How much capacitance can I add (upgrade) to the amplifier's PSU? - Page 1
Forum section: electronics / beginners

author: kris2ff3r
author_rank: Contributor
timestamp: August 06, 2017, 11:25:02 pm
content: HiI am thinking of upgrading the capacity on my power amplifiers PSU.The Amplifier is a dual mono 100w A/B Design using a capacity of 20000µF per channel. I was thinking of upgrading to 30000µF, by changing the two 10000µF caps with 15000µF (in each channel).If I'm not mistaken a power supply can't be too big, so this should not be a problem? I could in theory change it to x000µF'sOr will it do some things worse?These are the caps for the VCC supply.Will the VDD work as well? It's 4400µF, and thinking of upgrading to 6600µF, using two 3300µF, instead of the standard 2200µF's

author: DrGeoff
author_rank: Frequent Contributor
timestamp: August 06, 2017, 11:32:05 pm
content: Why? What do you hope to achieve?Is there a problem with ripple in your current power supply?

author: IanB
author_rank: Super Contributor
timestamp: August 06, 2017, 11:34:34 pm
content: Precisely. Why do you think this would be an "upgrade"?

author: kris2ff3r
author_rank: Contributor
timestamp: August 06, 2017, 11:38:10 pm
content: This has nothing to do with my (or others) personal preference. I hope to achieve a bigger power supply.I'm simply asking if it would be a problem

author: DrGeoff
author_rank: Frequent Contributor
timestamp: August 06, 2017, 11:42:40 pm
content: Quote from: kris2ff3r on August 06, 2017, 11:38:10 pmIt may be.The discharged capacitors appear as a short circuit at switch on. So the rectifiers must be able to handle the expected peak current at this time.Once it settles down it should be OK, just check the switch on transient.Also, it will take longer for the capacitor to discharge through the bleed resistor, so allow for that when tinkering.

author: Ian.M
author_rank: Super Contributor
timestamp: August 06, 2017, 11:50:41 pm
content: Quote from: IanB on August 06, 2017, 11:34:34 pm+1.Aluminium foil, paper and electrolyte is a lot cheaper than copper or silicon power devices. Also electrolytic caps typically have quite a high tolerance range, so tend to be over-specced in the first place to guarantee the minimum capacitance required. The way to bet isn't that the OEM skimped on the caps as they are far far more likely to have cut corners on the transformer, output devices and/or heatsink.If you are unlucky and the output devices or their heatsinking are marginal, stiffening the power rails by increasing the bulk capacitance may push them over the edge into destructive overload and failure.Also, for linear supplies, increasing the bulk capacitance decreases the conduction angle of the diodes in the rectifier, increasing peak currents and thus radiated and conducted EMI as the suppression components aren't designed to handle the higher pulse currents.. Other system components or the earlier stages of this amplifier may therefore pick up more 100Hz hum and RF impulse noise masking any improvement you may expect from reduced output stage rail ripple.

author: kris2ff3r
author_rank: Contributor
timestamp: August 06, 2017, 11:54:36 pm
content: Quote from: DrGeoff on August 06, 2017, 11:42:40 pmI forgot to tell that it looks to be some sort of series wiring, with ground in the middle. See attached for the schematic.The amp has a slowstart circuit, not sure how ''slow'', but it starts very fast (way under a second).When the amp is turned on, it starts with a 20ohm resistor wired directly to the primary side of the transformers.When the slowstart timeup is done, the relay kicks in and there is ''no'' resistance from mains to the transformers

author: ejeffrey
author_rank: Super Contributor
timestamp: August 07, 2017, 05:45:06 am
content: Quote from: kris2ff3r on August 06, 2017, 11:38:10 pmMaybe I am not understanding what you are asking for, but adding capacitors does not make a power supply bigger in terms of higher load capacity, assuming the supply was designed properly in the first place. For that you need to upgrade the transformer. You might also need more capacitors. Increasing capacitance by itself will reduce ripple but also can have problems mentioned above. Given the relative cost of transformers vs. capacitors, I agree it is unlikely someone would build a linear power supply and not put enough capacitance to get the maximum power from the expensive transformer.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 07, 2017, 06:20:47 am
content: Ah yes, the audiophiles' fascination with excessive capacitance and using two FWBs where one will suffice. Now how was I expecting that...Tim

author: kris2ff3r
author_rank: Contributor
timestamp: August 07, 2017, 09:27:36 am
content: Quote from: ejeffrey on August 07, 2017, 05:45:06 amThat's exactly what I think, it it too small. In the later design they used 60000µF in the powersupply.I think the manufacturer noticed it was to small. I don't know if the supply is too small, I haven't meassured ripple.It's really an easy question; can I upgrade the capacity in the powersupply without breaking anything, or introducing new noise, or other unwanted parameters (as mentioned by Ian.M).

