| Mick_F |
Now that the new Gaincard pictures have appeared in the recent 6moons review, I felt that the old pictures frequently shown in the web (and disapproved by the US importer of 47 systems) showed the real thing.
Therefore I had a closer look at them and tried to figure out the schematic and parts used. I came to a consistent conclusion, shown below, but there is still at least one thing I dont understand.
You may feel that this topic has been discussed too many times. In this case just disregard this thread. The information may nevertheless be interesting to some people here.
The values of the resistors are: Rg: 22k, Rf: 22k, Ri: 680.
What I dont understand is the use of R0. What is it needed for?
More pictures, more words and the sizes of the caps (probably it is possible to identify their make according to the size) are shown on my website DogBreath.de
Mick |
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| Mick_F |
| And anonther thing I do not really understand: Why is the resistor of the Zobel hidden in an isolator tube? |
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| peranders |
There are many questions and right now I feel that it's rather uninteresting now when I know how Sakura Systems design their stuff all pictures are confirmed to be true. Totally uninteresting besides a big WHY.
I don't understand either why the american importer is so ashamed that he can't confirm how his product looks inside. Most high-end people are really proud of the inside and don't mind showing the world.
The review if you have missed it.
http://www.6moons.com/audioreviews/...gaincard_2.html
http://www.6moons.com/audioreviews/...5/gaincard.html |
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| Stabist |
| R0 - simpl - since they use simple 12 step switch - by adding that resistor you get another step - but then you have to use mute switch to achieve total silence ... |
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| Mick_F |
Thanks, Stabist, for the solution. Indeed, that should work!
Mick |
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| Mick_F |
I am referring to that review in my text. It is exactly this review and the "official" pictures therein that convinced me that the old pictures show the real thing. I am not impressed by the repeated denial of Yoshi quoted in the text.
I also dont understand why the importer plays this game. Most probably, he wants to unsettle those who want to copy the Gaincard. The practice of sealing the screws on the Giancard case fits also in that view.
Mick |
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| Mick_F |
Ok, one more question: The Gaincard is offered in two versions - a 2 x 25 W and a 2 x 50 W version. Are different amp chips used in these?
Mick |
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| wintermute |
If I sold a product that cost thousands and it looked like something that I would have posted in the ugliest prototype thread, I don't know that I would want people to see it either ;)
one problem with consumers is that the expect to get something for their cash, and obviously if they knew the actual cost of the components and saw the insides with what would appear to most as extremely poor quality workmanship, they would be very unhappy indeed.
Something like Peter Daniel's Patek whilst still minimal in component count is a work of art, the picture you just posted most certainly isn't, and I don't think the people forking out big money for one (no matter how good it sounds) would be very impressed if they saw what it looked like inside!!
Tony. |
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| I_Forgot |
| quote: | Originally posted by peranders
There are many questions and right now I feel that it's rather uninteresting now when I know how Sakura Systems design their stuff all pictures are confirmed to be true. Totally uninteresting besides a big WHY.
I don't understand either why the american importer is so ashamed that he can't confirm how his product looks inside. Most high-end people are really proud of the inside and don't mind showing the world.
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| quote: | Originally posted by Mick_F
I also dont understand why the importer plays this game. Most probably, he wants to unsettle those who want to copy the Gaincard. The practice of sealing the screws on the Giancard case fits also in that view. |
Sometimes the obvious answer is the correct answer. How do they "design" their stuff? Some guy sits down with a data sheet, a soldering iron, and a piece of perf board and haywires an amp. Then he makes the simplest possible PCB so he can make a bunch of identical units. Then some marketing hack from the wine industry pushes them as something special and adds a special price tag to match the specialness of the amp. Then the audio suckers line up and plunk down big bux and rave about them, then forums like this are born.
Sealing the screws prevents people who have paid big bux from opening the amp and seeing how badly they were ripped-off. Sealing screws isn't going to stop anyone intent on copying the amp. Even ICs get opened and copied all the time. A few little screws mean nothing.
90% of the chip amps made by "amateurs" in these forums are better built and more atractively packaged that that POS in the photos.
Does that mean any of them are worth the price of a "genuine" gain card? Only if you have a hole in your head the size of the hole that will be left in your wallet.
I_F |
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| peranders |
| quote: | Originally posted by Mick_F
I also dont understand why the importer plays this game. Most probably, he wants to unsettle those who want to copy the Gaincard. The practice of sealing the screws on the Giancard case fits also in that view. |
I understand :nod:
You don't want people to take a peek and maybe get them disapointed of paying so much for so little, not even looking good! A good product starts from inside, good looking inside, good looking outside. At least I think a customer may require a professional look inside, meaning assembly above the ugliest chinese stuff you ever seen (sorry all you Chinese people, but some stuff China isn't a beautiful sight) |
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| carlosfm |
| quote: | Originally posted by Mick_F
Ok, one more question: The Gaincard is offered in two versions - a 2 x 25 W and a 2 x 50 W version. Are different amp chips used in these?
Mick |
Yes, LM1875 and LM3875.
I heard the (original) 25W - LM1875 version some 4 years ago.
They had it well set up, with a pair of french fullrange speakers, those very thin dedicated speaker cables and a Naim CDSII cdp as source.
Sound was very good.
The amp is really small, cute. On the pics it's usually hard to understand their real dimensions.
Regarding the distributors, or you know how to demo a product, or you don't.
These guys knew how to choose the right speakers for them, but others don't have any idea. I've heard reports of demoing these amps with the most absurd speakers.
These amps are as picky with speakers as SET amps.
Naturally. |
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| Panelhead |
A friend used one with two power humpties to drive Lowthers in a factory horn cabinet. He loved it, but went back to tubes quickly.
He ended up with a Rowland amp that uses chips. Said it was better. Cheaper also.
Carlos, has you ever compared a Gaincard to any of the chip amps you have built? Unless the two amps are heard in the same system on the same day it is hard to be objective.
George |
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| carlosfm |
| quote: | Originally posted by Panelhead
Carlos, has you ever compared a Gaincard to any of the chip amps you have built? |
No, I never had a Gaincard at home.
I listened to that system on the local distributor.
| quote: | Originally posted by Panelhead
Unless the two amps are heard in the same system on the same day it is hard to be objective. |
George, I'm not trying to be objective, I just said that the music I heard there coming from that system sounded good, that's all.
But it was not my type of music and it's not my type of system.
The music that was playing was slow jazz, very detailed.
I also listen to this type of music, but it's not the thing for a real test.
I'm almost sure that with a couple of my CDs I could defeat that amp, even with those sensitive speakers.
Ben Harper would kill it. :D :D :D |
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| Marlowe |
They both have no good-looking inside.
