| carlosfm |
For a long time that I know this excellent article on power supplies:
http://www.tnt-audio.com/clinica/ssps1_e.html
Lately I've been thinking...:scratch:
Why the hell don't these chips like high capacitance?:xeye:
Why do they sound bad?
The reason is so simple that in the end I just wanna kick myself.
Bigger caps have higher inductance, and the amp will have lower damping factor at mid/high fequencies.
The thing is: these chips are really sensitive to this.
Go higher than 1500uf per rail/chip and you start noticing that the midband and treble magic goes away.
The more capacitance you add, the worse it sounds.
The solution is...
A snubber.:D
I've been testing tonight on my main system, with a new LM4780 amp that is :hot:in' in for 3 days on my bench, and it really works.
The original unregulated test PSU ended at C5/C6 on my schematic.
For some time ago - since I tested and use regulated PSUs - that I use 100uf on the chip's PSU pins (not 1,000~1,500uf), and as I reported off-topic on another thread, this works better even with unregulated PSU.
I tested adding to the PSU on the schematic 10,000uf (after C5/C6) and it sounded bad, as usual, but then I tested several snubber values until I settled with this.
It sounded better and better as I lowered the value of C9/C10, the resistors were always 1R.
This is preliminary, more and more tests can be made, but I don't feel that going to a much lower value for C9/C10 will improve things even further.
This is very old stuff, I'm surprized nobody ever tested this with chip amps, or had an explanation for these chips prefering low capacitance...:xeye:
Here's the schematic, have fun.:cool: |
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| sek |
Good work ;)
As this is a real quantitative and qualitative claim, it would be good to actually have measurement data on it.
It's great that high capacitance finally sounds good for you.
Now why not make it reproducible for everyone?
What inductance is acceptble, what value is bad, which capacitor is the best with what snubber, etc. ;)
I'm not into questioning your results, I just never experienced a problem with different capacitor sizes, nor any overall improvement with reducing the value below 4.7uF. While minorly improving the midrange at low levels, small sizes always worsened many other aspects of the sound. I'd like to see a systematic approach to wether the snubber can really be a cure in all situations. :D
Cheers,
Sebastian. |
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| Upupa Epops |
| Carlos, little bit of theory : damping factor not depend only on impedance of PS ;) , so your thinking is simplyfied. |
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| carlosfm |
| quote: | Originally posted by Upupa Epops
Carlos, little bit of theory : damping factor not depend only on impedance of PS ;) , so your thinking is simplyfied. |
Pavel, read my post more carefully, as I didn't talk about impedace at all.
I talked about the inductance of larger caps.
http://zero-distortion.com/start.htm
Read the article "Designing your own power supply", on the last pages you have the snubber (although with different values) and an explanation on why to use it.
Same author (Dejan V. Veselinovic), same artice, a little more detailed. |
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| carlosfm |
| quote: | Originally posted by sek
Good work ;)
As this is a real quantitative and qualitative claim, it would be good to actually have measurement data on it. |
Sebastian, I have a broken scope:bawling: in my basement and I didn't find the time to look at it yet.
The part that burned out is on a such a difficult place to get access that I have to dismantle the whole thing, including the screen.:xeye:
As I said, this is a preliminary with an existing test PSU, it may not be a final schematic, or you may even have to tune it in every implementation.
What I say is that the effect of the snubber is quite amazing, and I've got to a value that works fine with this PSU/amp.
Everyone is welcome to test, measure, suggest, listen.
Who dares?;)
PS: I'm sorry, I've been very busy at work, so lately I've had less time to DIY (so many things to test:bawling: ) and please be patient if I take a little longer to repply. |
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| carlosfm |
| quote: | Originally posted by sek
I'd like to see a systematic approach to wether the snubber can really be a cure in all situations. :D |
One more thing:
It's so easy to test this that I hope you guys don't start asking for proofs no end.
The 10,000uf caps I added and also the snubbers are connected to the PSU with aligators.
The amp doesn't even have a case yet.
Neither does the PSU.
If this wasn't worth a try I would not even open this thread, even after testing it.
But it's worth a try.:cool: |
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| m0tion |
| Maybe this is a bit of a novice question here, but how does adding 10,000uF to each PS rail effect the sound? I suppose I mean how as in subjectively "Does it make it sound better? If so, in what way?" and how as in objectively "Why does it effect the sound at all?". |
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| sek |
Hi,
| quote: | | how does adding 10,000uF to each PS rail effect the sound? |
Le'me start with a little introduction: :D
The supply capacitors basically form an RC filter network between transformer and load (in our case: amplifier), consisting of a resistance R and a capacitance C. As the resistances in the power wiring (transformer, cables, etc.) should be as low as possible, we have a very low value for R in the equation of the RC filter.
Basically, the product of R and C in the supply wiring forms a so called 'time constant' t = R*C. Now, t corresponds to the frequency 1/t where the RC filter starts to - well - filter.
Ideally, we want to have the filter work from frequencies of 0Hz and up, so that no noise or hum can pass the RC filter. This would then mean that the supply voltage would always be constant and contain no hum or noise. So, in order to let the filter work at very low frequencies, we have to compensate for the low value for R with a high value for C.
From another point of view, there's also the problem that the value of R changes, depending on the power that the amplifier draws. Accordingly, a higher value of C would compensate for a higher change of R to be still tolerable.
Simplified, the whole filter thing determines the 'regulation' of the supply voltage, e.g. how much (or better: less) the supply voltage sags under load. Consequentially, the more powerful the amplifier, the larger our C has to be for an equally good regulation. Or the other way 'round: With a larger C and thus better supply regulation, our amplifier gets less influenced by how much power it consumes (or 'how loud it plays').
As for the objective benefit of larger C: :D
When high current is drawn into the (loudspeaker) load, a poorly regulated power supply sags significantly, reducing it's voltage. Now, enough voltage is unfortunately exactly what we need in high power situations. The situation seems paradox: as the output power (and simplified: the output voltage) goes up, the supply voltage goes down!