author: kris2ff3r
author_rank: Contributor
timestamp: August 07, 2017, 09:28:39 am
content: Quote from: T3sl4co1l on August 07, 2017, 06:20:47 amStick to the topic, or find a different post...

author: DrGeoff
author_rank: Frequent Contributor
timestamp: August 07, 2017, 09:44:50 am
content: Quote from: kris2ff3r on August 07, 2017, 09:27:36 amYes, you can add more bulk capacitance to the simple unregulated power supply.It will, most likely, have no audible effect at all.

author: Dave
author_rank: Super Contributor
timestamp: August 07, 2017, 11:58:55 am
content: No, you cannotjust add a shitload of capacitance to a power supply.Excessive capacitance means that the current spikes through the rectifier are going to be shorter and have a much higher in amplitude (the same amount of charge needs to be transferred in a shorter amount of time).So where's the problem?Higher RMS current on the windings, so hotter windings.Odd current harmonics introduced to the mains, interfering with pretty much everything.Unless the capacitors need replacement (bulging, high ESR, reduced capacitance), leave them be.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: August 07, 2017, 12:18:56 pm
content: Will not make one iota of difference to sound quality. If you make a wiring mistake though it might just result in smoke and empty pockets.Functionally, a regulated PSU would make more difference to quality at the expense of small loss of output power. Reason manufacturers do not regulate is 'specmanship' - Using unreg rails for the output stage gives the highest possible peak output power from a cheap PSU.

author: kris2ff3r
author_rank: Contributor
timestamp: August 07, 2017, 02:36:25 pm
content: Quote from: alm on August 07, 2017, 12:52:09 pmTrue, only regulated power supplies on A/B amplifiers I've seen is in preamps, but that's a different story.So far I have one saying it shouldn't be a problem, but not necessary eitherAnd one saying ''I can't add a shit load of capacitance''. - The plan was to increase the capacitance with a third (total of 30000µF). stock is 20000µF, not sure if you think it's too much.. Or should be okay?The powersupply isNOTregulated. For the VCC, it's only a bridge rectifier, and the capacitors (in series, with ground in the middle).There is one 500VA transformer for each channel. Please see the schematics in one of my posts above

author: IanB
author_rank: Super Contributor
timestamp: August 07, 2017, 06:12:21 pm
content: Quote from: kris2ff3r on August 07, 2017, 09:27:36 amEasy questions don't necessarily have easy answers. If it was an easy question you wouldn't be coming here asking for answers. You would already know the answer yourself. (It's an easy question, right?)

author: CJay
author_rank: Super Contributor
timestamp: August 07, 2017, 09:12:27 pm
content: Quote from: kris2ff3r on August 07, 2017, 09:28:39 amUmm, rude much?Yes, you can add capacitance, no it might not work as others have said.You say the manufacturer changed the design for later versions, are you sure it was only the capacitance they changed?Can you be absolutely sure they didn't fit a heavier bridge, change that slow strt circuit, the transformer, any number of other 'small' tweaks?Does it sound good now?What are you trying to achieve that makes you believe extra capacitance would be the answer?

author: DrGeoff
author_rank: Frequent Contributor
timestamp: August 07, 2017, 10:14:10 pm
content: Quote from: Dave on August 07, 2017, 11:58:55 amExcept the OP is not proposing to add a "shitload". Only raise it by 50% of its original value per rail.The bridge will be already quite large with regards to peak forward current, probably in excess of 50A.The 500VA transformer already has a soft start circuit for inrush current mitigation, which will also cause initial slow ramping of the capacitor charge.The load on the transformer is not constant and, unless the unit is being used in a nightclub, unlikely to be reaching anywhere near its rated output power.It is highly unlikely that any of the potential problems described here will have any audible or other effect on the OP's equipment. The initial values for the capacitors were probably chosen at random to be as big as they could fit in the enclosure anyway.Too many whiny children here.

author: Zero999
author_rank: Super Contributor
timestamp: August 07, 2017, 10:25:58 pm
content: Quote from: CJay on August 07, 2017, 09:12:27 pmThey probably took offence to the word audiophile. Heck I probably would have used a more derogatory term.Hence why I've kept out of this thread.Yes, adding capacitors won't improve the sound quality. My guess is it won't make any difference. It could cause more heating in the transformer and rectifier, as mentioned above, so don't do it.

author: kris2ff3r
author_rank: Contributor
timestamp: August 07, 2017, 11:30:34 pm
content: Thank you all for your great mindsI never ment to be rude to anyone here, but please stick to the topic.This tread is only about the different parameters I can expect from such a change in the powersupply.I do see most here think it's unnecessary (maybe it is)...Talking about how unnecessary it is, was not the point.Again, thank you all for your input, and DrGeoff for answering my actual question

author: Zero999
author_rank: Super Contributor
timestamp: August 08, 2017, 08:31:30 am
content: Quote from: kris2ff3r on August 07, 2017, 11:30:34 pmThe trouble is people have minds of their own and the forum has its own rules set by a team of administrators and moderators. When you create a thread, you don't get to decide what's acceptable and what is not.

