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Old 13th August 2007, 03:44 PM   #11
AndrewT is offline AndrewT  Scotland
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Hi,
I didn't realise that 47 Lab's gain card was that bad.
They only ask for 24W into 8ohms and it can't even manage that easy bit of the spec.
Then the output falls 2.0dbV into 4r0. Terrible.
Talk about brass neck and profit margin.
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Old 13th August 2007, 05:16 PM   #12
john65b is offline john65b  United States
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Now I would never pay $3000 for an original Gaincard, but if you look at all those clones, they all have bypasses, snubbers etc added to the original design. No more 9 components.

I have alway heard that Gainclones (at 1/50 the cost) don't sound as good as the original Gaincard, but could it be that it is those that acually own the Original are the poor blokes that are saying this???

I like Gain Clones. For $60 in parts, they sound great. I just don't expect or claim it to be one of the best sounding amps on the planet, like the Gaincard.
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Old 12th September 2007, 01:04 PM   #13
klitgt is offline klitgt  Denmark
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Quote:
Originally posted by theChris
the issue is that there is significant ESR and ESL in the larger caps, they make poor caps at higher frequencies. So some designs call for the addition of film caps, which act like caps to a higher frequency.

in industry, ceramic caps are used for the smaller size. because the ceramic caps are not in the signal path, there is less concern about possible issues.

Some claim that the power supply is a part of the signal path and therefore one would believe that caps in the power supply should be as "audiophile" as possible.

In my SiriuS power amp (now marketed under the name of GamuT) the power supply elcaps are bypassed by film caps.
I understand that copper foil paper in oil signal capacitors sound better as signal coupling caps than any type of film cap. Does this predict that copper foil paper in oil signal capacitors would be good for bypassing power supply elcaps?
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Old 12th September 2007, 02:11 PM   #14
Eva is offline Eva  Spain
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To demonstrate that high inductance in modern electrolytic capacitos is a plain myth, check the following datasheet:

http://www.epcos.com/inf/20/30/db/aec_07/B43501.pdf

Self inductance is rated at approx 20nH (0.125 ohms reactance at 1Mhz) for those medium sized high voltage electrolytics. Big film capacitors exhibit similar inductance values. Electrolytics should be considered good up to 1Mhz.

Contrary to popular wisdom, the main purpose of local bypass near high speed ICs is to compensate for PCB inductance (at frequencies considerably higher than 1Mhz). Remember that wire self inductance figures are in the 5nH per cm range (so one of those medium sized electrolytics is not more inducive than two inches of plain wire or PCB track).
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Old 12th September 2007, 04:03 PM   #15
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"....the Gaincard doesn't seem to be one (I'd say it rather is a money making machine)....."

Yes.....business ia a money making machine !

This fact has bugged me for a long time. I've been on both sides of the business. Manufacturing and buying.
I've also been lectured ( in a university ) a lot on this by professionals from Switzerland.

My conclusion is that one cannot complain about costing . You aren't being forced to buy anything and it isn't essential for living comfortably. The maker might have spent a lot of man hours perfecting 'their implementation' and might want to get back their 'man hours money' over a 'limited sales' that they project.
If you like what they make then you might need to cough up for their product. If not , there are several other products to choose from.

You will never get to know how much they spent on developing their product and so it's very hard for outsiders to determine what the product really should cost . It can never be just the cost of parts. In fact that is just a fraction of the overall cost.

That's what DIY is all about . You spend a pittance ( not always !)on parts and don't have to plonk down on your time ( far more expensive ) and help ( others time and hence money ) that is not visible at all. But it does make us happy and think we got it done cheap !

So maybe we needn't clobber the makers for thier prices . Just clone them and be happy ! You don't have to buy it of course.
Cheers.
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Old 12th September 2007, 05:29 PM   #16
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Eva, I've been measuring various caps on a $16K Agilent LCR meter that is accurate to 2Mhz. Though I believe electrolytics have gotten a bad rap, they aren't that good either. Smallish low ESR electrolytics that I'd expect to be quite good are still all done in terms of capacitance and ESR well below 100khz. Even a similar value OS-CON is in trouble at 200khz. Larger caps will lose effectiveness at surprisingly low frequencies like 5 or 10khz. Yes, they still display reasonably low impedance and will shunt high frequencies to ground, but their ability to store and return energy is greatly diminished. IOW, they act as a low value resistor with a phase angle closer to -45 or even 0, than to -90 degrees. I don't believe in bypassing filter caps at the cap- this is far better done at the circuit where the cap can do some good, or at the bridge, where the RF can be shunted, but the electrolytic can't do the job alone. FWIW, though I've been measuring caps for decades, I've changed my thinking on this matter greatly since having access to a meter that can do both high frequencies and low impedances at the same time. Traditional bridges, though I love 'em, aren't up to the task.

edit/addition- Notice how in that cap data sheet they concentrate on impedance and ESR, but make no mention of effective capacitance at high frequencies- nobody does.
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Old 12th September 2007, 06:35 PM   #17
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I ran some equations here:

http://www.diyaudio.com/forums/showt...83#post1229783

which show that bypassing isn't a matter of spraying random smaller capacitors on top of big ones. You do want to know the parasitic values for the large cap, and low-ESR capacitors paradoxically can get you in trouble if you bypass them with too small a film cap.

The math gets a bit involved, but the end result is simple: find the equivalent series inductance (ESL) and equivalent series resistance (ESR) of the large capacitor and apply the equation

Cb = ESL/(ESR*ESR)

to find the optimum value of Cb, the bypass capacitor.


Some folks avoid the whole mess by running a few smaller electrolytics in parallel instead of a single large one, which increases capacitance while also decreasing ESR and ESL. It's a neat trick if you have the room.
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Old 12th September 2007, 09:52 PM   #18
Eva is offline Eva  Spain
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Quote:
Originally posted by Conrad Hoffman
Eva, I've been measuring various caps on a $16K Agilent LCR meter that is accurate to 2Mhz. Though I believe electrolytics have gotten a bad rap, they aren't that good either. Smallish low ESR electrolytics that I'd expect to be quite good are still all done in terms of capacitance and ESR well below 100khz. Even a similar value OS-CON is in trouble at 200khz. Larger caps will lose effectiveness at surprisingly low frequencies like 5 or 10khz. Yes, they still display reasonably low impedance and will shunt high frequencies to ground, but their ability to store and return energy is greatly diminished. IOW, they act as a low value resistor with a phase angle closer to -45 or even 0, than to -90 degrees.
We are more or less telling the same story. People must understand that electrolytic capacitors are *not* inductive, which would result in phase shift becoming +90 (positive) at very low frequencies rather than remaining at -45 or close to 0 as you mention, and in impedance rising at 6dB/oct. However, as frequency increases, capacitive reactance becomes negligible and ESR dominates progressively resulting in a phase shift that sweeps to 0 and an impedance that tends to become flat. Thus electrolytic capacitors behave as very low value resistors at least up to a few Mhz, *not* as inductors.
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Old 12th September 2007, 10:40 PM   #19
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Agreed- I think the idea may come from the fact that most capacitors are wound, but the geometry is not such as to form an inductor. More important is keeping the leads short.

I don't have the answer, but wonder what it would take in terms of caps and their type, to create a high value (100uF or so) composite cap that would maintain all it's parameters to 100khz or so? That means it would show close to full capacitance value and close to -90 degrees over the full range. I did a brief paper exercise with some known caps, and it's harder than one might think!
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Old 13th September 2007, 11:50 AM   #20
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...simply measuring.. that's it. Much better than guessing!


Conrad,
I would be quite happy to get your paper exercise!
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