This could lead to amplifier clipping once the output voltage reaches a certain amount of the supply voltage, as now the amplifier has no voltage left to 'supply itself'...
Clipping means distortion, but distortion can already occur way before clipping. E.g. when a bass signal draws much power, the weak supply takes a while to 'recover'! Thus, the music signals that occur during this 'recovery' find the amplifier in a situation of 'power compression', where it can't work up to spec and distorts and weakens the output signal...
As for the subjective improvement on the sound: :D
Less clipping means better sound, that's easy. But that easier 'recovery' from high power situations (with less power compression) also improves the sound.
For a better understanding, it should be noted that both power compression and clipping due to supply sagging are easier perceived at higher power levels, because the effect is stronger when more power is drawn. Thus, the improvement is something for us loud-listeners. Bass is stronger and more natural. Loudness of mids and highs doesn't get affected by the bass. Overall sound is more natural and impressive. ;)
But that doesn't mean that listening at lower levels can't get improved by a better supply regulation. Even at low power levels, slight power compression and distortion could occur with signals of high dynamics, such as attacks of instruments. Preventing this by using large capacitors would not be so obvious, as the quantitative amount is lower, but the sound could become less coloured and listening less 'tiring' to the ear even in longer listening sessions.
The amount of improvement of course depends on many factors. But in general, the usually recommended 1,000uF for a Gainclone are considered already extremely low. 4,700uF is probably what an engineer would settle for a commercial 50W amplifier. 10,000 is probably where audiophiles would start, whatever that means... ;)
------
As a bottom line, It can be assumed that most people actually know the bad influence of a weak supply on the sound. Remember what happens to the volume and sound quality of a 'ghetto-blaster' when the batteries drain?
Cheers,
Sebastian. :D |
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| TwoSpoons |
Personally I would use 10x 1000uF instead of 1x 10000uF, connected using a sheet bus, and as close as practical to the chip supply pins.
Paralleling all those ESR's and ESL's really works in your favour, ripple current handling goes right up, and you get to choose from the ultra-low impedance types from Nichicon, Rubicon etc. |
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| jackinnj |
Carlos
time to invest in a network analyzer --
most of the time the ESL of a capacitor is stated in nano-henries -- quite important for switching regulators where di/dt is quite large -- or if you are trying to couple an RF circuit since the inductance can swamp the capacitance.
i wonder whether the effects you experience with the LM338 regulator for your GC's isn't compensating for a transformer which has poor coupling, or is overheating -- i don't think that the series inductance of the filter caps is going to materially affect the power supply impedance at the kind of frequencies we are talking about. |
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| m0tion |
Sek:
Thanks very much, I appreciate the time you took to write that. I now have a much better understanding of why higher capacitance filters are better, even for smaller gainclone amps. |
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| sek |
| quote: | Originally posted by m0tion
Thanks very much, I appreciate the time you took to write that. |
Glad I could help. ;)
| quote: | | I now have a much better understanding of why higher capacitance filters are better, even for smaller gainclone amps. |
Well, that's the culprit! They should, but many report they aren't. Not because what I describe doesn't apply to chip amps, too. But because the sound in the midrange is reportedly compromised with a higher capacitance PSU. That's why Carlos is so happy about his results with a compensation circuit for higher capacitances. I suspect we'll have to wait until further investigation has been done... (unfortunately I don't have the time, nor the need at the moment) ;)
There's also a neat article on TNT audio about designing PSUs. It also describes the method discussed in this thread.
Sebastian. |
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| carlosfm |
| quote: | Originally posted by jackinnj
i wonder whether the effects you experience with the LM338 regulator for your GC's isn't compensating for a transformer which has poor coupling, or is overheating -- i don't think that the series inductance of the filter caps is going to materially affect the power supply impedance at the kind of frequencies we are talking about. |
The first GC I made was with a 2x24V 384VA custom made toroid, unregulated PSU with MUR860s and 1,000uf per rail on each LM3875 board.
A typical GC, then.
This toroid didn't ever get hot, did never vibrate.
And it was quite a good trafo for two channels.
Unfortunately this amp, although good sounding, was not able to drive my speakers properly.
Bass was not tight, even at low volume.
I added 2x4,700uf caps on the PSU diodes and at first it seamed to sound better. At least bass was tighter.
Listening more carefully a week later, I found out that the amp was sounding like a cheap one. Low-level detail, midband, treble, "air", "ambience", soundstage, all went to the toilet.:bawling:
I then made plenty of tests with capacitance and got my conclusions.
Then I made another modules with LM3886 and never looked back again to the LM3875.
But with the low capacitance unregulated PSU it was still not there as I wanted. There was more to be gained in driving ability, and I knew it.
Regulation did solve this problem in a way that I call my power amp a mini-Krell.:clown:
This test now with high-capacitance unregulated PSU is just because I felt that it could be made to work much better.
I don't say it's better than to regulate, in my oppinion it's not, but it will be enough to use with a much more variety of speakers tham the typical GC can cope with.
If one can't detect a difference for the worse in changing caps for bigger ones on the unregulated PSU with these chips, then there's a lack of transparency in the system that prevents it to be detected.
I don't ever take conclusions with my test speakers, the final and cruel test is always in my main system, where it gets all exposed.
Of course, I'm so used to it that I can detect any change for better or for worse. |
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| carlosfm |
| quote: | Originally posted by sek
There's also a neat article on TNT audio about designing PSUs. It also describes the method discussed in this thread. |
:rolleyes:
:dodgy:
:rolleyes:
Have you really read my first post on this thread?
And also post #4?
No?
Yes?
Nah...
