Member
Joined 2004
Member
Joined 2004
carlosfm said:
A big disgust?
Nausea?
Let it be closed!
Grrrunf. Naysayer!
Edit: come on, let´s hear it from who still owns the thing.
If I purchased one I would open it right after (and would share the pictures obviously). "Alea jacta est".
Who´d care about manufacturer´s guarantee anyway? The stuff is so simple I´d do the repair myself.
I just came to think about something. Assuming there actually is an audible difference between using very small caps and reasonably sized ones, what is then the explanation? I get the impression most people assume it must have something to do with the caps themselves, but that is of course not necessarily the right explanation. If we take we coarse figures from my previous (simplified) ripple calculation we see that we need 8 V higher rails to get the same maximum output power than would be necessary with ten times larger caps. Taking the ripple into account, this means that at full power we have an average rail voltage which is 4 V higher. With an average current of almost 2 A, that means the chip has to dissipate an average 8 W more than necessary, thus running hotter than necessary (under the same thermal conditions, ie. same heatsink etc.). So what does this tell us? It says that another possible explanation for an audible difference could be that the chip runs hotter, which of course affects the electrical parameters inside it. I am not claiming this is the explanation. The point is just that one shouldn't jump to conclusions about the reasons for observed phenomenae. Even if the capacitors cause the difference, it may be due to some secondary effect rather than the caps themselves.
Well, I did some measurements yesterday night on a half finished Gaincard copy. I had one channel ready and the supply connections of the other channel were directly connected to my scope. I have 2200uF filter caps on the chips, no capacitors in the PSU, no bypassing (just as in the 50W gaincard). The chip was a LM3886 and the rail voltage (without load) is 26.7 V.
When the amp gets no signal (CD player off) the ripple voltage is about 100 mV pp. When the music is played relatively loud (pot at slightly more than 12.00) it is about 500mV pp, always below 1 V pp. I also tested with a multimeter in parallel with the same result. The reading is not clear when playing music as the signal changes rapidly, but this is the order of magnitude you get. I will repeat the test with sine tones as soon as I have burned some on CD. I also could not do the test at full volume since my children were sleeping upstairs
The values measured should most probably be multiplied by two as I used only one channel of the amp.
Mick
When the amp gets no signal (CD player off) the ripple voltage is about 100 mV pp. When the music is played relatively loud (pot at slightly more than 12.00) it is about 500mV pp, always below 1 V pp. I also tested with a multimeter in parallel with the same result. The reading is not clear when playing music as the signal changes rapidly, but this is the order of magnitude you get. I will repeat the test with sine tones as soon as I have burned some on CD. I also could not do the test at full volume since my children were sleeping upstairs
The values measured should most probably be multiplied by two as I used only one channel of the amp.
Mick
Interesting I got the first channel of my GC up and running this afternoon. I have 1000uF caps (one per rail per channel) in the PS, and 100uF caps on the chip. (transformer is 300VA)
I played it at a level that was too loud to be comfortable but before the amp was starting to clip noticably, and watched the rail voltage (only with the DMM) the voltage sag was a bit less than a volt with what I would guess was getting close to max power. so on music at least the small caps don't seem to be having an adverse effect.... of course maybe my DMM isn't sampling quick enough to show the true voltage drop....
I'll do a test with a 1Khz sine wave and dummy load, as well as check the ripple and see how it fairs, but I might finish the other channel first
I was expecting weak bass from everything I have read, and to my ears there wasn't anything lacking at all.... maybe my 100W mosfet has weak bass
Tony.
I got the first channel of my GC up and running this afternoon. I have 1000uF caps (one per rail per channel) in the PS, and 100uF caps on the chip. (transformer is 300VA)I played it at a level that was too loud to be comfortable but before the amp was starting to clip noticably, and watched the rail voltage (only with the DMM) the voltage sag was a bit less than a volt with what I would guess was getting close to max power. so on music at least the small caps don't seem to be having an adverse effect.... of course maybe my DMM isn't sampling quick enough to show the true voltage drop....
I'll do a test with a 1Khz sine wave and dummy load, as well as check the ripple and see how it fairs, but I might finish the other channel first
I was expecting weak bass from everything I have read, and to my ears there wasn't anything lacking at all.... maybe my 100W mosfet has weak bass
Tony.
wintermute said:
That depends very much of your speakers.
With low capacitance I had boomy and untight bass (not weak at all) with my Epos speakers, while others reported weak bass.
Your rail voltage measurements will also vary depending on the speakers.
Difficult speakers will produce more voltage sag on the PSU rails.
A fast DMM also helps.
... and I still have no caps!
See here:
Carlos knows the sound this 'masterpiece of art' produce!
Of course, it lacks the real bass!
I'm selling it for 1.250 EUR. Anyone interested?
See here:
An externally hosted image should be here but it was not working when we last tested it.
Carlos knows the sound this 'masterpiece of art' produce!
Of course, it lacks the real bass!
I'm selling it for 1.250 EUR. Anyone interested?