author: Dave
author_rank: Super Contributor
timestamp: August 08, 2017, 01:46:45 pm
content: Quote from: DrGeoff on August 07, 2017, 10:14:10 pmWhile I agree that the word "shitload" is excessive for a 50% increase, your previous post seemed to imply that you can just freely increase bulk capacitance without consequences.Quote from: DrGeoff on August 07, 2017, 09:44:50 amDid I misinterpret your words?Quote from: DrGeoff on August 07, 2017, 10:14:10 pmThe way I understand it OP wants to increase the output power of his current power supply, which implies that he is already loading it to the maximum and wants more out of it.Relying that a use case is unlikely to happen is a pretty bad approach to engineering. Reliable designs always have safety margins.

author: Zero999
author_rank: Super Contributor
timestamp: August 08, 2017, 07:44:30 pm
content: Yes, if more power is required, then a transformer with a higher current rating is required. Unfortunately, that won't increase the volume by itself. A lower impedance speaker or more speakers in parallel should be connected to the amplifier, assuming it's capable of driving a lower impedance load. If the amplifier's output is distorted due to clipping, then increasing the voltage and current rating of the power supply will work, but the amplifier will need to be able to withstand the higher voltage and current.

author: DrGeoff
author_rank: Frequent Contributor
timestamp: August 08, 2017, 09:33:42 pm
content: Quote from: Dave on August 08, 2017, 01:46:45 pmRead the application. A 500VA transformer for a 100W A/B amplifier. You can work out the loading for ordinary listening levels of audio program material.It is not a bad approach to engineering. It is experience. Stop being pedantic.

author: floobydust
author_rank: Super Contributor
timestamp: August 08, 2017, 10:10:09 pm
content: I find increasing filter capacitance is audible, it does affect an amplifier's fidelity.But it's not the mains ripple you are reducing in the hopes of getting better sound. This is counter to most intuition.Adding filter capacitance can make things sound worse... if the amplifier does not have proper grounding because you are increasing the peak ripple current. This shows up as more 2xmains (100/120Hz) hum occurring and head scratching because the smaller filter capacitors were quieter.Rectifier reverse-recovery time is also longer with higher peak currents, you'll need to consider snubbers across the rectifiers to reduce RFI.It is the (rail's) 1/2 wave audio ripple under load, that adds intermod distortion, poorer channel separation.Some audio power amps have poor PSRR and say 10kHz ripple can make it through the internals. It's not just 100/120Hz happening there.Power supply rail noise scope picture by Bonsai; taken fromhifisonix.comOvation Power Amplifier 150W at 8ohms.

author: Dave
author_rank: Super Contributor
timestamp: August 09, 2017, 08:32:21 am
content: Quote from: DrGeoff on August 08, 2017, 09:33:42 pmYup, I did miss that.Quote from: DrGeoff on August 08, 2017, 09:33:42 pmI still disagree with this. A circuit should be able to handle any reasonable user input (reasonable being cranking the volume knob to the maximum, not shoving a 10Vpp signal into the input) without the risk of self-destruction.

author: CJay
author_rank: Super Contributor
timestamp: August 09, 2017, 08:57:06 am
content: I really do wonder what advantage the OP hopes to gain from making these changes, I'd love to know what make and model of amp it is to see if I can track the changes and work out what the manufacturer achieved by making them too, looks like there's a schematic available so it could be an interesting exercise.

author: Brumby
author_rank: Unknown
timestamp: August 09, 2017, 10:46:39 am
content: Quote from: CJay on August 09, 2017, 08:57:06 amThat's the question I would like to see an answer to, as well.

author: kris2ff3r
author_rank: Contributor
timestamp: August 25, 2017, 12:54:40 pm
content: Quote from: CJay on August 09, 2017, 08:57:06 amThe next version of the amp had 20 watts more, a total of 120W.How ever the schematics is almost identical, with a few changes (including two more output transistors).. And three times the capacitance (60000µF).. As I said the 100W ''edition'' had only 20000µF.. Yes there is a difference, but I still don't get that it should be big enough to 3x the power supply capacitance of the 100W amp.There is no schematics available. I only have them available since I worked in the same company that made the amps, but I didn't work in the engineering section

author: drussell
author_rank: Super Contributor
timestamp: August 25, 2017, 04:06:25 pm
content: Adding a bit more capacitance isn't going to make the amplifier more powerful. It is still going to clip at the point set by the circuitry. It will still output the same maximum 100 Watts.It might potentially improve the transient response on large peaks a little bit, though, especially if you're driving a very low impedance load... You might get a bit more solid bass "punch", for example. Probably not much, though. The manufacturer chose 20,000 uF for a reason, however, if you think it seems a bit anemic you can always try it and see if you like the result.It is virtually impossible for it will blow anything up but it will likely not make a noticeable difference and might actually make any power supply diode noise worse, as floobydust pointed out, but I don't think you'd hear that either with a change of 20,000 -> 30,000 uF.