:bawling: |
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| m0tion |
| How about increasing the capacitance along with adding a voltage regulator? Is there some reason why adding a voltage regulator makes increasing the capacitance no longer useful? Or impossible? Anyone considering implementing these PS changes using BrianGT's kits? |
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| carlosfm |
You could search this forum instead of going all over it again.
As Pedja says, there's a "ground shaking thread" about this.:D |
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| moving_electron |
I am having trouble making out the capacitor value in the figure 4 at the top of part Part 2. http://www.tnt-audio.com/clinica/ssps2_e.html
Does any body know what value the writer was recommending?
Carlosfm, I know you have tested and have a recommended value you like for chipamps, but I am curious as well about what the author of the article was recommending for (presumably) solid state amps. |
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| sek |
| quote: | Originally posted by carlosfm
Have you really read my first post on this thread? |
This one was addressed to m0tion. Although I could have choosen my words better, I only wanted to recommend him to really read it (as it appeared he hadn't, assuming he might not have noticed).
So, just add "in case you didn't notice" to my previous post...
Sorry to be redundant,
Sebastian. |
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| thomas997 |
| quote: | Originally posted by moving_electron
I am having trouble making out the capacitor value in the figure 4 at the top of part Part 2. http://www.tnt-audio.com/clinica/ssps2_e.html
Does any body know what value the writer was recommending?
Carlosfm, I know you have tested and have a recommended value you like for chipamps, but I am curious as well about what the author of the article was recommending for (presumably) solid state amps. |
Going left to right after the rectifiers: 10,000uF, 10,000uF, 100uF, 100nF, 560nF (or 580nF not sure). |
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| carlosfm |
| quote: | Originally posted by moving_electron
Carlosfm, I know you have tested and have a recommended value you like for chipamps, but I am curious as well about what the author of the article was recommending for (presumably) solid state amps. |
He suggests a starting point, but he also says it can be fine-tuned in every implementation between 220nf and 560nf.
Check the link I posted on post #4 of this thread, as that article is a little more detailed.
I started with 560nf, then 330nf, then 120nf and...:eek:
That's it for now.:D
It's :hot:in'-in, sounds good.:) |
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| Cobra2 |
-but did not do much experimenting...just added 220nF & R.
BTW, tried different resistors?
Arne K |
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| carlosfm |
| quote: | Originally posted by Cobra2
-but did not do much experimenting...just added 220nF & R.
BTW, tried different resistors?
Arne K |
:)
No, just 1 ohm.
I think it's better to deal with one component at each time.
Maby there's more to test, and more to improve, any beta testers out there?:cool: |
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| Cobra2 |
I was more thinking of inductive vs non-inductive resistors...
Arne K |
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| carlosfm |
| quote: | Originally posted by Cobra2
I was more thinking of inductive vs non-inductive resistors...
Arne K |
That is a really good question.
Carbon (or film) resistors is the way to go, no bobinated resistors here.
I'm testing with a 1 ohm 3w resistor, although I think that two 2.2ohms 3w in parallel would be fine too.
It's recommended something from 5 to 10w.
3w carbon resistors I can find easily.
More than that is not so easy around here, only bobinated.
I could order (more expensive) film resistors, but for test purposes it's carbon.
And it works fine. |
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| ChuckT |
Very interesting.
Does the small value RC bypass include the small cap directly across +/- pins on the chip? |
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| matjans |
since i've built my ucd180 based class d amp i've got a few gc's laying around doing nothing. i think i'll give it a try.
How much influence do the small caps have that are soldered to the chip? In all of my current clones these are ~1000uF panasonics or black gates. Do i need to replace them with smaller value ones? |
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| carlosfm |
| quote: | Originally posted by ChuckT
Very interesting.
Does the small value RC bypass include the small cap directly across +/- pins on the chip? |
I'm not using it on this LM4780 board, due to lack of space (and the crazy pinout this chip has), but with LM3886 and others I normaly use 270nf poly between + and - pins on the chip. |
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| carlosfm |
| quote: | Originally posted by matjans
since i've built my ucd180 based class d amp i've got a few gc's laying around doing nothing. i think i'll give it a try. |
Do it.;)
| quote: | Originally posted by matjans
How much influence do the small caps have that are soldered to the chip? In all of my current clones these are ~1000uF panasonics or black gates. Do i need to replace them with smaller value ones? |
Yes, after the snubber there should not be big caps.
It would defeat the snubber's job.
100uf is what I use on the chip.
Alas, what works fine with regulated PSU also works fine here.:cheerful: |
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| matjans |
| obrigado, amigo ;) |
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| Upupa Epops |
| To Carlos : All what you now discover, you may to see on my 4780 PCB :cool: . |
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| carlosfm |
| quote: | Originally posted by Upupa Epops
To Carlos : All what you now discover, you may to see on my 4780 PCB :cool: . |
I was about to test this for some time.
I know your schematic and I didn't see a snubber on the caps.
Also, your pdf schematic file has many question marks (?), it doesn't show the values of many components. |
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| Upupa Epops |
| To Carlos : Look at www. czechaudio.com. There is all. For what snubber ? |
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| carlosfm |
| quote: | Originally posted by Upupa Epops
To Carlos : All what you now discover, you may to see on my 4780 PCB :cool: . |
| quote: | Originally posted by Upupa Epops
For what snubber ? |
Now I'm confused.
What do you mean?
Can you elaborate?
| quote: | Originally posted by Upupa Epops
To Carlos : Look at www.czechaudio.com. There is all. |
You only have a PA03 amp in the Projects seccion.:confused: |
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| roibm |
Would be nice if someone would use black gate for the snubber? Bad or good?
Carlos, do you have any? |
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| carlosfm |
| quote: | Originally posted by roibm
Would be nice if someone would use black gate for the snubber? Bad or good?
Carlos, do you have any? |
100~120nf?
Does it exist?
Polyester or polyprop is fine... |
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| roibm |
| quote: | Originally posted by carlosfm
100~120nf?