However, the difference is that 47Labs Gaincard sounds good but Grado RA-1 does not. |
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| motherone |
| Funny stuff. I read last night in an issue of The Absolute Sound said that the RA-1 sounded lush and tube like. Of course, 90% of audio reviews are BS, but I do love looking at the purty pictures of gear :D |
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| vladimir |
| quote: | Originally posted by Mick_F
Now that the new Gaincard pictures have appeared in the recent 6moons review, I felt that the old pictures frequently shown in the web (and disapproved by the US importer of 47 systems) showed the real thing.
Therefore I had a closer look at them and tried to figure out the schematic and parts used. I came to a consistent conclusion, shown below, but there is still at least one thing I dont understand.
You may feel that this topic has been discussed too many times. In this case just disregard this thread. The information may nevertheless be interesting to some people here.
The values of the resistors are: Rg: 22k, Rf: 22k, Ri: 680.
What I dont understand is the use of R0. What is it needed for?
More pictures, more words and the sizes of the caps (probably it is possible to identify their make according to the size) are shown on my website DogBreath.de
Mick |
One interesting think to learn from 47 labs is how they're grounding the amp : the transformer and diode bridge are away, the PCB uses the same plane for the power ground and for the signal ground.
In this arrangement the tricky think is how to connect every components to the ground in such a way that the hum and oscillations are minimised. I tried several "exact copies" versions inspired by this photos and what I've learned is that if even one of the resistors (or the input signal ground) is shifted as little as 1 mm you've got hum and oscillation. IIRC someone explained that the trick they're using is a re-injection of the hum in the - input (near the Ri) in such a way that CMRR of the chip helps to reject it.
If you find the exact arrangement of grounding you will find a kind of Ŧ local optimum ŧ in which the amp play wonderful music with no hum and no oscillations. Also, in this arrangement, one bridge sounds better than two (more transparency) and ....;-). |
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| motherone |
| quote: | Originally posted by vladimir
If you find the exact arrangement of grounding you will find a kind of Ŧ local optimum ŧ in which the amp play wonderful music with no hum and no oscillations. Also, in this arrangement, one bridge sounds better than two (more transparency) and ....;-). |
Sounds like a lot of design work went into something that could've been easily solved by some proper PCB layout... You'd think that they could've at least sprung for some of the nice stuff, like PD and Brian did.
I don't think that the price would be as much of an issue if the insides didn't look someone was having a seizure when they designed and soldered the thing. The PCB work is seriously an embarassment and they should be ashamed of it. At least if they fixed it, they might be justified in asking 1/3rd of the price they are currently :D |
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| tlf9999 |
| quote: | Originally posted by motherone
Of course, 90% of audio reviews are BS |
that isn't just limited to professional (marketing driven) reviews but also user / builder / designer reviews we see frequently here. Not that people intend to deceive but sometimes we want to believe we made a difference (for the better) after having spent hours researching and building our own amps.
| quote: | Originally posted by vladimir
if even one of the resistors (or the input signal ground) is shifted as little as 1 mm you've got hum and oscillation. |
I have breardboarded and p2ped quite a few gainclones and none exhibited such sensitivity.
I think the gainclones own a lot of its success to its exorbinant price tag. I have heard quite a few stories of how certain clothing items sold well only after their prives had been raised substantially. the high prices helped establish its superior sound quality, in the minds of their owners. |
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| Christer |
| quote: | Originally posted by tlf9999
I have breardboarded and p2ped quite a few gainclones and none exhibited such sensitivity.
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Of course not. It requires a very carefylly planned PCB design to achieve such sensitivity. ;) |
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| wintermute |
| quote: | Originally posted by Christer
Of course not. It requires a very carefylly planned PCB design to achieve such sensitivity. ;) |
LMAO :D
and to think that sweedish freinds told me that the sweedish don't understand sarcasm ;)
Tony. |
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| Christer |
| quote: | Originally posted by wintermute
LMAO :D
and to think that sweedish freinds told me that the sweedish don't understand sarcasm ;)
Tony. |
You must have met some of those boring swedes who don't understand sarcasms. :) |
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| wintermute |
They caught on quick spending some time in Aus ;) I think they got some strange looks when they got back to Sweeden though with their newly adjusted sense of humour ;)
Tony. |
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| KT |
| quote: | Originally posted by Mick_F
The practice of sealing the screws on the Giancard case fits also in that view. |
I wouldn't assume by this one photo that this is standard practice on Gaincards.
I own a Gaincard and I used to work for an audio store that sold the Gaincard, and I've never seen any sort of epoxy sealing up the nuts or screws on any of the amps.
My older Humpty did have some yellow and purple wax in four of the bolt holes, but this was easily removed and I think it was more of an indicator of tampering for warranty purposes. There was no way the soft wax would have prevented anyone from opening it.
Also, aside from the wax in my Humpty, I never saw any sort of sealing material in any other Humpty. I think after a while they stopped doing that.
If anything, I'd think that if it were epoxy in the photo, they probably did it recently and only on the review units. Given the hubub surrounding the circuit board photos, I wouldn't be surprised that they wouldn't want a snooping reviewer from opening the review unit (which they don't personally own, so might not have any qualms about cracking open) and publishing photos of the insides worldwide.
It would be good to see the what the genuine thing looks like, but since when has it been a requirement for a manufacturer to offer the worldwide press access to the insides their non-userservicable products? Given the fuss surrounding this amp, I think it's perfectly understandable if they wanted to keep the inside of their review units secure.
Also note that of the dozens photos of review units that have appeared in audio magazines and on the web worldwide, this is the only time I have seen a Gaincard with this epoxy in it. In no other instance have I seen anything similar.
So unless some new Gaincard owners can tell us if their personal units have epoxy in them, I think that this may be something 47Labs is doing with their review units.
Btw, did you know my Chord amp and preamp uses some security-head screws that kept me from examining the insides and from fixing a faulty pushbutton myself? I don't hear anyone griping about Chord and their desire to keep people from opening their amps. I don't think the argument against a manufacturer sealing up their amp holds water unless you make that argument against all amp manufacturers who do it.
Best,
KT |
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| superhkm |
About the qualities of the Gaincard:
I still haven't read or heard anyone that has actually tested/ heard the Gaincard play in any setup say it's not worth the money.
In fact (almost ) all reviews say that the kind of natural reproduction af acoustic instruments is unattainable at any price with any other manufacterer.
If you consider the experience of it's creator as research and development and that it is in fact hand made, the price is stiff, but not a ripoff. Take on the hi-end cable market if you want to talk about ripoffs.
If 47 labs posted their scematics and partslist we would all be able to make something not to far off their results, for a fraction of the cost, but hey, there is a man sitting crouched over a workbench somewhere in Japan trying to make a living , am I right ?