author: Zero999
author_rank: Super Contributor
timestamp: August 25, 2017, 05:50:08 pm
content: Quote from: kris2ff3r on August 25, 2017, 12:54:40 pm120W is hardly any more powerful than 100W. I doubt most people would be able to tell the difference. It certainly isn't worth the extra capacitance and transistors.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 25, 2017, 08:21:08 pm
content: 20000 µF is already enough capacity for a 100 W amplifier - that is at least with normal 4 or 8 Ohms speakers.Adding more would reduce the voltage ripple but increase the current ripple. With modern, not too bad amplifier one would not notice a difference as neither of both can be heard. To much capacitance can cause problems like noted before - likely not yet at 50% more.A 500 VA transformer for a 100 W amplifier is rather large. Assuming 50% PF and 50 % amplifier efficiency, it could deliver 125 W continuous. Amplifiers for private use are more the opposite way around: like a 50 VA transformer for a 100 W amplifier.

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 01:05:23 pm
content: Quote from: kris2ff3r on August 07, 2017, 09:28:39 amMaybe listen to the advice you are being given, from what I can tell you still can't explain why you want to modify a unit that has been designed "just so", what do you know that the manufacturer does not, if you do know more than the manufacturer then I suggest you share that before you go around telling very experienced members to get lost, unless of course you don't actually want help......

author: kris2ff3r
author_rank: Contributor
timestamp: August 26, 2017, 03:08:51 pm
content: We'll see how it goes...As the schematics states; there are two sets of rectifiers, one for the + VCC, and one for the -VCC. Both rectifiers has it's own secondary winding.Meaning the VCC+, and the VCC- are not the same winding and therefore each rectifier only ''work'' with 10000µF, and not the whole 20000µF supply for the channel(?).I am not an electronics engineer so correct me if I'm wrong. I only work production and the amp is not mine either.The owner requested the bigger cap source. I said I could do the upgrade, but I want to consult with the pros here first, don't want to mess up he's amp.

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 04:10:13 pm
content: Well if you have that resistor in series then clearly there was a concern, if you really have to change it then if your increase the capacitance by 50% you should do the same to the resistor. But really why bother, unless the amplifier is suffering at high volume then why change the caps ? If you get 50% more caps in the same space they will be 2/3 the quality, you will have things like increased ESR which is unlikely to cause a problem here (if anything help) but it just demonstrates how pointless the exercise is.

author: drussell
author_rank: Super Contributor
timestamp: August 26, 2017, 04:19:18 pm
content: Quote from: Simon on August 26, 2017, 04:10:13 pmNot necessarily!There have been major advancements in capacitor technology. Depending on the age of this amplifier, far, far better capacitors (both performance and physical quality, longevity, etc.) may be available in the same or smaller package than the originals. Most certainly if you compare typical, older 60s, 70s, 80s capacitors to those manufactured today, you will findhugeperformance increases in a smaller package. It would be nice to know what amplifier he's talking about and the age of it, of course, though...If the amplifier is reasonably old the caps have probably started to degrade at least somewhat from their original performance specifications anyway. If there is any question as to their performance currently it is most certainly justified to be replacing them, and I would do the same thing as the OP is asking. I would put in a somewhat larger-value, better quality capacitor if I could fit in in the space for this application.Why all the hate for the OP's amplifier owner's request?It seems to be a perfectly logical and valid course of action to me. It is probably exactly what I would do if I were replacing the main filter caps in an older amplifier.

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 04:21:11 pm
content: Yes that is true if they are old capacitors but information has been vague. I don't quite see the point of increasing the capacitance unless necessary.

author: kris2ff3r
author_rank: Contributor
timestamp: August 26, 2017, 04:25:57 pm
content: Quote from: drussell on August 26, 2017, 04:19:18 pmThank you, the amp is made between 95-97 I believe.

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 04:28:48 pm
content: ok so you can cram some more capacitance in, but has the owner reported an actual problem ? once upon a time diodes would be supplied with a maximum capacitance rating they could work wih for this very reason, hence your 20 ohm series resistors, this kit was well thought out, but apparently the owner knows more than the designer. Just make sure you apply gold coloured sticky sheet to the outside and charge him 100x the actual price of the caps and you will be okoh and you will have to come up with a bit wank word for the new technology you have applied, do that and he will be happy

author: drussell
author_rank: Super Contributor
timestamp: August 26, 2017, 04:28:54 pm
content: Quote from: Simon on August 26, 2017, 04:21:11 pmDoes it really matterwhythe amplifier's owner wants to change the capacitors?The original question was whether a (somewhat) moderate increase in capacitance would have any potential downsides and what those potential downsides were. I find that to be a perfectly valid question regardless of the original motivation.Just my $.02 CAD, YMMV...