Does it exist?
Polyester or polyprop is fine... |
Well, Black Gate NX Hi-Q 0.1uF/50V would be the one to use in this case. I doubt it would do much good if at all, but still would be interesting to try. |
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| Upupa Epops |
| To Carlos : Do you mean this RC element on your schematic? Do shorter traces on PS and you don't need it. By the way, wattage of this resistor is enough 0.25 W, not 3 W. |
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| jkeny |
Matjans,
I know this is off topic but I am thinking of buying a 2 x UCD180 class D modules. How does it compare sonically to the gainclone? I have asked this question on class D forum but no direct comparisons given. I have built gainclone and know the sound and wondered how much better UCD180 modules were?
John |
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| roibm |
| quote: | Originally posted by jkeny
I have built gainclone and know the sound and wondered how much better UCD180 modules were? |
Is it a given that UCD180 is better? |
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| carlosfm |
| quote: | Originally posted by Upupa Epops
To Carlos : Do you mean this RC element on your schematic? Do shorter traces on PS and you don't need it. |
Nah, I tested bigger caps on the chip's pins and with higher than 1,500uf per rail/chip it starts sounding worse and worse.
Upupa, read my posts and those articles, as I think it should be quite clear that it's not a question of cabling or PCB traces. |
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| jkeny |
| quote: | | Is it a given that UCD180 is better? |
Roibm,
I believe it is a given - just a matter of how much better - maybe Matjans can answers this?
John |
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| matjans |
i don't think it's a given per se. you can't compare the two, really. the ucd is a plug-n-play amp, a clone you have to build yourself.
the ucd delivers 9,5A continously whereas a single lm3875 delivers way less.
I can only say that my ucd based amp sounds way better than every clone i've built. a linn klimax is a chipamp too. ;) |
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| roibm |
After looking through the "UCD180 questions" thread(18 BIG pages...), I can't really say who would be able to tell the story by it's name(i.e. what is better and why...)
And let's not forget, better is relative, and personal taste can influence the result a lot. |
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| roibm |
After looking through the "UCD180 questions" thread(18 BIG pages...), I can't really say who would be able to tell the story by it's name(i.e. what is better and why...)
And let's not forget, better is relative, and personal taste can influence the result a lot.
PS: bug in vBB, see the timestamp of the two posts ;) |
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| carlosfm |
| quote: | Originally posted by matjans
the ucd delivers 9,5A continously whereas a single lm3875 delivers way less.
I can only say that my ucd based amp sounds way better than every clone i've built. a linn klimax is a chipamp too. ;) |
Have you ever tried an LM3886 with regulated PSU?
The LM3875 is not suited to drive most modern speakers, just forget it. |
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| yuri777 |
Hi Carlos
Could you describe the function of R1 and R2 on your unregulated PSU schematic?
Are R3 and R4 there to discharge the caps once the power supply has been turned off like Dejan suggests in his articles?
Thanks :) |
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| SheldonD |
I am not Carlos, but to answer your questions:
R3 and R4 are in series with a small capacitor, these can not pass DC which is what is stored inthe large filter caps. They do provide a very low impedance to high frequencies, as such will short out high frequency transients and suppress high frequency oscillation.
R1 and R2 are however a conducting path across the storage capacitors, and will in a short time drain the caps after shut down.
For Carlos: I am glad to see you are pursuing this area. But the problem can not be simply the higher inductance of larger caps as adding more caps to existing caps will lower the inductance. as inductors in parallel become smaller not larger. |
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| carlosfm |
| quote: | Originally posted by SheldonD
I am not Carlos, but to answer your questions:
R3 and R4 are in series with a small capacitor, these can not pass DC which is what is stored inthe large filter caps. They do provide a very low impedance to high frequencies, as such will short out high frequency transients and suppress high frequency oscillation.
R1 and R2 are however a conducting path across the storage capacitors, and will in a short time drain the caps after shut down.
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I've been out, thanks Sheldon.
| quote: | Originally posted by SheldonD
For Carlos: I am glad to see you are pursuing this area. But the problem can not be simply the higher inductance of larger caps as adding more caps to existing caps will lower the inductance. as inductors in parallel become smaller not larger. |
Maby there are other reasons too, I'm open to suggestions.
Anyway, on the chip there are 100uf caps bypassed with 100nf ceramics.
I've made many amps with several chips, several implementations, and tried too many combinations regarding unregulated PSU.
2x3,300uf per rail sound worse than single 4,700uf caps per rail.
Really.
2x4700uf sound as awful as 10,000uf.
Go lower to 1,000~1,500uf per rail/chip and that's the sweet spot.
But then most probably it won't drive your speakers.:bawling:
This snubber lets me go higher in capacitance without mucking up the sound. |
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| yuri777 |
Thanks alll for your answers.
I thought the discharge resistors had to be in front of the capacitors like on Dejan's schematics, which is why i asked.
Anyway, i have more questions:
1-Carlos, why didn't you implement the snub capacitors across each one of the bridge diodes like on Dejan's schematic?
I know Nuuk also recommends doing this on his web pages...
2-How come nobody here building PSUs recommends using at least one termistor (Digikey Part#KC006L-ND) to limit the Inrush current in the PSU?
From what i have read, it has many the benefits..
I know Nelson Pass has termistors in at least one of his PSU designs
Thanks |
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| scottw |
Having a little trouble understanding why the R in the snubber has to be such high wattage. Regardless of the interaction with filter capacitor inductance, isn't it still just "snubbing" high frequency? In the case of Carlos' schematic with 1R/0.120uf snubber the f > 1MHz. Can there be this much energy at high frequency in the PSU or is there something else going on?