About tamper seals: I have a Meridian tuner that has a seal and the screwheads laquered, and my Bryston bp 20 has the most peculiar screwheads that I have never found a tool for. ( but Bryston i exused, they post their scematics. )
And lastly; I have a 50w Gaincard, and it's fab. |
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| tlf9999 |
| quote: | Originally posted by superhkm
In fact (almost ) all reviews say that the kind of natural reproduction af acoustic instruments is unattainable at any price with any other manufacterer. |
what would happen if you stuff this gaincard in a Radioshack boombox, attach a $20 price tag, and send it to the same reviewers? Would they give the same glaring reviews? |
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| KT |
| quote: | Originally posted by tlf9999
what would happen if you stuff this gaincard in a Radioshack boombox, attach a $20 price tag, and send it to the same reviewers? Would they give the same glaring reviews? |
Take the case of the Sonic Impact T-amp: the reverse of what I think you're suggesting would happen happened. Instead of dismissing it because of it's toy-like price, the reviewers gave the T-amp rave reviews.
For a retail price of $20 to $40, several reviewers even compared it favorable to the several $K Gaincard.
I have several of these SI amps and they do sound very good with the right source and speaker load. Turns out, however, there are some sonic characteristics that keep this amp from being my long term solution, as a lot of folks on this forum are finding out for themselves as well.
But yes, just because an amp is cheap doesn't mean a reviewer will dismiss it outright. Hopefully reviewers will leave their price biases on the side and judge by sound quality.
Best,
KT |
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| carlosfm |
| quote: | Originally posted by superhkm
About the qualities of the Gaincard:
I still haven't read or heard anyone that has actually tested/ heard the Gaincard play in any setup say it's not worth the money. |
Indeed.
From a commercial point of view, an audio product is worth what it sounds.
Cruel?
No, that's how it is.
The normal 'audiophile' customer doesn't care what's inside, even if it's a single chip.
He will just listen and compare side by side with other amps.
Does it sound better then another more expensive amp?
Great, then it's cheap.
Of course, the Gaincard is much more picky with speakers than other amps, but given a good matching pair of speakers it can sound very good.
Another beauty: the Lavardin IT.
Guys, we are biased because we have the knowledge and we want to know what's inside and how things are made.
I know it's shocking for some that a chip amp can sound very good, but open your minds and listen. |
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| Mick_F |
I did not intend to start the pricing discussion once again with this thread, but now it is going on anyway I will dispense by own opinion here as well.
I dont think that the Gaincard is overpriced. Two reasons for this opinion:
1. A lot of research has been put into its development. This concerns the concept itself, the schematic, the choice of value and type of each component, and even the case. I am convinced that the original gaincard is so far developed that it is untweakable. There is simple nothing left to be improved. Such research is expensive and of course reflects in the retail price.
2. If you compare the gaincard to other hifi equipment on the market, there is not much difference in parts cost / retail price ratio. Indeed the gaincard has only very few parts in it, but keep in mind that one of the parts, namely the chip, is rather expensive. It costs a couple of dollars, and you can buy A LOT of transistors, resistors and other parts for that money. Therefore, even if the inside of other amps looks much more busy than the gaincard, the parts cost is not necessarily much higher. On the other hand, the case of the gaincard is very well crafted. At a considerably higher quality than other gear on the market.
Mick |
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| reMC |
I think the reason that 47labs sealed it's Gaincard and make it really difficult to get in is not because it looks awful. To me, it's art.
The special screws used in Gaincard are to prevent that a reviewer opens it, takes a look and closes it. Why? Because the Gaincard sounds really different if you don't close it in the way you opened it! The strenght which the screws are turned with makes the sound different. Since the gaincard off course leaves Japan in optimal condition it's not that good if a reviewer makes it sound less beautiful.
By the way, I've experienced this myself :)
I've seen my own Gaincard's inside and it not like the one in the first post, as Yoshi already said. The lay-out is different. You can tell by Yoshi's pictures in the 6moons review.
And yes, the Lavardin IT is beautiful. Not as rich and colorfull as a Gaincard but really good for a transistor amp! |
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| Mick_F |
| quote: | | I've seen my own Gaincard's inside and it not like the one in the first post, as Yoshi already said. The lay-out is different. You can tell by Yoshi's pictures in the 6moons review. |
I have of course noticed that there are some differences in the pictures above and those in the 6moons review. The orientation of the chip on the board is the most obvious one. There are, however, also a lot of commonalities, e.g. the size and look of the caps, the red wima, the attenuators and the switch, the cables and connectors etc, etc.
Note that the first pictures were shown in a thread on AA in 2002, and the pictures in 6moons are from a model built three years later. There might have been made some minor design changes in the meantime.
Did you make pictures of the inside of your Gaincard, and if so, are you willing to show them here?
Mick |
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| reMC |
In the picture, EVERYTHING looks the same, except the PCB. To my knowledge, the Gaincard was never build with the chip placed like this.
I didn't take any pictures. |
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| tlf9999 |
| quote: | Originally posted by carlosfm
Of course, the Gaincard is much more picky with speakers than other amps, |
if that indeed is true, we should have heard from some of the reviewers that their gaincards didn't sound as good with their particular speakers, at least initially.
Yet, none of those reviews I have herad has mentioned speaker matching being a particularly sensitive issues here.
To me, that makes sense as this is a high gain and high feedback device. |
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| carlosfm |
| quote: | Originally posted by tlf9999
if that indeed is true, we should have heard from some of the reviewers that their gaincards didn't sound as good with their particular speakers, at least initially.
Yet, none of those reviews I have herad has mentioned speaker matching being a particularly sensitive issues here. |
If you see what speakers they use, you will understand.
It's taken as a fact and a necessity for anyone who is going to review these amps: you need sensitive and very easy to drive speakers. SET territory.
Also, you can search at TNT-audio their review(s). I've read it many years ago, not sure if it's still there, but they did make a second review with a different pair of speakers (easier) and the conclusions were slightly different from the first review.
| quote: | Originally posted by tlf9999
To me, that makes sense as this is a high gain and high feedback device. |
No, that's not exactly the problem.
It uses very low capacitance on the PSU (1,000uf per rail).
Miracles don't exist. |
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| carlosfm |
| quote: | Originally posted by reMC
And yes, the Lavardin IT is beautiful. Not as rich and colorfull as a Gaincard but really good for a transistor amp! |
Yes, its a good amp. :cool: |
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| tlf9999 |
| quote: | Originally posted by carlosfm
If you see what speakers they use, you will understand. |
what speakers have you seen them using? |
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| carlosfm |
| quote: | Originally posted by tlf9999
what speakers have you seen them using? |
I use Epos ES11, and I don't have a Gaincard. |
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| wintermute |
| quote: | Originally posted by superhkm
About the qualities of the Gaincard:
I still haven't read or heard anyone that has actually tested/ heard the Gaincard play in any setup say it's not worth the money.
