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Portable Passive Pre?

post #1 of 15
4/17/05 at 10:35am
Thread Starter 
I've posted another message concerning this in the Portable forum, but it might be best here. I'm getting fed up of making compromises, but it's beginning to seem best to me to use the iPod as the source over other players and then hook up a 10K passive pre to the Line Out.


I think it's pretty feasible to hook up a Sik Din/Ram/Pocketdock to a (let's just go overkill here) DACT and a 3.5mm socket, and maybe shroud the whole thing in a couple of layers of heatshrink.


How would a DACT (for example, I'm not wedded to this) react to such treatment? And is there a flaw with my thinking? (There must be, otherwise surely others would have attempted this before)
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post #2 of 15
4/17/05 at 10:56am
I own a Luminous Audio Passive Preamp. Its about the size and height of 2 ipods stacked and sounds pretty good. It costs about $150 US. I use it in home stereo and Im pretty please. www.luminousaudio.com
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post #3 of 15
4/17/05 at 11:00am
Is a DACT that much better than a good pot in your amp to justify the large size?
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post #4 of 15
4/17/05 at 11:28am
Quote:
Is a DACT that much better than a good pot in your amp to justify the large size?
better yet,is your portable rig worth that much in added expense ?

I realise many use their portable kit as their traver gear, for multimedia audio at the computer and for some is the primary music source but if stricly for on the go use or as background music why spend that much for a volume control that in the context of the use would not even be noticeable as an improvement ?

I don't place the same priorities on my "grab it and go" gear that i place on my serious lsitening equipment and actually refuse to get crazy on it,like adding an expensive stepper,when there are already many limitations built in just by being portable.

dual use "single system" for all music I say go for it if that is what you like (the stepper) but strictly for on the go music I think ambient background noise alone would mask any "perceived" improvement a single volume control could even make

just an opinion man
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post #5 of 15
4/17/05 at 12:46pm
Thread Starter 
Quote:
better yet,is your portable rig worth that much in added expense ?
With the Qualia 010 "Shord cord" in use, I think it's not a significant added expense.


Actually because I place so much emphasis on my portable equipment it's of a higher priority to me. A portable passive Pre can be used even out of my transportable gear, which is an advantage.


bundee1, thanks for the heads-up, if anyone is not sure what a passive pre is, the Luminous Audio Axiom is one. I want a pocketable version of that (with appropriate headphone fittings)... Something the size of two iPods is unfortunately far too big... it needs to be barely bigger than the pot, with sprouting captive plugs/jacks.


As I said, I'm not stuck to the idea of a DACT. It can be a Noble pot, whatever. However the argument for a DACT could be that since the iPod is not a great source to begin with, any further signal degredation especially in a passive component is highly detrimental if you're looking to extract the last 0.00001% of the sound, especially as the signal may have to start in a slightly poor quality way (sik din cable, if it's not re-cablable at source).


The idea remains the same whatever pot/dact is used and I'd like the idea of using a passive pre with the iPod validated by you guys.
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post #6 of 15
4/17/05 at 3:02pm
Quote:
With the Qualia 010 "Shord cord" in use, I think it's not a significant added expense.
I meant the addition of the DACT which is by no means cheap and mosre than many use as their portable source.


Quote:
Actually because I place so much emphasis on my portable equipment it's of a higher priority to me. A portable passive Pre can be used even out of my transportable gear, which is an advantage.
Be aware of output/input impedances when selecting the attenuator value.

Quote:
As I said, I'm not stuck to the idea of a DACT. It can be a Noble pot, whatever. However the argument for a DACT could be that since the iPod is not a great source to begin with, any further signal degredation especially in a passive component is highly detrimental if you're looking to extract the last 0.00001% of the sound, especially as the signal may have to start in a slightly poor quality way (sik din cable, if it's not re-cablable at source).
Not my job to dissuade you from personal choice.My thoughts on steppers vs. pots is well known and documented in a recent thread in the amp forum.I don't like them much and epecially for the price/performance (?) ratio.
The TDK or noble would be enough pot for the application in my mind but again that is me.

One thing I would do is to either go DIY or contract build by one of the advertisers in the mall area and add in options right at the start like multiple inputs,multiple outputs,an insert loop and volume control bypass so this could be used with any possible future equipment combination.
Still would be compact if only mini phone jacks are used for audio connections and small switches.always look to any future possibles before leaping for a "stuck with it" solution..

again.just a suggestion
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post #7 of 15
4/17/05 at 3:18pm
Thread Starter 
Quote:
Originally Posted by rickcr42
I meant the addition of the DACT which is by no means cheap and mosre than many use as their portable source.
I'm aware of that. However a £40 volume knob or a £100 volume knob in this instance is irrelevant. What I said applies regarding the last-yard performance variation between the Noble and a DACT, unless there's an issue with my theory. I'm not an expert by any means though.


Quote:
Be aware of output/input impedances when selecting the attenuator value.
I'm aware of that. I have an idea, but this is part of why I need opinions.