Veselinovic was using up to 17 watt R's for 50 to 100 watt amps(me thinks). Did some digging. The original design of the Otala inspired amp that Veselinovic based his usage of the RC snubber on used 1 watt R's:
http://home.online.no/~tsandstr/Ota...%20original.htm
and the production design built by Electrocompaniet used 0.5 watt R's for the snubber:
http://home.online.no/~tsandstr/sch...l_ec_25w_am.htm
This was a 25 watt amp.
I understand a little wattage headroom will be a good idea for a stable filter but shouldn't two watts be enough for a 30 to 50 watt GC?
And thanks Carlos for pointing out this filter.
scottw |
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| Cobra2 |
It was those big watt resistors that made me think that they must be inductive...if it makes a difference?
Arne K
Termistors...benifit??? none other than power-surge when turn on? |
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| jackinnj |
| quote: | Originally posted by carlosfm
Yes, after the snubber there should not be big caps.
It would defeat the snubber's job.
100uf is what I use on the chip.
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the snubber's job is to damp the ringing of the diodes as they switch on and off -- the frequency of the ringing is a lot higher than the audio spectrum -- but this also means that the snubber itself should be placed as closely as possible to the rectifiers -- any trace distance adds inductance to the circuit -- and this changes the impedance of the supply -- of course this is a problem of enormous import to switchers, a lot less so for linear supplies .... perhaps tomorrow I will import the SPICE models for the MUR860 ... |
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| carlosfm |
| quote: | Originally posted by jackinnj
the snubber's job is to damp the ringing of the diodes as they switch on and off |
Aren't we talking different things here? |
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| carlosfm |
| quote: | Originally posted by yuri777
1-Carlos, why didn't you implement the snub capacitors across each one of the bridge diodes like on Dejan's schematic?
I know Nuuk also recommends doing this on his web pages... |
Everytime I take those caps across diodes on a CDP I have improvements.
So, I don't use that approach on my amps.
| quote: | Originally posted by scottw
Having a little trouble understanding why the R in the snubber has to be such high wattage. Regardless of the interaction with filter capacitor inductance, isn't it still just "snubbing" high frequency? In the case of Carlos' schematic with 1R/0.120uf snubber the f > 1MHz. Can there be this much energy at high frequency in the PSU or is there something else going on? |
My schematic is preliminary, It is based on my test.
I also think that Dejan quite exagerated on the power of the snubber resistors.
Maby 2~3W is enough. |
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| jackinnj |
ok, here's the math --
somehow my last post disappeared when I hit enter, i hope i am not being repetitive.
you have to look at the snubbers as part of the network made up of the power supply elements and the amplifier. it doesn't matter that you have two of them (100nF and the RC of 120nF and 1R) as was drawn.
you need to know at least 2 things, and probably 3: 1) the inductance of the transformer secondary (with the primary shorted) [br] 2) the combined capacitance of the diode AND transformer primary to secondary, and [br] the peak to peak "repetitive" voltage.
for one of my 60Hz torroids I measured the secondary leakage inductance as 180 uH, the MUR860 has capacitance of 100pF at 30V, and the transformer capacitance is 300pF. The pk to pk Vrrm maybe 100mV.
the resonant frequency is F= 1/(2pi sqrt LC) = 593kHz
the snubber resistor is Rs = sqrt (L/C) = 670R
the snubber capacitor is Cs = 1/(Rs * F) = 2.5 nF
the resistive dissipation is P = 1/2 * Cs * (Vrrm^2) * F = 7.4 uW
the math is a little easier on ON-Semi's website than Hagerman's paper. http://www.onsemi.com/pub/Collateral/HB214-D.PDF -- look at page 170.
if you use much larger capacitors the power dissipation in the snubber resistor is going up a lot, but not enough to spoil a 1/2 watt resistor -- in a switcher it becomes problematic. It would appear that a larger capacitor will add more damping and reduce the ill-effects of diode-ringing. |
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| ALW |
There's some confusion here it seems.
The snubbers in the original schematic are going to be innefective at damping the transformer resonance, since they are the wrong side of the rectifiers and way too far away to be of any practical use, in this respect.
Any benefits Carlos is getting are much more likely to be related to the decoupling to the IC itself.
As an addition though, the 100n caps in parallel with the transformer don't seem like a good idea either. Based on the fact that the transformer will have a resonance, these just add more C and lower the resonant frequency closer to the audio band, solving one problem (RF noise) and making another (AF noise). It may be a better net result if the reservoir caps are lower Z at this frequency, but it's far from ideal. Better to snub the oscillation properly (which requires R not C), the C is there solely to reduce Pd in the resistor - it is, in effect, an AC-coupled resistor.
If you use the figures presented by jackinj as an example of a typical transformer, you move it's self-resonance from 600kHz to around 37kHz by adding that 100n.
| quote: | | It would appear that a larger capacitor will add more damping and reduce the ill-effects of diode-ringing. |
It shouldn't have any significant effect, if the C value / type is chosen correctly (i.e. is low Z at the resonant frequency). The R provides the damping.
It's not the diodes ringing either...
Andy. |
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| jackinnj |
i'm sure we've all had this problem - the circuit is working OK, but not great (distortion is high, etc.) and you put your finger on an IC -- WOW is it HOT !!! -- the problem with these resonant circuits is that the oscillations find their way to where they shouldn't be! the IC gets overdriven, etc., etc.
not that 600kHz is a particularly short wavelength, but you know what I mean.
and with a GC chip we know to be mindful...
Hagerman sources an article in Audio Amateur 3/94 which discusses snubbers. |
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| carlosfm |
| quote: | Originally posted by ALW
Any benefits Carlos is getting are much more likely to be related to the decoupling to the IC itself. |
You and jackinnj are missing the point here.
I can understand that caps on the primary may not always be good, ok.
But the snubber after the big caps have nothing to do with the diodes.
