Hello guys, (I need memory jolt)
I have seen in amp power supplies where they connect
caps in parallel to increase capacitance where they would
have one smaller cap in parallel with the larger one. The idea
was obviously to increase overall capacitance to a certain level.
But it seems to me there is another reason I just can’t remember
exactly what it is. It seems to me it had something to do with
charge and discharge time but I’m not sure.
Thanks
I have seen in amp power supplies where they connect
caps in parallel to increase capacitance where they would
have one smaller cap in parallel with the larger one. The idea
was obviously to increase overall capacitance to a certain level.
But it seems to me there is another reason I just can’t remember
exactly what it is. It seems to me it had something to do with
charge and discharge time but I’m not sure.
Thanks
To lower ESR over multiple frequencies.
Small bypasses .01-10uf are mainly for bypassing a larger cap at higher frequencies due to its poorer ESR, impedence path to ground for AC at these frequencies. But with everything there is of course always a catch, you can very easily go overboard with bypassing and cause more problems than without bypassing. Many will say stager them in 1/10th values downward but even that can very easily be overkilll. Typically an audio grade capacitor will have datasheets which list their ESR at high frequencies, with bypassing you dont want to cover too much of the frequencies already taken care of by the large caps but frequencies above at which it will be weakest and drop out of the circuit at as a decent rule of thumb
Colin.
Small bypasses .01-10uf are mainly for bypassing a larger cap at higher frequencies due to its poorer ESR, impedence path to ground for AC at these frequencies. But with everything there is of course always a catch, you can very easily go overboard with bypassing and cause more problems than without bypassing. Many will say stager them in 1/10th values downward but even that can very easily be overkilll. Typically an audio grade capacitor will have datasheets which list their ESR at high frequencies, with bypassing you dont want to cover too much of the frequencies already taken care of by the large caps but frequencies above at which it will be weakest and drop out of the circuit at as a decent rule of thumb
Colin.
Thanks for the reply,
I have seen cases including some of the diy amps
where for example they would have a 10,000uf cap
coupled with a smaller cap "say 8200uf or smaller".
I knew there was a reason other than the obvious
increase in capacitance. I just couldnt remember what
the advantage of doing this was
I have seen cases including some of the diy amps
where for example they would have a 10,000uf cap
coupled with a smaller cap "say 8200uf or smaller".
I knew there was a reason other than the obvious
increase in capacitance. I just couldnt remember what
the advantage of doing this was
If they have used 8,200uF in parallel with 10,000 uF , it is most likely because they wanted 20,000uF but did not have any other 10,000uF available. Using 2 in parallel like this to achieve the higher capacitance also results in lower impedance at HF. If space permits, this may be far more cost effective than a larger , more expensive type with low ESR.
SandyK
SandyK
" .. But it seems to me there is another reason I just can’t remember exactly what it is. It seems to me it had something to do with charge and discharge time ..."
There is a relatively new trick with audio op-amps involving parallel caps of differing types. Take a look at Page 15 of this: http://www.analog.com/UploadedFiles/Data_Sheets/AD8065_8066.pdf Note the parallel caps bypassing the power rails. These are usually speced out as a combination regular electrolytic and plastic (polypropylene, polystyrene, MKT type). The plastic caps are usually placed very close to the op-amp (close coupled), but the electrolytics can be anywhere on the smaller boards.
The results are much better specifications for the op-amps (better THD, less phase shifting, better CRMM & PSRR, etc.).
😕 
😕 😀 😉 😎
(SandyK is also correct ... parrallel caps are "additive" [C + C + C = 3C], serial caps not [1/C + 1/C + 1/C = 3/3C] ... http://en.wikipedia.org/wiki/Capacitor .)
There is a relatively new trick with audio op-amps involving parallel caps of differing types. Take a look at Page 15 of this: http://www.analog.com/UploadedFiles/Data_Sheets/AD8065_8066.pdf Note the parallel caps bypassing the power rails. These are usually speced out as a combination regular electrolytic and plastic (polypropylene, polystyrene, MKT type). The plastic caps are usually placed very close to the op-amp (close coupled), but the electrolytics can be anywhere on the smaller boards.
The results are much better specifications for the op-amps (better THD, less phase shifting, better CRMM & PSRR, etc.).
😕 😕 😀 😉 😎 (SandyK is also correct ... parrallel caps are "additive" [C + C + C = 3C], serial caps not [1/C + 1/C + 1/C = 3/3C] ... http://en.wikipedia.org/wiki/Capacitor .)
