start conducting. The highest voltage in the manual for checkout is 205V. But it will probably be higher when starting.
-
Thanks for the clarification Grainger! If you have a chance, could you elaborate a bit on your 4/18 post from page one?
I'm trying to better understand exactly what is accomplished by adding a small bypass cap in parallel with the third cap in the power supply. Are you basically just further reducing ripple voltage, as discussed on: http://www.seattlerobotics.org/encoder/jun97/basics.html
-
Thanks for the clarification Grainger! If you have a chance, could you elaborate a bit on your 4/18 post from page one?
I'm trying to better understand exactly what is accomplished by adding a small bypass cap in parallel with the third cap in the power supply. Are you basically just further reducing ripple voltage, as discussed on: http://www.seattlerobotics.org/encoder/jun97/basics.html
Dang! And I thought I had written too much already.
There can be reactions between the larger power supply caps and a bypass cap because of the combination of capacitance, resistance and inductance in capacitors. (BTW, resistors and inductors also have capacitance, resistance and inductance.) For my pragmatic way of doing things I first put the bypass caps in with jumpers. If I like the results I then solder them in. I have bypassed my Foreplay power supply caps (220uF@250V) with Russian military surplus 2.2uF paper in oil (PIO) and 0.1uF Teflon caps.
-
The vishay mkp-1832 caps are very nice, but unfortunately, due to the voltages in the crack, there is really no place for them -- definitely not in the power supply, and they are most likely not even rated high enough for use as bypass caps ion the output caps. We discussed their use as output coupling cap bypasses some time ago in the earliest thread on cap rolling for the crack. They're also fairly small.
-- Jim
-
Thought I should update this thread with my findings on the o-scope seeing as I brought it up earlier.
Well the results are in and well, there was no measurable amount ripple on the last cap - the stock design works perfectly! :D
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FF04of.jpg&hash=fe8841f8080d0bbd902e1b949555bcbec76e77dc)
N.b. The spikes with the regular interval in this image appear whether the scope is connect to anything or not at maximum sensitivity and so can be discounted. This was taken at the maximum sensitivity and shows a straight a line as can be.
Here is the second cap at a much lower sensitivity.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FIz1Vh.jpg&hash=98237d15318c8de82ec39afb56f6e51b5659473c)
That doesn't mean any upgrade on the last cap won't reduce any residual noise further though, so I'll still be upgrading it!
-
I initially purchased a Solen 220uF film cap to replace the last capacitor, however it was just too large to fit without extremely creative mounting. I ended up bypassing with a Auricap 2.2uF I happened to have in the parts bin. I felt that there could have been a slight difference in the smoothness of the presentation, but it could have easily been placebo in this case. People like John Broskie recommend film bypasses in the power supply, so it can't be a bad thing ;)
-
I think Doc should offer an separate blank case kit for just this requirement! Just a solid metal top and wooden sides ready to filled with big poly and oil caps. :D
-
Outboard power supplies have been around for quite a long time. I built my first two Bottlehead kits with the power supplies in outboard boxes. Having all AC three feet away reduces any chance of hum.
That leaves room in the audio chassis for all sorts of goodies where the power supply was designed to be.
-
I think Doc should offer an separate blank case kit for just this requirement! Just a solid metal top and wooden sides ready to filled with big poly and oil caps. :D
That's quite available right now. We can sell you a wood base kit and you could order a custom plate from Front Panel Express.
-
Hi Guys stupid question but i have to ask it. Lets say I want to bypass the last cap in the power supply. What value would you suggest? Must it match the 250v output of the original cap. as in I would sourche a 0.22uf 250v cap to do this? Or can the voltage be higher as in 400v 0r 600v ie 0.22uf 600v. And is there a recomended value for the UF value. as in 0.1uf etc. That being said IF i used a 250v cap could I aplly that on the output caps as well. ie I have the same make and model 0.22uf 250v cap bypassing the 2 output caps and the last power cap- or am i missing the boat here??
IF i am correct in my understanding then I would have two options availbe to me
Option A replace the two stock output caps with 2 ERSE 100.0μF 250v PulseX - Metallized Polypropylene Film Capacitors
and
BYPASS the last Power cap with a 1.0μF 250v PulseX - Metallized Polypropylene Film Capacitor
Option B
BYPAS the two stock output caps and the stock power cap with a 1.0μF 250v PulseX - Metallized Polypropylene Film Capacitor on each?
for the sake of interest should the above be viable could I then bypass the first two power caps as well with the same 1.0μF 250v PulseX - Metallized Polypropylene Film Capacitor? or should I push up the power caps bypas to something in the 2.2uf range since I read somewhere that a good rule of thumb is using a 1/100 value for bypassing?
-
Ok, I'll take a stab but just to get you started. Im not an expert at this by any stretch so take it as food for thought, not gospel.
There is no advantage in using a bypass cap of a higher voltage than required ( than the cap you are bypassing). In fact, if Im not mistaken, higher voltage caps may even be a disadvantage over using a cap with a lower (but still ample) voltage rating (related to higher inductance of the larger/higher V caps compared to the smaller lover V caps).
There is the possibility of audible resonance when bypassing a larger value cap with a small value (because of interaction with the inductance of the larger cap) . Not sure if it's really, normally a problem because bypassing seems to be the "norm". Ive read it argued that it would only occur at frequencies well above the audible range and then arguments that it can indeed be audible.
The ratio between bypass cap and cap that is being bypassed is of much debate. 1/100, 1/10, 1/1000, multiple bypass caps ... seems like there is an argument for any and all of them.
Remember, this is all general stuff from my laymens grasp. Im sure Ive missed a lot and I dont understand all the tech. aspects of it. Others will jump in and correct me or elaborate, or both.
But here is a thread on the forum that discusses some of this to get you started ... http://www.bottlehead.com/smf/index.php/topic,1723.0.html
-
To piggy back on Laudanum's excellent post . . . higher voltage caps often have higher ESR, equivalent series resistance, and inductance than a similar series cap of a lower voltage. For instance, if you measure two Mundorf M-Caps of the same value and of different voltage ratings you will probably find a higher ESR and inductance from the one with the higher voltage rating.
When a circuit is called upon to release the energy stored in the capacitor the series resistance slows that release. So that is a reason not to select a higher voltage. A reason to select a higher voltage is it is in your parts box and costs nothing.
Parallel capacitors can cause resonance because of the capacitance, inductance and resistance that they contain. That is just one reason to try first using jumpers.
That said I have never had a problem with a bypass cap that I could hear. I haven't measured the circuit with a sweep to check.