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Old 22nd April 2008, 04:32 AM   #21
dfdye is offline dfdye  United States
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No, none of these will make a difference (with the possible exception of volume preference).

At issue is whether your power supply is beefy enough to adequately supply transients. If you have an under-powered PSU then transients on one channel will impact the other channel due to sagging of the PSU rails. If your power supply is sufficient and your circuits are well designed, you won't have significant (meaning audible) issues.

Whether you like music in the park or in your car makes ZERO difference.

PS I just realized that my last post trailed off mid sentence. The end of that statement should have been: "you must decide whether the very subtle reduction in crosstalk is worth the additional cost. Remember that in addition to buying another transformer, you would need a new PSU unit too."
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Old 22nd April 2008, 04:35 AM   #22
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Quote:
Originally posted by dfdye
No, none of these will make a difference (with the possible exception of volume preference). . .
Oh, my apologies! I had mistakenly assumed that we were discussing an audio amplifier.
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Old 22nd April 2008, 05:17 AM   #23
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Your sarcasm aside, the issue is crosstalk between channels. Though this of course reproduces audible signals once we feed the electrons into speakers, at issue is the electronic behavior of the amplifier. It doesn't care if it is playing Mozart or Motorhead.

The only one of your questions that could impact the magnitude of crosstalk is volume. Since you were being snarky, let's take your original post line by line so that you can follow.

1) Classical vs. pop: Both have migrated toward "higher level" recording over the years, reducing dynamic range and resulting in more distortion of loud transients. Both also have many high quality recordings that preserve adequate dynamic range. Assuming good recording of each, they both require large transient power outputs for high volume passages, meaning both would be susceptible to crosstalk due to similar electronic signals being fed to the amplifier. Keep this in mind for later--the electronic signal doesn't know if it is pop or classical, or artificially generated by a function generator.

2) Preferred listening levels: As noted before, this is the ONLY pertinent question, and even this doesn't really matter all that much. A properly designed PSU won't sag under high demands. If it does, your rail capacitance is too low and the PSU is poorly designed for the application. I'll tell you what, Daniel, why don't you check the PSU layout for the amp being discussed in this thread (the circuit is readily available) and tell us how much we should worry about this at different listening levels. Charts and graphs are always welcome. I'll even get you started: Put a sine wave into one channel while tying the other channel to ground. Measure the output of the two channels and see what the relative intensity of the two sine waves are. That gives you a quick and dirty measure of crosstalk.

3) Computer vs. CD: ZERO ability to contribute to crosstalk. Both sources will behave similarly once in the amplifier. See #1--the amp doesn't know where the input electrons come from.

4) Speaker preference: The goal here is eliminating crosstalk. Speakers won't contribute to this at all. This one is straight out of left field and I have no idea how to respond, quite frankly. This is rather like asking if I like oranges, and then using my answer to recommend tires for the car I use to drive to the store to buy the oranges.

5) Location preference: Again, irrelevant. If I like listening to guitar on the street corner, listening to my iPod on the subway, or listening to music at the Sydney Opera House, it doesn't impact how the amplifier will reproduce an audio signal.

6) Definition of the application: This one is simple! Regardless of the answers to these questions, the application is to reproduce an electronic signal faithfully! How to do that returns to the original question of crosstalk. The problem is clearly defined before ANY of these questions are answered.

7) Narrower scope allows more focused response: Again, unnecessary. The question of crosstalk between channels of an amplifier using a shared power supply is quite well documented. You simply were regurgitating a recommendation made on this board for a dual mono-block amplifier without understanding ANY of the considerations one would make when choosing whether to utilize this design or not. You are, intentionally or not, obfuscating the central question: will there be significant (noticeable) crosstalk between channels of the amp in question.

Now, Daniel, I have intentionally left off the practical effect that you should be worried about when crosstalk rears its head. I notice you never mention it either, so I will leave you with this challenge: WHAT should one notice musically if crosstalk DOES become an issue? You have a pretty firm assertion that we are worried about AUDIO amplifiers, so please, for the peanut gallery, what are the audible effects of amplifier crosstalk. (Consider this a take-home test since you should be able to look it up pretty easily, but then at least you will know what we are actually talking about.)

Once we have established that fairly important little nugget, we can continue the discussion.
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Old 22nd April 2008, 07:01 AM   #24
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Quote:
Originally posted by dfdye
. . . I am running a LM3886 dual monoblock amp straight out of my soundcard at my office, and it sounds fantastic. . . .
This is interesting.

If you must know what I consider an important caveat with dual mono, it is that the harmonic resonance of both power supplies need to be nearly identical or a hetrodyne could result, causing errata at the centerpoint of the audio image.

This is my only concern with dual mono, as other concerns are tradeoffs (and you have already mentioned that aspect).
EDIT: One tradeoff not explored is that a true monophonic source "may" or "may not" be rendered as devoid of centerpoint if used with a dual mono amplifier.

Instead of the current activity, howabout something I really can't handle?
Okay, here it is.
That power supply contains at least six possible configurations, and with no specific mention of the optimum, the very specific RC can be like Russian roulette. What do you recommend?
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Old 22nd April 2008, 08:36 AM   #25
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WOW lol! guys your brains are huge
On a serious note, from what i could follow crosstalk seems to be my biggest enemy yes? So aslong as my PS is up to the job, which by all acounts it is, crosstalk is what i want to banish.

