[Joe Bloggs]

Quote:

Hmm... don't know what to say, then. The people who actually make these amps commercially seem to think that you can't really get a "good" pot in this price range.

And Sony can get a pot that neither crackles nor changes channel balance from min. to max. in my old $100 D-E554? I just took it out to check that I'm not beautifying something that I haven't listened to for a long time--and no I am not!

Perhaps the problem with the pot on the PC is that it is too small. (10mm) If that were the problem I'd rather they made the amp bigger and used a better pot that can be had in the same price range, only bigger than 10mm.

And again--my problem is with channel imbalance at different parts of the pot on my Porta Corda, not scratchy sound when changing volume on the Airhead, which I do not have

 

[tangent]

Totally ignoring the "pot noise" issue....


On the pot imbalance issue, all potentiometers have channel imbalances.

Most pots suitable for audio are spec'd to have a channel balance within 3 dB down to -40 dB. 3 dB of imbalance is VERY audible, and the "-40 dB" part means it gets worse at lower volume levels.

Channel imbalance isn't the biggest problem, it's channel tracking. If the two channels were 3dB apart and stayed that way, you could fix it by just adding a resistor to one side. But when the relative imbalance shifts over the rotation of the pot, you hear "dips". That simply isn't fixable without changing to a different pot.

Even high-dollar audiophile pots like the ALPS Blue have channel imbalance and tracking problems -- "only" 2dB for that particular part. That's still quite audible.

I've always kind of doubted the audibility of carbon/cermet/whatever resistive elements in pots vs. that of the high-tolerance resistors used in stepped attenuators. But what is without a doubt is that stepped attenuators can be made so that channel balance and tracking is as perfect as you could care for.

What I would advise you, Joe, is to measure your Porta Corda and see what's coming out. If the channels stay within 3dB of each other, I think there's nothing Jan Meier is obligated to do for you, since that's probably the rated tolerance on the ALPS pot he uses. (Ask him to be sure, though.) If it's outside that range, then you have a defective pot and should get it replaced.

(To calculate a voltage difference in decibels, play a 1 kHz 0dB test tone from a CD player through the amp, then measure the AC voltage of each channel, divide one by the other, take the base-10 log of that value and multiply by 20. Take measurements along the full sweep of the pot from -40 dB from full-scale up to as high as you'd want to listen. If you turn it up higher, you might be measuring amp distortion, which isn't fair to this test.)

 

[kelly]

Jeff, are you honestly proposing that I am somehow unwilling to render or respect negative criticism of a product? Read some of my other posts and see if you can gather why I think that's funny. Better, read the comments by the people who respond to my posts!

I'm not saying you should accept the low quality amps. I'm saying you should buy a better amp if you don't like the low quality ones. At the $200 price point for a new amp from a commercial company, you only have two companies--Meier and Headroom. You want to spend more, then we have competition. Then we can nitpick. Then I can argue about minutia. At the Airhead and PortaCorda pricepoint, I'm sorry but no one is building a better mousetrap. The things are selling and only a couple of people are complaining about them (out of many, many sales). How can you argue with that?

Headroom is likely unmotivated to build anything better than the Total Airhead because it was canibalize their Supreme and Cosmic sales. Meier is probably unlikely to come up with a Super-PortaCorda because he couldn't generate the sales. And frankly, no one else is willing to enter the market at that price point.

For me personally, the Airhead and Porta aren't options. For me, portable battery powered amps come in two varieties - Headroom Cosmic and non-commercial DIY. Don't need it to be battery powered? Then buy something wall powered because at a lower price point, you can get better sound and there are more options.

This is the long version of Markl's "you get what you pay for" motto that he uses to justify $4000 headphones.

I realize you guys think I'm a snob but I really think you should more strongly consider the DIY route if you can't afford a better commercial amp and you're discriminating enough to be reading this thread.

 

[Joe Bloggs]

DIY it is then

But really...