In fact (almost ) all reviews say that the kind of natural reproduction af acoustic instruments is unattainable at any price with any other manufacterer.
If you consider the experience of it's creator as research and development and that it is in fact hand made, the price is stiff, but not a ripoff. Take on the hi-end cable market if you want to talk about ripoffs.
If 47 labs posted their scematics and partslist we would all be able to make something not to far off their results, for a fraction of the cost, but hey, there is a man sitting crouched over a workbench somewhere in Japan trying to make a living , am I right ?
|
Hi superhkm,
can't really speak for anyone else, but I'm not sure that anyone was saying the gaincard isn't worth the money (at least for the average consumer in that market who doesn't have the knowledge or inclination to make their own, assuming of course that anyones gainclone does really compete).
What you have said about R&D and development costs is very true, and especially so with a non mass produced item!
My observation was simply that the pictures of the internals look like something I wouldn't want any body looking at considering the price (or possibly at all in a comercial unit priced above about $49.95 ;) , this of course doesn't affect how it sounds :). I think the point is that for the price a little bit more care could be taken, things like a high quality PCB, and maybe a bit more care with the soldering..... the soldering to me looked absolutely shocking!!! I'd question the long term reliability...
anyway I guess maybe it is within the realms of possibility that any change to the setup as is will degrade the sound, but I'd be surprised.
The sound is Ultimately what you are paying for, but I can fully understand that someone would not be impressed with the internals regarless how good it sounds :)
Tony. |
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| superhkm |
| quote: | Originally posted by tlf9999
what speakers have you seen them using? |
Check sakurasystems.com for links to reviews, high-sensitive fulltone or twoways dominate. I use cabasse iOs at the time, Kef Refs 102 worked well too. |
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| lohk |
| The Zobel resistor probably is isolated because it can be not a carbon or MOX type but a vitreous wirewound enamel resistor type, those can get electrically conductive at the outside when getting hot. |
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| KT |
Now that it's well known that 47 Labs uses the General Semiconductor FE5D diodes in the Power Humpty, I wonder if anyone's gotten around to comparing them to the BrianGT/Peter Daniel recommended Semi-On diodes in their Gainclone.
Seems like a logical step to take if trying to mimic the performance of the original. If anyone does this, we're all very interested to hear how things compare!
Best,
KT |
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| Peter Daniel |
| quote: | Originally posted by wintermute
and maybe a bit more care with the soldering..... the soldering to me looked absolutely shocking!!! I'd question the long term reliability...
|
I don't see anything wrong with soldering; contrary, long term reliability may be here much better than with some other commercial units. Both the way PCB and soldering are done, are probably for a reason, not because of sloppy workmanship. After all this is an "exotic" product at a substantial price, so the looks have to be uncommon as well ;)
| quote: | Originally posted by KT
I wonder if anyone's gotten around to comparing them to the BrianGT/Peter Daniel recommended Semi-On diodes in their Gainclone. Seems like a logical step to take if trying to mimic the performance of the original. |
The Premium kits I'm selling are not intended to mimic GainCard, and 6moons review clearly shows it. The voicing of the circuit represents my personal view on the sound of the amp. The transormer will also have bigger effect than rectifiers, so choose it wisely ;) |
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| wintermute |
| quote: | Originally posted by Peter Daniel
I don't see anything wrong with soldering; contrary, long term reliability may be here much better than with some other commercial units. Both the way PCB and soldering are done, are probably for a reason, not because of sloppy workmanship. After all this is an "exotic" product at a substantial price, so the looks have to be uncommon as well ;)
|
my sarcasm meter is going off somewhat ;) but.........
I just went back and looked, I think I'll have to reserve judgement until after I can look at this on my CRT tomorrow, this laptop screen isn't good enough.... maybe I'm confused with something else I looked at, but I could have sworn the joints were dull and grey, like cold solder joints, specially on the p2p bits....
Tony. |
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| tlf9999 |
| quote: | Originally posted by carlosfm
I use Epos ES11, and I don't have a Gaincard. |
not the question wasn't about what you use. but instead what you know about the speakers used by reviewers.
| quote: | Originally posted by wintermute
the soldering to me looked absolutely shocking!!! |
my thoughts exactly. a highschool student can do a better job than that. |
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| carlosfm |
| quote: | Originally posted by tlf9999
not the question wasn't about what you use. but instead what you know about the speakers used by reviewers. |
Fullranges, horns, simple crossovers...
Very similar to what I've seen when I've heard the Gaincard.
I've heard reports of listening tests with JMLab floorstanders and the amp sounded very bad.
Well, 'average' quoted impedance means nothing, some JMLab speakers are not an easy load at all (although they are sensitive).
I've built LM3886 chip amps with 1,000uf PSU capacitance, big toroid, and tested with lots of commercial speakers.
I know what these amps can do, they really need easy to drive speakers, they sound bad with most 'normal' speakers you try.
The PSU voltage sags miserably and those poor small caps 'dry' out before the next cycle. :D
Bass suffers a lot, and so does all the rest.
The Gaincard can't be so much different from what I've experienced, or else it must be the nice volume knobs that make the miracle. :devily: |
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| PauSim |
:eek:
Carlos, with what voltages did you feed the chips?
I hope you (and everyone else here) realize the 50 Watt Gaincard used 2200uf. The famous 1000uf caps were only used in the lower powered version.
[Sexta-feira... feira dos horrores... Audioshow!:D ] |
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| carlosfm |
| quote: | Originally posted by PauSim
:eek:
Carlos, with what voltages did you feed the chips? |
At around +/-33V.
| quote: | Originally posted by PauSim
I hope you (and everyone else here) realize the 50 Watt Gaincard used 2200uf. The famous 1000uf caps were only used in the lower powered version. |
Yes, I know.
I later tested 2,200uf caps and it's still far from enough.
4,700uf is what I consider the minimum acceptable for the amp to start driving a larger choice of speakers.
| quote: | Originally posted by PauSim
[Sexta-feira... feira dos horrores... Audioshow!:D ] |
Oh... I almost forgot.
Gotta make a phone call, I always get in for free.:D
Gonna punish my ears this weekend, then... |
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| PauSim |
| quote: | Originally posted by carlosfm
I always get in for free.:D |
Who doesnīt ? :D
| quote: | | Gonna punish my ears this weekend, then... |
As long as you donīt punish your wallet...