Let me explain how I made the tests:
1. LM4780 PCB with 100uf+100nf on-board.
2. PSU with (basically) 3,300uf caps per rail.
4. Listen - sounds fine, but my speakers ask for tighter bass
5. Add another 10,000uf cap per rail on the PSU
6. Listen - bass ok, but sounds bad (midband and treble like a cheap amp)
7. Add the snubber (1R + 560nf) - better
8. After testing several snubbers, final 1R+120nf - :eek:
So, the chip is the same, the bypassing on the chip too.
What made those big 10,000uf caps sound good with this chip was the snubber.
13,300uf of capacitance per rail with and unregulated PSU and with a chip amp never sounded so good to me. |
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| carlosfm |
| quote: | Originally posted by jackinnj
i'm sure we've all had this problem - the circuit is working OK, but not great (distortion is high, etc.) and you put your finger on an IC -- WOW is it HOT !!! |
The LM4780 is palyin' on my main system for almost a week, with my tough EPOS ES11 speakers.
Heatsing is a black anodized P3 CPU cooler, without isolator on the chip.
Actually, this works very well, between the chip and the heatsink there's only thermal paste, but the chip is isolated.
I've pushed it hard and the heatsink doesn't get hot to touch, and in normal listening levels it doesn't even get warm.
I would not put this on my main system for a test if it got too hot as you say.
On my bench it had been playing for some days, with 4 ohm test speakers. |
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| jackinnj |
| quote: | Originally posted by carlosfm
You and jackinnj are missing the point here.
I can understand that caps on the primary may not always be good, ok.
But the snubber after the big caps have nothing to do with the diodes.
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Carlos, the first (100n) AND second (120n + 1R) snubbers are parallel with the reservoir caps -- it's a network ! You should look at it in series. |
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| ALW |
| quote: | | You and jackinnj are missing the point here. |
I didn't, but I may not have explained myself very clearly though, I'm well aware it has nothing to do with the diodes (even though it apepars across them), that was my point.
| quote: | | So, the chip is the same, the bypassing on the chip too. |
Here I disagree, the chip sees the 1R + cap as part of it's decoupling. It looks like a cap with high-ish ESR.
Andy. |
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| carlosfm |
| quote: | Originally posted by ALW
It looks like a cap with high-ish ESR.
Andy. |
It does.:D
But somehow it makes using big caps before it have much less impact to the sound. |
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| ChuckT |
Hi Carlos,
sorry for asking again, but could clarify if you still use a small cap between +/- pins after the RC (1R + 0.12uf)?
Right now, I am using 4700uf Sikorel and 1uf Auricap across +/- pins.
BTW, thanks for posting result. Very good info.:) |
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| 300_baud |
Hey Carlosfm,
Quick question... did the unregulated psu you have here sound better than the regulated psu for the GC that you posted earlier on? I'd like to know so I can choose the better one and go ahead with my GC upgrade :D Thanks |
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| carlosfm |
| quote: | Originally posted by ChuckT
sorry for asking again, but could clarify if you still use a small cap between +/- pins after the RC (1R + 0.12uf)? |
Can you clarify?
I don't understand your question...
It's all in the schematic.
The amp has 100uf+100nf per rail.
No cap between + and - rails. |
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| carlosfm |
| quote: | Originally posted by 300_baud
Hey Carlosfm,
Quick question... did the unregulated psu you have here sound better than the regulated psu for the GC that you posted earlier on? I'd like to know so I can choose the better one and go ahead with my GC upgrade :D Thanks |
I haven't yet made a direct comparison, but as I said on a previous post, I still think that regulated PSU is better.
If your speakers are easy to drive you can go unregulated. |
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| D_GR8_1 |
I simulated the Regulated Power Supply in Protel and the software kept on complaining that the ADJ pin had no "driving source".
Once I removed the capacitor that connects ADJ to GND it worked fine.
Does the design really need these caps. I mean what is their underlying purpose? |
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| carlosfm |
| quote: | Originally posted by D_GR8_1
I simulated the Regulated Power Supply in Protel and the software kept on complaining that the ADJ pin had no "driving source".
Once I removed the capacitor that connects ADJ to GND it worked fine.
Does the design really need these caps. I mean what is their underlying purpose? |
:confused:
This thread is not about regulated PSUs.
Anyway, are you talking about the LM338?
The CAdj cap reduces ripple, check the datasheet. |
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| carlmart |
| quote: | Originally posted by D_GR8_1
I simulated the Regulated Power Supply in Protel and the software kept on complaining that the ADJ pin had no "driving source".
Once I removed the capacitor that connects ADJ to GND it worked fine.
Does the design really need these caps. I mean what is their underlying purpose? |
Go read page 8 on the LM317 datasheet. This capacitor is very important on chips like the 3X7, 338 and other variable regulators, where it's not advisable to use large capacitors at the output, to improve ripple rejection.
National claims that more than 10uF does not "appreciably" improve ripple rejection at frequencies above 120Hz. But they also advise to use tantalum caps, which in my experience and other diyer's is ominous. That proves that sometimes the datasheet can and should be twisted a bit.
Many designers claimed great improvements by using medium to large caps at this pin, properly diode protected, of course.
Carlos |
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| rs1026 |
This may seem a bit not directly connected to the current discussion.But after reading this thread I thought of doing a slight experiment. I had a unregulated PS with 6800uf per rail.It is just ordinary bridge rectifier without any snubber or anything else.I am using diodes that are capable of handling 6A current. I replaced the 6800uf with a 1000uf capacitor. I am using lm3886 based GC.
The difference that I could make out was the amp sounded somewhat lighter and a bit nice to hear.But when I had used the 6800uf capcitor on rails it sounded more kind of heavy.
Is it beacuse of the big caps?? |
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| jackinnj |
| quote: | Originally posted by carlmart
National claims that more than 10uF does not "appreciably" improve ripple rejection at frequencies above 120Hz. But they also advise to use tantalum caps, which in my experience and other diyer's is ominous. That proves that sometimes the datasheet can and should be twisted a bit.
