[tofu]

yes. it is perfectly fine. it is exactly how i have mine set up

audiophile 192 --> mcintosh mc250

attenuation done through foobar

 

[tschanrm]

Quote:

Does a passive preamp raise source impedence as compared with a direct connection?

There are different types of passive pre-amps (buffered, shunt, etc.), so it depends on what type of passive pre-amp we are talking about. Generally, a passive pre-amp lowers the impedance your source sees (which can be bad) and also raises the impedance your amp sees (which can also be bad). To reduce this problem, some passive pre-amps use a 10-20k pot in the schematic design. High impedance input amps (100k or so) are then used, so even if the pot were turned to its extreme, the amp would only see a maximum 10k (which is acceptable). However, a 10k pot at that same volume level would load the source, causing increased distortion (the source would see only a couple hundred ohms). Furthermore, I believe using a 20k pot attenuates the signal at full turn (max volume) by a couple of db (forget the exact number), so there is always a give and take with passive designs.

Longwinded answer, but to directly address your question-yes certain passive pre-amp designs raise the source impedance compared to a direct connection. Does this help answer your question?

In my opinon passive pre-amps are a good alternative if you can live with three shortcomings:

1. You need short interconnects (less than 1m) to prevent frequency rolloff and frequency phase inversion. Using a lower ohm pot lowers these problems, allowing for a longer interconnect, but has the side effect of signal attenuation.

2. You need an amplifier that has a high ohm input; 100k input impedance and above is the general rule.

3. Finding a passive design that would not load the source component.

I've always thought it would be a cool idea to build a shunt-type configured passive pre-amp with the outputs of a 1212/1820 in 10+ mode. The "hotter" +10 professional setting would reduce the attenuation caused by using a 10k or 20k pot. Cheap, easy, and only two resistors in the signal path!

Using the digital volume control is a quick and dirty way of ditching the active pre-amp and allowing a direct connection to the amp. As long as you don't attenuate the digital volume too much, you could end up (as others have explained) with a better sound than a passive volume control setup. If you found an amp with a high voltage input sensitivity, this could also be a very real scenario with audiophile results. Only drawback is you would not be able to crank the volume to extreme levels, but we're audiophiles not rockstars, right?

 

[rickcr42]

Quote:

In my opinon passive pre-amps are a good alternative if you can live with three shortcomings:

Everything in audio is tradeoffs.Passive=zero added noise but no added drive power either plus will be sensitive to matchups.
Active means noise WILL be added even if that noise is at a low level,cost is increased dramatically because you not only need the actual circuit but the sometimes even more important power supply but you gain a pretty much "load nuetral" output able to drive cables over a longer distance.


Quote:

1. You need short interconnects (less than 1m) to prevent frequency rolloff and frequency phase inversion. Using a lower ohm pot lowers these problems, allowing for a longer interconnect, but has the side effect of signal attenuation.

that would be 99% of all PC based systems where the playback monitors are right there on the desk or at worst to the sides on stands.If the PC is being used as a server at a distand location this topic would not be valid anyway and instead would be about "long line driving and avoiding noise pickup"

Quote:

2. You need an amplifier that has a high ohm input; 100k input impedance and above is the general rule.

nope.

Quote:

3. Finding a passive design that would not load the source component.

10K dual pot.Will present a stable 10K load to the sound card which is within the range of every single sound card I know of while in real use the output would be "worst case" around 2K which will work into anything from 10K on up with 25K pretty much being ideal .

Quote:

If you found an amp with a high voltage input sensitivity, this could also be a very real scenario with audiophile results. Only drawback is you would not be able to crank the volume to extreme levels, but we're audiophiles not rockstars, right

Pretty much all soundcards will put out 2 Volts and it would be a very rare amp (headphone or speaker) that could not reach full volume with a 2V input signal so at best a unity gain buffered volume control would be needed if there is a drive problem or impedance mismatch,also rare.

Quote:

I've always thought it would be a cool idea to build a shunt-type configured passive pre-amp with the outputs of a 1212/1820 in 10+ mode. The "hotter" +10 professional setting would reduce the attenuation caused by using a 10k or 20k pot. Cheap, easy, and only two resistors in the signal path!

And this would be one of those "rare" potentially.A "shunt" volume control unlike a "series" volume control does actually change impedance as it is rotated so the sound card outputs would not "see" a stable single value resistor but a varying load.Depending on systme could be either just fine or disastrous when the volume control went from controliing level to being in effect a treble control.

All comes down to what is in the individual system and what are the goals.If those goals are simply to adjust volume at the PC then I would go with what is called an "internet keyboard" that has the volume controls built in.Fast, easy,no lag and no resources used that matter.
If the ability to find the "sweet spot" between the machine "virtual" volume control and the external analog world then passive pot of around 10-20K would be fine.
If this same system needs to drive remotely located amps then hang an open loop buffer on the output of the volume control and if you need additional gain insert an opamp into a "combo-amp" which is an opamp/buffer combination or use a high current output opamp for everything (basic CMOY type headphone amp as HP amp/linestage).
All depends on what you need

 

[tschanrm]

Quote:

10K dual pot.Will present a stable 10K load to the sound card which is within the range of every single sound card I know of while in real use the output would be "worst case" around 2K which will work into anything from 10K on up with 25K pretty much being ideal .

