Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Marnay]

Hello to all,
Can someone confirm that the value capacitor of C7 in the AKG 451E is 3.3 mfd?
Thanks in advance

http://www.gyraf.dk/schematics/AKG_C451E.GIF

[Marnay]

I just received the answer: it is 33 micro farad, rated 6.3V

[Jim Williams]

6.3 volts is pretty close to the split rail at 4.5 volts. I would use 10 volt ratings. Tantalum caps can be found a bit smaller than in the past. I use a 47 uf Panasonic FR 25 volt el cap bent sideways to clear. A small .01 uf Wima MKP-2 across it lets the 'air' out. Also, the input blocking cap may be a yellow Wima polycarbonate. Replace that with the FKP-2 polyprop version, much better.

[Marnay]

Thank you!! good idea for Wima 0.01micro, I often use this solution in my analog console with Panasonic FC and Ero capacitors

[Marnay]

I just make the change and the result is very good! Thank you!!
I also made this change on my old C 414 EB and I am satisfied with the result!

[klaus]

(...) A small .01 uf Wima MKP-2 across it lets the 'air' out.

Please explain in simple language what the effect is when you put a small capacitor in parallel with the large electrolytic cap.

Thanks, KH

[Jim Williams]

A simple analogy is a gate. The cap is the gate. A larger gate lets more low end in. The smaller gate lets the smaller stuff in (high frequency, low level details) that the larger gate doesn't due to it's size and construction.

A smaller value "bypass" cap lets those electrons through that are normally converted to heat and wasted in larger, less conductive capacitor formulations. Examine the frequency response of a cap and you will see different fomuations roll-off earler than others, the worst are electrolytic caps and tantalums. Polystyrene and polypropylene films are the best along with some exotics like teflon caps. Dialectric absorbtion and dissapation factors are the specs that degrade a capacitor. They are very good for those film caps.

When you audition these parts and hear new, low level high frequency audio details, that's telling you that they were always there, but the gear/parts were "chewing your food for you" so to speak. When I first heard them I felt like the gear designers were robbing me of some of my music. That no longer happens here.

[klaus]

There was a time when, I, too, thought using bypass caps would bring audible progress: in the 1990s I equipped virtually every job with polystyrene-bypass 001's, after I theorized in a similar vein as Jim, and after I bought into the "MultiCap" mega-dollar-capacitor story.  Then I actually heard the MultiCap, and I realized that all that supposedly better high frequency pass-through, courtesy of the bypass cap, was nothing but phase smear due to the paralleling of two diverse components with unequal time constants/arrive times.

 I have since abandoned that tack, and rely instead on better capacitor material for the single coupling cap I use. Now I have my relaxed sound back without the grit.

[Jim Williams]

My experience with bypass caps is much different. All capacitor formulations have limitations. Larger value caps are inherently slower with reduced rise times and increased DA. Smaller value caps are faster and have less DA losses. Higher voltage rated caps of the same value have increased rise times.

This technique is also used in timing, power supply bypassing and other circuits, it's a common, well known and used technique in the electronics industry. Look at the innards of your audio gear and you will see larger electrolytic caps used for the power supply filtering along with smaller local ceramic bypass caps. This is done to lower the impedance of the power network, a requirement in high speed analog and digital circuit design. Other audio manufacturers have also used this technique for the audio path including Studio Technologies, Manley Labs, Dolby Labs, dbx, etc. Even some low cost Chi-com mics from MXL have film cap bypasses added.

Besides needing a bit of basic engineering to avoid crossing over capacitor impedance curves, the properly selected bypass capacitor more closely approaches the open sonics of no capacitor.

The best way to emperically select a bypass capacitor is to evaluate them in a circuit that will also allow direct coupling, the operation without any capacitor. Only then can you completely remove the DUT (device under test) from the equation. That way you can compare the sonic results of a single cap, with a bypass added and also be able to compare to the "Holy Grail", no capacitor. To not do this is to come to a false conclusion without using all the facts and data available.

If one finds increased grit from a quality film capacitor, I would suggest that the grit is a form of THD that a slower, less revealing cap filters out for you. That grit is most likely still there no matter what cap you select. I would treat the circuit first to remove the non-linearities that are adding grit to the signal before blaiming a capacitor for revealing it. If it doesn't sound good without any capacitor, it doesn't sound good. I found I need the rest of the audio system to be direct coupled, that removes any additional audio reaction from other capacitors in the chain. This includes the mic preamp, monitor amps, etc. Here there are no capacitors in the chain when evaluating any capacitor. Listening to the sound of one cap through another is misleading, especially an electrolytic capacitor. My monitoring path on the bench is free of coupling capacitors so I can focus on the DUT, not my monitoring path.