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 04:39:26 pm
content: Well given the protection circuitry it will probably be ok, but it is worth the OP understanding that you can't just do this and no it's not a case of more is better but more is pointless. As the protection circuitry is in place it will limit the peak current so adding more will likely be ok, given the fact that the designer went to such pains to design the thing right in the first place clearly a very well thought out value of capacitance was put in. The resistors are probably also to stop the traditional pop sound you get when powering an amplifier up (soft start ? ever heard of that OP?) and in this case may save your bacon if you decide to just add capacitance. like i said, wrap gold foil around them and charge the guy and arm and a leg, he will probably not bat an eyelid and have better bragging rights about his system

author: drussell
author_rank: Super Contributor
timestamp: August 26, 2017, 04:40:59 pm
content: Quote from: Simon on August 26, 2017, 04:28:48 pmWhy does it matter if there is currently a "problem" or not? This wasn't arepairquestion. The owner wants to change the capacitors. Maybe he's going to install it into a permanent installation and doesn't want to have to worry about component life for another 20 years. Who careswhy? That is a completely different conversation.QuoteMost certainly! Especially tube rectifiers with capacitor input rather than choke input filters, you most definitely don't want more than the recommended capacitance on the rectifier (typically about 20 uF for a small receiving-tube sized rectifier) or you'd blow the daylights out of it in short order.This amplifier presumably has one or more beefy bridge rectifiers which can easily handle more surge than they were previously handling and it even has soft-start. He's not going to be blowing up rectifier diodes adding some more filter capacitance in this case.QuoteMaybe the owner is after audiophoolery and maybe not. The original question, though, wasn't whether there was some audible benefit from increasing the capacitance and we have no idea why the owner wants to do it, it was whether it would work or not.Replacing 20 year old electrolytics isn't some kind of insane, crazy idea, especially if they have been in constant service! That is reasonable maintenance philosophy, IMHO, and going from 10,000 to 15,000 uF is also reasonable from an engineering perspective.

author: kris2ff3r
author_rank: Contributor
timestamp: August 26, 2017, 04:51:58 pm
content: Jesus Christ.. And you wounder why I tell you to stick to the topic?And where do you find the 20ohm series resistors? Or other protection circuitry? Do you mix up different posts?And if I know what slow start is.. I said that the amplifier has a slow start circuitry with a 20 ohm resistor. But not in the power supply it self, or did I misunderstand you?

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 04:55:55 pm
content: You said there was 20 ohms and a bypass relay and you posted a diagram about the time you started to tell people to get lost and I started getting reports. The guy you told to get lost was probably the most qualified to answer your question but apparently you know it all.Sent from my Moto G (4) using Tapatalk

author: drussell
author_rank: Super Contributor
timestamp: August 26, 2017, 04:56:24 pm
content: Quote from: kris2ff3r on August 26, 2017, 04:51:58 pmHe's talking about the 20in the soft-start circuit.There is no need to mess with that, will be fine at 20.

author: kris2ff3r
author_rank: Contributor
timestamp: August 26, 2017, 05:02:13 pm
content: Quote from: Simon on August 26, 2017, 04:55:55 pmSeriously?''Ah yes, the audiophiles' fascination with excessive capacitance and using two FWBs where one will suffice. Now how was I expecting that...''You're right. Best answer I ever got..Anyway, I do consider the case closed. Thank you all for your input (On topic of course)...I will check up those rectifiers. But they are no longer in production.. Don't know what will be most like the RS603

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 05:10:11 pm
content: Well now that we have more information than your original post yes it is unlikely that adding more will do harm but very certain that it won't help much, I don't know in which year diodes with huge surge capabilities came about but if this was out of the 80s or earlier the answer would be a definite no, if you had not been so hasty in your dismissals of a light jibe Tim may have written you an essay in reply and left you in no doubt.best thing to do when you join a forum is not to jump on the difensive too fast. No question here is too stupid to ask but when you are clueless a bit of humility helps you go far as genuine people readily share knowledge on here if those asking are with bothering with.Sent from my Moto G (4) using Tapatalk

author: kris2ff3r
author_rank: Contributor
timestamp: August 26, 2017, 05:19:26 pm
content: Quote from: Simon on August 26, 2017, 05:10:11 pmI'm truly sorry, it that was never my intention to be rude, or on defence. I do appreciate all input regarding the case, but there was a lot of ''not necessary, why on earth would you do that?'' - The same ''stupid audiophiles'' song.I never asked this question for super audio conditions. I asked them because I would like to know more about the electronics