I got my invitation from a friend dealer too. Others just need to buy Audioīs last issue. If the organization didnīt give away so many tickets perhaps they wouldnīt need to charge dealers so heavily, and also they could arrange a spare room for us DIYers to gather in and show the public our "sonic marvels"... Yeah, I keep dreaming.
Sorry for the off-topic, guys :apathic: |
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| carlosfm |
| quote: | Originally posted by PauSim
Others just need to buy Audioīs last issue. |
You're right, in the last years it has been that way.
Btw, too much car audio, too much AV... I just go there as an old ritual, to see some friends and to listen to some good music when people go away. |
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| PauSim |
Thereīs a couple of pictures of the inside of the Shigaraki amp around, and they clearly show the same building techniques were employed i.e. flux stains and solder sculptures.
Maybe itīs a japanese thing:
Final Labs also use the same "technique" with their battery operated gear. Their amplifiers innards even look messier than the 47īs: the music-5 preamp uses perforated breadboard!
I wouldnīt be put away by this if I wanted to buy a Gaincard, like the typical buyer just cares for the sonics and the whole concept.
DIYers of course "know better", but if I thought it to be a rip-off, finding a Brian board in there wouldnīt change my mind either.
These things are overpriced just like everything that comes from Japan these days, I think.
About the concept, didnīt everybody feel intrigued while reading 47 Labs claims for the first time? The worldīs shortest signal path, minimum number of components, 1000uf capacitance, etc? How did they do it? Thatīs why itīs so tough to open the little ampīs guts.
Ironically, that messy job is what still keeps copycats away. Had we found a professional looking, clear layout from the beginning and there wouldnīt be Gainclones, but Gaintwins as they all would look as equal as two waterdrops... and maybe we wouldnīt be admiring Peter, Carlos and otherīs own creations... |
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| Mick_F |
| quote: | Originally posted by carlosfm
I later tested 2,200uf caps and it's still far from enough.
4,700uf is what I consider the minimum acceptable for the amp to start driving a larger choice of speakers.
|
Carlos, are you going to update your LM3886 design with a new version using 4700 uF caps?
I'd be interested to see your recent developments....
Mick |
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| peranders |
| quote: | Originally posted by Peter Daniel
I don't see anything wrong with soldering; contrary, long term reliability may be here much better than with some other commercial units. Both the way PCB and soldering are done, are probably for a reason, not because of sloppy workmanship. After all this is an "exotic" product at a substantial price, so the looks have to be uncommon as well |
In this case I'll agree :nod: with Peter only if we compare small parts solders by hand or by machine but in the long run it's better with machine soldered pcb's because you will get an more even result. "Hand soldered" isn't any quality mark and sure is not when it comes to SMT parts. |
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| peranders |
| quote: | Originally posted by Mick_F
Carlos, are you going to update your LM3886 design with a new version using 4700 uF caps?
I'd be interested to see your recent developments....
Mick |
Have you check this:
http://www.ettnet.se/~tobias/diy/lm3886/lm3886_2.htm
I did choose up to 10000 uF as "normal" in my gainclone project and 4700 uF as "minimum"(per rail and channel). I have never been a fan of small smoothing caps. |
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| carlosfm |
| quote: | Originally posted by PauSim
DIYers of course "know better", but if I thought it to be a rip-off, finding a Brian board in there wouldnīt change my mind either. |
Paulo, there's no problem in using perforated board, sometimes I do that for myself.
But to produce more than a couple of units a PCB makes your life easier.
Unless the man work is really cheap.
What I find shocking is the unmasked PCB, which on some climates can oxidate fast, and the lowsy solder joints.
Probably it is silver solder and the guy had a very weak soldering iron. :D
Manual soldering is more reliable, but still, that's a dirty work! |
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| carlosfm |
| quote: | Originally posted by Mick_F
Carlos, are you going to update your LM3886 design with a new version using 4700 uF caps?
I'd be interested to see your recent developments....
Mick |
Mick, there's no new version with 4,700uF caps.
I made all those tests years ago.
This is what I'm using. :yikes:
PS: I use 30,000uf after the series resistors. |
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| reMC |
| quote: | Originally posted by KT
Now that it's well known that 47 Labs uses the General Semiconductor FE5D diodes in the Power Humpty |
How do you know for sure that they are not Vishay FE5D? |
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| KT |
| quote: | Originally posted by reMC
How do you know for sure that they are not Vishay FE5D? |
They could be Vishay. When I peeked into my Power Humpty several years ago, I believe the datasheet that I found online was from General Semiconductor. At least I think so, hard to remember exactly. They could very well have been Vishay, assuming Vishay made them at that time.
In any case, they are FE5D.
Best,
KT |
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| KT |
| quote: | Originally posted by carlosfm
Yes, LM1875 and LM3875.... |
Carlos,
I always thought that the the 25watt Gaincard used the LM3875. That's not from anything I read or heard specifically, but just an idea that was in my head from all the discussion on the LM3875. Your suggestion makes sense, though, as the wattage ratings for the LM1875 and LM3875 correspond to 25watts and 50watts respectively.
Are you sure, though, that the 25watt Gaincard uses the LM1875? Once when I was at an audio show in NYC, I briefly talked to Yoshi. This was just after 47Labs had introduced the Shigiraki components. He told me that the Shigiraki amp used a different chip than that used in the Gaincard, and that the Shigiraki's sound was softer and possibly more agreeable to some people. The Shigiraki, of course, uses the LM1875, so that's another reason I thought the Gaincard used the LM3875.
For a short time I owned the 50watt Gaincard, and I found that it ran quite hot. In contrast, my 25watt Gaincard runs just slightly warm. Do you find that your LM3875 based Gainclones run hot or cool? I was under the impression from reading all the post that most folk's Gainclones run fairly cool, so that's making even more confused as to which chip is in which amp.
Best,
KT |
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| carlosfm |
| quote: | Originally posted by KT
Are you sure, though, that the 25watt Gaincard uses the LM1875? |
That's what I've always heard, but I never opened one.
| quote: | Originally posted by KT
Once when I was at an audio show in NYC, I briefly talked to Yoshi. This was just after 47Labs had introduced the Shigiraki components. He told me that the Shigiraki amp used a different chip than that used in the Gaincard, and that the Shigiraki's sound was softer and possibly more agreeable to some people. The Shigiraki, of course, uses the LM1875, so that's another reason I thought the Gaincard used the LM3875. |
Well, the LM1875 doesn't sound 'softer' to me, it just has less dynamics in the bass.
