Hello Christian,
another advantage of using a lot of small caps is that you can "shape" them to fit your amps package. I used 100 x 1000microF per channel and they fit nicely below the amplifier pcb´s on a sheat of plexiglas placed on the heatsink. (about 400mm x 100mm and only 40mm high)
This way I´ve got a very short path from cap to amp pcb.
william
another advantage of using a lot of small caps is that you can "shape" them to fit your amps package. I used 100 x 1000microF per channel and they fit nicely below the amplifier pcb´s on a sheat of plexiglas placed on the heatsink. (about 400mm x 100mm and only 40mm high)
This way I´ve got a very short path from cap to amp pcb.
william
Parralleling caps
It is usually a good idea to parallel caps but the some knowledge of the behavior of the capacitors being used is required. The goal is usually to spread the self-resonant frequencies of the capacitors in such a manor that the impedance presented by the capacitors remains fairly constant over a range of 10 to 50 Mhz or more.
This will require capacitors of many different values and types. Using parallel caps without knowledge of the capacitors behavior does not guaranty good results. Using audiophile specialty caps also does not guaranty good results.
There have been some very good articles posted on the Internet that address is issue. Capacitor selection has always presented a special problem to me so a number of years back I added a top of the line HP LCR analyzer to my work bench to help me resolve some of these problems. I have found this to be a good investment.
John Fassotte
Alaskan Audio
It is usually a good idea to parallel caps but the some knowledge of the behavior of the capacitors being used is required. The goal is usually to spread the self-resonant frequencies of the capacitors in such a manor that the impedance presented by the capacitors remains fairly constant over a range of 10 to 50 Mhz or more.
This will require capacitors of many different values and types. Using parallel caps without knowledge of the capacitors behavior does not guaranty good results. Using audiophile specialty caps also does not guaranty good results.
There have been some very good articles posted on the Internet that address is issue. Capacitor selection has always presented a special problem to me so a number of years back I added a top of the line HP LCR analyzer to my work bench to help me resolve some of these problems. I have found this to be a good investment.
John Fassotte
Alaskan Audio
ME SOUND (peter stein, nsw, australia) in ME850 class a amp, uses 50 * 3300 uF caps connected in "power matrix" per rail (amplifier total 330,000 uF). Gives extremely low impedence/frequency power supply section - requires soft start - one of these amps driving Duntech Sovereigns lifts the roof big time - Works for peter! Well worth it, If you are prepaired to spend the money on this technique.
Maybe this helps.
Maybe this helps.
Smaller Caps
I for one do believe in a larger numer of smaller caps. I do not use so-called audiophile caps but good quality low inpedance units(Philips, Seimens, RIFA would be fine!). I have built a number of amps of 100W output with 2/3 pairs of power devices and I designed the layout myself. What I do is to use a piece of low impedance cap of between 4700 - 10000uF per device and the pcb is designed in such a manner that the legs of the power transistor solders directly onto the leg of the cap(sorry, impossible for TO3's!!) which is further paralleled with a piece of ultra low impedance 100uF electrolytic cap and a 2.2uF film cap(available from Farnell & RS). For wiring, each cap/output device is fed by a SEPARATE wire from the rectifier and also a SEPARATE earth return to the main chassis earth (kind of messy and reminds you of hard wiring in early tube hifi sets). This way, you avoid the eddy currents that bounce around when many devices share a common power and earth track. (BTW, if you try this, use equal wiring lengths for each device- I'm paranoid about connection symmetry!!)You'll be pleasantly surprised with the difference in sound when you listen to quiet passages. Details are more and the sound is lively and bouncy while big tin can size caps tend to give a heavier and more sluggish sound but killer heavy weight bass! You will also find that you can "tune" the sound by changing the small paralleled E cap and film cap!
If you're happy with the sound, you may want to try running separate grounds with a "star chassis ground" arrangement for ALL other parts of your power amp or at least run a separate ground for the input section. Mixing your signal grounds with the power supply decoupling caps ground is a strict no! no!
Happy experimenting!
ckt
I for one do believe in a larger numer of smaller caps. I do not use so-called audiophile caps but good quality low inpedance units(Philips, Seimens, RIFA would be fine!). I have built a number of amps of 100W output with 2/3 pairs of power devices and I designed the layout myself. What I do is to use a piece of low impedance cap of between 4700 - 10000uF per device and the pcb is designed in such a manner that the legs of the power transistor solders directly onto the leg of the cap(sorry, impossible for TO3's!!) which is further paralleled with a piece of ultra low impedance 100uF electrolytic cap and a 2.2uF film cap(available from Farnell & RS). For wiring, each cap/output device is fed by a SEPARATE wire from the rectifier and also a SEPARATE earth return to the main chassis earth (kind of messy and reminds you of hard wiring in early tube hifi sets). This way, you avoid the eddy currents that bounce around when many devices share a common power and earth track. (BTW, if you try this, use equal wiring lengths for each device- I'm paranoid about connection symmetry!!)You'll be pleasantly surprised with the difference in sound when you listen to quiet passages. Details are more and the sound is lively and bouncy while big tin can size caps tend to give a heavier and more sluggish sound but killer heavy weight bass! You will also find that you can "tune" the sound by changing the small paralleled E cap and film cap!