On the side of volume, it's mid to high levels, the girlfriend and neighbours arnt great fans of Queen, bob marley and hard dance music so its only the rare times the missus and the neighbours are out together i get to pump up the volume; Its just nice to be able to now and again more than anything.

As for new drivers, my music at the moment sounds hollow and tinny, i put this down to the fact im using a less than high end cinema surround amp for stereo applications. The drivers are doing there job and trying to give me bass and clarity but the amp is just doing a ***** job of providing it i think. This is the culprit in question( yes i have changed that garstly colour and desk)
Click the image to open in full size.
This was what had inspired me to this project, then after seeing the world of DIY audio and other poeples efforts i started wanting a high end DIY set-up to call my own; It's the glits and glamour
Here are the drivers i purchased a couple of weeks ago.
Eltax monitor III
Click the image to open in full size.

Later on i would like to move onto floor standers, id do DIY but i dont have the wood skills/tools or workspace to build the Cabinets. The ones id like are around 300 which is i think around $600 and a little out of my price range at the moment so i want to concentrate on this for now if these will cut it for a while longer.
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Old 22nd April 2008, 10:48 AM   #26
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Okay, well, a likely spot to start is going with what you have built as a good stereo amp and also give it an adjustable preamp.

Here's a kit.
http://store.qkits.com/moreinfo.cfm/QK100 This has the aforementioned TDA1524A, and it doesn't run your signal through a bunch of potentiometers or up against an RC like the usual baxandall (so, much less distortion than usual for the features provided). In addition to the adjustment knobs, its also a preamp. As its a Qkits, it could probably use a component upgrade. The device can be quite useful for the music styles described.

Regardless of the minor considerations, the combo should be able to beat that cinema amp.

One great advantage to the stereo layout, shown pictured at the top is. . . a headphone jack is rather easily done.

Tips:

There's a fairly good method to prevent hums, and that is to use a longer, thinner wire for your input circuit;
but, use a shorter (much shorter) and fatter wire for your power circuit.

I also like to make sure that left side wires are the same length as right side wires--That's just a personal preference of mine, and the term is symmetry.

For metal enclosures, do be sure that the connections and potentiometer (depending on type) are insulated away from the metal enclosure. Some potentiometers don't ground to their shells, and those are easier to install in a metal chassis. Of course, a wooden chassis is even easier.

If heatsinks are inside the enclosure, its great to put a cool air intake underneath the heatsink, and also allow the hot air to exit at the uppermost part of the back panel--That's a basic description of some working airflow (in low, out high, because heat goes up), although external heatsinks are even better.

Have fun!
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Old 22nd April 2008, 10:53 PM   #27
dfdye is offline dfdye  United States
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Quote:
Originally posted by danielwritesbac
If you must know what I consider an important caveat with dual mono, it is that the harmonic resonance of both power supplies need to be nearly identical or a hetrodyne could result, causing errata at the centerpoint of the audio image.
I don't know what in the world you are talking about. Power supplies should be DC in the audio band (heck, they should be DC through ALL frequencies!). If they are generating ANY frequency that could cause modulation of the audio signal, there is something seriously out of sorts with your power supply!

Once again, you are pulling random arguments out of thin air that are patently false, but I don't really feel like keeping on with the pig in the mud, so to speak, so feel free to wander off into your own little word on this one.
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Old 23rd April 2008, 01:48 AM   #28
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Quote:
Originally posted by dfdye
I don't know what in the world you are talking about. Power supplies should be DC in the audio band (heck, they should be DC through ALL frequencies!). If they are generating ANY frequency that could cause modulation of the audio signal, there is something seriously out of sorts with your power supply!
If I may, I'd like to distract you for a moment onto a related topic that really does bother me.
Its the RC on that power supply, and because it is non-specific.
Any applicable suggestions would be greatly appreciated.
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Old 23rd April 2008, 02:12 AM   #29
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Quote:
Originally posted by danielwritesbac


Its the RC on that power supply, and because it is non-specific.
Any applicable suggestions would be greatly appreciated.


Daniel, Daniel, Daniel, you do get around, don't you?
The RC you refer to is a snubber? Research "power supply snubber".
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Old 23rd April 2008, 07:26 AM   #30
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Originally posted by MJL21193
Daniel, Daniel, Daniel, you do get around, don't you?
The RC you refer to is a snubber? Research "power supply snubber".
Hi John!

I wish I got around. I know its a snubber, but the directions for that particular power supply don't specify the optimal configuration. Instead, there's a wide list of possibilities, only one of which could be optimal, and its not clearly stated. So, here we have an RC, representing a specific tuning for particulars that aren't clearly specificed? Yes, that's the case.

You guys know that I have a tendency towards esoteric; however, for any sort of approach, I think its best to start with an optimized baseline. . . which is missing. And I believe that results on frequency response/tonality are left up to chance because of that.

EDIT: Another missing detail would be the optimal preamp--or at least the one used by the developers when making and measuring the kit. Its probably the nearest handy high-end model that was used in the fellow's home. But, it would be nice to know exactly what that is.

I had assumed that some of the experts here would have a suggestion that could beat my "preamp with voltage controlled bass-n-treble" suggestion. . . but there was entire page worth of crosstalk instead. OMG!! No pun intended! Oh sorry.
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