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 05:35:38 pm
content: No one here holds a grudge. It is often easy to assume something will have a simple answer. My boss does that a lot. He thinks that because I don't have any qualifications he can do as well as I can, the result then is that he comes back from visiting a customer overseas and had to make a second trip to take me with him, but strangely when you put the guy that designed it and the guy that miswired it all together they work miracles.Sent from my Moto G (4) using Tapatalk

author: drussell
author_rank: Super Contributor
timestamp: August 26, 2017, 05:57:51 pm
content: People need to always remember, too, that English is not everyone on this forum's primary language. A simple difference in the way a question is phrased can elicit completely different responses. I wonder how this thread would have gone if the original question were more like:"I need to replace the main filter capacitors in XYZ audio amplifier. The originals are 10,000 uF. What are the potential pitfalls of using a 15,000 uF part to replace them?"

author: drussell
author_rank: Super Contributor
timestamp: August 26, 2017, 06:12:06 pm
content: Quote from: kris2ff3r on August 26, 2017, 05:02:13 pmAre they actually RS603s? I think they're still produced. Regardless, the datasheet says:QuoteThere is a graph on the Diodes Inc. datasheet that shows a curve for "MAXIMUM NON-REPETITIVE FORWARD SURGE CURRENT" for 1 to 100 cycles of 60 Hz AC that still shows about 75A capability at 10 cycles, so I'm pretty sure he's gonna be fine, even on some kind of transient where the soft start failed to function on a restart, etc.

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 06:21:13 pm
content: Indeed if the data on the diodes allows for such surges then it will be fine (while making no positive difference), no doubt the soft start resistors were calculated so that the surge current was not exceeded on start in the dead short situation of discharged capacitors and the charging time of the capacitors taken into account.

author: G0MJW
author_rank: Regular Contributor
timestamp: August 26, 2017, 06:48:54 pm
content: The simple answer is none - if it really is getting on for 20 years old I wouldreplacethe capacitors rather than add any more capacitance. Chances are more modern capacitors will have more capacitance for the same size. I doubt the value is important within 50%. Older capacitors can degrade - depending on the sort of life they have had. They may be and probably are just fine, but starting from a new replacement gives a good baseline. Its very important to get the voltage rating right. You also need to pay attention to ripple current ratings and ESR. ESR will have the greatest impact on the audio, ripple rating on the fire hazard.Mike

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 06:52:46 pm
content: The voltage should be 2x the RMS voltage, equipment from the 60's like the quad 303 had capacitors rated too low and were infamous for failure (and then idiots on ebay would advertise compatible replacements also rated too low). Depending on the construction of the amp/psu I'd use the space savings of the modern capacitor to increase the voltage if necessary and the temperature rating.

author: drussell
author_rank: Super Contributor
timestamp: August 26, 2017, 07:01:52 pm
content: Quote from: G0MJW on August 26, 2017, 06:48:54 pmHe isreplacingthem. He just wanted to know if he can replace the 10,000 uF units with 15,000 uF units and have the amplifier function correctly.The choice of filter capacitance in that kind of application is somewhat arbitrary anyway and the manufacturer might well have almost chosen 15,000 uF originally anyway. I'm sure it will be just fine with the higher capacitance capacitors capably clarifying the current.Quote from: Simon on August 26, 2017, 06:52:46 pmIndeed. When replacing bulk filter capacitors in an application like this it is wise to select for the best temperature rating, life specification, robust physical construction and ripple rating while also ensuring adequate operating voltage margin in addition to the capacitance value when choosing a replacement.These are all trade-offs with physical size and is the reason there are a zillion different electrolytic capacitor series / types. I would think good quality parts with all those good specs, even at 15,000 uF should easily be available to fit the bill.

author: Simon
author_rank: Unknown
timestamp: August 26, 2017, 07:17:35 pm
content: My take on most parts is that if you multiply all of the specs together or in some cases the inverses for some you will come up with a constant, keeping that constant you could alter another variable and see how it affects the others or you part grows in size, increases in cost ect. This is just an idea i have and not scientific, but if you look through a few datasheets of mosfets you start to get my drift, want stupidly high current handling capability ? sure..... but your input capacitance will go through the roof..... this has other knock-on effects that many beginners will overlook and think more current capacity is better when in fact it can be disastrous in a replacement situation.If the capcitor technology has matured to the point where you can get a higher voltage rating (if required) and a higher temp rating AND a higher capacitance without having high ESR then sure put the capacitance up a bit. Obviously if we are being scientific increasing the capacitance by 50% means that the new value will still be -20% +50% so although we are talking 10'000 uF nominal, that was factored in for a maximum of 15'000uF, now if you fit a nominal 15'000uF you could have a 22'500uF at +50%, this is significant but may still work.

