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Old 26th December 2006, 12:51 PM   #1
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Default Some simple/stupid audio questions

I have a few questions and thought rather than clutter up the individual forums this would be a good place to ask them all.

I'm not new to this but I am new to some of the additional equipment or non traditional setups.

1. What is a pre-amp and why do I want one? I am building one of the chipamps as soon as the parts arrive. I'll be using my CD player plugged into my receiver, then the preouts into this chipamp. Is my receiver then the preamp? Why could I not just plug the CD player directly into the amp? Is there an advantage of using an external pre-amp versus using the receiver as a preamp?

2. What makes one DAC better than another. Also why is an external DAC better than an internal one. The assumption is that its a digital signal and if every bit of data represents a particular frequency then why is one better than another. How do the DIY ones stack up against some high dollar units out there?

3. Why does digital bass management suck I have an ICBM 8 channel cross over for bass management on the analog side. I've played around as much as I could and nothing on the digital side comes close. This is with a Yamaha RXV2600 receiver. I asked this question on some other sites and even people with much higher end equipment said the same thing that analog bass management is superior to what they heard in the digital realm.

4. What is the best setup for listening to CD's. Transport-external DAC-pre-amp-amp-speakers or some other combination and what sets this combo away from a more traditional CD-receiver-speaker setup.

I'm trying to come up with a game plan of what I want to do. I'm building my tube subs this week and once they are done I'll be putting my current speakers up for sale and starting construction of set of line arrays.

Might as well plan for the rest. I'm asking all these questions because even with my setup now there are things I'd like to address. I keep telling myself that if I knew last year what I knew today I would have taken a totally different approach. I'm trying to avoid as much of that as possible next time around

Thanks in advance,

Eric
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Old 26th December 2006, 01:53 PM   #2
Aengus is offline Aengus  Canada
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Hi Eric

I'll let others respond to the digital questions (and asking what is the "best" anything often generates as much heat as light). But the preamp one is pretty straightforward.

A traditional pre-amp contained:

- a phono stage with two jobs: to amplify the very low-level signal from the cartridge, and to apply the RIAA equalization to the response curve.

- switching/volume control: source selection, balance, volume control, sometimes tone controls, sometimes other things (phono input loading, for example)

- usually, a second amplification stage following the source selection, to drive the line to the amp (and provide additional amplification for the sources if necessary).

When (some) people stopped playing records, manufacturers came out with line stages, some of which had switching/volume control and an amplification stage (active line stages), and some of which had only switching/volume control (passive line stages).

A receiver can be thought of as a tuner, a pre-amp, and a power amp in one box. If you plug your CDP into the receiver, and the pre-outs into the chipamp, then you are using the receiver as a pre-amp - that is, you are using the pre-amp stage in the receiver box. Since the CDP will almost certainly have enough output voltage to drive the chipamp, you only need the receiver (or an external preamp) to supply volume (and any other of the controls you might use). If you build a volume pot into the chipamp, or if the CDP has a volume control, you don't need to use anything else - just plug the CDP into the chipamp [edit: note that the volume pot on the CDP may not be of the highest quality].

Advantages to going direct? Fewer components in the signal path tends to improve the sound; disadvantage is that you would have to plug/unplug cables to listen to your tuner or other sources, if you plan to do that.

Going through the receiver has the advantage that you can switch between the CDP, tuner, and any other source you have plugged into the receiver using the controls on the receiver.

The external pre-amp will give you the same benefits as going through the receiver (assuming it has the same switching options). The reason you _might_ want to do this is that most receivers are built to a price point, and you can probably do better with a dedicated preamp, either DIY or commercially sourced.

Of course, if you plan to play records you will need a phono stage, in the receiver, the separate pre-amp, or in a discrete phono stage.

Quote:
I keep telling myself that if I knew last year what I knew today I would have taken a totally different approach
Ah, if that were only restricted to the realm of audio...

Regards.

Aengus
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Old 26th December 2006, 02:40 PM   #3
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Thanks you answered one of the big questions. For right now I can scratch pre-amp off of my list.