The parallel 4.7uF shown is a tantalum capacitor, as mentioned in a later page. I have seen this Data sheet before, as I am using both AD8065 and AD8066 in some equipment. I do agree with a 4.7uF electro used as stated.
BTW, I hate tantalum capacitors in audio circuitry. I have also had several tantalum bypass capacitors, that were well within their ratings, go short circuit. Where tantalums can be worthwhile, is on much larger PCBs with long circuit traces. at the power supply end. e.g. DAT players, Cassette decks etc.
SandyK
BTW, I hate tantalum capacitors in audio circuitry. I have also had several tantalum bypass capacitors, that were well within their ratings, go short circuit. Where tantalums can be worthwhile, is on much larger PCBs with long circuit traces. at the power supply end. e.g. DAT players, Cassette decks etc.
SandyK
" ... agree with a 4.7uF electro used as stated. ... BTW, I hate tantalum capacitors in audio circuitry ... I have also had several tantalum bypass capacitors ... go short circuit. ... "
Likewise, and I've also seen 'em go zzzzzttt ... smoke and stink
The electro / plastic combo rules, dudes. 😎
There are several interesting articles on this very subject ... ask Bob Pease.
Likewise, and I've also seen 'em go zzzzzttt ... smoke and stink
The electro / plastic combo rules, dudes. 😎
There are several interesting articles on this very subject ... ask Bob Pease.
I built a UCD400AD a while back and have a 56,000uF cap per rail with no bypass...some may say way too much if not a Class A, but I had them already.. Sounds just fine on both upper and lower end.
Anyway, been thinking of bypassing them with two .047uF Polystyrene caps that I have, totaling just under .1uF - don't really have a problem with sound, but what the hey... and I heard Polystyrene cap is the next best cap after no cap at all...
Anyway, been thinking of bypassing them with two .047uF Polystyrene caps that I have, totaling just under .1uF - don't really have a problem with sound, but what the hey... and I heard Polystyrene cap is the next best cap after no cap at all...
" ... been thinking of bypassing them [56,000uF x 2] with two .047uF Polystyrene caps that I have, totaling just under .1uF ..."
Good choice ... you may discover a slight improvement with results of spectrum analysis, but probably not too much of a "golden ear" difference. You might consider putting the plastic caps as close as possible in parallel with the onboard electrolytics on the main board(s), which may require four instead of two. ( Close to the tall electrolytics in back, close to the output FETs & heat sink(s) = http://www.hypex.nl/pics/products/UcD400.gif )
I use 0.33 uF yellow MKT type rated to 100 volts ... I buy 'em by the hand full = ~US$0.25 each, but any value above about 0.01 uF will work. The basic idea is just to smooth out the higher frequency noise of any power supply, that is trying to get past the fat electrolytics on the PS rails and interconnecting wiring. Mounting them close to the output MOSFETs or Bi-Polars works best and covers a world of sins ... 😉
IMOP: another place where this quick and easy mod sometimes does a whole lot of good is on CD and DVD players that have analog output circuits (like a built in DAC). A couple of those 0.033 uF yellow MKT types right across the +/- internal power rails leading to the op-amp(s) on the DAC board(s). ... The switching supplies on the cheaper players are notoriuosly noisy and this helps a lot = Example: Oppodigital.com model 981 has such a DAC for 24bit / 96K / dolby 5.1 output. I just popped a couple of these plastic caps into the bus / power connections ... and immediately noticed a significant difference in clarity of the analog audio. Even my old ears could tell the difference. 😀
(FYI: the above is a common DIY fix and is documented elsewhere on the 'Net = works great.)
Good choice ... you may discover a slight improvement with results of spectrum analysis, but probably not too much of a "golden ear" difference. You might consider putting the plastic caps as close as possible in parallel with the onboard electrolytics on the main board(s), which may require four instead of two. ( Close to the tall electrolytics in back, close to the output FETs & heat sink(s) = http://www.hypex.nl/pics/products/UcD400.gif )
I use 0.33 uF yellow MKT type rated to 100 volts ... I buy 'em by the hand full = ~US$0.25 each, but any value above about 0.01 uF will work. The basic idea is just to smooth out the higher frequency noise of any power supply, that is trying to get past the fat electrolytics on the PS rails and interconnecting wiring. Mounting them close to the output MOSFETs or Bi-Polars works best and covers a world of sins ... 😉
IMOP: another place where this quick and easy mod sometimes does a whole lot of good is on CD and DVD players that have analog output circuits (like a built in DAC). A couple of those 0.033 uF yellow MKT types right across the +/- internal power rails leading to the op-amp(s) on the DAC board(s). ... The switching supplies on the cheaper players are notoriuosly noisy and this helps a lot = Example: Oppodigital.com model 981 has such a DAC for 24bit / 96K / dolby 5.1 output. I just popped a couple of these plastic caps into the bus / power connections ... and immediately noticed a significant difference in clarity of the analog audio. Even my old ears could tell the difference.