Quote:
Not my job to dissuade you from personal choice.My thoughts on steppers vs. pots is well known and documented in a recent thread in the amp forum.I don't like them much and epecially for the price/performance (?) ratio.
The TDK or noble would be enough pot for the application in my mind but again that is me.
I would be fine with the Noble, especially if it makes the total package smaller. I agree that the DACT will offer a decidedly marginal increase in performance for the disproportionate spend increase but once again, my comment re: last yard performance applies, especially as it looks as though there will not be a huge disparity in potential package sizes.


Quote:
One thing I would do is to either go DIY or contract build by one of the advertisers in the mall area and add in options right at the start like multiple inputs,multiple outputs,an insert loop and volume control bypass so this could be used with any possible future equipment combination.
Still would be compact if only mini phone jacks are used for audio connections and small switches.always look to any future possibles before leaping for a "stuck with it" solution..

I don't plan to build it myself. This is an application-specific solution and it'll be as small as possible given the application. No multiple ins/outs. Just one application-specific input, the pot/attenuator and an application-specific output. If I no longer need it... well, I no longer need it. As for 'stuck with it', I'll only be in that situation if it doesn't work for my uses. Which is why I'm asking people to assure me of the functional validity of a passive pre in this situation.
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post #8 of 15
4/17/05 at 3:31pm
Thread Starter 
Just one last point... I don't want to sound rude, but I don't want to know if this is a good way to spend money. IMO, if I can be reasonably sure that the phones will be adequately powered by this method, then this is in fact much less crazy (and far more portable) than for example spending $400 amping a relatively inferior source and adding further distortion, no matter how small, or sticking $700's worth of DAC and amplification onto a relatively inferior digital transport.


I hope you can see what i'm trying to do. All I'm trying to bypass is whatever they put in on a portable (in this case the iPod) in the headphone-out signal path. I'm trying to figure out a way to do it as simply and purely as possible.


The reason for using an iPod are many, but here are the key points:
- Sound quality through the Line Out is among the best and output power is among the highest
- Line Out is independent of the headphone out/remote socket and therefore allows for basic remote + LO operation
- I like the iPod's OS
- Ripping Lossless / high-bitrate files requires the least kludgy workarounds of any other player


I'd just like the functional validity of this confirmed and some suggestions for the layout if possible, as well as values for the attenuator and parts bearing in mind that the source is the iPod line Out and the client will be mainly the Sony Qualia. Thanks.
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post #9 of 15
4/17/05 at 6:05pm
Quote:
I'm aware of that. I have an idea, but this is part of why I need opinions.
10:1 ratios man.

line out Z X10 is the pot value then X10 that the headphone amp in Z

drop it all into a box that if you really want toi miniaturize should have a mini phon in but a captive line output which will eliminate another signal degrader in the path, the jack,so jack/pot/captive wire/plug and you are done
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post #10 of 15
4/17/05 at 8:09pm
bangraman...

...I'm not quite sure about your intention: So you want to drive your Qualia with the iPod's line out with an attenuator switched into the signal path? I fear this won't work, at least not ideally, and probably will offer worse results than the headphone out. Because the line out most likely has a high output impedance (since it's designed to «drive» a high load impedance) as well as a relatively low coupling capacitance inevitably leading to a bass drop-off and other impedance-induced frequency-response distortions. I may be wrong and maybe you have already hooked up the Qualia directly to the line out with promising results (?), but keep in mind that the attenuator will introduce a further aggravation of the unfavorable ratio between output and load impedance -- which actually should be at least 1:10.

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post #11 of 15
4/17/05 at 8:16pm
Thread Starter 
I was looking for more information on how this issue can be bypassed or reduced.


At the simplest level, well it is sticking the attenuator between the iPod and the HP but I realise that there are potential problems with this. I would imagine the actual output impedance of the iPod could be quite low for a line out, but the problem is more likely the interaction of the Q010 in the chain (I know a 300 ohm load worked fine through the Line Out, but 70? I really don't know. A 24 ohm load did indeed reveal a notable bass dropoff). I was hoping someone with more specific knowledge of the iPod LO would come in to the discussion.


The problem is at the moment I don't have a working iPod and I've had to return a borrowed one. I'm currently undecided whether to have my iPod repaired again or to buy another one, and if so which one... more studying needs to be done on that as there have been unfavourable comments about the Photo iPods (I was thinking about the 30Gb Photo).
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post #12 of 15
4/17/05 at 9:39pm
Try to find a 4G 40GB. Ive owned mine for close to 6 months now and Its only had 1 software glitch in which you get a corrupt file message if it goes into deep sleep. You can fix it by running fdisk. Ive had a friend go through 4 or 5 IPod Photos in a week. They all kept freezing with no way to get them unstuck. Who needs the added complication of photo transfers when all you want to do is listen to music?
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post #13 of 15
4/17/05 at 9:55pm
Thread Starter 
Actually I wanted the 30Gb for the size... not as thick as the 40Gb.
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post #14 of 15
4/17/05 at 10:17pm
The noble is something like a 1" cube plus lugs on one side, so it's not exactly small. Might be something to consider.
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post #15 of 15
4/17/05 at 10:34pm
Thread Starter 
It's something I can live with. I'd be aiming for 1" x 1" x 2 ~ 2.5" for the "core package".
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