Somebody tell me where Sony gets the pots for their pcdps.

 

[Jeff Guidry]

Quote:

Originally posted by kelly Jeff, are you honestly proposing that I am somehow unwilling to render or respect negative criticism of a product.

I re-read my post. It never mentioned you.

 

[kelly]

Quote:

Originally posted by Jeff Guidry I re-read my post. It never mentioned you.

You said "we", which seemed to include the respondants in the thread. I answered not only for myself but on "our" behalf. If you want a specific answer from an individual, address him or her. Otherwise, I'm inclinded to interject.

 

[jpelg]

Quote:

The people who actually make these amps commercially seem to think that you can't really get a "good" pot in this price range.

Well, that's all of two designers visions. There are at least two or more Head-Fiers that make DIY amps for others here, and those designs make other choices and many believe they are better than those available commercially*. I assume that these benevolent folks are at least covering their costs. Add a little profit to those prices and you have a product that competes with the "big" guys on both price and performance. C'mon Mac, as an Apple Macintosh expert you are used to thinking outside the box. Imagine the other possibilities. That is ALL I am really saying. I know you can do it!
Quote:

When the guy who designed the amp says that this design accounts for a difference in sound, I tend to give him the benefit of the doubt.

I guess this is where i have a problem with your statements. Since you never actually answered my question, I will assume that you have not actually heard the new Airheads. By your "logic", ALL Sennheiser headphones would sound good too.
Quote:

I'm sure there are lots of people on Head-Fi who can easily hear the difference.

Having actually heard a new TA, I am sure that the crackling sound thru a pair of Ety's* would just sound more obvious and noisy.
Quote:

Geesh, why is it so difficult for people to have rational, logical, and most of all, civil discussions about topics on which they disagree? It always has to turn into bickering and "us vs. them" defensiveness...

I think this has always remained a civil argument. But by you stating at the end of every one of your posts that you are being "rational" or "logical" does not make it so. I have no problem being placed on one side of an argument or another. It is the denigration of an coherently stated opinion that has been based on actual experience, especially with an argument that does not have the same experience as its basis, that I have a problem with. I really don't care if you prefer Headroom, Jan Meier, Sennheiser, AKG, or whatever produts you choose for whatever reason. I would never state an opinion, much less jump into a thread and argue about something I have not actually experienced.


OK, REALLY bored now. Time to do some work.


*Disclaimer #1 - I have never heard any of those amps.
*Disclaimer #2 - I have never heard a pair of Ety's.

 

[tangent]

Quote:

There are at least two or more Head-Fiers that make DIY amps for others here, and those designs make other choices and many believe they are better than those available commercially*

We DIYers aren't immune from the pot imbalance problem. I only have extensive personal experience with two pot types, the Panasonic EVJ series and the ALPS Blue. The EVJs will mistrack pretty badly at low volume levels. They're specified just like I described above: 3 dB channel matching down the -40 dB. The ALPS Blues have never audibly mistracked for me, but I still don't have as much experience with them as the Panasonics. Unless I'm mistaken, the Corda HA-1 uses an ALPS Blue, and I've never seen any reports about audible mistracking with the HA-1.

Some DIYers have stashes of the hard-to-find Clarostat and Noble mini pots. Maybe they're better...it's academic for me, though, since these seem to be impossible to find in small quantities now.

 

[Jan Meier]

Dear Headfellows,

Just read this thread and decided to throw in my 2 cents

As tangent rightly noticed all potentiometers have a certain imbalance, especially at low volumes. Even the expensive Alps Blue Velvet is specified to be accurate within 2 dB only.

The tracking imbalance is one of the reasons that the overall (maximum) gain of the CORDA HA-1 is rather low. Thus people are forced to turn-up the potentiometer a little bit more than usual, thus operating in a region of optimal tracking. Another positive effect is an increased signal to noise ratio.