author: kris2ff3r
author_rank: Contributor
timestamp: August 27, 2017, 04:29:05 pm
content: The replacement capacitor (15000µF) is of the same brand as the original (Nippon Chemi-con). It's also the only one I can find that can be mounted on the PCB without any further modifications.- SMH series- Same lead spacing, same diameter, bit longer (of course) but not too much.- Max operating temp of 85ºC- Max 0.017 ohm ESR @ +20ºC,120Hz (80V, 100V Surge)

author: Simon
author_rank: Unknown
timestamp: August 27, 2017, 04:31:39 pm
content: How does it compare to the old one on temperature, how good is the PSU cooling? Is the PSU 40V RMS?Sent from my Moto G (4) using Tapatalk

author: kris2ff3r
author_rank: Contributor
timestamp: August 27, 2017, 06:25:03 pm
content: Quote from: Simon on August 27, 2017, 04:31:39 pmThe old one is also specified to 85ºC.There is no active cooling in the powersupply, the only heatsinks are in the amplifier section.In standard configuration I haven't noticed any heat in the powersupply (without load). Hard to tell while in use...I want to check with a Fluke IR cam, but that would require me to own a cam..Not sure about the voltage, I'm out of town at the moment, but IBELIEVEthe VCC is 63VDC (no load/no signal input)

author: Simon
author_rank: Unknown
timestamp: August 27, 2017, 06:27:00 pm
content: A thermocouple poked into the cap area will do fine. Costs less than £10, it cameras have their pitfalls too.Sent from my Moto G (4) using Tapatalk

author: kris2ff3r
author_rank: Contributor
timestamp: August 27, 2017, 07:04:35 pm
content: Quote from: Simon on August 27, 2017, 06:27:00 pmDo you know about a good thermocouple?The capacitance will also be 50% larger in the VDD supply. Same wiring, but using two sets of MUR120 in FWB, and two 2200µF (Now 3300µF).I can't monitor the heating in the powersupply with the 10000µF's, cause they are already removed.One of the caps were bulky, that's why this whole thing came up ''maybe use 15000µF, when they're already removed''Before I came here with the question I actually believed that you could add ashitloadof capacitance if you really wanted. It could never be too much to damage anything. Now I see different, but I remember another hifi manufacturer (also from Norway).They made a A/B 70W (in 8) SS Amp.The amplifier had a reservoir of 41600µF. They do sell the unit also as an UP edition. The UP edition is the exact same amplifier, but with a reservoir of 87600µF, and this is still a 70W amp. Still produced today with the standard reservoir, but they offer the upgrade.(Not my statement) It gives noticeable sonic improvements. Makes the unit more stable with low impedance speakers. And in bridge mode it gives you more bass, and ''tonality''.- What do you all think about these statements?

author: Simon
author_rank: Unknown
timestamp: August 27, 2017, 07:09:08 pm
content: The statements are for audiofools. The signal goes in and the amplifier should faithfully amplify it. provided you meet the minimum required to not have mains hum it makes no difference.Sent from my Moto G (4) using Tapatalk

author: IanB
author_rank: Super Contributor
timestamp: August 28, 2017, 06:37:54 pm
content: Quote from: Simon on August 27, 2017, 07:09:08 pmNot necessarily. A larger buffer can affect dynamics and transient performance. See the comment below from drussell:Quote from: drussell on August 25, 2017, 04:06:25 pm

author: Simon
author_rank: Unknown
timestamp: August 28, 2017, 06:48:28 pm
content: I would have thought the amplifier would have a design slew rate etc and therefore the original capacitance be set to cope with any eventuality. Presumably the lack of sufficient capacitance will mean that for a large output the capacitor would be over discharged and the amplifier would start to clip and distort.I can't really see how in a well designed amplifier the power supply capacitance would have any effect on sound "quality" providing the minimum is met. The frequencies we can hear are not exactly that high, if anything I'd be adding some faster caps if that sort of thing was a concern. My assumption is that if the capacitance is too small it won't hold the voltage up very well and so the output will clip and the mains hum will come through, once you are over that what more is there to gain ?If we are talking about capacitors in series with a speaker on a single supply then yes i can see a bigger cap being better but most power amps have a split supply and don't need output capacitors.

author: IanB
author_rank: Super Contributor
timestamp: August 28, 2017, 07:10:55 pm
content: The power supply reservoir capacitors provide the power supply voltage that the amplifier "sees". If you draw power from the reservoir faster than it can be replenished then the supply voltage drops, which will reduce the maximum instantaneous output power the amplifier can develop (crudely, output power = output voltage squared over output impedance). If the supply voltage drops, the output voltage drops and the output power sags. This can cause output transients to lose their accuracy. How bad this is in practice depends on what the amplifier designers thought was acceptable. Every amplifier design has constraints on what is expected of it.

author: IanB
author_rank: Super Contributor
timestamp: August 28, 2017, 07:12:56 pm
content: And of course, this may only be noticed at full volume, by which time performance will probably be at its worst anyway.