I would point that 'softness' to the volume pot, not the chip. :D
| quote: | Originally posted by KT
For a short time I owned the 50watt Gaincard, and I found that it ran quite hot. In contrast, my 25watt Gaincard runs just slightly warm. Do you find that your LM3875 based Gainclones run hot or cool? I was under the impression from reading all the post that most folk's Gainclones run fairly cool, so that's making even more confused as to which chip is in which amp. |
I don't use an LM3875 for years, but they didn't run hot, only when pushed hard.
This all depends on the PSU voltage you use and also your speakers.
Your 25W version has a lower PSU voltage.
The chassis of the Gaincard, specially on the 50W version, may not be so effective as a heatsink.
I can imagine that those electrolythics inside won't last long... |
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| PauSim |
Carlos,
I didnīt say thereīs anything wrong about perfurated board. I used it too, for my DAC.
I tried to say that the Finals look as a DIY job as the GC and still achieved some kind of a cult status AFAIK.
| quote: | What I find shocking is the unmasked PCB, which on some climates can oxidate fast, and the lowsy solder joints.
|
You may be right. However, the solder joints and the flux stains are so huge, thereīs not much bare copper left :D
BTW, I donīt think the solder joints arenīt that terrible. They look sturdy enough. Canīt see any dry joint there also, as someone pointed out.
Now, seeing that the various components are located so near the chip and variations in temperature affect their values, could it be the wide copper area and the big solder joints are acting as local heatsinking? Look at the T-amp...
Also, the PCB was designed aiming at the shortest signal path possible. A commercial PCB with its right angles and such, canīt achieve it so easily, I think.
Cheers |
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| carlosfm |
| quote: | Originally posted by PauSim
Carlos,
I didnīt say thereīs anything wrong about perfurated board. I used it too, for my DAC. |
I have some 'perforated' dacs too. :cool: |
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| PauSim |
| quote: | Originally posted by KT
The Shigiraki, of course, uses the LM1875, so that's another reason I thought the Gaincard used the LM3875.
|
I think youīre right.
Looks like the main difference between the 25 to the 50 Watt versions are the 1000uf and the 2200uf. Both using LM3875.
They had to be made that way because the caps need to be close to the chip, not inside the power cans.
As both amps look identical on the outside, if the LM1875 was used 47 Labs would have to stick a "CAUTION: 25 WATT VERSION! DONīT USE POWER DUMPTY!" type of disclaimer. |
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| carlosfm |
| quote: | Originally posted by PauSim
As both amps look identical on the outside, if the LM1875 was used 47 Labs would have to stick a "CAUTION: 25 WATT VERSION! DONīT USE POWER DUMPTY!" type of disclaimer. |
If there aren't two versions of the PSU with different voltages and the chip is the same, then what makes the 25W amp... 25W?
Look: too Power Humpty versions:
http://www.audio-cube.nl/47lab.htm |
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| wintermute |
| quote: | Originally posted by PauSim
Carlos,
BTW, I donīt think the solder joints arenīt that terrible. They look sturdy enough. Canīt see any dry joint there also, as someone pointed out.
Cheers |
The joint on pin one of the IC looks sus to me, as do some of the ones at the center front of the pcb (closest to us in the image). It's not a terribly good photo though so it could be the photo that is giving me the impression. Pin one though looks like the solder hasn't bonded to the leg of the IC to me.....
Tony. |
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| PauSim |
| quote: | If there aren't two versions of the PSU with different voltages and the chip is the same, then what makes the 25W amp... 25W?
Look: too Power Humpty versions:
http://www.audio-cube.nl/47lab.htm
|
Now Iīm lost.
I always thought the Dumpty was a higher V rated trafo for the 50 Watt version :confused: .
What would be the difference between the two Humpties?
Edit: quote |
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| DC Dave |
| quote: | Originally posted by PauSim
Now Iīm lost.
I always thought the Dumpty was a higher V rated trafo for the 50 Watt version :confused: .
What would be the difference between the two Humpties?
Edit: quote |
The "Dumpty" is for the Flatfish transport and DAC. The "Humpty" is for the Gaincards.
There are two versions of the Power Humpty.
One for the 25 watt amp which most likely outputs about +-23 volts.
The other version for the 50 watt amp must have an output of around +-33 volts.
So the difference is in the transformers.
I believe both amps use the LM3875. |
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| PauSim |
| quote: | Originally posted by wintermute
The joint on pin one of the IC looks sus to me, as do some of the ones at the center front of the pcb (closest to us in the image). It's not a terribly good photo though so it could be the photo that is giving me the impression. Pin one though looks like the solder hasn't bonded to the leg of the IC to me.....
Tony. |
Hi Tony,
On a second look the center joints specially donīt appear so good.
But take a look in the joints in the corners. I wouldnīt call it SOTA soldering but they look shiny and evenly formed, donīt they? To me itīs a positive sign of a good soldering so yes, it has to be the quality of the photo.
Cheers |
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| PauSim |
Hi, DC Dave
Ok, so I stand more or less corrected.
Well, the disclaimer would be something like this, then: Caution - not to be used with 50W Power Humpty... |
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| PauSim |
| quote: | Originally posted by carlosfm
I have some 'perforated' dacs too. :cool: |
Iīve seen that one in another forum. Very nice :cool:
Yours look "better" than mine, but I used fewer parts (TDA1543...) |
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| Ipanema |
Hi,
Can someone pls tell me what is the function of series 220ohms resistor at the positive input of BrianGT LM3875 board? For LM3886 it is 1Kohms. Gaincard doesn't have those. :xeye:
Thanks. |
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| KT |
| quote: | Originally posted by PauSim
As both amps look identical on the outside, if the LM1875 was used 47 Labs would have to stick a "CAUTION: 25 WATT VERSION! DONīT USE POWER DUMPTY!" type of disclaimer. |
| quote: | Originally posted by carlosfm
If there aren't two versions of the PSU with different voltages and the chip is the same, then what makes the 25W amp... 25W?
Look: too Power Humpty versions:
http://www.audio-cube.nl/47lab.htm |
Here is an interesting thing - I've spoken to Yoshi a couple of times about this, once regarding my personal system and once when he brought the Gaincard to the store: He suggests that the best sounding combination is a 25watt Gaincard driven by a 50watt Power Humpty. This is the pairing that I use at home and it was what he brought for use as the store demo unit.
I've never owned anything but the 50watt Power Humpty so I can't make a full comparison, but I can say that hooked up to the 50watt Power Humpty, the 25watt Gaincard has more delicacy and subtlety than the 50watt version. The 50watt definitely has more grunt and balls, but not as much subtlety and nuance. It really is a matter of taste. Also, if you have less sensitive or more difficult to drive speakers, I imagine the 50watt GC will be a more suitable match.