😀 (FYI: the above is a common DIY fix and is documented elsewhere on the 'Net = works great.)
Thanks for all the info,
The reason I’m asking is because I have a Dynaco ST-150 solid state amp I’m in the process of restoring and the main power supply caps need replaced. I’ve been toying with the idea to increase supply capacitance over stock I can get a larger capacitance and get the same size can. However given the fact that I have plenty of room in the case I was wondering in this case if it wouldn’t be better to divide the total capacitance up among two caps instead. Or even use a layout like that is
shown on the datasheet where one of the caps is smaller.
BTW the op amp you show looks interesting. It’s too bad they didn’t have it in an 8 pin DIP package.
The reason I’m asking is because I have a Dynaco ST-150 solid state amp I’m in the process of restoring and the main power supply caps need replaced. I’ve been toying with the idea to increase supply capacitance over stock I can get a larger capacitance and get the same size can. However given the fact that I have plenty of room in the case I was wondering in this case if it wouldn’t be better to divide the total capacitance up among two caps instead. Or even use a layout like that is
shown on the datasheet where one of the caps is smaller.
BTW the op amp you show looks interesting. It’s too bad they didn’t have it in an 8 pin DIP package.
" ... However given the fact that I have plenty of room in the case I was wondering in this case if it wouldn’t be better to divide the total capacitance up among two caps instead. ..."
Or even into three caps per rail ... no problem-o. (Our point of interest re: plastic caps in parallel with electrolytics, would then suggest a total of four, or even more, caps ... three electrolytics of, say, 20,000 uF each, and then plastic caps of, say, 0.010 uF to 0.100 uF each, across each of the output transistors' +/- power rails.)
Parallel caps are "additive" and as long as the voltage rating is the same (and higher than the actual PS rail voltage) then you can parallel them and parallel them and parallel them, ad infinitum ... until you run out of caps or get tired of installing them ... more is better and the plastic ones do some real good, audio quality wise ...
(" ... op-amp looks interesting ... It ’s too bad they didn’t have it in an 8 pin DIP package. ..." ... check out: http://focus.ti.com/lit/ds/symlink/ths4226.pdf = 2 channel, 8-pin, surface mounted "DIP" ('4225 is single channel version) ... TI.com is still making several other types of op-amps in "old fashioned" 8-pin, "mini DIP" that will plug into PCB sockets ... I use these myself 'cause I'm old fashioned too, and understand your desire to find 'em. Analog Devices does make a lot of 8-pin mini-DIP op-amps too: http://www.analog.com/UploadedFiles/Data_Sheets/AD711.pdf )
Or even into three caps per rail ... no problem-o. (Our point of interest re: plastic caps in parallel with electrolytics, would then suggest a total of four, or even more, caps ... three electrolytics of, say, 20,000 uF each, and then plastic caps of, say, 0.010 uF to 0.100 uF each, across each of the output transistors' +/- power rails.)
Parallel caps are "additive" and as long as the voltage rating is the same (and higher than the actual PS rail voltage) then you can parallel them and parallel them and parallel them, ad infinitum ... until you run out of caps or get tired of installing them ... more is better and the plastic ones do some real good, audio quality wise ...
(" ... op-amp looks interesting ... It ’s too bad they didn’t have it in an 8 pin DIP package. ..." ... check out: http://focus.ti.com/lit/ds/symlink/ths4226.pdf = 2 channel, 8-pin, surface mounted "DIP" ('4225 is single channel version) ... TI.com is still making several other types of op-amps in "old fashioned" 8-pin, "mini DIP" that will plug into PCB sockets ... I use these myself 'cause I'm old fashioned too, and understand your desire to find 'em. Analog Devices does make a lot of 8-pin mini-DIP op-amps too: http://www.analog.com/UploadedFiles/Data_Sheets/AD711.pdf )
john65b said:
Paralleling big capacitors with smaller ones might lead to problems because the series inductance of the large one will create a parallel resonant circuit with the smaller capacitor. For example, look at:
http://www.cde.com/catalogs/DCMC.pdf
The impedance curve for the 8400 uF 150 V part shows the equivalent series inductance (ESL) as about 50 nanoHenries. Put that in parallel with the proposed 50 nF (0.05 uF) capacitor, and you get a parallel resonance at about 3 MHz, damped only by the equivalent series resistance of both capacitors. Q = (1/R) * sqrt(L/C). ESR of the larger capacitor is about 0.01 ohms, so doing the math leads to a Q of about 100. There will be parasitic resistances in the circuit, but even with 0.05 ohm ESR you're still looking at a Q of about 20. This would bump the supply output impedance to roughly 20 ohms; some amplifiers could become unstable with that much supply Z.