The "plan" is to test the chipamp on my DIY's, then on my mains in the living room but once thats done I plan on building a set of monitors for the bedroom, plus a very small sub that can be hidden away and driving the monitors with the chipamp run directly into either a CD player, although most likely some kind of digital audio source that will run off of a NAS somewhere in the house. There will be no pre-amp or receiver at all.

Then I'll build a more sophisticated chipamp for the living room once the new array is done.

Thanks!
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Old 26th December 2006, 03:07 PM   #4
lineup is offline lineup  Sweden
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at the risk of
repeating previous poster's reply:

1. If you can use CD-out ----> Power amplifier input, with good result
then do so!
Especially if your CD-player has got Built In Volume control. (most have these days).

* Preamp can be need when using other sources,
like turntable, tape-recorders, mp3-players and whatever source has a bit too output voltage/current.
In these cases a preamp will adjust to a proper output - for PowerAmp.

* The other case is when adding a Volume Control between CD and PowerAmp.
But even in this case,
first you can try using only one Potentiometer (=passive preamp)
between CD - PowerAmp.
The value in OHM of this, often dual ganged stereo potentiometer,
can in some cases be a bit critical - for best performance.
Something like 2x10kOhm - 2x22kOhm can be a good try.

But you have to read about 2 data, specifications, that will effect this:
a) CD-player Output
For example my CD: Minimum 10kOhm load
this means I could use one 10kOhm Volume control at CD out.
But not 2x5kOhm potentiometer.

b) PowerAmp input Impedance, CD RCA-inputs, usually like: 22-100kOhm.
The hint here is:
Volume Pot should have preferably LOWER Value, than the PowerAmp input impedance.
If possible good if 5 times lower.
For example: poweramp input impedance 47kOhm
Volume Potentiometer 10kOhm, is alright, as is 5 times lower.

lineup - preamp expert
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Old 27th December 2006, 09:55 PM   #5
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Quote:
Thanks you answered one of the big questions. For right now I can scratch pre-amp off of my list.
I love to hear people say that. To me, the whole concept of the Gainclone is to use minimal parts in the signal path. While building my first LM3875 amp I was already planning to build/buy a preamp with all the bells and whistles. But, after hearing the pure and musical sound of the chipamp with no signal prosessing, I doubt I'll every build anything but a passive pre. (input selector)
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Old 28th December 2006, 02:08 PM   #6
AndrewT is offline AndrewT  Scotland
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Hi David,
Quote:
I doubt I'll every build anything but a passive pre. (input selector)
a passive pre is good sounding.

But, it is very difficult to select all the passive component values to ensure the variables do not impinge on the audio pass band.
By difficult I mean near impossible.

Have you considered some kind of variable gain in the gainclone circuit (but still meeting min. gain)? and a switchable attenuator with correctly scaled filters preceeding the gainclone?

Or keep it simple and just buffer the attenuator.
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Old 28th December 2006, 04:07 PM   #7
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Quote:
Have you considered some kind of variable gain in the gainclone circuit (but still meeting min. gain)? and a switchable attenuator with correctly scaled filters preceeding the gainclone?
Andrew,

No I haven't. I really don't have a problem. I use one amp on my PC. I feed the other with a CD player. I MAY fire up my old turntable someday. But until then, I'm fine with a straight in hook up. But, it's an interesting thread!

Thanks!
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Old 29th December 2006, 03:50 AM   #8
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Note: Two interly differant systems.
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Old 2nd January 2007, 11:39 PM   #9
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to at least partially answer your question about DACs.....
i'm guessing you're talking about the dac in a cd player. most off-the-shelf dacs (Datel, Analog Devices, etc...) are made for the data accquisition market (digital voltage and current measurements), and not for audio. they have nonlinearities and errors that would render them unuseable for high quality audio. and, most of them are parallel input as well. DACs for audio are built for speed and accuracy. the DAC in a cd player also is designed as part of the decoding system either contained in the processing chipset, or very close to it on the pc board, and iirc is usually a serial input DAC using an external DAC would require rather long (compared to their length within the system) set of cables which could degrade the data transfer and introduce errors. there is a lot going on in the decoder circuitry, such as error correction and decoding data frames, and a lot of this is done synchronously
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