The overall gain of the PORTA CORDA is much higher. The reason is that in most cases the source will be a portable CD-player. These players have a much lower output level than home-units and therefore a higher gain is required to drive high impedance headphones to an adequate sound-level (for the headbangers among us).

As far as tracking is concerned, Joe's configuration is far from optimal. If I'm well informed his CD-player has a rather high output level and his headphones (EX70) are very sensitive. Thus he can't turn up volume to a (normal) level of improved tracking .

My suggestion to Joe was (and still is) to reduce the effective output of his CD-player by using an interconnect cable with a voltage divider integrated. Thus the potentiometer can be turned up much further and his problem will be solved.

Of course we can also reduce the gain factor of his amp but what happens if Joe wants to buy a very inefficient K501, using a low level output PCDP?! We would have to increase the gain factor again. With a different interconnect cable he will be more flexible for the future.

As for the quality of potentiometers.

The potentiometer inside the HA-1 indeed is the renowned ALPS BLUE VELVET. It's quite expensive and counts for approximately 10% of the total costs for the parts (housing included!). Nonetheless tracking is specified within 2dB only at lower volumes. Some time ago ALPS also produced an even more noble potentiometer with an accuracy of 1dB. It costed around $500,- !!!!

Stepped attenuators are very nice, but one such attenuators normally costs more than a complete HA-1.

The potentiometer inside the PORTA CORDA is also made by ALPS and actually, considering its size, is quite a good one. It is completely sealed and thereby insensitive to moisture and dust. Not unimportant for a portable. Within its size hardly anything better can be found.
However, everything that is to be made small also has higher tolerances in accuracy and this potentiometer is specified within 3dB tracking only. Anything better, if available at all, will be much more expensive

Joe told that his old CD-player has an analog potentiometer with better tracking, but my guess is that the maximum gain factor of this portable is such that the potentiometer has to be turned up much further to obtain the same sound level. It thus operates in the region of optimal tracking. With his 580 Joe probably can turn up his PCDP to maximum volume and it will be loud. If he turns up his PC to maximum he will be deaf. That's the difference!
(Of course Joe also could have been lucky and he simply obtained a pot with better than specified tolerances. There always is a certain production variance)

The digital potentiometer on his new CD-player indeed will have a much better tracking than any analog potentiometer. It's by design. However, digital volume controls do have a certain number of drawbacks not given by analog potis.

A very common method is to mathematically divide the digital signal. Thus the "input signal" of the DAC is reduced and therefore the output signal of the DAC is lowered. Although tracking imbalance is not affected, at low volumes the signal resolution is strongly impaired. (much lower than 16bit)

Another method is to use a digital potentiometer with a chain of resistors on-chip and by selecting different contact points within this chain. To select the proper point electronic switches are found on-chip. These switches are known to effect the clarity of the signal. Moreover additional circuitry is required to control the potentiometer. This kind of circuitry is rather expensive if used in a product that is produced in small numbers only.

As for crackling noises. As BenG indicated these are most likely due to some oxidation or dirt on the slider or conductive path inside the potentiometer. They normally disappear after a certain period of use. Of course it shouldn't be there from the beginning, but as I don't produce these potentiometers myself I unfortunately don't have any control on this one. Again be noted that the potentiometer on the PORTA CORDA is sealed and therefore no external dust could have entered the pot after being made.

Last note: As far as parts-quality and build-quality are involved it's rather unfair to compare a product like the PC or the TA with a PCDP of $100,-.
Portable CD-players are made in large series (>> 100.000) by computer controlled assembly lines. The PC is completely made by hand and is produced in small numbers only. Bying parts in small numbers is expensive and the labour to produce one amp also isn't cheap. In my opinion the PC is a good deal, very well worth its money. It's not a perfect amp but a better amp simply costs more.

Cheers,

Jan

 

[jpelg]

Wow, cool!! Thanks Jan for taking the time for such an extensive response.