If you're happy with the sound, you may want to try running separate grounds with a "star chassis ground" arrangement for ALL other parts of your power amp or at least run a separate ground for the input section. Mixing your signal grounds with the power supply decoupling caps ground is a strict no! no!
Happy experimenting!
ckt
Capacitor size
If you have a choice between 2 capacitors, same manufacturer, same series, same voltage, same value........except one is tall and skinny, and the other is short and fat:
Choose the short and fat one. It will handle more ripple current, and last longer. Might even sound better.
Jcko.
If you have a choice between 2 capacitors, same manufacturer, same series, same voltage, same value........except one is tall and skinny, and the other is short and fat:
Choose the short and fat one. It will handle more ripple current, and last longer. Might even sound better.
Jcko.
Form factor
It is such that the short, fat ones are better able to dissipate the heat generated internally by the ripple currents. Mepco used to put out some good technical advice on this stuff. Now that Philips owns them........well, who knows.
Built an amp once with an array of tall, skinny caps with good specs. Sounded awful. There was no short, fat counterpart in that series. Rebuilt the amp with one big one, much better. Doesn't mean it will always be that way. Just worked out that way on that project. I have some other thoughts on filter caps you might want to hear, but they are subjective.
It is such that the short, fat ones are better able to dissipate the heat generated internally by the ripple currents. Mepco used to put out some good technical advice on this stuff. Now that Philips owns them........well, who knows.
Built an amp once with an array of tall, skinny caps with good specs. Sounded awful. There was no short, fat counterpart in that series. Rebuilt the amp with one big one, much better. Doesn't mean it will always be that way. Just worked out that way on that project. I have some other thoughts on filter caps you might want to hear, but they are subjective.
Fat and skinny of it
Hmmmmm...... I always liked tall and skinny ones for Panasonic HFQs under 1000uF. I am well familiar to your preference for fat ones when it comes to the response to the bottom end. Am dying to hear your subjective observations...... I have a feeling that there are some mechanical resonance considerations in the form factor. I have heard differences in caps from the same manufacter,
the same series, the same voltage, the same value, but different
height and diameter.
H.H.
Hmmmmm...... I always liked tall and skinny ones for Panasonic HFQs under 1000uF. I am well familiar to your preference for fat ones when it comes to the response to the bottom end. Am dying to hear your subjective observations...... I have a feeling that there are some mechanical resonance considerations in the form factor. I have heard differences in caps from the same manufacter,
the same series, the same voltage, the same value, but different
height and diameter.
H.H.
Hairy Holler:
You may be right for HFQs and the like. They probably have lower ESL. There is a place for skinny ones here, and they do come in handy as decoupling. Especially for digital stuff.
Unless you can afford those expensive carbon types.
I was refering to filter caps. 10,000 uF and up types.
Yep, that amp I built with skinny caps had no bottom at all. Not my plate of shrimp..........
You may be right for HFQs and the like. They probably have lower ESL. There is a place for skinny ones here, and they do come in handy as decoupling. Especially for digital stuff.
Unless you can afford those expensive carbon types.
I was refering to filter caps. 10,000 uF and up types.
Yep, that amp I built with skinny caps had no bottom at all. Not my plate of shrimp..........
A few things no one mentioned, i think.... using multiple caps have other advantages besides ESR and the works.
- 1. More voltages rating available on smaller caps than bigger ones. This came in handy for me, as my PSU delivers 22vdc, so i was able to order 35v caps instead of the "regular" 50v ones and save quite a few bucks. The bigger "can" caps came only in 50v and 100v ratings.
-2. Smaller caps are cheaper than a bigger cap at the same capacitance. I didn't expect this, but it is so My cap-x power supplies has 54,400 uF in total, and that costed me $40; about 1300uF per buck (not counting bypass caps included in that too). Not bad!
- 1. More voltages rating available on smaller caps than bigger ones. This came in handy for me, as my PSU delivers 22vdc, so i was able to order 35v caps instead of the "regular" 50v ones and save quite a few bucks. The bigger "can" caps came only in 50v and 100v ratings.
-2. Smaller caps are cheaper than a bigger cap at the same capacitance. I didn't expect this, but it is so
My cap-x power supplies has 54,400 uF in total, and that costed me $40; about 1300uF per buck (not counting bypass caps included in that too). Not bad!Normally alot of small caps cost less at the same capacitance. But you have to remember that you need a lot more work and maybe a heavy duty pcb to carry all the caps. I like a lot more small caps than 1-2 big ones. But you DO have to know the specs of them because it is very important when designing.
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