Member
Joined 2004
Didn´t want to scare away potential repliers
carlosfm said:
hmmmm yes boomy could be a problem, but then until I make new cabinets for the 10" vifas, I won't really be able to be sure if that is the amp or the speakers
though I do have a bunch of 63V 4700uF caps on an old mainframe PS board, wouldn't be too hard to desolder a few and wire them into the ps.... hmmmm this amp is supposed to be a build and forget one, must resist temptation to get sidetracked I was thinking about what you said about easy to drive speakers too carlos, and I think maybe the reason is that hard to drive speakers will tend to cause the amp to clip the transients more (due to having less headroom because you are having to push it harder to get the desired SPL) ... and from what I have read elsewhere, the clipping behaviour of these chips is not very nice.
Once I have done the other channel, I'll do some tests and see what the waveform looks like when clipping to see for myself
... my 3 ways are about 88db efficient. at normal listening levels it sounded very nice, but when I pushed it, it got nasty, didn't sound like hd just sounded nasty (don't really know how to describe, kinda harsh and edgey). Tony.
wintermute said:
With low capacitance I had untight bass even at low, late night listening levels.
It's definitely not the amp clipping, it's the PSU voltage dropping, and even a small amount affects the bass.
I've measured as much as 0.5~1V voltage drop at low levels, depending on the music.
Of course, I could also not listen very LOUD because the amp started to 'shout' and clearly compressed the dynamics.
All this is past...
PS: guys, test your amps with Ben Harper. Listening LOUD even the (non-heatsinked) MUR860 diodes got hot.
OK thanks Carlos
I still can't help wondering whether it is only the amount of capacitance or if there is someting else... the aksa's have a reputation for very tight bass, and as far as I'm aware, the 55 has only 4700uF/rail and the 100 double that..... not huge amounts by any standard....
you reminded me too I need to check the diodes to see if I need a heatsink on the one that's using both diodes in the package
Tony.
I still can't help wondering whether it is only the amount of capacitance or if there is someting else... the aksa's have a reputation for very tight bass, and as far as I'm aware, the 55 has only 4700uF/rail and the 100 double that..... not huge amounts by any standard....
you reminded me too I need to check the diodes to see if I need a heatsink on the one that's using both diodes in the package
Tony.
don't get me wrong carlos, I'm not questioning whether 1000uF is going to cut it, just whether or not it is necessary to have say 20,000uF or more
for the amp I built, I want to use it mostly for speaker testing, and also for a test run when biamping my new speakers, in that case it will only be fed signals above 300Hz, so I think it will be ok with low capacitance
for the amp I built, I want to use it mostly for speaker testing, and also for a test run when biamping my new speakers, in that case it will only be fed signals above 300Hz, so I think it will be ok with low capacitance
wintermute said:don't get me wrong carlos, I'm not questioning whether 1000uF is going to cut it, just whether or not it is necessary to have say 20,000uF or more
I didn't say it's really necessary, but it helps alot.
There's some difference between the 'ok' and the 'good'.
If you want an amp that drives almost everything you throw at it, you have to elaborate a little more than a couple of small caps.
I made a small amp that I use on my bench (listening to it now) where I use 5,700uf capacitance per rail, unregulated.
It works fine for what it was made for, but I don't ask it (and don't need it) to drive difficult speakers.
This PSU gives you a rock-steady voltage, and it sounds very good. No need for big caps here.
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PauSim said:
Paul,
About a year ago I was going to open up my Gaincard to look inside. Problem was, the hex nuts are nested into deepish countersunk holes that are fairly tight. That meant I couldn't use a standard socket wrench head to unscrew it. It has to be a bit that fits the nut but also has extremely thin walls (or else it can't fit into the hole). Not a standard part, I don't think.
Well, I didn't have time to look for it, so the project fell by the wayside.
Right now I'm just happy to let things be. I don't know if it's some urban legend or the truth, but that thing about the vibration and tensioning of the fasteners contributing to the sound of the Gaincard also makes me hesitate a bit.
But it sounds good the way it is and I may just leave it at that.
It heartens me, however, to see that Peter Daniel's Patek SE amp compares favorably to the Gaincard on the 6moons.com review. It tells me he's on the right track and maybe has figured out much, if not all, of what's to figure out about the circuit.
It would be good to see the real insides, though, wouldn't it?
Best,
KT
That's a full on PS carlos!! more complicated than the poweramp circuit itself I'm going to stick with my very basic supply for now, IMO as long as I'm happy with it, that is all that matters (though I may add another 1200uF - 2200uF per rail some time down the track since I allowed for it on my PS board).
Tony.
I'm going to stick with my very basic supply for now, IMO as long as I'm happy with it, that is all that matters (though I may add another 1200uF - 2200uF per rail some time down the track since I allowed for it on my PS board). Tony.
Member
Joined 2004
KT said:
Hi KT,
That´s too bad. In the 6moons pictures the countersunk holes are sealed so it´s impossible to help. But inmate reMC did open his so maybe he could track a suitable wrench for you...
Ok, if you´re happy with it that´s what counts most.
I kind of feared it would happen. Even so, I´d like to read a second opinion
I guess Junji, based on his experience chose the right concept among others, while Peter, based on his listening tests chose the right variables within the winning concept.
These things happen all the time. It´s like cars: The original Lotus 7 was revolutionary in its time, but has long since been beaten, in terms of performance and reliability, by its less spartan replica, the Caterham 7 . But for the joys of riding a true classic... (I´d sure like to know, never drove neither
)It would be good to see the real insides, though, wouldn't it?
Best,
KT
You bet it would
Regards
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