Even the best caps have a sonic signature and audible quality losses. That is why I am proponent of direct coupled audio design. Most of my condenser mics here are designed without a coupling cap off the capsule, the most offending place to use one. The diaphrams are directly coupled to the jfet gate. These mics are down to one cap in the signal path, I wish I could also remove that too but 48 volts must be tamed. It's a bypassed 1 uf mylar film cap.

I also use Bas Lim's excellent Rel-Caps and MIT MultiCaps here. If I am reading correctly, you discontinued the use of .001 polystyrene film caps as a bypass after you heard another brand of cap, the MIT?

[boz6906]

Very interesting discussion on caps, really scratches that brain itch...

I get Klaus' concern about varying phase shift, etc across two different caps.  There's also different dialectric constants and velocity properties as well, all frequency-dependant.

But I'd think these differences would be tiny at audio frequencies.

Also, with differing phyisical sizes come differing properties such as self-inductance and wavelenght-related electrical resonances within the component itself.

I think the self-inductance of the larger cap is what necessitates the smaller "hi-freq bypass" cap.

And no matter how many caps, they still smear the signal, current leads voltage as much as 90 degrees in capacitors...

It's the continuously varying audio signal with it's dynamic history that creates a varying
phase difference.

Just a few thoughts...

[klaus]

(...) But I'd think these differences would be tiny at audio frequencies.
(...) I think the self-inductance of the larger cap is what necessitates the smaller "hi-freq bypass" cap.

How about taking off the thinking cap for a moment, and putting your ears to work? Listen with bypass, then without, then report back!
Thanks,
KH

[soapfoot]

for what it's worth, the human ear is incredibly sensitive (especially when trained) and is more than capable of detecting "tiny" differences, particularly in certain sensitive bands of hearing!

[Kai]

And no matter how many caps, they still smear the signal, current leads voltage as much as 90 degrees in capacitors...

Not globally, but only on the crossover frequency of a filter arrangement.
In the stop band the phase shift is going up to 180°.
In the pass band shift aproximates 0°. The (ideal) cap behaves as if it's almost not there.

So finally it's a matter of the correct size of the cap that makes the biggest difference in sound, as it defines the x-over frequency of a filter in a given circuit.

Besides there might be other effects like:
- Losses due to internal resistance.
- Dielectric losses.
- Internal resonances caused by stray inductance (usually far out ouf the audio band).
- Microfonics.
- Nonlinearities, specially if used inproperly, e.g. polarized Elko used without DC precharge.

All of these can easily be measured, no "golden ears" necessary to detect them.
No wonder that a cap can have a "sound".

Regards
Kai

[klaus]

I don't understand (maybe I actually do*) the constant dismissal of using the sensory organ for which the medium was designed as a good indicator for quality. "Golden" or otherwise perceptive ears are the measuring mark with which we build, choose, and enjoy the finest musical instruments humankind has ever invented. It also happens to be a most useful measuring mark for selecting microphones and other audio components, as well as their sub-components, intended for recording and reproducing music. We surely would start with the visually perceived quality of the picture when examining a good photograph.

When it becomes unclear which exact feature of a capacitor is responsible for smear or otherwise inaccurate and unpleasant sound transmission (see your list of at least six possible culprits above) perceptive ears remain in the end the most helpful factor for choosing or rejecting said capacitor. More scientific speculation (a valid oxymoron) becomes quickly academic and unproductive towards the goal of identifying which of the culprits is responsible. So let's stop knocking good hearing, and decision-making based on it, once and for all.

I think it's most useful to refine audio components and make improvements in their design AFTER detecting which ones sound good, or lack artifacts, but clearly in that order. Otherwise we end up with more Multi-Caps©.

* could it be a low self-regard for one's own abilities to hear well enough to judge with confidence?

[Jim Williams]

Excellent test equipment has a place as well in evaluating electronic components. The human ear is just too unpredictable to use it as a benchmark simply because everyone hears differently. Test gear is used in the electronics industry for consistancy. Like analog tape, the human hearing fades with time, test gear doesn't. Your "Golden Ears" will not remain that way forever, they will change and suffer losses.

Test gear levels that all out eliminating the euphonic variations and biases. It won't tell you when something sounds good but is unparalled in finding errors or limitations. That's if you care about that stuff.