On the other hand, if you parallel the large cap with 5 uF instead of .05 uF, Q decreases by a factor of 10. The resonance does occur at one-tenth the frequency, 300 kHz, but with a much lower peak impedance - in this example something like 0.2 ohms. Maximum phase angle of the impedance is also a lot lower, which helps with stability.
Paralleling with 50 uF is even better, because then the resonant peak is barely visible above the ESR. Then you might worry about the 50 uF capacitor's series inductance, but the same analysis can be applied to that case.
In conclusion, proper bypassing for real-world parts seems to work best for capacitance ratios of 1000:1 or less.
Parallel Capacitance
FastEddy
Interesting info on the Oppo. A friend and I each have one. We have already replaced the switchmode's BR diodes with BYV26C (30nS) and fitted a 100nF 630V poly. across the associated electro.Also quite a bit of self adhesive felt in strategic places .
There is a very worthwhile improvent in both audio via SPDIF, AND video takes on a more 3D look. The video improvement is also obvious via HDMI. I presume you know that the 981 has an undocumented feature, whereby if you change SPDIF output to LPCM, you can then use remote control of audio volume through a DAC? I have tried this method shown me by a friend , to achieve stunning audio through a highly modified Musical Fidelity X-DAC V3 , then direct into a Class A amplifier.
Regards
SandyK
FastEddy
Interesting info on the Oppo. A friend and I each have one. We have already replaced the switchmode's BR diodes with BYV26C (30nS) and fitted a 100nF 630V poly. across the associated electro.Also quite a bit of self adhesive felt in strategic places .
There is a very worthwhile improvent in both audio via SPDIF, AND video takes on a more 3D look. The video improvement is also obvious via HDMI. I presume you know that the 981 has an undocumented feature, whereby if you change SPDIF output to LPCM, you can then use remote control of audio volume through a DAC? I have tried this method shown me by a friend , to achieve stunning audio through a highly modified Musical Fidelity X-DAC V3 , then direct into a Class A amplifier.
Regards
SandyK
sandyK: " ... We have already replaced the switchmode's BR diodes with BYV26C (30nS) and fitted a 100nF 630V poly. across the associated electro.Also quite a bit of self adhesive felt in strategic places . ... There is a very worthwhile improvent in both audio via SPDIF, AND video ... The video improvement is also obvious via HDMI. ... the 981 has an undocumented feature, whereby if you change SPDIF output to LPCM, you can then use remote control of audio volume through an [external?] DAC? I have tried this method shown me by a friend , to achieve stunning audio through a highly modified Musical Fidelity X-DAC V3 , then direct into a Class A amplifier. ..."
* Super * ... we should have you start a new thread explaining these and other mods. I woukld welcome a rundown of the various mods ...
... The Diode exchange trick = got pics?
... Location for the 100 nF (0.100 uF) poly ? Got a picture?
... Application and locations of the felt ? Got a pic?
(Example of another undocumented Oppo Mod: a simple programming adjustment to the builtin firmware allows playback of all zone 2 videos in additiion to the zone 1 videos = All those great 24bit European music videos can be played !! plus some great Euro movies denied to us here in the states ... without losing the capability of playing the zone 1 stuff. An Oppo engineer told me that they don't document this because they are afraid of law suits from the stateside publishers.)
Also: any word on improvement (or not) in "stunning" results through a 24 bit external DACs? (I have just about given up on CD / 16bit recordings = CDs SLS = "CDs suck" - Bob Dylan).
DSP-Geek: " ... Paralleling big capacitors with smaller ones might lead to problems because the series inductance of the large one will create a parallel resonant circuit with the smaller capacitor. ..."
I would have thought that increases in impedence v. frequency would be a good thing, since that is the whole purpose of paralleling the different types of caps ?? 😕
* Super * ... we should have you start a new thread explaining these and other mods. I woukld welcome a rundown of the various mods ...
... The Diode exchange trick = got pics?
... Location for the 100 nF (0.100 uF) poly ? Got a picture?
... Application and locations of the felt ? Got a pic?