 

[Joe Bloggs]

Thank you Jan

I *would* have been satisfied with your explanation if I were satisfied about the condition of my amp

The way I tested the tracking on the old pcdp was by connecting the PC to the headphone out, and starting with the PC on at max. and the pcdp on at min.,

1. Turn up the volume on the pcdp and listen for channel balance changes (I was using the EX70, and combined with a maxed-out PC I could hear the music loud even at a very low level on the pcdp pot)

2. When the volume becomes too loud, turn down the volume on the PC and continue with (1).

As I went on I did not notice any scratchies or change in volume balance when I'm turning the pcdp.

Now, taking into account what Jan pointed out--that the PC is hand assembled while the pcdps are built in an automated assembly line--this starts to look more sensible.

So it seems that either Sony has a great deal for some very cheap, very high quality pots (time to break into a Sony warehouse

) or they save a lot of money in assembly, and buys an even more expensive pot than Jan because they know stupid customers would use pot tracking as the biggest factor in sonic evaluation

Or a combination of both...

Someone also pointed out to me that the Sony pots may only seem great because they track over a much smaller dynamic range than the pot on the Porta Corda. If Jan asked for a pot that would only attenuate 90dB (or lower) he might well have got a pot that tracked as well as the pot on the pcdp?

Now here's the part I don't get--if there's gonna be a part in a high-attenuation pot that is near unusable, why try to make the pot work over such a big range at all? Why not ask for a pot that tracks over a smaller range of volume with more precision? That way we'd get a whole pot to work with instead of something like half of it

The channel imbalance problem is smaller with the HD580 but even then I'm *just* skimming over the region where the pot balance goes nuts.

So what's the output voltage on that Sony D-EJ725? Or are my ears just too sensitive? Should I just listen louder?

Shameless pimping for my DIY attenuator cable thread: http://head-fi.com/forums/showthread...threadid=12138

 

[danny]

Jan is correct.

The pots in ALL versions of the arihead are the same, no matter what year they were built.

The old 3V regular airhead had some design issues. That is why it was discontinued. For those of you who have to have one of the 3V Total Airheads, I suggest you call Todd. We will not build anymore, but several were returned by people who wanted the new version within 30 days of buying the old version before it was discontinued. I am not aware of a single one of the people who asked for a swap asking to swap back. (I could be wrong, but I track that pretty closely)

As far as the channel imbalance on the pcdp, it may have a phenomenal pot, but I would suspect that the pot is only a single channel pot, and they are controlling the gain electronically. While there are several ways to do this, none of the acceptable are applicable to LOW COST portable amp designs. It is actually easier to do so in the pcdp.


The pots HAVE to cover a wide dynamic range. In fact, they have to cover a wider dynamic range than the pcdp. The reasons are

Input Voltage variance between sources 20 dB
Headphone impedance variation (30 to 600 ohm) 26 dB
Headphone Sensitivity variations (same impedance) 10 dB

Add it up, and you have 56 dB of variation to account for BEFORE you cover the actual volume control.

And don't forget the variations in hearing and environment.

ANY electrical engineer will tell you that they HATE batteries, pots, and switches. If is bigger than an electron, it should not be moving.

 

[Joe Bloggs]

Well I hate pots.

For a really cheap pot design, perahaps you can just use two pots for the two channels, as cheap as you like, and get the user to balance the channels all he wants while he is changing the volume

Or a cheap pot and a balance control

 

[kelly]

Quote:

Originally posted by Joe Bloggs Well I hate pots. For a really cheap pot design, perahaps you can just use two pots for the two channels, as cheap as you like, and get the user to balance the channels all he wants while he is changing the volume Or a cheap pot and a balance control

It seems like Tyll actually mentioned doing something to that effect...

 

[danny]

We do have a two pot option.

It is called the BlockHead.

For a slight fee, we will be more than happy to upgrade your Airhead to the BlockHead.