I don't know what it tells you about the transformers or the chips, but the 25watt Gaincard can be driven by the 50watt Humpty with no ill effects.
Also, using the 50watt Power Humpty on both 50 and 25 watt Gaincards, I observed that the 50watt Gaincard ran quite hot while the 25watt Gaincard just got barely warm while in use.
Best,
KT |
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| peranders |
| quote: | Originally posted by Ipanema
Hi,
Can someone pls tell me what is the function of series 220ohms resistor at the positive input of BrianGT LM3875 board? For LM3886 it is 1Kohms. Gaincard doesn't have those. :xeye:
Thanks. |
If you read the sheet page 6, item 5 about Rb you'll find the answer.
http://www.national.com/ds/LM/LM3875.pdf |
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| reMC |
Hi,
I've heard all possible Gaincard combinations. That means with one and two and with the 25w and 50w power supplies. The 25w Gaincard with two 50w dumpty's sounds indeed the best.
In comparison with one PS on a 25w Gaincard you get more air, precision in the sound stage and a bit more emotional content is revealed. But the most important for me: instrument are better to follow on there own. They have their own color, less greyish and more tangible. Nothing gets worse.
In comparison with the 25w humpty, the 50w offers more drive, low range definition and dynamics. Looks more like the Shigaraki, who also has this drive that the 25w/25w Gaincard doesn't have.
I always prefer the 25w Gaincard. The 50w is more dynamic powerfull but if you know the 25w version, you're gonna mis natural timbres and rich and tangible sound that the 25w Gaincard can offer.
And last of all, 50w Gaincard with 25w PS makes no sense ;) |
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| Peter Daniel |
Could it be that the only difference between 25W Gaincard and 50W one is the size of the filter caps (1000uF vs 2200uF)?
I was using the amp with 100uF caps only and the subtlety and nuance were outstanding, the drive suffered. |
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| Mick_F |
| quote: | Originally posted by Peter Daniel
Could it be that the only difference between 25W Gaincard and 50W one is the size of the filter caps (1000uF vs 2200uF)? |
:confused:
How can that lead to a different output power?
Mick |
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| Peter Daniel |
| The output power depends only on the PS voltage. |
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| Mick_F |
| quote: | Originally posted by Peter Daniel
The output power depends only on the PS voltage. |
Aha. So if you use the 25 W Gaincard with the 50 W power humpty there is no difference but the filter caps.
I understand.
Mick |
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| Peter Daniel |
| Assuming of course same chips are being used. |
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| Mick_F |
| quote: | Originally posted by Peter Daniel
Assuming of course same chips are being used. |
Thats understood.
;) |
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| reMC |
In both Gaincard versions, the LM3875 is used. It's just 'programmed' differently (I don't know how) so the output is different. The filter cap's also make a big difference in sound. In general with Gaincard and clones, less is more ;)
That's why the 25w Gaincard mostly sounds better then the 50w version: smaller caps. But when used with a 50w transformer (also other diodes then the 25w version) is gives in the end more 'power' but still remain extremly fast.
25w Gaincard with 50w PS won't play much louder then 25w/25w. So I'm not sure that the output just depends on the PS voltage... |
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| Christer |
But the size of the caps affect how much the rails will sag between recharges. Since we are talking very small caps here the rails may sag many Volts at full power. If we run at 25 W into an 8 Ohm speaker, we get an average current draw of 0.9 A per rail, which means that each rail will drop by 9 V before the cap is recharged. I assume 50 Hz, full wave rectification and 1000 uF caps. With 2200 uF caps, the rails would only drop about 4 V, but for 50 W we would get a higher current, once again causing a larger voltage drop. I have always wondered what the point is to use such small caps since we have to rely heavily on the PSRR of the chip.
BTW, the calculation above only holds for frequencies considerably higher than 100 Hz. For lower frequencies we have to take also the peak value of the current into consideration and the rails can drop even more. I really hope I have made som mistake in my calculations, since the result is scary, but I am afraid they are reasonably correct. |
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| Mick_F |
I have measured the amplitude of the voltage drop under load (resistor) with a 2200uF cap and it amounts to 10 mV pp (at 27 V rail voltage).
Mick |
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| Christer |
| quote: | Originally posted by Mick_F
I have measured the amplitude of the voltage drop under load (resistor) with a 2200uF cap and it amounts to 10 mV pp (at 27 V rail voltage).
Mick |
Then you are not drawing much current.
I = C dV/dt
For 50 Hz fullwave rect. we get dt = 0.01 (actually slightly less but ignore that) so with 10 mV drop we get
I = 0.0022*0.01/0.01 = 2.2 mA !!!
I would strongly suggest there was something wrong with your measurement. |
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| wintermute |
Hi Christer,
I thought that provided the transformer can deliver the current then provided the caps provide enough smoothing then there wasn't an issue...... I think maybe I have misunderstood smoothing and ripple :) are you saying that it is actually the 50Hz mains freq (or 60) which limits how much current can be delivered continuously???? I'm confused :xeye: Thinking about how ripple gets larger as current draw goes up, I'm sort of grasping it, but not fully :)
edit: posted before I saw your formula, what are each of the items in the formula?? (apart from current and capacitance ;) )
Tony. |
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| Christer |
Tony,
the ripple depends on the size of the caps and how much current you draw from them. If you just connect the caps but no load, you will get no ripple with ideal caps, a little ripple with real caps since they leak.
The size of the caps decide how much the voltage over them drop depending on the current you draw from them. Take a charged cap and draw a constant current I from it, then the voltage will drop linearly and the voltage drop dV after time dt will be
dV = I * dt / C
If the load is resistive or varying the relationship will not be linear, so you have to solve a diff equation instead, but the above formlula is usually a good approximation if you use the average current drawn. For 50 Hz and fullwave rectification, we get a charge cycle every 10 ms so that also limits how much the voltage can drop. Actually dt is less than 10 ms, since the recharging also takes some time, but using 10 ms is a safe approximation. For 60 Hz we get a slightly shorter dt and thus slightly less voltage drop for the same current and capacitance.
Example:
50 Hz, fullwave rect., average load current 2 A, C = 22000 uF
dV = 2 * 0.01 / 0.022 = 0.9 V
If we instead use 2200 uF we get dV = 9 V
If this is a power amp, it means we have 9 V less rail voltage under heavy load, which is usally when we need as much voltage as possible. The current and power into a certain load is restricted by the rail voltage (and other factors), but in this case the rail voltage will severly limit the available power and cause unnecessary heat in power dissipation for no purpose. Besides, we also need a 20 dB better PSRR in the amplifier, than if using the 10 times bigger caps. |
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| Mick_F |
| quote: | Originally posted by Christer
Then you are not drawing much current.
......
