Direct Path on Test

[Rameish 0]

So Jazz, what you're saying is:

 

1) the regular 2 volts out of a cdp is sufficient.

 

2) I should use a 50K ohm pot instead of the 100K ohm pot. Or would a lower value pot like a 20 K ohm pot be better?

 

3) Pick an op-amp that has a lower rating than 600 ohm in its spec sheet - preferably lower than 100 ohm.

[JaZZ 0]

Rameish...

 

...just a little misunderstanding: the ideal pot value is 500 ohm, not one in the kiloohm range... The serial resistance of a 100 kiloohm pot is much too high in view of the say 300-ohm drivers.

 

[matbon0013 0]

Gawd! Call me dumb but all this is too damn confusing

No wonder people like me pay for all this assumptions/speculations whatnots, it reflects in the hardware costs no??

 

But seriously folks is it worth the hassle?

[Rameish 0]

Jazz,

 

Okay re-read. Thanks

 

Guys,

 

Yikes! So a 500 ohm pot is required - hmm. Well...where do I get a volume pot with such a value from - in Singapore? Any idea guys??? It must be reasonably good like an Alps Blue.

 

Matbon, looks like "Direct Path - Take 2" is required - hey I don't give up that easily u know ;-).

 

 

 

 

 

 

 

 

[ablaze 0]

mat, I'm confused too!

Rameish, once again kudos to you, for willing to do whatever it takes

 

btw, does the Rotel have a variable rca output? that'd make things considerably easier?

[Rameish 0]

Ablaze, unfortunately not. However, I shall get one. The reason is this - I have always been an advocate of "less is more" approach - or at least it has the potential to be more.

 

The more boxes and it get more complex so you're dealing with more issues. Being a turntable guy you can understand why - choice of cart (high or Low output), step up trans, phono stage, pre,amp etc etc.

[JaZZ 0]

Hi Rameish!

 

It seems that I've been lucky to find some 500-ohm pots. They're nothing special, a no-name product, with the usual wire inside as it seems, but sufficiently precise. If I find some more I could send them to you if you like...

 

...but it may be easier to use a switched attenuator instead; it could be a simple one with say 6 or 12 positions for test purposes. You just have to equip it with the equivalent resistors.

[Firefox 0]

choose a DAC/CDP line out with a low output impedance! I think 100 ohm should be seen as an upper limit - the more so as the indispensable passive attenuator will add even more resistance. As already mentioned in an earlier thread below, it looks like the majority of common players have line-out impedances of 200 ohm and above. Don't waste your time which such players! They're not suitable for direct-path purposes.

Actually, he mentioned that the OPA2604 has an open-loop impedance of 600 ohms as it's meant to drive cables directly. However, other opamps used in swapping include the OPA2227 & 4556D with lower output impedances.

 

Note that the opamps directly drive the cable without any fet output stage so the output impedance is decided by the opamp & the gain factor.

 

In any case at all, I don't know but paying to experiment with this is, IMO, a big waste of money. Like you said, most line-outs of CDP's are not meant to drive low impedance loads like headphones.

So there is no point trying to make a passive post-amp for the headphones. It'd work (if at all) only with selected CDP's or heavily modified ones.

[Rameish 0]

Jazz,

 

If you have any lying around - sure as getting an attenuator just to test it out is gonna be expensive. I never realised the direct method was/is so complex. Hmm.. maybe I just try using my Marantz CD-6000 that has vol control on the remote (without another volume pot in the stream).

 

I'll make an RCA to female headphone jack tomorrow - hopefully with better results.

[JaZZ 0]

Firefox...

 

...why is it a waste of money? It's an interesting experiment (not just buying gear, but also being sort of creative), and it's really cheap, just the price of a 500-ohm stereo potentiometer (though hard to find) or a switched attenuator, resp., with as a result, in the ideal case, an accuracy unbeatable even by the most expensive amps. And even if you don't like the sound: who isn't interested to know how his amp or any amp alters the original source sound?

 

Of course the precondition of a low output impedance has to be observed. But this isn't really hard to do.

 

 

Rameish...

 

...OK, I'll have a look in the store.

[JaZZ 0]

...maybe I just try using my Marantz CD-6000 that has vol control on the remote (without another volume pot in the stream).

But beware: it's rather likely that this output has a high impedance as well.

[Rameish 0]

Jazz,

 

true true, but I had slightly better results with the Marantz via the 100 K ohm volume pot so it's worth a try any way. As for firefox's comment on it being now expensive in reference to the attenuator - most cost as much as a basic amplifier and then you'll still have to op-amp roll to get it right.

 

Well, I doing this now because of trying to save money but out of curiosity. Of course I don't want to buy an attenuator just for this. But if successful with a brandless pot then maybe I might spend big money on an attnuator.

 

Firefox,

 

Jazz- the main advocate of the direct path on head-fi - has a Corda HA-2 (and a HA-1 MKI) as well. He is well aware of the positive benefits of a headphone amplifier. However, he did the direct path method to satisfy a curiosity.

Edited September 4, 2003 by Rameish

[JaZZ 0]

Well, I still don't see how direct-path experiments are expensive. Basically all you need is a (cheap) potentiometer. You can even use some stepped switch instead (e.g. an input selector) and equip it with resistors corresponding to a 500-ohm pot at the different settings. If you decide to make a lasting solution out of it, there's just some handicraft with some available aluminum housings to be accomplished to mount RCA and headphone jacks - and that's it. Maybe US$ 25 totally. I for one wouldn't dare to swap op-amps in a player, so if I don't have a low-impedance source, I'm no direct-path candidate...

 

Yes, I know the sonic merits of headphone amps - in the form of a Corda HA-2 and an Earmax Pro. I may be a «direct-path advocate» , but I use the amps clearly more often than my 500-ohm pot: because of the «better» sound. Don't get me wrong: the «better» (= more euphonic) sound in fact is a fake and doesn't represent greater accuracy, but quite the opposite! The sound directly from the source (or its proprietary line-out amp, resp.) without the detour through an additional amplification stage represents the sonic truth - in the ideal case.

[Firefox 0]

Don't get me wrong: the «better» (= more euphonic) sound in fact is a fake and doesn't represent greater accuracy, but quite the opposite! The sound directly from the source (or its proprietary line-out amp, resp.) without the detour through an additional amplification stage represents the sonic truth - in the ideal case.

Maybe you can try taking the opamps and/ or buffers off your CDP. Then drive your speakers/ phones out of the DAC chip directly. =)

 

I seriously think there is more than just a 500ohm pot to achieve this direct path thingy.. Perhaps a custom wound tranny from extremely pure silver/ copper wires + dual-gang log pot. or attenuator. Even then, you'd need some form of buffering.

 

[Rameish 0]

Maybe you can try taking the opamps and/ or buffers off your CDP. Then drive your speakers/ phones out of the DAC chip directly. =)

Firefox,

 

Okay this is gonna start sounding like a head-fi thread (in the -ve sense). I still think an amp is a better approach but we should explore this throughly and properly. Jazz has offered to send me a 500 phm pot so I'm gonna try again. Maybe we should call it the shorter path instead :-)

 

Jazz,

 

Sonic truth? There is no such thing as in the recording process alone the amount of electronics involved in the initial recording and the subsequent mixing would have altered the "live" version (ie. being there while the musicians were playing).