Carlos |
There's a very good reason for using a tantalum -- they are much better in preventing oscillation in low-dropout regulators (not the LM317 -- this isn't an LDO) because of their low ESR, they are more temperature stable, and smaller-- so says Nat Semi.
I doubt they sound very good in a signal path, however. I measured the distortion of some tantalums (2 back to back) just now at around 1.0% -- compare this to a polypropylene at a negligible level. |
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| carlosfm |
| quote: | Originally posted by jackinnj
There's a very good reason for using a tantalum |
For a regulated PSU to use on a GC, normal voltage is around 30V.
I don't think that tantalum caps exist at more than 35v rating, and even these are already big.
They are not reliable when working close to their voltage rating.
Huh.... no, let me put it this way: they are not reliable.:D |
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| carlmart |
| quote: | Originally posted by jackinnj
There's a very good reason for using a tantalum -- they are much better in preventing oscillation in low-dropout regulators (not the LM317 -- this isn't an LDO) because of their low ESR, they are more temperature stable, and smaller-- so says Nat Semi.
I doubt they sound very good in a signal path, however. I measured the distortion of some tantalums (2 back to back) just now at around 1.0% -- compare this to a polypropylene at a negligible level. |
There's a very good reason for no using tantalums: they catch on fire. Seen several cases of that. A good low ESR from Panasonic should do better.
For a good attack on tantalums by serious people read this:
http://www.capacitors.com/picking_c...ors/pickcap.htm
Carlos |
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| jackinnj |
| quote: | Originally posted by carlmart
There's a very good reason for no using tantalums: they catch on fire. Seen several cases of that. A good low ESR from Panasonic should do better.
For a good attack on tantalums by serious people read this:
http://www.capacitors.com/picking_c...ors/pickcap.htm
Carlos |
having been a subscriber to Audio in the 1980's I read Walt's article in its original form!yet there are a few recidivists who continue to believe that tantalums have a place in the signal path.
here's my experience with an LDO -- ultralow noise units from Linear -- they worked OK with an aluminum electrolytic, but very very well with tantalum.
in the regulated GC as put forward by Carlos, a standard, off the shelf regulator is employed so I wouldn't expect the same kind of problem as with an LDO. I don't have any tantalum's over 35V in my lunchbox anyway.
when tantalums fail, they fail miserably, shorting out -- and they can take the regulator with them !
it may not be as important in Brazil or Port -- but tantalums have better ESR over temperature -- in cold temperatures an aluminum electrolytic isn't what it's thought to be! |
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| carlosfm |
| quote: | Originally posted by jackinnj
when tantalums fail, they fail miserably, shorting out -- and they can take the regulator with them ! |
That is exactly what happened to my old scope.
It's broken, no image, smoke at power-on.
Two weeks ago I opened it and the problem was a shorted tantalum cap that took the life out of a bunch of transistors.:bawling:
Curiously, the tantalum cap was intact, no sign of anything wrong, but shorted.
What :hot:ed was the transistors.
On regulators I would rather use an electrolythic bypassed with a ceramic than use tantalums. |
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| Mr Evil |
| The benefit of tantalum capacitors is their size. If you're building something to a size limit then they can be a good choice. |
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| carlosfm |
| quote: | Originally posted by Mr Evil
The benefit of tantalum capacitors is their size. If you're building something to a size limit then they can be a good choice. |
Yes, but depends on the capacitance and voltage rating.
A 10uf/35v tantalum is usually bigger than an electolythic of the same value.
Lower capacitances (even at 35v) are smaller in tantalum caps. |
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| falcott |
| quote: | Originally posted by carlosfm
On regulators I would rather use an electrolythic bypassed with a ceramic than use tantalums. |
Waay off topic, arn't we?
;)
Carlos, do you think bypassing with a ceramic here is better than with a film cap? On my dual bench supply I have just thrown away the 1uF tantalums and fitted 47uF electrolytics bypassed with 470nF MKT. Would 100nF ceramic be good here instead?
(And it doesn't take up too much more space, if the bypass cap is under the board.) |
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| DigitalJunkie |
Just my .02
I try to avoid ceramics in audio gear as much as possible..*Especialy* in the signal path.. But,PSU bypassing with them might not be so bad..
I dislike tantalums,except as power supply bypassing in digital circuits,they perform well there aslong as you overspec the voltage 2-3x! I've had 16V tantalums explode at 12V...25V caps were okay though (35V would be safer.) I dunno why tantalums are so picky about the voltage thing. |
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| carlosfm |
| quote: | Originally posted by falcott
Waay off topic, arn't we?
;) |
Yup.:)
| quote: | Originally posted by falcott
Carlos, do you think bypassing with a ceramic here is better than with a film cap? On my dual bench supply I have just thrown away the 1uF tantalums and fitted 47uF electrolytics bypassed with 470nF MKT. Would 100nF ceramic be good here instead?
(And it doesn't take up too much more space, if the bypass cap is under the board.) |
If the space is small I use multi-layer ceramics.
You can do that across the CAdj. cap.
But the cap at the reg's output, in the case of the LM338 (with LM chips) is the most important, as it has influence on the sound of the whole amp.
Here I use Philips 47nf MKT caps (polyester) with excellent results. Feel free to use polypropilene if you want. |
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| D_GR8_1 |
Ok.
So, why does the software complain that the ADJ pin has no "driving source" when there is a capacitor connected between it and ground? |
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| SheldonD |
Carlos : did you ever check the voltage regulation dynamically under heavy load.
Using the snubbers and large caps? What voltage sag percentage did you get? |
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| carlosfm |
| quote: | Originally posted by D_GR8_1
Ok.
So, why does the software complain that the ADJ pin has no "driving source" when there is a capacitor connected between it and ground? |
I presume you have a cap and a resistor from Adj. pin to ground? |
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| carlosfm |
| quote: | Originally posted by SheldonD
Carlos : did you ever check the voltage regulation dynamically under heavy load.