Thanks for correcting me about the source load, I got mixed up with shunt-style configurations. As for passive designs, this design I feel is an easy and effective one (I built one about a year ago):

http://www.diyaudio.com/forums/showt...608&highlight=

Quote:

You need an amplifier that has a high ohm input; 100k input impedance and above is the general rule. Quote: nope.

From what I've read, a 10:1 or higher ratio is optimal. Could you explain what you are refuting a little more?


Quote:

If you found an amp with a high voltage input sensitivity, this could also be a very real scenario with audiophile results. Only drawback is you would not be able to crank the volume to extreme levels, but we're audiophiles not rockstars, right Quote: Pretty much all soundcards will put out 2 Volts and it would be a very rare amp (headphone or speaker) that could not reach full volume with a 2V input signal so at best a unity gain buffered volume control would be needed if there is a drive problem or impedance mismatch,also rare.

My point was to try and find an amp that doesn't reach full volume at say 2v, so you would not have to digitally attenuate as much. If you listened to music at low or moderate levels, this method would allow you to have a direct connection to the amp, while still maintaining 16-bit resolution for a majority of your listening levels. If for some reason you wanted louder passages, you could invest in or build a simple active stage. This isn't a great option, and leaves you limited in your amp selection, but it's still an option if you only wanted digital volume control and keep at or above 16 bit. As a side note, I know that some volume controls act as passive volume until a certain point at which an active gain stage is turned on. Does this help clarify what was previously posted?

 

[rickcr42]

Quote:

From what I've read, a 10:1 or higher ratio is optimal. Could you explain what you are refuting a little more?

Optimal does not translate to etched in stone and my 10K passive goes to a 47K effective amp load without any problems using a two meter interconnect.What the 1:10 is in reality is a loose guideline kinda like "you need a minimum of X power to drive Y speaker" when what it really comes down to is situational.The main weakness of the passive is trying to get a high input impedance but low output impedance,usually the domain of the active stage though in real life I have used as high as 20K into a 100K load without real world problems (upper octave attenuation)

Quote:

My point was to try and find an amp that doesn't reach full volume at say 2v, so you would not have to digitally attenuate as much.....

Ever consider a simple inline -10dB Pad ? Two resistors per channel and if you add a DPDT switch in or out at will.Way easier to implement and could be considered a single stage step of a step attenuator so even say -0dB/-5dB/-10dB on a 4P3T rotary could be used which would give you a lot of adjustment range in discrete "steps"that would be repeatable/defeatable at the flip of a switch.
Many ways to skin the same cat dude

 

[keiron99]

Thanks for all the replies, though I can't pretend to understand the more technical ones it's still appreciated.

Anyway, I put some time aside yesterday while the wife and kids were out to conduct the experiment. My speaker rig is PC > Perpetual Technologies P3A DAC > Rotel 1066 Pre > Rotel power > Dynaudio 1.3mk2 speakers. Not bad sounding at all.

Anyway, I removed the pre and ran the DAC straight into the power amp, using the volume slider on Itunes (or Foobar) in place of the pre.

Result? Couldn't detect any audible difference whatsoever. There may have been a slightly bigger soundstage and more transparency, indeed in some cases the soundstage was so wide that it almost seemed as though I had surround speakers firing at the sides! But, when I switched back to the pre, I heard the same effects too! (This is a recent improvement in my system brought about by the introduction of the P3A DAC which I just bought, absolutely outstanding.) I wouldn't bet a single penny on my ability to discern between the two set ups in a blind test.

Maybe I have cloth ears - I've never detected a difference in my system when swapping out interconnects for example, and can't distinguish between Foobar, Itunes, FLAC, ALAC, WAV etc - but I'm sure there are many with the same limited hearing abilities as myself! (Just be honest to yourself!) What I have learned from this is that if you have a single PC source and no requirement for any other sources, you'd do well to try this configuration before dropping a month's salary on a pre-amp.

 

[rickcr42]

Quote:

Anyway, I put some time aside yesterday while the wife and kids were out to conduct the experiment. My speaker rig is PC > Perpetual Technologies P3A DAC > Rotel 1066 Pre > Rotel power > Dynaudio 1.3mk2 speakers. Not bad sounding at all.

well there was your first mistake !

whenever i want an honest opinion from an impartial "non" audio geek i ask my wifes opinion and she is 100% dead on every time.If I can weasle her into listening for five minutes.
She is a "music first/what is equipment" type that is very hard to impress so on the rare occasions i do impress her i know i am on to something

 

[keiron99]

Quote:

Originally Posted by rickcr42 well there was your first mistake !

My other mistakes being.....?

 

[rickcr42]

signing up as a member of headfi which means you will NEVER be totally happy with what you have

 

[keiron99]

Quote:

Originally Posted by rickcr42 signing up as a member of headfi which means you will NEVER be totally happy with what you have

You're not wrong there...I thought you were going to say 1) getting married 2) having kids !!

 

[rickcr42]

Quote:

You're not wrong there...I thought you were going to say 1) getting married 2) having kids !!

Never her that from me man.I was born to be married and have kids

 

[CSMR]

Quote:

Originally Posted by tschanrm Does this help answer your question?

Many times over! Thanks!