author: Simon
author_rank: Unknown
timestamp: August 28, 2017, 07:25:37 pm
content: Quote from: IanB on August 28, 2017, 07:12:56 pmQuite, I don't know what the slew rate of the average audio power amp is but the caps will be replenished at 100Hz, unless you demand a 0 to Vmax rise instantly you should not see a problem, at the end of the day if your are expecting to pulse the speakers like an idiot teenager because you think that is bass then you deserve to loose performance

author: rdl
author_rank: Super Contributor
timestamp: August 28, 2017, 08:08:01 pm
content: Quote from: kris2ff3r on August 27, 2017, 04:29:05 pmIt isn't necessary but, all else being equal, I always replace 85C capacitors with 105C rated.

author: Zero999
author_rank: Super Contributor
timestamp: August 28, 2017, 08:11:38 pm
content: Quote from: Simon on August 28, 2017, 06:48:28 pmThe reservoir capacitors do more to boost low frequency response, than high frequencies. The larger capacitance can be useful, when the volume is high and it's playing bass heavy music, such as reggae, drum & bass, rap and funk, which I know you love.

author: Simon
author_rank: Unknown
timestamp: August 28, 2017, 08:14:19 pm
content: Quote from: Hero999 on August 28, 2017, 08:11:38 pmExactly, unnecessary music so unnecessary requirement

author: Simon
author_rank: Unknown
timestamp: August 28, 2017, 08:16:29 pm
content: Quote from: rdl on August 28, 2017, 08:08:01 pmWhich is why i was asking what the temperature is in the capacitor compartment.

author: kris2ff3r
author_rank: Contributor
timestamp: September 01, 2017, 11:47:35 pm
content: Quote from: drussell on August 26, 2017, 06:12:06 pmSee attached

author: Gyro
author_rank: Super Contributor
timestamp: September 02, 2017, 12:39:31 pm
content: Quote from: Simon on August 28, 2017, 08:14:19 pmActually I think you'll find that it's large orchestral works that typically have the lowest fundamentals and demand the most sustained bass handling. A lot of the stuff mentioned above actually relies on higher bass frequencies to give the 'in the chest' feeling when played at high volume through PA speakers.

author: Simon
author_rank: Unknown
timestamp: September 02, 2017, 12:49:15 pm
content: oh all rightBut I say again, the amplifier will have a slew rate, after you have provided enough capacity to reach the output the amplifier is capable of more won't help. If a manufacturer is advertising an "upgrade" is makes you wonder why they didn't just make it right in the first place. Clearly the manufacturer is aiming at a certain market, capacitors are not that expensive in the grand scheme of things.

author: Gyro
author_rank: Super Contributor
timestamp: September 02, 2017, 03:38:25 pm
content: I'm not going to disagree with you there. There's really no point in going past a certain value - you might just as well go for regulated supply rails, as used by John Linsley Hood in his ultimate Mosfet amp designs.Of course you wantrealbass you need to go to the Proms on a night when they fire up the 64' stop (8.2Hz) on the Royal Albert Hall organ. Or even better, if you're man enough, there's a Cathedral in Germany with a 128' pipe (4.1Hz) - probably enough to do interesting thing to your bowels!

author: Loboscope
author_rank: Regular Contributor
timestamp: September 02, 2017, 11:32:04 pm
content: I am sorry, but this video is a fake and pure nonsense. Nowhere in the world exists a 128´-Organ Stop.And there are only two organs in the world with a true 64´-Stop going down to the subcontra-C: Australia, Sydney, Town Hall and USA, Atlantic City, Convention Hall. Sometimes there do exist ´fake´ 64´-Stops, that means, that this Stop is build with a 32´ together with a 21 1/3´-Stop (Quint). This combination gives a sub-octave tone qua a difference-tone, but this virtual sub-octave sounds relatively weak.The Organ in the video might let hear a 32´-Stop. But anyway a 32´-Stop goes down to 16 Hz which is nearly the lower audition limit of men and a 32´ open pipe Stop or 32´ tongue-pipe Stop will give a great sound impression and will demand really good audio gear. But so will do a 16´ Stop as well - it goes down to about 32 Hz.For further information look here (sorry, I only can find this german site):http://www.die-orgelseite.de/kurioses.htm

author: Beamin
author_rank: Super Contributor
timestamp: September 02, 2017, 11:46:46 pm
content: Isn't an A/B class amp used for audio; powering speakers? Well I know it is but are there other uses?

author: Simon
author_rank: Unknown
timestamp: September 03, 2017, 08:04:43 pm
content: AB is the usual option, you could use class A for low power but being only 50% efficient if not less is the reason AB is used. You can also these days use a class D that is basically a power PWM encoder, running at a higher PWM frequency than you can hear or than the speaker can react to you never hear the PWM and just the encoded sound with maximum amplifier efficiency as the transistors are on or off and not acting as power potential dividers like classes A and AB.