Clipping with HD600 and porta corda

As I understand it, clipping is an amplifier problem that occurs when the amp is driven beyond its rated power and distortion goes up logrithmically. Solid state clipping, as both your amps are SS, is especially awful and to be avoided.

In your listening circuit as I understand it, you have amplifying circuits in both you MD and your porta CORDA. They are driving headphones with 300 ohms of nominal impedance (nominal meaning the impedance varies across the frequency range). If you are hearing amp-type clipping distortion, you have to rule out which amp is the source of it by turning down volume levels indepedently until you isolate the cause of the distortion. Higher impedance cans like the HD600s take more power to be driven to a given volume than do low impedance cans. High impedance cans would therefore be easier to clip with for a portable battery powered amp. One fix might be going to a lower impedance can like the CD3Ks or W1000s.

On its internal batteries, your porta CORDA is limited to 4.5V to 9.0V of DC current (depending on the model). The ports CORDA is capable of using DC inpot up to 32VDC; I realized a considerable improvement in sound through my HD580s by obtaining and connectioning a regulated 24VDC PSU to my porta CORDA I. Supplying a more stable source of greater power can help an amp operate better and avoid clipping.

I had serious distorsion problems with my Porta Corda when it was connected with my Theta DAC, which has a very strong output (up to 6 volt). I asked Jan about this. He recommended me to use an external power supply with higher voltage up to 30 volt. I bought a regulated one with a maximum voltage of 24 volt. This fixed the problem completely: the Porta Corda now can handle the high-level signals from the Theta. BTW it never had any problem to drive the HD 600 with the internal 9 volt battery (and any other source than the Theta DAC) to very high volumes without distortion.

JaZZ

[QUOTE]Originally posted by AdamZuf
I should not have used the abbreviation without defining it. A PSU is a power supply unit, commonly known as a "wallwart". Most are unregulated; you want one that is regulated. Since you are in a 220/240 country, I am not sure if my supplier will work. Do an internet search for electrical equipment supply houses which will sell retail. Which porta CORDA do you own (what color is it?)?

I tend to preach about clean electromechanical connections. These include interconnects, cables and any components (like tubes) which press fit into sockets. www.caig.com makes a number of cleaning/conditioning products. I like D100 and ProGold; D100 goes on ordinary metal connections and ProGold goes on precious. D100 is about four times more effective in removing corrosion. There's no real sense in getting into swifty esoteric interconnects if you are not supplying a clean solid mechanical connection.

MD is one format I know little about because I chose not to get involved in it. The porta CORDA II that you have has provisions for pluggung in a PSU, but you will have to drill a hole in the case for the lead or otherwise route it in. I would suggest you contact Jan Meier for specifics and also ask him about a european source for the PSU and what the correct nomenclature is for a regulated PSU in a language useful to you. Good luck.

A slight clarification: clipping is when an amplifier is driven beyond it's VOLTAGE limit. The term refers to the top of the waveform being "clipped" off. The amp can't deliver more voltage, so it just stays at it's max until the signal comes back in range. Pa is right, horrible distortion. It also produces high frequency artifacts (from the corners of the clipped waves) that go right through a crossover and make molten copper out of tweeter voice coils.

The HD600 are pretty easy to clip with due to their high impedence. They require more voltage to deliver a given amount of power than a low impedence set of cans.

Another sort of clipping can occur when a digital source is driven beyond the highest number that it knows of. Similar results. Be very careful not to overdrive your digital recordings.

An interesting sub-category of the digital thing can happen if you have a digital equalizer engaged. For example, if I turn on any kind of bass boost in my ipod, it will clip and distort at any volume setting with any headphones simply because I ran it out of bits. Solution is to cut the other frequencies rather than boost.

Sources can clip and distort if confronted with a low impedence load. An example: a friend of mine was complaining about her car stereo sounding terrible when using a portable CD player and one of those awful cassette adapters. Trouble was that this one really did sound amazingly terrible. The problem was that she had plugged the adapter into the "line out" jack. Apparently that particular adapter was made to run off the headphone output, and it worked just fine when connected to that slot.

In your case you should be using the line out from your MD to the inputs on the PortaCorda.


gerG

Hi Adam!

Consider a sine wave as input (and therefore, the output). As you turn up the gain, the sine wave gets taller (increasing amplitude). When you reach the voltage threshold, the sine wave will start looking like it bumped into the ceiling, getting flat at the voltage limit. More gain and it becomes a square wave, bearing very little resemblence to the original sine wave. What this means to your ears is very distorted sound. High amplitude square waves also put significant demand on drivers.

Bad things can also happen if you overjuice the inputs to an amp. I don't know the details, but very ugly output, up to and including smoke.

I hope that I did not come across as correcting Old Pa. I was sort of in a hurry (as always) and was not very tactful. I want to stay on OP's good side in hopes that he will let me try out those Nautilus 800s in nearfield some day!

The reason that I like to distinguish between voltage and power (besides that analretentive engineering behavior) is that there is more than one way to overdrive an amp. The other one is to hit the current limit. Amps are typically designed so that voltage clipping happens first, but it is possible to cross the current threshold first if you use very low impedence loads (like several speakers wired in parallel). This is not something to try unless you are fond of the smell of burned insulation and desire to torture the amp to death (although most will trigger circuit protection before you hit the smoke threshold).

Did I answer your question? Are you really encountering distortion, or just curious?


gerG

You had to butt in and explain clearly what I was rambling on incoherantly about, didn't you. Thanks to you, Adam has some facts that I can see he is using. As for the B&Ws, I would suggest waiting for Spring breakup up here.

Adam, I don't have a clue whether increasing the supply voltage will affect the output limit. It sort of depends on the power supply design inside the amp. When in doubt, ask the manufacturer. Jan is a great source of information.

Old Pa, sorry, I realize that a little knowledge is a dangerous thing. I am surviving proof of that! Thanks for the warning on the spring thaw. I had forgotten that I am alergic to water in the solid state. I have to coat all frozen surfaces with Scotch, so exposure to a glacier could prove fatal.


gerG