Using the snubbers and large caps? What voltage sag percentage did you get? |
Yes, I did.
The tests were made with an LM4870 and a weak PSU, made with two 15V/3A trafos, MUR860s and, initially, 3,300uf caps on the PSU, as you can see on the first post of this thread.
The LM4780 has 100uf+100nf on board.
This PSU, under load, produced around 22.5V, and with music playin' LOUD it sagged to around 18~18.5V.
I know, this PSU was just for test purposes, it's weak, and I don't listen to choral music.:cool:
Inserting 10,000uf caps the PSU voltage under load decreased some 0,5 volts, to around 22V.
But with LOUD music it very rarely went below 20V.
Better trafos should be used, this was a test.
Anyway, I prefered the sound of the final PSU (with the big caps added and the snubbers) to the initial low capacitance PSU. |
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| D_GR8_1 |
| my schematic is exactly the same as the one you posted here on the forum. |
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| carlosfm |
| quote: | Originally posted by D_GR8_1
my schematic is exactly the same as the one you posted here on the forum. |
You can sell that software on ebay.:D :D :D |
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| D_GR8_1 |
Considering that Protel licenses cost around $10k, i think i will be making myself quite a profit!:D
if only my company allowed it...:bawling: |
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| carlosfm |
| What happens if you change the LM338 for LM317? |
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| D_GR8_1 |
The library model of LM338 & LM317 in Protel has the ADJ pin specified as "INPUT" pin. IN & OUT are "POWER" pins.
So what happens is that the circuit expects to see a source of current going into the ADJ pin, however the CAP prevents this. |
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| carlosfm |
| Sell it on ebay.:D |
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| percy |
Carlosfm (or anyone for the matter of fact),
have you tried different resistor values ? Especially using the methods described in the article(pdf) posted elsewhere in the thread about "Calculating Optimum Snubbers". I think it was from HagTech.com
Also, did you notice any improvement by simply putting a polyprop cap like 220nf-580nf across the filter caps with NO resistor ? or is the resistor required ?
Wondering what are BrianGT's and Planet10's thoughts about incorporating these mods in the kits ? |
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| Peter Daniel |
I'm not Planet10, but I will comment.
This is definitely an interesting thing to try, but clearly I don't see a reason to incorporate that in a kit. The rectifiers board as it is now, works fine in most cases, and if someone wants to experiment with this supply, it can be built as an addition to an existing setup. Besides, the size of the current rectifier board will not allow using all those components on board anyway.
This is a design that Carlos came up with, and was intended for personal use only and not putting together in a form of a kit. It's up to an individual to try it out and possibly implement if the results are to his taste.
I'm pretty sure that digi01 will be putting it in a form of PCB, at some time ;) |
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| percy |
| quote: | | I'm not Planet10.... |
Ooops ! :dunno: Sorry I was thinking Peter Daniel and typed Planet10 - who is actually the moderator if I am not wrong..
Anyhoo, you don't have to use Carlos's design exactly. You and team could experiment and come up with something and maybe create another "new and improved" version of the rectifier pcb. If the snubber really has the advantages as claimed to be then why not ? |
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| demogorgon |
well, percy, there are limits to how much help people need, and should be given. you can practically buy an entire amp with all those "group buys" and put it together in 10 minutes.. this is not DIY.
Brian impresses me though, not making printcards of everything he comes across like some others..
well, of to try this snubber thingy now then.. wish me luck.. |
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| grege |
| quote: | Originally posted by demogorgon
well, percy, there are limits to how much help people need, and should be given. you can practically buy an entire amp with all those "group buys" and put it together in 10 minutes.. this is not DIY. |
DIY is do it yourself. If you buy the bits and put it together yourself, its DIY. There no such thing as a 10 minute amp. You might be able the solder the components onto one of BrianGT GC PCB in ten minutes but that's the easy part. Assembling all the mechanical components takes a lot longer.
If you look closely you will see the Brian has made a few PCBs - there not all Gainclones though. There is NOTHING wrong with that. He's offerring a great service to many.
demogorgon, let people do what they want, its good there are simple amps to build that take minimal effort, it is good that some like making PCBs and making them available for those that want them. |
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| maxw |
| quote: | Originally posted by demogorgon
put it together in 10 minutes.. this is not DIY. |
I dont think this is true - Think of your average audio enthusiast, they generally dont know how stuff works (eg. an amp, or electronics), they read magazine reviews and buy from a shop then read the manual and away they go. Compared to that scenario, buying a kit from BrianGT is VERY DIY!! :angel: |
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| demogorgon |
| quote: | Originally posted by grege
DIY is do it yourself. If you buy the bits and put it together yourself, its DIY. There no such thing as a 10 minute amp. You might be able the solder the components onto one of BrianGT GC PCB in ten minutes but that's the easy part. Assembling all the mechanical components takes a lot longer.
If you look closely you will see the Brian has made a few PCBs - there not all Gainclones though. There is NOTHING wrong with that. He's offerring a great service to many.
demogorgon, let people do what they want, its good there are simple amps to build that take minimal effort, it is good that some like making PCBs and making them available for those that want them. |
It's not as if I can stop people now is it? people always do as they want for them selves, or should anyways. I'm just the kind of guy who cant keep his opinions to himself.
| quote: | Originally posted by maxw
I dont think this is true - Think of your average audio enthusiast, they generally dont know how stuff works (eg. an amp, or electronics), they read magazine reviews and buy from a shop then read the manual and away they go. Compared to that scenario, buying a kit from BrianGT is VERY DIY!! :angel: |
Yes, well been there, done that, and i guess i agree with you.
but still, i think true diy is not buing kits, simply because then you haven't done it all yourself. :rolleyes:
and thats what i will always think regardless. |
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