Newbie: What is the "audio path?"

[Guest]

Hi folks,

This might be a simple question. It may not be. It might be a dumb question.

Anyway:

People talk about capacitors in the audio path. I'm just wondering how you actually trace the audio path in a mic pre.

I'm asking specifically because, after shorting a power supply, the fine gain adjustment (on my 7th circle n72) isn't providing the specified adjustment of 6dB of gain. That pot is just a three terminal resistor, and I'm wondering how pressing this is (on the list of things to worry about). I mean, I'm getting the same gain as before and it still sounds great across the frequency range, but I'm wondering if such an issue is affecting the fidelity in some sort of subtle way.

Simply put, if I'm just losing some of that adjustment, I'm going to put it at the end of the line. If it could be affecting frequency response or bias or something, I'll probably dig a little deeper.

Thanks...any input is greatly appreiated. Here's a link to the i/o schematic for the pre: http://www.seventhcirclestudios.com/SCA/N72/docs/10.pdf

It's Friday,

Kelly

 

[NewYorkDave]

I don't mean to cause confusion; but really, the whole notion of "audio path" and power supply being distinct from one another is nonsense because the audiofrequency currents DO flow through the power supply. Don't forget that "circuit" comes from the same root as "circle." Do a little reading about Kirchhoff's Laws for more detail.

 

[clintrubber]

from NYD:

I don't mean to cause confusion; but really, the whole notion of "audio path" and power supply being distinct from one another is nonsense because the audiofrequency currents DO flow through the power supply.

Ehh, well, and then the next thing you'll tell us would be that a DC-servo is in the audio path as well ?!?! :wink: :grin: :wink:

Kidding aside, I'm fully with you - and hope you're fully with me on the second one.

 

[microx]

The audio path is the only true light, reject all other forms of relgion.
Steve

 

[Gus]

NewYorkDave's

Point about the PS in the audio path is a good one. When I say Audio path I also think of the parts of the PS that have the greatest effect on the sound. Lets think about a big SS amp the big electros in the ps are in the circuit luckly for use they have a good forming voltage on them.

FWIW I "modded" my laney vc30 guitar amp. The mod was solen polypros in the ps and PETs as cathode bypass caps there are still some electros in the SS reverb section and a good one at the output tube cathode resistor. I like the look on good guitar player's face when they try the laney It was just a cap upgrade.

 

[neilium]

Trust your ears on this one. If it sounds good to you, it's probably OK. Right now you have a working mic pre that sounds good, but one of the knobs doesn't do what it's supposed to. I'd say all in all, life's pretty good as it stands.

If you find yourself idle and you have a spare pot to swap in and your iron is hot, maybe try replacing it. In my list of priorities I'd put it just above watching bad TV and just below balancing my checkbook.

As far as what's in the audio path, someone once said, "an amplifier is a modulated power supply."

-neil

 

[Moby]

Ehh, well, and then the next thing you'll tell us would be that a DC-servo is in the audio path as well ?!?!

From theoretic side it is not audio path, but poor designed DC filters can hurt audio range... :roll:

 

[clintrubber]

From theoretic side it is not audio path, but poor designed DC filters can hurt audio range...

Must say I actually regretted it bringing up DC-servo's right after having posted it - we had a discussion about this at the old place.

W.r.t. 'theoretic': if you write out the transfer of such a stage (formula), the maths don't really take into account if a certain component is in the 'forward' path (= the obvious signal path) or in the path back (the servo). They just show up somewhere in that transfer-formula so they join the party as I understand it.

 

[Kev]

audio path
clean earth
dirty earth
control line
control earth

:roll:

yes it is possible that all parts of the circuit can have an ultimate effect on the signal passing through the circuit BUT we all know what he meant.
If the powers supply is functioning properly and over spec'd enough I don't believe that "audio path" and power supply being distinct from one another is nonsense.

If I use a 24 volt TRUCK battery as a power supply to a single Neve 1272 module with large short power lines, I don't think you will hear the difference if I then use a High Performance TRUCK battery.

If the power supply is faulty or under spec ... then fix it.
... and that goes for the main AC power supply feeding the whole studio.

 

[Mark Burnley]

Hi Kelly,

Just a simple idea, but you might want to check the connections on the board to the level trim pot. If you've had the board out of its chassis for testing/tweaking, it can be very easy to accidentally knock components mounted to the board. A slight knock can dislodge a solder connection, and this would take one or more terminals of the pot out of the circuit.

Might be worth checking before going on a hunt?

Mark

 

[Steve Jones]

[quote author="NewYorkDave"]I don't mean to cause confusion; but really, the whole notion of "audio path" and power supply being distinct from one another is nonsense because the audiofrequency currents DO flow through the power supply. Don't forget that "circuit" comes from the same root as "circle." Do a little reading about Kirchhoff's Laws for more detail.[/quote]

I agree. The problem with teaching electronics as "blocks" really shows up here - it is easy to think of an "amplifier" block attatched to a "power supply" block. But when you step back and look at it, what is an amplifier in the real world? It is simply a modulated power supply! When you build an amplifier, what you really are building is a power supply that is controlled by your input signal, or, perhaps more accurately, you are building a device to modulate your power supply. So the PSU is critical!

 

[CJ]

Power amps modulate the supply.
Does line level stuff really modulate the supply?
I don't know. Voltage amps don't draw too much current.
I guess it's important, but not as component critical as a power amp.
You can mmake a guitar amp sound bad by adding too much capacitance to the supply, but I doubt that would make any difference on say, a mic pre.

 

[Moby]

Many times i jumped in to discussion with my colleagues about same thing, and i figure that its never-ending story :!: From electronics point of view, signal path do not include PSU and side-chain electronics, but when you start to listen, and trust your ears, lot of details can be found "around". Of course, thats not "magic" almost everything is measurable, but most of experienced technicians can imagine what is happening with sound if you change PSU caps, or maybe values. What about ground? Is that signal path? :green:

 

[NewYorkDave]

These discussions of semantics border on the mystical and useless, but there's a couple of simple logical points that can be made.

Just because this hypothetical "truck battery" is of a low impedance, appropriate voltage, etc. and causes no audible defects, the audiofrequency currents still flow through it and therefore it is indeed part of the "signal path."

Any amplifier, great or small, is indeed a power supply modulator, insofar as the signal is modulating current that originates at the supply, passes through the circuit elements and returns to the supply.

It's just basic electronics.