I would strongly suggest there was something wrong with your measurement. |
You are completely right. I used too high a resistor value and the current was very small.
I will repeat the measurement under normal operating conditions later on.
Mick |
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| Christer |
| quote: | Originally posted by Mick_F
You are completely right. I used too high a resistor value and the current was very small.
|
That was actually what I guessed. :) |
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| Mick_F |
Christer, to come back to your original question - the reason why such small caps are used is simply the sound. People have tried larger caps and found that the particular midrange, which makes up the special sound of the Gaincard (or clones) degraded. The solution for this problem was provided by CarlosFM, who introduced the snubberized PSU to chipamps, which allows using larger caps while preserving the qualities of the midrange.
Mick |
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| Christer |
| Yes, I know they claim it sounds better with small caps and that is the reason. I won't argue with peoples listening impressions, but from a technical point of view it seems questionable both since you waste power and since you get some 20 dB more ripple on the output. Maybe it is the ripple that causes an interesting sound that some people like? :) |
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| wintermute |
Thanks Christer :) I'll be interested to stress test my GC (once I finish) :) I had been thinking that because I had a bigish transformer my low capacitance might be mittigated somewhat, I guess I was wrong! ah well it's only for testing speakers anyway :) and I do still have room for some more caps on the ps board ;)
Tony. |
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| wintermute |
| quote: | Originally posted by Christer
Maybe it is the ripple that causes an interesting sound that some people like? :) |
and the snubber adds somthing back when the big caps remove it ;)
Tony. |
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| carlosfm |
| quote: | Originally posted by Christer
...but for 50 W we would get a higher current, once again causing a larger voltage drop. I have always wondered what the point is to use such small caps since we have to rely heavily on the PSRR of the chip. |
That's right, voltage drop is high, and the more difficult are the speakers the worse it gets.
If a speaker was a purely resistive load it would not be so bad.
Even at moderate/low volumes and a piece of music with strong bass the DMM shows a dancing voltage of several volts.
And this was with a 400VA toroid, 8 ohm speakers.
What does this tell?
It tells that either on the 25W and the 50W versions the output power rating is just theoretical.
In reality the picture is not nice. |
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| tlf9999 |
| quote: | Originally posted by Christer
For 50 Hz and fullwave rectification, we get a charge cycle every 10 ms so that also limits how much the voltage can drop. |
your methodology is correct but shouldn't have been used on the charging side: on the charging side, the burst actually is very short and as a result the charging current is much much greater than load current and depends on many other factors as well.
the key is to understand the "discharge" side: on much voltage drop there is. During discharge, the amp is essentially full turned on (think about RMS) and the capacitor is discharging via the speaker load for half of the cycle. As a result of that discharge, the voltage on the capacitor (rail voltage) declines -> you got ripple!
Take the 50wrms/8ohm as an example. It should be discharging about 2.5A (RMS).
Let's say the lowest frequency is 20hz? (or dt=1/20/2=0.025s).
dV=-2.5*0.025/.0022~=3v (peak to trough), or 1.5v peak.
and to output 2.5Arms on 8ohm load, you got to have at least 30v rails. or ripple is about 5% (1.5v over 30v).
However, PSRR is incredibly high at 20hz so it shouldn't be that big of a deal. And the problem is even less severe if you play at a higher frequency. |
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| tlf9999 |
| quote: | Originally posted by tlf9999
Let's say the lowest frequency is 20hz? (or dt=1/20/2=0.025s). |
actually, dt shouldn't be that long as the capacitor is charged on the next ac cycle. But the above calculation gives more of a worst-case scenario. |
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| Christer |
dt will be slightly less than 10 ms, since that is how often the cap is recharged, assuming, of course, that the transformer is capable of supplying a much higher charge current than the load current. Otherwise we will naturally see the voltage drop over longer time than one discharge/recharge cycle.
You are quite right that a low signal frequency may discharge the caps quicker, and I said clearly that I assumed a high frequency in order to simplify the calculations. A low frequency can cause an even higher current draw, but just using the peak signal current is overly conservative. Getting a reasonable figure in this case is non-trivial, which is why I skipped this case. Spice is quite useful for investigating this behaviour. |
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| carlosfm |
| quote: | Originally posted by tlf9999
However, PSRR is incredibly high at 20hz so it shouldn't be that big of a deal. And the problem is even less severe if you play at a higher frequency. |
I'm sorry but I'll have to put some 'subjectivity' into the conversation. :D
[Subjectivity 1]
PSRR is high at 20Hz, true, but when you are listening to a demanding piece of music, it is audible that bass is untight.
[End of Subjectivity 1]
Measure and the voltage is dancing alot, big sags. The chip is obviously not immune to these voltage variations.
As for the higher frequencies, the LM3875 (as an example) has ~55db PSRR on the negative voltage, at 20Khz.
[Subjectivity 2]
A better PSU will make the treble 'cleaner' (I mean more precise), less 'fizzzzy'.
[End of Subjectivity 2]
:cool: |
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| DC Dave |
| quote: | Originally posted by DC Dave
The "Dumpty" is for the Flatfish transport and DAC. The "Humpty" is for the Gaincards.
There are two versions of the Power Humpty.
One for the 25 watt amp which most likely outputs about +-23 volts.
The other version for the 50 watt amp must have an output of around +-33 volts.
So the difference is in the transformers.
I believe both amps use the LM3875. |
After further review I would like to change my statement.
What I said should be true regarding the power supply voltages and amplifier output power. But that is only if the amplifiers really output 25 watts and 50 watts.
Who is to say that they do?
I have not seen any measurements or data to prove it.
I have seen one piece of conflicting data on the 47labs website:| quote: | | Gaincard is capable of driving any speakers as long as their impedance stays over 4 ohms. If your speaker's impedance drops below 4 ohms at any frequency, we recommend the 50W version. |
According to the datasheet, a LM3875 powered by supply voltages sufficient for producing 50 watts into 8 ohms (+-32 volts) cannot drive a 4 ohm load. It would make more sense if they said that the 25 watt version was capable of driving 4 ohm loads or below.
Anybody willing to measure the voltage coming out of the Humpty. |
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| carlosfm |
Dave, I agree with their claim:
"Gaincard is capable of driving any speakers as long as their impedance stays over 4 ohms. If your speaker's impedance drops below 4 ohms at any frequency, we recommend the 50W version."
...although I don't agree that the amp can produce 50W RMS with that PSU.
Anyway, related to that claim, think about this: there are many speakers out there that dip lower than 4 ohms at a given frequency, but they are... 8 ohms.
Average quoted impedance doesn't tell the whole picture.
They are not recommending the '50W' version for 4 ohm speakers:att'n: |
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