(Example of another undocumented Oppo Mod: a simple programming adjustment to the builtin firmware allows playback of all zone 2 videos in additiion to the zone 1 videos = All those great 24bit European music videos can be played !! plus some great Euro movies denied to us here in the states ... without losing the capability of playing the zone 1 stuff. An Oppo engineer told me that they don't document this because they are afraid of law suits from the stateside publishers.)
Also: any word on improvement (or not) in "stunning" results through a 24 bit external DACs? (I have just about given up on CD / 16bit recordings = CDs SLS = "CDs suck" - Bob Dylan).
DSP-Geek: " ... Paralleling big capacitors with smaller ones might lead to problems because the series inductance of the large one will create a parallel resonant circuit with the smaller capacitor. ..."
I would have thought that increases in impedence v. frequency would be a good thing, since that is the whole purpose of paralleling the different types of caps ?? 😕
As it has been mentioned, paralleling dissimilar capacitors usually results in increased supply impedance rather than reduced in the 1 to 10Mhz range. There are a few threads documenting this effect with real measurements in the power supply forum.
One of the combinations that seems to work fine is a small electrolytic with high ESR in parallel with a 100n ceramic, and that's because the ESR damps the resulting CLC system. On the other hand, low-ESR big electrolytics resonate badly when paralleled with small plastic capacitors and this may result in amplifier instability.
Those recommendations about adding small film capacitors are almost always based in subjective criteria and made by people that does not have an oscilloscope among their usual tools.
One of the combinations that seems to work fine is a small electrolytic with high ESR in parallel with a 100n ceramic, and that's because the ESR damps the resulting CLC system. On the other hand, low-ESR big electrolytics resonate badly when paralleled with small plastic capacitors and this may result in amplifier instability.
Those recommendations about adding small film capacitors are almost always based in subjective criteria and made by people that does not have an oscilloscope among their usual tools.
FastEddy said:
You want the power supply to source the same voltage independently of current across the frequency range, therefore a low output impedance. You might be thinking of permittance, also known as admittance, which is the inverse of impedance. High output admittance means low voltage drop with respect to current, same as low output impedance.
I have a wine tasting to visit now, but remind me and I'll get to writing out some equations later. No calculus, just a bit of math with a few imaginary numbers sprinkled in.
FastEddy
I didn't take any photos as similar the mods are well documented
elsewhere. Rock Grotto Audio Forum, for example suggests using UF4007 with ceramic "snubbers" . I prefer the 30nS BYV26c.Other sites also recommend expensive and larger parallel capacitors, but IMHO, that is overkill. I have attached one such link. Search for part 2 as well
SandyK
http://www.soundstage.com/maxdb/maxdb.htm
I didn't take any photos as similar the mods are well documented
elsewhere. Rock Grotto Audio Forum, for example suggests using UF4007 with ceramic "snubbers" . I prefer the 30nS BYV26c.Other sites also recommend expensive and larger parallel capacitors, but IMHO, that is overkill. I have attached one such link. Search for part 2 as well
SandyK
http://www.soundstage.com/maxdb/maxdb.htm
Eva
I normally use 47-100uf electros paralleled with 100nF.
I never use low esr types in analogue circuits. I reserve their use for some digital circuitry. NOT around DACS.The low esr types seem to often cause metallic sounding treble.
SandyK
I normally use 47-100uf electros paralleled with 100nF.
I never use low esr types in analogue circuits. I reserve their use for some digital circuitry. NOT around DACS.The low esr types seem to often cause metallic sounding treble.
SandyK
" .. have a wine tasting to visit now, but remind me and I'll get to writing out some equations later ..."
I got it ... I'll google it and get back as well ... Hope you find a nice dry Dry Creek Chard or a mellow Alexander Valley Merlot ... Sonoma County = best vino in the world ... so far. 😎
" ... Rock Grotto Audio Forum ..." for the latest Oppo Mods = got it, thanks. As for the link, I wonder which archived article you mean?? (I guess I could read 'em all ... ) 😕
" ... The low esr types seem to often cause metallic sounding treble. ..." I've noticed that as wel, but assumed that it was me and my tired old ears, not the particular type / spec of a cap ..
I got it ... I'll google it and get back as well ... Hope you find a nice dry Dry Creek Chard or a mellow Alexander Valley Merlot ... Sonoma County = best vino in the world ... so far. 😎
" ... Rock Grotto Audio Forum ..." for the latest Oppo Mods = got it, thanks. As for the link, I wonder which archived article you mean?? (I guess I could read 'em all ... ) 😕
" ... The low esr types seem to often cause metallic sounding treble. ..." I've noticed that as wel, but assumed that it was me and my tired old ears, not the particular type / spec of a cap ..
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